Browsing by Subject "Heavy Ion Experiments"

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Now showing items 1-15 of 15
  • 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)
    The elliptic (v(2)), triangular (v(3)), and quadrangular (v(4)) flow coefficients of pi(+/-), K-+/-, p + (p) over bar, Lambda + (Lambda) over bar, K-S(0)), and the phi-meson are measured in Pb-Pb collisions at root(NN)-N-s = 5.02 TeV. Results obtained with the scalar product method are reported for the rapidity range vertical bar y vertical bar < 0.5 as a function of transverse momentum, P-T, at different collision centrality intervals between 0-70%, including ultra-central (0-1%) collisions for pi(+/-), K-+/-, and p + (p) over bar. For P-T < 3 GeV/c, the flow coefficients exhibit a particle mass dependence. At intermediate transverse momenta (3 < p(T) < 8-10 GeV/c), particles show an approximate grouping according to their type (i.e., mesons and baryons). The phi-meson v(2), which tests both particle mass dependence and type scaling, follows p + <(p)over bar> v(2) at low P-T and pi(+/-) v(2) at intermediate p(T). The evolution of the shape of v(n) (p(T)) as a function of centrality and harmonic number n is studied for the various particle species. Flow coefficients of pi(+/-), K-+/- , and p + (p) over bar for p(T) < 3 GeV/c are compared to iEBE-VISHNU and MUSIC hydrodynamical calculations coupled to a hadronic cascade model (UrQMD). The iEBE-VISHNU calculations describe the results fairly well for P-T < 2.5 GeV/c, while MUSIC calculations reproduce the measurements for p(T) < 1 GeV/c. A comparison to vn coefficients measured in Pb-Pb collisions at root(NN)-N-s = 2.76 TeV is also provided.
  • Adam, J.; Adamova, D.; Aggarwal, M. M.; Rinella, G. Aglieri; Agnello, M.; Agrawal, N.; Ahammed, Z.; Ahmad, S.; Ahn, S. U.; Aiola, S.; Akindinov, A.; Alam, S. N.; Albuquerque, D. S. D.; Aleksandrov, D.; Alessandro, B.; Alexandre, D.; Alfaro Molina, R.; Alici, A.; Alkin, A.; Alme, J.; Alt, T.; Altinpinar, S.; Altsybeev, I.; Alves Garcia Prado, C.; Andrei, C.; Andronic, A.; Anguelov, V.; Anticic, T.; Antinori, F.; Antonioli, P.; Aphecetche, L.; Appelshaeuser, H.; Arcelli, S.; Arnaldi, R.; Arnold, O. W.; Arsene, I. C.; Arslandok, M.; Audurier, B.; Augustinus, A.; Averbeck, R.; Azmi, M. D.; Brucken, E. J.; Chang, B.; Kim, D. J.; Mieskolainen, M. M.; Orava, R.; Rak, J.; Räsänen, S. S.; Snellman, T. W.; Trzaska, W. H. (2016)
    The elliptic flow of electrons from heavy-flavour hadron decays at mid-rapidity (|y| <0.7) is measured in Pb-Pb collisions at TeV with ALICE at the LHC. The particle azimuthal distribution with respect to the reaction plane can be parametrized with a Fourier expansion, where the second coefficient (v (2)) represents the elliptic flow. The v (2) coefficient of inclusive electrons is measured in three centrality classes (0-10%, 10-20% and 20-40%) with the event plane and the scalar product methods in the transverse momentum (p (T)) intervals 0.5-13 GeV/c and 0.5-8 GeV/c, respectively. After subtracting the background, mainly from photon conversions and Dalitz decays of neutral mesons, a positive v (2) of electrons from heavy-flavour hadron decays is observed in all centrality classes, with a maximum significance of 5.9 sigma in the interval 2 <p (T) <2.5 GeV/c in semi-central collisions (20-40%). The value of v (2) decreases towards more central collisions at low and intermediate p (T) (0.5 <p (T) <3 GeV/c). The v (2) of electrons from heavy-flavour hadron decays at mid-rapidity is found to be similar to the one of muons from heavy-flavour hadron decays at forward rapidity (2.5 <y <4). The results are described within uncertainties by model calculations including substantial elastic interactions of heavy quarks with an expanding strongly-interacting medium.
  • 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)
    Measurements of anisotropic flow coefficients with two-and multi-particle cumulants for inclusive charged particles in Pb{Pb collisions at root s(NN) = 5 : 02 and 2.76TeV are reported in the pseudorapidity range vertical bar eta vertical bar <0 : 8 and transverse momentum 0 : 2 <p(T) <50 GeV/c. The full data sample collected by the ALICE detector in 2015 (2010), corresponding to an integrated luminosity of 12.7 (2.0) mu b(-1) in the centrality range 0{80%, is analysed. Flow coefficients up to the sixth flow harmonic (v6) are reported and a detailed comparison among results at the two energies is carried out. The pT dependence of anisotropic flow coefficients and its evolution with respect to centrality and harmonic number n are investigated. An approximate power-law scaling of the form v(n) (p(T)) similar to p(T)(n/3) is observed for all flow harmonics at low p(T) (0.2 <p(T) <3 GeV/c). At the same time, the ratios v(n)/v(m)(n/m) are observed to be essentially independent of pT for most centralities up to about pT = 10 GeV/c. Analysing the di ff erences among higher-order cumulants of elliptic flow (v(2)), which have di ff erent sensitivities to flow fluctuations, a measurement of the standardised skewness of the event-by-event v(2) distribution P (v(2)) is reported and constraints on its higher moments are provided. The Elliptic Power distribution is used to parametrise P (v(2)), extracting its parameters from fi ts to cumulants. The measurements are compared to di ff erent model predictions in order to discriminate among initial-state models and to constrain the temperature dependence of the shear viscosity to entropy-density ratio.
  • The ALICE collaboration; Acharya, S.; Brucken, E. J.; Chang, B.; Hilden, T. E.; Kim, D.; Litichevskyi, V.; Mieskolainen, M. M.; Parkkila, J. E.; Rak, J.; Räsänen, S. S.; Saarinen, S.; Slupecki, M.; Snellman, T. W.; Trzaska, W. H.; Vargyas, M.; Viinikainen, J.; Yoon, J. H.; Zhou, Z.; Zhu, Y. (2019)
    Two-particle correlations in high-energy collision experiments enable the extraction of particle source radii by using the Bose-Einstein enhancement of pion production at low relative momentum q proportional to 1/R. It was previously observed that in pp collisions at root s = 7 TeV the average pair transverse momentum k(T) range of such analyses is limited due to large background correlations which were attributed to mini-jet phenomena. To investigate this further, an event-shape dependent analysis of Bose-Einstein correlations for pion pairs is performed in this work. By categorizing the events by their transverse sphericity S-T into spherical (S-T > 0.7) and jet-like (S-T <0.3) events a method was developed that allows for the determination of source radii for much larger values of k(T) for the first time. Spherical events demonstrate little or no background correlations while jet-like events are dominated by them. This observation agrees with the hypothesis of a mini-jet origin of the non-femtoscopic background correlations and gives new insight into the physics interpretation of the k(T) dependence of the radii. The emission source size in spherical events shows a substantially diminished k(T) dependence, while jet-like events show indications of a negative trend with respect to k(T) in the highest multiplicity events. Regarding the emission source shape, the correlation functions for both event sphericity classes show good agreement with an exponential shape, rather than a Gaussian one.
  • 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.
  • The CMS collaboration; Sirunyan, A. M.; Eerola, P.; Kirschenmann, H.; Pekkanen, J.; Voutilainen, M.; Havukainen, J.; Heikkilä, J. K.; Järvinen, T.; Karimäki, V.; Kinnunen, R.; Lampén, T.; Lassila-Perini, K.; Laurila, S.; Lehti, S.; Lindén, T.; Luukka, P.; Mäenpää, T.; Siikonen, H.; Tuominen, E.; Tuominiemi, J.; Tuuva, T. (2018)
    Modifications of the properties of jets in PbPb collisions, relative to those in pp collisions, are studied at a nucleon-nucleon center-of-mass energy of,root S-NN = 5.02 TeV via correlations of charged particles with the jet axis in relative pseudorapidity (Delta eta), relative azimuth (Delta phi), and relative angular distance from the jet axis Delta r = root(Delta eta)(2) + (Delta phi)(2). This analysis uses data collected with the CMS detector at the LHC, corresponding to integrated luminosities of 404 mu b(-1) and 27.4 pb(-1) for PbPb and pp collisions, respectively. Charged particle number densities, jet fragmentation functions, and jet shapes are presented as a function of PbPb collision centrality and charged-particle track transverse momentum, providing a differential description of jet modifications due to interactions with the quark gluon plasma.
  • The ALICE collaboration; Acharya, S.; Brucken, E. J.; Chang, B.; Kim, D. J.; Litichevskyi, V.; Mieskolainen, M. M.; Orava, R.; Rak, J.; Räsänen, S. S.; Saarinen, S.; Slupecki, M.; Snellman, T. W.; Trzaska, W. H.; Vargyas, M.; Viinikainen, J. (2018)
    The p(T)-differential production cross section of prompt Lambda(+)(c) charmed baryons was measured with the ALICE detector at the Large Hadron Collider (LHC) in pp collisions at root s = 7 TeV and in p-Pb collisions at root s(NN) = 5.02 TeV at midrapidity. The Lambda(+)(c) and (Lambda) over bar (-)(c) were reconstructed in the hadronic decay modes Lambda(+)(c) -> pK(-)pi(+), Lambda(+)(c)-> pK(S)(0)) and in the semileptonic channel Lambda(+ )(c)-> e(+)nu(e)Lambda (and charge conjugates). The measured values of the Lambda(+)(c)/D-0 ratio, which is sensitive to the c-quark hadronisation mechanism, and in particular to the production of baryons, are presented and are larger than those measured previously in different colliding systems, centre-of-mass energies, rapidity and p(T) intervals, where the Lambda(+)(c) production process may differ. The results are compared with the expectations obtained from perturbative Quantum Chromodynamics calculations and Monte Carlo event generators. Neither perturbative QCD calculations nor Monte Carlo models reproduce the data, indicating that the fragmentation of heavy-flavour baryons is not well understood. The first measurement at the LHC of the Lambda(+)(c) nuclear modification factor, R-ppb, is also presented. The R-ppb is found to be consistent with unity and with that of D mesons within the uncertainties, and consistent with a theoretical calculation that includes cold nuclear matter effects and a calculation that includes charm quark interactions with a deconfined medium.
  • The ALICE collaboration; Acharya, S.; Brücken, 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)
    We report measurements of the production of prompt D-0, D+, D*+ and D TeV. For D mesons, the values of R-AA are larger than those of non-strange D mesons, but compatible within uncertainties. In central collisions the average R-AA of non-strange D mesons is compatible with that of charged particles for p 8 GeV/c, while it is larger at lower p(T). The nuclear modification factors for strange and non-strange D mesons are also compared to theoretical models with different implementations of in-medium energy loss.
  • Adam, J.; Adamova, D.; Aggarwal, M. M.; Rinella, G. Aglieri; Agnello, M.; Agrawal, N.; Ahammed, Z.; Ahn, S. U.; Aiola, S.; Akindinov, A.; Alam, S. N.; Aleksandrov, D.; Alessandro, B.; Alexandre, D.; Alfaro Molina, R.; Alici, A.; Alkin, A.; Almaraz, J. R. M.; Alme, J.; Alt, T.; Altinpinar, S.; Altsybeev, I.; Alves Garcia Prado, C.; Andrei, C.; Andronic, A.; Anguelov, V.; Anielski, J.; Anticic, T.; Antinori, F.; Antonioli, P.; Aphecetche, L.; Appelshaeuser, H.; Arcelli, S.; Arnaldi, R.; Arnold, O. W.; Arsene, I. C.; Arslandok, M.; Audurier, B.; Augustinus, A.; Averbeck, R.; Brucken, E. J.; Chang, B.; Kim, D. J.; Krizek, F.; Mieskolainen, M. M.; Orava, R.; Rak, J.; Räsänen, S. S.; Snellman, T. W.; Trzaska, W. H. (2016)
    The measurement of prompt D-meson production as a function of multiplicity in p-Pb collisions at TeV with the ALICE detector at root s(NN) the LHC is reported. D-0, D+ and Dau+ mesons are reconstructed via their hadronic decay channels in the centre-of-mass rapidity range -0.96 <y(cms) <0.04 and transverse momentum interval 1 <p(T) <24 GeV/c. The multiplicity dependence of D-meson production is examined by either comparing yields in p-Pb collisions in different event classes, selected based on the multiplicity of produced particles or zero-degree energy, with those in pp collisions, scaled by the number of binary nucleon-nucleon collisions (nuclear modification factor); as well as by evaluating the per-event yields in p-Pb collisions in different multiplicity intervals normalised to the multiplicity-integrated ones (relative yields). The nuclear modification factors for D-0, D+ and D*(+) are consistent with one another. The D-meson nuclear modification factors as a function of the zero-degree energy are consistent with unity within uncertainties in the measured p(T) regions and event classes. The relative D-meson yields, calculated in various p(T) intervals, increase as a function of the charged-particle multiplicity. The results are compared with the equivalent pp measurements at root s = 7 TeV as well as with EPOS 3 calculations.
  • 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.; Viinikainen, J.; The ALICE collaboration (2017)
    The production of beauty hadrons was measured via semi-leptonic decays at mid-rapidity with the ALICE detector at the LHC in the transverse momentum interval 1 <PT <8 GeV/c in minimum-bias p-Pb collisions at root(NN)-N-S = 5.02 TeV and in 1.3 <PT <8 GeV/c in the 20% most central Pb-Pb collisions at root(NN)-N-S = 2.76 TeV. The pp reference spectra at root s = 5.02 TeV and root s = 2.76 TeV, needed for the calculation of the nuclear modification factors RpPb and R-PbPb, were obtained by a pQCD-driven scaling of the cross section of electrons from beauty-hadron decays measured at root s = 7 TeV. In the PT interval 3 <PT <8 GeV/c, a suppression of the yield of electrons from beauty-hadron decays is observed in Pb-Pb compared to pp collisions. Towards lower PT, the R-PbPb values increase with large systematic uncertainties. The R-ppb is consistent with unity within systematic uncertainties and is well described by theoretical calculations that include cold nuclear matter effects in p-Pb collisions. The measured R-pPb and these calculations indicate that cold nuclear matter effects are small at high transverse momentum also in Pb-Pb collisions. Therefore, the observed reduction of R-PbPb below unity at high PT may be ascribed to an effect of the hot and dense medium formed in Pb-Pb collisions.
  • The ALICE collaboration; Acharya, S.; Brücken, 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)
    Transverse-momentum (p(T)) differential yields of electrons from semileptonic heavy-flavour hadron decays have been measured in the most central (0-10%) and in semi-central (20-40%) Pb-Pb collisions at TeV. The corresponding production cross section in pp collisions has been measured at the same energy with substantially reduced systematic uncertainties with respect to previously published results. The modification of the yield in Pb-Pb collisions with respect to the expectation from an incoherent superposition of nucleon-nucleon collisions is quantified at mid-rapidity (|y| <0.8) in the p(T) interval 0.5-3 GeV/c via the nuclear modification factor, R-AA. This paper extends the p(T) reach of the R-AA measurement towards significantly lower values with respect to a previous publication. In Pb-Pb collisions the p(T)-differential measurements of yields at low p(T) are essential to investigate the scaling of heavy-flavour production with the number of binary nucleon-nucleon collisions. Heavy-quark hadronization, a collective expansion and even initial-state effects, such as the nuclear modification of the Parton Distribution Function, are also expected to have a significant effect on the measured distribution.
  • The ALICE collaboration; Acharya, S.; Chang, B.; Kim, D. J.; Krizek, F.; Mieskolainen, M. M.; Orava, R.; Parkkila, J. E.; Rak, J.; Rytkonen, H.; Saarinen, S.; Slupecki, M.; Snellman, T. W.; Trzaska, W. H.; Viinikainen, J.; Zhou, Z. (2019)
    Production cross sections of muons from semi-leptonic decays of charm and beauty hadrons were measured at forward rapidity (2.5 <y <4) in proton-proton (pp) collisions at a centre-of-mass energy root s = 5.02 TeV with the ALICE detector at the CERN LHC. The results were obtained in an extended transverse momentum interval, 2 <p(T)<20 GeV/c, and with an improved precision compared to previous measurements performed in the same rapidity interval at centre-of-mass energies root s = 2.76 and 7 TeV. The p(T)- and y-differential production cross sections as well as the p(T)-differential production cross section ratios between different centre-of-mass energies and different rapidity intervals are described, within experimental and theoretical uncertainties, by predictions based on perturbative QCD.
  • 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 measurement of azimuthal correlations of charged particles is presented for Pb-Pb collisions at root S-NN 2.76 TeV and p-Pb collisions at root S-NN 5.02 TeV with the ALICE detector at the CERN Large Hadron Collider. These correlations are measured for the second, third and fourth order flow vector in the pseudorapidity region vertical bar eta vertical bar 0.8 as a function of centrality and transverse momentum pT using two observables, to search for evidence of PT-dependent flow vector fluctuations. For Ph-Ph collisions at 2.76 TeV, the measurements indicate that PT-dependent fluctuations are only present for the second order flow vector. Similar results have been found for p-Pb collisions at 5.02 TeV. These measurements are compared to hydrodynamic model calculations with event-by-event geometry fluctuations in the initial state to constrain the initial conditions and transport properties of the matter created in Ph-Ph and p-Pb collisions.
  • The ALICE collaboration; Acharya, S.; Brücken, E. J.; Chang, B.; Hilden, T. E.; Kim, D. J.; Litichevskyi, V.; Mieskolainen, M. M.; Orava, R.; Rak, J.; Räsänen, S. S.; Saarinen, S.; Slupecki, M.; Snellman, T. W.; Trzaska, W. H.; Vargyas, M.; Viinikainen, J. (2018)
    We report the measured transverse momentum (pT) spectra of primary charged particles from pp, p-Pb and Pb-Pb collisions at a center-of-mass energy p sNN = 5 : 02TeV in the kinematic range of 0 : 15 < pT < 50 GeV/c and jj < 0 : 8. A signi fi cant improvement of systematic uncertainties motivated the reanalysis of data in pp and Pb-Pb collisions at p sNN = 2 : 76TeV, as well as in p-Pb collisions at p sNN = 5 : 02TeV, which is also presented. Spectra from Pb-Pb collisions are presented in nine centrality intervals and are compared to a reference spectrum from pp collisions scaled by the number of binary nucleon-nucleon collisions. For central collisions, the pT spectra are suppressed by more than a factor of 7 around 6-7 GeV/c with a signi fi cant reduction in suppression towards higher momenta up to 30 GeV/c. The nuclear modi fi cation factor RpPb, constructed from the pp and p-Pb spectra measured at the same collision energy, is consistent with unity above 8 GeV/c. While the spectra in both pp and Pb-Pb collisions are substantially harder at p sNN = 5 : 02TeV compared to 2.76TeV, the nuclear modi fi cation factors show no signi fi cant collision energy dependence. The obtained results should provide further constraints on the parton energy loss calculations to determine the transport properties of the hot and dense QCD matter.
  • Adam, J.; Adamova, D.; Aggarwal, M. M.; Rinella, G. Aglieri; Agnello, M.; Agrawal, N.; Ahammed, Z.; Ahmad, S.; Ahn, S. U.; Aiola, S.; Akindinov, A.; Alam, S. N.; Albuquerque, D. S. D.; Aleksandrov, D.; Alessandro, B.; Alexandre, D.; Alfaro Molina, R.; Alici, A.; Alkin, A.; Alme, J.; Alt, T.; Altinpinar, S.; Altsybeev, I.; Alves Garcia Prado, C.; An, M.; Andrei, C.; Andrews, H. A.; Andronic, A.; Anguelov, V.; Anson, C.; Anticic, T.; Antinori, F.; Antonioli, P.; Anwar, R.; Aphecetche, L.; Appelshaeuser, H.; Arcelli, S.; Arnaldi, R.; Arnold, O. W.; Arsene, I. C.; Brucken, E. J.; Chang, B.; Kim, D. J.; Mieskolainen, M. M.; Orava, R.; Rak, J.; Räsänen, S. S.; Snellman, T. W.; Trzaska, W. H.; Viinikainen, J. (2017)
    The W and Z boson production was measured via the muonic decay channel in proton-lead collisions at root s(NN) = 5.02 TeV at the Large Hadron Collider with the ALICE detector. The measurement covers backward (4.46 <y(cms) <2.96) and forward (2.03 <y(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(mu mu) <120 GeV/c(2) and muon transverse momentum (p(T)(mu)) larger than 20 GeV/c, is measured. The production cross section and charge asymmetry of muons from W-boson decays with p(T)(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.