HIGH-ENERGY HADRON-NUCLEUS COLLISIONS MEASURED WITH ALICE MPI@LHC - - PowerPoint PPT Presentation

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HIGH-ENERGY HADRON-NUCLEUS COLLISIONS MEASURED WITH ALICE MPI@LHC - - PowerPoint PPT Presentation

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STUDY OF COLLECTIVE EFFECTS IN HIGH-ENERGY HADRON-NUCLEUS COLLISIONS MEASURED WITH ALICE MPI@LHC TRIESTE, 23-27 NOVEMBER 2015 ENRICO FRAGIACOMO INFN TRIESTE ON BEHALF OF THE ALICE COLLABORATION RELATIVISTIC HEAVY-ION COLLISIONS p Pb Pb

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SLIDE 1

ENRICO FRAGIACOMO INFN TRIESTE

ON BEHALF OF THE ALICE COLLABORATION

STUDY OF COLLECTIVE EFFECTS IN HIGH-ENERGY HADRON-NUCLEUS COLLISIONS MEASURED WITH ALICE

MPI@LHC – TRIESTE, 23-27 NOVEMBER 2015

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SLIDE 2

RELATIVISTIC HEAVY-ION COLLISIONS

MPI@LHC, 23-27 NOVEMBER 2015, ENRICO FRAGIACOMO

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p p p Pb Pb Pb

  • Initial state effect
  • Reference for Pb-Pb
  • Thermal production
  • Collective flow
  • Final state effects
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SLIDE 3

WHY STUDY PROTON-NUCLEUS COLLISIONS

  • Proton-nucleus (pA) collisions intermediate

between proton-proton an nucleus-nucleus;

  • Comparison between systems → separate

initial and final state effects due to hot and dense matter;

  • At LHC, density of final state particles in p-Pb

comparable to Au-Au and Cu-Cu at top RHIC energies;

  • Final state effects in pA?

MPI@LHC, 23-27 NOVEMBER 2015, ENRICO FRAGIACOMO

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SLIDE 4

SELECTED RESULTS FROM p-Pb

  • Transverse momentum spectra
  • Blast-wave fits
  • Mean pT

Other results:

  • Angular correlations (→ talk by M. Floris)
  • Strangeness enhancement (→ talk by B. Hess)

MPI@LHC, 23-27 NOVEMBER 2015, ENRICO FRAGIACOMO

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SLIDE 5

ALICE DETECTOR

MPI@LHC, 23-27 NOVEMBER 2015, ENRICO FRAGIACOMO

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SLIDE 6

PARTICLE TRACKING AND IDENTIFICATION

MPI@LHC, 23-27 NOVEMBER 2015, ENRICO FRAGIACOMO

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  • Good momentum resolution ~1-5%
  • Excellent particle identification capabilities in a

large pT range 0.1-20 GeV/c

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SLIDE 7

TRANSVERSE M0MENTUM SPECTRA

MPI@LHC, 23-27 NOVEMBER 2015, ENRICO FRAGIACOMO

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  • Hardening with increasing

multiplicity

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SLIDE 8

TRANSVERSE M0MENTUM SPECTRA

MPI@LHC, 23-27 NOVEMBER 2015, ENRICO FRAGIACOMO

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  • Hardening with increasing

multiplicity

  • In Pb-Pb explained in terms
  • f collective radial

expansion

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SLIDE 9

TRANSVERSE M0MENTUM SPECTRA

MPI@LHC, 23-27 NOVEMBER 2015, ENRICO FRAGIACOMO

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  • Hardening with increasing

multiplicity

  • In Pb-Pb explained in terms
  • f collective radial

expansion

  • Radial flow → Blast-wave

parameterization

  • Combined Blast-wave fit of

pion, kaon, proton, KS

0 and

L spectra

ALICE, Phys. Lett. B 728 (2014) 25

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SLIDE 10

BLAST-WAVE FIT PARAMETERS

MPI@LHC, 23-27 NOVEMBER 2015, ENRICO FRAGIACOMO

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ALICE, Phys. Lett. B 728 (2014) 25

Tkin → kinetic freeze-out temperature <bT> → average radial flow velocity

  • Blast-wave fit

parameters as function of multiplicity: similar evolution in p-Pb and Pb-Pb

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SLIDE 11

BLAST-WAVE FIT PARAMETERS

MPI@LHC, 23-27 NOVEMBER 2015, ENRICO FRAGIACOMO

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ALICE, Phys. Lett. B 728 (2014) 25

Tkin → kinetic freeze-out temperature <bT> → radial flow velocity

  • Blast-wave fit

parameters as function of multiplicity: similar evolution in p-Pb and Pb-Pb

  • PYTHIA8 pp

(no hydrodynamics): same trend if Color Reconnection is on

  • Effect similar to flow
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SLIDE 12

PREDICTING SPECTRA

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Parameters from combined fit of pion, kaon, proton KS

0 and L

spectra describe spectra of X- and W-.

MPI@LHC, 23-27 NOVEMBER 2015, ENRICO FRAGIACOMO

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SLIDE 13

COMBINED FIT

  • Combined fit

extended to include X- and W-.

  • Values of fit

parameters depend on the fit range

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SLIDE 14

COMPARISON TO MODELS

DPMJET:

  • Reproduces pseudo-rapidity

distributions in NSD p-Pb collisions Kraków:

  • Expansion of the system via

viscous hydrodynamic approach

  • Statistical hadronization at

freeze-out EPOS:

  • Bulk matter described in terms of

hydrodynamics

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ALICE, Phys. Lett. B 728 (2014) 25

Models with hydro describe data in p-Pb → flow effects?

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SLIDE 15

Hardening vs. multiplicity stronger for heavier particles (mass ordering) → suggest presence of hydrodynamics

MEAN TRANSVERSE MOMENTUM

MPI@LHC, 23-27 NOVEMBER 2015, ENRICO FRAGIACOMO

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SLIDE 16

MEAN TRANSVERSE MOMENTUM

MPI@LHC, 23-27 NOVEMBER 2015, ENRICO FRAGIACOMO

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Results for X(1530)0 consistent with multi-strange hyperons

Multiplicity classes for X(1530)0: 0-20%, 20-40%, 40-60% and 60-100%

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SLIDE 17

<pT> VS. PARTICLE MASS

MPI@LHC, 23-27 NOVEMBER 2015, ENRICO FRAGIACOMO

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  • Common trend or

mesons (baryons) deviate?

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SLIDE 18

RE-SCATTERING IN HADRONIC MATTER

MPI@LHC, 23-27 NOVEMBER 2015, ENRICO FRAGIACOMO

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  • Suppression of K*0/K- ratio

in central Pb-Pb due to re- scattering effects of K*0 daughters in hadronic matter after hadronization

  • f not affected due to

lifetime longer than K*0

  • Trend in p-Pb consistent

with pp and peripheral Pb-Pb within uncertainties

  • No evidence for re-

scattering effects in p-Pb

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SLIDE 19

CONCLUSIONS

  • Multiplicity- and mass-dependent hardening
  • f spectra suggestive of hydrodynamics in

p-Pb collisions at LHC

  • Models with hydro describe data better
  • Alternative explanations (e.g. color

reconnection) are possible

  • No evidence for hadronic matter effects

(e.g. re-scattering) in p-Pb collisions

MPI@LHC, 23-27 NOVEMBER 2015, ENRICO FRAGIACOMO

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