Inclusive quarkonium production in pp collisions at $$\sqrt{s}$$ = 5.02 TeV

Eur. Phys. J. C (2023) 83:61 https://doi.org/10.1140/epjc/s10052-022-10896-8 Regular Article - Experimental Physics Inclusive quarkonium production in pp collisions at √ s = 5.02 TeV ALICE Collaboration CERN, 1211 Geneva 23, Switzerland Received: 26 November 2021 / Accepted: 9 October 2022 © CERN for the benefit of the ALICE collaboration 2023 Abstract This article reports on the inclusive production cross section of several quarkonium states, J/ψ, ψ(2S), ϒ(1S), ϒ(2S), and ϒ(3S), measured with the ALICE detec√ tor at the LHC, in pp collisions at s = 5.02 TeV. The analysis is performed in the dimuon decay channel at forward rapidity (2.5 < y < 4). The integrated cross sections and transverse-momentum ( pT ) and rapidity (y) differential cross sections for J/ψ, ψ(2S), ϒ(1S), and the ψ(2S)-to-J/ψ cross section ratios are presented. The integrated cross sections, assuming unpolarized quarkonia, are: σJ/ψ ( pT < 20 GeV/c) = 5.88 ± 0.03 ± 0.34 μb, σψ(2S) ( pT < 12 GeV/c) = 0.87 ± 0.06 ± 0.10 μb, σϒ(1S) ( pT < 15 GeV/c) = 45.5 ± 3.9 ± 3.5 nb, σϒ(2S) ( pT < 15 GeV/c) = 22.4 ± 3.2 ± 2.7 nb, and σϒ(3S) ( pT < 15 GeV/c) = 4.9 ± 2.2 ± 1.0 nb, where the first (second) uncertainty is the statistical (systematic) one. For the first time, the cross sections of the three ϒ states, as well as the ψ(2S) one as a function of pT and y, √ are measured at s = 5.02 TeV at forward rapidity. These measurements also significantly extend the J/ψ pT reach and supersede previously published results. A comparison √ with ALICE measurements in pp collisions at s = 2.76, 7, 8, and 13 TeV is presented and the energy dependence of quarkonium production cross sections is discussed. Finally, the results are compared with the predictions from several production models. 1 Introduction Quarkonium production in high-energy hadronic collisions is an important tool to study the perturbative and nonperturbative aspects of quantum chromodynamics (QCD) calculations [1,2]. Quarkonia are bound states of either a charm and anti-charm (charmonia) or a bottom and antibottom quark pair (bottomonia). In hadronic collisions, the scattering process leading to the production of the heavyquark pair involves momentum transfers at least as large as twice the mass of the considered heavy quark, hence it can  e-mail: 0123456789().: V,-vol be described with perturbative QCD calculations. In contrast, the binding of the heavy-quark pair is a non-perturbative process as it involves long distances and soft momentum scales. Describing quarkonium production measurements in proton– proton (pp) collisions at various colliding energies represents a stringent test for models and, in particular, for the investigation of the non-perturbative aspects that are treated differently in the various approaches. These measurements also provide a crucial reference for the investigation of the properties of the quark–gluon plasma formed in nucleus–nucleus collisions and of the cold nuclear matter effects present in proton–nucleus collisions [2,3]. Quarkonium production can be described by various approaches that essentially differ in the treatment of the hadronization part. The Color Evaporation Model (CEM) [4,5] considers that the quantum state of every heavy-quark pair produced with a mass above its production threshold and below twice the open heavy flavor (D or B meson) threshold production evolves into a quarkonium. In this model, the probability to obtain a given quarkonium state from the heavy-quark pair is parametrized by a constant phenomenological factor. The Color Singlet Model (CSM) [6] assumes no evolution of the quantum state of the pair from its production to its hadronization. Only color-singlet heavy-quark pairs are thus considered to form quarkonium states. Finally, in the framework of Non-Relativistic QCD (NRQCD) [7], both color-singlet and color-octet heavy-quark pairs can evolve towards a bound state. Long Distance Matrix Elements are introduced in order to parametrize the binding probability of the various quantum states of the heavy-quark pairs. They can be constrained from existing measurements and do not depend on the specific production process under study (pp, electron–proton, etc.). This article presents measurements of the inclusive production cross section of charmonium (J/ψ and ψ(2S)) and bottomonium (ϒ(1S), ϒ(2S), and ϒ(3S)) states in pp col√ lisions at a center-of-mass energy s = 5.02 TeV with the ALICE detector. The analysis is performed in the dimuon decay channel at forward rapidity (2.5 < y < 4). In this 123 61 Page 2 of 27 rapidity interval, the total, transverse momentum ( pT ) and rapidity (y) differential cross sections for J/ψ as well as the total cross section for ψ(2S), were published by the ALICE collaboration based on an earlier data sample [8,9], corresponding to a factor 12 smaller integrated luminosity. These measurements with improved statistical precision supersede the ones from earlier publication. The pT and y differential measurements for the ψ(2S) and ϒ(1S) as well as the total cross sections for all the measured ϒ states are presented here √ for the first time at s = 5.02 TeV and at forward rapidity. The pT coverage of the J/ψ measurement is extended up to 20 GeV/c. The inclusive differential cross sections are obtained as a function of pT for pT < 20 GeV/c and as a function of y for pT < 12 GeV/c for J/ψ, for pT < 12 GeV/c for ψ(2S), and for pT < 15 GeV/c for ϒ(1S). Only the pT -integrated cross sections are measured for ϒ(2S) and ϒ(3S) due to statistical limitations. The inclusive ψ(2S)-to-J/ψ ratio is also presented as a function of pT and y. The comparison of the J/ψ cross section with recent results from LHCb [10] is discussed. The results are compared with previous ALICE mea√ surements performed at s = 2.76, 7, 8, and 13 TeV [9,11– 13]. Earlier comparisons with LHCb quarkonium results at √ s = 7, 8, and 13 TeV [14–17] were performed in [9,12,13]. Finally, the results are compared with theoretical calculations based on NRQCD and CEM. The measurements reported here are inclusive and correspond to a superposition of the direct production of quarkonium and of the contribution from the decay of higher-mass excited states (predominantly ψ(2S) and χc for J/ψ, ϒ(2S), χb , and ϒ(3S) for ϒ(1S), ϒ(3S) and χb for ϒ(2S), and χb for ϒ(3S)). For J/ψ and ψ(2S) a non-prompt contribution from beauty hadron decays is also present. The article is organized as follows: the ALICE detectors used in the analysis and the data sample are briefly described in Sect. 2, the analysis procedure is presented in Sect. 3, and in Sect. 4 the results are discussed and compared with theoretical calculations and measurements at other center-ofmass energies from ALICE. 2 Apparatus and data samples A detailed description of the ALICE setup and its performance are discussed in Refs. [18,19]. In this section, the subsystems relevant for this analysis are presented. Muons from quarkonium decays are detected in th (...truncated)