Publications

Order by: publication date number of citations

• Spin Density Matrix Elements for Exclusive $\rho^{0}$ Meson Muoproduction at COMPASS

  W.~Augustyniak

  SciPost Phys. Proc. 8, 073 (2022) · published 12 July 2022 | Toggle abstract · pdf

  Spin density matrix elements were extracted from COMPASS data for exclusive $\rho^{0}$ meson muoproduction on a liquid hydrogen target. The measurement cover the kinematic range of 1.0 (GeV/$c$)$^2$ $< Q^{2} <$ 10.0 (GeV/$c$)$^2$, 5.0 GeV/$c^2$ $< W <$ 17.0 GeV/$c^2$ and 0.01 (GeV/$c$)$^2$ $<p^{2}_{T} < $ 0.5 (GeV/$c$)$^2$. Here, $W$ denotes the mass of the final hadronic system, $Q^{2}$ the virtuality of the exchanged photon and $p_{T}$ the transverse momentum of the $\rho^{0}$ meson with respect to the virtual-photon direction. We observe a violation of s-channel helicity conservation for the transition $\gamma^{*}_{T} \to \rho^{0}_{L}$. Additionally, we find a dominant contribution of the natural-parity-exchange transitions.

• Studying hadronization at LHCb

  Sookhyun Lee

  SciPost Phys. Proc. 8, 075 (2022) · published 12 July 2022 | Toggle abstract · pdf

  LHCb is a fully instrumented forward spectrometer with particle identification and muon reconstruction covering the pseudorapidity ($eta$) range from 2 to 5. Its full jet reconstruc- tion capability makes the LHCb experiment a suitable venue to explore jet substructure observables, particularly formation of hadrons and heavy quarkonia resonances inside jets. This contribution presents a brief overview of ongoing research program and dis- cusses recent results on non-identified charged hadron distributions in Z-tagged jets and charmonium distributions within jets. Future works towards furthering the knowledge of hadronizion are also discussed.

• 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.

• Azimuthal single- and double-spin asymmetries in semi-inclusive deep-inelastic lepton scattering by transversely polarized protons

  Luciano L. Pappalardo, Gunar Schnell

  SciPost Phys. Proc. 8, 024 (2022) · published 11 July 2022 | Toggle abstract · pdf

  A comprehensive set of azimuthal single-spin and double-spin asymmetries in semi- inclusive leptoproduction of pions, charged kaons, protons, and antiprotons from transversely polarized protons is presented. These asymmetries include the previously published HERMES results on Collins and Sivers asymmetries, the analysis of which has been extended to include protons and antiprotons and also to an extraction in a three-dimensional kinematic binning and enlarged phase space. They are complemented by corresponding results for the remaining single-spin and double-spin asymmetries for transverse target-polarization orientation.

• Sivers asymmetry in inelastic $J/ψ$ leptoproduction at the EIC

  Sangem Rajesh, Umberto D'Alesio, Asmita Mukherjee, Francesco Murgia, Cristian Pisano

  SciPost Phys. Proc. 8, 017 (2022) · published 11 July 2022 | Toggle abstract · pdf

  We study the Sivers asymmetry in inelastic $J/\psi$ leptoproduction, $ep^\uparrow \to e+ J/\psi+X$, within a transverse momentum dependent scheme, the so-called generalized parton model (GPM). The effects of final-state interactions are properly taken into account by employing the color-gauge invariant GPM (CGI-GPM). For the $J/\psi$ formation the non-relativistic QCD (NRQCD) framework is adopted. Predictions for unpolarized cross sections and maximized Sivers asymmetries at EIC energies are given.

• Ambiguous Ages, Ambivalent Youths: How Asylum Seekers in Germany Navigate Age Categorization

  Ulrike Bialas

  Mig. Pol. 2, 003 (2023) · published 5 September 2023 | Toggle abstract · pdf

  Many of the unaccompanied young migrants who have sought asylum in Germany since 2015 do not own documentation of their birth dates or even know their exact ages. Yet asylum and youth welfare laws distinguish precisely between minors and adults, down to the day, thus making it necessary for the German state to estimate the birth dates of young migrants and compelling some of the migrants to claim to be minors. In this article, drawing on years of ethnographic fieldwork in Berlin, I examine four features of the German state’s age categorization regime that make it so powerful: the discretion of street-level bureaucrats; the weight of written records; a prioritization of precision over accuracy; and—most important—the ability of bureaucrats to switch between the previous three features at will. I analyze the strategies young migrants employ against this regime to influence the outcomes of their own age categorization as well as the challenges inherent in living as a minor or within liminal, uncertain age categories. The latter include widespread distrust and fear of being found out as well as feelings of infantilization and emasculation. I use age categorization as a context in which to reflect on the agency of migrants vis-à-vis state bureaucracies and conclude that young migrants can try to affect only the determination of their own birth dates but have little impact on the prevailing definitions of age and youth. This article thus contributes to the study of categorization processes in international migration, the possibilities for migrants’ resistance, and the politics of time.

• Few-nucleon system dynamics studied via deuteron-deuteron collisions at 160 MeV

  I. Ciepał , K. Bodek, N. Kalantar-Nayestanaki , G. Khatri , St. Kistryn , B. Kłos, A. Kozela , J. Kuboś, P. Kulessa , A. Łobejko, A. Magiera , J. Messchendorp , I. Mazumdar, W. Parol , R. Ramazani-Sharifabadi, D. Rozpędzik , I. Skwira-Chalot , E. Stephan, A. Wilczek , B. Włoch, A. Wrońska , J. Zejma

  SciPost Phys. Proc. 3, 018 (2020) · published 25 February 2020 | Toggle abstract · pdf

  Four nucleon scattering at intermediate energies provides unique opportunities to study effects of the two key ingredients of the nuclear dynamics, the nucleon-nucleon P-wave (NNP-wave) and the three-nucleon force (3NF). This is possible only with systematic and precise data, in conjunction with exact theoretical calculations. Using the BINA detector at KVI Groningen, the Netherlands, a rich set of differential cross section of the 2H(d, dp)n breakup reaction at 160 MeV deuteron beam energy has been measured. Besides the three-body breakup, also cross sections of the 2H(d, 3He)n proton transfer reaction have been obtained. The data are compared to the recent calculations for the three-cluster breakup.

• Multi-differential studies to explore strangeness enhancement in pp with ALICE at the LHC

  Francesca Ercolessi

  SciPost Phys. Proc. 10, 028 (2022) · published 11 August 2022 | Toggle abstract · pdf

  The study of energy and multiplicity dependence of strange hadron production in proton-proton collisions provides a powerful tool to understand similarities and differences between small and large collision systems. In order to better understand the origin of strangeness enhancement in pp new multi-differential analyses have been performed. The first separates the contribution of soft and hard processes, such as jets, to strange hadron production through two-particle correlation techniques. The second exploits the concept of the effective energy available for particle production in the event, which is estimated by an anti-correlation with the energy deposited in ALICE's Zero Degree Calorimeters. The results indicate that strangeness production emerges from the growth of the underlying event and confirm it is related to the final state multiplicity.

• The Scintillating Bubble Chamber Experiment

  Ben Broerman

  SciPost Phys. Proc. 12, 023 (2023) · published 3 July 2023 | Toggle abstract · pdf

  The Scintillating Bubble Chamber (SBC) collaboration is combining the well-established liquid argon and bubble chamber technologies to search for low-mass, GeV-scale dark matter. Liquid-noble bubble chambers benefit from the excellent electron-recoil insensitivity inherent in bubble chambers with the addition of energy reconstruction provided from the scintillation signal for background rejection. The projected sensitivity with a quasi-background-free 10-kg-year exposure at a 100 eV nuclear recoil threshold is approximately 10$^{-43}$ cm$^2$ for a 1 GeV/c$^2$ dark matter mass.

• Prompt hadroproduction of C-even quarkonia in the light-front $k_T$ -factorization approach

  Wolfgang Schäfer, Izabela Babiarz, Roman Pasechnik, Antoni Szczurek

  SciPost Phys. Proc. 8, 032 (2022) · published 11 July 2022 | Toggle abstract · pdf

  We present a new approach for the prompt production of quarkonia which is based on the $k_T$-factorization method. The production of even C-parity quarkonia proceeds via the fusion of two (off-shell) gluons. Especially in the kinematics of the LHCb experiment these processes are thus expected to be a sensitive probe of the small-x gluon distribution. We calculate the relevant off-shell matrix elements in terms of the light-front wave functions of the quarkonium states. We present our results for scalar and pseudoscalar charmonia and discuss photon transition form factors as well as cross sections for prompt hadroproduction. We compare our results for the $\eta_c$ to recent LHCb data.