# Presentation: 820417

## J/ Production and Nuclear Effects for d+Au and p+p Collisions in PHENIX

- Raphaël Granier de Cassagnac
- LLR – Ecole polytechnique, France
- for the PHENIX collaboration
- Quark Matter 2004
- Oakland, California
- January 12-17, 2004

## Physics motivation

- Goal: disentangle normal nuclear effects
- Antishadowing & Shadowing (gluon saturation ?)
- Energy loss of initial parton
- pT broadening (Cronin effect)
- J/ (or cc ) absorption
- Tool: d+Au collisions
- over a broad range of pT, rapidity and centrality.
- Interests:
- Intrinsically probes interesting nuclear effects
- Baseline for Au+Au: Why do J/ disappear / appear ?

** ̄**

## How does PHENIX see the J/ ?

- How does PHENIX see the J/ ?

- J/  e+e– identified in RICH and EMCal
- || < 0.35
- p > 0.2 GeV
- J/μ+μ–
- identified in  2 fwd spectrometers
- 1.2 < || < 2.4
- p > 2 GeV
- Centrality and vertex given by
- BBC in 3<||<3.9

## Short history of RHIC

| Year | Ions | sNN | Luminosity | Detectors | J/ |
| --- | --- | --- | --- | --- | --- |
| 2000 | Au-Au | 130 GeV | 1 b-1 | Central (electrons) | 0 |
| 2001 | Au-Au | 200 GeV | 24 b-1 | Central | 13 + 0 [1] |
| 2002 | p-p | 200 GeV | 0.15 pb-1 | + 1 muon arm | 46 + 66 [2] |
| 2002 | d-Au | 200 GeV | 2.74 nb-1 | Central | 300+800+600 |
| 2003 | p-p | 200 GeV | 0.35 pb-1 | + 2 muon arms | 100+300+120 |
| 2004 | Au-Au | 200 GeV | 300 nb-1 ? | ! taking data ! | ~400+2x1600 ? |

- [1] _[nucl-ex/0305030](http://xxx.lanl.gov/nucl-ex/0305030)_
- [2] _[hep-ex/0307019](http://xxx.lanl.gov/hep-ex/0307019)_

- All data shown are from the run 3
- and results are PHENIX preliminary !

## Di-electron analysis

- Identify electron
- 0.5 < E/p < 1.5
- Di-electron invariant mass spectra
- Subtract combinatorial background
- Signal = N+- - (N++ - N--)
- Count J/
- Correct for acceptance and efficiencies
-  Cross section

- Example : dAu sample

- Mass Resolution ~ 100 MeV

## Di-muon analysis

- Identify muons
- Depth in Identifier
- Di-muon inv. mass spectra
- Subtract combinatorial backgrounds (N++ **** N--)
- Signal = N+- -2(N++)(N--)
- Work in progress to quantify physical backgrounds :
- Open charm & beauty,
- Drell-Yan,
- A hint of ’
- For now: fit gauss J/+exp bg
- Correct for acceptance and efficiencies
-  Cross section

- Example : dAu north sample

- Mass Resolution ~ 150 to 200 MeV

## Deuteron               Gold 

- In PHENIX, J/ mostly produced by gluon fusion, and thus sensitive to gluon pdf
- Three rapidity ranges probe different momentum fraction of Au partons
- South (y < -1.2) : large X2 (in gold)   ~ 0.090
- Central (y ~ 0) : intermediate X2        ~ 0.020
- North (y > 1.2) : small X2 (in gold)    ~ 0.003

- d

- Au

## Cross section versus pT

- J/  +-

- Cross section versus pT

- pT is broadened for dAu

- <pT2> =
- <pT2>dAu – <pT2>pp
- 1.77 ± 0.35 GeV2
- 1.29 ± 0.35 GeV2
- (preliminary)

## dAu/pp versus pT

- dAu/pp versus pT

**Low x****2**

**High x****2**

- Broadening comparable to lower energy       (s = 39 GeV in E866)

- RdA

## Cross section versus rapidity

- Total cross section (preliminary)
- BR pp = 159 nb ± 8.5 % (fit) ± 12.3% (abs)

- J

## dAu/pp versus rapidity

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

- Data favours (weak) shadowing

- +  (weak) absorption ( > 0.92)
- With limited statistics difficult to disentangle nuclear effects

- RdA

##  versus X compared to lower s

-  versus X compared to lower s

- Not universal versus X2 : shadowing is not the whole story.
- Same versus XF for diff s. Incident parton energy loss ? (high Xd = high XF)
- Energy loss expected to be weak at RHIC energy.

- X2 (in gold)

- E866: PRL 84, 3256 (2000)NA3: ZP C20, 101 (1983)

## Centrality analysis

- Au breaks up in our south beam counter
- Define 4 centrality classes
- Relate centrality to <Ncoll>
- through Glauber computation
- <Ncoll> = 8.4 ± 0.7

**<N****coll****> = 3.2 ± 0.3**

**<N****coll****> = 15.0 ± 1.0**

- South BBC Charge

- Central

- Peripheral

- Counts

- MB

## Central/peripheral versus Ncoll

- Low and med x2 have small variations
- Weak nuclear effects
- Small shadowing centrality dependence
- High x2 has a steep rising shape
- How can antishadowing be so steep ?

**High x****2**
**~ 0.09**

**Low x****2**** ~ 0.003**

- RCP

## dAu / pp versus Ncoll

- dAu / pp versus Ncoll

- Low x2 shape consistent with shadowing models
- High x2 shape steeper than corresponding antishadowing...
- What could it be ?
- Effect of being closer     to the Au frame ?

**High x****2**** ~ 0.09**

**Low x****2**** ~ 0.003**

- RdA

## Conclusion & perspectives

- We have seen small nuclear effects !
- Weak shadowing
- Smaller absorption than expected    ( > 0.92)
- pT broadening similar to lower energies
- Something above antishadowing ?
- Rising RdA versus centrality at high x2        (y < -1.2)
- Difficult to disentangle given statistics
- Need more luminosity !
- But, no large nuclear effect !
- Good news to see J suppression in Au-Au !

## PHENIX charmonia related posters

- Jane M. Burward-Hoy: "Centrality Dependence of J -> + - in High-Energy d+Au Collisions"
- Xiaorong Wang: "J  Polarization Study for d Au collisions at RHIC"
- DongJo Kim: "J production in p+p collisions at s = 200 GeV with the PHENIX experiment at RHIC"
- Alexandre Lebedev: "Measurement of c -> J +  in dAu Collisions at RHIC/PHENIX"
- Gobinda Mishra: "Study of J polarization in p+p collisions at             sNN = 200 GeV with PHENIX experiment at RHIC"
- Kyoichiro Ozawa: "Measurements of J -> e+e- in Au-Au collisions at    s = 200 GeV"
- David Silvermyr: "First observation of the ' at RHIC - Techniques for fitting dimuon spectra in d-Au collisions at sNN = 200 GeV"