Patricia Fachini Brookhaven National Laboratory for the STAR Collaboration

1. STAR ρ0(770) and f0(980) Production in Au + Au and pp Collisions at sNN=200 GeV Patricia Fachini Brookhaven National Laboratory for the STAR Collaboration Motivation Data Analysis Results Conclusions Patricia Fachini Strange Quark Matter 2003

2. π- ρ0 π+ ρ0 ρ0 ρ0 π- π+ π- ρ0 + + + π+ - - - Motivation • ρ0(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 onlylate 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 ρ0(770) π+π-(B.R. 1) and f0(980) π+π-(B.R. 2/3) at |y|  0.5 ρ0 c = 1.3 fm f0 c ~ 2.6 fm Patricia Fachini Strange Quark Matter 2003

3. K0Sπ+π- ω(782) (π+π-) π0and π+ π- K0S ω η (π+π-) π0 and (π+π-) η’ (π+π-)ηand (π+π-) ρ0 η + η’ K*(892)0 Kπwith K misidentified as π K*0 + K*0misidentified π+π- Invariant Mass Distribution from Monte Carlo • HIJING events with a realistic simulation of TPC response STAR Preliminary ρ0(770)  π+π- sNN= 200 GeV ρ0 • Use ωandK*0shape from HIJING to fit the data • K*0signal is fixed using our measurement Patricia Fachini Strange Quark Matter 2003

4. π+π- Raw Invariant Mass Distribution from Data Au+Au 40% to 80% Minimum Bias pp sNN = 200 GeV ρ0 f0 K0S ωK*0f2 ρ0 f0K0S ωK*0 STAR Preliminary STAR Preliminary counts/(10 MeV/c2) 1.2 pT 1.4 GeV/c |y|  0.5 0.8 pT 0.9 GeV/c |y|  0.5 Statistical error only Statistical error only • 1.2106 peripheral Au+Au events and 1.1107 minimum bias pp events • Follow previous e+e- and pp measurements that do not extract l = 1 ρ0 production • Relativistic Breit-Wigner  Phase Space fixed width ρ0Г = 160 MeV and f0Г = 75 MeV nominal width + detector resolution • f0massfixed  M ~ 980 MeV/c2 Patricia Fachini Strange Quark Matter 2003

5. Phase Space = π+ ρ0 π+ π- π- -  M2 + pT2 M e T  M2 + pT2 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 Note, March 2000, unpublished; E.V. Shuryak and G.E. Brown, hep-ph/0211119; P.K. Kolb and M. Prakash, nucl-th/0301007; H.W. Barz et.al., Phys.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) • Au+Au between chemical and kinetic freeze-out  resonances formed until particles too far apart  resonances emittedT = 120 MeV E.V. Shuryak and G.E. Brown, hep-ph/0211119 Patricia Fachini Strange Quark Matter 2003

6. ρ0Mass STAR Preliminary BW  PS BW STAR Preliminary |y|  0.5 |y|  0.5 Statistical errors only Statistical errors only ρ0mass 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 ρ0 M= 769.0  0.9 MeV/c2 • PDG average e+e-ρ M= 775.9  0.5 MeV/c2 • ρ0 mass pt dependent and systematically lower than previous pp measurement in both minimum bias pp and peripheral Au+Au collisions Patricia Fachini Strange Quark Matter 2003

7. ρ0Mass Minimum Bias pp Peripheral Au+Au STAR Preliminary STAR Preliminary ρ0mass 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 π+π- invariant mass distribution • Systematic errors  correlated between minimum bias pp and peripheral Au+Au Patricia Fachini Strange Quark Matter 2003

8. π π a1 ρ ρ 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)… • ρ0interacting with surrounding matter  lower ρ0mass ~60  18 MeV/c2 in AuAu collisions • No apparent width modification STARmeasurement  No resolution for systematic study of ρ0width Patricia Fachini Strange Quark Matter 2003

9. BW  PS Transport Model - UrQMD M. Bleicher, hep-ph/0212378 Au+Au Au+Au 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 Au+Au ρ0 mass shifted ~30 MeV at low pT • ρ0 shape reproduced by p-wave Breit-Wigner  Phase Space • M = 765.6  0.4MeV/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 Г= 150 MeV Patricia Fachini Strange Quark Matter 2003

10. π+ π+ π+ ρ0 ρ0 A A D π- π- π- π+ A π- Partial-Wave Analysis R. Longacre, to be published ρ0 f0 K0S ωK*0f2 ρ0 f0 K0S ωK*0f2 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 + π+π-scattering reproduce 0 mass measured in minimum bias pp • M= 779.1 MeV/c2Г= 150 MeV/c2 • Distance of interaction in π+π-scattering 1/3 fm T = 180 MeV Interference Patricia Fachini Strange Quark Matter 2003

11. ρ0 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 Au+Au |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 Patricia Fachini Strange Quark Matter 2003

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 Au+Au |y|  0.5 dN/dy = 1.370  0.063(stat)  0.685(syst) Inverse Slope = 341  13(stat)  102(syst)MeV Statistical error only Strongly dependent on 0 spectral shape Patricia Fachini Strange Quark Matter 2003

13. ρ0/π and f0/πEnergy and System Dependence STAR Preliminary STAR Preliminary • ρ0 production increases with sNN • ρ0/π-inpp and Au+Au at sNN = 200 GeV comparable • f0 andf0/π- similar behavior? • STAR measurement statistical and systematic errors added in quadrature Patricia Fachini Strange Quark Matter 2003

14. Conclusions • Significantρ0(770) and f0(980)production observed from hadronic interactions from RHIC data at sNN= 200 GeV • First ρ0(770) and f0(980) measurements indication production increases with sNN • ρ0/π-inpp and peripheral Au+Au at sNN= 200 GeV comparable • Minimum bias pp and peripheral Au+Au at sNN= 200 GeV ρ0 mass systematically lower than previous pp measurement at sNN= 27.5 GeV even after phase space correction • Lower ρ0 mass expected due to dynamic interactions with matter • UrQMD central Au+Au at sNN= 200 GeV  ρ0 mass shifted and ρ0 shape p-wave Breit-Wigner  Phase Space • Partial-wave analysis + π-π+scattering reproduce ρ0 mass measured in ppat sNN= 200 GeV  what about Au+Au? • Short-lived resonancescan provide information on the collision dynamics Patricia Fachini Strange Quark Matter 2003

15. ρ0 ρ0 π- π- Th Au+Au = = 1.06  0.22 ρ0 ρ0 π- π- pp Ch ρ0/π- Double Ratio [3+exp(0.63/Tch)]/[3+exp(0.63/Tth)] STAR Preliminary [3+exp(0.63/Tch)]/[3+exp((0.63-0.1)/Tth)] [3+exp(0.63/Tch)]/[3+exp((0.63-0.12)/Tth)] Patricia Fachini Strange Quark Matter 2003