fMeson Production in Au Au Collisions at vsNN 200 GeV

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f-Meson Production in Au - Au Collisions at vsNN
200 GeV
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Outline

• Physics motivations
• PHENIX Experimental set-up
• Data analysis
• Results from Au-Au collisions _at_ vs 200 GeV
• Line shape measurements
• Yield (dN/dy and inverse slope, T)
• Centrality dependence
• Particle ratio
• Rcp
• Summary and outlook

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Physics Motivation
f mesons

• Sensitive to strangeness production
• Probe of deconfined phase
• Strange to non-strange particle ratios

• - ss bound state
• - Main decay modes
• f à KK- (BR 49.2)
• f à ee- (BR 2.96 x 10-4)
• f à mm- (BR 2.87 x 10-4)
• - Mass 1.019456 0.000020 GeV/c2
• Width 4.26 0.05 MeV/c2
• Lifetime, t 45 fm/c
• Small interaction cross-section
• with nucleons (compared to p,
• K and ps)

Probe of chiral symmetry restoration
à Medium effect - mass, width
modification - double peak
- yields in KK- and di-lepton decay
channels
Information on the initial state - Particle
production nuclear modification
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PHENIX Setup

• Tracking
• DC - PC1 - PC3
• Provides momentum
• f à ee-
• Electron id RICH and EMCAL
• Acceptance h lt 0.35, Df 2 x 90o
• f à KK-
• Kaon id TOF or EMCAL
• TOF acceptance h lt 0.35 , Df 450
• st 120 ps, kaon identification within
• 0.3 lt p (GeV/c) lt 2
• EMCAL acceptance h lt 0.35 ,
• Df 90 0
  x 2
• st 480 ps, kaon identification
• within 0.3 lt p (GeV/c) lt 1.

1. TOF K ßà TOF K- (TOF TOF)
3 Combinations
2. PbSc(E) K ßà PbSc (E) K-
(PbSc - PbSc)
3. TOF K ßà PbSc(E) K-
(TOF
PbSc)
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f meson reconstruction

• Invariant mass distribution
• - All Kaons are paired together to
• form N-
• Large combinatorial background (CB)
• - Combinatorial background determined
• by mixed event technique
• à mix and - tracks from
• different events with same centrality
• and vertex
• - Mixed event normalization
• CB 2 vNN--
• Signal S N- - CB

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Line shape analysis - 1
Combined data from all subsystem combinations to
obtain the f à K K- invariant mass spectra with
good statistics.

• Minimum-bias trigger
• Nevt 20 M
• Full east arm
• Nf 5670 240, S/B 1/8.5
• (within 5 MeV/c2 mass window about
• the measured centroid )
• The f mass spectrum is fitted
• with relativistic Breit Wigner function convolved
  with Gaussian f mass resolution function (s 1.2
  MeV/c2)
• Minimum-bias centroid and width
• are consistent with PDG.

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Line shape analysis - II
f mass centroids and widths for different
centralities
èCentroids at all centralities are consistent
with PDG within errors. è widths are within
less than 2s of PDG at different centralities.
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Yield analysis
mT spectra of f
Invariant yield
Au Au _at_ vsNN 200 GeV, full east arm

• Fitted with exponential function in mT

• Inverse slopes (T) are almost
• constant over all centralities.

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Centrality dependence - I
Inverse slope
è Inverse slope is independent of centrality.
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Centrality dependence - II
Yield per participant pair rises at small Npart
and then saturates.
Centrality dependence in heavy ion Collisions at
different collision energies. f production
at RHIC behaves differently than
AGS and SPS.
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Particle ratios in PHENIX _at_ RHIC
PHENIX Au Au _at_ vsNN 200 GeV

• è Kaon production increases
• faster than pions as a function
• Npart.
• Both f/p and f/K ratios look
• constant as a function of Npart for
• these centrality bins within errors.
• Need more statistics to split
• up the data into larger number
• of centrality bins.

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Rcp of f
Ncoll scaled central-to- peripheral ratio Rcp.
Yield (0 10)/Ncoll(0 10)
Rcp
Yield (40 92)/Ncoll(40 92)
PHENIX, Au-Au _at_ vsNN 200 GeV
Rcp of f is consistent with pions. è Particle
yields in intermediate pT depends on the number
of valance quarks in the particle as opposed to
the mass of the particles.
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Summary

• PHENIX has measured f mesons in Au-Au
  collisions at vsNN 200 GeV.
• Centroids and widths are consistent with PDG.
• dN/dy per participant pair as a function of
  Npart shows different behaviour than AGS and SPS.
  
• The inverse slope remains constant with
  centrality.
• f production rate looks similar to the kaons
  (and pions).
• à need more statistics for a more rigorous
  conclusion.
• The Rcp of f is consistent with that of p0s
• à Baryon meson effect.

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Future directions

• PHENIX has recorded 1.5 x 109 Au-Au collision
  events at vsNN 200 GeV in the 2003-2004 run.
• è Better control on statistical and systematic
  effects for exploring f meson line shape and
  yields at different centralities.
• è Explore whether there is any difference in f
  yield in KK- and ee-
• decay channels.
• è study v2 of f mesons.

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Backup slides
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Particle ratio at AGS and SPS
SPS (NA50 _at_ vsNN 17.27 GeV)
AGS (E917 _at_ vsNN 4.87 GeV)
f à mm-
f à KK-

• Enhancement in f production compared to
  non-strange p mesons for central
• Au Au collisions.
• Both f and K has the similar degree of
  enhancement towards central collisions.

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mT spectra of f for different datasets
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Radial Flow (I)
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Blast wave fits (II)
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Blast wave fits (III)
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Blast wave fits (IV)