Publications

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Shadow generalized parton distributions: a practical approach to the deconvolution problem of DVCS

V. Bertone, H. Dutrieux, C. Mezrag, H. Moutarde, P. Sznajder

SciPost Phys. Proc. 8, 107 (2022) · published 13 July 2022 | · pdf

Deeply virtual Compton scattering (DVCS) attracts a lot of interest due to its sensitivity to generalized parton distributions (GPDs) which provide a rich access to the partonic structure of hadrons. However, the practical extraction of GPDs for this channel requires a deconvolution procedure, whose feasibility has been disputed. We provide a practical approach to this problem based on a next-to-leading order analysis and a careful study of evolution effects, by exhibiting shadow GPDs with arbitrarily small imprints on DVCS observables at current and future experimental facilities. This shows that DVCS alone will not allow for a model independent extraction of GPDs and a multi-channel analysis is required for this purpose.
Latest ALICE results on J/$ψ$ photoproduction in ultra-peripheral collisions at the LHC

Tomas Herman

SciPost Phys. Proc. 8, 106 (2022) · published 13 July 2022 | · pdf

Ultra-peripheral collisions (UPCs), studied using the ALICE detector, allow us to investigate the low-$x$ behavior of the gluon distribution of the colliding particles. Two new measurements of coherent J/$\psi$ photoproduction cross section from Pb-Pb UPCs at $\sqrt{s_{\rm NN}}=5.02$ TeV are presented: the first measurement of the $|t|$-dependence of the cross section providing a new tool to investigate the transverse gluonic structure at low Bjorken-$x$ and a rapidity-differential measurement at midrapidity allowing us to provide stringent constraints on nuclear gluon shadowing and saturation models. In addition, prospects for heavy vector meson photoproduction measurements in LHC Run 3 and 4 are presented.
Understanding the proton mass in QCD

Andreas Metz, Barbara Pasquini, Simone Rodini

SciPost Phys. Proc. 8, 105 (2022) · published 13 July 2022 | · pdf

Understanding the proton mass in quantum chromodynamics (QCD) is a very important and current topic in hadronic physics. The decomposition (sum rule) of the proton mass is not unique, and different sum rules, which are related to the QCD energy-momentum tensor, can be found in the literature. We review and compare these sum rules and identify open questions in this field.
Three-loop soft anomalous dimensions for top-quark processes

Nikolaos Kidonakis

SciPost Phys. Proc. 8, 104 (2022) · published 13 July 2022 | · pdf

I present results for soft anomalous dimensions through three loops for several processes involving the production of top quarks. In particular, I discuss single-top and top-pair production. I also present some numerical results for double-differential distributions in $t{\bar t}$ production through approximate N$^3$LO.
Single-Logarithmic Corrections to Small-$x$ Helicity Evolution

Yossathorn Tawabutr

SciPost Phys. Proc. 8, 103 (2022) · published 13 July 2022 | · pdf

The small-$x$ quark helicity evolution equations at double-logarithmic order, with the kernel $\sim\alpha_s\ln^2(1/x)$, have been derived previously. In this work, we derive the single-logarithmic corrections to the equations, to order $\alpha_s\ln(1/x)$ of the evolution kernel. The new equations include the effects of the running coupling and the unpolarized small-$x$ evolution, both of which are parametrically significant at single-logarithmic order. The large-$N_c$ and large-$N_c\& N_f$ approximations to the equation are computed. (Here, $N_c$ and $N_f$ are the numbers of quark colors and flavors, respectively.) Their solutions will provide more precise estimates of the quark helicity distribution at small $x$, contributing to the resolution of the proton spin puzzle.
Azimuthal correlations in diffractive scattering at the Electron-Ion Collider

Adrian Dumitru, Heikki Mäntysaari, Risto Paatelainen, Kaushik Roy, Farid Salazar, Björn Schenke

SciPost Phys. Proc. 8, 102 (2022) · published 13 July 2022 | · pdf

We calculate azimuthal correlations between the exclusively produced vector meson and the scattered electron in Deep Inelastic Scattering processes at the future Electron-Ion Collider (EIC). We identify "kinematical" and "intrinsic" contributions to these correlations, and show that the correlations are sensitive to the non-trivial correlations in the gluon distribution of the target. Realistic predictions at the EIC kinematics are provided using two different approaches to describe the dipole-proton interaction at relatively small $x$.
PDF4LHC21: Update on the benchmarking of the CT, MSHT and NNPDF global PDF fits

Thomas Cridge

SciPost Phys. Proc. 8, 101 (2022) · published 13 July 2022 | · pdf

There have been recent updates to the three global PDF fits (CT, MSHT and NNPDF), all adding large amounts of data from the LHC, and this has resulted in significant changes to the global PDFs. Given the impact that the new PDFs will have on physics comparisons at the LHC, it is crucial to perform a benchmarking among the PDFs, similar in spirit to that which was carried out for PDF4LHC15, widely used for LHC physics. In this article we detail a benchmarking comparison of three global PDF sets - CT18, MSHT20 and NNPDF3.1 - and their similarities and differences that have been observed. The end result of this study will be a new PDF4LHC21 ensemble of combined PDFs suitable for a wide range of LHC applications.

3 citations
Possible studies of gluon transversity in the spin-1 deuteron at hadron-accelerator facilities

S. Kumano, Qin-Tao Song

SciPost Phys. Proc. 8, 100 (2022) · published 13 July 2022 | · pdf

Chiral-odd gluon transversity distribution could shed light on a new aspect of hadron physics. Although we had much progress recently on quark transversity distributions, there is no experimental measurement on the gluon transversity. The gluon trasversity does not exist in the spin-1/2 nucleons and it exists in the spin-1 deuteron. Therefore, it could probe new hadron physics in the deuteron beyond the basic bound system of a proton and a neutron because the nucleons cannot contribute directly. Here, we explain that the gluon transversity can be measured at hadron accelerator facilities, such as Fermilab and NICA, in addition to charged-lepton scattering measurements at lepton accelerator facilities by showing cross sections of the proton-deuteron Drell-Yan process as an example.
ATLAS Results with Beauty Mesons

Ann-Kathrin Perrevoort

SciPost Phys. Proc. 8, 099 (2022) · published 13 July 2022 | · pdf

A broad range of measurements involving $B$ mesons are performed with the ATLAS experiment at the Large Hadron Collider, of which a selection is discussed in this note. This includes a measurement of the relative $B_c^\pm$ to $B^\pm$ production cross section in $pp$ collisions at a centre-of-mass energy $\sqrt{s}$ of 8 TeV, as well as the latest results on the branching ratios of the rare decays $B^0_s\to\mu^+\mu^-$ and $B^0\to\mu^+\mu^-$ using $pp$ collisions recorded at $\sqrt{s}=$ 7, 8 and 13 TeV. Furthermore, accurate measurements of mixing and CP violation in $B_s^0 \to J/\psi\, \phi$ decays are performed. The latest results on the CP violating phase $\phi_s$ and other parameters describing the decay obtained at $\sqrt{s}=$ 7, 8 and 13 TeV are reported.
Simultaneous Extraction of Unpolarized PDFs and Nuclear Effects

C. Cocuzza, A. Metz, N. Sato

SciPost Phys. Proc. 8, 098 (2022) · published 13 July 2022 | · pdf

We present a new global QCD analysis of unpolarized parton distribution functions (PDFs) and nuclear effects including for the first time data from the SeaQuest and MARATHON experiments in addition to high-energy weak-boson-production data from the Tevatron and Large Hadron Collider. Simultaneously extracting the PDFs and nuclear effects, we examine the impact of the SeaQuest and MARATHON data on the light-quark sea asymmetry and the EMC ratios of deuterium, helium, and tritium.

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Publications

3 citations