# Presentation: 797914

## Quarkonia Production in p-A Collisions Mike Leitch - Los Alamos National Laboratoryleitch@lanl.gov

***Hard Probes 2004, Ericeira, Portugal  -- 4 -10 November, 2004***

** ****production**
** ****mechanisms**
** ****cross section & polarization**
** ****complications**
** ****nuclear effects**
** ****shadowing**
** ****p****T**** broadening**
** ****absorption**
** ****parton energy loss**
** ****contrasting open & closed charm**
** ****summary**

## J/ψ & open-charm production, parton level structure & dynamics

- CEM
- CTEQ5L

## Production & Hadronization into J/ψ 

- _Production & Hadronization into J/__ψ__ _

- CDF Data first uncovered short-comings of CSM

**CSM**

**COM**

- total

**hep-ph/0311048 &**
**Beneke, Kramer PRD 55, 5269 (1997)**

## J/ψ  Production—Polarization

- _J/__ψ_ _ Production—Polarization_
- Color Octet Model predicts J/ψ polarization at large pT  - NOT SEEN in data

-  CDF and Fermilab E866 data show little polarization of J/ψ - opposite trend from predictions
-  But  maximally polarized for (2S+3S) but not (1S)
-  Is feed-down washing out polarization? (~50% of 1S from feed-down)
-  NRQCD predicts 0.25 <  < 0.7 (feed-down from  states included).

***E866/NuSea – PRL ***_***86***_***, 2529 (2001)***

**ψ****’ Polarization**

**NRQCD**

**NRQCD**

**J/****ψ**** Polarization**

**E866**
**very small J/****ψ**** polarization**

** ****PRL 91, 211801 (2003)**

**E866 800 GeV**

##  Nuclear dependence of parent resonance, e.g. χC is probably different than that of the J/ψ

***E705 @ 300 GeV/c, PRL ***_***70***_***, 383 (1993)***

-  Large fraction of J/ψ’s are not produced directly

-  Effect on Nuclear dependence:
-  Nuclear dependence of parent resonance, e.g. χC is probably different than that of the J/ψ
-  e.g. in proton production ~21-30% of J/**ψ****’****s** will have effectively stronger absorption because they were actually more strongly absorbed (larger size) χC’s while in the nucleus

|  | Proton | Pion |
| --- | --- | --- |
| χ,1,2  J/Ψ | 30% | 37% |
| Ψ ́  J/Ψ  | 5.5% | 7.6% |

**HERA-B**
******c****/J/****ψ**** = 0.21********0.05    from 15% of available statistics**
**(********s****NN**** = 42 GeV)**
** **

- m-mJ/

## PHENIX - J/ψ cross section versus rapidity & √s

- _PHENIX - J/__ψ__ cross section versus rapidity & √s_

- More pp J/ψ’s coming from PHENIX 2004 run (~300/muon arm) + many more expected in 2005
- (Ψ’ so far out of reach with present RHIC luminosities)

**HERA-B ****Ψ****’**

- #J/ψ’s:  ~400 (), ~100 (ee)

## CDF Run II J/Psi vrs pT now down to pT=0

- hep-ex/0408020

**Current NLO QCD calculations can describe observed CDF J/****ψ**** cross sections**
**Cacciari, Frixione, Mangano, Nason, Ridolfi,      hep-ph/0312132 - FONLL or MC@NLO.**
** ****but I guess they still don’t get (lack of ) polarization correct??**

- CDF J/ψ cross section down to pT=0 using new silicon trigger

## Nuclear modification of parton level structure & dynamics

-  e.g. shadowing – depletion of low-momentum partons (gluons)
-  color glass condensate – specific/fundamental model that gives gluon shadowing in nuclei

- _Nuclear modification of parton level structure & dynamics_

**Nuclear effects on parton “dynamics”**
-  energy loss of partons as they propagate through nuclei
-  and (associated?) multiple scattering effects (Cronin effect)
-  absorption of J/ψ on nucleons or co-movers; compared to no-absorption for open charm production

- = x1-x2

**Gluon shadowing**
***Gerland, Frankfurt, Strikman,***
***Stocker & Greiner (hep-ph/9812322)***

## Gluon Shadowing

-  **Shadowing** of gluons  depletion of the small x gluons
-  Very low momentum fraction partons have large size & number density, overlap with neighbors, and fuse; thus enhancing the population at higher momenta at the expense of lower momenta
-  Or alternate but equivalent picture: coherent scattering resulting in destructive interference for coherence lengths longer than the typical intra-nucleon distance

***Increasing y***
***(smaller x)***

- D. Kharzeev hep-ph/0307037

- Color-glass condensate or saturation

## J/ψ at fixed target: Absorption at mid-rapidity

- Breakup by nucleus of J/**ψ**** or pre-**J/**ψ**** (ccbar) as it exits nucleus**
- Power law parameterization s = sN * Aa
- a = 0.92		(E772, PRL _66 _(1991) 133) (limited pT acceptance bias)
- a = 0.919 ± 0.015 	(NA38, PLB _444 _(1998)516)
- a = 0.954 ± 0.003	(E866 @ xF=0. PRL _84 _(2000),3258 )
- a = 0.941 ± 0.004	(NA50, QM2004)
- Absorption model parameterization
- = 6.2 mb (NA38/50/51) to 4.3 ± 0.3 mb (NA50, QM2004)
- Small difference between J/ψ  and ψ(2S) (E866)
- a(J/**ψ**) – a(**ψ**(2S)) ~ 0.02-0.03 @ xF = 0  (NA50 **σ****ψ****’ - ****σ****J/****ψ**** ****= 3.5 ****±** 0.7 mb)

## J/ψ suppression in pA fixed-target

**800 GeV p-A (FNAL)**
***PRL 84, 3256 (2000); PRL 72, 2542 (1994)***

**Hadronized**
**J/****ψ****?**

**open charm: no A-dep**
**at mid-rapidity**

- _J/__ψ__ suppression in pA fixed-target_

**Kopeliovich, Tarasov, Hufner**
**Nucl Phys A696 (2001) 669-714**

**Energy loss** of incident parton shifts effective xF  and produces nuclear suppression which increases with xF

**stat. errors only**

**(C,W targets)**

## PT Broadening for J/ψ’s

- _P__T__ Broadening for J/__ψ__’s_

**Upsilons**

**Drell-Yan**

**J/******** & ********’**

**p****T**** broadening comparable**
**to lower energy**
**(********s = 39 GeV in E866)**

**Usually interpreted as initial-state multiple scattering**

## J/ψ nuclear dependence vrs rapidity, xAu, xFPHENIX compared to lower energy measurements

- _J/__ψ__ __nuclear dependence vrs rapidity, x__Au, __x__F_PHENIX compared to lower energy measurements

**Klein,Vogt, PRL 91:142301,2003**** **
**Kopeliovich, NP A696:669,2001 **

- RdA

**Low x****2**** ~ 0.003**
**(shadowing region)**

**Data favors (weak) shadowing + (weak) absorption (******** > 0.92)**
**With limited statistics difficult to disentangle nuclear effects**
**Will need another dAu run! (more pp data also)**

- (in gold)

**Not universal versus X****2**** : shadowing is not the story.**
**BUT does scale with x****F ****! - why?**
**(Initial-state gluon energy loss -which goes as x1~xF - expected to be weak at RHIC energy)**

****** ****compared to lower ********s**

- = Xd - XAu

## Some Critical Onia Physics Issues

-  Production & absorption
-  octet, singlet → absorption differences, polarization?
-  feed-down – dilution of polarization → need to de-convolute J/ψ, ψ’, C
-  mid-rapidity absorption is combination of physical and c-cbar states → need to understand both vrs xF and √S
-  why does J/ψ nuclear dependence scale with xF (& not with x2)?
-  why is 2s+3s polarized, but not 1s & J/ψ? And what about ψ’ polarization?
-  If above were understood better, then:
-  can go after gluons and their nuclear modification (shadowing, initial-state energy loss)
-  have a firm baseline for A-A (QGP studies with onia)
-  What can NA60 contribute (from a non-NA60 member)?
-  excellent mass resolution, separation of ψ’ (better for polarization since no feed-down)    & add C
-  high-precision, broad xF, pT coverage at several new √S. By comparisons with E866,    Hera-B, NA3 - unravel scaling mystery, understand absorption, etc.
-  coverage up to xF ≥ 0.5 and xF < 0 important → can be obtained by moving dimuon spectrometer back from target, and via Pb-Be collisions
-  problem – for clear physics comparisons, SPS & LHC both need pp, pA baseline at same √S as AA!

- _Some Critical Onia Physics Issues_

- NA60 test run
-  450 GeV p+Be

## Summary & Comments

-  Progress on onia production cross sections and polarizations but still doesn’t seem to be well understood
-  causes uncertainties in the understanding of nuclear effects (e.g. J/ψ absorption)
-  Weak shadowing has been observed at RHIC for the J/ψ in dAu collisions but statistics are low, so will need another dAu run
-  but scaling with xF (and not with x2) is still a puzzle!
-  Complementary studies of open charm and of other onia are also critical
-  no apparent nuclear effects for open charm in d-Au (at mid-rapidity at least)
-  upgrades to the RHIC detectors to allow exclusive measurements of open charm and beauty are critical for completing the physics puzzle
-  and NA60 can contribute now, particularly if priority is placed on pA (and Ap) measurements over broad ranges in xF and pT

## E866 - J/Nuclear dependence even for Deuterium/Hydrogen

**From fits to E866/NuSea**
**p + Be, Fe, W data:**

- Nuclear dependence in deuterium seems to follow the systematics of larger nuclei, but with an effective A smaller than two.

## ?

**← ****Au**

**d ******

- _Centrality Dependence – new at RHIC_

## Fermilab E789: D0 & B  J/ψ X(charm & beauty using silicon)

- Dimuon spectrometer
- +

- 16-plane, 50m pitch/8.5k strip silicon vertex detector

## BELLE – Double Charm !

- PRL 89, 142001 (2002).

- For e+e- collisions at the energy of  the Upsilon(4S)