Patricia Fachini

1
?0(770) and f0(980) Production 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

• ?0(770) ? In-medium modification of mass and/or
  width ? Chiral Symmetry Restoration, Collision
  Broadening or Phase Space?
• Leptonic decay channel ? probes all stages of the
  collision
• Hadronic decay channel ? probes only late stages
  of the collision
• Regeneration and daughter rescattering ? time
  scale
• f0(980) ? KK molecule (bound state) ? insight
  strangeness behavior in relativistic collisions
• STAR
• Measure hadronic decay mode of ?0(770) ? p p-
  (B.R. 1) and f0(980) ? p p- (B.R. 2/3) at y
  ? 0.5

?0 c? 1.3 fm
f0 c? 2.6 fm
3
pp- Invariant Mass Distribution from Monte Carlo

• HIJING events with a realistic simulation of
  TPC response

STAR Preliminary
?0(770) ? p p-
?sNN 200 GeV
?0

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

4
pp- Raw Invariant Mass Distribution from Data
AuAu 40 to 80
Minimum Bias pp
?sNN 200 GeV
?0 f0 K0S ? K0f2
STAR Preliminary
?0 f0 K0S ? K0
STAR Preliminary
counts/(10 MeV/c2)
0.8 ? pT ? 0.9 GeV/c y ? 0.5
1.2 ? pT ? 1.4 GeV/c y ? 0.5
Statistical error only
Statistical error only

• 1.2?106 peripheral AuAu events and 1.1?107
  minimum bias pp events
• Follow previous ee- and pp measurements that do
  not extract l 1 ?0 production
• Relativistic Breit-Wigner ? Phase Space ? fixed
  width ? ?0 ? 160 MeV and f0 ? 75 MeV ?
  nominal width detector resolution
• f0 mass fixed ? M 980 MeV/c2

5
Phase Space
P. Braun-Munzinger et.al., CERES Int. Note, March
2000, unpublished E.V. Shuryak and G.E. Brown,
hep-ph/0211119 P.K. Kolb and M. Prakash,
nucl-th/0301007 H.W. Barz et.al., Phys. Lett. B
265, 219 (1991).

• 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, hep-ph/0211119

6
?0 Mass
STAR Preliminary
BW
BW ? PS
STAR Preliminary
y ? 0.5
y ? 0.5
Statistical errors only
Statistical errors only
?0 mass measured in pp at ?s 27.5 GeV (pT ? 0
and xF ? 0) M. Aguilar-Benitez et.al., Z. Phys.
C50, 405 (1991)

• 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 systematically lower
  than previous pp measurement in both minimum bias
  pp and peripheral AuAu collisions

7
?0 Mass
Peripheral AuAu
Minimum Bias pp
STAR Preliminary
STAR Preliminary
?0 mass measured in pp at ?s 27.5 GeV (pT ? 0
and xF ? 0) M. Aguilar-Benitez et.al., Z. Phys.
C50, 405 (1991)

• Statistical and systematic errors added in
  quadrature
• Systematic errors ? dominated by uncertainty in
  describing the correlations in the pp- invariant
  mass distribution
• Systematic errors ? correlated between minimum
  bias pp and peripheral AuAu

8
Dynamical Effects
E.V. Shuryak and G.E. Brown, hep-ph/0211119

• t-channel scalar attraction (Brown-Rho Scaling)
• G.E. Brown and M. Rho, Phys. Rev. Lett. 66, 2720
  (1991)
• Interaction with s-channel resonances ? a1(1260),
  a2(1320)
• ?0 interacting with surrounding matter ? lower ?0
  mass 60 ? 18 MeV/c2 in AuAu collisions
• No apparent width modification
• STAR measurement ? No resolution for systematic
  study of ?0 width

9
Transport Model - UrQMD
M. Bleicher, hep-ph/0212378
AuAu
AuAu
b ? 3 fm
b ? 3 fm
?0
?0
?sNN 200 GeV
0.2 ? pT ? 0.4 GeV/c y ? 0.5
1.2 ? pT ? 1.4 GeV/c y ? 0.5
M? 769 MeV/c2

• Central AuAu ? ?0 mass shifted 30 MeV at low pT
• ?0 shape reproduced by p-wave Breit-Wigner ?
  Phase Space
• M? 765.6 ? 0.4 MeV/c2 for 0.2 ? pT ? 0.4 GeV/c
• M? 761.2 ? 0.9 MeV/c2 for 1.2 ? pT ? 1.4 GeV/c
• M? 769 MeV/c2 input

? 150 MeV
10
Partial-Wave Analysis
R. Longacre, to be published
?0 f0 K0S ? K0f2
?0 f0 K0S ? K0f2
pp Minimum Bias
pp Minimum Bias
STAR Preliminary
STAR Preliminary
counts/(10 MeV/c2)
1.9 ? pT ? 2.0 GeV/c y ? 0.5
0.3 ? pT ? 0.4 GeV/c y ? 0.5
Statistical error only
Statistical error only

• Partial-wave analysis pp- scattering reproduce
  ?0 mass measured in minimum bias pp
• M? 779.1 MeV/c2 ? 150
  MeV/c2
• Distance of interaction in pp- scattering ? 1/3
  fm

T 180 MeV
Interference
11
?0 Spectra
STAR Preliminary
Minimum Bias pp
dN/dy 0.2450 ? 0.0016(stat) ? 0.0368(syst)
?pT? 0.6414 ? 0.0029(stat) ? 0.0641(syst) MeV/c
y ? 0.5
Statistical error only
Contribution pQCD processes larger than soft
processes?
STAR Preliminary
Peripheral AuAu
y ? 0.5
dN/dy 5.914 ? 0.104(stat) ? 1.717(syst) Inverse
Slope 318.9 ? 3.9(stat) ? 16.0(syst) MeV
Statistical error only
12
f0 Spectra
STAR Preliminary
Minimum Bias pp
dN/dy 0.0397 ? 0.0009(stat) ? 0.0199(syst)
?pT? 0.654 ? 0.010(stat) ? 0.196(syst) MeV/c
y ? 0.5
Statistical error only
Contribution pQCD processes larger than soft
processes?
STAR Preliminary
Peripheral AuAu
dN/dy 1.370 ? 0.063(stat) ? 0.685(syst)
Inverse Slope 341 ? 13(stat) ? 102(syst) MeV
y ? 0.5
Statistical error only
Strongly dependent on ?0 spectral shape
13
?0/p and f0/p Energy and System Dependence
STAR Preliminary
STAR Preliminary

• ?0 production increases with ?sNN
• ?0/p- in pp and AuAu at ?sNN 200 GeV
  comparable
• f0 and f0/p- ? similar behavior?
• STAR measurement ? statistical and systematic
  errors added in quadrature

14
Conclusions

• Significant ?0(770) and f0(980) production
  observed from hadronic interactions from RHIC
  data at ?sNN 200 GeV
• First ?0(770) and f0(980) measurements ?
  indication production increases with ?sNN
• ?0/p- in pp and peripheral AuAu at ?sNN 200
  GeV comparable
• Minimum bias pp and peripheral AuAu at ?sNN
  200 GeV ? ?0 mass systematically lower than
  previous pp measurement at ?sNN 27.5 GeV even
  after phase space correction
• Lower ?0 mass expected due to dynamic
  interactions with matter
• UrQMD central AuAu at ?sNN 200 GeV ? ?0 mass
  shifted and ?0 shape p-wave Breit-Wigner ? Phase
  Space
• Partial-wave analysis p-p scattering ?
  reproduce ?0 mass measured in pp at ?sNN 200
  GeV ? what about AuAu?
• Short-lived resonances can provide information on
  the collision dynamics

15
?0/p- Double Ratio
3exp(0.63/Tch)/3exp(0.63/Tth)
STAR Preliminary
3exp(0.63/Tch)/3exp((0.63-0.12)/Tth)
3exp(0.63/Tch)/3exp((0.63-0.1)/Tth)