(ProQuest: ... denotes formulae and/or non-USASCII text omitted; see image).The ALICE Collaboration at the LHC has measured the J/ psi and psi ' 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 mu b super(-1). The cross section for coherent and incoherent J/ psi production in the rapidity interval -0.9<y<0.9, are ... and ..., respectively. The results are compared to theoretical models for J/ psi production and the coherent cross section is found to be in good agreement with those models incorporating moderate nuclear gluon shadowing at Bjorken-x around 10 super(-3), such as EPS09 parametrization. In addition the cross section for the process gamma gamma arrow right e super(+) e super(-) has been measured and found to be in agreement with models implementing QED at leading order.
The production cross section of electrons from semileptonic decays of beauty hadrons was measured at mid-rapidity (| y | < 0.8) in the transverse momentum range 1 < p T < 8 GeV / c with the ALICE ...experiment at the CERN LHC in pp collisions at a center of mass energy s = 7 TeV using an integrated luminosity of 2.2 nb - 1 . Electrons from beauty hadron decays were selected based on the displacement of the decay vertex from the collision vertex. A perturbative QCD calculation agrees with the measurement within uncertainties. The data were extrapolated to the full phase space to determine the total cross section for the production of beauty quarkaantiquark pairs.
The inclusive transverse momentum (p T) distributions of primary charged particles are measured in the pseudo-rapidity range | IDT | 30 GeV / c . In peripheral collisions (70a80%), only moderate ...suppression (R A A = 0.6 a 0.7) and a weak p T dependence is observed. The measured nuclear modification factors are compared to other measurements and model calculations.
The elliptic, v 2 , triangular, v 3 , and quadrangular, v 4 , azimuthal anisotropic flow coefficients are measured for unidentified charged particles, pions, and (anti-)protons in PbaPb collisions at ...s NN = 2.76 TeV with the ALICE detector at the Large Hadron Collider. Results obtained with the event plane and four-particle cumulant methods are reported for the pseudo-rapidity range | IDT | 8 GeV / c . The small p T dependence of the difference between elliptic flow results obtained from the event plane and four-particle cumulant methods suggests a common origin of flow fluctuations up to p T = 8 GeV / c . The magnitude of the (anti-)proton elliptic and triangular flow is larger than that of pions out to at least p T = 8 GeV / c indicating that the particle type dependence persists out to high p T .
The ALICE Collaboration has measured inclusive J / I production in pp collisions at a center-of-mass energy s = 2.76 TeV at the LHC. The results presented in this Letter refer to the rapidity ranges ...| y | < 0.9 and 2.5 < y < 4 and have been obtained by measuring the electron and muon pair decay channels, respectively. The integrated luminosities for the two channels are L int e = 1.1 nb - 1 and L int mu = 19.9 nb - 1 , and the corresponding signal statistics are N J / I e + e - = 59 +/- 14 and N J / I mu + mu - = 1364 +/- 53 . We present d I J / I / d y for the two rapidity regions under study and, for the forward-y range, d 2 I J / I / d y d p t in the transverse momentum domain 0 < p t < 8 GeV / c . The results are compared with previously published results at s = 7 TeV and with theoretical calculations.
The p T -differential inclusive production cross section of the prompt charm-strange meson D s + in the rapidity range | y | < 0.5 was measured in protonaproton collisions at s = 7 TeV at the LHC ...using the ALICE detector. The analysis was performed on a data sample of 2.98 X 10 8 events collected with a minimum-bias trigger. The corresponding integrated luminosity is L int = 4.8 nb - 1 . Reconstructing the decay D s + a I pi + , with I a K - K + , and its charge conjugate, about 480 D s +/- mesons were counted, after selection cuts, in the transverse momentum range 2 < p T < 12 GeV / c . The results are compared with predictions from models based on perturbative QCD. The ratios of the cross sections of four D meson species (namely D 0 , D + , D a + and D s +) were determined both as a function of p T and integrated over p T after extrapolating to full p T range, together with the strangeness suppression factor in charm fragmentation. The obtained values are found to be compatible within uncertainties with those measured by other experiments in e + e - , ep and pp interactions at various centre-of-mass energies.
In high-energy collisions, the spatio-temporal size of the particle production region can be measured using the Bose–Einstein correlations of identical bosons at low relative momentum. The source ...radii are typically extracted using two-pion correlations, and characterize the system at the last stage of interaction, called kinetic freeze-out. In low-multiplicity collisions, unlike in high-multiplicity collisions, two-pion correlations are substantially altered by background correlations, e.g. mini-jets. Such correlations can be suppressed using three-pion cumulant correlations. We present the first measurements of the size of the system at freeze-out extracted from three-pion cumulant correlations in pp, p–Pb and Pb–Pb collisions at the LHC with ALICE. At similar multiplicity, the invariant radii extracted in p–Pb collisions are found to be 5–15% larger than those in pp, while those in Pb–Pb are 35–55% larger than those in p–Pb. Our measurements disfavor models which incorporate substantially stronger collective expansion in p–Pb as compared to pp collisions at similar multiplicity.
A measurement of the multi-strange I a and ICO a baryons and their antiparticles by the ALICE experiment at the CERN Large Hadron Collider (LHC) is presented for inelastic protonaproton collisions at ...a centre-of-mass energy of 7 TeV. The transverse momentum ( p T ) distributions were studied at mid-rapidity ( | y | 6.0 GeV / c . We also illustrate the difference between the experimental data and model by comparing the corresponding ratios of ( ICO a + ICO A= + ) / ( I a + I A= + ) as a function of transverse mass.
The ALICE Collaboration reports the measurement of the relative J / I yield as a function of charged particle pseudorapidity density d N ch / d IDT in pp collisions at s = 7 TeV at the LHC. J / I ...particles are detected for p t > 0 , in the rapidity interval | y | 0 . In the highest multiplicity interval with a d N ch / d IDT ( bin ) a = 24.1 , corresponding to four times the minimum bias multiplicity density, an enhancement relative to the minimum bias J / I yield by a factor of about 5 at 2.5 < y < 4 (8 at | y | < 0.9 ) is observed.
(ProQuest: ... denotes formulae and/or non-USASCII text omitted; see image).The W and Z boson production was measured via the muonic decay channel in proton-lead collisions at ... TeV at the Large ...Hadron Collider with the ALICE detector. The measurement covers backward (-4.46 < y sub(cms) < -2.96) and forward (2.03 < y sub(cms) < 3.53) rapidity regions, corresponding to Pb-going and p-going directions, respectively. The Z-boson production cross section, with dimuon invariant mass of 60 < m sub( ) mu mu < 120 GeV/c super(2) and muon transverse momentum (p sub(T) super( ) mu larger than 20 GeV/c, is measured. The production cross section and charge asymmetry of muons from W-boson decays with p sub(T) super( ) mu > 10 GeV/c are determined. The results are compared to theoretical calculations both with and without including the nuclear modification of the parton distribution functions. The W-boson production is also studied as a function of the collision centrality: the cross section of muons from W-boson decays is found to scale with the average number of binary nucleon-nucleon collisions within uncertainties. Figure not available: see fulltext.
PDF
