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Introduction ALICE Detector and PID Results on identified hadrons from :

Transverse momentum spectra and nuclear modification factors of identified charged hadrons in p- Pb and Pb-Pb collisions at  s NN = 5.02 TeV with ALICE Maria Vasileiou on behalf of the ALICE Collaboration National and Kapodistrian University of Athens Physics Department. Outline.

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Introduction ALICE Detector and PID Results on identified hadrons from :

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  1. Transverse momentum spectra and nuclear modification factors of identified charged hadrons in p-Pb and Pb-Pb collisionsat sNN = 5.02 TeV with ALICEMaria Vasileiouon behalf of the ALICE CollaborationNational and Kapodistrian University of AthensPhysics Department ICNFP2017

  2. Outline • Introduction • ALICE Detector and PID • Results on identified hadrons from : ● Pb-Pb Collisions ● p-Pb Collisions • Nuclear Modification Factors • Conclusions ICNFP2017 - International Conference on New Frontiers in Physics M.Vasileiou

  3. Introduction ALICE is designed to study the physics of strongly interacting matter under extremely high temperature and energy density conditions to investigate the properties of the quark-gluon plasma (QGP) • pp collisions at s = 0.9, 2.76, 5.02, 7, 8, 13 TeV ● Test QCD inspired models ● Provide reference for p-Pb and Pb-Pb data • p-Pb collisions at sNN = 5.02, 8.16 TeV ● Discriminate between initial (cold nuclear matter) and final state (QGP) effects ● Provide reference for Pb-Pb data • Pb-Pb collisions at sNN = 2.76, 5.02 TeV ● Study QGP properties and its evolution ICNFP2017 - International Conference on New Frontiers in Physics M.Vasileiou

  4. ALICE Detector ICNFP2017 - International Conference on New Frontiers in Physics M.Vasileiou

  5. TPC • PID via dE/dxin gas – Ne/CO2 • (90:10) – up to 159 samples • Truncated mean dE/dx calculated • and used for particle identification • (PID) in a wide momentum range • Largest π/K and K/p separation • achieved at low p (< 2.0 GeV/c ) ALICE, Int. J. Mod. Phys. A29 (2014) 1430044 ICNFP2017 - International Conference on New Frontiers in Physics M.Vasileiou

  6. TPC (II) ALICE, Int. J. Mod. Phys. A29 (2014) 1430044 • At high pT: particles separated on a statistical basis via multi-Gaussian fits ICNFP2017 - International Conference on New Frontiers in Physics M.Vasileiou

  7. TOF • Time - Of - Flight: • Multigap Resistive Plate Chambers (MRPC) • PID at intermediate momenta • Resolution ~ 80 ps ALICE, Int. J. Mod. Phys. A29 (2014) 1430044 ICNFP2017 - International Conference on New Frontiers in Physics M.Vasileiou

  8. HMPID • High Momentum Particle • Identification Detector : • Consists of 7 RICH modules • Proximity focusing configuration • In Pb-Pb collisions, 3σseparation for π/Κ • up to 3 GeV/c and for Κ/p up to 5 GeV/c ALICE, Phys. Lett. B 736 (2014) 196-207 ALICE, Int. J. Mod. Phys. A29 (2014) 1430044 ICNFP2017 - International Conference on New Frontiers in Physics M.Vasileiou

  9. PID Separation Power ALICE, Int. J. Mod. Phys. A29 (2014) 1430044 • Demonstration of the complementarity of the different • detector systems. ICNFP2017 - International Conference on New Frontiers in Physics M.Vasileiou

  10. Combined PID ALICE, Int. J. Mod. Phys. A29 (2014) 1430044 • Separation of hadron species further improved by • combining information from multiple detectors ICNFP2017 - International Conference on New Frontiers in Physics M.Vasileiou

  11. Particle Spectra in Pb-Pb Collisions ICNFP2017 - International Conference on New Frontiers in Physics M.Vasileiou

  12. Identified Particle Spectra in Pb-Pb Collisions • Spectra get harder with increasing centrality; hardening more pronounced • for more massive particles • Particles with similar mass have similar mean pTin central Pb-Pb collisions •  Expected in presence of collective hydrodynamic expansion • Clear signature of radial flow ICNFP2017 - International Conference on New Frontiers in Physics M.Vasileiou

  13. Particle Ratios : K/π in Pb-Pb Collisions • Compared with measurements in Pb-Pb collisions at sNN = 2.76 TeV • No significant evolution between the two energies ICNFP2017 - International Conference on New Frontiers in Physics M.Vasileiou

  14. Particle Ratios : p/π in Pb-Pb Collisions • The pT differential proton-to-pion ratios show a clear centrality evolution • Compared with measurements in Pb-Pb collisions at sNN = 2.76 TeV • Shift of the maximum of p/π to higher pTwith respect to lower energy ICNFP2017 - International Conference on New Frontiers in Physics M.Vasileiou

  15. Identified Particle Spectra in p-Pb Collisions • ALICE, Phys. Lett. B 760 (2016) 720 • Spectra get harder with increasing multiplicity and the change is most • pronounced for heavier particles • In heavy-ion collisions this effect is commonly attributed to radial flow ICNFP2017 - International Conference on New Frontiers in Physics M.Vasileiou

  16. Particle Ratios : K/π in p-Pb Collisions • ALICE, Phys. Lett. B 760 (2016) 720 • The pT differential kaon-to-pion ratios do not show any multiplicity • dependence ICNFP2017 - International Conference on New Frontiers in Physics M.Vasileiou

  17. Particle Ratios : p/π in p-Pb Collisions • ALICE, Phys. Lett. B 760 (2016) 720 • ThepT differential proton-to-pion ratios show a clear multiplicity dependence • at low and intermediate pT • Effect qualitatively similar to the centrality evolution observed in Pb-Pb • collisions ICNFP2017 - International Conference on New Frontiers in Physics M.Vasileiou

  18. Blast-Wave Fit Parameters • In Pb-Pb collisions at sNN = 5.02 TeV • Blast-Wave parameters follow trends • observed at lower energy • Radial flow velocity increases and • kinetic freeze-out temperature • decreases with centrality • Largest expansion velocity for central • Pb-Pb collisions at sNN = 5.02 TeV Boltzmann-Gibbs Blast-Wave model A simplified hydrodynamic model with 3 free fit parameters: -Tkin : kinetic freeze-out temperature - βΤ : transverse radial flow velocity - n: velocity profile E. Schnedermann et al., Phys. Rev. C48 (1993) 2462 ALICE, Phys.Lett. B 728 (2014) 25-38 ALICE, Phys.Rev. C88 (2013) 044910 ICNFP2017 - International Conference on New Frontiers in Physics M.Vasileiou

  19. Blast-Wave Fit Parameters (II) • In pp and p-Pb collisions, similar • evolution of the parameters towards • high multiplicity • Higher <βΤ> for smaller collision • systems at comparable multiplicities ALICE, Phys.Lett. B 728 (2014) 25-38 ALICE, Phys.Rev. C88 (2013) 044910 ICNFP2017 - International Conference on New Frontiers in Physics M.Vasileiou

  20. Ratios of Integrated Yields • Smooth evolution of the p/π and K/π ratios across different systems • High multiplicity pp at 7 TeV and peripheralPb-Pb at 2.76 and 5.02 TeV • are consistent • No significant energy dependence in Pb-Pb collisions from 2.76 to 5.02 TeV ICNFP2017 - International Conference on New Frontiers in Physics M.Vasileiou

  21. Nuclear Modification Factor of Inclusive Charged Particles • Suppression for all centrality intervals • Larger suppression for more central • events • Minimum at around pT= 6 GeV/c • Suppression of high-pTparticles • strongly depends on event centrality ALICE, Phys. Lett. B720 (2013) 52-62 ICNFP2017 - International Conference on New Frontiers in Physics M.Vasileiou

  22. Nuclear Modification Factor in Central Pb-Pb Collisions Comparison with STAR and PHENIX • Position and shape of the maximum at • pT~ 2 GeV/c and subsequent decrease, • similar at RHIC and LHC • At pT= 6 GeV/c , RAAsmaller than at RHIC •  an enhanced energy loss at LHC • attributed to a denser medium put ALICE, Phys. Lett. B696(2011) 30-39 STAR, Phys. Rev. Lett. 91 (2003) 172302 PHENIX, Phys.Rev. C 69 (2004) 034910 ICNFP2017 - International Conference on New Frontiers in Physics M.Vasileiou

  23. Nuclear Modification Factors in p-Pb Collisions • At intermediate pTa small • Cronin peak is observed • At high pTno significant • species dependence is • observed ALICE, Phys. Lett. B 760 (2016) 720 ICNFP2017 - International Conference on New Frontiers in Physics M.Vasileiou

  24. RpPbCompared to RPbPb • RpPb consistent with unity for pT • up to 50 GeV/c • ALICE p-Pb results at high-pTconsistent • with the observation of binary collision • scaling • Strong suppression observed in central • Pb-Pb collisions not due to an initial • state effect  a fingerprint of the hot • matter created in Pb-Pb collisions ALICE, Eur. Phys. J. C74 (2014) 3054 ALICE, Phys.Lett. B720 (2013) 52 CMS, Eur.Phys.J. C72 (2012) 1945 CMS.Phys.Lett. B 710 (2012) 256 CMS, Phys. Rev.Lett. 106 (2011) 212301 CMS, Phys.Lett.B 715 (2012) 66 ICNFP2017 - International Conference on New Frontiers in Physics M.Vasileiou

  25. Energy Dependence of the RAA • Nuclear Modification Factor of primary • charged particles in Pb-Pb at sNN = 5.02TeV • compared with • values from Pb-Pb at sNN = 2.76 TeV • No significant evolution with collision energy • is measured ICNFP2017 - International Conference on New Frontiers in Physics M.Vasileiou

  26. RAAof Pions, Kaons and Protons at 5.02 TeV • All three species are equally suppressed for all centralities at high pT • Light-flavor independent energy loss at high pT as observed at 2.76 TeV ICNFP2017 - International Conference on New Frontiers in Physics M.Vasileiou

  27. RAA of Kaons – Energy Dependence • No significant evolution with the collision energy is found • Similar observations for pions and protons ICNFP2017 - International Conference on New Frontiers in Physics M.Vasileiou

  28. Conclusions • ALICE can perform unique measurements of identified particle production in pp, p-Pb and Pb-Pbcollisions • A higher expansion velocity is observed in central Pb-Pb collisions at 5.02 TeV than at 2.76 TeV : Stronger radial flow is measured at the higher energy • In Pb-Pb collisions p/π and K/π relative abundances exhibit no significant energy dependence • Strong suppression of high-pThadrons observed in central Pb-Pbcollisions is not due to an initial state effect but instead due to the energy loss of partonstraversing a hot and dense QCD medium • Nuclear modification factor has no significant evolutionwith the collision energy ICNFP2017 - International Conference on New Frontiers in Physics M.Vasileiou

  29. Thank you! ICNFP2017

  30. Centrality Selection in Pb-Pb Collisions ALICE, Phys. Rev. C88, 044909 (2013) • Event multiplicity/centrality classes are defined based on the • amplitude measured in the V0 scintillators placed at : • 2.8<η<5.1 (V0A) and -3.7<η<-1.7 (V0C) • Curve: Glauber model fit to the measurement ICNFP2017 - International Conference on New Frontiers in Physics M.Vasileiou

  31. Identified Particle Spectra in pp Collisions ALICE, Phys. Rev. C88, 044909 (2013) ALICE, Phys. Lett. B 760 (2016) 720 • Hardening of the reference spectra with respect to lower • energy ICNFP2017 - International Conference on New Frontiers in Physics M.Vasileiou

  32. RAA Compared to Model Calculations Vitev et al., Phys. Rev. D 93 074030 (2016) Djordjevic et al., arXiv:1601.07852 (2016) Majumber et al.,Phys. Rev .Lett. 109 202301 (2012) • Measurement at high pT in agreement with all three model • predictions within their uncertainties ICNFP2017 - International Conference on New Frontiers in Physics M.Vasileiou

  33. Multiplicity Dependence of p/π • p/π ratio as a function of multiplicity at low, intermediate • and highpT for pp, p-Pb and Pb-Pb collisions ICNFP2017 - International Conference on New Frontiers in Physics M.Vasileiou

  34. Multiplicity Dependence of < pT> • Mean Transverse Momentum of identified hadrons measured in • p-Pb collisions at sNN = 5.02TeV as a function of multiplicity ICNFP2017 - International Conference on New Frontiers in Physics M.Vasileiou

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