Study of  and  Production via Di-Electron Decay Channel at RHIC-PHENIX

1. Study of  and  Production via Di-Electron Decay Channel at RHIC-PHENIX RHIC-PHENIX実験における電子・陽電子対崩壊過程を用いた 低質量ベクトル中間子生成の研究 Kotaro Kijima for the PHENIX Collaboration

2. RHIC Introduction • The most of light Hadron masses are generated due to the spontaneous breaking of chiral symmetry. • Light vector meson(, , ) production carries information about possible mass modification at Heavy ion collision at RHIC. • : mass 783MeV/c2, =23fm/c • : mass 1020MeV/c2, =46fm/c • e+e- decay channel • Electron is good probe • Not interact strongly in the medium • measure  &  at low pT, where modification is expected • 2-body decay

3. Importance of p+p collisions proton + proton • We need to confirm what’ happen in p+p collision!! • Comparing with hadronc decay channel • Comparing with other mesons • mT scaling • /, / ratio • proton+proton collision • nucleon+nucleon • Base line for various collision system • Au+Au • Cu+Cu • d+Au A+A x Ncoll ??

4. The result in this presentation is almost final! • I talked at JPS on 2007/09/24. What is updated from previous JPS talk?? • Evaluation for combinatorial Background • exponential Event mixing method was used. • Evaluation for contribution of Internal radiation • Using full statistics • 45G 55G events of MB equivalent • Changing finer pT binning • 500MeV/c 250MeV/c (low pT range)

5. Run5 p+p s = 200GeV at RHIC-PHENIX #MB equivalent events ~ 55G events ERT sampled events / Red :: Same event Blue:: Event mixing  J/psi BG subtraction /  J/psi arXiv: 0802.0050 Invariant mass distribution Invariant mass spectrum of ee, after subtraction We can see clear peak of , and J/psi. Combinatorial BG shape is reproduced by event mixing method. Remaining component is a cocktail of known source.

6. 0.25 < pT < 0.5 0.5 < pT < 0.75 0 < pT < 0.25 0.75 < pT < 1.0 1.25 < pT < 1.5 1.0 < pT < 1.25 3.0 < pT < 4.0 1.5 < pT < 2.0 2.0 < pT < 3.0 Invariant mass distribution as a function of pT • Invariant mass distribution as a function of pT is shown. • Uncorrelated BG shape is re-produced by Event mixing method in all pT binning.

7. 0.25 < pT < 0.5 0.5 < pT < 0.75 0 < pT < 0.25 0.75 < pT < 1.0 1.25 < pT < 1.5 1.0 < pT < 1.25 3.0 < pT < 4.0 1.5 < pT < 2.0 2.0 < pT < 3.0   Invariant mass [GeV/c2] Signal Extraction  mesons BG for correlated pair • Fitting Function • Gaussian convoluted r.BW + radiative tail + B.W + (expo+constant)  & ee  &  ee Internal radiation Phys.Rev.D54(1996)7067 hep-ex/0510076 • What’s Free Parameter ?? •  &  • center of mass • detector mass resolution • raw yield BG shape • 3parameters

8. Invariant Cross Section Red: work in progress Red: work in progress   We measured  and  at low pT region for more finer binning. There is no difference between other hadronic decay channel for overlap region. Compare with other mesons(, K, )

9. π x10000 K x1000 η x100 ω x10 φ x 1 Comparing with other mesons mT is defined blow. We minutely measured various mesons (, K, , , ) in wide range.  We will show the ratio to 0 data ( assumption 0=(++-)/2 at low pT). K   

10. K0s/, /, /, / These ratio seems like constant value for same particle as a function of mT. mT scaling work out for all mesons! / / K0s/, / mT [GeV/c2] mT [GeV/c2] mT [GeV/c2] Ratio to 0

11. AuAu?? Next talk by Nakamiya-san!! Summary • We measured  and  meson via di-lepton decay channel. •  &  analysis is almost final results in Proton+Proton collisions at Run5. • Evaluation of BG shape by Event mixing method • Evaluation of contribution for internal radiation • Finer binning at low pT region • There is no difference between other hadronic decay channel for overlap region. • We minutely compared with various mesons (, K, ) in wide range at p+p collisions, and mT scaling work out for all mesons.