Patricia Fachini

1
?0(770), K(892)0 and f0(980) Productions in Au
Au and pp Collisions at ?sNN200 GeV

• Patricia Fachini
• Brookhaven National Laboratory
• for the STAR Collaboration

Motivation Data Analysis Results Conclusions
2
Motivation

• Why measure short-lived resonances?
• Lifetimes comparable to lifetime of dense matter
  (few fm) ? resonance properties sensitive to
  lifetime of dense matter
• K0/K sensitive to mass modification and dynamic
  evolution of source
• Comparison to other resonances and particles ?
  information on chemical and thermal freeze-out
  conditions (thermal models)
• If resonance decay inside dense matter before
  kinetic freeze-out ? not reconstructed due to
  re-scattering of daughters ? probe time between
  chemical and kinetic freeze-out
• Resonance v2 ? momentum space ? comparison
  hadrons v2 ? information on the geometry of the
  system
• STAR
• Measure hadronic decay mode of K0(892) ? ? K
  (B.R. 2/3), ?0(770) ? ? ?- (B.R. 1) and f0(980)
  ? ? ?- (B.R. 2/3) at y ? 0.5

3
? ?- Invariant Mass Distribution from Monte Carlo

• HIJING events with a realistic simulation of
  TPC response
• ?0(770) ? ? ?-

STAR Preliminary
?sNN 200 GeV
?0

• Use ? and K0 shape from HIJING to fit the
  data
• K0 signal is fixed using our measurement

4
? ?- Invariant Mass Distribution from Data
pp
AuAu 40 to 80
STAR Preliminary
STAR Preliminary
?sNN 200 GeV
0.2 ? pT ? 0.8 GeV/c y ? 0.5
?0 f0 K0S ? K0
?0 f0 K0S ? K0
0.2 ? pT ? 0.9 GeV/c y ? 0.5
Statistical error only
Statistical error only

• 2.1?106 AuAu minimum bias events and 4.7?106 pp
  events
• Follow previous ee- and pp measurements that do
  not extract l 1 ?0 production
• Breit-Wigner ? fixed width ? ?0 ? 150 MeV and
  f0 ? 75 MeV
• ?0 and f0 masses ? working on understanding of
  scale ? pT vs. mT

5
K ? Invariant Mass Distribution from Data
STAR Preliminary
STAR Preliminary
pp
0.2 ? K pT ? 0.75 GeV/c ? pT ? 0.2 GeV/c y ?
0.5
?sNN 200 GeV
AuAu minimum bias
pT ? 0.2 GeV/c y ? 0.5
Statistical error only
Statistical error only

• 2.1?106 AuAu minimum bias events and 4.7?106 pp
  events
• Breit-Wigner ? K0 ? 50 MeV and K0 mass 896
  MeV fixed
• K0/K0 0.93 0.10 (stat) ? K0/K0 ? 1
  within error ? (K0K0 )/2

6
(K0 K0 )/2 MT Spectra
STAR Preliminary
pp
Statistical error only
y ? 0.5
y ? 0.5
Statistical error only
AuAu
STAR Preliminary
pp ? not corrected for trigger bias and vertex
finding efficiency
7
?0(770) and f0(980) MT Spectra
STAR Preliminary
STAR Preliminary
Yield 6.59 ? 1.08 Inverse Slope 163 ? 63 MeV
y ? 0.5
Statistical error only
pp
y ? 0.5
AuAu 40 to 80
?0
Yield 0.264 ? 0.021 Inverse Slope 137 ? 16
MeV
?0
Statistical error only
STAR Preliminary
Yield 1.73 ? 0.96 Inverse Slope 200 ? 177 MeV
STAR Preliminary
Statistical error only
pp
y ? 0.5
y ? 0.5
Yield 0.034 ? 0.017 Inverse Slope 162 ? 132
MeV
f0
f0
AuAu 40 to 80
Statistical error only
pp ? not corrected for trigger bias and vertex
finding efficiency
8
?0/? and f0/? Energy and System Dependence
STAR Preliminary
STAR Preliminary

• ?0/? and f0/? ? follow ee- and pp trend ?
  indication ?0 and f0 productions increase with
  ?sNN
• STAR measurement ? statistical error only

9
K0/?- Energy and System Dependence

• AuAu K0/?- at RHIC ? comparable to those at
  pp and ee- ? no enhancement in contradiction to
  other strange particles (K, ?, ?, ?, ?)
• ?sNN 130 GeV at RHIC ? statistical and
  systematic errors added in quadrature
• ?sNN 200 GeV at RHIC ? statistical error
  only

STAR Preliminary
10
K0/K Energy and System Dependence

• K0 ? JP 1-
• K ? JP 0-
• K0 and K ? similar quark content and
  different spin
• ?sNN 200 GeV at RHIC ? AuAu K0/K lower
  than pp K0/K by a factor of 2!
• pp at RHIC ? statistical error only
• AuAu at RHIC ? statistical and systematic
  errors added in quadrature

STAR Preliminary
11
?/K0 Energy and System Dependence

• ?/K0 ? measures strangeness suppression in
  elementary collisions ? small mass difference and
  ?S 1
• ?/K0 AuAu at RHIC ? increase compared to pp
  and ee-
• Strangeness Enhancement ? not that simple
  due to additional effects on short-lived
  resonances in heavy ion collisions

STAR Preliminary

• ?sNN 130 GeV ? statistical and systematic
  errors added in quadrature
• ?sNN 200 GeV ? statistical error only

12
K0 Survival Probability

• K0 (c? 4 fm) survival probability ? time
  between chemical and kinetic freeze-out, source
  size and pT of K0
• Chemical freeze-out ? elastic interactions ?K ?
  K0? ?K regenerate K0(892) until kinetic
  freeze-out
• Difference K0/K in AuAu and pp ? K0 survival
  probability ? consistent with short time
• Long time ? only if K0 regeneration is assumed ?
  K0/K cannot be used in thermal fits (chemical
  freeze-out)

13
K0 Elliptic Flow v2
K
STAR Preliminary
Statistical error only
?
STAR Preliminary

• No daughters re-scattering ? K0 v2 hadrons
  v2
• Daughters re-scattering ? K0 v2 sensitive
  coordinate phase space

Statistical error only
14
Conclusions

• Significant ?0(770), K0(892) and f0(980)
  productions observed from hadronic interactions
  from RHIC data at ?sNN 200 GeV
• First ?0(770) and f0(980) measurements ?
  indication productions increase with ?sNN
• K0/?- comparable to those at pp and ee- ? no
  enhancement observed in contradiction to other
  strange particles (K, ?, ?, ?, ?)
• ?/K0 from AuAu higher than those at pp and ee-
  ? information on strangeness enhancement and
  re-scattering
• AuAu K0/K lower than pp K0/K by a factor of 2
  at ?sNN 200 GeV ? consistent with short time
  (few fm)
• K0(892) production at RHIC ? rule out long time
  (20 fm) without regeneration
• First K0(892) v2 measurement
• Short-lived resonances can provide information on
  the collision dynamics

15
Backup Slides
16
Scale ? pT vs. mT
STAR Preliminary
pT
mT
STAR Preliminary
STAR Preliminary
Breit Wigner Mass 770 MeV
? 150 MeV
Breit Wigner fit Invariant Mass from pp
17
? ?- Invariant Mass Distribution from Monte Carlo

• HIJING events with a realistic simulation of
  TPC response
• protons and Kaons misidentified as pions
• ?sNN 200 GeV

STAR Preliminary