1 identified particle production in the beam energy scan from star anthony timmins for the star...
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Identified particle production in the Beam Energy Scan from STAR
Anthony Timmins for the STAR Collaboration
The Beam energy scan The STAR experiment Pions, protons, and kaons. Freeze out parameters Strange and multi-strange hyperons Summary
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Beam energy scan Lattice QCD predicts
1st order phase transition
At critical point, transition becomes cross-overCan we find it?
Scan beam energies (BES): Vary T and μB simultaneously…
Schematic representation
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Beam energy scan Determine onset of
de-confinement Lower beam
energy, lower energy density
Get an experimental handle on εc
Key signatures:– Strangeness
production
– Baryon/meson differences
J. Phys. G 32 (2006) S105-S114
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The STAR experiment
TPC and TOF used for subsequent analyses
Fixed acceptance wrt beam energyAdvantage over SPS
Energies scanned:Run 8: 9.2 GeV (no TOF)Run 10: 7.7, 11.5, 39, 62.4, 200 GeVRun 11: 19, 27 GeV
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Particle identification
Excellent PID in STAR for primary tracks: dE/dx: Proton/pion separation to p~1 GeV/c TOF: Proton/pion separation to p~3 GeV/c
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V0 and cascade reconstruction
Weak decays reconstructed in the STAR TPC V0 finding Cascade finding
No momentum limit for PID.
Top Au+Au energy highest values (stats limited)– V0 pT ~ 9 GeV
– Cascade pT ~ 5 GeVAu+Au 7 GeV CPOD 2011
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Pions, protons, kaons at Au+Au 39 GeV
BES spectra obtained with TPC and TOF: Consistent with dE/dx in overlapping range
QM & CPOD 2011
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Pions, protons and kaons (all energies)
Kaon and proton yields increase relative to pions with decreasing energy– Larger baryon transport to mid rapidity.
QM & CPOD 2011
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Pions, protons and kaons (all energies)
Increase in anti-particles relative to pions with increasing energy
QM & CPOD 2011
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Freeze out parameters Use 2 models to determine
freeze-out properties.
1. Blast wave model Obtains Tkin and <β>
Fit proton, kaon, pion spectra (PRC 70 (2004) 044907)
2. Thermal model Obtains Tchem and μB
Uses Grand Canonical ensemble (Comp. phys. Comm. 180 (2009) 84)
Fit proton, kaon, pion yields
QM & CPOD 2011
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Freeze out parameters
Kinetic freeze temperature and expansion velocity depend on centrality and beam energy.
QM & CPOD 2011
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Freeze out parameters First observation:
Tchem and μB depend on centrality
Stronger dependence for μB
Centrality offers further dial in critical point search.
Result holds when strange particles included (not shown)
CPOD 2011
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Kaon and pions in Cu+Cu 22.4 GeV Ratios higher in lighter
systems with similar <Npart> at AGS/SPS
CM energy < 22.4 GeV, yields over 4π
PRC 60, (1999) 044904, NPA 715 (2003) 474c
Not the case for RHIC at lower energy
Top RHIC energy: Yields of strange and non strange
particles higher in Cu+Cu Ratio the same
SQM 2011
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Strange and multi-strange hyperons
Extensive strange particle spectra
(Anti) Lambda corrected for Cascade feed-down
CPOD 2011
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Hyperons yields
CPOD 2011
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Hyperons ratios
Anti-particle/particle ratios increase for peripheral events Lower baryon
transport
Consistent with μB decreasing for peripheral events
CPOD 2011
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Strange baryon/meson ratios
Mid-pT ratios get higher at lower energy– More baryon stopping?
Centrality dependence for Au+Au 39 GeV– Breaks at lower energies?
CPOD 2011
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Strange baryon/meson ratiosCPOD 2011
Mid-pT ratios get lower at lower energies
Ratios still rise from low to mid-pT at lower energies
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Nuclear modification factor
No K0s suppression for Au+Au 7.7
and 11.5 GeV
Baryon-meson splitting in Au+Au 39 reduces for lower energies.
CPOD 2011
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Summary
Results from spectra and yields critical in characterizing state of matter in BES.
Bulk Production Particle ratios, Tkin and β depend on energy and centrality
First observation of Tchem and μB centrality dependence
Strangeness production Anti particle/particle ratios depends on centrality Baryon/meson differences disappear in Au+Au 7.7 and 11.5 GeV
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Outlook…
Run 11 Au+Au 19 and Au+Au 27 GeV data on the way!
DNP 2011 Statistical uncertainties only
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