Publications

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• Measurement of the $\textit{CP}$ structure of the Higgs-tau Yukawa coupling

  Vinaya Krishnan MB

  SciPost Phys. Proc. 8, 008 (2022) · published 11 July 2022 | Toggle abstract · pdf

  The CMS experiment at the LHC has performed the first measurement of the CP structure of the Yukawa coupling between the Higgs boson and tau leptons. The measurement is based on data collected in proton-proton collisions at $\sqrt{s} = 13$ TeV during 2016-18, corresponding to an integrated luminosity of $137\text{ fb}^{-1}$. The analysis utilizes the angular correlation between the decay planes of tau leptons produced in Higgs boson decays, where dedicated analysis techniques are used to optimise the reconstruction of tau decay planes. The measured value of the CP mixing angle is $4\pm17^{\circ}$, at $68\%$ confidence level. The pure $\textit{CP-}$odd hypothesis is excluded by $3.2$ standard deviations. The analysis strategies and the results of the measurement are presented.

• Recent results from heavy ion collisions at LHCb

  Óscar Boente García

  SciPost Phys. Proc. 8, 007 (2022) · published 11 July 2022 | Toggle abstract · pdf

  LHCb is a fully instrumented spectrometer covering the forward rapidity region at the LHC, which provides unique access to the small Bjorken-x region inside the nucleus. In this contribution, a selection of recent results from the LHCb heavy-ion program are presented, including a measurement of charged hadron production in proton-proton (pp) and proton-lead (pPb) collisions, chic2/chic1 production in pPb collisions, and coherent J/psi production in peripheral and ultra-peripheral PbPb collisions. Comparisons with calculations and effects from the nuclear PDFs and dense QCD medium are discussed.

• Measurements and searches of Higgs boson production involving fermion couplings with the ATLAS detector

  Shigeki Hirose

  SciPost Phys. Proc. 8, 006 (2022) · published 11 July 2022 | Toggle abstract · pdf

  In the standard model, fermions acquire the mass via the Yukawa interaction. This mechanism can be tested by measuring couplings of the fermions with the Higgs boson. At the ATLAS experiment, the Higgs-fermion coupling measurements became possible thanks to the abundant dataset: the integrated luminosity of 139~fb$^{-1}$ at the centre-of-mass energy of 13~TeV as well as 25~fb$^{-1}$ at 7--8~TeV. This paper presents recent results from measurements of the Higgs boson productions in decays to a fermion pair in the final state with the ATLAS detector.

• NNLO constraints on proton PDFs from the SeaQuest and STAR experiments and other developments in the CTEQ-TEA global analysis

  Marco Guzzi, T. J. Hobbs, Tie-Jiun Hou, Xiaoxian Jing, Keping Xie, Aurore Courtoy, Sayipjamal Dulat, Jun Gao, Joey Huston, Pavel M. Nadolsky, Carl Schmidt, Ibrahim Sitiwaldi, Mengshi Yan, C.-P. Yuan

  SciPost Phys. Proc. 8, 005 (2022) · published 11 July 2022 | Toggle abstract · pdf

  We review progress in the global QCD analysis by the CTEQ-TEA group since the publication of CT18 parton distribution functions (PDFs) in the proton. Specifically, we discuss comparisons of CT18 NNLO predictions with the LHC 13 TeV measurements as well as with the FNAL SeaQuest and BNL STAR data on lepton pair production. The specialized CT18X PDFs approximating saturation effects are compared with the CT18sx PDFs obtained using NLL/NLO small-x resummation. Short summaries are presented for the special CT18 parton distributions with fitted charm and with lattice QCD inputs. A recent comparative analysis of the impact of deuteron nuclear effects on the parton distributions by the CTEQ-JLab and CTEQ-TEA groups is summarized.

  5 citations

• Structure Functions and Parton Densities: a Session Summary

  Benjamin Nachman, Katarzyna Wichmann, Pia Zurita

  SciPost Phys. Proc. 8, 004 (2022) · published 11 July 2022 | Toggle abstract · pdf

  Studies of fragmentation and parton density functions are a core component of researchin high energy particle and nuclear physics. These quantities are inherently interestingas a probe of the quantum nature of the strong force and are also essential ingredients toadditional studies in high energy scattering experiments. These proceedings provide anoverview of the state of the art in this area, as presented at the Deep-Inelastic ScatteringConference in the Spring of 2021.

  1 citation

• Ultraperipheral collisions and low-x physics

  Tuomas Lappi

  SciPost Phys. Proc. 8, 003 (2022) · published 11 July 2022 | Toggle abstract · pdf

  Ultraperipheral collisions at the LHC and RHIC offer the highest currently available energy for photon-nucleon and photon-nucleus collisions. Thus they are a valuable tool for studying the gluonic structure of hadrons and nuclei at small x. We discuss recent theoretical work towards understanding such exclusive processes at NLO accuracy in QCD perturbation theory. These theoretical advances are also immediately relevant for understanding the physics of deep inelastic scattering at small x. We also discuss experimental results in ultraperipheral collisions, most prominently for exclusive vector meson production.

• Recent Highlights from Spin-Physics Experiments

  Caroline Riedl

  SciPost Phys. Proc. 8, 002 (2022) · published 11 July 2022 | Toggle abstract · pdf

  A snapshot of the current experimental status of spin-dependent nucleon structure prior to the arrival of the Electron Ion Collider will be attempted. Highlights of recent results from fixed-target experiments at JLab, Fermilab, CERN and DESY and collider experiments from RHIC are presented. Many of the recent results address the topics of transverse proton or parton spin and transverse parton momenta (TMDs), and their their (spin-orbit) correlations. Results on generalized parton distributions (GPDs), which provide an alternative pathway to mapping nucleon structure, are also discussed.

  1 citation

• Recent Highlights on Higgs Physics from the LHC

  Elisabeth Schopf

  SciPost Phys. Proc. 8, 001 (2022) · published 11 July 2022 | Toggle abstract · pdf

  Many of the Higgs boson production and decay channels, predicted by the StandardModel, have been observed since its 2012 discovery. Today, measurements of the Higgsboson’s properties in these channels deepen our understanding of the nature of thisfundamental particle by providing better information about its mass, production kine-matics, and CP structure. Increasing precision also enables targeting rare Higgs bosondecay modes and probing di-Higgs-boson production. In addition, searches for beyondStandard Model physics in the Higgs sector are performed. This article presents the lat-est Higgs boson measurement highlights from the ATLAS and CMS collaborations usingLHC proton-proton collision data at a centre of mass energy of 13 TeV.

• Excitations and ergodicity of critical quantum spin chains from non-equilibrium classical dynamics

  Stéphane Vinet, Gabriel Longpré, William Witczak-Krempa

  SciPost Phys. Core 5, 035 (2022) · published 7 July 2022 | Toggle abstract · pdf

  We study a quantum spin-1/2 chain that is dual to the canonical problem of non-equilibrium Kawasaki dynamics of a classical Ising chain coupled to a thermal bath. The Hamiltonian is obtained for the general disordered case with non-uniform Ising couplings. The quantum spin chain (dubbed Ising-Kawasaki) is stoquastic, and depends on the Ising couplings normalized by the bath's temperature. We give its exact ground states. Proceeding with uniform couplings, we study the one- and two-magnon excitations. Solutions for the latter are derived via a Bethe Ansatz scheme. In the antiferromagnetic regime, the two-magnon branch states show intricate behavior, especially regarding their hybridization with the continuum. We find that that the gapless chain hosts multiple dynamics at low energy as seen through the presence of multiple dynamical critical exponents. Finally, we analyze the full energy level spacing distribution as a function of the Ising coupling. We conclude that the system is non-integrable for generic parameters, or equivalently, that the corresponding non-equilibrium classical dynamics are ergodic.

  1 citation

• Exact hydrodynamic solution of a double domain wall melting in the spin-1/2 XXZ model

  Stefano Scopa , Pasquale Calabrese, Jérôme Dubail

  SciPost Phys. 12, 207 (2022) · published 28 June 2022 | Toggle abstract · pdf

  We investigate the non-equilibrium dynamics of a one-dimensional spin-1/2 XXZ model at zero-temperature in the regime $|\Delta|< 1$, initially prepared in a product state with two domain walls i.e, $|\downarrow\dots\downarrow\uparrow\dots\uparrow\downarrow\dots\downarrow\rangle$. At early times, the two domain walls evolve independently and only after a calculable time a non-trivial interplay between the two emerges and results in the occurrence of a split Fermi sea. For $\Delta=0$, we derive exact asymptotic results for the magnetization and the spin current by using a semi-classical Wigner function approach, and we exactly determine the spreading of entanglement entropy exploiting the recently developed tools of quantum fluctuating hydrodynamics. In the interacting case, we analytically solve the Generalized Hydrodynamics equation providing exact expressions for the conserved quantities. We display some numerical results for the entanglement entropy also in the interacting case and we propose a conjecture for its asymptotic value.

  13 citations