Browsing by Subject "PPB COLLISIONS"

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  • Lappi, T. (2015)
    Recent experimental results have revealed a surprisingly rich structure of multiparticle azimuthal correlations in high energy proton-nucleus collisions. Final state collective effects can be responsible for many of the observed effects, but it has recently been argued that a part of these correlations are present already in the wavefunctions of the colliding particles. We evaluate the momentum space 2-particle cumulant azimuthal anisotropy coefficients v(n){2}, n = 2, 3, 4 from fundamental representation Wilson line distributions describing the high energy nucleus. These would correspond to the flow coefficients in very forward proton-nucleus scattering. We find significant differences between Wilson lines from the MV model and from JIMWLK evolution. The magnitude and qualitative transverse momentum dependence of the v(n){2} values suggest that the fluctuations present in the initial fields are a significant contribution to the observed anisotropies. (C) 2015 The Author. Published by Elsevier B.V.
  • Eskola, Kari J.; Paakkinen, Petja; Paukkunen, Hannu; Salgado, Carlos A. (2017)
    We introduce a global analysis of collinearly factorized nuclear parton distribution functions (PDFs) including, for the first time, data constraints from LHC proton-lead collisions. In comparison to our previous analysis, EPS09, where data only from charged-lepton-nucleus deep inelastic scattering (DIS), Drell-Yan (DY) dilepton production in proton-nucleus collisions and inclusive pion production in deuteron-nucleus collisions were the input, we now increase the variety of data constraints to cover also neutrino-nucleus DIS and low-mass DY production in pion-nucleus collisions. The new LHC data significantly extend the kinematic reach of the data constraints. We now allow much more freedom for the flavor dependence of nuclear effects than in other currently available analyses. As a result, especially the uncertainty estimates are more objective flavor by flavor. The neutrino DIS plays a pivotal role in obtaining a mutually consistent behavior for both up and down valence quarks, and the LHC dijet data clearly constrain gluons at large momentum fraction. Mainly for insufficient statistics, the pion-nucleus DY and heavy-gauge-boson production in proton-lead collisions impose less visible constraints. The outcome - a new set of next-to-leading order nuclear PDFs called EPPS16 - is made available for applications in high-energy nuclear collisions.
  • Adam, J.; Brucken, E. J.; Chang, B.; Hilden, T. E.; Kim, D. J.; Kral, J.; Mieskolainen, M. M.; Orava, R.; Rak, J.; Räsänen, S. S.; Snellman, T. W.; Trzaska, W. H.; The ALICE collaboration (2016)
    Two-particle angular correlations between trigger particles in the forward pseudorapidity range (2.5 <vertical bar eta vertical bar <4.0) and associated particles in the central range(vertical bar eta vertical bar <1.0) are measured with the ALICE detector in p-Pb collisions at a nucleon-nucleon centre-of-mass energy of 5.02 TeV. The trigger particles are reconstructed using the muon spectrometer, and the associated particles by the central barrel tracking detectors. In high-multiplicity events, the double-ridge structure, previously discovered in two-particle angular correlations at midrapidity, is found to persist to the pseudorapidity ranges studied in this Letter. The second-order Fourier coefficients for muons in high-multiplicity events are extracted after jet-like correlations from low-multiplicity events have been subtracted. The coefficients are found to have a similar transverse momentum(p(T)) dependence in p-going (p-Pb) and Pb-going (Pb-p) configurations, with the Pb-going coefficients larger by about 16 +/- 6%, rather independent of p(T) within the uncertainties of the measurement. The data are compared with calculations using the AMPT model, which predicts a different p(T) and eta dependence than observed in the data. The results are sensitive to the parent particle v(2) and composition of reconstructed muon tracks, where the contribution from heavy flavour decays is expected to dominate at p(T) > 2GeV/c. (C) 2015 CERN for the benefit of the ALICE Collaboration. Published by Elsevier B. V.
  • The ALICE collaboration; Acharya, S.; Brucken, E. J.; Chang, B.; Hilden, T. E.; Kim, D. J.; Litichevskyi, V.; Mieskolainen, M. M.; Orava, R.; Parkkila, J. E.; Rak, J.; Räsänen, S. S.; Saarinen, S.; Slupecki, M.; Snellman, T. W.; Trzaska, W. H.; Vargyas, M.; Viinikainen, J. (2018)
    Inclusive J/psi production is studied in p-Pb interactions at a centre-of-mass energy per nucleon-nucleon collision root s(NN) = 8.16 TeV, using the ALICE detector at the CERN LHC. The J/psi meson is reconstructed, via its decay to a muon pair, in the centreof-mass rapidity intervals 2.03 < Y-cms < 3.53 and -4.46 < Y-cms < -2.96, where positive and negative Y(cms )refer to the p-going and Pb-going direction, respectively. The transverse momentum coverage is PT < 20 GeV/c. In this paper, Y-cms- and P-T-differential cross sections for inclusive J/psi production are presented, and the corresponding nuclear modification factors R-pPb are shown. Forward results show a suppression of the J/psi yield with respect to pp collisions, concentrated in the region P-T less than or similar to 5 GeV/c. At backward rapidity no significant suppression is observed. The results are compared to previous measurements by ALICE in p-Pb collisions at root s(NN) = 5.02 TeV and to theoretical calculations. Finally, the ratios R-FB between forward- and backward-Y-cms R-pPb values are shown and discussed.
  • Adam, J.; Brucken, E. J.; Chang, B.; Hilden, T. E.; Kim, D. J.; Kral, J.; Mieskolainen, M. M.; Rak, J.; Rasanen, S. S.; Snellman, T. W.; Trzaska, W. H.; The ALICE collaboration (2015)
    Charged jet production cross sections in p-Pb collisions at root s(NN) = 5.02 TeV measured with the ALICE detector at the LHC are presented. Using the anti-k(T) algorithm, jets have been reconstructed in the central rapidity region from charged particles with resolution parameters R = 0.2 and R = 0.4. The reconstructed jets have been corrected for detector effects and the underlying event background. To calculate the nuclear modification factor, R-pPb, of charged jets in p-Pb collisions, a pp reference was constructed by scaling previously measured charged jet spectra at root s = 7 TeV. In the transverse momentum range 20
  • Adam, J.; Brucken, E. J.; Chang, B.; Kim, D. J.; Mieskolainen, M. M.; Orava, R.; Rak, J.; Räsänen, S. S.; Snellman, T. W.; Trzaska, W. H.; The ALICE collaboration (2016)
    The production of charged pions, kaons and (anti)protons has been measured at mid-rapidity (-0.5 <y <0) in p-Pb collisions at root s(NN) = 5.02 TeV using the ALICE detector at the LHC. Exploiting particle identification capabilities at high transverse momentum (p(T)), the previously published p(T) spectra have been extended to include measurements up to 20 GeV/c for seven event multiplicity classes. The p(T) spectra for pp collisions at = 7 TeV, needed to interpolate a pp reference spectrum, have also been extended up to 20 GeV/c to measure the nuclear modification factor (R-ppb) in non-single diffractive p-Pb collisions. At intermediate transverse momentum (2 <p(T) <10 GeV/c) the proton-to-pion ratio increases with multiplicity in p-Pb collisions, a similar effect is not present in the kaon-to-pion ratio. The p(T) dependent structure of such increase is qualitatively similar to those observed in pp and heavy-ion collisions. At high p(T) (>10 GeV/c), the particle ratios are consistent with those reported for pp and Pb-Pb collisions at the LHC energies. At intermediate p(T) the (anti)proton R-ppb shows a Cronin-like enhancement, while pions and kaons show little or no nuclear modification. At high p(T) the charged pion, kaon and (anti)proton R-ppb are consistent with unity within statistical and systematic uncertainties. (C) 2016 The Author. Published by Elsevier B.V.
  • Abelev, B.; Chang, B.; Hilden, T. E.; Kim, D. J.; Kral, J.; Pohjoisaho, E. H. O.; Rak, J.; Räsänen, S. S.; Trzaska, W. H.; The ALICE collaboration (2015)
    Two-particle angular correlations between unidentified charged trigger and associated particles are measured by the ALICE detector in p-Pb collisions at a nucleon-nucleon centre-of-mass energy of 5.02 TeV. The transverse-momentum range 0.7 <p(T),(assoc) <p(T),(trig) <5.0 GeV/c is examined, to include correlations induced by jets originating from low momentum-transfer scatterings (minijets). The correlations expressed as associated yield per trigger particle are obtained in the pseudorapidity range vertical bar eta vertical bar <0.9. The near-side long-range pseudorapidity correlations observed in high-multiplicity p-Pb collisions are subtracted from both near-side short-range and away-side correlations in order to remove the non-jet-like components. The yields in the jet-like peaks are found to be invariant with event multiplicity with the exception of events with low multiplicity. This invariance is consistent with the particles being produced via the incoherent fragmentation of multiple parton-parton scatterings, while the yield related to the previously observed ridge structures is not jet-related. The number of uncorrelated sources of particle production is found to increase linearly with multiplicity, suggesting no saturation of the number of multi-parton interactions even in the highest multiplicity p-Pb collisions. Further, the number scales only in the intermediate multiplicity region with the number of binary nucleon-nucleon collisions estimated with a Glauber Monte-Carlo simulation. (C) 2014 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license (
  • Helenius, Ilkka; Paukkunen, Hannu; Eskola, Kari J. (2017)
    A well-established observation in nuclear physics is that in neutron-rich spherical nuclei the distribution of neutrons extends farther than the distribution of protons. In this work, we scrutinize the influence of this so called neutron-skin effect on the centrality dependence of high-p(T) direct-photon and charged-hadron production. We find that due to the estimated spatial dependence of the nuclear parton distribution functions, it will be demanding to unambiguously expose the neutron-skin effect with direct photons. However, when taking a ratio between the cross sections for negatively and positively charged high-p(T) hadrons, even centrality-dependent nuclear-PDF effects cancel, making this observable a better handle on the neutron skin. Up to 10% effects can be expected for the most peripheral collisions in the measurable region.
  • Albacete, Javier L.; Arleo, Francois; Barnafoldi, Gergely G.; Biro, Gabor; D'Enterria, David; Ducloue, Bertrand; Eskola, Kari J.; Ferreiro, Elena G.; Gyulassy, Miklos; Harangozo, Szilvester Miklos; Helenius, Ilkka; Kang, Zhong-Bo; Kotko, Piotr; Kulagin, Sergey A.; Kutak, Krzysztof; Lansberg, Jean Philippe; Lappi, Tuomas; Levai, Peter; Lin, Zi-Wei; Ma, Guoyang; Ma, Yan-Qing; Mantysaari, Heikki; Paukkunen, Hannu; Papp, Gabor; Petti, Roberto; Rezaeian, Amir H.; Ru, Peng; Sapeta, Sebastian; Schenke, Bjorn; Schlichting, Soren; Shao, Hua-Sheng; Tribedy, Prithwish; Venugopalan, Raju; Vitev, Ivan; Vogt, Ramona; Wang, Enke; Wang, Xin-Nian; Xing, Hongxi; Xu, Rong; Zhang, Ben-Wei; Zhang, Hong-Fei; Zhang, Wei-Ning (2018)
    Predictions for cold nuclear matter effects on charged hadrons, identified light hadrons, quarkonium and heavy flavor hadrons, Drell-Yan dileptons, jets, photons, gauge bosons and top quark pairs produced in p+Pb collisions at, root S-NN = 8.16 TeV are compiled and, where possible, compared to each other. Predictions of the normalized ratios of p+Pb to p+ p cross sections are also presented for most of the observables, providing new insights into the expected role of cold nuclear matter effects. In particular, the role of nuclear parson distribution functions on particle production can now be probed over a wider range of phase space than ever before. (C) 2018 Elsevier B.V. All rights reserved.
  • Acharya, S.; Brucken, E. J.; Chang, B.; Kim, D. J.; Litichevskyi, V.; Mieskolainen, M. M.; Orava, R.; Rak, J.; Räsänen, S. S.; Snellman, T. W.; Trzaska, W. H.; Viinikainen, J.; The ALICE collaboration (2017)
    The production of muons from heavy-flavour hadron decays in p-Pb collisions at root s(NN) = 5.02 TeV was studied for 2 <p(T) <16 GeV/c with the ALICE detector at the CERN LHC. The measurement was performed at forward (p-going direction) and backward (Pb-going direction) rapidity, in the ranges of rapidity in the centre-of-mass system (cms) 2.03 <y(cms) <3.53 and -4.46 <y(cms) <-2.96, respectively. The production cross sections and nuclear modification factors are presented as a function of transverse momentum (P-T). At forward rapidity, the nuclear modification factor is compatible with unity while at backward rapidity, in the interval 2.5 <p(T) <3.5 GeV/c, it is above unity by more than 2 sigma. The ratio of the forward -to -backward production cross sections is also measured in the overlapping interval 2.96 <|y(cms)| <3.53 and is smaller than unity by 3.7 sigma in 2.5 <p(T) <3.5 GeV/c. The data are described by model calculations including cold nuclear matter effects. (C) 2017 The Author(s). Published by Elsevier B.V.