12/02/2022 - 12/04/2022

Chirality, Vorticity and Magnetic Field in Heavy Ion Collisions

Physics and Astronomy Building, Room 4-330

12/01/2022

What carries the baryon quantum number?

Prithwish Tribedy, BNL
2:00 PM Thursday, Hybrid (Knudsen Hall 5-142 and online ZOOM)

One puzzling feature of ultra-relativistic nucleus-nucleus collisions is the apparent substantial baryon excess in the mid-rapidity region. Contrary to standard assumptions it has been proposed that the baryon quantum number could be carried by a non-perturbative Y-shaped topology of gluon fields called the baryon junction rather than by the valence quarks. The gluon junctions as baryon carriers can lead to significantly larger baryon-stopping at mid-rapidity compared to that of quarks and could resolve the puzzle. To test whether quarks or gluon junctions carry the baryon quantum number, we propose to study the correlation between baryon and charge stopping in isobar collisions at RHIC. We also argue that semi-inclusive photon-induced processes (γ+p/A) at RHIC kinematics provide an ideal opportunity to search for the signatures of the baryon junction by studying the production of baryons correlated with enhanced production of mesons. In this case we discuss the recent preliminary measurements in photonuclear processes from STAR and point out how such measurements can be further validated in e+p/A collisions at the EIC. Ref: [1] J. D. Brandenburg, N. Lewis, P. Tribedy and Z. Xu, [arXiv:2205.05685 [hep-ph]].

11/14/2022

Quantum Simulation for Phase Transitions

Fanyi Zhao, UCLA
11:00 AM Monday, Hybrid (Knudsen Hall 5-142 and online ZOOM)

The Nambu-Jona-Lasinio (NJL) model has been widely studied for investigating the chiral phase structure and chirality charge of strongly interacting matter. The study of the thermodynamics of field theories within the framework of Lattice Field Theory is limited by the sign problem, which prevents Monte Carlo evaluation of the functional integral at a finite chemical potential. Using the quantum imaginary time evolution (QITE) algorithm, we construct a quantum simulation for the (1+1) dimensional NJL model at finite temperatures, chemical potentials and chiral chemical potentials. We observe consistency among digital quantum simulation, exact diagonalization and analytical solution, indicating further applications of quantum computing in simulating QCD thermodynamics.

11/14/2022

Generalized TMDs and parton Orbital Angular Momentum

Shohini Bhattacharya, Brookhaven National Lab
11:00 AM Monday, online ZOOM

Generalized TMDs (GTMDs) of hadrons are the most general two-parton correlation functions. The Fourier transforms of GTMDs are partonic Wigner functions. During the past few years, several interesting developments have taken place in this field. In this talk, we give a brief overview of these objects and the various developments that has taken place, including, in particular, the state-of-the-art of observables for these quantities.

10/24/2022

Study of Lambda hyperon's spin polarization within the formalism of hydrodynamics with spin

Rajeev Singh, Stony Brook University
11:00 AM Monday, online ZOOM

Since the first positive measurement of the Λ-hyperon global spin polarization in heavy-ion collisions by STAR in 2017, the understanding of the nature of this phenomenon is one of the most intriguing challenges for the scientific community. As relativistic fluid dynamics celebrates multiple successes in describing the collective dynamics of the QCD matter in such reactions, the natural question arises of whether the spin dynamics can also be modeled in such a framework. In this talk, the motivation for and recent outcomes of the experimental hunt for the macroscopic footprints of quantum spin in the relativistic heavy-ion collisions will be presented and the theoretical challenges connected with formulating its collective description will be discussed. In addition, I will also present the recent results of the space-time evolution of spin polarization within the framework of hydrodynamics with spin based on the de Groot - van Leeuwen - van Weert forms of energy-momentum and spin tensors in the non-boost invariant background. Related papers: https://arxiv.org/abs/2112.01856, https://arxiv.org/abs/2103.01013, https://arxiv.org/abs/2103.02592, https://arxiv.org/abs/2011.14907, https://arxiv.org/abs/1901.09655.

09/15/2022

3D structure of the proton: from partons to strong fields

Yacine Mehtar-Tani, Brookhaven National Lab
2:00 PM Thursday, Hybrid (Knudsen Hall 5-142 and online ZOOM)

At short distances the inner structure of the proton is well described by weakly interacting partons. However, at high enough energy or equivalently small Bjorken x, gluon proliferate and nonlinear interactions set in leading to the phenomenon of gluon saturation which is best described by strong classical fields dynamics. I will discuss in this talk a novel approach to inclusive DIS that allows from first principles to connect these two seemingly different pictures of the proton structure that are reminiscent of the more familiar wave/particle duality. I will derive a new factorization formula and its associated 3D gluon operator that interpolates between gluon PDF and the dipole operator in the Bjorken and Regge limits, respectively. I will discuss how this top down approach accounts systematically for the large collinear logs whose resummation is necessary to circumvent the problem of negative cross-sections encountered in small x evolution at NLO.

08/26/2022

A Maximally entangled proton and charged hadron multiplicity in Deep Inelastic Scattering

Krzysztof Kutak, Institute of Nuclear Physics, Polish Academy of Sciences
9:00 AM Friday, online ZOOM

We study the proposal by Kharzeev-Levin to determine entanglement entropy in Deep Inelastic Scattering (DIS) from parton distribution functions (PDFs) and relates the former to the entropy of final state hadrons. We find several uncertainties in the current comparison to data, in particular uncertainties related to the overall normalization, the relation between charged versus total hadron multiplicity in the comparison to experimental results as well as different methods to determine the number of partons in Deep Inelastic Scattering. We further provide a comparison to data based on leading order HERA PDF as well as PDFs obtained from an unintegrated gluon distribution subject to next-to-leading order Balitsky-Fadin-Kuraev-Lipatov and Baltisky-Kovchegov evolution. Within uncertainties we find good agreement with H1 data. We provide also predictions for entropy at lower photon virtualities, where non-linear QCD dynamics is expected to become relevant.

08/12/2022

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.

07/29/2022

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.

07/15/2022

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

07/06/2022

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.

06/17/2022

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.

06/03/2022

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.

Refs:
[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

05/20/2022

The fragmentation region of a heavy-ion collision

Isobel Kolbé, Institute for Nuclear Theory at the University of Washington
9:00 AM Friday, Knudsen Hall  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.

05/06/2022

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 η_c), 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^-, µ⁺ µ^- and the branching fraction is logarithmically enhanced by the charm-quark fragmentation mechanism.

04/29/2022

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 studying 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.

04/26/2022

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).

04/15/2022

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.

02/16/2022

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.

02/09/2022

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.