1. STAR Patricia Fachini 1 Brookhaven National Laboratory Motivation Data Analysis Results Conclusions Resonance Production in Au+Au and p+p Collisions at  s NN =200 GeV

2. STAR Patricia Fachini 2 Motivation - I In-medium modification of mass and/or width  Chiral Symmetry Restoration, Collision Broadening or Phase Space? ρ 0 (770)  Leptonic decay channel  probes all stages of the collision. Hadronic decay channel  probes only late stages of the collision Φ  Information from early time ? f 0 (980)  KK molecule (bound state)  insight strangeness behavior in relativistic collisions K *0 (892)  Regeneration and daughter rescattering  time scale ? ρ0ρ0 ρ0ρ0 π-π- π+π+ π+π+ π-π- ρ 0 c  = 1.3 fm ρ0ρ0 ρ0ρ0 + + - - π-π- π+π+ ρ0ρ0 - + Φ c  = 44 fm

3. STAR Patricia Fachini 3 Motivation - II If resonance decays before kinetic freeze-out  not reconstructed due to rescattering of daughters K *0 (c  = 4 fm) survival probability  time between chemical and kinetic freeze-out, source size and p T of K *0 Chemical freeze-out  elastic interactions πK  K *0  πK regenerate K *0 (892) until kinetic freeze-out K *0 /K may reveal time between chemical and thermal freeze-out Λ * /Λ, ρ 0 /π, f 0 /π ? Chemical freeze-out Kinetic freeze-out K * lost K * measured π π K K*K* K K*K* K*K* π K π π K*K* K K

4. STAR Patricia Fachini 4  0 (770)  π + π - B.R. ~1c  = 1.3 fm K *0 (892)  π K B.R. 2/3c  = 4 fm f 0 (980)  π + π - B.R. 2/3c  = 2.6 fm Φ(1020)  K + K - B.R. 0.492c  = 44 fm Φ(1020)  e + e - B.R. 0.000296c  = 44 fm Λ(1520)  p K B.R. 0.45 c  = 12.6 fm |y| ≤ 0.5 Mixed Event or Like Sign Technique Resonance Production at RHIC

5. STAR Patricia Fachini 5 Raw Invariant Mass Distribution from Data P. Fachini, L. Gaudichet, J. Ma, C. Maguire, H. Zhang SQM2003 Invariant Mass (GeV/c 2 ) p+p Au+Au STAR Preliminary PHENIX Preliminary K *0 Φ Φ ΦK+K-ΦK+K- Φe+e-Φe+e- Statistical error only J. Adams et al. nucl-exp/0307023 STAR p+p 40%-80% Au+Au J. Adams et al. nucl-exp/0307023 STAR K *0 STAR Preliminary |y|<0.5  s NN = 200 GeV Au+Au STAR Preliminary Λ(1520) p+p60%-80% Au+Au STAR Preliminary Λ(1520)

6. STAR Patricia Fachini 6 K *0 Mass and Width K *0 mass  shifted in p+p and Au+Au at low p T K *0 width  agrees with the MC (GEANT) calculation Systematic and statistical error added in quadrature H. Zhang, SQM2003 STAR Preliminary |y|<0.5  s NN = 200 GeV

7. STAR Patricia Fachini 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 Note, March 2000, unpublished; E.V. Shuryak and G.E. Brown, Nucl.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. ρ0ρ0 π-π- π+π+ π-π- π+π+ M = Invariant Mass; p T = 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 emitted T = 120 MeV E.V. Shuryak and G.E. Brown, Nucl. Phys. A 717 (2003) 322 e -  M 2 + p T 2 T M  M 2 + p T 2 Phase Space = BW(M) = Γ(M) (M 2 – M  2 ) 2 + M  2 Γ(M) 2 Γ(M) = Γ ρ M 2 – 4m π 2 M ρ 2 – 4m π 2 3 2 MρMρ M

8. STAR Patricia Fachini 8 ρ 0 Mass J. Adams et al. nucl-exp/0307023 p+p at  s = 27.5 GeV  M  = 762.6 ± 2.6 MeV/c 2 PDG average hadroproduced ρ 0  M  = 769.0 ± 0.9 MeV/c 2 PDG average e + e - ρ  M  = 775.9 ± 0.5 MeV/c 2 ρ 0 mass p t dependent and lower than previous p+p measurement in both p+p and peripheral Au+Au collisions ρ 0 mass high multiplicity p+p lower than minimum bias p+p  multiplicity dependent Systematic errors  common and correlated between p+p and peripheral Au+Au ρ 0 width  no sensitivity for systematic study 10% of minimum bias p+p for |η|<0.5 |y|<0.5  s NN = 200 GeV

9. STAR Patricia Fachini 9 Mass Shift… Dynamical Effect E.V. Shuryak and G.E. Brown, Nucl. Phys. A 717 (2003) 322; R. Rapp, hep-ph/0305011. –ρ 0 interactions at late stages of the collision nucleons, hyperons and baryon resonances pions, kaons and ρ 0 -mesons t-channel exchanges  Distortion of the ρ 0 spectral shape  mass shift and/or broadening Interference between various π + π - scattering channels R. Longacre, nucl-exp/0305015 Bose-Einstein correlations between ρ 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/c 2 shift in the ρ 0 mass -38 MeV/c 2 shift in the ρ 0 mass due to t-channel attraction

10. STAR Patricia Fachini 10 Spectra Au+Au  spectra fit to exponential in m T -m 0 p+p  spectra fit to power-law  contribution pQCD processes larger than soft processes ? P. Fachini, SQM2003 J. Adams et al. nucl-exp/0307023 L. Gaudichet, SQM2003 STAR Preliminary Λ(1520) pp ρ0 f0 ρ0 f0 Φ J. Ma, SQM2003 STAR Preliminary H. Zhang, SQM2003 K*0K*0 STAR Preliminary Statistical error only STAR Preliminary  s NN = 200 GeV |y|<0.5

11. STAR Patricia Fachini 11 Φ/K - independent of centrality  Φ not produced via kaon coalescence ? Cross-section  regeneration or rescattering ? M. Bleicher et al. J. Phys. G 25 (1999) 1859 Particle Ratios STAR Preliminary J. Adams et al. nucl-exp/0307023 H. Zhang SQM2003 L. Gaudichet, SQM2003 J. Ma SQM2003 P. Fachini SQM2003 Statistical and systematic errors added in quadrature

12. STAR Patricia Fachini 12 Φ and K *0  No centrality dependence Φ  Flows differently ? K *0  Rescattering dominates at peripheral collisions and regeneration becomes significant for central collisions ? H. Zhang, SQM2003 J. Ma, SQM2003 H. Zhang, SQM2003 J. Ma, SQM2003 STAR Preliminary Charged Particle Dependence Statistical and systematic errors added in quadrature

13. STAR Patricia Fachini 13 Thermal Models Short-lived resonances  Kinetic freeze-out ? Chemical freeze-out Kinetic freeze-out Chemical = kinetic freeze-out m ρ =700MeV m ρ =770MeV f0f0 π-π- ρ0ρ0 π-π- K *0 K-K- Φ K-K- Λ(1520) Λ Statistical and systematic errors added in quadrature  s NN = 200 GeV

14. STAR Patricia Fachini 14 Significant resonance production measured from hadronic interactions from RHIC data at  s NN = 200 GeV ρ 0 and K *0  mass shift observed even after phase space correction in p+p and Au+Au collisions Lower mass expected due to in-medium modifications, interference and Bose-Einstein correlations ? Φ/K - independent of centrality  Φ not produced via kaon coalescence ? Short-lived resonances  Regeneration and rescattering  driven by hadronic cross sections ? Resonances can provide information on the collision dynamics Conclusions