Browsing by Subject "ENERGY-LOSS"

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  • Adam, J.; Adamova, D.; Aggarwal, 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.; Rasanen, S. S.; Snellman, T. W.; Trzaska, W. H. (2015)
    We present a measurement of inclusive J/psi production in p-Pb collisions at root S-NN = 5.02 TeV as a function of the centrality of the collision, as estimated from the energy deposited in the Zero Degree Calorimeters. The measurement is performed with the ALICE detector down to zero transverse momentum, p(T), in the backward (-4.46 <y(cms) <-2.96) and forward (2.03 <y(cms) <3.53) rapidity intervals in the dimuon decay channel and in the mid-rapidity region (-1.37 <y(cms) <0.43) in the dielectron decay channel. The backward and forward rapidity intervals correspond to the Pb-going and p-going direction, respectively. The p(T)-differential J/psi production cross section at backward and forward rapidity is measured for several centrality classes, together with the corresponding average p(T) and p(T)(2) values. The nuclear modification factor is presented as a function of centrality for the three rapidity intervals, and as a function of p(T) for several centrality classes at backward and forward rapidity. At mid-and forward rapidity, the J/psi yield is suppressed up to 40% compared to that in pp interactions scaled by the number of binary collisions. The degree of suppression increases towards central p-Pb collisions at forward rapidity, and with decreasing p(T) of the J/psi. At backward rapidity, the nuclear modification factor is compatible with unity within the total uncertainties, with an increasing trend from peripheral to central p-Pb collisions.
  • The ALICE collaboration; Acharya, S.; Adamova, D.; Kim, D. J.; Krizek, F.; Parkkila, J. E.; Rak, J.; Rytkönen, Heidi Maria; Räsänen, Sami; Saarimäki, Oskari Antti Matti; Slupecki, M.; Trzaska, W. H.; Zhou, Zhipeng (2021)
    The elliptic flow of electrons from beauty hadron decays at midrapidity (vertical bar y vertical bar < 0.8) is measured in Pb-Pb collisions at root s(NN) = 5.02 TeV with the ALICE detector at the LHC. The azimuthal distribution of the particles produced in the collisions can be parametrized with a Fourier expansion, in which the second harmonic coefficient represents the elliptic flow, v(2). The v(2) coefficient of electrons from beauty hadron decays is measured for the first time in the transverse momentum (p(T)) range 1.3- 6 GeV/c in the centrality class 30%-50%. The measurement of electrons from beauty-hadron decays exploits their larger mean proper decay length c tau approximate to 500 mu m compared to that of charm hadrons and most of the other background sources. The v(2) of electrons from beauty hadron decays at midrapidity is found to be positive with a significance of 3.75 sigma. The results provide insights into the degree of thermalization of beauty quarks in the medium. A model assuming full thermalization of beauty quarks is strongly disfavored by the measurement at high p(T), but is in agreement with the results at low p(T). Transport models including substantial interactions of beauty quarks with an expanding strongly interacting medium describe the measurement within uncertainties.
  • 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.
  • 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, R.; Aphecetche, L.; Appelshaeuser, H.; Arcelli, S.; Armesto, N.; Arnaldi, R.; Arsene, I. C.; Arslandok, M.; Audurier, B.; Augustinus, A.; 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)
    The elliptic flow, v(2), of muons from heavy-flavour hadron decays at forward rapidity (2.5 <y <4) is measured in Pb-Pb collisions at root s(NN)= 2.76TeVwith the ALICE detector at the LHC. The scalar product, two- and four-particle Q cumulants and Lee-Yang zeros methods are used. The dependence of the v(2) of muons from heavy-flavour hadron decays on the collision centrality, in the range 0-40%, and on transverse momentum, p(T), is studied in the interval 3 <p(T)<10 GeV/c. A positive v(2) is observed with the scalar product and two-particle Q cumulants in semi-central collisions (10-20% and 20-40% centrality classes) for the p(T) interval from 3 to about 5GeV/c with a significance larger than 3 sigma, based on the combination of statistical and systematic uncertainties. The v(2) magnitude tends to decrease towards more central collisions and with increasing pT. It becomes compatible with zero in the interval 6 <p(T)<10 GeV/c. The results are compared to models describing the interaction of heavy quarks and open heavy-flavour hadrons with the high-density medium formed in high-energy heavy-ion collisions. (C) 2015 CERN for the benefit of the ALICE Collaboration. 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)
    The production yield of prompt D mesons and their elliptic flow coefficient v(2) were measured with the Event-Shape Engineering (ESE) technique applied to mid-central (10-30% and 30-50% centrality classes) Pb-Pb collisions at the centre-of-mass energy per nucleon pair sNN=5.02 TeV, with the ALICE detector at the LHC. The ESE technique allows the classification of events, belonging to the same centrality, according to the azimuthal anisotropy of soft particle production in the collision. The reported measurements give the opportunity to investigate the dynamics of charm quarks in the Quark-Gluon Plasma and provide information on their participation in the collective expansion of the medium. D mesons were reconstructed via their hadronic decays at mid-rapidity, || < 0.8, in the transverse momentum interval 1 < p(T) < 24 GeV/c. The v(2) coefficient is found to be sensitive to the event-shape selection confirming a correlation between the D-meson azimuthal anisotropy and the collective expansion of the bulk matter, while the per-event D-meson yields do not show any significant modification within the current uncertainties.
  • Abelev, B.; Chang, B.; Kim, D. J.; Kral, J.; Krizek, F.; Morreale, A.; Pohjoisaho, E. H. O.; Rak, J.; Räsänen, S. S.; Trzaska, W. H.; Viinikainen, J.; The ALICE collaboration (2014)
  • 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.; 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.
  • PHENIX Collaboration; Aidala, C.; Kim, D. J.; Krizek, F.; Novitzky, N.; Rak, J. (2018)
    Production of pi(0) and eta mesons has been measured at midrapidity in Cu+Au collisions at root S-NN = 200 GeV. Measurements were performed in pi(0) (eta) -> gamma gamma decay channel in the 1(2)-20 GeV/c transverse momentum range. A strong suppression is observed for pi(0) and eta meson production at high transverse momentum in central Cu+Au collisions relative to the p + p results scaled by the number of nucleon-nucleon collisions. In central collisions the suppression is similar to Au + Au with comparable nuclear overlap. The eta/pi(0) ratio measured as a function of transverse momentum is consistent with m(T)-scaling parametrization down to p(T) = 2 GeV/c, its asymptotic value is constant and consistent with Au + Au and p + p and does not show any significant dependence on collision centrality. Similar results were obtained in hadron-hadron, hadron-nucleus, and nucleus-nucleus collisions as well as in e(+)e(-) collisions in a range of collision energies root S-NN = 3-1800 GeV. This suggests that the quark-gluon-plasma medium produced in Cu+Cu collisions either does not affect the jet fragmentation into light mesons or it affects the pi(0) and eta the same way.
  • 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.; Siikonen, H.; Tuominen, E.; Tuominiemi, J.; Tuuva, T. (2018)
    Measurements of azimuthal angle and transverse momentum (p(T)) correlations of isolated photons and associated jets are reported for pp and PbPb collisions at root s(NN) = 5.02 TeV. The data were recorded with the CMS detector at the CERN LHC. For events containing a leading isolated photon with p(T)(gamma) > 40 GeV/c and an associated jet with p(T)(jet) > 30 GeV/c, the photon+jet azimuthal correlation and p(T) imbalance in PbPb collisions are studied as functions of collision centrality and p(T)(gamma). The results are compared to pp reference data collected at the same collision energy and to predictions from several theoretical models for parton energy loss. No evidence of broadening of the photon+jet azimuthal correlations is observed, while the ratio p(T)(jet)/p(T)(gamma) decreases significantly for PbPb data relative to the pp reference. All models considered agree within uncertainties with the data. The number of associated jets per photon with p(T)(gamma) > 80GeV/c is observed to be shifted towards lower p(T)(jet) in central PbPb collisions compared to pp collisions. (C) 2018 The Author. Published by Elsevier B.V.
  • 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 (2018)
    The Transition Radiation Detector (TRD) was designed and built to enhance the capabilities of the ALICE detector at the Large Hadron Collider (LHC). While aimed at providing electron identification and triggering, the TRD also contributes significantly to the track reconstruction and calibration in the central barrel of ALICE. In this paper the design, construction, operation, and performance of this detector are discussed. A pion rejection factor of up to 410 is achieved at a momentum of 1 GeV/c in p-Pb collisions and the resolution at high transverse momentum improves by about 40% when including the TRD information in track reconstruction. The triggering capability is demonstrated both for jet, light nuclei, and electron selection. (c) 2017 CERN for the benefit of the Authors. Published by Elsevier B.V.