INSTITUTE FOR NUCLEAR THEORY |
||||||
Aneesh Manohar University of California, San Diego Thursday, April 26, 2018, 2:00 PM Physics/Astronomy Tower C421 "The Photon PDF" The photon PDF of the proton is needed for precision comparisons of LHC cross sections with theoretical predictions. A new approach allows the photon PDF to be computed in terms of proton deep-inelastic structure functions, reducing the uncertainty over previous methods by about a factor of 40. W and Z PDFs can be computed by similar methods. The talk discusses the determination of the photon and electroweak gauge boson PDFs. Raghav Kunnawalkam Elayavalli Wayne State University Thursday, May 10, 2018, 2:00 PM Physics/Astronomy Tower C421 "Exploiting Machine Learning Techniques in High Energy Nuclear Physics" The high energy physics community at the LHC have utilized state of the art machine learning (ML) techniques quite successfully including the discovery of the Higgs boson. While such methods are quite common and readily applicable in big data style analysis, they are only recently being formulated and employed in nuclear physics. We shall go through a very brief overview of machine learning techniques and some of its recent applications to the study of the Quark Gluon Plasma. We study the phenomenon of jet quenching utilizing quark and gluon jet substructures as independent probes of heavy ion collisions. We exploit jet and sub-jet features to highlight differences between quark and gluon jets in vacuum and in a medium with the jet-quenching model implemented in JEWEL MC. To systematically extract jet substructure information, we introduce the telescoping deconstruction framework exploiting subjet kinematics at multiple angular scales. We find that the quark gluon discrimination performance worsens in heavy ion jets due to significant soft event activity affecting the soft jet substructure. Our work suggests a systematically improvable framework for studying modifications to quark and gluon jet substructures and facilitating direct comparisons between theoretical calculations, simulations and measurements in heavy ion collisions. Andrey Sadofyev Los Alamos National Laboratory Thursday, May 17, 2018, 2:00 PM Physics/Astronomy Tower C421 "Chiral vortical effect for higher spin particles" In a medium of massless fermions rotation can source a polarization current known as chiral vortical effect (CVE). Within a semi-classical description this phenomenon originates in the Berry phase and can be seen as a 3d analogue of the spin-Hall effect. It is well known that the spin-Hall effect takes place also for photons indicating a more general nature of topological polarization effects. In this talk we will discuss how CVE can be generalized to a system of massless particles with an arbitrary spin. Jacquelyn Noronha-Hostler Rutgers University Thursday, June 7, 2018, 2:00 PM Physics/Astronomy Tower C421 "Locating the Quantum Chromodynamic Critical Point" Strongly interacting matter undergoes a crossover phase transition at high temperatures T ~ 10^12 K and zero net-baryon density. A fundamental question in the theory of strong interactions, Quantum Chromodynamics (QCD), is whether a hot and dense system of quarks and gluons displays critical phenomena when doped with more quarks than antiquarks, where net-baryon number fluctuations diverge. Recent lattice QCD work indicates that such a critical point can only occur in the baryon dense regime of the theory, which defies a description from first principles calculations due to the Fermi sign problem. In this talk, the latest Lattice QCD efforts to find the QCD critical point will be discussed in the context of the interplay between strange and light flavors in the crossover section of the phase diagram. In the baryon dense regime where Lattice QCD results are not yet available I will show how the holographic correspondence can be used to map the fluctuations of baryon charge in the dense quark-gluon liquid onto a numerically tractable gravitational problem involving the charge fluctuations of holographic black holes. Christian Drischler University of California, Berkeley Thursday, June 21, 2018, 2:00 PM Physics/Astronomy Tower C421 "Many-Body Perturbation Theory for Nuclear Matter at High Orders" Nuclear matter is an ideal testbed for nuclear interactions with important consequences for nuclear astrophysics as well as finite nuclei. In particular, recent ab initio calculations of medium-mass to heavy nuclei have demonstrated the importance of realistic saturation properties of infinite matter for nuclear forces. We present an efficient Monte-Carlo framework for perturbative calculations of infinite nuclear matter based on two-, three-, and four-nucleon forces derived within chiral effective field theory. It enables to incorporate all many-body contributions in a transparent and also straightforward way, making it well-suited for pushing the limits of current state-of-the-art calculations to high orders in both the chiral as well as the many-body expansion. Furthermore, uncertainty estimates can be systematically extracted by order-by-order calculations, which provides important insights into the rate of convergence of each of the two expansions. After demonstrating its versatility, we make use of this novel framework to explore new chiral interactions up to next-to-next-to-next-to-leading order (N3LO) and study the equation of state of neutron and symmetric nuclear matter. Remarkably, simultaneous fits to the triton and to saturation properties can be achieved with natural 3N low-energy couplings. Taking advantage of the framework's efficacy, future chiral potentials may be optimized with respect to empirical saturation properties. Martha Constantinou Temple University Thursday, August 23, 2018, 2:00 PM Physics/Astronomy Tower C421 "Light-cone PDFs from Lattice QCD" Lattice QCD (LQCD) is a theoretical non-perturbative approach for the study of QCD dynamics numerically and from first principles. For more than a decade, LQCD has been very successful in the calculation of the hadronic spectrum, making postdictions of well-measured hadronic masses, as well as, predictions. Nowadays, LQCD is widely used for hadron structure calculations and is becoming a reliable tool, providing input to the experimental and phenomenological communities. Over the last years, progress in the simulation of LQCD has been impressive, driven by improvements in the algorithms and increase in computational power, that have enabled simulations to be carried out at parameters very close to their physical values (physical point). In this talk I will present recent results for the so-called quasi-PDFs, a new direct approach to compute parton distributions functions (PDFs) directly in LQCD. The quasi-PDF approach was introduced by Xiangdong Ji in 2013 and was intensively developed thereafter. We present results for the unpolarized, helicity and transversity PDFs calculated at the physical point. A careful investigation of systematic uncertainties, such as excited states and renormalization will be presented, that aims at obtaining reliable estimates. The light-cone PDFs are reconstructed using large momentum effective theory (LaMET) that allows comparison with phenomenological parameterizations of experimental data. We find several similarities between the lattice and phenomenological estimates of PDFs, and demonstrate the importance of simulations at the physical point. Of particular importance are the results on the transversity PDFs, that are not well-constrained experimentally, This presents a major success for the emerging field of direct calculations of quark distributions using Lattice QCD. Peter Stoffer University of California, San Diego Thursday, September 27, 2018, 2:30 PM Physics/Astronomy Tower C421 "Hadronic corrections to the anomalous magnetic moment of the muon" The anomalous magnetic moment of the muon g-2 has been measured and computed to very high precision of about 0.5 ppm. For more than a decade, a discrepancy has persisted between experiment and Standard Model prediction, now of about 3-4 sigma. The main uncertainty of the theory prediction is due to strong-interaction effects, the hadronic vacuum polarisation (HVP) and hadronic light-by-light (HLbL) contributions. While the most precise HVP evaluation is based on dispersion relations and data input, HLbL is currently plagued by uncontrolled model uncertainties. Within a dispersive framework based on unitarity and analyticity, we scrutinize the uncertainty estimates for the two-pion HVP channel and we calculate model-independently two-pion contributions in HLbL, which shows an avenue towards a data-driven evaluation of g-2 of the muon. Jocelyn Read California State University, Fullerton Thursday, October 4, 2018, 2:00 PM Physics/Astronomy Tower C421 "Neutron star matter constraints from gravitational wave observations" Neutron stars host the densest stable matter in the universe. Accurately modeling their multi-messenger astrophysics relies on a detailed description of the equation of state above nuclear density. Astronomical observations of neutron stars can in turn be used to constrain the properties of this dense matter. On August 17, 2017 the Advanced LIGO and Advanced Virgo detectors discovered the first gravitational-wave signal consistent with a binary neutron star inspiral. The three-dimensional localization of the source using LIGO and Virgo data enabled a successful electromagnetic follow-up campaign that identified an associated kilonova in a galaxy ~40 Mpc from Earth. We are also able to constrain the equation of state of dense matter in neutron stars using the observed gravitational waves. I will outline how these constraints are made, how they connect with other astronomical observations, and outline future prospects for connecting gravitational-wave astronomy with above-nuclear-density physics. |