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Hadronic resonance production in Pb+Pb collisions from the ALICE experiment

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

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Hadronic resonance production in Pb+Pb collisions from the ALICE experiment

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

  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: f lifetime may change by up to factor of 10* Introduction * L. Holt and K. Haglin, J. Phys. G31, S245 (2005) Statistical Model G. Torrieri and J. Rafelski, Phys. Lett. B 509 239 (2001)

  4. To probe QGP: compare resonances that passed through medium with those that did not • Hadron-resonance correlations Hadron-Resonance Correlations jet, leading hadron Resonance in near side: no medium interaction Method proposed by: C. Markert, R. Bellwied, I. Vitev, Phys. Lett. B669 92-97 (2008) Resonance in away side: Low pT (below ~2 GeV/c): dominated by interactions in hadronic medium High pT: dominated by interactions with early hadronic or partonic medium Resonance transverse to jet: Thermal production in hadronic medium

  5. f Yield

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

  7. Signal Extraction BACKGROUND SUBTRACTION f Analysis • Invariant mass • |ypair|<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 Fit Region (exact boundaries varied)

  8. Uncorrected f Yields • Statistics up to pT~10 GeV/c • Coming for Quark Matter: • Corrected Spectra • dN/dy • Ratios: f/p, f/K Uncorrected f Yields

  9. f/p: • NA49 (17.5 GeV) and STAR (200 GeV): A+A higher than p+p • PHENIX 200 GeVAu+Au • f/p = 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? • f/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 f/K = 0.0911 ± 0.021 • STAR higher than PHENIX Particle Ratios ? ? Lower energy: see PRC71 064902 (2005) and PRC79 064903 (2009)

  10. K*0 Mass and Width

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

  12. No centrality dependence • Mass: • High pT: Pb+Pb consistent with p+p and HIJING • Low pT: Pb+Pb consistent with p+p(deviation from PDG not due to medium) • Low pT: Pb+Pb not consistent with HIJING • detector effects in simulation under investigation • Width: consistent with simulation; no width change beyond 10 MeV/c2 K*0 Mass and Width K*0 Width K*0 Mass

  13. Hadron-Resonance Correlations

  14. Hadron-Resonance Correlations C. Markert, R. Bellwied, I. Vitev, Phys. Lett. B669 92-97 (2008) Want to select for resonances produced early in collision and reduce contribution from hadronic phase: look for high-pT resonances in away side

  15. Angular Correlation of trigger hadron with a f meson • pT(h)>3 GeV/c • pT(f)>1.5 GeV/c Angular Correlations Pb+Pb p+p

  16. Mass and Width vs. Df p+p p+p 12/9/2011 12/9/2011 mass/expected value width/expected value Pb+Pb Pb+Pb 12/9/2011 12/9/2011 f mass and width as a function of angle (Dφ) w.r.t. leading hadron pT(h)>3 GeV/c pT(f)>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: f signal may be dominated by non-jet f for this pT range

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

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