The Nordic Tier-1 centre for LHC is distributed over several computing centres. It uses ARC as the internal computing grid middleware. ALICE uses its own grid middleware AliEn to distribute jobs and ...the necessary software application stack. To make use of most of the AliEn infrastructure and software deployment methods for running ALICE grid jobs on ARC, we are investigating different possible virtualisation technologies. For this a testbed and possible framework for bridging different middleware systems is under development. It allows us to test a variety of virtualisation methods and software deployment technologies in the form of different virtual machines.
Understanding the role of parton mass and Casimir color factors in the quantum chromodynamics parton shower represents an important step in characterizing the emission properties of heavy quarks. ...Recent experimental advances in jet substructure techniques have provided the opportunity to isolate and characterize gluon emissions from heavy quarks. In this Letter, the first direct experimental constraint on the charm-quark splitting function is presented, obtained via the measurement of the groomed shared momentum fraction of the first splitting in charm jets, tagged by a reconstructed D^{0} meson. The measurement is made in proton-proton collisions at sqrts=13 TeV, in the low jet transverse-momentum interval of 15≤p_{T}^{jet ch}<30 GeV/c where the emission properties are sensitive to parton mass effects. In addition, the opening angle of the first perturbative emission of the charm quark, as well as the number of perturbative emissions it undergoes, is reported. Comparisons to measurements of an inclusive-jet sample show a steeper splitting function for charm quarks compared with gluons and light quarks. Charm quarks also undergo fewer perturbative emissions in the parton shower, with a reduced probability of large-angle emissions.
(ProQuest: ... denotes formulae and/or non-USASCII text omitted; see image) Abstract A measurement of the transverse momentum spectra of jets in Pb-Pb collisions at ... = 2.76TeV is reported. Jets ...are reconstructed from charged particles using the anti-k ^sub T^ jet algorithm with jet resolution parameters R of 0.2 and 0.3 in pseudo-rapidity |eta| < 0.5. The transverse momentum p ^sub T^ of charged particles is measured down to 0.15 GeV/c which gives access to the low p ^sub T^ fragments of the jet. Jets found in heavy-ion collisions are corrected event-by-event for average background density and on an inclusive basis (via unfolding) for residual background fluctuations and detector effects. A strong suppression of jet production in central events with respect to peripheral events is observed. The suppression is found to be similar to the suppression of charged hadrons, which suggests that substantial energy is radiated at angles larger than the jet resolution parameter R = 0.3 considered in the analysis. The fragmentation bias introduced by selecting jets with a high p ^sub T^ leading particle, which rejects jets with a soft fragmentation pattern, has a similar effect on the jet yield for central and peripheral events. The ratio of jet spectra with R = 0.2 and R = 0.3 is found to be similar in Pb-Pb and simulated PYTHIA pp events, indicating no strong broadening of the radial jet structure in the reconstructed jets with R < 0.3. Figure not available: see fulltext.
Neutral pion and Formula omitted meson invariant differential yields were measured in non-single diffractive p-Pb collisions at Formula omitted = 5.02 TeV with the ALICE experiment at the CERN LHC. ...The analysis combines results from three complementary photon measurements, utilizing the PHOS and EMCal calorimeters and the Photon Conversion Method. The invariant differential yields of Formula omitted and Formula omitted meson inclusive production are measured near mid-rapidity in a broad transverse momentum range of Formula omitted and Formula omitted, respectively. The measured Formula omitted ratio increases with Formula omitted and saturates for Formula omitted > 4 Formula omitted at Formula omitted. A deviation from Formula omitted scaling is observed for Formula omitted 2 Formula omitted. The measured Formula omitted ratio is consistent with previous measurements from proton-nucleus and pp collisions over the full Formula omitted range. The measured Formula omitted ratio at high Formula omitted also agrees within uncertainties with measurements from nucleus-nucleus collisions. The Formula omitted and Formula omitted yields in p-Pb relative to the scaled pp interpolated reference, Formula omitted, are presented for Formula omitted 20 Formula omitted and Formula omitted 20 Formula omitted, respectively. The results are compared with theoretical model calculations. The values of Formula omitted are consistent with unity for transverse momenta above 2 Formula omitted. These results support the interpretation that the suppressed yield of neutral mesons measured in Pb-Pb collisions at LHC energies is due to parton energy loss in the hot QCD medium.
We report on the measurement of the inclusive J/ Formula omitted polarization parameters in pp collisions at a center of mass energy Formula omitted TeV with the ALICE detector at the LHC. The ...analysis is based on a data sample corresponding to an integrated luminosity of 1.23 pb Formula omitted. J/ Formula omitted resonances are reconstructed in their di-muon decay channel in the rapidity interval Formula omitted and over the transverse-momentum interval Formula omitted Formula omitted. The three polarization parameters ( Formula omitted, Formula omitted, Formula omitted) are measured as a function of Formula omitted both in the helicity and Collins-Soper reference frames. The measured J/ Formula omitted polarization parameters are found to be compatible with zero within uncertainties, contrary to expectations from all available predictions. The results are compared with the measurement in pp collisions at Formula omitted TeV.
Formula omitted meson measurements provide insight into strangeness production, which is one of the key observables for the hot medium formed in high-energy heavy-ion collisions. ALICE measured ...Formula omitted production through its decay in muon pairs in Pb-Pb collisions at Formula omitted TeV in the intermediate transverse momentum range Formula omitted GeV/c and in the rapidity interval Formula omitted. The Formula omitted yield was measured as a function of the transverse momentum and collision centrality. The nuclear modification factor was obtained as a function of the average number of participating nucleons. Results were compared with the ones obtained via the kaon decay channel in the same Formula omitted range at midrapidity. The values of the nuclear modification factor in the two rapidity regions are in agreement within uncertainties.
A measurement of beauty hadron production at mid-rapidity in proton-lead collisions at a nucleon–nucleon centre-of-mass energy sNN=5.02 TeV is presented. The semi-inclusive decay channel of beauty ...hadrons into J/ψ is considered, where the J/ψ mesons are reconstructed in the dielectron decay channel at mid-rapidity down to transverse momenta of 1.3 GeV/c. The bb¯ production cross section at mid-rapidity, dσbb¯/dy, and the total cross section extrapolated over full phase space, σbb¯, are obtained. This measurement is combined with results on inclusive J/ψ production to determine the prompt J/ψ cross sections. The results in p–Pb collisions are then scaled to expectations from pp collisions at the same centre-of-mass energy to derive the nuclear modification factor RpPb, and compared to models to study possible nuclear modifications of the production induced by cold nuclear matter effects. RpPb is found to be smaller than unity at low pT for both J/ψ coming from beauty hadron decays and prompt J/ψ.
An invariant differential cross section measurement of inclusive π0 and η meson production at mid-rapidity in pp collisions at s=8 TeV was carried out by the ALICE experiment at the LHC. The spectra ...of π0 and η mesons were measured in transverse momentum ranges of 0.3<pT<35 GeV/c and 0.5<pT<35 GeV/c, respectively. Next-to-leading order perturbative QCD calculations using fragmentation functions DSS14 for the π0 and AESSS for the η overestimate the cross sections of both neutral mesons, although such calculations agree with the measured η/π0 ratio within uncertainties. The results were also compared with PYTHIA 8.2 predictions for which the Monash 2013 tune yields the best agreement with the measured neutral meson spectra. The measurements confirm a universal behavior of the η/π0 ratio seen for NA27, PHENIX and ALICE data for pp collisions from s=27.5 GeV to s=8 TeV within experimental uncertainties. A relation between the π0 and η production cross sections for pp collisions at s=8 TeV is given by mT scaling for pT>3.5 GeV/c. However, a deviation from this empirical scaling rule is observed for transverse momenta below pT<3.5 GeV/c in the η/π0 ratio with a significance of 6.2σ.
Two-particle angular correlations were measured in pp collisions at Formula omitted TeV for pions, kaons, protons, and lambdas, for all particle/anti-particle combinations in the pair. Data for ...mesons exhibit an expected peak dominated by effects associated with mini-jets and are well reproduced by general purpose Monte Carlo generators. However, for baryon-baryon and anti-baryon-anti-baryon pairs, where both particles have the same baryon number, a near-side anti-correlation structure is observed instead of a peak. This effect is interpreted in the context of baryon production mechanisms in the fragmentation process. It currently presents a challenge to Monte Carlo models and its origin remains an open question.
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