# Presentation: 265534

## Cold Nuclear Matter Effects on J/ψ as Constrained by d+Au Measurements at √sNN = 200 GeV in the PHENIX Experiment 

- Matthew Wysocki
- University of Colorado
- For the PHENIX Collaboration

## Introduction

- There is much interest in*J/*ψ suppression in hot nuclear matter!
- For the latest PHENIX charm-onia measurements, see:
- Session XVIII: Susumu Odaand Catherine Silvestre
- poster by Cesar Luiz da Silva
- Unfortunately, this is not sufficient to understand hot nuclear matter effects.  We must also understand the _cold nuclear matter effects_ on the *J/*ψ.  That is our baseline.

- 2/5/2008

- M. Wysocki - QM2008, Jaipur, India

- Run-4 Au+Au

- Phys. Rev. Lett. 98 (2007) 232301
- nucl-ex/0611020

## Cold Nuclear Matter Effects onJ/y Production

- Cold nuclear matter is a complicated place!
- Shadowing, gluon saturation, anti-shadowing, EMC effect...
- Initial and final state partonic multiple scattering...
- Cronin effect...
- One way that we can study CNM is through high-energy p+A or d+A collisions.
- At RHIC we use √sNN=200 *GeV* d+Au, which was first collided in Run-3 and now again in Run-8.

- 2/5/2008

- M. Wysocki - QM2008, Jaipur, India

## What Can We Do Now?

- New p+p data set in 2005 with an order of magnitude better statistics.
- Two years of improvements in:
- Reconstruction software
- Signal extraction
- Understanding of detector
- Need d+Au analysis done using same method as the new p+p data, so we can do an apples-to-apples comparison.
- Run-4 and Run-7 *R*AA also use this p+p reference.
- For details of the analysis, see arXiv:0711.3917 (accepted for publication in Phys. Rev. C).

- 2/5/2008

- M. Wysocki - QM2008, Jaipur, India

## The PHENIX Experiment

- 2/5/2008

- deuteron
- y>0

- Au ion
- y<0

- MuTr and MuID detect J/ψ®mm at forward & backward rapidities.

- Drift Chamber, Pad Chamber, EMCal & RICH detect J/ψ®ee at mid-rapidity.

- Beam-Beam Counter used to measure centrality and collision z-position.

- M. Wysocki - QM2008, Jaipur, India

## Parton Momentum Cartography

- Nuclear PDFs are modified in various x-ranges.
- Shadowing, anti-shadowing, EMC effect, etc.
- Here we probe 3 ranges of *x*, in both the shadowing and anti-shadowing regions, using PHENIX detectors at forward, x~0.002-0.01backward, x~0.01-0.05and mid-rapidity, x~0.05-0.2.

- 2/5/2008

- M. Wysocki - QM2008, Jaipur, India

- x

**Saturation?**

**shadowing**

**Fermi****Effect**

**anti-shadowing**

**EMC****effect**

## J/ψ pT Spectra

- d+Au data are from Run-3,p+p are from Run-5.
- Fits are to a power law over *p*T Î [0,5] GeV/c, then integrated to get <*p*T2>.
- Can compare to other systems to study *p*T-spectrum broadening from Cronin Effect/multiple scattering.
- For discussion of this see the talk by Susumu Oda in XVIII.

- 2/5/2008

- M. Wysocki - QM2008, Jaipur, India

- arXiv:0711.3917

## J/ψInvariant Yields

- 2/5/2008

- d+Au

- p+p

- Au

- d

- M. Wysocki - QM2008, Jaipur, India

- arXiv:0711.3917

- arXiv:0711.3917

## J/ψ Nuclear Modification Factor

- 2/5/2008

- Calculate using new p+p data and new d+Au analysis.
- Suppression at forward rapidity (deuteron-going direction).  This is sensitive to low-x partons in the Au nucleus.

- M. Wysocki - QM2008, Jaipur, India

- arXiv:0711.3917

## Comparison to Nuclear Models

- 2/5/2008

- One can use EKS1 and NDSG2 nuclear modified PDFs to calculate *R*dAu as a function of rapidity.
- Assume that all additional J/ψ suppression can be accounted for by a single parameter due to interactions with the Au ion.  Express this in terms of a breakup cross section, sbreakup.
- Then we can fit our measured *R*dAu to extract sbreakup.
- 1K. J. Eskola, V. J. Kolhinen, and R. Vogt, Nucl. Phys.  A696, 729 (2001)
- 2D. de Florian and R. Sassot, Phys. Rev. D69, 074028 (2004)

- M. Wysocki - QM2008, Jaipur, India

- sbreakup

*R*dAu from nuclear-modified PDFs

## Comparison to Nuclear Models

- 2/5/2008

- Using EKS (NDSG) model we get **s****breakup**** = 2.8****+1.7****-1.4 ****(2.2****+1.6****-1.5****) ****mb****.**
- Both are compatible (within very large error bars) with sbreakup = 4.2±0.5 mb measured at the CERN SPS.
- B. Alessandro et al., Euro. Phys. J. C48, 329 (2006), nucl-ex/0612012

- M. Wysocki - QM2008, Jaipur, India

- arXiv:0711.3917

- arXiv:0711.3917

## Extrapolation to Au+Au

- 2/5/2008

- We can use the calculated sbreakup due to CNM effects to extrapolate to CNM effects in Au+Au collisions.
- Assuming these nuclear modified PDFs are exactly correct, there is statistically significant J/ψ suppression beyond CNM effects at forward rapidity in Au+Au collisions.
- It must be noted that the error bands are correlated between forward and mid-rapidity.

- Mid-rapidity

- Forward rapidity

- M. Wysocki - QM2008, Jaipur, India

- ±12% Global Scale Uncertainty

- ±7% Global Scale Uncertainty

- arXiv:0711.3917

- PHENIX Au+Au |y|<0.35
- EKS Shadowing + sbreakup
- NDSG Shadowing + sbreakup

- PHENIX Au+Au 1.2<|y|<2.2
- EKS Shadowing + sbreakup
- NDSG Shadowing + sbreakup

## Centrality in d+Au

- M. Wysocki - QM2008, Jaipur, India

- At RHIC we are also able to make measurements vs. impact parameter.
- In Run-3 we use 4 centrality bins, each corresponding to a range of impact parameters.
- We can also express the bins in terms of the average number of nucleon-nucleon collisions in that bin (*N*coll).

## J/ψ RdAu vs. Ncoll

- J/ψ *R*dAu vs. *N*coll

- Again, significant suppression only at forward rapidity.
- Possible hint of a trend w.r.t. *N*coll, at forward and mid-rapidity, but we are hitting the limits of our Run-3 statistics.  Looking forward to Run-8 result (QM2009?).

- 2/5/2008

- M. Wysocki - QM2008, Jaipur, India

## A More Data-Driven Projection

- 2/5/2008

- However, if we do not want to assume either of the previous models, then we may try a different approach.
- In this case we assume that the modification factor depends only on the radial position in the nucleus.  We can then use the measured *R*dAu vs. impact parameter to constrain this Â.  We also appropriately incorporate the statistical and systematic errors on the data1.
- Â is the modification on J/ψ due to one  Au nucleus, so we take Â(+y)*Â(-y) for Au+Au collisions.

- M. Wysocki - QM2008, Jaipur, India

- 1For details of statistical analysis method,
- see poster by Jamie Nagle.
- For more details see:
- Proposal:     R. Granier de Cassagnac, hep-ph/0701222.
- Calculation:  A. Adare et al., arXiv:0711.3917

- r1

- r2

- Â(r1,r2)

## Data-driven Projection to Au+Au

- 2/5/2008

- Mid-rapidity

- Forward rapidity

- M. Wysocki - QM2008, Jaipur, India

- Larger uncertainty bands than those from nuclear-modified PDFs and  sbreakup.  In this case we cannot rule out  Au+Au suppression entirely from cold nuclear matter effects, within the statistical and systematic uncertainties.
- It should be noted that contrary to the previous Au+Au projection, these uncertainty bands are *not *directly correlated between rapidities.

- PHENIX Au+Au |y|<0.35
- Data-driven Projection of CNM Effects at mid-rapidity

- PHENIX Au+Au 1.2<|y|<2.2
- Data-driven Projection of CNM Effects at forward rapidity

- arXiv:0711.3917

- ±12% Global Scale Uncertainty

- ±7% Global Scale Uncertainty

## Data-driven Projection to Au+Au

- 2/5/2008

- Mid-rapidity

- Forward rapidity

- M. Wysocki - QM2008, Jaipur, India

- Larger uncertainty bands than those from nuclear-modified PDFs and  sbreakup.  In this case we cannot rule out  Au+Au suppression entirely from cold nuclear matter effects, within the statistical and systematic uncertainties.
- It should be noted that contrary to the previous Au+Au projection, these uncertainty bands are *not *directly correlated between rapidities.

- PHENIX Au+Au |y|<0.35
- Data-driven Projection of CNM Effects at mid-rapidity

- PHENIX Au+Au 1.2<|y|<2.2
- Data-driven Projection of CNM Effects at forward rapidity

- arXiv:0711.3917

- ±12% Global Scale Uncertainty

- ±7% Global Scale Uncertainty

## Run-8 d+Au J/y

- Already many J/y recorded inRun-8 d+Au.
- Over 50x as many *J/*ψ as Run-3!
- Should allow for a much-improved *R*dAu measurement in the near future, with smaller statistical errors as well as better constrained systematic uncertainties.

- 2/5/2008

- South Arm Dimuon Mass

- Central Arm Dielectron Mass

- M. Wysocki - QM2008, Jaipur, India

## Summary

*R*dAu measured using new p+p data and a new analysis of d+Au data at forward, backward, and mid-rapidity, and in 4 centrality bins.
- Statistically-significant suppression observed at forward rapidity.
- Comparison to EKS and NDSG nuclear shadowing calculations used to estimate sbreakup.  Extrapolation of these models to Au+Au do not reproduce the full J/ψ suppression at forward rapidity.
- A less model-dependent extrapolation from the measured *R*dAu is unable to constrain the CNM contribution to the measured suppression in Au+Au.
- Looking forward to much better constraints on CNM effects in Run-8 results!

- 2/5/2008

- M. Wysocki - QM2008, Jaipur, India

## Backup

- 2/5/2008

- M. Wysocki - QM2008, Jaipur, India

## <pT2> from All Runs

- 2/5/2008

- M. Wysocki - QM2008, Jaipur, India

- arXiv:0801.0220

## Centrality in d+Au

- At RHIC we are also able to make measurements vs. impact parameter.
- In Run-3 we use 4 centrality bins, each corresponding to a range of impact parameters.
- We can also express the bins in terms of the average number of nucleon-nucleon collisions in that bin (*N*coll).

- 2/5/2008

- M. Wysocki - QM2008, Jaipur, India