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Misaki Ouchida (Hiroshima University) For the PHENIX collaboration

Measurement of ω mesons via radiative decay mode in A+A collisions at √S NN =200GeV RHIC-PHENIX. Misaki Ouchida (Hiroshima University) For the PHENIX collaboration. 2007 Autumn JPS Meeting. OUTLINE. Low Mass Vector Mesons Hadron Suppression RHIC-PHENIX Apply Cuts Estimate Background

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Misaki Ouchida (Hiroshima University) For the PHENIX collaboration

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  1. Measurement of ω mesons via radiative decay mode in A+A collisions at √SNN=200GeV RHIC-PHENIX Misaki Ouchida (Hiroshima University) For the PHENIX collaboration 2007 Autumn JPS Meeting

  2. OUTLINE • Low Mass Vector Mesons • Hadron Suppression • RHIC-PHENIX • Apply Cuts • Estimate Background • Efficiency • Results • Discussion & Conclusion Introduction Experimental Setup Analysis Results Conclusion

  3. Introduction Low Mass Vector Mesons QGP ~10fm/c Heavy Ion Collisions Measure this! life time: 46fm/c 23fm/c Lots of advantages… Why ? • Short lifetime (23 fm/c)-> Include the information of QGP • Large branching ratio (9%) • No ρ-contribution (major problem for e+e-measurement) Why ? Physics… Siganl for Chiral Symmtery Restoration Siganl for Hadron Suppression Low pT High pT

  4. Suppression as a Probe of QGP Hadron Production will be suppressed due to the jet quenching occurred in the heavy-ion collisions as an effect of the matter The inclusive pi0 production in Au+Au QGP Nuclear Modification Function In the absence of nuclear effects: RAA=1 PRL 91. 072301 (2003)

  5. Experimental Setup RHIC-PHENIX circumference:3.8 km 99.7% of the speed of light Data Set : Au+Au collisions √SNN=200 GeV (taken in 2003~2004), The number of event : 1.06 G PHENIX Detector Trigger detectors 2 muon arms 2central arms (include Electro Magnetic Calorimeter)

  6. Analysis Apply Cuts Quest for omega in huge huge Background at Au+Au Collisions! ~ Resolution 1 ~ Cuts for photon ID Shower Shape, TOF Cut Chose the symmetric energy - both photons in the same sector Cuts for pi0 legs Kinematical Cuts for Reconstruction Best Cuts ･Transverse Momentum of ･Photon Energy ･Width of Invariant Mass Rising Minimum Cuts S/√B (significance) No Cuts Use Best Cuts that improve S/√B (significance) the most pT(ω) [GeV/c]

  7. ~ Resolution 2 ~ Estimate Background Reconstructed invariant mass Peripheral (cent 60~92 %) 3.5<pT<4.5[GeV/c] BG2 Mixed event Black: FG count BG3 BG1 Magenta:BG1+BG2+BG3 after subtraction of BG1+BG2+BG3 [GeV/c^2] Gaussian (Mean and With are Fixed by Embedding simulation) There it is!!!!

  8. Analysis Efficiency The number of measured ω Efficiency＝ The number of input ω Embedding to the background Central Peripheral Back ground

  9. Results Lines reporesent estimated yield from p+p collisions scaled by Ncoll Without nuclear matter effect, measurements follow lines

  10. Results

  11. Discussion & Conclusion It is suggested that omega meson yield suppressed in central Au+Au collisions We could extract omega via radiative decay mode in Au+Au by overcoming huge combinatorial backgrounds by Applying Best Cut, and Subtracting Background. From the results, we could suggest the sign of Hadron Suppression as the probe of the matter created in the heavy ion collisions. Au+Au Results should be finalized… (detail systematic study is needed) How about Cu+Cu collisions? Out Look

  12. Back Up

  13. Introduction Chiral Symmetry Restoration ｰ Hadron masses link to the quark condensate, <qq>. Chiral Symmetry is spontaneously broken, <qq>~250 MeV3 ｰ There is a transition of the system that constitute mass Hardron masses change !? Chiral Symmetry Restored <qq> → 0 ｰ

  14. Resolution 3 Correct Mass Distributionusing correlation between pi0 and omega Expected Improvement of S/N PROFILE Apply this correction function to all pT 782 [GeV/c] Pi0 mass [GeV/c^2] . Omega mass [GeV/c^2] ・・・・

  15. Other R_AA

  16. K0short Estimation Check Peripheral (cent 60~92 %) 3.5<pT<4.5[GeV/c] previous plot ~Question~ “Isn’t it too much?” K0->2pi0 Production Estimated Au+Au peripheral spectrum AN535(Run5 p+p) Results Fitted by Hagedorn function Ks/pi0 ratio --- 0.438 (AN535) Ks BR --- 31.05% Omega/pi0 ratio --- 0.85(PPG64) Omega BR --- 8.92 % Ncoll scaling Calculate estimated number (much more than omega num.)

  17. K0short Estimation Check Efficiency of reconstructing 3 gamma from K0s must be much higher than reconstructing 4 gammas Using K0s single simulation catch 4 gammas and reconstruct catch 3 gammas and reconstruct about 10 times

  18. Cut Optimization If there’s no cut, S/B< 1/1000…. →Have to improve it by the selection ･Pi0 Momentum Cuts ･Photon Energy Cuts ･Pi0 Mass Width Great influence on the peak significance Pi0 Momentum Cuts Photon Energy Cut Pi0 Mass Width S/√B Cut#4 Cut#3 Cut#2 Cut#1 Default ex. 4.5<ωpT<5.5 (GeV/c)

  19. Best Cuts

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