Production of J/ψ and $ \varUpsilon $ mesons in pp collisions at $ \sqrt{s}=8 $ TeV

Abstract

The production of J/ψ and Υ mesons in pp collisions at √ s = 8 TeV is studied with the LHCb detector. The J/ψ and Υ mesons are reconstructed in the µ + µ − decay mode and the signal yields are determined with a fit to the µ + µ − invariant mass distributions. The analysis is performed in the rapidity range 2.0 < y < 4.5 and transverse momentum range 0 < p T < 14 (15) GeV/c of the J/ψ (Υ ) mesons. The J/ψ and Υ production crosssections and the fraction of J/ψ mesons from b-hadron decays are measured as a function of the meson p T and y. The LHCb collaboration 27 IntroductionSuccessfully describing heavy quarkonium production is a long-standing problem in QCD. An effective field theory, non-relativistic QCD (NRQCD) [1,2], provides the foundation for much of the current theoretical work. According to NRQCD, the production of heavy quarkonium factorises into two steps: a heavy quark-antiquark pair is first created at short distances and subsequently evolves non-perturbatively into quarkonium at long distances. The NRQCD calculations depend on the colour-singlet (CS) and colour-octet (CO) matrix elements, which account for the probability of a heavy quark-antiquark pair in a particular colour state to evolve into a heavy quarkonium state. The CS model (CSM) [3,4], which provides a leading-order description of quarkonium production, was initially used to describe experimental data. However, it underestimates the observed cross-section for single J/ψ production at high transverse momentum (p T ) at the Tevatron [5]. To resolve this discrepancy, the CO mechanism was introduced [6]. The corresponding matrix elements were determined from the high-p T data, as the CO cross-section decreases more slowly with p T than that predicted by CS. More recent higher-order calculations [7][8][9][10] close the gap between the CS predictions and the experimental data [11], reducing the need for large CO contributions.

Study of ϒ $$ \varUpsilon $$ production and cold nuclear matter effects in pPb collisions at s NN $$ \sqrt{s_{NN}} $$ = 5 TeV

“…The measurements of R nS/1S in pPb collisions are compatible with those in pp collisions [47][48][49].…”

“…[47][48][49]. The Υ candidates are reconstructed from two oppositely charged particles consistent with a muon hypothesis based on particle identification information from the RICH detectors, the calorime- ters and the muon system.…”

“…The shape parameters of the CB functions have been fixed using large samples collected in pp collisions [48], which determine the mass resolution for the Υ (1S) to be 43.0 MeV/c 2 . The resolutions for the Υ (2S) and Υ (3S) signals are obtained by scaling this value by the ratio of their masses to the Υ (1S) meson mass [51].…”

Towards an automated tool to evaluate the impact of the nuclear modification of the gluon density on quarkonium, D and B meson production in proton–nucleus collisions

“…4 We have performed 2 times 2 χ 2 fits of d 2 σ/d P T dy of prompt J/ψ production in pp collisions with 2 PDF sets (CT14NLO and CT10LO) using, on the one hand, LHCb data [55,56] and, on the other, ATLAS [57] and CMS [58] data. The fit parameters (λ, κ, P T and n of Eq.…”

Charm production in pp collisions at 5 and 13 TeV at LHCb

“…2. From these results, several additional results are derived, most notably single differential cross-sections integrated over y and their ratios between 13 TeV and 8 TeV [11]. Both of these are shown in Fig.…”