1. Hadronic resonance production in Pb+Pb collisions from the ALICE experiment Anders Knospe on behalf of the ALICE Collaboration The University of Texas at Austin 29 May 2012

2. Outline Introduction  Yield K* 0 Mass and Width Hadron-Resonance Correlations Summary 2

3. Introduction 3 Temperature and Lifetime of Fireball –Resonance formation through recombination –Rescattering prevents resonance reconstruction –Statistical Model, UrQMD, fit to resonance/non-resonance ratios Chiral Symmetry Restoration –Resonances can be produced with jets in QGP –Produced off-shell or interact with medium  mass shift –Interactions with medium  width broadening (reduced lifetime) For T=250 MeV:  lifetime may change by up to factor of 10* G. Torrieri and J. Rafelski, Phys. Lett. B 509 239 (2001) Statistical Model * L. Holt and K. Haglin, J. Phys. G31, S245 (2005)

4. Hadron-Resonance Correlations 4 To probe QGP: compare resonances that passed through medium with those that did not –Hadron-resonance correlations jet, leading hadron Resonance in near side: no medium interaction Resonance in away side: Low p T (below ~2 GeV/c): dominated by interactions in hadronic medium High p T : dominated by interactions with early hadronic or partonic medium Resonance transverse to jet: Thermal production in hadronic medium Method proposed by: C. Markert, R. Bellwied, I. Vitev, Phys. Lett. B 669 92-97 (2008)

5.  Yield

6. Event & Track Selection 6 Pb+Pb collisions at √s NN =2.76 TeV –9.5 M events –|v z | < 10 cm   K - K + (B.R.=0.489) PID with TPC dE/dx: |n  K |<2 TPC: PID and Tracking ITS: Tracking Centrality estimate: from measurement of multiplicity in V0 detector (scintillator arrays on each side of collision vertex)

7. Signal Extraction 7 Invariant mass –|y pair |<0.5 Combinatorial Background –Event Mixing (default) –Like-Sign Residual Background Fit: polynomial Yield: integrate histogram, subtract residual background Peak Fit: res. back. + BW peak –Find yield, mass, width BACKGROUND SUBTRACTION Background Fit Region (exact boundaries varied)  Analysis

8. Uncorrected  Yields Statistics up to p T ~10 GeV/c Coming for Quark Matter: –Corrected Spectra –dN/dy –Ratios:  / ,  /K 8 Uncorrected  Yields

9. Particle Ratios 9  /  : –NA49 (17.5 GeV) and STAR (200 GeV): A+A higher than p+p –PHENIX 200 GeV Au+Au  /  = 0.015 ± 0.003 lower than STAR Au+Au Consistent with STAR and ALICE p+p –Ratio for p+p appears to saturate at LHC energies: Is this also true for A+A?  /K: A single trend for both p+p and A+A over a wide energy range –Will Pb+Pb agree? –Au+Au 200 GeV: PHENIX  /K = 0.0911 ± 0.021 STAR higher than PHENIX Lower energy: see PRC 71 064902 (2005) and PRC 79 064903 (2009) ? ?

10. K* 0 Mass and Width

11. Signal Extraction 11 3.4 M events K* 0   ± K + (BR=0.67) PID with TPC dE/dx: |n   |<2, |n  K |<2 Calculate invariant mass of  K pairs –rapidity cut: |y pair |<0.5 Combinatorial Background: –Event Mixing –Like-Sign Pairs Fit signal: BW peak + linear background Uncorrected spectra: –Statistics up to p T ~10 GeV/c –Corrected spectra for QM 2012 Uncorrected K* 0

12. K* 0 Mass and Width 12 No centrality dependence Mass: –High p T : Pb+Pb consistent with p+p and HIJING –Low p T : Pb+Pb consistent with p+p (deviation from PDG not due to medium) –Low p T : Pb+Pb not consistent with HIJING detector effects in simulation under investigation Width: consistent with simulation; no width change beyond 10 MeV/c 2 K* 0 Mass K* 0 Width

13. Hadron-Resonance Correlations 13

14. Hadron-Resonance Correlations 14 Want to select for resonances produced early in collision and reduce contribution from hadronic phase: look for high-p T resonances in away side C. Markert, R. Bellwied, I. Vitev, Phys. Lett. B 669 92-97 (2008)

15. Angular Correlations 15 Angular Correlation of trigger hadron with a  meson –p T (h)>3 GeV/c –p T (  )>1.5 GeV/c Pb+Pb p+pp+p

16. Mass and Width vs.  16 mass/expected value width/expected value p+pp+p p+pp+p Pb+Pb  mass and width as a function of angle (  φ) w.r.t. leading hadron p T (h)>3 GeV/c p T (  )>1.5 GeV/c Measured values divided by expected value No clear difference in behavior between p+p and Pb+Pb In Pb+Pb: no mass shift or width broadening observed in away side However:  signal may be dominated by non-jet  for this p T range 12/9/2011

17. Summary 17 K* 0 and  signals observed in Pb+Pb collisions at 2.76 TeV –Corrected  and K* 0 spectra and ratios to non-resonances will be presented at Quark Matter 2012 K* 0 mass: Pb+Pb consistent with p+p and with HIJING at high p T –any mass shift is not due to a medium effect K* 0 width: Pb+Pb consistent with HIJING h-  correlations: away side looks like near side –No mass shift or width broadening in away side –Will things be different for higher p T (  ) or higher p T (trigger)? We do not observe the signatures of chiral symmetry restoration.