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Keping Xie:The photon content of the nucleon


Title: The photon content of the nucleon

Speaker: Keping Xie 谢可平 (Michigan State University)

Time: 1:30 pm, Dec 25 (Monday) 2023

Location: 理科楼C109

Abstract: Building upon the most recent CT18 global fit, we present a new calculation of the photon content of the nucleon, including both proton and neutron, based the LUXqed methodology. We explore two principal variations of the LUX ansatz. In one approach, which we designate “CT18lux”, the photon PDF is calculated directly using the LUX formula for all scales, μ. In an alternative realization, “CT18qed”, we instead initialize the photon PDF in terms of the LUX formulation at a lower scale, μ ∼ O(1 GeV), and evolve to higher scales with a combined QED+QCD kernel at O(α), O(ααs) and O(α2). While we find these two approaches generally agree, especially at intermediate x (10−3 ≲x ≲ 0.3), we discuss some moderate discrepancies that can occur toward the end-point regions at very high or low x. We also study effects that follow from variations of the inputs to the LUX calculation originating outside the pure deeply-inelastic scattering (DIS) region, including from elastic form factors and other contributions to the photon PDF. The impacts of the momentum sum rule as well as isospin symmetry violation have been explored, and turn out to be negligible. Finally, we investigate the phenomenological implications of these photon PDFs for the LHC, including high-mass Drell-Yan, vector-boson pair, top-quark pair, and Higgs associated with vector-boson production. Meanwhile, the neutron’s photon content is essential for nucleus scattering, such as neutrino-nucleus W-boson production, which is important for the near-future TeV–PeV neutrino observations, and the axion-like particle production at a high-energy muon beam-dump experiment.

Bio: Keping Xie 谢可平

Education and training

• Research Associate, 09/2023 – present

Department of Physics and Astronomy, Michigan State University, East Lansing, MI 48825 Supervisors: Kirtimaan Mohan and C.-P. Yuan

• Postdoctoral Associate, 09/2019 – 08/2023

Pittsburgh Particle Physics, Astrophysics, and Cosmology Center (PITT PACC), Department of Physics and Astronomy, University of Pittsburgh, Pittsburgh, PA 15260 Supervisors: Ayres Freitas and Tao Han

• Ph.D. in Physics, 08/2014 – 08/2019

Department of Physics, Southern Methodist University, Dallas, TX 75275-0181 Advisors: Pavel Nadolsky and Roberto Vega

Thesis: Massive elementary particles in the Standard Model and its supersymmetric triplet Higgs extension [link]

• B.S. in Physics, 09/2010 – 07/2014

School of Physics, Peking University, Beijing 100871, China Advisor: Han-Qing Zheng

Research interests

I work on the high-energy phenomenology, which bridges the theoretical and experimental par- ticle physics. My efforts mainly focus on the precision and resummation calculations. As a member of the CTEQ-TEA (CT) collaboration, I participate in the development of a new generation of QCD parton distribution functions (PDFs), CT18, and the corresponding QED corrections (CT18QED), which are widely used for physics exploration at the hadron colliders. Recently, I dedicate to the electroweak (EW) factorization, which involves the EW gauge bosons as well as Higgs bosons as partons to resum large logarithms as PDFs for initial-state radiations and fragmentation functions (FFs) for final-state radiations. Another focus of my research is heavy-flavor physics, which requires a general-mass composite scheme to match the high energy regime, where the heavy-flavor particle can be excited as an active massless parton, to the low energy region, in which heavy flavors can be only dynamically created through light flavors. I am also interested in perturbative high-order calculations, small-x and qT resummations, Higgs bosons beyond the Standard Model, and effective field theory.