Abstract
AbstractThe ALICE experiment at the LHC has studied J/ψproduction at mid-rapidity in pp collisions at$ \sqrt{s}=7 $TeV through its electron pair decay on a data sample corresponding to an integrated luminosityLint= 5.6 nb−1. The fraction of J/ψfrom the decay of long-lived beauty hadrons was determined for J/ψcandidates with transverse momentumpt>1.3 GeV/cand rapidity |y|<0.9. The cross section for prompt J/ψmesons, i.e. directly produced J/ψand prompt decays of heavier charmonium states such as theψ(2S) and χcresonances, is σprompt J/ψ(pt>1.3 GeV/c,|y|<0.9) = 8.3 ± 0.8 (stat.) ± 1.1 (syst.)$ _{-1.4}^{+1.5 } $(syst.pol.)μb. The cross section for the production of b-hadrons decaying to J/ψwithpt>1.3 GeV/cand |y|<0.9 is$ {\sigma_{{{J \left/ {{\psi \leftarrow {{\mathrm{h}}_{\mathrm{B}}}}} \right.}}}} $(pt> 1.3 GeV/c, |y| < 0.9) = 1.46 ± 0.38 (stat.)$ _{-0.32}^{+0.26 } $(syst.)μb. The results are compared to QCD model predictions. The shape of theptandydistributions of b-quarks predicted by perturbative QCD model calculations are used to extrapolate the measured cross section to derive the$ \mathrm{b}\overline{\mathrm{b}} $pair total cross section and dσ/dyat mid-rapidity.
Highlights
The shape of the pt and y distributions of b-quarks predicted by perturbative QCD model calculations are used to extrapolate the measured cross section to derive the bb pair total cross section and dσ/dy at mid-rapidity
The results presented in this paper were obtained with the central barrel tracking detectors, in particular the Inner Tracking System (ITS) [26, 27] and the Time Projection Chamber (TPC) [28]
Prompt J/ψ production is well described by next-to-leading order (NLO) non-relativistic QCD (NRQCD) models that include color-octet processes
Summary
The ALICE experiment [26] consists of a central barrel, covering the pseudorapidity region |η| < 0.9, and a muon spectrometer with −4 < η < −2.5 coverage. The effective parameters λ+, λ− and λsym, and optionally the corresponding fractions, were determined, prior to the likelihood fit maximization, with a fit to the x distribution in the sidebands of the dielectron invariant mass distribution, defined as the regions 1.8–2.6 and 3.2–5.0 GeV/c2 The introduction of these components is needed because the background consists of random combinations of electrons from semi-leptonic decays of charm and beauty hadrons, which tend to produce positive x values, as well as of other secondary or mis-reconstructed tracks which contribute both to positive and negative x values. In figure 2 the distributions of the invariant mass and of the pseudoproper decay length are shown in different pt bins with superimposed results of the fits
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