# Seminars

**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. For travel information such as flight, direction, parking, and etc, please refer to our **Visiting UCLA** information.

**05/03/2019**

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.

**02/08/2019**

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

**01/07/2019**

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 collison 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.

**10/31/2018**

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.

**10/17/2018**

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.

**08/10/2018**

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.

**06/01/2018**

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.

**04/05/2018**

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.

**03/01/2018**

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 pseudorapidity 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.

**02/08/2018**

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.

**01/08/2018**

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 pseudorapidity |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.

**12/04/2017**

Power corrections to TMD factorization

Andrey Tarasov, *Brookhaven National Laboratory*

12:00 PM Monday, Knudsen 4-134

In this talk, I wil 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.

**11/29/2017**

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

**11/07/2017**

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.

**10/06/2017**

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.

**08/14/2017**

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

**05/02/2017**

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

**03/09/2017**

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.

**02/16/2017**

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.