Λ+c production in pp collisions at $$ \sqrt{s}=7 $$ TeV and in p-Pb collisions at $$ \sqrt{s_{\mathrm{NN}}}=5.02 $$ TeV

Abstract

The p T -differential production cross section of prompt Λ + c charmed baryons was measured with the ALICE detector at the Large Hadron Collider (LHC) in pp collisions at √ s = 7 TeV and in p-Pb collisions at √ s NN = 5.02 TeV at midrapidity. The Λ + c and Λ -c were reconstructed in the hadronic decay modes Λ + c → pK − π + , Λ + c → pK 0 S and in the semileptonic channel Λ + c → e + ν e Λ (and charge conjugates). The measured values of the Λ + c /D 0 ratio, which is sensitive to the c-quark hadronisation mechanism, and in particular to the production of baryons, are presented and are larger than those measured previously in different colliding systems, centre-of-mass energies, rapidity and p T intervals, where the Λ + c production process may differ. The results are compared with the expectations obtained from perturbative Quantum Chromodynamics calculations and Monte Carlo event generators. Neither perturbative QCD calculations nor Monte Carlo models reproduce the data, indicating that the fragmentation of heavy-flavour baryons is not well understood. The first measurement at the LHC of the Λ + c nuclear modification factor, R pPb , is also presented. The R pPb is found to be consistent with unity and with that of D mesons within the uncertainties, and consistent with a theoretical calculation that includes cold nuclear matter effects and a calculation that includes charm quark interactions with a deconfined medium. Keywords: Heavy Ion Experiments, Quark gluon plasmaArXiv ePrint: 1712.09581Open Access, Copyright CERN, for the benefit of the ALICE Collaboration. Article funded by SCOAP 3 .https://doi.org/10.1007/JHEP04(2018)108 The ALICE collaboration 40 JHEP04(2018)108 IntroductionThe study of charm production at the Large Hadron Collider (LHC) is an important tool to test predictions obtained from perturbative Quantum Chromodynamics (pQCD) calculations for proton-proton (pp) collisions. These calculations are based on the factorisation approach that describes heavy-flavour production as a convolution of the parton distribution functions, the parton hard-scattering cross section and the fragmentation function. The cross section for heavy-flavour hadron production can be obtained from perturbative calculations at next-to-leading order with next-to-leading-log resummation, like the General-Mass Variable-Flavour-Number Scheme (GM-VFNS [1, 2]) and 4]) approaches. No predictions are, however, available for baryons in the latter approach due to lack of knowledge of the fragmentation function of charm quarks into baryons. Cross section calculations are available also with the k T factorisation framework [5]. These theoretical calculations generally describe within uncertainties the measurements at the LHC, with the central predictions for beauty production lying closer to data than the central predictions for charm production [6]. The measured -1 - JHEP04(2018)108transverse momentum differential cross section of charm mesons lies in the upper part of the FONLL uncertainty band and is systematically below th...

Improvement of heavy flavor production in a multiphase transport model updated with modern nuclear parton distribution functions

“…This results from the anti-shadowing effect at large x and the shadowing effect at small x. We also see that the AMPT result agrees with the charm quark pair yield for 0- [50] and Λc data [52]. mated based on the STAR data of dσ(D 0 )/dy = 41 µb and dσ(D 0 + D + + D + s + Λ + c )/dy = 152 µb for 10-40% Au+Au collisions at √ s N N = 200 GeV [53].…”

Measurement of $${{\mathrm{D}}^0}$$, $${{\mathrm{D}}^+}$$, $${{\mathrm{D}}^{*+}}$$ and $${{\mathrm{D}}^+_{\mathrm{s}}}$$ production in pp collisions at $${\sqrt{{\textit{s}}}~=~5.02~{\text {TeV}}}$$ with ALICE

“…[49] by averaging the measurements in e + e − collisions at LEP. However, recent measurements of the + c baryon production cross section in pp collisions at √ s = 7 TeV and in p-Pb collisions at √ s = 5.02 TeV [50] show a significant enhancement of the + c /D 0 ratio for p T > 1 GeV/c as compared to the values measured in e + e − and ep collisions at lower centreof-mass energies. This suggests that the fragmentation fractions of charm quarks into charmed baryons in pp collisions at LHC energies might differ significantly from the LEP results reported in Ref.…”

Dielectron production in proton-proton collisions at $$ \sqrt{s}=7 $$ TeV

“…An additional uncertainty of 9.3% is added in quadrature for the BR c→e to take into account differences in the Λ + c /D 0 ratio measured by the ALICE Collaboration, 0.543±0.061(stat.)±0.160(syst.) (for p T > 1 GeV/c) in pp collisions at √ s = 7 TeV [95], and the LEP average of 0.113 ± 0.013(stat.) ± 0.006(syst.)…”