Abstract
The high collision energies reached at the LHC open the possibility to study extensively the production of light (anti-)(hyper-)nuclei and exotic bound states in proton-proton (pp), proton-lead (p-Pb) and lead-lead (Pb-Pb) collisions.ALICE has excellent particle identification (PID) capability which allows the detection of these rarely produced particles. PID is perfomed using several techniques, namely by exploiting the measurement of the specific ionization energy loss in the Time Projection Chamber (TPC) and the information of the Time-Of-Flight (TOF) detector.The transverse momentum spectra and the yields (dN/dy) of light nuclei and anti-nuclei were obtained and results are discussed here, and the first measurement of deuteron elliptic flow is presented. Furthermore, the study of the production of (anti-)hypertriton and the status of the searches for exotic bound states, i.e. Λ-Λ and Λ-n, are discussed.Results are compared to predictions from thermal and coalescence models in order to enquire into the production mechanisms of nuclei, hypernuclei and exotic bound states.
Highlights
The deuteron and 3He spectra exhibit a hardening with increasing centrality in Pb-Pb collisions, which can be explained by hydrodynamic models as an effect of the radial flow
Assuming a B.R. = 54% and the free Λ lifetime, this led to an upper limit (99% C.L.) on dN /dy ∼ 9.0×10−4 that is a factor 45 below values predicted by thermal models [10]
The results on nuclei and hypernuclei production in heavy-ion collisions can be rather well described by thermal and coalescence models. In this direction it is crucial to measure with better precision the d/p ratio
Summary
Hypernuclei are nuclei where a nucleon has been replaced with a hyperon and the hypertriton, a bound state of a proton, a neutron and a Λ, is the lightest known hypernucleus. The (anti-)hypertriton production yields were measured in Pb-Pb collisions exploiting the mesonic weak decay into two charged particles [6] From the ct-differential production spectrum, shown in Fig. 2 (right), it has been possible to compute the lifetime of the hypertriton with an exponential fit (red line). Being a loosely bound object, the theory predicts a value of the lifetime compatible with the free Λ lifetime. The fact that the ALICE value, as well as previous heavy-ion experiments results, is lower than the free Λ lifetime is still an open question. An improvement on this result might come from the study of the mesonic weak decay into three charged particles, 3ΛH
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