Abstract
The production of (anti-)deuteron and (anti-)$^{3}$He nuclei in Pb-Pb collisions at $\sqrt{s_{\rm NN}}$ = 2.76 TeV has been studied using the ALICE detector at the LHC. The spectra exhibit a significant hardening with increasing centrality. Combined blast-wave fits of several particles support the interpretation that this behavior is caused by an increase of radial flow. The integrated particle yields are discussed in the context of coalescence and thermal-statistical model expectations. The particle ratios, $^3$He/d and $^3$He/p, in Pb-Pb collisions are found to be in agreement with a common chemical freeze-out temperature of $T_{\rm chem} \approx 156$ MeV. These ratios do not vary with centrality which is in agreement with the thermal-statistical model. In a coalescence approach, it excludes models in which nucleus production is proportional to the particle multiplicity and favors those in which it is proportional to the particle density instead. In addition, the observation of 31 anti-tritons in Pb-Pb collisions is reported. For comparison, the deuteron spectrum in pp collisions at $\sqrt{s} = 7$ TeV is also presented. While the p/$\pi$ ratio is similar in pp and Pb-Pb collisions, the d/p ratio in pp collisions is found to be lower by a factor of 2.2 than in Pb-Pb collisions.
Highlights
Collisions of ultrarelativistic ions create suitable conditions for producing lightnuclei, because a high energy density is reached over a large volume
The results presented in this paper are obtained from the data collected by the ALICE experiment at the LHC
The V0 amplitude distribution was used to determine the centrality of the heavy-ion collisions. It was fitted with a Glauber Monte Carlo model to compute the fraction of the hadronic cross section corresponding to a given range of V0 amplitude
Summary
Collisions of ultrarelativistic ions create suitable conditions for producing light (anti-)nuclei, because a high energy density is reached over a large volume. The production scenarios are typically discussed within two approaches: (i) The thermal-statistical approach has been very successful in describing the integrated yield of the hadrons and of composite nuclei [1,2,3]. In this picture, the chemical freeze-out temperature Tchem (predicted around 160 MeV) acts as the key parameter. The measurement of (anti-)alphas and (anti-)hypertritons will be shown in subsequent publications
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