This publication describes the methods used to measure the centrality of inelastic Pb-Pb collisions at a center-of-mass energy of 2.76 TeV per colliding nucleon pair with ALICE. The centrality is a key parameter in the study of the properties of QCD matter at extreme temperature and energy density, because it is directly related to the initial overlap region of the colliding nuclei. Geometrical properties of the collision, such as the number of participating nucleons and the number of binary nucleon-nucleon collisions, are deduced from a Glauber model with a sharp impact parameter selection and shown to be consistent with those extracted from the data. The centrality determination provides a tool to compare ALICE measurements with those of other experiments and with theoretical calculations.
In this paper measurements are presented of π ± , K ± , p, andp production at midrapidity (|y| < 0.5), in Pb-Pb collisions at √ s NN = 2.76 TeV as a function of centrality. The measurement covers the transverse-momentum (p T ) range from 100, 200, and 300 MeV/c up to 3, 3, and 4.6 GeV/c for π , K, and p, respectively. The measured p T distributions and yields are compared to expectations based on hydrodynamic, thermal and recombination models. The spectral shapes of central collisions show a stronger radial flow than measured at lower energies, which can be described in hydrodynamic models. In peripheral collisions, the p T distributions are not well reproduced by hydrodynamic models. Ratios of integrated particle yields are found to be nearly independent of centrality. The yield of protons normalized to pions is a factor ∼1.5 lower than the expectation from thermal models.
We present the perturbative renormalization group functions of O(n)-symmetric φ 4 theory in 4 − 2ε dimensions to the sixth loop order in the minimal subtraction scheme. In addition, we estimate diagrams without subdivergences up to 11 loops and compare these results with the asymptotic behaviour of the beta function. Furthermore we perform a resummation to obtain estimates for critical exponents in three and two dimensions.
The ALICE Collaboration at the LHC has measured the J/ψ and ψ′ photoproduction at mid-rapidity in ultra-peripheral Pb–Pb collisions at .The charmonium is identified via its leptonic decay for events where the hadronic activity is required to be minimal. The analysis is based on an event sample corresponding to an integrated luminosity of about 23 μb−1. The cross section for coherent and incoherent J/ψ production in the rapidity interval −0.9
We report on a completely analytical calculation of the field anomalous dimension γ ϕ and the critical exponent η for the O(n)-symmetric ϕ 4 model at the record six loop level. We successfully compare our result for γ ϕ with n = 1 with the predictions based on the method of the Borel resummation combined with a conformal mapping [Kazakov/Shirkov/Tarasov (1979)]. Predictions for seven loop contribution to the field anomalous dimensions are given.
The ratios of yields of anti-baryons to baryons probes the mechanisms of baryon-number transport. Results for p/p, / , + / − and + / − in pp collisions at √ s = 0.9, 2.76 and 7 TeV, measured with the ALICE detector at the LHC, are reported. Within the experimental uncertainties and ranges covered by our measurement, these ratios are independent of rapidity, transverse momentum and multiplicity for all measured energies. The results are compared to expectations from event generators, such as PYTHIA and HIJING/B, that are used to model the particle production in pp collisions. The energy dependence of p/p, / , + / − and + / − , reaching values compatible with unity for √ s = 7 TeV, complement the earlier p/p measurement of ALICE. These dependencies can be described by exchanges with the Regge-trajectory intercept of α J ≈ 0.5, which are suppressed with increasing rapidity interval y. Any significant contribution of an exchange not suppressed at large y (reached at LHC energies) is disfavoured.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.