The design, construction, and commissioning of the ALICE Time-Projection Chamber (TPC) is described. It is the main device for pattern recognition, tracking, and identification of charged particles ...in the ALICE experiment at the CERN LHC. The TPC is cylindrical in shape with a volume close to 90m3 and is operated in a 0.5T solenoidal magnetic field parallel to its axis.
In this paper we describe in detail the design considerations for this detector for operation in the extreme multiplicity environment of central Pb–Pb collisions at LHC energy. The implementation of the resulting requirements into hardware (field cage, read-out chambers, electronics), infrastructure (gas and cooling system, laser-calibration system), and software led to many technical innovations which are described along with a presentation of all the major components of the detector, as currently realized. We also report on the performance achieved after completion of the first round of stand-alone calibration runs and demonstrate results close to those specified in the TPC Technical Design Report.
In high-energy nuclear collisions the degree of thermalization at the partonic level is a key issue. Due to their large mass, heavy quarks and their possible participation in the collective flow of ...the QCD-medium constitute a powerful probe for thermalization. We present studies with PYTHIA for
pp collisions at the top LHC energy of
s
=
14
TeV
applying the two-particle transverse momentum correlator
〈
Δ
p
t
,
1
,
Δ
p
t
,
2
〉
to pairs of heavy-quark hadrons and their semi-leptonic decay products as a function of their relative azimuth. Modifications or even the complete absence of initially existing correlations in
Pb
+
Pb
collisions might indicate thermalization at the partonic level.
(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 .
We report on results of a measurement of {phi} meson production in central Pb-Au collisions at E{sub lab}=158A GeV. For the first time in the history of high energy heavy-ion collisions, {phi} mesons ...were reconstructed both in the K{sup +}K{sup -} and the dilepton decay channels in the same experiment. This measurement yields rapidity densities near midrapidity, from the two decay channels, of 2.05{+-}0.14(stat){+-}0.25(syst) and 2.04{+-}0.49(stat){+-}0.32(syst), respectively. The shape of the measured transverse momentum spectrum is also in close agreement in both decay channels. The data rule out a possible enhancement of the {phi} yield in the leptonic over the hadronic decay channel of a factor 1.6 or larger at the 95% C.L. This rules out the discrepancy reported in the literature between measurements of the hadronic and dimuon decay channels by two different experiments.
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.
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