# Presentation: 010104

## A d+Au data-driven prediction of cold nuclear matter (CNM) effects on J/ψ production in Au+Au collisions at RHIC

- Raphaël Granier de Cassagnac
- LLR – École polytechnique / IN2P3
- (thanks to Jean Gosset
- & Klaus Reygers)

**Notes:**
ABSTRACT

Heavy quarkonia production is expected to be sensitive to the
formation of a quark gluon plasma. It is also sensitive to cold
nuclear matter and subtracting the ``normal'' suppression is a key
point in any interpretation of quarkonia production in heavy ion
collisions. Data from p+A or d+A collisions provide good insights
into the various effects cold nuclear matter has on quarkonia
(shadowing, absorption, etc.) To extrapolate them to A+A collisions,
one always rely on models.

After a quick review of models used so far, I will present a new
Glauber-inspired approach. It uses the first centrality dependent
d+A quarkonia measurement, namely $J/\psi$ in d+Au collisions seen
by the PHENIX experiment to derive the Au+Au nuclear modification
factor in a as much as possible model-independent way.

## Motivation & outline

- ±11% global systematics
- ±12% global systematics
- ± 7% global systematics

- Subtracting cold nuclear matter (CNM) effects is crucial to interpret    J/ψ suppression
- How is it done @ SPS ?
- How is it done @ RHIC ?
- A new method for RHIC...

- J/ψ nuclear modification factor

- Cold nuclear matter toy model - raphael@in2p3.fr

- QM2006, November 19th

**Notes:**
(or not done in fact) @ RHIC
@SPS, Et analysis.

## Cold nuclear matter @ SPS

- _Normal nuclear absorption alone_ does a splendid job in describing pA, SU, and peripheral PbPb & InIn...
- (including preliminary pA  @ 158 GeV from NA60)
- exp(-σabs ρ0 L)
- (or in Glauber model)
- σabs = 4,18 ± 0,35 mb
- L nuclear thickness:

- NA50, EPJ C39 (2005) 335
- & E. Scomparin’s talk

- J/ψ / DY rescaled to 158 GeV

- NA60 preliminary

- Cold nuclear matter toy model - raphael@in2p3.fr

- QM2006, November 19th

## (Anti) shadowing @ SPS ?

- Do we fully understand CNM @ SPS ?
- Not these surprising rapidity distribution asymmetries 
- Variation of ~30 to ~50% in one unit of rapidity !
- Is it (anti)shadowing ?
- Not taken into account in CNM extrapolation...

- NA50, CERN-PH-EP/2006-018,
- to appear in Eur. Phys. J. C.

- J/ψ yield

- Cold nuclear matter toy model - raphael@in2p3.fr

- QM2006, November 19th

## First centrality dependence in dA (or pA) of J/ψ production !
Reproduced by Ramona Vogt
Black lines: EKS98 shadowing
+ σabs = 0 to 3 mb
Colored lines: FGS shadowing + σabs = 3 mb
Favoring moderate shadowing + moderate absorption...

- First centrality dependence in dA (or pA) of J/ψ production !
- Reproduced by Ramona Vogt
- Black lines: EKS98 shadowing
- + σabs = 0 to 3 mb
- Colored lines: FGS shadowing + σabs = 3 mb
- Favoring moderate shadowing + moderate absorption...

- RdAu

- Cold nuclear matter @ RHIC

- PHENIX, PRL96 (2006) 012304
- Klein,Vogt, PRL91 (2003) 142301

- Y = +1.8

- Y = 0

- Y = –1.7

- Cold nuclear matter toy model - raphael@in2p3.fr

- QM2006, November 19th

## From dA to AA @ RHIC

- What is on the market ?
- Model of nuclear absorption +
- inhomogeneous (anti)shadowing
- (Ramona Vogt, nucl-th/0507027)
- exp –[ (σdiss(y)+σdiss(-y)) ρ0L ]
- (Karsch, Kharzeev & Satz PLB637(2006)75)
- σdiss from fits on dA data 
- (unrealistic error bars)
- But shadowing doesn’t go like L...

- Cold nuclear matter toy model - raphael@in2p3.fr

- QM2006, November 19th

**Notes:**
First, the dA data are poor...

## 3. Another approach...

- Goal
- Predict RAA from RdA
- Concerns
- Stay as much as possible data-driven
- Take full advantage of dAu centrality-dependence...

- © Uderzo & Goscinny,
- Asterix chez les helvètes

- Cold nuclear matter toy model - raphael@in2p3.fr

- QM2006, November 19th

**Notes:**
« We have not sacrificed this poor little child for nothing »

## RdA vs impact parameter b

- RdA vs impact parameter b

- Re-plot PHENIX RdA vs impact parameter b from Glauber model
- Phenomenological fit to RdA(b) 
- Cut off RdA=1 at high b
- Physically expected
- OK for an upper bound of CNM

- b(fm)

**0- 20% ****20- 40% ****40- 60%      ****60- 88%**

- b(fm)

- Y = +1.8

- Y = 0

- Y = -1.7

- RdA

- Cold nuclear matter toy model - raphael@in2p3.fr

- QM2006, November 19th

**Notes:**
Negative – Nul – Positive

## Plugged in Glauber model

- Glauber provides, for a given A+A collision at bAA, a set of N+N collisions occurring at bi1 and bi2.
- One minimal assumption is rapidity factorization: RAA(|y|,bAA) =
- Σcollisions [ RdA (-y,bi1) x RdA (+y,bi2) ] / Ncoll
- Works (at least) for absorption & shadowing since production
- ~ pdf1 x pdf2 x exp –ρσ(L1+L2)

- Cold nuclear matter toy model - raphael@in2p3.fr

- QM2006, November 19th

## Propagating dA error

- Varying the fit parameters
- Uncorrelated
- Within ±1σ
- to propagate the statistic + systematic dAu uncertainties throughout the Glauber computation

- Y = -1.7

- Y = 0

- Y = +1.8

- RdA

- b(fm)

- Cold nuclear matter toy model - raphael@in2p3.fr

- QM2006, November 19th

## Systematic uncertainties

- Varying line shapes 
- 3 to 5% @ y ~ 1.7
- 3 to 12% @ y ~ 0
- (asymmetric and depending on centrality)
- Varying Glauber parameters (pp total cross section, Woods Saxon parameters,...)
- 2% @ y ~ 1.7
- 4% @ y ~ 0

- Y = -1.7

- Y = 0

- Y = +1.8

- RdA

- b(fm)

- Cold nuclear matter toy model - raphael@in2p3.fr

- QM2006, November 19th

## The output: RAA (Ncoll)

- Black curves reflect stat. and syst. errors from dAu
- Much less constrained @ y~0 because:
- RdA(0) measurements are less precise than RdA(-1.7) and RdA(+1.7)
- and squared while computing RdA(-y) x RdA (+y)
- Then, take the average in _experimental_ centrality classes

- RAA extrapolation
- 1.2 < |y| < 2.2

- RAA extrapolation
- |y| < 0.35

- Cold nuclear matter toy model - raphael@in2p3.fr

- QM2006, November 19th

## Comparison to models & data

-  Consistent with Vogt’s prediction (EKS shadowing + 1 or 3 mb σabs)
-  Prediction @ y~1.7 is much more powerful than @ y~0

- See T. Gunji & A. Glenn talks

- Cold nuclear matter toy model - raphael@in2p3.fr

- QM2006, November 19th

## RAA / CNM @ RHIC

- ±35% global systematics
- ±30% global systematics

- J/ψ survival beyond CNM

- ← This will decrease by recomputing
- RdA with new pp data (A.Bickley’s talk)

- First RAA/CNM extraction including (proper) error propagation
- Boxes are correlated errors from AuAu & _dominant_ CNM
- _Important_: missing overall global _relative_ uncertainty
- 30% @ y ~ 1.7 / 35% @ y ~ 0
- Due to different pp references that don’t cancel in RdA and RAA
-         RAA(|y|) / RdA(-y) x RdA(+y)

- Cold nuclear matter toy model - raphael@in2p3.fr

- QM2006, November 19th

## Quick comparison to SPS

- At mid-rapidity, the amount of surviving J/ψ @ RHIC is compatible with SPS (~60%) but depends a lot on CNM (and pp references)...
- At forward rapidity, RHIC anomalous suppression is much stronger !

- ±11% global systematics
- ±35% global systematics
- ±30% global systematics

- J/ψ survival beyond CNM

- Cold nuclear matter toy model - raphael@in2p3.fr

- QM2006, November 19th

## Conclusions

- Pro’s
- Very little model dependence (apart from Glauber)
- (no σabs , no shadowing scheme, y=0 & 1.7 independence,...)
- Proper error propagation from dAu (and pp)
- Proper centrality selection (experimental classes)
-  J/ψ survival of 25±12% @ y=1.7 & 44±23% @ y=0
- Con’s
- Not applicable without p+A (or d+A) centrality dependence at _same energy_ and at _both_ +y and –y wrt A+A collisions (thus not at SPS or LHC)
- Limited by dAu statistic ! We need more !
- Especially @ y~0 (and dCu to apply this to CuCu)

- Cold nuclear matter toy model - raphael@in2p3.fr

- QM2006, November 19th

## Back-up slides

## Collision display

- Disappearance probability
- No assumption on production point
- Weighted by Woods Saxon

- y ~ 0
- 2 fm

- Disappearance probability

- y ~ 1.7
- 5 fm

- Cold nuclear matter toy model - raphael@in2p3.fr

- QM2006, November 19th

## Nuclear absorption only

- Compute L with Glauber model
- Fit exp(-σabs ρ0 L)
- Results are different wrt KKS numbers

- KKS, PLB637(2006)75

- Cold nuclear matter toy model - raphael@in2p3.fr

- QM2006, November 19th

## Sampling local impact parameter in AuAu

- Cold nuclear matter toy model - raphael@in2p3.fr

- QM2006, November 19th

## Varying Glauber parameters

- Cold nuclear matter toy model - raphael@in2p3.fr

- QM2006, November 19th

## Varying the line shape

- Cold nuclear matter toy model - raphael@in2p3.fr

- QM2006, November 19th

## Deuteron             Gold 

- In PHENIX, J/ψ 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

- Cold nuclear matter toy model - raphael@in2p3.fr

- QM2006, November 19th

**Notes:**
...
“ If we see a Jpsi at negative rapidity, it has to come from a high x in the gold. Indeed our average X in the south is 0.09. On the contrary, if we see a northern psi, is has to come from a low X in the gold, and our average is 3.10 ^ -3. The midrapidity measurement is around 0.02. Here is a example of theoretical prediction of shadowing. This is the ratio of the gluon pdf in a lead nucleon to the gluon pdf in a proton versus X. You can see that our forward measurement is sitting in shadowing-land, while the backward should see anti-shadowing. ”
Shadowing diffère d’un facteur trois entre modèles... 

## Cold nuclear matter effects ?

- gluons in Pb / gluons in p

- x

- J/ψ (or cc) absorption
- (Anti) shadowing
- (gluon saturation, CGC...)
- Energy loss of initial parton
- pT broadening (Cronin effect)
- Complications from feeddown ψ’ & χc ?
- Something else ?

- Eskola, Kolhinen, Vogt
- NPA696 (2001) 729

- _An example of gluon shadowing prediction_

- Anti
- Shadowing

- Shadowing

- Cold nuclear matter toy model - raphael@in2p3.fr

- QM2006, November 19th

## Cold nuclear matter effects ?

- open charm

- dE/dx ?
- Intrinsic
- Charm ?

- Shadowing ?

- Absorption ?

- σψ(pA) =
- σψ(pp) x A****

-  = xp- xA

-  = xA

- A real puzzle ! Especially when one goes to low x2, high xF...

- Cold nuclear matter toy model - raphael@in2p3.fr

- QM2006, November 19th

**Notes:**
NA50 from pA only...
E866 is Be, Fe, W...

## Slide 26

- Cold nuclear matter toy model - raphael@in2p3.fr

- QM2006, November 19th