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Non-perturbative effects and soft-gluon dynamics in low-$p_T$ Drell-Yan production

D. Subotić, H. Jung, A. V. Kotikov, N. Raičević

Abstract

The transverse-momentum spectrum of Drell-Yan lepton pairs at small $p_T$ probes non-perturbative QCD effects, including intrinsic partonic transverse momentum and initial-state soft-gluon radiation. The novel approach PDF2ISR is employed to study the transverse-momentum spectrum of Drell-Yan lepton pairs in the small-$p_T(\ell\ell)$ region. This framework is particularly well suited for such investigations, as it provides a systematic treatment of the dominant non-perturbative effects and their interplay. In order to extract robust physical conclusions, a detailed analysis of the technical aspects involved in the simulation of the intrinsic transverse momenta of partons inside the proton, as well as the remnant recoil schemes, was carried out. Furthermore, different approaches for the treatment of the strong coupling at low scales were investigated and confronted with available experimental data. This comparison enabled an assessment of the sensitivity of the experimental measurements to the chosen low-scale behaviour of $α_s$.

Non-perturbative effects and soft-gluon dynamics in low-$p_T$ Drell-Yan production

Abstract

The transverse-momentum spectrum of Drell-Yan lepton pairs at small probes non-perturbative QCD effects, including intrinsic partonic transverse momentum and initial-state soft-gluon radiation. The novel approach PDF2ISR is employed to study the transverse-momentum spectrum of Drell-Yan lepton pairs in the small- region. This framework is particularly well suited for such investigations, as it provides a systematic treatment of the dominant non-perturbative effects and their interplay. In order to extract robust physical conclusions, a detailed analysis of the technical aspects involved in the simulation of the intrinsic transverse momenta of partons inside the proton, as well as the remnant recoil schemes, was carried out. Furthermore, different approaches for the treatment of the strong coupling at low scales were investigated and confronted with available experimental data. This comparison enabled an assessment of the sensitivity of the experimental measurements to the chosen low-scale behaviour of .
Paper Structure (6 sections, 8 equations, 10 figures, 2 tables)

This paper contains 6 sections, 8 equations, 10 figures, 2 tables.

Table of Contents

  1. Introduction
  2. Pdf2Isr and DY pair production
  3. Intrinsic-k_T distributions in PB and Pdf2Isr
  4. DY data vs Pdf2Isr predictions at different sqrts
  5. The non-perturbative region in alpha_s
  6. Conclusion

Figures (10)

  • Figure 1: Comparison of input $\sigma$ to the extracted one as a function of the centre-of-mass energy $\sqrt{s}$ obtained from Pythia -default (left) and the modified recoil treatment (right).
  • Figure 2: Comparison of $p_{\rm T}(\ell\ell)$ for the DY pairs with invariant mass $7 \le m(\ell\ell) \le 8~\text{GeV}$ produced at $\sqrt{s}=38.8$ GeV for two different intrinsic-$k_{\rm T}$ widths in Pdf2Isr and PB ( Cascade ): $q_s = 0.5$ GeV (left) and $q_s = 1.0$ GeV (right). For comparison the prediction of Pdf2Isr with the default recoil scheme is shown. The uncertainty bands show the 7-point theoretical uncertainties.
  • Figure 3: Comparison between PB ( Cascade ) and Pdf2Isr predictions obtained with parton shower and TMD evolution (without intrinsic $k_{\rm T}$) for $p_{\rm T}(\ell\ell)$ of DY pairs with invariant mass $7 \le m(\ell\ell) \le 8~\text{GeV}$ produced at $\sqrt{s}=38.8$ GeV (left) and for DY pairs in the $Z$-peak region produced at $\sqrt{s}=13$ TeV (right). The uncertainty bands show the 7-point theoretical uncertainties.
  • Figure 4: Comparison between PB ( Cascade ) and Pdf2Isr predictions obtained with an intrinsic-$k_{\rm T}$ width of $q_s = 1~\text{GeV}$ and with parton shower and TMD evolution for $p_{\rm T}(\ell\ell)$ of DY pairs with invariant mass $7 \le m(\ell\ell) \le 8~\text{GeV}$ produced at $\sqrt{s}=38.8$ GeV (left) and for DY pairs in the $Z$-peak region produced at $\sqrt{s}=13$ TeV (right). For comparison the prediction of Pdf2Isr with the default recoil scheme is also shown. The uncertainty bands show the 7-point theoretical uncertainties.
  • Figure 5: Transverse-momentum distributions of DY lepton pairs at $\sqrt{s} = 13$ TeV obtained with the Pdf2Isr approach using PB-NLO-2018-Set2, compared to measurements CMS:2022ubq in three invariant-mass bins, as indicated above the histograms. The uncertainty bands show the 7-point theoretical uncertainties.
  • ...and 5 more figures