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Direct photon interferometry

Direct photon interferometry. D.Peressounko RRC “Kurchatov Institute”. Outlook. Photons are special: Penetrating => Specific R(K T ) dependence Massless => Unusual R inv and l inv interpretation Rare => Strong background Experimental review Completed experiments

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Direct photon interferometry

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  1. Direct photon interferometry D.Peressounko RRC “Kurchatov Institute”

  2. Outlook • Photons are special: • Penetrating => Specific R(KT) dependence • Massless => Unusual Rinv and linv interpretation • Rare => Strong background • Experimental review • Completed experiments • TAPS,WA98 • Ongoing • PHENIX,STAR • Developing • ALICE • Conclusions D.Peressounko, WPCF, Kromeriz, 2005

  3. Accessing space-time dimensions of different stages of the collision • 3+1 hydro with first order phase transition. • QGP phase includes pre-equilibrium pQCD contribution Pb+Pb @ 17.2 AGeV Rout Rside Rlong hadr QGP mixed D.P. Phys.Rev.Lett.93:022301,2004 D.Peressounko, WPCF, Kromeriz, 2005

  4. KT dependence of photon correlation radii D.Srivastava, Phys.Rev.C71:034905,2005 RHIC Au+Au @ 200 AGeV D.P. Phys.Rev.Lett.93:022301,2004 T.Renk, hep-ph/0408218 D.Peressounko, WPCF, Kromeriz, 2005

  5. Predictions for correlation radii RHIC, Au+Au@200 AGeV, KT=2GeV *Not LCMS system D.Peressounko, WPCF, Kromeriz, 2005

  6. Qinv parameterization for massless particles S(x) = exp( - t2/t2 – x2/Ro2 - y2/Rs2 - z2/Rl2), C2(qo,qs,ql)=1 + exp( -qo2(Ro2 +t2b2) -qs2Rs2 -ql2Rl2) ∫d3q/qeC2(qo,qs,ql) d(Qinv2+q2) C2(Qinv)= (integrate in CM frame of the pair) ∫d3q/qed(Qinv2+q2) = 1/(4p)∫[1+ exp{-Qinv2(K02/M2cos2q (Ro2+b2t2) + Rs2 sin2qsin2f + Rl2sin2qcos2f ) }] dW = 1+linvexp{-Qinv2Rinv2) linv = 1/(4p) ∫exp{ - 4KT2(Ro2 + t2)cos2q}dW Rinv = <Rs,Rl> (not Ro!) For massless particles (g,e) Qinv parameterization is very special! D.Peressounko, WPCF, Kromeriz, 2005

  7. Qinv parameterization for massless particles (MC) linv = Erf(2KT√Ro2 + t2)/(2KT√Ro2 + t2) linv=1/(2KT√Ro2 + t2) D.Peressounko, WPCF, Kromeriz, 2005

  8. Background photon correlations • Bose-Einstein p0 correlations • Resonance decays • Collective flow g g p0 } g p0 g p0 h } p0 p0 D.Peressounko, WPCF, Kromeriz, 2005

  9. p0 BE residual correlations Rpp=4 fm Rpp=5 fm Rpp=6 fm C2pp=1+exp(-Qinv2Rpp2) D.P. Phys.Rev.Lett.93:022301,2004 D.Peressounko, WPCF, Kromeriz, 2005

  10. p0 BE residual correlations A.Deloff and T.Siemiarczuk, ALICE internal note INT-98-50 C2pp(D)=1+l/(1+D2Rpp2)2 dNp/dp=p·epx(-p/[3GeV]) D=1/2(k1-k2) D.Peressounko, WPCF, Kromeriz, 2005

  11. p0 BE residual correlations Varying strength Varying width (and strength) O.V.Utyuzh, G.Wilk, Nukleonika 49:S15 (2004), hep-ph/0312364 D.Peressounko, WPCF, Kromeriz, 2005

  12. TAPS: detector setup BaF2 25 cm long (12 X0) prism of hexagonal cross section, the diameter of the inner circle being 5.9 cm (69% of the Moliere radius). Distance to IP 62 cm Min angle cut between photons 8.30 Typical photon energy ~10 MeV D.Peressounko, WPCF, Kromeriz, 2005

  13. TAPS: mgg distribution and C2 86Kr+natNi @ 60 AMeV 181Ta+197Au @ 40 AMeV Geant simulations Comparison to BUU calculations D.Peressounko, WPCF, Kromeriz, 2005

  14. WA98 setup Number of events collected: Peripheral (20% min bias) 3897935 Central (10% min bias) 5817217 D.Peressounko, WPCF, Kromeriz, 2005

  15. Two photon correlation functions D.Peressounko, WPCF, Kromeriz, 2005

  16. WA98: apparatus effects Lmin = 20 cm (5 modules) Lmin = 25 cm (6 modules) Lmin = 30 cm (7 modules) Lmin = 35 cm (9 modules) 100 < KT < 200 MeV 100 < KT < 200 MeV 200 < KT < 300 MeV 200 < KT < 300 MeV D.Peressounko, WPCF, Kromeriz, 2005

  17. Hadrons and photon conversion Contamination, (charged + neutral) pid 100<KT<200 200<KT<300 “All” (37 + 4)% (22 + 4)% “Narrow” (16 + 1)% (4 + 1)% “Neutral” ( 1 + 4)% (1 + 4)% “Narrow neutral” (1 + 1)% (1 + 1)% ltrue 1 (Ngdir)2 lobs = = 2 (Ngtot + cont)2 (1+ cont/ Ngtot)2 D.Peressounko, WPCF, Kromeriz, 2005

  18. Photon background correlations Simulations p0p0 Bose-Einstein correlations: Slope: -(4.5±0.4)·10-3 (GeV-1) Elliptic flow: Slope: -(3.1±0.4)·10-3 (GeV-1) Decays of resonances: K0s→2p0→4g K0L→3p0→6g h→3p0→6g w→p0g→3g D.Peressounko, WPCF, Kromeriz, 2005

  19. Invariant correlation radius C2(Qinv) =1 + l/(4p) ∫ do exp{ - Qinv2 (Rs2 sin2q sin2f + Rl2 sin2q cos2f ) - (Qinv2 + 4KT2)cos2q Ro2 } Rpplong Rgg Rppside (for massless particles!) Rinv = f(Rs,Rl) Erf(2KTRo) linv = l 2KTRo D.Peressounko, WPCF, Kromeriz, 2005

  20. Yield of direct photons Correlation method: The lowest yield (Ro=0) Most probable yield (Ro=6 fm) Ngdir = Ngtotal√2l Subtraction method Subtraction method, upper limit Predictions Erf(2KTRo) linv = l hadronic gas 2KTRo QGP pQCD sum Predictions: S. Turbide, R. Rapp, and C. Gale, hep-ph/0308085. D.Peressounko, WPCF, Kromeriz, 2005

  21. PHENIX setup Lead Scintillator Lead + scintillating plates of 5.5*5.5 cm2 at a distance 510 cm from IP. Lead Glass PbGl crystals 4*4 cm2 cross section distance 550 cm from IP D.Peressounko, WPCF, Kromeriz, 2005

  22. PHENIX: Comparison to data d+Au collisions at √sNN=200 GeV D.Peressounko, WPCF, Kromeriz, 2005

  23. STAR Use 1 gamma in TPC, 1 gamma in calorimeter. Conclusions from the talk of J. Sandweiss on “RHIC-AGS users meeting”, June 21, 2005, BNL: • A procedure has been developed which permits the measurement of gamma-gamma HBT signals despite the large background of gammas from π0 mesons • Gamma energy > 1.0 GeV is required for the residual π0 correlation to be “small” • “No HBT” calculation may be needed but appears to be doable. D.Peressounko, WPCF, Kromeriz, 2005

  24. ALICE setup PHOS: crystals PbW04 2*2 cm cross section Distance to IP 460 cm D.Peressounko, WPCF, Kromeriz, 2005

  25. ALICE: unfolding and resolution D.Peressounko, WPCF, Kromeriz, 2005

  26. ALICE: photon correlations in HIJING event Kt=200 MeV D.Peressounko, WPCF, Kromeriz, 2005

  27. Direct photon and electron interferometry is rather special subject due to penetrating nature, zero mass and low yield. Two-photon correlations were observed in two experiments up to now. Photon correlations are analyzed now at PHENIX and STAR. PHOS detector at ALICE is very promising tool due to fine granularity and high spatial and energy resolutions. Summary D.Peressounko, WPCF, Kromeriz, 2005

  28. PHENIX: MC simulations Kt = 0.2 GeV K+→p+p0 ct=4.7 m K0S→p0p0 ct=0.02 m K0L→3p0 ct=15. m h→3p0 Using measured spectra and yields for p0, kaons and h D.Peressounko, WPCF, Kromeriz, 2005

  29. Jan-e Alam et al., ee correlations KT=1 GeV Not LCMS J.Alam et al., Phys.Rev.C70:054901,2004 D.Peressounko, WPCF, Kromeriz, 2005

  30. side T.Renk Side out Long T.Renk, hep-ph/0408218 D.Peressounko, WPCF, Kromeriz, 2005

  31. Penetrating probes: probe all stages? RHIC Au+Au @ 200 AGeV D.P. Phys.Rev.Lett.93:022301,2004 D.Peressounko, WPCF, Kromeriz, 2005

  32. Possible sources of distortion of correlation function • Apparatus effects (cluster splitting and merging) • Hadron misidentification • Photon conversion • Photon background correlations: • Bose-Einstein correlations of parent p0; • Collective (elliptic) flow; • Residual correlations due to decays of resonances; D.Peressounko, WPCF, Kromeriz, 2005

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