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Cold nuclear matter effects on quarkonium

Rencontres Ions Lourds / Heavy Ion Meeting SPhN Saclay Septembre 17, 2010. Cold nuclear matter effects on quarkonium. Elena G. Ferreiro Universidade de Santiago de Compostela, Spain. Work done in collaboration with F. Fleuret , J-P. Lansberg , N. Matagne and A. Rakotozafindrabe

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Cold nuclear matter effects on quarkonium

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  1. RencontresIonsLourds / Heavy Ion Meeting SPhNSaclaySeptembre 17, 2010 Cold nuclear matter effects on quarkonium Elena G. Ferreiro Universidade de Santiago de Compostela, Spain Work done in collaboration with F. Fleuret, J-P. Lansberg , N. Matagneand A. Rakotozafindrabe arXiv:0912.4498 PRC81 (2010)

  2. Introduction and motivation • A lot of work trying to understand A+A data (since J/y  QGP signal) Quakonium as a hint of deconfinement QGP hint • Here we focalise on p+A data (where no QGP is possible) only cold nuclear matter (CNM) effects are in play here: shadowingand nuclear absorption nPDFhint Quakonium as a hint of coherence • In fact, the question is even more fundamental: p+pdata we do not know the specific production kinematics at a partoniclevel: CS (2→2) vs CO (2→1) Quakonium as a hint of QCD QCD hint E. G. Ferreiro USC CNM effects on quarkoniumSPhN 17 Sept 10

  3. Introduction and motivation Ourgoal: ToinvestigatetheCNM effects and the impact of the specific partonic production kinematics • ResultsonJ/y production • Extend our study to ϒ CNM effects E. G. Ferreiro USC CNM effects on quarkoniumSPhN 17 Sept 10

  4. COLD and HOT effects hint of QCD •cold effects: wothermalisationNO QGP hint of coherence CGC gluon shadowing partonic comovers percolation hadronic comovers nuclear structure functions in nuclei ≠ superposition of constituents nucleons parton saturation dissociation of the c-cbar pair with the dense medium produced in the collision partonic or hadronic non-lineal effects favoured by the high density of partons become important and lead to eventual saturation of the parton densities NI@SPS, IMP@RHIC suppression by a dense medium, not thermalized nuclear absorption multiple scattering of a pre-resonance c-cbar pair within the nucleons of the nucleus non thermal colour connection Others: Cronineffect energyloss IMP@SPS, RHIC? w thermalisation QGP •hot effects: hint of deconfinement QGP sequential suppression recombination E. G. Ferreiro USC CNM effects on quarkoniumSPhN17 Sept 10

  5. J/yproduction mechanisms p soft g c p J/y c c J/y c p hard g p 2→2 g+g → J/y+g • Color Singlet Model: • perturbative creation of the ccbar pair in color singlet state with subsequent binding to J/y with same quantum numbers • hard gluon emission • underpredicts J/ production cross section • predicts no polarization • Color Evaporation Model: • phenomenological approach • perturbative creation of the ccbar pair in the color octet state with subsequent non-perturbativehadronization to color singlet via unsuppressed soft gluon emission • predicts no polarization 2→1 g+g → J/y • NRQCD Color Octet Model: • uses NRQCD formalism to describe the non-perturbativehadronization of the ccbar color octet to the color singlet state via soft gluon emission • factorizes the charmonium production into a short distance hard part and a long distance matrix element which is claimed to be universal • predicts large transverse polarization at high pT(not seen by data) Abigail Bickley, August 9, 2007 E. G. Ferreiro USC CNM effects on quarkoniumSPhN17 Sept 10

  6. Shadowing: aninitialcold nuclear mattereffect nPDFhint • Nuclear shadowing is an initial-state effect on the partons distributions • Gluon distribution functions are modified by the nuclear environment • PDFs in nuclei different from the superposition of PDFs of their nucleons Shadowing effects increases with energy (1/x) and decrease with Q2 (mT) antishadowing Theshadowingcorrectionsstrongly dependonthepartonicprocessproducingtheJ/Y sinceitaffectskinematics (x,Q2) shadowing QCD hint E. G. Ferreiro USC CNM effects on quarkoniumSPhN17 Sept 10

  7. Nuclear absorption: a final cold nuclear mattereffect Particlespectrumalteredbyinteractionswiththe nuclear mattertheytraverse => J/Ysuppressiondueto final stateinteractionswithspectatornucleons • Usual parameterisation: (Glaubermodel) Sabs = exp(-r sabs L ) nuclear matterdensity break-up crosssection pathlength Energydependence • At lowenergy:the heavy systemundergoessuccessiveinteractionswithnucleons in itspath and has tosurviveall of them=> Strong nuclear absorption • At highenergy:thecoherencelengthislarge and theprojectileinteractswiththe nucleusas a whole=> Smaller nuclear absorption coherencehint In terms of formation time: sabs@ mid y < sabs@forward y? Rapiditydependenceof nuclear absorption? E. G. Ferreiro USC CNM effects on quarkoniumSPhN17 Sept 10

  8. On the kinematics of J/y production: two approaches • CNM -shadowing- effects depends completly on J/y kinematics (x,Q2) • J/y kinematics depends on the production mechanism => Investigating two production mechanisms (including pT for the J/y): g+g → J/y • intrinsicscheme: thepTof the J/y comes frominitialpartons 2→1 g+g → J/y+g • extrinsicscheme: thepTof the J/yisbalancedbytheoutgoinggluon 2→2 E. G. Ferreiro USCCNM effects on quarkoniumSPhN 17 Sept 10

  9. Intrinsic J/yproductionkinematics • Intrinsic scheme: 2 → 1 process CEM @ LO • y, pT can be determined using PHENIX p+p data Phys. Rev. Lett. 98, 232002 (2007) • Easy to handle : yJ/y and pTJ/ydirectly give x1,2 Q2=(2mc)2+(pT)2=mT • Straightforward evaluation of the gluon PDF shadowed in the nucleus at x2 (and x1 in AA) E. G. Ferreiro USCCNM effects on quarkoniumSPhN 17 Sept 10

  10. Extrinsic J/yproductionkinematics • We deal with a 2 → 2 partonic process with collinear initial gluons • The quadri-momentum conservation results in a complex expression of x2 as a function of (x1, y, pT) • Information from the data alone – the y and pT spectra– is not sufficient to determinex1 and x2: the presence of a final-state gluon authorizes much more freedom to choose (x1, x2) for a given set (y, PT) • Models are mandatory to compute the proper weighting of each kinematically allowed (x1, x2) •We use s—channel cut mechanism Extension of CSM Haberzettl and Lansberg, Phys.Rev.Lett.100,032006 (2008) Good results at low pT E. G. Ferreiro USCCNM effects on quarkoniumSPhN 17 Sept 10

  11. On the kinematics of J/y production: equations shadowing partonic cross section nuclear absorption fit to data s-channel cut model kinematic variables E. G. Ferreiro USC CNM effects on quarkoniumSPhN 17 Sept 10

  12. Extrinsic vs intrinsickinematics I Intrinsic scheme Extrinsic scheme both implemented in a Monte Carlo code: JIN E.G. Ferreiro, F. Fleuret, and A. Rakotozafindrabe ,Eur. Phys. J. C61, 859 (2009) E.G. Ferreiro, F. Fleuret, J-P. Lansberg and A. Rakotozafindrabe, Phys.Lett.B680, 50 (2009) E. G. Ferreiro USCCNM effects on quarkoniumSPhN 17 Sept 10

  13. Extrinsic vs intrinsickinematics II 2 → 1 2 → 2 For a given set (y, pT): extrinsic scheme: more freedom for x for a given y => larger x in extrinsic scheme We expect different shadowing effects in both cases E. G. Ferreiro USCCNM effects on quarkoniumSPhN 17 Sept 10

  14. Resultsford+Au: J/y rapiditydependence 2→1 g+g → J/y 2→2 g+g → J/y+g for a given y x larger in extrinsic • shadowingdependsonthepartonicprocess: 2→1 or2→2 • antishadowingpeak shifted toward larger y in the extrinsic case • in ordertoreproduce data: nuclear absorption sabsextrinsic > sabsintrinsic arXiv:0912.4498 PRC E. G. Ferreiro USCCNM effects on quarkoniumSPhN 17 Sept 10

  15. Fit of sabswith EKS, EPS and nDS(g) fromRdAu EKS98: compatible with intrinsic & extrinsic EPS08:extrinsic scheme is favorized nPDFhint nDSg:neither extrinsicnor intrinsic… QCD hint E. G. Ferreiro USCCNM effects on quarkoniumSPhN 17 Sept 10

  16. Resultsford+Au: J/y rapiditydependence of RCP Extrinsic scheme: sabs= 0, 2, 4, 6 mb in 3 shadowing models Data dependence on y: • Suppression for the most forward points in the three centrality ranges • In the negative rapidity region, dominated by large x, no nuclear effects Data at back and mid-y can be described with a σabs of 2–4 mb, while the most forward points seem to decrease more than our evaluation sabs(y)? E. G. Ferreiro USCCNM effects on quarkoniumSPhN 17 Sept 10

  17. Fit of sabswith EKS, EPS and nDS(g) fromRdAu and RCP sabsint < sabsext sabs from RCP Intrinsic: increase of σabs with y Extrinsic: softer increase of σabs a constant behavior cannot be ruled out (see EPS08) sabs (y) EKS98 EPS08 nDSg E. G. Ferreiro USC CNM effects on quarkoniumSPhN 17 Sept 10

  18. Resultsford+Au: J/y centralitydependence Extrinsic scheme: sabs= 0, 2, 4, 6 mb in 3 shadowing models EKS98 EPS08 nDSg • in the backward region: antishadowing=>progressive increase of RdAu vs Ncoll • in the forward region: shadowing => progressive decrease of RdAu vs Ncoll E. G. Ferreiro USCCNM effects on quarkoniumSPhN 17 Sept 10

  19. Resultsford+Au: J/y transversemomentumdependence Extrinsic scheme: sabs= 0, 2, 4, 6 mb in 3 shadowing models EKS98 EPS08 nDSg Growth of RdAu not related to Cronin effect: it comes from the increase of xfor increasing PT • in the mid and forward-y region: xgoes through the antishadowingregion => enhancement in RdAu • In the backward region: x sits in an antishadowingregion=> decrease in RdAu E. G. Ferreiro USCCNM effects on quarkoniumSPhN 17 Sept 10

  20. ResultsforAu+Au: J/y centralitydependence Intrinsicscheme: Same CNM suppression at forward and central rapidity Extrinsicscheme: More CNM suppression at forward than central rapidity Extrinsicscheme : RAA @ forward y < RAA@mid y Hot Nuclear matter effects still needed, but… Less need for recombination effects E. G. Ferreiro USCCNM effects on quarkoniumSPhN 17 Sept 10

  21. ResultsforAu+Au: J/y rapiditydependence • Intrinsic: flat behaviour • Extrinsic: maximun at y=0 Again, this indicates that less recombination would be required in the extrinsic case E. G. Ferreiro USCCNM effects on quarkoniumSPhN 17 Sept 10

  22. Resultsfor A+A: J/y transversemomentumdependence Extrinsic scheme: sabs= 0, 2, 4, 6 mb in 3 shadowing models RAAincreases with PT partially matching the trend of PHENIX and STAR data Nuclear modification factor larger than one for PT ≈ 8GeV (STAR results)? J/ψ behavior closer to the one of photons than to the one of other hadrons? Hypotesis: energy losss + Landau-Pomeranchuk-Migdal effect ? The energy loss of a colored object in CNM is limited to be constant However, by the LPM effect , its magnitude will be larger for a CO than for a CS Rather a colorless state than a colored one which propagates in the NM? E. G. Ferreiro USCCNM effects on quarkoniumSPhN 17 Sept 10

  23. On the kinematics of ϒ production Results at 1.8 TeV: • CSM describes well the data at NNLO • LO CSM is sufficient to describe low pT data 2 → 2 process Results at 200 GeV: LO upper line: mb = 4.5 GeV, μR = MT , μF = 2MT LO lower line: mb = 5.0 GeV, μR = 2MT , μF = MT We take the parameters of the upper curve in the following. E. G. Ferreiro USCCNM effects on quarkoniumSPhN 17 Sept 10

  24. Resultsford+Au: ϒrapiditydependence Intrinsic vs extrinsic scheme • Different shadowing effects in the 2 approaches • Antishadowing peak shifted toward larger y in the extrinsic case E. G. Ferreiro USCCNM effects on quarkoniumSPhN 17 Sept 10

  25. Resultsford+Au: ϒrapiditydependence Extrinsic scheme: sabs= 0, 0.5, 1 mb in 3 shadowing models • backward: ok within uncertainties • central: reasonable job • forward : clearly too high (for any σabs) E losstool Physical interpretation • backward: EMC effect • central: antishadowing • forward : shadowing≈1 energy loss is needed E. G. Ferreiro USCCNM effects on quarkoniumSPhN 17 Sept 10

  26. Work in progress: EMC effect EMC antishadowing Let us try to increase the suppression of g(x) in the EMC region, keeping momentum conservation : ʃxg(x) dx = Cte Works better for backward region E. G. Ferreiro USCCNM effects on quarkoniumSPhN 17 Sept 10

  27. Conclusions • We have studied the influence of specific partonic kinematics within 2 schemes: intrinsic (2→ 1) and extrinsic (2→2) pT for different shadowings: EKS98, EPS08, nDGg including nuclear absorption • for J/y d+Au collisions: RdAu vs y 0 => sabs extrinsic > sabs intrinsic RCP vs y => sabs(y) Au+Au collisions: RAA vs y RAA vs Npart => less need for recombination in 2 →2 • for ϒ antishadowing and EMC region need of energy loss 2→2 process http://phenix-france.in2p3.fr/software/jin/index.html E. G. Ferreiro USCCNM effects on quarkoniumSPhN 17 Sept 10

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