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dAu results from STAR Gluon Saturation Studies

dAu results from STAR Gluon Saturation Studies. Akio Ogawa. Introduction RHIC & Experiments Results Summary. 2010 May 26. Gluon structure in Nucleon What do we know from DIS?. Phys. Rev. C70 (2004) 044905. DIS x-Q2 data From fixed to hera.

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dAu results from STAR Gluon Saturation Studies

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  1. dAu results from STARGluon Saturation Studies Akio Ogawa Introduction RHIC & Experiments Results Summary 2010 May 26

  2. Gluon structure in Nucleon What do we know from DIS? Phys. Rev. C70 (2004) 044905 DIS x-Q2 data From fixed to hera World data on nuclear DIS constrains nuclear modifications to gluon density only for xgluon > 0.02 arXiv:hep-ex/0507024 Scaling violation at x<0.01 indirectly indicate rapid growth of gluon density at low x

  3. Gluon density at low x small x x = Pparton/Pnucleon Gluon density can’t grow forever. Recombination ~ asr Bremsstrahlung ~ asln(1/x) Saturation must set in at forward rapidity when gluons start to overlap and when recombination becomes important

  4. Color Glass Condensate Qs2(x) saturation scale ln(1/x) CGC Forward Rapidity Parton Gas non-perturbative BFKL Mid Rapidity DGLAP lnLQCD2 lnQ2 CGC = Semi-classical color field New regime of QCD at high gluon density Initial state for HI collisions (Glasma)

  5. Why study forward rapidity @ hadron collider? • Hadronic probe = directly couple with gluons • Forward scattering probes asymmetric partonic collisions high-x valence quarks 0.25 < xq < 0.7 on low-x gluons 0.001 < xg < 0.1 Ep p0 qq PN qp N xgpN N =Au xqpN PN qg With heavy nucleus target, gluon density would be even bigger ~A1/3 (gluon saturation happens at higher x) In CGC picture, xg ~ few 10-4 Is gluon density universal between DIS and hadron collisions? Can RHIC see gluon saturation?

  6. Signature for gluon saturation (1) : Yield EPS09 Paukkunen et al (QM09) D. Kharzeev hep-ph/0307037 As y grows CGC expects suppression of forward hadron production Shadowing also expects some suppression

  7. Signature for gluon saturation (2) : di-hadron correlation pQCD 22 process = back-to-back di-jet (Works well for p+p) Forward jet p d+Au in HIJING p Mid-rapidity jet pQCD + shadowing Forward jet d Au Mid-rapidity jet Conventional shadowing changes yield, but not angular correlation

  8. Signature for gluon saturation (2) : di-hadron correlation Saturation / CGC 21 (or 2many or 1many) process = Mono-jet Kharzeev, Levin, McLerran(NPA748, 627) Mono-jet Dilute parton system (deuteron) Dense gluonfield (Au) PT is not balanced by one parton but something else (many gluons?) CGC predicts suppression of back-to-back correlation CGC predicts suppression of back-to-back correlation

  9. STAR The STAR Detector (run2003) TPC: -1.0 <  < 1.0 FPD: 3.3 <  < 4.1

  10. STAR d+Au forward π0 STAR PRL 97, 152302 η = 4.0 (NPA 765, 464) Sizable suppression pQCD+Shadowing expects suppression, but not enough CGC gives best description on pT dependence

  11. STAR The STAR Detector (run2008) BEMC: -1.0 <  < 1.0 TPC: -1.0 <  < 1.0 FMS: 2.5 <  < 4.1 • Forward Meson Spectrometer (FMS) • Pb-glass EM calorimeter • ~x50 more acceptance • enable forward-forward correlation

  12. STAR Forward-mid rapidity correlations in d+Au (Run8) See Ermes Braidot, QM092009 arXiv:0907.3473 ηtrig = 4.0 ηasso = 0.0 p+p00+X d+Au00+X High PT Cut xg~ 0.006 Dh~4.0 PT(leading)>2.5 GeV statistical errors only s(dAu)-s (pp)= 0.11±0.04 dAu pp Away-side peaks are evident. Low PT Cut PT(leading)>2.0 GeV Azimuthal broadening from pp to dAu. s(dAu)-s (pp)= 0.20±0.03 pp dAu Azimuthal broadening is PT dependent. Df (rad) Df (rad)

  13. Run8 FMS : Forward p0 - Forward p0 Correlation STAR • Near-side and away-side correlations observed for forward-π0 pair • Lowest Bjorken-x values probed by correlations between two forward π0 ηtrig = 3.0 ηasso = 3.0 xg~ 0.002 Dh~0

  14. Run8 FMS : Forward p0 - Forward p0 Correlation Normalized to number of events with leading PT(p0)> 2.0 GeV No efficiency corrections (may have some f dependence) (rad) (rad) pp data dAu data s(dAu)-s (pp)= 0.52±0.05 Strong azimuthal broadening from pp to dAu for away side, but near side is ~ unchanged. Azimuthal broadening is PT dependent. PT dependence is stronger for Forward-Forward than Forward-Central

  15. Centrality dependence of decorrelation pp data dAu all data dAu peripheral peripheral dAu Central central Away-side peaks evident in peripheral dAu and pp. Near side peaks unchanged in dAu for peripheral to central. Azimuthal decorrelations show significant dependence on centrality.

  16. Comparison to CGC prediction dAu Central CGC prediction for b=0 (central) by Cyrille Marquet Nucl.Phys.A796:41-60,2007 
arXiv:0708.0231 [hep-ph] ηtrig = 3.0 ηasso = 3.0 xg~ 0.002 Dh~0 Strong suppression of away side peak in central dAu is (almost quantitatively) consistent with CGC prediction

  17. Mapping out Qs,g2 Parton Gas CGC x in 2  2 process x in 2  1 process

  18. Summary • Forward rapidity at RHIC access to low-x physics • Run3 dAu Results • Hadron production : Large suppression in forward • Di-hadron correlation : Suppression at h=4 & low xF (pT ~1GeV) • Successful RHIC Run8 with dAu (and pp) • STAR FMS was built and took data! • Forward-Mid rapidity azimuthal broadening in dAu • Forward-Forward near side correlation remain unchanged • from pp to peripheral dAu to central dAu • Forward-Forward away side correlation is suppressed • at h=3 & pT ~2GeV • and shows strong pT dependence and centrality dependence • Mono-jet !! • Outlook • Finalizing analysis (normalization and systematic) • Scanning pT • Possible measurements in p(250)Au(100)

  19. Backup

  20. PYTHIA (p+p) vs HIJING (d+Au) • HIJING predicts similar correlations in d+Au as PYTHIA predicts for p+p. • Only significant difference is combinatorial background level 25<Ep<35GeV ηtrig = 4.0 ηasso = 0.0 35<Ep<45GeV

  21. STAR An initial glimpse: correlations in d+Au (Run3) suppressed at small <xF> and <pT,π> consistent with CGC picture PRL 97, 152302 (2006) <pT,π> ~ 1.0 GeV/c 25<Ep<35GeV xg~ 0.006 Dh~4.0 ηtrig = 4.0 ηasso = 0.0 π0:|<η>| = 4.0 h±: |η| < 0.75; pT > 0.5 GeV/c

  22. STAR An initial glimpse: correlations in d+Au (Run3) • suppressed at small <xF> and <pT,π> • consistent with • CGC picture • are similar in d+Au and p+p at larger <xF> and <pT,π> • as expected by HIJING PRL 97, 152302 (2006) <pT,π> ~ 1.0 GeV/c 25<Ep<35GeV Fixed h, as E & pT grows <pT,π> ~ 1.3 GeV/c xg~ 0.006 Dh~4.0 ηtrig = 4.0 ηasso = 0.0 π0:|<η>| = 4.0 h±: |η| < 0.75; pT > 0.5 GeV/c

  23. STAR Run8 FMS p0+h± pT scan (inclusive) Const (BG) “gsv” pp Peak Area Peak Width dAu Df pT1 1.5 2.0 2.5 3.0 GeV/c pT2 0.5 1.0 1.5 2.0 GeV/c • dAu width larger than pp (consistent with FMS-BEMC results) • dAu back-to-back peak area larger than pp at lower pT • Work in progress towards even lower pT

  24. Gold-side multiplicity dependence h±/π0 (TPC/EMC) 〈MBBC(E)〉 p/Au p/d π0 (FMS) 1 2 3 • Selection: charge sum from east (Au side) BBC • (-5.0 < ηBBC < -3.4) • (18 counts ~ 1MIP)

  25. STAR Gold-side multiplicity dep. pp 1 2 3 Const (BG) dAu 1 dAu 2 Peak Area dAu 3 Peak Width pT1 1.5 2.0 2.5 3.0 GeV/c pT2 0.5 1.0 1.5 2.0 GeV/c • Hints of back-to-back signal area increasing as East BBC multiplicity increases • No hints of width increasing as East BBC multiplicity increases

  26. STAR Run8 FMS p0+h± pT scan (inclusive) “gsv” “low-pT” pp 1.5GeV < pTFMS 0.5GeV < pTTPC < pTFMS 2.0GeV < pTFMS 1.0GeV < pTTPC < pTFMS (“lowpT”) 2.5GeV < pTFMS 1.5GeV < pTTPC < pTFMS (“GSV”) 3.0GeV < pTFMS 2.0GeV < pTTPC < pTFMS dAu Df • dAu width larger than pp (consistent with FMS-BEMC results) • dAu back-to-back peak area larger than pp at lower pT • Work going on to reach even lower pT

  27. Run8 FMS : Comparison to FPD (Run3) STAR Ermes Braidot QM2009 Phys. Rev. Lett. 97 (2006) 152302 • Emulate FPD from run-8 FMS: • FMS photons: x > 0cm; • |ηTPC| < 0.75 ; 3.8 < ηFMS < 4.1 ; • 0.5GeV < pT(TPC) • |αFMS| = |E1 - E2|/(E1 + E2) < 0.7 ; • 30 < EFMS < 55 GeV • leading (in pT) particles considered Run 8 data Run 8 data • Reproduce gaussian width and many similarities • Normalization requires more systematic studies: • Run-3/run-8 trigger • Efficiency corrections xg~ 0.006 Dh~4.0 ηtrig = 4.0 ηasso = 0.0

  28. Brhams pp2pp PHENIX STAR The Relativistic Heavy Ion Collider Au+Au Polarized p+p d+Au RHIC is a QCD lab

  29. STAR Mid-rapidity p+p MinBias p+p data Phys. Lett. B. 637 (2006) 161 Higher pT data Xu Y. QM09 PRL 91, 241803 PHENIXπ0 STAR (h++h-)/2 BRAHMS (h++h-)/2 STAR preliminary Calculations by W. Vogelsang At 200 GeV, pQCD does a very good job describing mid-rapidity hadron yields Universality of parton density!

  30. BRAHMS STAR Forward rapidity p+p PRL 97, 152302 PRL 98, 252001 At 200 GeV, pQCD does a very good job describing mid-rapidity hadron yields both mid and forward rapidity (0<|h|<4)

  31. STAR Pedestal&flow subtracted Mid-rapidity d+Au PRL 91, 072304 p+p and d+Ausimilar in inclusive yields (~1.5 enchancements at mid-pT) back-to-back di-hadron correlations In contrast, Au+Au collisions are very different from p+p and d+Au

  32. BRAHMS RdAu rapidity dependence STAR η = 04 PRL 93, 242303 PRL 97, 152302 η = 4 p0 Observe significant rapidity dependence similar to expectations from the CGC framework

  33. BRAHMS Is saturation really the explanation? B.Kopeliovich et. al.PRC72 054606 η = 3.2 Dumitru, Hayashigaki Jalilian-Marian NP A765, 464 PRL 93, 242303 Sudakov Suppression, not low-x phenomena Reproduce pT trend and centrality dependence. A CGCcalc.gives avery good description of the pT dependence Paukkunen et al (QM09) EPS09

  34. Scaning pT Normalized to number of events with leading PT(p0)> 2.0 GeV No efficiency corrections (may have some f dependence) Wider range pT scan (pTTrig =2.0 to 3.5GeV, pTAsso = pTTrig /2) for dAu is coming

  35. The Relativistic Heavy Ion Collider Quark-Gluon Plasma Gluon Saturation Color Glass Condensate Au+Au Polarized p+p d+Au RHIC is a QCD lab Nucleon Spin Structure

  36. Experimental evidences for CGC (and GLASMA) • eP geometrical scaling • eP diffraction • AuAu multiplicity • AuAu extended scaling • AuAu ridge • AuAu CP violation (?) • AuAu/dAu J/psi production • dAu RdA suppression at forward • dAu 2 particle correlations / “mono-jet”

  37. Run3 & 8 d+Au @ 200GeV Max expectation PHENIX STAR Min expectation Run3 ~x30 luminosity (from run3) Great success! +(polarized) pp run  reference data

  38. Run8 FMS : Forward p0 - Forward p0 Correlation Normalized to number of events with leading PT(p0)> 2.5 GeV No efficiency corrections (may have some f dependence) (rad) (rad) pp data (xg~10-3) dAu data s(dAu)-s (pp)= 0.11±0.06 Observation of expected away-side correlations in pp Near-side correlations similar for both pp and dAu ηtrig = 3.0 ηasso = 3.0 xg~ 0.002 Dh~0 Azimuthal broadening from pp to dAu

  39. Forward p0 - Forward p0 Correlation p+p in PYTHIA Forwad p0 Triggered Guzey, Strikman, Vogelsang, PL B603, 173 FMS TPC Barrel EMC FTPC hasso gives handle on xgluon Forward-forward di-hadron correlation to reach lowest <xg>~10-3 with 2 to 1 kinematics : <xg>~10-4

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