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d+Au Collisions at STAR

STAR. d+Au Collisions at STAR. Carl A. Gagliardi Texas A&M University for the Collaboration. Outline d+Au collisions and saturation physics at RHIC Recent STAR results STAR plans for the future. STAR detector. E-M Calorimeter.

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d+Au Collisions at STAR

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  1. STAR d+Au Collisions at STAR Carl A. Gagliardi Texas A&M University for the Collaboration • Outline • d+Au collisions and saturation physics at RHIC • Recent STAR results • STAR plans for the future

  2. STAR detector E-M Calorimeter Projection           Chamber Time of    Flight

  3. Mid-rapidity p+p at RHIC and NLO pQCD PRL 91, 241803 PHENIXπ0 STAR (h++h-)/2 BRAHMS (h++h-)/2 Calculations by W. Vogelsang At 200 GeV, pQCD does a very good job describing mid-rapidity yields

  4. STAR Pedestal&flow subtracted Mid-rapidity d+Au PRL 91, 072304 Inclusive yields and back-to-back di-hadron correlations are very similar in p+p and d+Au collisions In contrast, Au+Au collisions are very different from p+p and d+Au – but that’s not the subject of this talk

  5. Mid-rapidity vs. forward rapidity Mid Rapidity Forward Rapidity CTEQ6M • Gluon density can’t grow forever. • Saturation may set in at forward rapidity when • gluons start to overlap. • Can be explored by comparing p(d)+A to p+p.

  6. BRAHMS Forward particle production in d+Au collisions BRAHMS, PRL 93, 242303 Sizable suppression in charged hadron production in d+Au collisions relative to p+p collisions at forward rapidity

  7. Expectations for a color glass condensate t related to rapidity of produced hadrons. D. Kharzeev, hep-ph/0307037 As y grows Iancu and Venugopalan, hep-ph/0303204 Are the BRAHMS data evidence for gluon saturation at RHIC energies?

  8. Recent saturation model calculation Very good description of the pT dependence of the BRAHMS d+Au → h− + X cross section at η= 3.2 (Dumitru, Hayashigaki, and Jalilian-Marian, NP A765, 464)

  9. Is saturation really the explanation? Difficult to explain BRAHMS results with standard shadowing, but in NLO pQCD calculations <xg> ~ 0.02 is not that small (Guzey, Strikman, and Vogelsang, PL B603, 173) In contrast, <xg> <~ 0.001 in CGC calculations (Dumitru, Hayashigaki, and Jalilian-Marian, NP A765, 464) Basic difference: pQCD: 2  2 CGC: 2  1

  10. √s=23.3GeV √s=52.8GeV Data-pQCD differences at pT=1.5GeV NLO calculations with different scales: pT and pT/2 Ed3s/dp3[mb/GeV3] Ed3s/dp3[mb/GeV3] q=5o q=10o q=15o q=53o q=22o xF xF Do we understand forward π0 production in p + p? Bourrely and Soffer, EPJ C36, 371: NLO pQCD calculations underpredict the data at low s from ISR Ratio appears to be a function of angle and √s, in addition to pT

  11. STAR p+p  p0+X at 200 GeV nucl-ex/0602011 • The error bars are statistical plus point-to-point systematic • Consistent with NLO pQCD calculations at 3.3 < η < 4.0 • Data at low pT trend from KKP fragmentation functions toward Kretzer. PHENIX observed similar behavior at mid-rapidity.

  12. STAR d+Au  p0+X at 200 GeV nucl-ex/0602011 pT dependence of d+Au π0 cross section at <η>= 4.0 is best described by a LO CGC calculation. (Dumitru, Hayashigaki, and Jalilian-Marian, NPA 765, 464)

  13. STAR  dependence of RdAu nucl-ex/0602011 • Observe significant rapidity dependence. • pQCD calculations significantly over predict RdAu.

  14. Any difference between p+p and d+Au? p+p: Di-jet d+Au: Mono-jet? Dilute parton system (deuteron) PT is balanced by many gluons Dense gluon field (Au) Kharzeev, Levin, McLerrangives physics picture (NPA748, 627) Color glass condensate predicts that the back-to-back correlation from p+p should be suppressed

  15. Back-to-back correlations with the color glass The evolution between the jets makes the correlations disappear. (Kharzeev, Levin, and McLerran, NP A748, 627)

  16. Forward + mid-rapidity di-hadron correlations • HIJING predicts similar correlations in d+Au as PYTHIA predicts for p+p. • Only significant difference is combinatorial background level. 25<Ep<35GeV 35<Ep<45GeV

  17. STAR Fixed h, as E & pT grows Forward + mid-rapidity correlations in d+Au nucl-ex/0602011 • are 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 <pT,π> ~ 1.0 GeV/c 25<Ep<35GeV <pT,π> ~ 1.3 GeV/c π0:|<η>| = 4.0 h±: |η| < 0.75; pT > 0.5 GeV/c

  18. STAR Forward Meson Spectrometer • FMS increases areal coverage of forward EMC from 0.2 m2 to 4 m2 • Addition of FMS to STAR provides nearly continuous EMC from -1<η<+4 • Available for Run 7

  19. p+p and d+Au  p0+p0+X correlations with forward p0 p+p in PYTHIA d+Au in HIJING hep-ex/0502040 Conventional shadowing will change yield, but not angular correlation. Saturation will change yield and modify the angular correlation. Sensitive down to xg ~ 10-3 in pQCD scenario; few x 10-4 in CGC scenario.

  20. Conclusions • Forward rapidity inclusive π0production at RHIC is well described by pQCD calculations • d+Au results at RHIC provide hints that saturation effects are becoming important • Future STAR measurements will elucidate the dynamics underlying forward inclusive particle suppression at RHIC • RHIC may be the ideal accelerator to explore the onset of saturation

  21. STAR The STAR Collaboration U.S. Labs: Argonne, Lawrence Berkeley, and Brookhaven National Labs U.S. Universities: UC Berkeley, UC Davis, UCLA, Caltech, Carnegie Mellon, Creighton, Indiana, Kent State, MIT, MSU, CCNY, Ohio State, Penn State, Purdue, Rice, Texas A&M, UT Austin, Washington, Wayne State, Valparaiso, Yale Brazil: Universidade de Sao Paolo China: IHEP - Beijing, IPP - Wuhan, USTC, Tsinghua, SINAP, IMP Lanzhou Croatia: Zagreb University Czech Republic: Nuclear Physics Institute England: University of Birmingham France: Institut de Recherches Subatomiques Strasbourg, SUBATECH - Nantes Germany: Max Planck Institute – Munich University of Frankfurt India: Bhubaneswar, Jammu, IIT-Mumbai, Panjab, Rajasthan, VECC Netherlands: NIKHEF/Utrecht Poland: Warsaw University of Technology Russia: MEPHI – Moscow, LPP/LHE JINR – Dubna, IHEP – Protvino South Korea: Pusan National University Switzerland: University of Bern

  22. STAR Pseudo-rapidity yield asymmetry vs pT Au direction / d direction PRC 70, 064907 Back/front asymmetry in 200 GeV d+Au consistent with general expectations of saturation or coalescence; doesn’t match pQCD prediction.

  23. Nuclear Gluon Density e.g., see M. Hirai, S. Kumano, T.-H. Nagai, Phys. Rev. C70 (2004) 044905 and data references therein World data on nuclear DIS constrains nuclear modifications to gluon density only for xgluon > 0.02

  24. One calculation within the saturation picture RdAu RCP Saturation model calculation with additional valence quark contribution (Kharzeev, Kovchegov, and Tuchin, PL B599, 23)

  25. x values in saturation calculations In CGC calculations, the BRAHMS kinematics corresponds to <xg> <~ 0.001(Dumitru, Hayashigaki, and Jalilian-Marian, NP A765, 464)

  26. Many recent descriptions of low-x suppression A short list (probably incomplete) Saturation (color glass condensate) Shadowing • R. Vogt, PRC 70 (2004) 064902. • Guzey, Strikman, and Vogelsang, PLB 603 (2004) 173. • Jalilian-Marian, NPA 748(2005) 664. • Kharzeev, Kovchegov, and Tuchin, PLB 599(2004) 23; PRD 68 (2003) 094013. • Armesto, Salgado, and Wiedemann, PRL 94 (2005) 022002. • Dumitru, Hayashigaki, and Jalilian-Marian, NPA 765 (2006) 464 Parton recombination • Hwa, Yang, and Fries, PRC 71 (2005) 024902. Others? Multiple scattering • ... • Qiu and Vitev, PRL 93 (2004) 262301; hep-ph/0410218. Factorization breaking • Kopeliovich et al., PRC 72 (2005) 054606. • Nikolaev and Schaefer, PRD 71 (2005) 014023.

  27. <z> <xq> <xg> Forward π0 production at a hadron collider Ep p0 EN qq qp N xgp N xqp qg EN (collinear approx.) • Large rapidity π production (η~4) probes asymmetric partonic collisions • Mostly high-x quark + low-x gluon • 0.3 < xq< 0.7 • 0.001< xg < 0.1 • <z> nearly constant and high ~ 0.7-0.8 • A probe of low-x gluons NLO pQCD S. Kretzer

  28. For 22 processes Log10(xGluon) TPC Barrel EMC FTPC FTPC FPD FPD Gluon Constraining the x-values probed in hadronic scattering Guzey, Strikman, and Vogelsang, Phys. Lett. B 603, 173 Log10(xGluon) Collinear partons: • x+ = pT/s (e+h1 + e+h2) • x = pT/s (eh1 + eh2) • FPD: ||  4.0 • TPC and Barrel EMC:|| < 1.0 • Endcap EMC:1.0 <  < 2.0 • FTPC: 2.8 <  < 3.8 Measure two particles in the final state to constrain the x-values probed

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