Brookhaven National Laboratory

1
Resonance Production in AuAu and pp Collisions
at ?sNN200 GeV

• Patricia Fachini
• Brookhaven National Laboratory

Motivation Data Analysis Results Conclusions
2
Motivation - I

• In-medium modification of mass and/or width ?
  Chiral Symmetry Restoration, Collision Broadening
  or Phase Space?
• ?0(770) ? Leptonic decay channel ? probes all
  stages of the collision. Hadronic decay channel ?
  probes only late stages of the collision
• F ? Information from early time ?
• f0(980) ? KK molecule (bound state) ? insight
  strangeness behavior in relativistic collisions
• K0(892) ? Regeneration and daughter rescattering
  ? time scale ?

?0 c? 1.3 fm
F c? 44 fm
3
Motivation - II

• If resonance decays before kinetic freeze-out ?
  not reconstructed due to rescattering of
  daughters
• K0 (c? 4 fm) survival probability ? time
  between chemical and kinetic freeze-out, source
  size and pT of K0
• Chemical freeze-out ? elastic interactions pK ?
  K0? pK regenerate K0(892) until kinetic
  freeze-out
• K0/K may reveal time between chemical and
  thermal freeze-out
• ?/?, ?0/p, f0/p ?

4
Resonance Production at RHIC

• ?0(770) ? p p- B.R. 1 c? 1.3 fm
• K0(892) ? p K B.R. 2/3 c? 4 fm
• f0(980) ? p p- B.R. 2/3 c? 2.6 fm
• F(1020) ? K K- B.R. 0.492 c? 44 fm
• F(1020) ? e e- B.R. 0.000296 c? 44 fm
• ?(1520) ? p K B.R. 0.45 c? 12.6 fm
• y 0.5
• Mixed Event or Like Sign Technique

5
Raw Invariant Mass Distribution from Data
P. Fachini, L. Gaudichet, J. Ma, C. Maguire, H.
Zhang SQM2003
Statistical error only
pp
pp
40-80 AuAu
K0
STAR Preliminary
J. Adams et al. nucl-exp/0307023
J. Adams et al. nucl-exp/0307023
STAR
STAR
pp
AuAu
AuAu
F
STAR Preliminary
STAR Preliminary
?sNN 200 GeV
K0
F
ylt0.5
STAR Preliminary
AuAu
AuAu
pp
60-80 AuAu
PHENIX Preliminary
STAR Preliminary
PHENIX Preliminary
STAR Preliminary
F?KK-
F?ee-
?(1520)
?(1520)
Invariant Mass (GeV/c2)
Invariant Mass (GeV/c2)
Invariant Mass (GeV/c2)
Invariant Mass (GeV/c2)
6
K0 Mass and Width
H. Zhang, SQM2003
STAR Preliminary
STAR Preliminary
?sNN 200 GeV
ylt0.5

• K0 mass ? shifted in pp and AuAu at low pT
• K0 width ? agrees with the MC (GEANT)
  calculation
• Systematic and statistical error added in
  quadrature

7
Phase Space
P. Braun-Munzinger et.al., CERES Int. Note, March
2000, unpublished E.V. Shuryak and G.E. Brown,
Nucl. Phys. A 717 (2003) 322 P.K. Kolb and M.
Prakash, nucl-th/0301007 H.W. Barz et al., Phys.
Lett. B 265, 219 (1991) R. Rapp, hep-ph/0305011.

• M Invariant Mass pT transverse momentum T
  Temperature
• pp ? particle composition reasonably reproduced
  by statistical model ? T 160 MeV
• F. Becattini, Nucl. Phys. A 702, 336 (2002) Z.
  Phys. C 69, 485 (1996) F. Becattini and U.
  Heinz, Z. Phys. C 76, 269 (1997)
• AuAu ? between chemical and kinetic freeze-out ?
  resonances formed until particles too far apart ?
  resonances emitted T 120 MeV
• E.V. Shuryak and G.E. Brown, Nucl. Phys. A 717
  (2003) 322

8
?0 Mass
J. Adams et al. nucl-exp/0307023

• pp at ?s 27.5 GeV ? M? 762.6 2.6 MeV/c2
• PDG average hadroproduced ?0 ? M? 769.0 0.9
  MeV/c2
• PDG average ee- ? ? M? 775.9 0.5 MeV/c2
• ?0 mass pt dependent and lower than previous pp
  measurement in both pp and peripheral AuAu
  collisions
• ?0 mass high multiplicity pp lower than minimum
  bias pp ? multiplicity dependent
• Systematic errors ? common and correlated between
  pp and peripheral AuAu
• ?0 width ? no sensitivity for systematic study

10 of minimum bias pp for ?lt0.5
?sNN 200 GeV
ylt0.5
9
Mass Shift

• Dynamical Effect
  
  E.V. Shuryak and G.E. Brown, Nucl. Phys. A 717
  (2003) 322 R. Rapp, hep-ph/0305011.
• ?0 interactions at late stages of the collision
• nucleons, hyperons and baryon resonances
• pions, kaons and ?0-mesons
• t-channel exchanges
• ? Distortion of the ?0 spectral shape ?
  mass shift and/or broadening
• Interference between various pp- scattering
  channels R. Longacre,
  nucl-exp/0305015
• Bose-Einstein correlations between ?0 decay
  daughters and pions in the surrounding matter
  
  G.D. Lafferty, Z. Phys. C 60, 659
  (1993) R. Rapp, hep-ph/0305011 S. Pratt et al.,
  nucl-th/0308087.

-23 MeV/c2 shift in the ?0 mass
-38 MeV/c2 shift in the ?0 mass due to t-channel
attraction
10
Spectra
J. Adams et al. nucl-exp/0307023
J. Ma, SQM2003
H. Zhang, SQM2003
P. Fachini, SQM2003
K0
F
?0 f0
STAR Preliminary
STAR Preliminary
STAR Preliminary
Statistical error only
?sNN 200 GeV
ylt0.5
L. Gaudichet, SQM2003

• AuAu ? spectra fit to exponential in mT-m0
• pp ? spectra fit to power-law ? contribution
  pQCD processes larger than soft processes ?

?(1520)
pp
STAR Preliminary
11
Particle Ratios
M. Bleicher et al. J. Phys. G 25 (1999) 1859
J. Adams et al. nucl-exp/0307023
P. Fachini SQM2003
J. Ma SQM2003
L. Gaudichet, SQM2003
H. Zhang SQM2003
STAR Preliminary
Statistical and systematic errors added in
quadrature

• F/K- independent of centrality ? F not produced
  via kaon coalescence ?
• Cross-section ? regeneration or rescattering ?

12
ltpTgt Charged Particle Dependence
H. Zhang, SQM2003
J. Ma, SQM2003
H. Zhang, SQM2003
J. Ma, SQM2003
Statistical and systematic errors added in
quadrature
STAR Preliminary
STAR Preliminary

• F and K0 ? No centrality dependence
• F ? Flows differently ?
• K0 ? Rescattering dominates at peripheral
  collisions and regeneration becomes significant
  for central collisions ?

13
Thermal Models
Chemical freeze-out
Kinetic freeze-out
Chemical kinetic freeze-out
m?770MeV
m?700MeV
?sNN 200 GeV

• Short-lived resonances ? Kinetic freeze-out ?

Statistical and systematic errors added in
quadrature
14
Conclusions

• Significant resonance production measured from
  hadronic interactions from RHIC data at ?sNN
  200 GeV
• ?0 and K0 ? mass shift observed even after phase
  space correction in pp and AuAu collisions
• Lower mass expected due to in-medium
  modifications, interference and Bose-Einstein
  correlations ?
• F/K- independent of centrality ? F not produced
  via kaon coalescence ?
• Short-lived resonances ? Regeneration and
  rescattering ? driven by hadronic cross sections
  ?
• Resonances can provide information on the
  collision dynamics