Invariant differential yields of deuterons and antideuterons in pp collisions at √ s = 0.9, 2.76 and 7 TeV and the yields of tritons, 3 He nuclei, and their antinuclei at √ s = 7 TeV have been measured with the ALICE detector at the CERN Large Hadron Collider. The measurements cover a wide transverse momentum (p T ) range in the rapidity interval |y| < 0.5, extending both the energy and the p T reach of previous measurements up to 3 GeV/c for A = 2 and 6 GeV/c for A = 3. The coalescence parameters of (anti)deuterons and 3 He nuclei exhibit an increasing trend with p T and are found to be compatible with measurements in pA collisions at low p T and lower energies. The integrated yields decrease by a factor of about 1000 for each increase of the mass number with one (anti)nucleon. Furthermore, the deuteron-to-proton ratio is reported as a function of the average charged particle multiplicity at different center-of-mass energies.
Midrapidity production of π ± , K ± , and (p)p measured by the ALICE experiment at the CERN Large Hadron Collider, in Pb-Pb and inelastic pp collisions at √ s NN = 5.02 TeV, is presented. The invariant yields are measured over a wide transverse momentum (p T) range from hundreds of MeV/c up to 20 GeV/c. The results in Pb-Pb collisions are presented as a function of the collision centrality, in the range 0-90%. The comparison of the p T-integrated particle ratios, i.e., proton-to-pion (p/π) and kaon-to-pion (K/π) ratios, with similar measurements in Pb-Pb collisions at √ s NN = 2.76 TeV show no significant energy dependence. Blast-wave fits of the p T spectra indicate that in the most central collisions radial flow is slightly larger at 5.02 TeV with respect to 2.76 TeV. Particle ratios (p/π , K/π) as a function of p T show pronounced maxima at p T ≈ 3 GeV/c in central Pb-Pb collisions. At high p T , particle ratios at 5.02 TeV are similar to those measured in pp collisions at the same energy and in Pb-Pb collisions at √ s NN = 2.76 TeV. Using the pp reference spectra measured at the same collision energy of 5.02 TeV, the nuclear modification factors for the different particle species are derived. Within uncertainties, the nuclear modification factor is particle species independent for high p T and compatible with measurements at √ s NN = 2.76 TeV. The results are compared to state-of-the-art model calculations, which are found to describe the observed trends satisfactorily.
Centrality dependence of the pseudorapidity density distribution for charged particles in Pb-Pb collisions at √ s NN = 2.76 TeV ✩ .ALICE Collaboration a r t i c l e i n f o a b s t r a c tWe present the first wide-range measurement of the charged-particle pseudorapidity density distribution, for different centralities (the 0-5%, 5-10%, 10-20%, and 20-30% most central events) in Pb-Pb collisions at √ s NN = 2.76 TeV at the LHC. The measurement is performed using the full coverage of the ALICE detectors, −5.0 < η < 5.5, and employing a special analysis technique based on collisions arising from LHC 'satellite' bunches. We present the pseudorapidity density as a function of the number of participating nucleons as well as an extrapolation to the total number of produced charged particles (N ch = 17 165 ± 772 for the 0-5% most central collisions). From the measured dN ch /dη distribution we derive the rapidity density distribution, dN ch /dy, under simple assumptions. The rapidity density distribution is found to be significantly wider than the predictions of the Landau model. We assess the validity of longitudinal scaling by comparing to lower energy results from RHIC. Finally the mechanisms of the underlying particle production are discussed based on a comparison with various theoretical models.ICE detector. The employed method relies on using so-called 'satellite' bunch collisions and is based on measurements from three ✩ © CERN for the benefit of the ALICE Collaboration. different ALICE sub-detectors. This method is applicable for the 30% most central events where the trigger efficiency for these 'satellite' collisions remains high. These measurements extend considerably the former results obtained at the LHC [8-10] and can be compared to the wealth of results on the charged-particle pseudorapidity density from lower energy Au-Au collisions at RHIC [6,11, 12] as well as model calculations. Experimental setupA detailed description of the ALICE detector can be found in [13]. In the following, we will briefly describe the detectors used in this analysis, namely the Silicon Pixel Detector (SPD), the Forward Multiplicity Detector (FMD), the VZERO, and the Zero Degree Calorimeter (ZDC) (see Fig. 1).The SPD is the innermost element of the ALICE inner tracking system [13]. It consists of two cylindrical layers of hybrid silicon pixel assemblies positioned at radial distances of 3.9 and 7.6 cm from the beam line, with a total of 9.8 × 10 6 pixels of size 50 × 425 μm 2 , read out by 1200 electronic chips. The SPD coverage for particles originating from the nominal interaction point at the center of the detector is |η| < 2 and |η| < 1.4 for the inner and outer layers, respectively.The VZERO detector [14] consists of two arrays of 32 scintillator tiles (4 rings of increasing radii each with 8 azimuthal sectors) placed at distances of 3.3 m (VZERO-A) and −0.9 m (VZERO-C) from the nominal interaction point along the beam axis, covering the full azimuth within 2.8 < η < 5.1 and −3.7 < η < −1.7, 0370-2693/
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