Publications

Order by: publication date number of citations

• Can $\overline{MS}$ parton distributions be negative?

  Alessandro Candido, Stefano Forte, Felix Hekhorn

  SciPost Phys. Proc. 8, 077 (2022) · published 12 July 2022 | Toggle abstract · pdf

  We review our recent paper, where we proved Parton distributions functions (PDFs) to be positive at NLO in the $\overline{MS}$ factorization scheme. We present some additional material that was useful in completing the steps for the actual proof, but we won't attempt to report on the full proof, but referring the reader to the paper itself.

• Opportunities for inclusive diffraction at EIC

  Wojciech Slominski, Nestor Armesto, Paul R. Newman, Anna Stasto

  SciPost Phys. Proc. 8, 069 (2022) · published 12 July 2022 | Toggle abstract · pdf

  The possibilities for inclusive diffraction in the Electron Ion Collider, EIC, in the US, are analyzed. We find that thanks to the excellent forward proton tagging, the EIC will be able to access a wider kinematical range of longitudinal momentum fraction and momentum transfer of the leading proton than at HERA. This opens up the possibility to measure subleading diffractive exchanges. The extended $t$-range would allow the precise extraction of 4-dimensional reduced cross section in diffraction. In addition, the varying beam energy setups at the EIC would allow for precise measurements of the longitudinal diffractive structure function.

• Hard exclusive $\pi^{+}n$ electro production beam spin asymmetries off the proton in the GPD and TDA regimes

  S. Diehl for the CLAS collaboration

  SciPost Phys. Proc. 8, 066 (2022) · published 12 July 2022 | Toggle abstract · pdf

  Hard exclusive $\pi^{+}$n electro-production can be used to gain access to the 3D nucleon structure. The QCD factorisation mechanism in the "nearly forward region" ($t/Q^{2}$ small) allows a description by Generalized Parton Distributions (GPDs), while for the "nearly backward" kinematic region ($u/Q^{2}$ small) a description based on nucleon to pion transitions (TDAs) is available. The paper presents a measurement of single beam spin asymmetries to extract the $A^{\sin\phi}_{LU}$ moments and the related cross section ratio $\sigma_{LT^\prime}/\sigma_{0}$ from the hard exclusive $\pi^{+}$ channel off the unpolarized hydrogen target in a wide range of kinematics based on data taken with the CLAS spectrometer at Jefferson Lab. In addition, under forward angles a detailed multidimensional study will be presented based on CLAS12 data and compared to theoretical predictions.

• $tW$ and $tZ'$ production at hadron colliders

  Nikolaos Kidonakis, Marco Guzzi, Nodoka Yamanaka

  SciPost Phys. Proc. 8, 064 (2022) · published 12 July 2022 | Toggle abstract · pdf

  We present theoretical results with soft-gluon corrections for two separate processes: (1) the production of a single top quark in association with a $W$ boson in the Standard Model; and (2) the production of a single top quark in association with a heavy $Z'$ boson in new physics models with or without anomalous couplings. We show that the higher-order corrections from soft-gluon emission are dominant for a wide range of collider energies. Results are shown for the total cross sections and top-quark transverse-momentum and rapidity distributions for $tW$ and $tZ'$ production at LHC and future collider energies up to 100 TeV. The uncertainties from scale dependence and parton distribution functions are also analyzed.

• Proton reconstruction with the Precision Proton Spectrometer (PPS) in Run 2 and the PPS at HL-LHC

  Fabrizio Ferro

  SciPost Phys. Proc. 8, 062 (2022) · published 12 July 2022 | Toggle abstract · pdf

  The Precision Proton Spectrometer (PPS) started operating in 2016 and has collected more than 110 fb$^{-1}$ of data over the course of the LHC Run 2, now fully available for physics analysis. This contribution covers the key features of the PPS alignment and optics calibration, which have been developed from scratch. The reconstructed proton distributions, the performance of the PPS simulation and finally the validation of the full reconstruction chain with physics data (dilepton events) are also illustrated.

• Measurement of splittings along a jet shower in $\sqrt{s} = 200$ GeV pp collisions at STAR

  Raghav Kunnawalkam Elayavalli

  SciPost Phys. Proc. 8, 059 (2022) · published 12 July 2022 | Toggle abstract · pdf

  Jets are algorithmic proxies of hard scattered partons, i.e. quarks and gluons, in high energy particle collisions. The STAR collaboration presents the first measurements of substructure observables at the first, second and third splits in the jet clustering tree via the iterative SoftDrop procedure. For each of these splits, we measure the fully corrected groomed shared momentum fraction (\zg) and groomed jet radius (\rg). We discuss the evolution of jet substructure in both the angular and momentum scales which allows for a self-similarity test of the DGLAP splitting function. We compare the fully corrected data to Monte Carlo models, providing stringent constraints on model parameters related to the parton shower and non-perturbative effects such as hadronization.

• Investigation of the background in coherent $J/\psi$ production at the EIC

  Wan Chang

  SciPost Phys. Proc. 8, 053 (2022) · published 12 July 2022 | Toggle abstract · pdf

  Understanding fundamental properties of nucleons and nuclei are among the most important scientific goals of the next-generation machine, the Electron-Ion Collider (EIC). With the unprecedented versatility provided by the EIC, it will provide answers to many standing puzzles and open questions in modern nuclear physics. One of the golden measurements at the EIC is coherent vector meson production in electron-nucleus (eA) scattering in order to obtain the spatial gluon density distribution in heavy nuclei. This requires the experiment to overcome an overwhelmingly large background arising from the incoherent diffractive production, where the nucleus mostly breaks up into fragments of particles in the far-forward direction close to the hadron beam rapidity. In this talk, we systematically study the rejection of incoherent $J/\psi$ production by vetoing products from the nuclear breakup - protons, neutrons, and photons, which is modeled with the BeAGLE event generator and the most up-to-date EIC Far-forward Interaction Region design.

• Transversity through Dihadron: a constrained fit

  Aurore Courtoy

  SciPost Phys. Proc. 8, 049 (2022) · published 12 July 2022 | Toggle abstract · pdf

  We present a study of the valence transversity PDF obtained through a constrained fit. The effects of the constraints on the uncertainties of the PDF are explored. We show that the resulting isovector tensor charge is largely undetermined and, hence, compatible with all lattice evaluations.

• Measuring the light meson nuclear modification factor in p-Pb collisions over an unprecedented $p_{\text{T}}$ range with ALICE

  Joshua König

  SciPost Phys. Proc. 8, 048 (2022) · published 12 July 2022 | Toggle abstract · pdf

  Differential invariant cross sections of light neutral mesons in p-Pb collisions at $\sqrt{s_{\text{NN}}}$ = 8.16 TeV and in pp collisions at $\sqrt{s}$ = 8 TeV have been measured up to very high transverse momentum ($p_{\text{T}}$). By combining independent reconstruction techniques available in ALICE using the EMCal and PHOS calorimeters as well as the central barrel tracking detectors, the combined spectra cover almost two orders of magnitude in $p_{\rm T}$ for the $\pi^{0}$ meson. The nuclear modification factor $R_{\text{pPb}}$ has been measured for the $\pi^{0}$ and $\eta$ mesons and is found to be consistent with NLO pQCD, CGC and energy loss calculations. Comparisons to the $R_{\text{pPb}}$ of $\pi^{0}$ measured in $\sqrt{s_{\text{NN}}}$ = 5.02 TeV hint at a stronger suppression at low $p_{\rm T}$ with increasing collision energy.

• Global Analysis of SSAs and the Impact of the EIC and SoLID on Tensor Charge Extractions

  Daniel Pitonyak

  SciPost Phys. Proc. 8, 044 (2022) · published 12 July 2022 | Toggle abstract · pdf

  Single transverse-spin asymmetries (SSAs) give great insight into the 3-dimensional structure of hadrons. We report on the first global QCD analysis of SSAs in semi-inclusive deep-inelastic scattering, electron-positron annihilation, Drell-Yan, and single-inclusive proton-proton collisions. One byproduct of the analysis is an extraction of the transversity function, from which the nucleon tensor charges can be computed, and we find, for the first time, agreement with lattice QCD for these quantities. Based on this analysis, we perform an impact study of future data on extractions of the nucleon tensor charges.