1. Cold nuclear matter effects on quarkonium Cold nuclear matter effects on quarkonium Rencontres QGP France Etretat, France Septembre 22, 2010 Elena G. Ferreiro Universidade de Santiago de Compostela, Spain Work done in collaboration with F. Fleuret, J-P. Lansberg, N. Matagne and A. Rakotozafindrabe arXiv:0912.4498 PRC81 (2010)

2. Introduction and motivation A lot of work trying to understand A+A data (since J/  QGP signal) Here we focalise on p+A data (where no QGP is possible) only cold nuclear matter (CNM) effects are in play here: shadowing and nuclear absorption In fact, the question is even more fundamental: p+p data we do not know the specific production kinematics at a partonic level: CS (2→2) vs CO (2→1) Quakonium as a hint of deconfinement Quakonium as a hint of coherence Quakonium as a hint of QCD QGP hint nPDF hint QCD hint E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10

3. Introduction and motivation Our goal: To investigate the CNM effects and the impact of the specific partonic production kinematics Results on J/  production Extend our study to ϒ CNM effects E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10

4. QGP recombination sequential suppression cold effects: hot effects: gluon shadowing nuclear structure functions in nuclei ≠ superposition of constituents nucleons NI@SPS, IMP@RHIC nuclear absorption multiple scattering of a pre- resonance c-cbar pair within the nucleons of the nucleus IMP@SPS, RHIC? CGC parton saturation percolation non-lineal effects favoured by the high density of partons become important and lead to eventual saturation of the parton densities non thermal colour connection hadronic comovers partonic comovers dissociation of the c-cbar pair with the dense medium produced in the collision partonic or hadronic suppression by a dense medium, not thermalized wo thermalisation NO QGP w thermalisation QGP COLD and HOT effects Others: Cronin effect energy loss hint of coherence hint of deconfinement hint of QCD E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10

5. Abigail Bickley, August 9, 20075 Color Singlet Model: –perturbative creation of the ccbar pair in color singlet state with subsequent binding to J/  with same quantum numbers –hard gluon emission –underpredicts J/  production cross section – predicts no polarization J/  production mechanisms NRQCD Color Octet Model: –uses NRQCD formalism to describe the non-perturbative hadronization 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 p T (not seen by data) Color Evaporation Model: –phenomenological approach –perturbative creation of the ccbar pair in the color octet state with subsequent non-perturbative hadronization to color singlet via unsuppressed soft gluon emission –predicts no polarization p p J/  soft g c c p p J/  hard g c c 2→1 g+g → J/  2→2 g+g → J/  g hard g E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10

6. 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: an initial cold nuclear matter effect Shadowing effects increases with energy (1/x) and decrease with Q 2 (m T ) shadowing antishadowing The shadowing corrections strongly depend on the partonic process producing the J/  since it affects kinematics (x,Q 2 ) nPDF hint QCD hint E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10

7. Particle spectrum altered by interactions with the nuclear matter they traverse => J/  suppression due to final state interactions with spectator nucleons At low energy: the heavy system undergoes successive interactions with nucleons in its path and has to survive all of them => Strong nuclear absorption At high energy: the coherence length is large and the projectile interacts with the nucleus as a whole => Smaller nuclear absorption  abs @ mid y <  abs @ forward y? Rapidity dependence of nuclear absorption? Usual parameterisation: (Glauber model) Nuclear absorption: a final cold nuclear matter effect coherence hint Energy dependence In terms of formation time: S abs = exp(-  abs L ) nuclear matter densitybreak-up cross sectionpath length E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10

8. On the kinematics of J/  production: two approaches Investigating two production mechanisms (including p T for the J/  : g+g → J/  intrinsic scheme: the p T of the J/  comes from initial partons g+g → J/  +g extrinsic scheme: the p T of the J/  is balanced by the outgoing gluon E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10 CNM -shadowing- effects depends completly on J/  kinematics (x,Q 2 ) J/  kinematics depends on the production mechanism => 2→2 2→1

9. Intrinsic J/  production kinematics Intrinsic scheme: 2 → 1 process CEM @ LO y, p T can be determined using PHENIX p+p data Phys. Rev. Lett. 98, 232002 (2007) Easy to handle : y J/  and p T J/   directly give x 1,2 E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10 Straightforward evaluation of the gluon PDF shadowed in the nucleus at x 2 (and x 1 in AA) Q 2 =(2m c ) 2 +(p T ) 2 =m T

10. We deal with a 2 → 2 partonic process with collinear initial gluons The quadri-momentum conservation results in a complex expression of x 2 as a function of (x 1, y, p T ) Information from the data alone – the y and p T spectra– is not sufficient to determine x 1 and x 2 : the presence of a final-state gluon authorizes much more freedom to choose (x 1, x 2 ) for a given set (y, P T ) Models are mandatory to compute the proper weighting of each kinematically allowed (x 1, x 2 ) We use s—channel cut mechanism Extension of CSM Haberzettl and Lansberg, Phys.Rev.Lett.100,032006 (2008) Also 2 -> 2: CSM @ LO, CEM @NLO Extrinsic J/  production kinematics E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10 Good results at low p T

11. E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10 shadowing nuclear absorption partonic cross section fit to datas-channel cut model kinematic variables On the kinematics of J/  production: equations

12. Extrinsic vs intrinsic kinematics I Intrinsic schemeExtrinsic scheme E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10 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)

13. Extrinsic vs intrinsic kinematics II For a given set (y, p T ): 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 USC CNM effects on quarkonium Etretat 22 Sept 10 2 → 12 → 2

14. antishadowing peak shifted toward larger y in the extrinsic case in order to reproduce data: nuclear absorption  abs extrinsic >  abs intrinsic for a given y x larger in extrinsic 2→2 g+g → J/  g 2→1 g+g → J/  shadowing depends on the partonic process: 2→1 or 2→2 arXiv:0912.4498 PRC Results for d+Au: J/  rapidity dependence E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10

15. EKS98: compatible with intrinsic & extrinsic EPS08: extrinsic scheme is favorized nDSg: neither extrinsic nor intrinsic… Fit of  abs with EKS, EPS and nDS(g) from R dAu nPDF hint QCD hint

16. Results for d+Au: J/  rapidity dependence of R CP E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10 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 σ abs of 2–4 mb, while the most forward points seem to decrease more than our evaluation Extrinsic scheme:  abs = 0, 2, 4, 6 mb in 3 shadowing models  abs (y) ?

17.  abs and  2 from R dAu EKSEPSnDS(g) LO intrinsic3.200.92.111.12.211.6 extrinsic3.901.13.600.53.001.4 Fit of  abs with EKS, EPS and nDS(g) from R dAu and R CP  abs int <  abs ext  abs from R CP Intrinsic: increase of σ abs with y Extrinsic: softer increase of σ abs a constant behavior cannot be ruled out (see EPS08) EKS98EPS08nDSg  abs (y) E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10

18. Results for d+Au: J/  centrality dependence Extrinsic scheme:  abs = 0, 2, 4, 6 mb in 3 shadowing models E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10 in the backward region: antishadowing => progressive increase of R dAu vs N coll in the forward region: shadowing => progressive decrease of R dAu vs N coll EKS98EPS08nDSg

19. Results for d+Au: J/  transverse momentum dependence E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10 Extrinsic scheme:  abs = 0, 2, 4, 6 mb in 3 shadowing models Growth of R dAu not related to Cronin effect: it comes from the increase of x for increasing P T in the mid and forward-y region: x goes through the antishadowing region => enhancement in R dAu In the backward region: x sits in an antishadowing region=> decrease in R dAu EKS98EPS08nDSg

20. Results for Au+Au: J/  centrality dependence Intrinsic scheme: Same CNM suppression at forward and central rapidity Extrinsic scheme: More CNM suppression at forward than central rapidity E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10 Extrinsic scheme : R AA @ forward y < R AA @ mid y Hot Nuclear matter effects still needed, but… Less need for recombination effects

21. Results for Au+Au: J/  rapidity dependence E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10 Intrinsic: flat behaviour Extrinsic: maximun at y=0 Again, this indicates that less recombination would be required in the extrinsic case

22. Results for A+A: J/  transverse momentum dependence E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10 Extrinsic scheme:  abs = 0, 2, 4, 6 mb in 3 shadowing models R AA increases with P T 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? Hypothesis: 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?

23. On the kinematics of ϒ production E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10 Results at 1.8 TeV: CSM describes well d  /dpT at NNLO LO CSM is sufficient to describe low pT data 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. 2 → 2 process

24. Results for d+Au: ϒ  rapidity dependence E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10 Intrinsic vs extrinsic scheme Antishadowing peak shifted toward larger y in the extrinsic case Different shadowing effects in the 2 approaches

25. Results for d+Au: ϒ  rapidity dependence E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10 Extrinsic scheme:  abs = 0, 0.5, 1 mb in 3 shadowing models backward: ok within uncertainties central: reasonable job forward : clearly too high (for any σ abs ) Physical interpretation backward: EMC effect central: antishadowing forward : shadowing≈1 energy loss is needed E loss tool

26. Work in progress: EMC effect E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10 antishadowing EMC Let us try to increase the suppression of g(x) in the EMC region, keeping momentum conservation : ʃ xg(x) dx = Cte Works better for backward region

27. Conclusions E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10 for J/  d+Au collisions: RdAu vs y 0 =>  abs extrinsic >  abs intrinsic RCP vs y =>  abs(y) Au+Au collisions: RAA vs y RAA vs Npart => less need for recombination in 2 →2 We have studied the influence of specific partonic kinematics within 2 schemes: intrinsic (2→ 1) and extrinsic (2→2) p T for different shadowings: EKS98, EPS08, nDGg including nuclear absorption for ϒ antishadowing and EMC region need of energy loss http://phenix-france.in2p3.fr/software/jin/index.html 2→2 process

28. Brain storming: can we distinguish shadowing vs nuclear absorption? p+A measurements for different species? J/  vs  ’ (or DY….) Assumption: shadowing J/  ≈ shadowing  ’ =>  abs J/   abs  ’ p+A measurements for different A @ fixed energy? Assumption:  abs =  abs (s,y) =>check of  abs J/   abs  ’ p+A measurements for fixed A @ different energies? =>  abs J/   abs  ’ =  abs J/   abs  ’ (s) Other possibilities: ϒ  vs continuum Even better: UPC No nuclear absorption => Only shadowing! E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10

29. Backup slides E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10 On the kinematics of J/  production: detail equations s-chanel cut model The Glauber Monte Carlo code Shadowing models Nuclear absorption Comparation with Vogt’s results (CEM @ LO without p T ) Fit procedure J/  production mechanisms Work in progress: RdAu vs Ncoll and RdAu vs pT for EKS98,EPS08, nDSg Some other results

30. Results for A+A: J/  centrality dependence Extrinsic scheme:  abs = 0, 2, 4, 6 mb in 3 shadowing models E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10 R AA systematically smaller in the forward region than in the mid-y region The difference increases for more central collisions This difference matches well the one of the data when σ abs = 0 One needs a larger σ abs if one wanted to reproduce the normalisation of the AuAu data, disregarding any effects of hot nuclear matter (HNM) However, for such large σ abs, surviving J/ψ from inner production points would be so rare that the difference between shadowing effects at mid and forward rapidities would nearly vanish Note that for a σ abs in the range of 2–4 mb, a difference remains

31. Results for A+A: J/  rapidity dependence Extrinsic scheme:  abs = 0, 2, 4, 6 mb in 3 shadowing models E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10 R AA peaks at y = 0, reducing the need for recombination which concentrates at mid y This effect is present in the three shadowing parametrizations we have used This effect reduces with the increase of  abs

32. Results for d+Au: ϒ centrality dependence E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10 Extrinsic scheme:  abs =0 mb,  abs = 0.5mb,  abs = 1 mb in 3 shadowing models EKSEPSnDSg

33. Results for d+Au: ϒ transvese momentum dependence E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10 Extrinsic scheme:  abs =0 mb,  abs = 0.5mb,  abs = 1 mb in 3 shadowing models EKSEPSnDSg

35. Extrinsic vs intrinsic kinematics II For a given couple (y, p T ), x 2 is larger in the extrinsic scheme We expect different shadowing effects in both cases E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10 Much more freedom to choose (x 1, x 2 ) for a given set (y, P T )

36. Work in progress: EKS98 centrality dependence E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10 Extrinsic sheme Intrinsic sheme EKS9 8

37. Work in progress: EPS08 centrality dependence E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10 Extrinsic sheme Intrinsic sheme EPS08

38. Work in progress: nDSg centrality dependence E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10 Extrinsic sheme Intrinsic sheme nDGg nDSg

39. Work in progress: EKS98 p T dependence E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10 Extrinsic sheme Intrinsic sheme EKS98

40. Work in progress: EPS08 p T dependence E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10 Extrinsic sheme Intrinsic sheme EPS08

41. Work in progress: nDSg p T dependence E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10 Extrinsic sheme Intrinsic sheme nDSg

42. E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10 On the kinematics of J/  production: equations I shadowing nuclear absorption partonic cross section fit to datas-channel cut model kinematic variables

43. On the kinematics of J/  production: equations II Concerning it can be factorized in the nuclear density distribution, the shadowing modification factor and the usual gluon PDFs: where we have included the centrality dependence of the shadowing: E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10

44. On the kinematics of J/  production: equations III E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10

45. s-channel cut model: motivation a suitable production model for low pT J/  E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10

46. s-channel cut contributions E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10

47. s-channel cut contributions E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10 s-channel cut contributions to the basic CSM: take into account the dynamics of the ccbar in the bound state need for 4-point coupling ccbar-J  -g new degrees of freedom constrained by fits so far the best description of low-p T data

48. s-channel cut contributions: first evaluations E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10

49. s-channel cut model vs. other models in the market E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10 Various models for the y spectra in p+p [NRQCD calculation] Cooper, Liu & Nayak, Phys. Rev. Lett. 93, 171801 (2004) [g(gg)s + Feed-down] Khoze, Martin, Ryskin Stirling, Eur. Phys. J. C39, 163 (2005)

50. The Glauber Monte Carlo code E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10 E.G. Ferreiro, F. Fleuret, A. Rakotozandrabe. arXiv :0801.4949 [hep-ph]

51. 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: a cold nuclear matter effect E. G. Ferreiro USC CNM effects on J/  production: intrinsic and extrinsic ECT Trento 25 May 09

52. EKS and EPS shadowing model Introduce an initial parameterisation for nuclear parton distributions R A (x,Q 2 0 ) based on a fit to DIS data at Q 2 0 = 2.25 GeV 2 The further evolution in Q 2 is predicted by the DGLAP equations at LO RHIC high-pT forward-rapidity hadron data suggest a stronger gluon shadowing than obtained in previous global analyses f i A (x,Q 2 )  R i A (x,Q 2 ) f i (x,Q 2 ) GRV-LO, CTEQ4L GRV-LO, CTEQ6L1 high pT RHIC data at Q 2 0 = 1.69 GeV 2 E. G. Ferreiro USC CNM effects on quarkonium Palaiseau 5 March 09

53. EKS shadowing model 1. Introduce an initial parameterisation for nuclear parton distributions R A (x,Q 2 0 ) based on the DIS data at Q 2 0 = 2.25 GeV 2 2. Once the nuclear parton distributions are given at an initial scale Q 2 0 >>Λ 2 QCD the further evolution in Q 2 is predicted by the DGLAP eqs: DGLAP eqs: relation between the logarithmic Q 2 -evolution of the structure functions and the gluon distribution, giving the possibility to calculate the value of ratios at any Q 2 if an initial value is known It is assume that at Q 2 >Q 2 0 the scale evolution of the nuclear parton densities is purely perturbative the initial conditions at Q 2 0 contain the nonperturbative input the evolution is made at leading order (LO) 3. The slope of the nuclear parton distributions in Q 2 is obtained in this way No centrality dependence is included in the model E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10 GRV-LO, CTEQ4L

54. EPS shadowing model Global fit to DIS, DY and high pT RHIC data E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10 LO, Q 2 0 = 1.69 GeV 2 RHIC high-pT forward-rapidity hadron data suggest a stronger gluon shadowing than obtained in previous global analyses

55. nDSg shadowing model Define nPDF using a convolution approach: the free nucleon parton densities are convoluted with very simple weight functions that parameterize nuclear effects Instead of: LO LO and NLO evolution Differences with other parameterizations: ESK98: less small x shadowing and very little antishadowing at intermediate x in gluon densities HKM: low x shadowing in the valence distribution (none in HKM), ratios for sea and gluon densities approach 1 as x grows while they strongly rise within HKM they use: E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10

56. Approach based on multiple collisions It takes into account triple pomeron interactions -equivalente to interaction among gluon- It leads to a shadowing due to coherence effects Shadowing increases with s (~1/x) and decreases with pT (~ mT) Pomeron shadowing model Shadowing corrections: integral of the triple P cross section over the single P one Reduction of multiplicity from shadowing corrections E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10

57. The primordial spectrum of particles is altered by interactions with the nuclear matter they traverse on the way out to the detector Rapidity dependence of the nuclear absorption:  abs at mid y <  abs at forward y Usual parameterisation: Nuclear absorption: a cold nuclear matter effect Nuclear absorption: interaction of the preresonant c-cbar pair with spectator nucleons S abs = exp(-  abs L ) nuclear matter densitypath lengthbreak-up cross section Note: some authors consider At high energy: the coherence length is large and the projectile interacts with the nucleus as a whole => Smaller nuclear absorption with growing energies E. G. Ferreiro USC CNM effects on quarkonium Palaiseau 5 March 09

58. EKS shadowing model: intrinsic vs. Vogt’s E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10

59. EKS shadowing model: intrinsic & extrinsic vs. Vogt’s E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10

60. EPS shadowing model: intrinsic vs. Vogt’s E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10

61. EPS shadowing model: intrinsic & extrinsic vs. Vogt’s E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10

62. nDSg shadowing model: intrinsic vs. Vogt’s NLO LO E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10

63. nDSg shadowing model: intrinsic & extrinsic vs. Vogt’s NLO LO Vogt’s: LO Ours: NLO E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10

64. Fit procedure E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10

65. Fit procedure: results I E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10

66. Fit procedure: results II E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10

67. Abigail Bickley, August 9, 200767 Color Singlet Model: – Color singlet cc pair created in same quantum state as J/  – Underpredicts J/  production cross section by a x10 – Predicts no polarization p p J/  hard g c c Lansberg, Int. J. Mod. Phys. A21 (2006) J/  production mechanisms: CSM E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10

68. Abigail Bickley, August 9, 200768 NRQCD Color Octet Model: – Includes octet state cc pairs that radiate soft gluons during hadronization – Color octet matrix elements derived from experimental data were expected to be universal, but are not – Predicts large transverse polarization (  >0) at high p T that is not seen in experimental data p p J/  soft g c c Reisert, Beauty 2006 J/  production mechanisms: COM E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10

69. Abigail Bickley, August 9, 200769 Color Evaporation Model: – Phenomenological approach – Charmonium states formed in proportions determined by experimental data for any cc pair that has a mass below the DD threshold – Uses emission of soft gluons to form J/  – Predicts no polarization Reisert, Beauty 2006 J/  production mechanisms: CEM E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10

70. Abigail Bickley, August 9, 200770 pQCD involving 3-gluons: – Hadronization mechanism includes channel involving the fusion of a symmetric color octet state with an additional gluon – Successfully reproduces experimental cross section and polarization measurements – Fails to reproduce experimental rapidity distribution => New result! Khoze et al Eur.Phys.J. C39 (2005) J/  production mechanisms: pQCD involving 3-gluons E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10