Abstract
In this letter, the production of deuterons and anti-deuterons in pp collisions at s=7 TeV is studied as a function of the charged-particle multiplicity density at mid-rapidity with the ALICE detector at the LHC. Production yields are measured at mid-rapidity in five multiplicity classes and as a function of the deuteron transverse momentum (pT). The measurements are discussed in the context of hadron–coalescence models. The coalescence parameter B2, extracted from the measured spectra of (anti-)deuterons and primary (anti-)protons, exhibits no significant pT-dependence for pT<3GeV/c, in agreement with the expectations of a simple coalescence picture. At fixed transverse momentum per nucleon, the B2 parameter is found to decrease smoothly from low multiplicity pp to Pb–Pb collisions, in qualitative agreement with more elaborate coalescence models. The measured mean transverse momentum of (anti-)deuterons in pp is not reproduced by the Blast-Wave model calculations that simultaneously describe pion, kaon and proton spectra, in contrast to central Pb–Pb collisions. The ratio between the pT-integrated yield of deuterons to protons, d/p, is found to increase with the charged-particle multiplicity, as observed in inelastic pp collisions at different centre-of-mass energies. The d/p ratios are reported in a wide range, from the lowest to the highest multiplicity values measured in pp collisions at the LHC.
Highlights
The production of light nuclei and anti-nuclei in elementary collisions has been described by phenomenological models in which nucleons coalesce into nuclei [1,2,3,4]
These models have successfully been tested with deuteron and anti-deuteron production measured in pp collisions at the CERN ISR [5,6] and Tevatron [7], photo-production and deep inelastic scattering of electrons at HERA [8,9], electron-positron collisions at ARGUS [10], BaBar [11], CLEO [12] and at LEP [13]
The transverse momentum spectra of deuterons and antideuterons in the considered multiplicity classes are shown in Fig. 2, in the left and right panels, respectively
Summary
The production of light nuclei and anti-nuclei in elementary collisions has been described by phenomenological models in which nucleons coalesce into nuclei [1,2,3,4]. Results on√the production of light (anti-)nuclei in inelastic pp collisions at s = 0.9, 2.76 and 7 TeV have been reported by the ALICE Collaboration in [14,15] and the validity of coalescence models [1,2,3,4] at the Large Hadron Collider. The abundances of nuclei are very sensitive to the freeze-out conditions, to the dynamics, and the size of the emitting source For these reasons, a systematic comparison of the production of light nuclei across different collision systems and, in particular, in events with similar final-state multiplicity but very different initial conditions and collision geometry can shed light on the production mechanisms.
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