Measurements of prompt charm production cross-sections in pp collisions at s = 13 $$ \sqrt{s}=13 $$ TeV

Abstract

Production cross-sections of prompt charm mesons are measured with the first data from pp collisions at the LHC at a centre-of-mass energy of 13 TeV. The data sample corresponds to an integrated luminosity of 4.98 ± 0.19 pb −1 collected by the LHCb experiment. The production cross-sections of D 0 , D + , D + s , and D * + mesons are measured in bins of charm meson transverse momentum, p T , and rapidity, y, and cover the range 0 < p T < 15 GeV/c and 2.0 < y < 4.5. The inclusive cross-sections for the four mesons, including charge conjugation, within the range of 1 < p T < 8 GeV/c are found to bewhere the uncertainties are due to statistical and systematic uncertainties, respectively.Keywords: Charm physics, Forward physics, Hadron-Hadron scattering, Heavy quark production, QCD A Absolute cross-sections 20 B Cross-section ratios at different energies 24 C Cross-section ratios for different mesons 28The LHCb collaboration 38 IntroductionMeasurements of charm production cross-sections in proton-proton collisions are important tests of the predictions of perturbative quantum chromodynamics [1][2][3]. Predictions of charm meson cross-sections have been made at next-to-leading order using the generalized mass variable flavour number scheme (GMVFNS) [3][4][5][6][7][8] and at fixed order with next-to-leading-log resummation (FONLL) [1,2,[9][10][11][12]. These are based on a factorisation approach, where the cross-sections are calculated as a convolution of three terms: the parton distribution functions of the incoming protons; the partonic hard scattering rate, estimated as a perturbative series in the coupling constant of the strong interaction; and a fragmentation function that parametrises the hadronisation of the charm quark into a -1 - JHEP03(2016)159given type of charm hadron. The range of y and p T accessible to LHCb enables quantum chromodynamics calculations to be tested in a region where the momentum fraction, x, of the initial state partons can reach values below 10 −4 . In this region the uncertainties on the gluon parton density functions are large, exceeding 30% [1,13], and LHCb measurements can be used to constrain them. For example, the predictions provided in ref.[1] have made direct use of these constraints from LHCb data, taking as input a set of parton density functions that is weighted to match the LHCb measurements at √ s = 7 TeV.The charm production cross-sections are also important in evaluating the rate of highenergy neutrinos created from the decay of charm hadrons produced in cosmic ray interactions with atmospheric nuclei [1,14]. Such neutrinos constitute an important background for experiments such as IceCube Charm mesons produced at the pp collision point, either directly or as decay products of excited charm resonances, are referred to as promptly produced. No attempt is made to distinguish between these two sources. This paper presents measurements of the crosssections for the prompt production of D 0 , D + , D + s , and D * (2010) + (henceforth denoted as D * + ) mesons, based ...

Measurements of prompt charm production cross-sections in pp collisions at s = 5 $$ \sqrt{s}=5 $$ TeV

“…The GMVFNS predictions provide a better description of the data, although the cross-sections decrease with p T at a higher rate than the data near their low p T limit of 3 GeV/c. Similar behaviour was observed for thewhere only central values were shown for the FONLL prediction, and for the √ s = 13 TeV measurement [22], where in both cases the predictions gave lower cross-sections than the data.The data generally agree well with the FONLL, POWHEG+NNPDF3.0L and GMVFNS predictions for the ratios of cross-sections at √ s = 13 TeV and 5 TeV, shown in figure 7. These ratio measurements are significantly more precise than those previ--17 -…”

“…The LHCb experiment has recorded the world's largest dataset of charm hadrons to date and this has led to numerous high-precision measurements of their production and decay properties. LHCb measured the cross-sections in the forward region 2.0 < y < 4.5 for 0 < p T < 8 GeV/c at √ s = 7 TeV [21] and for 0 < p T < 15 GeV/c at √ s = 13 TeV [22].Charm mesons produced at the pp collision point, either directly or as decay products of excited charm resonances, are referred to as promptly produced. No attempt is made to distinguish between these two sources.…”

“…This paper presents measurements of the crosssections for the prompt production of D 0 , D + , D + s , and D * (2010) + (henceforth denoted as D * + ) mesons, based on data corresponding to an integrated luminosity of 8.60 ± 0.33 pb −1 . Charm mesons produced through the decays of b hadrons are referred to as secondary charm and are considered here as a background process.The analysis techniques described in this paper are nearly identical to those used in the measurements made at √ s = 13 TeV [22], allowing for very precise determination of the ratios between the two results.Section 2 describes the detector, data acquisition conditions, and the simulation; this is followed by a summary of the data analysis in section 3. The differential cross-section results are given in section 4 while section 5 presents the measurements of integrated crosssections and of the ratios of the cross-sections measured at √ s = 5 TeV to those at 13 TeV.…”

“…Candidates for D * + mesons are formed by combining a D 0 and a charged pion candidate, requiring that both form a good quality vertex. Applying the selection, 1% of all events have more than one selected candidate, all of which are considered in this analysis.The efficiencies for the reconstruction and selection of charm meson candidates are obtained for each (p T , y) bin in a near-identical manner to the √ s = 13 TeV measurement [22].All efficiencies are evaluated using the event simulation, except for the efficiencies for identifying kaons and pions and the tracking efficiencies. Kaon and pion identification efficiencies are evaluated using a high purity calibration sample of D * + → D 0 (→ K − π + )π + decays which have been selected without PID requirements.…”

“…The computation of the extrapolation factors is described in ref. [22]. The first uncertainty on the cross-section is statistical, and the second is systematic and includes the contribution from the extrapolation factor.…”