Measurement of ϒ production in pp collisions at $$ \sqrt{s}=13 $$ TeV

Abstract

Abstract:The production cross-sections of Υ (1S), Υ (2S) and Υ (3S) mesons in protonproton collisions at √ s = 13 TeV are measured with a data sample corresponding to an integrated luminosity of 277 ± 11 pb −1 recorded by the LHCb experiment in 2015. The Υ mesons are reconstructed in the decay mode Υ → µ + µ − . The differential production cross-sections times the dimuon branching fractions are measured as a function of the Υ transverse momentum, p T , and rapidity, y, over the range 0 < p T < 30 GeV/c and 2.0 < y < 4.5. The ratios of the cross-sections with respect to the LHCb measurement at √ s = 8 TeV are also determined. The measurements are compared with theoretical predictions based on NRQCD. The LHCb collaboration 22 IntroductionThe study of heavy quarkonium (cc and bb) production in high-energy hadron collisions provides important information to better understand quantum chromodynamics (QCD). Thanks to theoretical and experimental efforts in the past forty years, the comprehension of hadronic production of heavy quarkonia has been improved significantly. The production of heavy quarkonium in proton-proton (pp) collisions at the Large Hadron Collider (LHC) is expected to start with the production of a heavy quark pair, QQ, followed by its hadronization into a bound state. The heavy quark pair QQ is produced mainly via Leading Order (LO) gluon-gluon interactions. Several models have been proposed to describe the underlying dynamics, such as the colour-singlet model (CSM) [1][2][3][4][5][6][7] and non-relativistic QCD (NRQCD) [8][9][10]. In the CSM the intermediate QQ state is supposed to be colourless and has the same quantum numbers as the quarkonium final state, while in NRQCD the calculations also include the colour-octet contribution. However, at present no model can describe both the heavy quarkonium production cross-section and polarisation simultaneously. The production of Υ (1S), Υ (2S) and Υ (3S) mesons has been studied at LHC by ATLAS [11,12] and CMS [13, 14] collaborations at centre-of-mass energies of 7 TeV and 13 TeV. The measurements have also been performed by LHCb at centre-of-mass energies of 2.76 TeV [15],[7][8][9][10][11][12][13][14][15][16][17][18][19] and 8 TeV [17][18][19][20]. The NRQCD calculations can describe the trends of the differential production cross-sections in data for all three Υ states within uncertainties. The measured production cross-section ratios between 7 TeV and 8 TeV [18] as a function of transverse momentum, p T , are consistently higher than the next-to-leading -1 - JHEP07(2018)134order NRQCD theory predictions [21], and the ratios as a function of rapidity show a different trend than the predictions [22,23]. The measurement performed at 13 TeV presented here provides valuable input to study the quarkonium production at a higher centre-of-mass energy, enabling ratios to be determined with respect to data taken at a lower centre-ofmass energy. Most of the theoretical and experimental uncertainties cancel in the ratios, and more stringent constraints on the th...

Production, spectroscopy and properties of heavy hadrons

“…The production cross sections of heavy quarkonia at central and forward rapidity have been measured with 13 TeV data by CMS [5] and LHCb [6], respectively. CMS used 2.3 − 2.7 fb −1 of data to measure the single-and double-differential production cross sections times branching fractions of five s-wave states (J/ψ, ψ(2S), and Y(nS), with n = 1, 2, 3) as a function of p T and rapidity.…”

“…Bottom panels show the data/theory and the 13/7 TeV differential ratios. Top right: the Y(nS) cross sections at 13 TeV measured by LHCb[6] at forward rapidity as a function of p T . Bottom right: the Y(2S)/Y(1S) cross section ratio measured by LHCb[6] as a function of p T and rapidity.…”

“…Top right: the Y(nS) cross sections at 13 TeV measured by LHCb[6] at forward rapidity as a function of p T . Bottom right: the Y(2S)/Y(1S) cross section ratio measured by LHCb[6] as a function of p T and rapidity. Color bands in figures show the NRQCD predictions.in order to achieve an excellent mass resolution (2.2 MeV) and observe the doublet separation with more than 5 σ significance.…”

Heavy Flavour production at LHCb

“…The data sample used corresponds to an integrated luminosity of 277 pb −1 collected at a centreof-mass energy of 13 TeV [24]. The ϒ candidates are built from two muons with large momentum and transverse momentum.…”

“…Several models have been proposed to discuss the underlying dynamics, such as the colour-singlet model (CSM) [1,2,3,4,5,6,7] and non-relativistic QCD (NRQCD) [8,9,10]. The production properties of ϒ(1S), ϒ(2S) and ϒ(3S) mesons have already been measured by LHCb at centre-of-mass energies of 2.76 [11], 7 [12,13,14,15] and 8 TeV [13,14,15]. The B + production measurements provide an important test for the most recent calculations based on fixed next-to-leading order (NLO) QCD with next-to-leading logarithm (NLL) large transverse momentum resummation (FONLL) approach [16,17].…”