Abstract
The high collision energies reached at the LHC lead to significant production yields of light (anti)-nuclei and hyper-matter in proton-proton and, in particular, Pb-Pb collisions. The excellent particle identification capabilities of the ALICE apparatus, in particular the specific energy loss in the Time Projection Chamber (TPC) and Time-of-Flight (TOF) measurement, allow for the detection of such rarely produced particles. Further, the Inner Tracking System (ITS) gives the possibility to separate primary nuclei from those coming from the weak decay of heavier systems. This offers the unique opportunity to search for exotica like the bound state of a A and a neutron which would decay into deuteron and pion, or the bound states of two As. We show here the performance of the ALICE apparatus in the sector on (anti-)nuclei and in particular the results on deuteron production in Pb-Pb collisions at = 2.76 TeV. These are compared with thermal model predictions. We further present the current state of the searches, by their upper limits on the production yields, and compare the results to thermal and coalescence model expectations.
Highlights
The measurement of lightnuclei and search for hyper-matter, created in heavy-ion collisions, is challenging since the production probability decreases with the increasing mass of the investigated particles
An open question in the field of heavy-ion collisions is if the production of nuclei and other multi-baryon states, such as hyper-nuclei or hyper-matter, is entirely described by a thermal model or if those objects are formed by coalescence of hadrons or even directly from quarks
This measurement is affected by a huge background, as for all nuclei, coming from knockout from material. This is not relevant for the measurement of anti-nuclei, like the anti-alpha. Rejection of this background is possible by restricting the distance-of-closest-approach of the track to the primary vertex in z-direction dcaz and fitting the dcaxy distribution to extract the signal in the pT window between 0.6 and 1.9 GeV/c
Summary
1. Introduction The measurement of light (anti-)nuclei and search for hyper-matter, created in heavy-ion collisions, is challenging since the production probability decreases with the increasing mass of the investigated particles. 2. Deuteron spectra and yields in Pb–Pb The excellent performance of the Time-Projection Chamber (TPC) [10] and the Time-Of-Flight detector (TOF) [11] allows for the clear identification of charged stable particles over a range of 0.15 to 5 GeV/c in rigidity R = p/z, where p is the track momentum and z is the charge number. The same technique is used to measure the yields of deuterons.
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