General information:

1. For a full list of all future talks, see the seminar list.
2. The seminar takes place usually at Knudsen 4-134, unless otherwise notified.
3. The refreshments or pizza will be served 15 minutes before the seminar.
4. We also actively participate in the seminars offered by Nuclear Science Division at Lawrence Berkeley National Laboratory: Hadron Ion Tea (HIT)  and Nuclear Theory Seminar.
5. For travel information such as flight, direction, parking, and etc, please refer to our Visiting page.


A Fragmentation Approach to Jet Flavor

Andrew Larkoski, SLAC National Accelerator Laboratory
9:00 AM Friday, online ZOOM

Intuitive or de facto definitions of jet flavor are typically only well-defined in the deep UV, where a jet consists of a single particle. However, measurements are performed in the IR, and any practical definition of jet flavor can only access information in the IR. In this talk, I will introduce a novel definition of jet flavor defined as the particle in the jet whose momentum lies exactly on the Winner-Take-All recombination scheme axis. I will also derive linear evolution equations of this WTA flavor in flowing from the UV to the IR that are a small modification to traditional DGLAP and demonstrate quantitative agreement with parton shower Monte Carlos.


Suppression of high pT Pi0 relative to prompt photon in central d+Au collision at 200 GeV

Niveditha Ramasubramanian, CEA, Saclay
9:00 AM Friday, online ZOOM

The initial motivation to study d+Au collisions was to use them as a control experiment to decouple the effects of cold nuclear matter effects in the nuclear modification factors (RAA) obtained from heavy ion collisions like Au+Au. Since the year 2013, there has been a growing evidence of the possibility of formation of Quark Gluon Plasma (QGP) in small systems. Suppression in the nuclear modification factor RAA of Pi0 and jets is observed in the central d+Au collisions, which could be attributed to formation of QGP droplets but, along with this, the results also indicate a counter-intuitive enhancement of RAA in peripheral events. Direct photons are transparent to the QGP and thus RAA of direct photons at high pT should be unity for all classes of event activity. We observe that, in d+Au system, for central collisions, the RAA of direct photons is close to unity but for peripheral collisions there is a significant enhancement which matches the degree of enhancement that is observed in RAA of Pi0s. This indicates a bias in centrality determination using Glauber model for small system collisions. Furthermore, the direct photon measurement for d+Au can be used to experimentally determine the effective number of binary collisions N_exp for each event sample. By using this N_exp, the RAA of pi0 is re-obtained and this is close to unity for peripheral collisions but still show a significant suppression in central collisions which could be an indication of a formation of QGP droplets in central d+Au collisions. In this talk, I will highlight preliminary approved results from d+Au collisions and the status of analysis in p+Au and 3He+Au systems.


Infrared structure of QED as a many-body theory of worldlines

Xabier Feal, Santiago de Compostela U., IGFAE
9:00 AM Friday, online ZOOM

We discuss a reformulation of QED in which matter and gauge fields are integrated out explicitly, resulting in a many-body Lorentz covariant theory of 0+1 dimensional worldlines describing super-pairs of spinning charges interacting through Lorentz forces. This provides a powerful, string inspired definition of amplitudes to all loop orders. In particular, one obtains a more general formulation of Wilson loops and lines, with exponentiated dynamical fields and spin precession contributions, and worldline contour averages exactly defined through first quantized path integrals. We discuss in detail the attractive features of this formalism for high order perturbative computations. We show that worldline S-matrix elements, to all loop orders in perturbation theory, can be constructed to be manifestly free of soft singularities, with infrared (IR) divergences captured and removed by endpoint photon exchanges at infinity that are equivalent to the soft coherent dressings of the Dyson S-matrix proposed by Faddeev and Kulish. We discuss these IR structures and make connections with soft theorems, the Abelian exponentiation of IR divergences and cusp anomalous dimensions. Preprint: 2206.04188


On Modeling Complex Systems in Astrophysics

Yuan-Sen Ting, Australian National University
10:00 AM Wednesday, Hybrid (PAB 4-330 and online ZOOM)

Astronomy today is fundamentally different than it was even just a decade ago. Our increasing ability to collect a large amount of data from ever more powerful instrumental has enabled many new opportunities. However, such opportunity also comes with new challenges. The bottleneck stems from the fact that most astronomical observations are inherently high dimension — from “imaging” the Universe at the finest details to fully characterizing tens of millions of spectra consisting of tens of thousands of wavelength pixels. In this regime, classical astrostatistics approaches struggle. I will present two different machine learning approaches to quantify complex systems in astronomy. (1) Reductionist approach: I will discuss how machine learning can optimally compress information and extract higher-order moment information in stochastic processes. (2) A generative approach: I will discuss how generative models, such as normalizing flow, allow us to properly model the vast astronomy data set, enabling the study of complex astronomy systems directly in their raw dimensional space.


A theoretical approach to jet substructure in heavy-ion collisions

Alba Soto-Ontoso, IPhT, Saclay
9:00 AM Friday, online ZOOM

Jet substructure represents a cornerstone in the on-going endeavor to pinpoint the effect of a hot, thermal medium, namely the quark-gluon plasma, on QCD dynamics. In particular, jet substructure observables can be engineered to enhance the sensitivity to certain regions of the radiation phase-space where perturbative QCD effects dominate, thus enabling first principles calculations. In this talk, I will focus on the analytic computation of jet substructure observables that are built out of one or a few splittings inside the jet. First, I will discuss the state-of-the-art of analytic resummation techniques that rely on the factorization in time between vacuum-like and medium-induced processes in the double-logarithmic approximation. Next, I will discuss how recent developments in jet quenching theory should be incorporated into jet substructure calculations to enable quantitative comparisons with the rich dataset recorded at RHIC and the LHC. I will conclude outlining the connection between these analytic resummation results and the building blocks of jet quenching Monte Carlo generators.


Universality aspects of quantum corrections to transverse momentum broadening in QCD media

Paul Caucal, Brookhaven National Lab
9:00 AM Friday, online ZOOM

Transverse momentum broadening (TMB) of energetic partons in QCD matter plays a central role in a variety of processes studied at colliders to probe QCD, ranging from transverse momentum dependent gluon distributions that encode information on the 3D structure of the proton and nuclei in eA or pA collisions, to jet suppression in heavy-ion collisions. In this talk, I will discuss the leading quantum corrections to the TMB distribution of high energy partons in dense QCD media. I will show that the resummation to all orders of double logarithmic contributions from gluon radiation in the presence of a saturation boundary yields a universal distribution for large system sizes. This universal distribution exhibits anomalous scaling of super diffusive type, in contrast with normal diffusion seen at tree level, and a heavy tail at large transverse momentum, akin to Lévy random walks. Exploiting a formal analogy with traveling waves in reaction-diffusion processes, I derive the universal pre-asymptotic solutions for fixed [1] and running coupling [2]. I will also address for the first time the impact of single logarithmic corrections to TMB in large systems, to all orders in pertubation theory [3]. I finally comment on possible applications to small-x phenomenology, dijet acoplanarity and search for rare large-angle deflections induced by point-like interactions in heavy-ion collisions.

[1] PC, Y. Mehtar-Tani (BNL), 2109.12041 [hep-ph]
[2] PC, Y. Mehtar-Tani (BNL), 2203.09407 [hep-ph]
[3] PC, Y. Mehtar-Tani (BNL), in preparation


The fragmentation region of a heavy-ion collision

Isobel Kolbé, Institute for Nuclear Theory at the University of Washington
9:00 AM Friday, PAB 5-142 (ZOOM)

The fragmentation region of a heavy-ion collision is the area of phase-space in which the products and fragments of the collision have the same (or very similar) rapidity as that of the beam. This region is critically understudied, despite offering the possibility of studying high-density regions of the QCD phase-diagram in existing collider experiments. I will present a series of initial explorations of the fragmentation region, beginning with a simple model that provides evidence that densities of 2-3 times the nuclear saturation density may be reached in this region. I will then show the most recent rigorous calculations of bremsstrahlung in the fragmentation region, a calculation that incorporates both the non-perturbative physics of gluon saturation (as described by the color-glass condensate) and the correct perturbative physics of high-frequency bremsstrahlung. These results offer insight into how one might correctly model the hydrodynamics of the fragmentation region, but also has implications for bremsstrahlung calculations in other theories such as QED.


Higgs boson decay to J/ψ via c-quark fragmentation

Yang Ma, University of Pittsburgh
10:00 AM Friday, online ZOOM

With the discovery of the Higgs boson at the CERN Large Hadron Collider (LHC), the particle spectrum of the Standard Model (SM) is complete. The next target at the energy frontier will be to study the Higgs properties and to search for the next scale beyond the SM. Experimentally, the H -> c cbar channel would be extremely difficult to dig out because of both the weak Yukawa coupling and the daunting SM di-jet background. We propose to test the charm-quark Yukawa coupling at the LHC and future hadron colliders with the Higgs boson decay to J/ψ via the charm-quark fragmentation. Using the non-relativistic quantum chromodynamics (NRQCD), we study the Higgs decay channel  H -> c cbar + J/ψ  (or ηc), where both the color-singlet and color-octet contributions are considered. Our result opens another door to improve determinations at the LHC of the Higgs Yukawa couplings: the final state from this decay mode is quite distinctive with J/ψ -> e+e-µµ- and the branching fraction is logarithmically enhanced by the charm-quark fragmentation mechanism.


Jet quenching in a digital quantum computer

Joao Barata, Brookhaven National Lab
9:00 AM Friday, online ZOOM

The fast development of quantum technologies over the last decades has offered a glimpse to a future where the quantum properties of multi-particle systems might be more fully understood. So far, quantum computing has seen ample application in areas such as quantum chemistry or condensed matter, but its usage in high energy physics is still in its infancy. In the particular case of QCD jets, these technologies might offer a way to more fully understand the intricate interference pattern arising from the multi-parton cascade. In this talk, I will discuss an approach to study the evolution of jets in the presence of a background field. I will consider single parton evolution, neglecting radiative energy loss and focusing on momentum diffusion. Using the typical approximations found in jet quenching literature, this problem is easily solved and thus it offers a good first step towards studying full jets. Besides the formulation of the problem in terms of operations on the quantum computer, I will also show some early numerical results using qiskit.


Beyond the Standard Model Physics with Low-Background Neutrinoless Double Beta Decay Experiments

Wenqin Xu, University of South Dakota
1:00 PM Tuesday, PAB 4-330 (ZOOM)

Neutrinoless double beta decay (0νββ) is a Beyond the Standard Model (BSM) process which, if discovered, would establish neutrinos are their own antiparticles, prove total lepton number violation, and provide a mechanism for generating non-zero neutrino masses. 0νββ is expected to be extremely rare with a half-time longer than 1026 years, resulting in a requirement of ultra-low background levels in experiments searching for 0νββ. Low backgrounds achieved in these experiments also open opportunities to effectively probe a wide range of BSM physics. The Majorana Demonstrator experiment searches for 0νββ in 76Ge with high purity germanium (HPGe) detectors. Excellent energy performance has been achieved with the Demonstrator HPGe detectors, including low energy threshold, great linearity, and a FWHM energy resolution that is approaching 0.1% at the double beta decay Q-value. The combination of ultra-low background and superb energy performance enables a rich physics program with the Demonstrator, including 0νββ decay, solar axions, dark matter, Pauli exclusion principle violation, quantum wavefunction collapse, and more BSM physics. In this talk, we will discuss physics results from the Demonstrator as well as the status of its successor, the Large Enriched Germanium Experiment for Neutrinoless beta-beta Decay (LEGEND).


Exclusive vector meson production at next-to-leading order in the Color Glass Condensate framework

Jani Penttala, University of Jyvaskyla
9:00 AM Friday, online ZOOM

Exclusive vector meson production is a powerful process to probe the small Bjorken-x structure of protons and nuclei, as such processes are especially sensitive to gluonic structure and also provide access to the spatial distribution of small-x gluons in nuclei. A powerful theoretical framework to study such high-energy processes is the Color Glass Condensate (CGC) effective field theory. So far, most calculations in the CGC framework have been done at the leading order. Recent theoretical developments on the NLO heavy vector meson wave function and the NLO virtual photon light-front wave function have made it possible to go beyond the leading order in exclusive vector meson production, allowing us to calculate this process at NLO in the dipole picture for the first time. In this talk, I will discuss the calculation of the NLO corrections to heavy vector meson production in the nonrelativistic limit, and to light vector meson production in the limit of large photon virtuality.


Quantum Thermalization of Gauge Theories: chaos, turbulence and universality

Niklas Mueller, University of Maryland
12:00 PM Wednesday, online ZOOM

The possibility to simulate quantum many-body systems with digital quantum computers and analog devices is an exciting opportunity for high energy and nuclear physics. However, over the next five to ten years (the noisy ‘NISQ era’), we will be forced to explore simpler models short of the ultimate goal: Quantum Chromodynamics (QCD). I will argue that, utilizing interdisciplinary connections, exciting physics problems lie nevertheless directly ahead and new perspectives are waiting to be investigated. One example is Entanglement Structure (ES), first explored in the context of non-Abelian fractional quantum Hall states, but largely unexplored for gauge theories and high energy and nuclear physics. ES is crucial e.g., to understand thermalization of the quark gluon plasma in ultra-relativistic heavy ion collisions, or the structure of QCD bound states in deeply inelastic scattering (DIS) at the future Electron-Ion Collider. To illustrate this, I will show how I used Entanglement Structure and Entanglement Tomography to gain insight into quantum thermalization of strongly-coupled gauge theories, which proceeds in characteristic stages and reveals quantum phenomena remarkably similar to their classical counterparts: chaos, turbulence and universality. I will also report on current developments, and I will lay out a physics program making use of interdisciplinary connections between high energy and nuclear physics, condensed matter theory and quantum information science.


Recent progress from the PandaX experiment

Jianglai Liu, Shanghai Jiaotong University
12:00 PM Wednesday, online ZOOM

PandaX is a series of xenon-based experiments to search for dark matter and to study the fundamental properties of neutrinos in the China Jinping underground Laboratory (CJPL). The current stage experiment, PandaX-4T, contains a sensitive time-projection-chamber with of 3.7-ton liquid xenon target. The commissioning to PandaX-4T has been completed in 2021. In this talk, after an overview of this project, I will present our first dark matter search with the commissioning data, and discuss future prospective of PandaX.


Open quantum systems and quantum computing for heavy ion collisions

Xiaojun Yao, MIT
2:00 PM Thursday, online ZOOM

The purpose of relativistic heavy ion collisions is to study the properties of the quark-gluon plasma (QGP). Heavy quarks and jets have been used as important probes of the QGP. To understand their production in heavy ion collisions, it is necessary to understand their evolution inside the QGP. Many previous studies applied semiclassical transport equations, which neglected quantum effects that could be crucial. In recent years, the quantum evolution of heavy quarks and jets inside the QGP was investigated by using the open quantum system framework. In this talk, I will discuss the open quantum system framework and its application to heavy quarks and jets, with a focus on the heavy quark bound state. Then I will discuss how quantum computing can help to solve these evolution equations. I will give two explicit simple examples of using quantum computers to solve the open quantum system time evolution: one is a simple two-level system and the other is the Schwinger model, both coupled with a thermal environment.


Quantum simulations for real-time observables in nuclear physics

Yukari Yamauchi, University of Maryland
1:00 PM Wednesday, online ZOOM

The application of quantum simulations to nuclear physics has been studied intensely in recent years. Important real-time observables in QCD, such as parton distribution functions (PDFs) and transport coefficients, can be computed on a large-scale quantum computer. Quantum algorithms for computing these real-time observables naively consist of five building blocks: representation of the Hilbert space of lattice QCD on qubits, implementation of the time evolution operator via QCD Hamiltonian, preparation of a suitable initial state, measurement of the expectation value of target observables, and error corrections. In this talk, I will discuss quantum algorithms for computing PDFs and transport coefficients. I will focus on two of these building blocks: initial state preparation and measurement of observables.


Rodeo Algorithm for Quantum Computation

Dean Lee, Michigan State
3:00 PM Thursday, online ZOOM

The rodeo algorithm is a new algorithm for preparing quantum eigenstates on a quantum computer. It follows a strategy that is opposite to adiabatic evolution. Instead of slowly evolving a Hamiltonian to preserve the instantaneous ground state, it violently shakes off all quantum states that are not desired. I first introduce another method that works in the same modality, called the projected cooling method. I then discuss the theory, performance, and implementation of the rodeo algorithm for arbitrary eigenstate preparation, energy spectrum determination, and calculation of transition matrix elements.


Study of global and local polarization of Lambda and anti-Lambda hyperons in Pb-Pb collisions in ALICE at the LHC

Debojit Sarkar, Wayne State
10:00 AM Tuesday, online ZOOM

The system created in relativistic nucleus-nucleus collisions may possess large orbital angular momentum leading to the global polarization of particles perpendicular to the reaction plane. The local asymmetries in the velocity fields due to anisotropic flow can also generate vorticity and particle polarization along the beam direction. In parity-violating weak decays of hyperons, the momentum direction of the decay baryon is correlated with the hyperon spin. This feature makes the hyperons suitable candidates to measure the polarization and thus estimate the local and global vorticity of the system created in relativistic heavy-ion collisions. In this talk, the recent experimental measurements of the local and global polarization of the Lambda and anti-Lambda hyperons in Pb-Pb collisions in ALICE will be presented. A comparison of the ALICE results with the previous STAR measurements will be shown, and the collision energy dependence of the hyperon polarization will be discussed. Also, the comparison of the measured local polarization with the hydrodynamic model calculations involving thermal and shear-induced vorticity will be discussed.


Development of a highly granular scintillator-tungsten electromagnetic calorimeter prototype for the CEPC

Yazhou Niu, USTC
3:00 PM Thursday, online ZOOM

Driven by the physics program at the Circular Electron Positron Collider (CEPC) for Higgs and electroweak physics, all possible final states need to be separately identified and reconstructed with high sensitivity. Properties agree with the particle flow algorithm principle, which makes use of the optimal sub-detector to determine the energy/momentum of each final particle. The electromagnetic calorimeter is required to have not only good energy resolution but an unprecedented three-dimensional spatial resolution for shower separation. An electromagnetic calorimeter, which features finely segmented and highly lateral granular, has been designed and optimized within the CALICE collaboration and CEPC calorimeter working group. Scintillator strips and silicon photomultipliers (SiPMs) are instrumented as sensitive layers and tungsten-copper alloy plates as absorber material. A complete technological prototype with 32 sampling layers with over 6700 channels in total has been constructed and commissioned in the middle of 2020. The whole prototype measures around 600*600*400 mm^3 in dimensions and roughly 250 kg in weight. A long term cosmic ray test (more than one month) has been performed for detailed studies of this prototype to quantitatively evaluate the key performance, including the position resolution and cell-to-cell response calibration, etc. This talk will cover some highlight aspects in the development process and some key performances of the ScECAL prototype.


Measurements of Dielectron Production with the STAR Experiment

Zaochen Ye, Rice University
3:00 PM Friday, online ZOOM

Dielectron production is suggested as an excellent probe of the hot and dense medium created in relativistic heavy-ion collisions due to their minimal interactions with the partonic and hadronic medium. They can carry the information from the initial to the final stage of a collision. The study of the dielectron mass spectrum could help to disentangle various contributions. In the low mass region (LMR, Mee < Mphi), the mass spectra of vector mesons are modified due to their interaction with the medium which could provide an access to the chiral symmetry restoration. In the intermediate mass region (IMR, Mphi < Mee < MJ/psi), dielectrons from thermal radiation are predicted as a QGP thermometer, meanwhile the contributions from heavy quark semi-leptonic decays make the extraction of the thermal radiation contribution very challenging. In this talk, I will review the recent progress of dielectron measurements with the STAR experiment and discuss the prospects of the STAR BES-II dielectron program.


Measurement of Direct Photon Cross Section and Double Helicity Asymmetry at sqrt(s) = 510 GeV in pp Collisions at PHENIX

Zhongling Ji, Stony Brook
10:00 AM Wednesday, online ZOOM

Understanding the gluon spin contribution to the proton spin is among the primary motivations of the spin program at the Relativistic Heavy Ion Collider (RHIC). Double helicity asymmetry A_LL of direct photon production in pp collisions at RHIC is sensitive to the gluon helicity in the polarized proton. Direct photons are dominantly produced by the quark-gluon Compton process at RHIC energies, and utilizing an isolation criteria can reduce the fragmentation contributions and photons from hadronic decays. The asymmetry measurement with isolation criteria provides clean access to the polarization of the gluon. I will present the cross section and double helicity asymmetry measurements of direct photon production in longitudinally polarized proton collisions at sqrt(s} = 510 GeV at midrapidity (|eta| < 0.25). These data are expected to provide additional constraints on the gluon helicity distribution in the gluon momentum fraction range 0.02 < x < 0.08.


Disappearance of Partonic Collectivity in 3 GeV Au+Au Collisions at RHIC

Shaowei Lan, CCNU/LBNL
10:00 AM Wednesday, online ZOOM

Searching for the onset of Quark-Gluon Plasma (QGP) has been one of the most important motivations of relativistic heavy-ion physics. Collectivity measurements could be served as powerful tool, since they are sensitive to dynamics of early stage of system evolution. In the lower energy collisions, measurements of light hadron collectivity would tell about the underlying collision dynamics and help to study the properties of QCD medium. On the other hand, measurements of light nuclei collectivity provide valuable information on the nucleon coalescence sum rule and lead to better understanding of light nuclei production mechanism in such collisions. In this talk, I will present new measurements of directed flow and elliptic flow for light hadron and light nuclei in Au+Au collisions at 3 GeV by the STAR experiment at RHIC. The rapidity, transverse momentum and energy dependence of and for these particles will be discussed. These results are compared with hadronic transport model calculations, indicating that baryonic interactions dominate in 3 GeV Au+Au collisions.


Entanglement and Quantum tomography for collider physics

Daniel Tapia Takaki, University of Kansas
11:00 PM Tuesday, online ZOOM

Quantum mechanics is experiencing an experimental and theoretical renaissance. In this talk, we will discuss novel ways to use quantum mechanics and provide several experimental applications of quantum tomography for proton-proton and heavy-ion collision experiments at the CERN Large Hadron Collider. We will discuss application of this model-independent analysis technique for Z bosons, dijets and quarkonia. The first observation of an unexpected correlation of spin and momentum in the experimental data will also be presented.


Machine Learning Applications and Observation of Higgs Boson Decays into a Pair of Bottom Quarks with the ATLAS Detector

Cecilia Tosciri, University of Chicago
12:00 PM Wednesday, online ZOOM
joint with HEAP seminar

The discovery of the Higgs boson at the Large Hadron Collider (LHC) in 2012 represents an outstanding success of the Standard Model (SM) of particle physics. Since then, the properties of the Higgs boson have been measured with increased precision and found to be consistent with the SM predictions. However, despite this remarkable agreement, many physical phenomena are not explained by the SM, and several questions remain unresolved. Indeed, the SM is envisioned to be only an effective manifestation of a more fundamental description of Nature. Precision measurements of the Higgs boson production cross sections and decay rates give us a sharp tool to search for new physics. Moreover, original analysis techniques, in addition to innovative technologies and computational resources, are essential to fully exploit the LHC physics potential in the next decades. In this talk I will present the VH(H->bb) signal strength analysis performed with the ATLAS experiment, leading to the observation of Higgs boson decays into pairs of bottom quarks, which is a prime example of the success of the LHC in testing the SM. A description of the cross section measurements for the VH(H->bb) processes and their interpretation based on an effective field theory approach will be also presented. This work represents an important step towards the era of precision Higgs physics measurements at the LHC. Furthermore, I will describe a novel technique for the fast simulation of the response of the forward calorimeter in ATLAS, based on an innovative unsupervised machine learning algorithm.


Simulating real-time dynamics of hard probes in nuclear matter on a quantum computer

Xiaojun Yao, MIT
10:00 AM Thursday, online ZOOM

I will present a framework to simulate the dynamics of hard probes such as heavy quarks or jets in a hot, strongly-coupled quark-gluon plasma (QGP) on a quantum computer. Hard probes in the QGP can be treated as open quantum systems and their evolution is governed in the Markovian limit by the Lindblad equation. However, due to the large computational costs, many current phenomenological calculations of hard probes evolving in the QGP use semiclassical approximations of the quantum evolution. Quantum computation offers the potential for a fully quantum treatment. I will demonstrate the framework by simulating a simple model on IBM Q quantum devices, and applying recently developed error mitigation techniques. The work demonstrates the feasibility of simulating open quantum systems on current and near-term quantum devices, which is of broad relevance to applications in both hot and cold nuclear matter.


Mapping out the phase diagram of QCD in hadronic transport

Agnieszka Sorensen, UCLA/LBL
2:00 PM Thursday, online ZOOM

Critical behavior in hadronic transport is largely unexplored. With few exceptions, hadronic potentials are neglected in hybrid simulations, which means that transport may be missing many-body effects likely to be increasingly important at high baryon densities. Moreover, a consistent treatment of the entire span of a hybrid heavy-ion collision simulation calls for employing hadronic interactions that reproduce properties of a particular EOS used in the hydrodynamic stage. However, the few hadronic transport codes that do employ mean-field potentials only take into account the behavior of ordinary nuclear matter without the possible QGP phase transition. In this talk, I will present an approach to this problem in which the EOS of nuclear matter and the corresponding single-particle equations of motion used in transport are both obtained from a relativistic density functional with fully parameterizable interactions. I will show that this model is readily constrained to reproduce desired sets of the QCD EOS properties, which include the known behavior of ordinary nuclear matter as well as a family of possible phase transitions at high baryon number density. I will then discuss the behavior of nuclear matter in a number of scenarios simulated in hadronic transport, including evolution in the vicinity of a critical point of the QCD phase transition. I will also discuss the relation between quantities calculated in infinite, continuous matter calculations and observables obtained from simulations using a finite number of particles.


Data-driven quark and gluon jet modification in heavy-ion collisions

Jasmine Brewer, CERN
1:00 PM Wednesday, online ZOOM

Whether quark- and gluon-initiated jets are modified differently by the quark-gluon plasma produced in heavy-ion collisions is a long-standing question that has thus far eluded a definitive experimental answer. A crucial complication for quark-gluon discrimination in both proton-proton and heavy-ion collisions is that all measurements necessarily average over the (unknown) quark-gluon composition of a jet sample. In the heavy-ion context, the simultaneous modification of both the fractions and substructure of quark and gluon jets by the quark-gluon plasma further obscures the interpretation. Here, we discuss a fully data-driven method for separating quark and gluon contributions to jet observables using a statistical technique called topic modeling. Assuming that jet distributions are a mixture of underlying "quark-like" and "gluon-like" distributions, we show how to extract quark and gluon jet fractions and constituent multiplicity distributions as a function of the jet transverse momentum. This proof-of-concept study is based on proton-proton and heavy-ion collision events from the Monte Carlo event generator Jewel with statistics accessible in Run 4 of the Large Hadron Collider. These results suggest the potential for an experimental determination of quark and gluon jet modifications.


The role of the chiral anomaly in polarized deeply inelastic scattering

Andrey Tarasov, The Ohio State University
2:00 PM Wednesday, online ZOOM

I will discuss the role of the chiral "triangle" anomaly in deeply inelastic scattering (DIS) of electrons off polarized protons employing a worldline formalism, which is a powerful framework for the computation of perturbative multi-leg Feynman amplitudes. I will demonstrate how the triangle anomaly appears at high energies in the DIS box diagram for the polarized structure function g1(xB,Q2) in both the Bjorken limit of large Q2 and in the Regge limit of small xB. I will show that the operator product expansion is not required to extract the anomaly in either asymptotics, and the infrared pole in the anomaly arises in both limits. The leading contribution to g1, in both Bjorken and Regge asymptotics, is therefore given by the expectation value of the topological charge density.


Open string QED meson description of X17, E38, and dark matter

Cheuk-Yin Wong, Oak Ridge National Laboratory
2:00 PM Wednesday, online ZOOM

A quark and an antiquark interact not only with the quantum chromodynamical (QCD) interaction but also with the quantum electrodynamical (QED) interaction. As a consequence, a quark-antiquark pair can form QED bound states in QED, analogous to the QCD meson states in QCD [1]. The predicted masses of the neutral isoscalar and isovector quark-antiquark QED meson states are close to the masses of the X17 and E38 particles observed recently at about 17 and 38 MeV, respectively. The matching of the masses leads to the suggestion that these particles may be the quark-antiquark QED meson states arising from the quantum electrodynamical interaction between a quark and an antiquark. The implication of the possible existence of such QED meson states on the occurrence of anomalous soft photons in high-energy hadron production, the dark matter, and the production of the primordial dark matter during the quark-gluon plasma phase transition at the early history of the universe will be discussed.


Quarkonium production and polarization in the color evaporation model

Vincent Cheung, UC Davis
2:00 PM Wednesday, online ZOOM

One of the best ways to understand hadronization in QCD is to study the production of quarkonium. The color evaporation model (CEM) and Nonrelativistic QCD (NRQCD) can describe production yields rather well but spin-related measurements like the polarization are stronger tests. In this talk, I will outline the quarkonium polarization puzzle and present recent attempts to use the color evaporation model to describe the polarization of quarkonium production.


The origin of single transverse-spin asymmetries in high-energy collisions

Alexei Prokudin, Penn State University Berks & JLab
12:00 PM Tuesday, Knudsen 5-142

We present, for the first time, a phenomenological analysis that demonstrates all single transverse-spin asymmetries (SSAs) in high-energy collisions have a common origin. Namely, they are due to the intrinsic quantum-mechanical interference between single- and multi-parton states. We perform the first global fit of data from Semi-Inclusive Deep Inelastic Scattering, Drell-Yan, e+e annihilation into hadron pairs, and proton-proton collisions. Consequently, we are able to identify a unique set of functions that describes all observed SSAs. Furthermore, we achieve the first phenomenological agreement with lattice on the tensor charge of the nucleon.


Jets at the EIC

Miguel Arratia, University of California, Riverside
12:00 PM Friday, Knudsen 4-134

The Electron-Ion Collider (EIC) will not only extend studies made in fixed-target experiments to uncharted kinematic domains, but also will enable measurements of an unprecedented type. For example, the EIC will yield the first jets in either electron-nucleus collisions or polarized electron-proton collisions. Given that jets are excellent proxies to partons, they will be instrumental to expand our knowledge of the structure and behavior of the nucleon and nuclei in terms of quarks and gluons - a key goal of modern nuclear physics. In this talk, I will focus on the prospects of using jets as precision probes of nuclei as well as for the 3D-imaging of the proton. I will discuss the experimental prospects of measurements such as electron-jet correlations, jet fragmentation, and jet substructure. These measurements will exploit the unprecedented combination of hermetic tracking, particle identification, and calorimetry of the future EIC detectors.


Spin polarization of gauge bosons in rotating plasma

Andrey Sadofyev, Los Alamos National Laboratory
12:00 PM Tuesday, Knudsen 4-134

I will show that the chiral vortical effect (CVE) known to take place for massless fermions in a rotating system can be, in fact, generalized to particles of arbitrary spin. These effects are particularly interesting since they describe the polarization of quarks, gluons, and photons in rotating QGP produced in heavy-ion collisions. For gauge bosons the local polarization current is not gauge invariant making it harder to use this object on practice. This issue can be resolved if one focuses on a class of gauge-invariant but non-canonical polarization currents of gauge bosons known as zilches. I will further show that CVE for gauge bosons has a counterpart in the general zilch current - zilch vortical effect (ZVE) and discuss how ZVE arises in a simple theoretical setup.


Partonic structure of the proton from large-momentum effective theory

Xiangdong Ji, University of Maryland
12:00 PM Friday, Knudsen 4-134

Partonic properties of the proton involve Minkowski light-front correlations and cannot directly be solved through the standard lattice field theory method. I propose an effective theory approach to obtain light-front physics through calculating the physical properties of the proton at moderately large momenta (boost factor gamma = 2~5) on lattice, and expanding them around gamma=infinity. Recent calculations have demonstrated significant potential of this large-momentum effective theory approach.


Transverse momentum dependent soft function and PDF from LaMET on lattice

Yizhuang Liu, T.D. Lee Institute
12:00 PM Friday, Knudsen 5-137

In the talk I will present our recent work on lattice TMDPDF and soft factor. I will show that the TMD soft function (or soft factor) in the off-light-cone scheme is equivalent to an equal-time form factor, thus can be simulated on lattice from Euclidean HQET or from large momentum light-meson form factor. This extends the large momentum effective theory (LaMET) to the case with two light-cone directions. With the help of the off-light-cone soft factor and lattice calculable quasi-TMDPDF one can match to physically important light-cone TMDPDF using perturbation theory. I will also present certain interesting relations between soft-factors and rapidity-regularization-independent factorization scheme directly in terms of quasi-TMDPDF.


Initial Conserved Charges in Nuclear Geometry

Mauricio Martinez Guerrero, North Carolina State University
2:00 PM Wednesday, Knudsen 4-134

In the modeling of the initial conditions for high energy nuclear collisions, it is usually assumed that the energy density is composed almost entirely of gluon fields. However, quarks, which constitute a minority of the overall energy density, carry conserved charges such as baryon number and electric charge which are sensitive to entirely different transport properties of the QGP. We present a new model for reconstructing the initial distribution of quarks and antiquarks in a heavy ion collision by sampling the (g-->qqbar) splitting function over the initial energy density. In this way, we provide a new numerical tool which can be used to supplement models for the initial energy density with the associated conserved charges. As a result, we find a strong flavor dependence of the initial geometries of different quarks, as characterized by their initial eccentricities. Importantly, we find that the strange quark geometry differs significantly from the geometry of the bulk energy density in an event, reflecting the geometry of the hot spots rather than the geometry of the bulk. This new tool for the initial conditions, when coupled to a charge-conserving viscous hydrodynamics code, will open the door to studying a wealth of new charge and flavor dependent correlations and transport parameters of the QGP.


XENON1T and beyond: the search for the heavy and light dark matter Particles

Kaixuan Ni, UCSD
12:00 PM Wednesday, Knudsen 4-134

Large underground detectors made significant progresses in recent years to push the sensitivity for dark matter detection. In particular, the XENON1T experiment with the world’s first ton-scale liquid xenon time projection chamber, located at Gran Sasso Underground Laboratory in Italy, is leading the frontier of heavy dark matter searches. Recently, the experiment also reported new constraints for light (sub-GeV) dark matter interactions with ordinary matter. In this talk, I will review these recent results and also present new efforts, including XENONnT, LBECA, DARWIN experiments that will continue to search for heavy and light dark matter particles with unprecedented sensitivity in the next decade.


The inner life of protons: QCD at work from the LHC to IceCube

Juan Rojo, VU University
12:00 PM Wednesday, Knudsen 4-134

The determination of the partonic structure of the proton, quantified by the Parton Distribution Functions (PDFs), is a central component of the physics program at the Large Hadron Collider (LHC). In this talk, I review our current understanding of the quark and gluon structure of the proton, which emphasis for the implications for LHC phenomenology and searches for new physics. I will then also discuss other recent perspectives of the nucleon structure for applications in other fields, in particular their impact in high-energy neutrino telescopes and for the characterization of the quark-gluon plasma in heavy ion collisions.


Jets, TMDs and resummation

Wounter Waalewijn, University of Amsterdam & Nikhef
12:00 PM Monday, Knudsen 4-134

I will discuss (i) my recent calculation of the jet shape at NLL’, (ii) a new method I proposed to extract transverse momentum dependent distributions parton distributions, using jets in semi-inclusive deep-inelastic scattering (iii) the resummation of multiple logarithms, considering beam thrust and qT for the Drell-Yan process as a concrete example.


Precision phenomenology at hadron colliders

Xiaohui Liu, Beijing Normal University
12:00 PM Monday, Knudsen 4-134

In the past few years, tremendous progress has been made in pushing the theoretical accuracy for understanding the processes at the hadron colliders out of the first principles. In this talk, I will give a short review on the collider physics precision frontier. Selected topics related to the Higgs, the electroweak gauge bosons and the jets will be presented to highlight the current status of the precision predictions for the collider phenomenology.


Precision Jet Substructure with the ATLAS Detector at 13 TeV

Benjamin Nachman, Lawrence Berkeley National Laboratory
12:00 PM Friday, Knudsen 4-134

We are in the midst of a QCD renaissance, with significant advances in both experimental and theoretical studies of jet substructure. I will discuss recent developments from the ATLAS experiment, including the first measurement of a jet substructure quantity at a hadron collider to be compared with next-to-next-to-leading-logarithm calculations as well as a recent measurement of gluon splitting inside large-radius jets. These measurements are part of an exciting program to measure fundamental parameters of the Standard Model, search for new particles, study quantum properties of inherently interesting emergent phenomena, and tune Monte Carlo event generators. I will conclude by briefly discussing future directions at the interface of jet physics and machine learning and quantum information.


Are there higher order corrections to Chiral Magnetic (vortical) Effects?

Defu Hou, Central China Normal University, China
12:00 PM Friday, Knudsen 4-134

Anomaly induced transport phenomena in systems with chiral fermions have attracted wide interests ranging from high energy physics to condensed matter physics. Because of the non-renormalization theorem of chiral anomalies, it is normally expected that the chiral magnetic (vortical) currents are free from higher order corrections. In this talk, I will present our study on the radiative corrections to chiral magnetic current at both zero and nonzero temperature. Our motivation is a radiative correction to the matrix element of the anomalous Ward identity in massless QED stemming from a three-loop diagram where the two photons coming from the one-loop anomalous triangle are re-scattered. Through the interplay between the Ward identity and the infrared subtlety of the fermion loop integral, we obtain the 3-loop corrections to the chiral magnetic current at zero temperature. The correction does not invalidate the Adler-Bardeen theorem but will contribute to the chiral magnetic current of massless fermions at zero temperature. At a nonzero temperature, the infrared subtlety disappeared in a static magnetic field and the three-loop diagram does not contribute to the chiral magnetic current any more. The generalization to all orders of the massless QED and the QCD corrections are discussed. We will also present possible higher-order corrections to the chiral vortical effect.

01/28/2019 - 01/30/2019

UCLA 2019 Santa Fe Jets and Heavy Flavor Workshop
Location: IDRE Portal, Math Sciences Building 5628


Holographic real-time dynamics near a critical point

Maximilian Attems, Universidade de Santiago de Compostela, Spain
11:00 AM Monday, Knudsen 4-134

Ever since the discovery of the quark-gluon plasma (QGP) the location of the critical point in the QCD phase diagram - the end point of the first-order transition between hadron matter and QGP - has been a main research goal for heavy-ion collision experiments. We use the gauge/gravity duality to study as first a four-dimensional, strongly-coupled gauge theory with a first-order thermal phase transition. In the dual gauge theory we calculate the evolution and saturation of the spinodal instability. We uncover a new surprising example of the applicability of hydrodynamics to systems with large gradients. We discover with shockwave collisions that in theories with a first-order phase transition, a long-lived, quasi-static state may be formed. Moreover, we show the Mueller-Israel-Stewart-type formulation of hydrodynamics to fail to describe pressures near a critical point.


Extraction of partonic unpolarized TMDs and Sivers function 

Filippo Delcarro, University of Pavia
11:00 AM Wednesday, Knudsen 4-134

A recent extraction of the Sivers function from azimuthal asymmetries in semi-inclusive deep inelastic scattering (SIDIS) will be presented. This analysis takes into account contributions of transverse momentum dependent (TMD) evolution and features a parametrization of unpolarized TMDs determined directly from data. Then, also an overview of a global extraction of TMDs from unpolarized SIDIS, Drell-Yan and Z boson production data will be given. Finally, a comparison of these studies with results obtained from other collaborations will be discussed, together with future outlooks for the phenomenological analysis of TMDs.


Nucleon 3D/spin structure: towards the precision era

Miguel G. Echevarria, INFN/Pavia
12:00 PM Wednesday, Knudsen 4-134

I will first review the formalism of transverse-momentum-dependent factorization, mainly from the effective field theory points of view, which gives access to transverse-momentum-dependent functions (TMDs). Then, I will summarize the current status of higher-order perturbative QCD calculations of TMD evolution/resummation. Finally, I will present new results for the QED corrections to the evolution of TMDs.


The (spin) structure of the nucleon beyond the Parton Model

Marc Schlegel, New Mexico State University
12:00 PM Friday, Knudsen 4-134

I will provide a brief review on the structure of the nucleon. In particular, I will discuss methods to access the nucleon structure beyond the parton model. This gives more detailed information on the 3-d structure as well as dynamics of partons in the nucleon. One generalization of the collinear parton model is Transverse Momentum Dependent (TMD) factorization. I will focus on gluon TMD distributions that may be constraint by data taken at the LHC. Another way to get more insight into the nucleon structure is to study transverse spin effects. I will present some examples to illustrate these effects.


Probing TeV physics with precision calculations of nucleon structure using lattice QCD

Rajan Gupta, Los Alamos National Laboratory
12:15 PM Friday, Knudsen 4-134

This talk will present a number of high precision results on matrix elements of quark bilinear operators between nucleon states using lattice QCD. From these, we extract a number of exciting quantities, at the intersection of nuclear and particle physics. We show that the axial charge g_A, a fundamental parameter encapsulating the weak interaction of nucleons, is calculated with a few percent accuracy. Results for the scalar and tensor charges, g_S and g_T, which combined with precision neutron decay distribution probe novel scalar and tensor interactions at the TeV scale. Vector form factors are probed in electron scattering, while axial vector form factors are used in the calculation of the cross-section of neutrinos on nuclear targets. These energy dependent cross-sections are needed to determine the neutrino flux, an important systematic in neutrino oscillation experiments. Finally we will present results for flavor diagonal charges that provide the contribution of the quark spin to the nucleon spin, the quark EDM to the neutron EDM, and needed to determine the cross-section of dark matter with nuclear targets.


Resummation of the D-parameter

Andrew Larkoski, Reed College
1:30 PM Thursday, Knudsen 4-134

The D-parameter is among the oldest and most experimentally well-studied hadronic event shape observables in electron-positron collisions.  Despite this, there does not exist a prediction for the D-parameter from perturbative QCD which captures all logarithmic corrections to any formal accuracy. In this talk, I will discuss our approach to this problem and its resolution, which utilizes recent advances in the field of jet substructure.


Mini-jet Clusters and Mini-Dijet Clusters in High-Energy pp Collisions

Cheuk-Yin Wong, Oak Ridge National Lab
1:30 PM Thursday, Knudsen 4-134

Mini-jets and mini-dijets provide useful information on multiple parton interactions in the low-pT region. We attempt to develop a clustering algorithm to identify minijets by using the k-means clustering method, with a cluster-number selection principle. Upon testing the algorithm using minimum-bias events generated by PYTHIA, for pp collision at sqrt{s}=200 GeV, we find that multiple mini-jet-like and mini-dijet-like clusters of low pT hadrons occur in high multiplicity events.  However similar clustering properties are also present for particles produced randomly in a finite pseudo-rapidity and azimuthal angle space. The ability to identify mini-jets and mini-dijets may need to depend on the additional independent assessment of the dominance of the parton-parton hard-scattering process in the low-pT region.


From the QCD phase diagram to jet quenching in heavy ion collisions

Jasmine Brewer, MIT
1:30 PM Thursday, Knudsen 4-134

In this talk, I will discuss a new observable for mapping the QCD phase diagram at RHIC, and a model for understanding the effects of dynamics in the quark gluon plasma on jet energy loss. In the first part of this talk, I will demonstrate that at RHIC energies around 20 GeV the non-trivial dependence of baryon density on rapidity can give rise to fluctuation measures which are non-monotonic in rapidity. I will propose an observable that exaggerates the signature of criticality in the rapidity dependence, and show that this kind of "rapidity scan" provides complementary signatures of criticality to those from the beam energy scan. In the second part of this talk, I will demonstrate that velocities and velocity gradients in the medium have a large effect on energy loss in a holographic model of jets. I will show that including the effects of velocities and velocity gradients in a reasonable model of the medium increases the stopping distance of high energy jets by as much as a factor of two.


Probe Quark-Gluon-Plasma with Heavy Quarks in sPHENIX Experiment at Relativistic Heavy Ion Collider

Ming Liu, Los Alamos National Laboratory
1:00 PM Monday, Knudsen 4-134

The 2015 US Nuclear Physics Long Range Plan calls for a state-of-the-art jet and upsilon detector at RHIC, called sPHENIX, to study the microscopic nature of the QGP, complementing similar studies at the CERN LHC. The sPHENIX detector will provide precision vertexing, tracking and full calorimetry over pseudo-rapidity |eta| < 1.1 and full azimuth at the full RHIC collision rate, delivering unprecedented data sets for jet and upsilon measurements at RHIC. This will enable the three pillars of the sPHENIX physics program, i.e., 1) studies of jet structure modifications, 2) measurements of heavy-flavor tagged jet production and 3) precision upsilon spectroscopy. In this talk I will present an overview of the sPHENIX heavy flavor physics program, from detector design, expected construction and running schedule and planned physics program.


Power corrections to TMD factorization

Andrey Tarasov, Brookhaven National Laboratory
12:00 PM Monday, Knudsen 4-134

In this talk, I will show how to calculate higher-twist power corrections to TMD factorization and consider two examples: Higgs production through gluon-gluon fusion and Z-boson production in hadron-hadron collisions.


Jet-medium interactions in dual models

Andrey Sadofyev, Los Alamos National Laboratory
12:00 PM Wednesday, Knudsen 4-134

Probably the most important experimentally accessible probes of the quark-gluon plasma (QGP) produced in heavy-ion collisions are sprays of energetic particles - jets. The jet evolution in medium involves multiple energetic scales making it difficult to study with any particular theoretical approach. We propose a novel way for hybridizing relevant inputs from perturbative QCD and a strongly coupled holographic gauge theory in the service of modeling jets in QGP. We construct an ensemble of back-to-back dijets to qualitatively study how the shapes of the individual jets and the asymmetry in the energy of the pairs of jets in the ensemble are modified by their passage through an expanding cooling droplet of strongly coupled plasma. Each jet in the ensemble is represented holographically by a string in the dual 5d theory with the distribution of initial energies and opening angles in the ensemble given by perturbative QCD.

11/08/2017 - 11/10/2017

Advances in QCD and Applications to Hadron Colliders Workshop
Location: PAB 4-330


Jet angularity and jet mass at the LHC

Kyle Lee, Stony Brook University
3:00 PM Tuesday, Knudsen 4-134

Jet substructure measurements have a wide range of important applications in the present day colliders like LHC and RHIC, such as improving reconstruction techniques, increasing sensitivity for new physics beyond SM, discriminating quark and gluon jets, and more. One of the most recent advancements was made in understanding the theoretical framework of measuring jet substructures in the inclusive jet production environment. In this talk, I will discuss the theoretical framework of jet substructure measurements in the semi-inclusive jet production. After discussing briefly some of the substructures that were calculated in the semi-inclusive setting, I will focus on the recent work on jet angularity and jet mass measurements as a particular substructure of interest. I will discuss the factorization, resummations using RG equation of different factorized parts, and nonperturbative shape function. Jet mass has already been measured for single inclusive jet production at the LHC, and we make comparison with the experimental data. On the other hand, jet angularity can be measured as well at the LHC in the future. 


Spin and cold nuclear matter physics at RHIC - now and the next 5 years

Ralf Seidl, RIKEN, Japan
2:00 PM Friday, Knudsen 4-134

RHIC has provided various important inputs for the study of the spin structure and cold nuclear matter effects. The contribution of gluons to the spin of the proton has been found to be substantial and sea quarks appear to be asymmetrically polarized. Furthermore various new asymmetries have been found related to the transverse spin structure of the nucleon which shed light onto the strong interaction itself. The RHIC data also shows interesting cold nuclear matter (CNM) effects which suggest a suppression of gluons in nuclei at small momentum fractions. Especially the CNM and transverse spin effects are most striking at high rapidities where both RHIC experiments, PHENIX and STAR, have so far only limited instrumentation. In the remaining years before the EIC the plan of the spin and CNM community is to concentrate on the forward region. An update of the existing measurements and future plans will be given.


Evidence for a critical endpoint in the QCD phase diagram from measuring mass and radius of compact stars

David Blaschke, University of Wroclaw, Poland & JINR Dubna, Russia & NRNU (MEPhI), Russia
2:00 PM Monday, Knudsen 4-134

There is a one-to-one relationship between the mass-radius relationship for compact stars and the equation of state of cold dense neutron star matter. Measuring simultaneously the masses and radii for a number of neutron stars (mostly seen as pulsars) at sufficient accuracy (as with the recently launched NASA mission NICER) thus allows to measure the equation of state and eventually to tell whether there is a phase transition to quark matter in compact star interiors. I shall discuss that the possible observation of high-mass twins in the mass-radius diagram might provide evidence for a strong first order phase transition which in turn would entail that there must exist a critical endpoint (CEP) of such phase transitions in the QCD phase diagram. The very existence and the possible location of the CEP is a major goal of research, in theory as well as in heavy-ion collision experiments.

05/04/2017 - 05/06/2017

Topical Workshop on QCD Structure of Nucleons in the Modern Era
Location: PAB 4-330


Towards a universal fit of PDFs and FFs

Nobuo Sato, Jefferson Lab/University of Connecticut
12:00 PM Tuesday, Knudsen 4-134

In this talk, I will discuss a recent progress on global QCD analysis of fragmentation functions and polarized parton distributions using Monte Carlo methods.

03/27/2017 - 03/29/2017

2017 QCD Workshop on Chirality, Vorticity and Magnetic Field in Heavy Ion Collisions
Location: PAB 2-434


Jet substructure and heavy flavor production at the LHC

Felix Ringer, Los Alamos National Laboratory
12:00 PM Thursday, Knudsen 4-134

We discuss the treatment of inclusive jets and their substructure within Soft Collinear Effective Theory (SCET). The cross section for these observables can be written in a factorized form in terms of hard functions and so-called semi-inclusive jet functions. The semi-inclusive jet functions satisfy renormalization group (RG) equations which take the form of standard timelike DGLAP evolution equations, analogous to collinear fragmentation functions. By solving these RG equations, the resummation of potentially large single logarithms in the jet size parameter R can be achieved. An important jet substructure observable is the distribution of hadrons inside a reconstructed jet which is known as the jet fragmentation function. In this talk, we consider the in-jet fragmentation of light charged hadrons, heavy flavor mesons and quarkonia. We also discuss the extension of these observables to heavy-ion collisions as they are currently in the focus of the experimental efforts at the LHC.


Jet quenching in heavy-ion collisions

Guang-You Qin, Central China Normal University
11:00 AM Thursday, Knudsen 4-134

The strongly-interacting quark-gluon plasma (QGP) was one of the most important discoveries in relativistic heavy-ion collisions at RHIC and the LHC. Jet quenching, mainly characterized by parton energy loss and transverse momentum broadening experienced by high energy partons as they traverse and interact with the produced QGP, provides one of the important tools to study the properties of the hot and dense nuclear matter. In this talk, I will present some recent works on jet-medium interaction, with focus on the nuclear modifications of jet rates, jet structures, and jet-like correlations.