12/10/2020

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.

12/03/2020

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.

09/30/2020

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.

09/09/2020

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(x_B,Q²) in both the Bjorken limit of large Q² and in the Regge limit of small x_B. 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.

08/12/2020

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.

08/05/2020

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.

03/10/2020

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.

02/14/2020

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.

01/14/2020

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.

01/10/2020

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.