December 10, 4:00PM

Online Seminar

Sanghwa Park, Stony Brook University

Title: New precision measurement of the neutral weak form factor of 208Pb

Abstract: High precision parity-violating electron scattering (PVES) experiments have been used to study a wide range of physics. Besides tests of the standard model a series of nuclear studies have shown the versatility of PVES. Polarized elastic electron-nucleus scattering is sensitive to the neutral weak form factor and therefore provides measurements of the neutron distribution in a nucleus. Neutron rich nuclei are of particular interest because of their sensitivity to important parameters in the nuclear equation of state. The PREX2 experiment has recently completed its new data taking in 2019 using a longitudinally polarized electron beam at the CEBAF accelerator impinging on a 208Pb target. In this talk, I will discuss the overview of the experiment, the result as well as its implications.

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November 12, 10:00AM

Online Seminar

Liupan An, Sezione INFN di Firenze

Title: Studies on exotic hadrons at LHCb

Abstract: Exotic hadrons, which are composed of more than three valence quarks, can provide new insights into the internal structure and dynamics of hadrons, thus improving our knowledge of the non-perturbative regime of QCD. Since 2003, various candidates for exotic states have been observed, to which the LHCb experiment has made major contributions. This seminar discusses the studies on exotic hadrons at LHCb. The most recent observation of structure in the $J/\psi$-pair invariant mass spectrum and study of resonant structure in $B^+ \to D^+ D^- K^+$ decays are presented.

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October 15, 4:00PM

Online Seminar

Xiaoxuan Chu, Brookhaven National Lab

Title: Signature of gluon saturation: from STAR to EIC 

Abstract: The gluon parton distribution function (PDF) grows with lower and lower x very fast. As the total scattering cross section is bound by quantum mechanics, the raise of the gluon density has to be tamed. A definitive discovery of non-linear effects in QCD and as such the saturation regime would significantly improve our understanding of the proton structure and of nuclear interactions at high energy. Data recorded during the 2015 RHIC run with the STAR Forward Meson Spectrometer (FMS, 2.6 ≤ η ≤ 4.0), allow to measure the azimuthal correlation between two particles, which has been proposed to be one of the most direct and sensitive channels to access the underlying nonlinear gluon dynamics. In this talk, we will present new results for di-hadron correlations as a function of A and transverse momenta in p+p, p+Au and p+Al collisions at STAR.  New opportunities for measurements with the STAR forward upgrade and future EIC to study non-linear effects in QCD will also be discussed. 

October 8, 4:00PM

Online Seminar

Pawel Nadel-Turonski, Stony Brook University

Title: A novel compact detector concept for the Electron-Ion Collider

Abstract: The Electron-Ion Collider (EIC) at Brookhaven National Laboratory is the next-generation US facility for “cold QCD” science, which includes understanding the spin structure of the proton and the spatial structure of the glue in nucleons and nuclei. The EIC will be the first collider capable of storing polarized electrons, protons, and light ions. It will also be able to accelerate all ions from deuterium to uranium. To support this extensive program, the collider will need one, and preferably two, general-purpose detectors. A unique challenge of the EIC detector is the inherent asymmetry between the two beam directions, both in terms of particle species and momenta, and the physics (low-x hadrons, for instance, tend go more in the electron beam direction while high-x ones go in the hadron beam direction). The resulting detector thus not only needs a fully hermetic suite of subsystems for tracking, calorimetry, and particle identification (which is of particular importance to EIC physics), but also needs to satisfy very different requirements at different angles (pseudorapidities) – and it needs to accomplish all of this within a moderate budget. This presentation will cover some of the key physics opportunities and requirements at the EIC, followed by a detailed look at an affordable compact EIC detector concept that makes it possible to reach all performance goals. As the name suggests, it does this by employing a combination of technologies that allows reducing cost by reducing subsystem size rather than compromising quality. The compact design is also beneficial for subsystem integration and integration into the interaction region of the accelerator.

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October 1, 4:00PM

Online Seminar

Edward Shuryak, Stony Brook University 

Title: Nonperturbative quark-antiquark interactions in mesonic form factors

Abstract: The existing theory of hard exclusive QCD processes is based on two assumptions: (i) factorization into a hard block times light front amplitudes (or wave functions); (ii) use of perturbative gluon exchanges within the hard block. However, unlike DIS and jet physics, the characteristic momentum transfer Q involved in the factorized block is not large enough for this theory to be phenomenologically successful. In this work, we revisit the latter assumption (ii), by explicitly calculating the instanton-induced contributions to the hard block, and show that they contribute substantially to the vector and scalar form factors of the pseudoscalar and vector mesons, over a wide range of momentum transfer.

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(Slides)

August 20, 4:00PM

Online Seminar

Raju Venugopalan, Brookhaven National Lab

Title: Separating fact from fantasy in the proton's spin*: the chiral anomaly and the proton spin puzzle

Abstract: Anomalies in gauge theories are of great interest because they represent topological features of the theory that are not contained in the Lagrangian. We will discuss here the role of the chiral anomaly in deeply inelastic scattering (DIS) of electrons off polarized protons where one observes a subtle interplay between hard parton dynamics and the topology of the QCD vacuum. Using a powerful worldline formalism, we demonstrate that the "triangle" graph provides the dominant contribution in the  DIS "box" diagram both in the Bjorken limit of large Q^2 and in the Regge limit of small x_Bj. We then discuss how the infrared pole of the anomaly is canceled in this formalism leading to novel emergent dynamics governing how the spin of the proton diffuses from fast (large x) modes to slow (small x) modes. In particular, we present an effective action, consistent with anomalous chiral Ward identities, that is governed by dynamical scales corresponding to the topological charge density and the gluon saturation scale. We conjecture how the latter influences the former and emphasize that these ideas can be tested at the Electron-Ion Collider.

* in homage to 30 years of the seminal paper by R. L. Jaffe and A. Manohar (Nucl. Phys. B 337, 509 (1990))

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August 6, 4:00PM

Online Seminar

Raghav Kunnawalkam Elayavalli, Wayne State University

Era of Jet-SubStructure and its utility in high energy collisions

Jets, originating from hard scatterings of quarks/gluons (partons), have been established as a very powerful tool of study in high energy colliders. Measurements utilizing jets have been performed at nearly all major collider experiments as probes of the standard model (and BSM), spin, polarization, fundamental QCD and also played an important role in studies of the Quark-Gluon Plasma (QGP) via parton energy loss or jet quenching. Since jet evolution in vacuum is intimately dependent on both the momentum and angular scales, disentangling these scales via jet substructure (JSS) tools can lead to a more differential study of the parton shower. In essence, understanding parton evolution and JSS in vacuum is a necessary prerequisite for qualitatively describing how jets are quenched in the QGP, which in turn leads to extracting the QGP microscopic properties via jet-tomography. In this talk, I will introduce JSS and present recent measurements from the STAR collaboration of JSS observables in p-p, p+Au and Au-Au collisions at $\sqrt{s_{NN}} = 200$ GeV. These results are aimed at describing the vacuum parton shower and study the impact of cold and hot nuclear matter effects differentially with jet topology. I will also discuss an important application JSS whereby we isolated a special selection of jets in heavy ion collisions who’s energy loss mechanism can then be further studied in a differential fashion. I will conclude the talk by contextualizing these measurements and briefly discuss some ongoing work related to upcoming heavy ion runs at RHIC and at the recently approved EIC, where JSS can contribute towards studies of quantum entanglement and hadronization within jets in a clean environment.

July 23, 4:00 PM

Online Seminar

Yuri Kovchegov, Ohio State University

Small-x Contribution to the Proton Spin Puzzle

An integral part of the proton spin puzzle is the contribution to the proton spin coming from quarks and gluons having small very values of the Bjorken x variable. This contribution is mostly beyond the reach of current experiments and is very hard to calculate numerically on the lattice. It appears that a theoretical understanding of quark and gluon helicity distributions at small x is needed to assess the amount of proton spin coming from this region. In my talk I will describe the recent theoretical work aimed at finding the small-x asymptotics of the quark and gluon helicity distributions, along with their orbital angular momenta (OAM). I will derive small-x evolution equations for helicity and solve them to find the small-x asymptotics of the parton helicity distributions and OAM. The results of this work can be compared to the data to be collected at the upcoming Electron-Ion Collider (EIC) in order to extrapolate the small-x helicity distributions to be measured at EIC to even smaller values of x, thus completely constraining the proton spin coming from small x and helping to resolve the proton spin puzzle.

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July 2, 4:00 PM

Online Seminar

Vadim Guzey, National Research Center “Kurchatov Institute”, Petersburg Nuclear Physics Institute (PNPI)

Diffractive dijet photoproduction at the EIC

We will present a detailed study of diffractive dijet photoproduction at the recently approved electron-ion collider (EIC) at BNL. Apart from establishing the kinematic reaches for various energies and kinematic cuts, we make precise predictions at next-to-leading order (NLO) of QCD in the most important kinematic variables. We show that the EIC will provide new and more precise information on the diffractive parton density functions (PDFs) in the pomeron than previously obtained at HERA, illuminate the still disputed mechanism of global vs. only resolved-photon factorization breaking, and provide access to diffractive PDFs. 

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June 18, 4:00 PM

Online Seminar

Felix Ringer, UC Berkeley / LBNL

The dynamics of leading jets and the jet energy loss

Leading jet cross sections play an important role at current and future collider experiments. In this talk I will review a new Effective Field Theory framework that allows for a systematic calculation of leading jet cross sections. Different than inclusive cross sections, leading and subleading jets follow non-linear evolution equations. Interestingly, leading jets allow for a meaningful definition of jet energy loss at the cross section level. I will discuss suitable observables that allow for a direct measurement of jet energy loss in proton-proton and heavy-ion collisions as well as cross sections relevant for the future Electron-Ion Collider. 

June 11, 4:00 PM

Online Seminar

Salina F. Ali, The Catholic University of America

Towards Femtography of the Nucleon: Neutral Pion Electroproduction in the Deeply Virtual Regime

Understanding the structure of the atom in terms of its most basic constituents, the quarks and gluons, is one of the thrusts of twenty first century physics research. Just as the earth orbits around the Sun while simultaneously spinning about its own axis, the quarks and gluons in a proton could have linear motion, orbital motion, and spin – the latter two responsible for the overall proton spin that is exploited daily in thousands of MRI images worldwide. Experimentally, one cannot isolate the quarks and gluons, but one can infer their properties from experiments on nuclei, e.g. protons. High-energy electron beam experiments leading to a final state of a completely-measured set of only a few particles allow to image the deep inside structure of the proton. This is the topic of a new science direction termed "nuclear femtography". In this talk I will discuss an experimental study using exclusive reactions, processes in which the deep inside of the proton is studied with a highly-energetic electron probe by a completely-measured set of only a few particles, e.g. a photon or a neutral pion. I will describe the experimental setup in Hall A of Jefferson Lab, calibrations, and a first look at preliminary extractions of the polarized and unpolarized neutral pion electroproduction cross sections from the DVCS-3 (E12-06-114).

May 7, 4:00 PM

Online Seminar

Miguel Arratia, University of California, Riverside

Jets at the EIC

The EIC will not only allow us to extend traditional studies from fixed-target experiments to uncharted kinematic regions, but also will give us a novel tool: jets. Given that jets are excellent proxies to partons, they will be instrumental to expand our knowledge of the structure 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 feasibility of measurements such as electron-jet and neutrino-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. I will argue that a jet program at the EIC could unleash a new era in the field of 3D imaging of the nucleon. I will discuss implications for the design of EIC detectors. 

March 12, 4:00 PM

BNL: Room 2-38, Physics, Building 510 A

Vladimir Skokov, RIKEN BNL and North Carolina State University

Entanglement, partial set of measurements, and diagonality of the density matrix in the parton model

The proton as a quantum object is in a pure state and is described by a completely coherent wave function with zero entropy. On the other hand in high energy experiments (DIS) when probed by a small external probe, it behaves like an incoherent ensemble of (quasi-free) partons.

In this talk, we define the "entropy of ignorance" which quantifies the entropy associated with ability to perform only a partial set of measurements on a quantum system. For a parton model the entropy of ignorance is equal to a Boltzmann entropy of a classical system of partons. We analyze a calculable model used for describing low x gluons in Color Glass Condensate approach, which has similarities with the parton model of QCD. In this model we calculate the entropy of ignorance in the particle number basis as well as the entanglement entropy of the observable degrees of freedom. We find that the two are similar at high momenta, but differ by a factor of order unity at low momenta. This holds for the Renyi as well as von Neumann entropies. We conclude that the entanglement does not seem to play an important role in the context of the parton model.

Feb 28, 12:30 PM

Stony Brook: Peter Paul Seminar Room C-120, Physics Building

Axel Schmidt, George Washington University

Short-range correlations and the nuclear forces at short distances

The nucleon-nucleon (NN) interaction is the fundamental starting point for a wide range of nuclear physics calculations. While our knowledge of the NN interaction at long range is directly constrained by NN scattering phase shifts and meson-exchange theory, at short distances the picture becomes dramatically more complicated, leading to considerable uncertainty in calculations of high-density nuclear matter, for example, found in the cores of neutron stars. I describe here a new approach: using short-range correlated (SRC) nucleons to learn about the short-distance NN interaction. Through a new theoretical tool called Generalized Contact Formalism, NN interaction models can be used to calculate fully differential cross sections for SRC pair break up reactions and benchmarked against data from the CLAS experiment at Jefferson Lab. I find that non-relativistic NN potential models, combined with Generalized Contact Formalism do a good job of explaining the electron-induced knock-out of correlated nucleons, even out to momenta approaching 1 GeV/c, well beyond the reach of input data to which these potentials were tuned. This lends strong support to the use of point-like nucleons and effective interactions in high-density calculations.

Jan 30, 4:00 PM

Stony Brook: Peter Paul Seminar Room C-120, Physics Building

Caryn Palatchi: Controlling Electron Beam Asymmetries in the Lead Radius Experiment

A broad program of parity-violation measurements in electron scattering from heavy nuclei will constrain nuclear structure models as well as search for new BSM physics. This program is comprised of PREX-II (Lead Radius Experiment), CREX(Calcium Radius Experiment), and MOLLER(Measurement of a Lepton-Lepton Electroweak Reaction) experiment. PREX-II is a PVES experiment which ran at Jefferson Laboratory in 2019 and CREX is currently running in 2020. The aim of PREX-II and CREX is to map the weak charge distribution in nuclei, with implications for the equation of state of highly dense matter, neutron stars, and gravitational waves produced in neutron star collisions. MOLLER is a future PVES experiment searching for new neutral currents, providing an unprecedented precision on the electron weak charge and electroweak mixing angle. One common crucial component of all these experiments is control of helicity correlated false asymmetries in the polarized electron beam. This talk will describe the development of the newly installed RTP Pockels cell system in the JLab injector source which enables this program of experiments. The summer 2019 run of PREX-II will be reviewed, including the demonstration of nm-level control of electron beam asymmetries.

Feb 20, 4:00 PM

BNL: Room 2-38, Physics, Building 510 A

Michael Engelhardt, New Mexico State University

Advances in quark transverse dynamics in the proton from Lattice QCD

Recent progress in an ongoing program of evaluating transverse momentum-dependent (TMD) observables in the proton within Lattice QCD is reviewed. These lattice calculations are based on a definition of TMDs through hadronic matrix elements of quark bilocal operators, including an appropriate gauge connection between the quarks. Results presented include data on the Sivers and Boer-Mulders effects, highlighting the decisive role of the gauge connection in encoding information about the struck quark in a deep inelastic scattering process. First lattice data obtained directly at the physical pion mass are exhibited, and an exploratory outlook on extracting the dependence of the Sivers shift on the quark momentum fraction x is given.