Browsing by Subject "QUARK-GLUON PLASMA"

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  • 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.; Ahmmed, Z.; Ahn, S. U.; Aiola, S.; Akindinov, A.; Alam, S. N.; Aleksandrov, D.; Alessandro, B.; Alexandre, D.; Molina, R. Alfaro; Alici, A.; Alkin, A.; Almaraz, J. R. M.; Alme, J.; Alt, T.; Altinpinar, S.; Altsybeev, I.; Prado, C. Alves Garcia; Andrei, C.; Andronic, A.; Anguelov, V.; Anielski, J.; Anticic, T.; Antinori, F.; Antonioli, R.; 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)
    We present measurements of the azimuthal dependence of charged jet production in central and semi-central root s(NN) = 2.76 TeV Pb-Pb collisions with respect to the second harmonic event plane, quantified as nu(ch)(2) (jet). Jet finding is performed employing the anti-k(T) algorithm with a resolution parameter R = 0.2 using charged tracks from the ALICE tracking system. The contribution of the azimuthal anisotropy of the underlying event is taken into account event-by-event. The remaining (statistical) region-to-region fluctuations are removed on an ensemble basis by unfolding the jet spectra for different event plane orientations independently. Significant non-zero nu(ch)(2) (jet) is observed in semi-central collisions (30-50% centrality) for 20 <p(T)(ch) (jet) <90 GeV/c. The azimuthal dependence of the charged jet production is similar to the dependence observed for jets comprising both charged and neutral fragments, and compatible with measurements of the nu(2) of single charged particles at high p(T). Good agreement between the data and predictions from JEWEL, an event generator simulating parton shower evolution in the presence of a dense QCD medium, is found in semi-central collisions. (C) 2015 CERN for the benefit of the ALICE Collaboration. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).
  • The CMS collaboration; Sirunyan, A. M.; Eerola, P.; Pekkanen, J.; Voutilainen, M.; Härkönen, J.; Järvinen, T.; Karimäki, V.; Kinnunen, R.; Lampén, T.; Lassila-Perini, K.; Lehti, S.; Lindén, T.; Luukka, P.; Tuominiemi, J.; Tuovinen, E.; Wendland, L.; Talvitie, J.; Tuuva, T. (2018)
    The Fourier coefficients v(2) and v(3) characterizing the anisotropy of the azimuthal distribution of charged particles produced in PbPb collisions at root S-NN = 5.02 TeV are measured with data collected by the CMS experiment. The measurements cover a broad transverse momentum range, 1 <p(T) <100 GeV/c. The analysis focuses on the p(T) > 10 GeV/c range, where anisotropic azimuthal distributions should reflect the path-length dependence of parton energy loss in the created medium. Results are presented in several bins of PbPb collision centrality, spanning the 60% most central events. The v(2) coefficient is measured with the scalar product and the multiparticle cumulant methods, which have different sensitivities to initial-state fluctuations. The values from both methods remain positive up to p(T) similar to 60-80 GeV/c, in all examined centrality classes. The v(3) coefficient, only measured with the scalar product method, tends to zero for p(T) greater than or similar to 20 GeV/c. Comparisons between theoretical calculations and data provide new constraints on the path-length dependence of parton energy loss in heavy ion collisions and highlight the importance of the initial-state fluctuations. (C) 2017 The Author. Published by Elsevier B.V.
  • Adam, J.; Adamova, D.; Aggarwal, M. M.; Rinella, G. Aglieri; Agnello, M.; Agrawal, N.; Ahammed, Z.; Ahn, S. U.; Aimo, I.; Aiola, S.; Ajaz, M.; Akindinov, A.; Alam, S. N.; Aleksandrov, D.; Alessandro, B.; Alexandre, D.; Molina, R. Alfaro; Alici, A.; Alkin, A.; Almaraz, J. R. M.; Alme, J.; Alt, T.; Altinpinar, S.; Altsybeev, I.; Prado, C. Alves Garcia; Andrei, C.; Andronic, A.; Anguelov, V.; Anielski, J.; Anticic, T.; Antinori, F.; Antonioli, P.; Aphecetche, L.; Appelshaeuser, H.; Arcelli, S.; Armesto, N.; Arnaldi, R.; Arsene, I. C.; Arslandok, M.; 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. (2016)
    We report on the measurement of freeze-out radii for pairs of identical-charge pions measured in Pb-Pb collisions at root s(NN) = 2.76 TeV as a function of collision centrality and the average transverse momentum of the pair k(T). Three-dimensional sizes of the system (femtoscopic radii), as well as direction-averaged one-dimensional radii are extracted. The radii decrease with k(T), following a power-law behavior. This is qualitatively consistent with expectations from a collectively expanding system, produced in hydrodynamic calculations. The radii also scale linearly with <dN(ch)/d eta >(1/3). This behavior is compared to world data on femtoscopic radii in heavy-ion collisions. While the dependence is qualitatively similar to results at smaller root s(NN), a decrease in the ratio R-out/R-side is seen, which is in qualitative agreement with a specific prediction from hydrodynamic models: a change from inside-out to outside-in freeze-out configuration. The results provide further evidence for the production of a collective, strongly coupled system in heavy-ion collisions at the CERN Large Hadron Collider.
  • Adam, J.; 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)
    We present the charged-particle pseudorapidity density in Pb-Pb collisions at root s(NN) = 5.02 TeV in centrality classes measured by ALICE. The measurement covers a wide pseudorapidity range from -3.5 to 5, which is sufficient for reliable estimates of the total number of charged particles produced in the collisions. For the most central (0-5%) collisions we find 21 400 +/- 1 300, while for the most peripheral (80-90%) we find 230 +/- 38. This corresponds to an increase of (27 +/- 4)% over the results at root s(NN) = 2.76 TeV previously reported by ALICE. The energy dependence of the total number of charged particles produced in heavy-ion collisions is found to obey a modified power-law like behaviour. The charged-particle pseudorapidity density of the most central collisions is compared to model calculations-none of which fully describes the measured distribution. We also present an estimate of the rapidity density of charged particles. The width of that distribution is found to exhibit a remarkable proportionality to the beam rapidity, independent of the collision energy from the top SPS to LHC energies. (C) 2017 The Author(s). Published by Elsevier B.V.
  • The CMS collaboration; Eerola, P.; Kirschenmann, H.; Pekkanen, J.; Voutilainen, M.; Havukainen, J.; Heikkila, J. K.; Jarvinen, T.; Kinnunen, R.; Lampen, T.; Lassila-Perini, K.; Laurila, S.; Lehti, S.; Linden, T.; Luukka, P.; Maenpaa, T.; Siikonen, H.; Tuominen, E.; Tuominiemi, J.; Sirunyan, A. M.; Karimäki, V.; Tuuva, T. (2019)
    Azimuthal correlations of charged particles in xenon-xenon collisions at a center-of-mass energy per nucleon pair of root s(NN) = 5.44 TeV are studied. The data were collected by the CMS experiment at the LHC with a total integrated luminosity of 3.42 mu b(-1). The collective motion of the system formed in the collision is parametrized by a Fourier expansion of the azimuthal particle density distribution. The azimuthal anisotropy coefficients v(2), v(3), and v(4) are obtained by the scalar-product, two-particle correlation, and multiparticle correlation methods. Within a hydrodynamic picture, these methods have different sensitivities to noncollective and fluctuation effects. The dependence of the Fourier coefficients on the size of the colliding system is explored by comparing the xenon-xenon results with equivalent lead-lead data. Model calculations that include initial-state fluctuation effects are also compared to the experimental results. The observed angular correlations provide new constraints on the hydrodynamic description of heavy ion collisions.
  • 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)
    A search has been performed for heavy resonances decaying to ZZ or ZW in 2l2q final states, with two charged leptons (l = e, mu) produced by the decay of a Z boson, and two quarks produced by the decay of a W or Z boson. The analysis is sensitive to resonances with masses in the range from 400 to 4500 GeV. Two categories are defined based on the merged or resolved reconstruction of the hadronically decaying vector boson, optimized for high- and low-mass resonances, respectively. The search is based on data collected during 2016 by the CMS experiment at the LHC in proton-proton collisions with a center-of-mass energy of root s = 13 TeV, corresponding to an integrated luminosity of 35.9 fb(-1). No excess is observed in the data above the standard model background expectation. Upper limits on the production cross section of heavy, narrow spin-1 and spin-2 resonances are derived as a function of the resonance mass, and exclusion limits on the production of W' bosons and bulk graviton particles are calculated in the framework of the heavy vector triplet model and warped extra dimensions, respectively.
  • 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. (2019)
    The elliptic flow of inclusive and direct photons was measured at mid-rapidity in two centrality classes 0-20% and 20-40% in Pb-Pb collisions at root s(NN) = 2.76 TeV by ALICE. Photons were detected with the highly segmented electromagnetic calorimeter PHOS and via conversions in the detector material with the e(broken vertical bar)e pairs reconstructed in the central tracking system. The results of the two methods were combined and the direct-photon elliptic flow was extracted in the transverse momentum range 0.9 < p(T) < 6.2 GeV/c. A comparison to RHIC data shows a similar magnitude of the measured direct-photon elliptic flow. Hydrodynamic and transport model calculations are systematically lower than the data, but are found to be compatible. (C) 2018 The Author. Published by Elsevier B.V.
  • 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. (2019)
    Measurements of inclusive and direct photon production at midrapidity in pp collisions at root s = 2.76 and 8 TeV are presented by the ALICE experiment at the LHC. The results are reported in transverse momentum ranges of 0.4 < p(T) < 10 GeV/c and 0.3 < p(T) < 16 GeV/c, respectively. Photons are detected with the electromagnetic calorimeter (EMCal) and via reconstruction of e(+) e(-) pairs from conversions in the ALICE detector material using the central tracking system. For the final measurement of the inclusive photon spectra the results are combined in the overlapping p(T), interval of both methods. Direct photon spectra, or their upper limits at 90% C.L. are extracted using the direct photon excess ratio R-gamma, which quantifies the ratio of inclusive photons over decay photons generated with a decay-photon simulation. An additional hybrid method, combining photons reconstructed from conversions with those identified in the EMCal, is used for the combination of the direct photon excess ratio R-gamma, as well as the extraction of direct photon spectra or their upper limits. While no significant signal of direct photons is seen over the full p(T), range, R-gamma, for p(T), > 7 GeV/c is at least one sigma above unity and consistent with expectations from next-to-leading order pQCD calculations.
  • Aarts, Gert; Alton, Chris; Amato, Alessandro; Giudice, Pietro; Hands, Simon; Shuiierd, Jon-Ivar (2015)
  • The CMS collaboration; Sirunyan, A. M.; Tumasyan, A.; Eerola, P.; Forthomme, Laurent; Kirschenmann, H.; Österberg, K.; Voutilainen, M.; Brücken, Erik; Garcia, F.; Havukainen, J.; Karimäki, V.; Kim, Minsuk; Kinnunen, R.; Lampén, T.; Lassila-Perini, K.; Lehti, S.; Lindén, T.; Luukka, P.; Siikonen, H.; Tuominen, E.; Tuominiemi, J.; Tuuva, T. (2021)
    The performance is presented of the reconstruction and identification algorithms for electrons and photons with the CMS experiment at the LHC. The reported results are based on proton-proton collision data collected at a center-of-mass energy of 13 TeV and recorded in 2016-2018, corresponding to an integrated luminosity of 136 fb(-1). Results obtained from lead-lead collision data collected at root S-NN = 5.02 TeV are also presented. Innovative techniques are used to reconstruct the electron and photon signals in the detector and to optimize the energy resolution. Events with electrons and photons in the final state are used to measure the energy resolution and energy scale uncertainty in the recorded events. The measured energy resolution for electrons produced in Z boson decays in proton-proton collision data ranges from 2 to 5%, depending on electron pseudorapidity and energy loss through bremsstrahlung in the detector material. The energy scale in the same range of energies is measured with an uncertainty smaller than 0.1 (0.3)% in the barrel (endcap) region in proton-proton collisions and better than 1(3)% in the barrel (endcap) region in heavy ion collisions. The timing resolution for electrons from Z boson decays with the full 2016-2018 proton-proton collision data set is measured to be 200 ps.
  • The ALICE collaboration; Acharya, S.; Brucken, E. J.; Hilden, T. E.; Kim, D. J.; Krizek, F.; Litichevskyi, V.; Novitzky, Norbert; Orava, R.; Parkkila, J. E.; Rak, J.; Rytkonen, H.; Räsänen, Sami; Saarimäki, Oskari Antti Matti; Slupecki, M.; Snellman, T. W.; Trzaska, W. H.; Zhou, Z. (2020)
    Measurements of K*(892)(0) and phi(1020) resonance production in Pb-Pb and pp collisions at root s(NN) = 5.02 TeV with the ALICE detector at the Large Hadron Collider are reported. The resonances are measured at midrapidity (vertical bar y vertical bar <0.5) via their hadronic decay channels and the transverse momentum (p(T)) distributions are obtained for various collision centrality classes up to p(T) = 20 GeV/c. The p(T)-integrated yield ratio K*(892)(0)/K in Pb-Pb collisions shows significant suppression relative to pp collisions and decreases towards more central collisions. In contrast, the phi(1020)/K ratio does not show any suppression. Furthermore, the measured K*(892)(0)/K ratio in central Pb-Pb collisions is significantly suppressed with respect to the expectations based on a thermal model calculation, while the phi(1020)/K ratio agrees with the model prediction. These measurements are an experimental demonstration of rescattering of K*(892)(0) decay products in the hadronic phase of the collisions. The K*(892)(0)/K yield ratios in Pb-Pb and pp collisions are used to estimate the time duration between chemical and kinetic freeze-out, which is found to be similar to 4-7 fm/c for central collisions. The p(T)-differential ratios of K*(892)(0)/K, phi(1020)/K, K*(892)(0)/pi, phi(1020)/pi, p/K*(892)(0) and p/phi(1020) are also presented for Pb-Pb and pp collisions at root s(NN) = 5.02 TeV. These ratios show that the rescattering effect is predominantly a low-p(T) phenomenon. (C) 2020 The Author(s). Published by Elsevier B.V.
  • DiNunno, Brandon S.; Grozdanov, Saso; Pedraza, Juan F.; Young, Steve (2017)
    In large-N-c conformal field theories with classical holographic duals, inverse coupling constant corrections are obtained by considering higher-derivative terms in the corresponding gravity theory. In this work, we use type IIB supergravity and bottom-up Gauss-Bonnet gravity to study the dynamics of boost-invariant Bjorken hydrodynamics at finite coupling. We analyze the time-dependent decay properties of non-local observables (scalar two-point functions and Wilson loops) probing the different models of Bjorken flow and show that they can be expressed generically in terms of a few field theory parameters. In addition, our computations provide an analytically quanti fiable probe of the coupling-dependent validity of hydrodynamics at early times in a simple model of heavyion collisions, which is an observable closely analogous to the hydrodynamization time of a quark-gluon plasma. We find that to third order in the hydrodynamic expansion, the convergence of hydrodynamics is improved and that generically, as expected from field theory considerations and recent holographic results, the applicability of hydrodynamics is delayed as the field theory coupling decreases.
  • 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 Xe-Xeinteractions at a centre-of-mass energy per nucleon pair of root s(NN) = 5.44 TeV, using the ALICE detector at the CERN LHC. The J/psi meson is reconstructed via its decay into a muon pair, in the centre-of-mass rapidity interval 2.5 <y <4 and down to zero transverse momentum. In this Letter, the nuclear modification factors R-AA for inclusive J/psi, measured in the centrality range 0-90% as well as in the centrality intervals 0-20% and 20-90% are presented. The R-AA values are compared to previously published results for Pb-Pbcollisions at root s(NN) = 5.02 TeV and to the calculation of a transport model. A good agreement is found between Xe-Xe and Pb-Pbresults as well as between data and the model. (C) 2018 Organisation europeenne pour la recherche nucleaire. Published by Elsevier B.V.
  • 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.; Aphecetche, L.; Appelshaeuser, H.; Arcelli, S.; Arnaldi, R.; Arnold, O. W.; Arsene, I. C.; Arslandok, M.; 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 inclusive J/Psi production has been studied in Pb-Pb and pp collisions at the centre-of-mass energy per nucleon pair root sNN= 5.02TeV, using the ALICE detector at the CERN LHC. The J/Psi meson is reconstructed, in the centre-of-mass rapidity interval 2.5 <y <4and in the transverse- momentum range p(T)<12GeV/c, via its decay to a muon pair. In this Letter, we present results on the inclusive J/Psi cross section in pp collisions at root s= 5.02TeV and on the nuclear modification factor R-AA. The latter is presented as a function of the centrality of the collision and, for central collisions, as a function of the transverse momentum p(T) of the J/Psi. The measured R-AA values indicate a suppression of the J/Psi in nuclear collisions and are then compared to our previous results obtained in Pb-Pb collisions at root sNN= 2.76TeV. The ratio of the R-AA values at the two energies is also computed and compared to calculations of statistical and dynamical models. The numerical value of the ratio for central events (0-10% centrality) is 1.17 +/- 0.04( stat)+/- 0.20(syst). In central events, as a function of p(T), a slight increase of R-AA with collision energy is visible in the region 2 <p(T)<6GeV/c. Theoretical calculations qualitatively describe the measurements, within uncertainties. (C) 2017 The Author. Published by Elsevier B.V.
  • PHENIX Collaboration; Adare, A.; Kim, D. J.; Krizek, F.; Novitzky, N.; Rak, J. (2018)
    We present a detailed measurement of charged two-pion correlation functions in 0-30% centrality root= 200 GeV Au+Au collisions by the PHENIX experiment at the Relativistic Heavy Ion Collider. The data are well described by Bose-Einstein correlation functions stemming from Levy-stable source distributions. Using a fine transverse momentum binning, we extract the correlation strength parameter lambda, the Levy index of stability alpha, and the Levy length scale parameter R as a function of average transverse mass of the parr m(T). We find that the positively and the negatively charged pion pairs yield consistent results, and their correlation functions are represented, within uncertainties, by the same Levy-stable source functions. The lambda(m(T)) measurements indicate a decrease of the strength of the correlations at low m(T). The Levy length scale parameter R(m(T)) decreases with increasing m(T), following a hydrodynamically predicted type of scaling behavior. The values of the Levy index of stability a are found to be significantly lower than the Gaussian case of alpha = 2, but also significantly larger than the conjectured value that may characterize the critical point of a second-order quark-hadron phase transition.
  • PHENIX Collaboration; Adare, A.; Kim, D. J.; Novitzky, N.; Rak, J. (2018)
    The PHENIX experiment at the Relativistic Heavy Ion Collider has measured the differential cross section of phi(1020)-meson production at forward rapidity in p + p collisions at root s = 510 GeV via the dimuon decay channel. The partial cross section in the rapidity and P-T ranges 1.2 <vertical bar y vertical bar <2.2 and 2 <p(T) <7 GeV/c is sigma(phi) = [2.28 +/- 0.09(stat) +/- 0.14(syst) +/- 0.27(norm)] x 10(-2) mb. The energy dependence of sigma(phi )(1.2 <vertical bar y vertical bar <2.2,2 <p(T) <5 GeV/c) is studied using the PHENIX measurements at root s = 200 and 510 GeV and the Large Hadron Collider measurements at root s = 2.76 and 7 TeV. The experimental results arc compared to various event generator predictions (PYTHIA6, PYTHIA8, PHOJET, AMPT, EPOS3, and EPOS-LHC).
  • The CMS collaboration; Sirunyan, A. M.; Eerola, P.; Pekkanen, J.; Voutilainen, M.; Härkönen, J.; Järvinen, T.; Karimäki, V.; Kinnunen, R.; Lampén, T.; Lassila-Perini, K.; Lehti, S.; Lindén, T.; Luukka, P.; Tuominen, E.; Tuominiemi, J.; Tuovinen, E.; Talvitie, J.; Tuuva, T. (2018)
    The prompt D-0 meson azimuthal anisotropy coefficients, v(2) and ?v(3), are measured at midrapidity ( |y| < 1.0) in Pb-Pb collisions at a center-of-mass energy root s(NN) = 5.02 TeV per nucleon pair with data collected by the CMS experiment. The measurement is performed in the transverse momentum (p(T)) range of 1 to 40 GeV/c, for central and midcentral collisions. The v(2) coefficient is found to be positive throughout the p(T) range studied. The first measurement of the prompt D-0 meson v(3) coefficient is performed, and values up to 0.07 are observed for p(T) around 4 GeV/c. Compared to measurements of charged particles, a similar p(T) dependence, but smaller magnitude for p(T) < 6 GeV/r, is found for prompt D-0 meson v(2) and v(3) coefficients. The results are consistent with the presence of collective motion of charm quarks at low p(r) and a path length dependence of charm quark energy loss at high p(r), thereby providing new constraints on the theoretical description of the interactions between charm quarks and the quark-gluon plasma.
  • 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)
    Electrons from heavy-flavour hadron decays (charm and beauty) were measured with the ALICE detector in Pb-Pb collisions at a centre-of-mass of energy root s(NN) = 2.76 TeV. The transverse momentum (pT) differential production yields at mid-rapidity were used to calculate the nuclear modification factor R-AA in the interval 3 <p(T) <18 GeV/c. The R-AA shows a strong suppression compared to binary scaling of pp collisions at the same energy (up to a factor of 4) in the 10% most central Pb-Pb collisions. There is a centrality trend of suppression, and a weaker suppression (down to a factor of 2) in semi-peripheral (50-80%) collisions is observed. The suppression of electrons in this broad p(T) interval indicates that both charm and beauty quarks lose energy when they traverse the hot medium formed in Pb-Pb collisions at LHC. (C) 2017 The Author. Published by Elsevier B.V.
  • 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.; Molina, R. Alfaro; 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.; 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.; Badala, A.; Brucken, E. J.; Chang, B.; Kim, D. J.; Mieskolainen, M. M.; Orava, R.; Rak, J.; Räsänen, S. S. (2016)
    We report the transverse energy (ET) measured with ALICE at midrapidity in Pb-Pb collisions at root s(NN) = 2.76 TeV as a function of centrality. The transverse energy was measured using identified single-particle tracks. The measurement was cross checked using the electromagnetic calorimeters and the transverse momentum distributions of identified particles previously reported by ALICE. The results are compared to theoretical models as well as to results from other experiments. The mean ET per unit pseudorapidity (eta), <dE(T)/d eta >, in 0%-5% central collisions is 1737 +/- 6(stat.) +/- 97(sys.) GeV. We find a similar centrality dependence of the shape of <dE(T)/d eta > as a function of the number of participating nucleons to that seen at lower energies. The growth in <dE(T)/d eta > at the LHC energies exceeds extrapolations of low-energy data. We observe a nearly linear scaling of <dE(T)/d eta > with the number of quark participants. With the canonical assumption of a 1 fm/c formation time, we estimate that the energy density in 0%-5% central Pb-Pb collisions at root s(NN) = 2.76 TeV is 12.3 +/- 1.0 GeV/fm(3) and that the energy density at the most central 80 fm(2) of the collision is at least 21.5 +/- 1.7 GeV/fm(3). This is roughly 2.3 times that observed in 0%-5% central Au-Au collisions at root s(NN) = 200 GeV.