# Presentation: 248197

## Physics Prospects from PMD in d+Au collisions at RHIC

- Photon Multiplicity distribution
- Longitudinal Scaling in asymmetric collisions
- Reference data for photon production in Au+Au collisions

- Like to address the following  physics issues :

- Photon-Charged hadron Azimuthal Angle Correlations
-  Similar rapidity range and forward-backward
-  High ADC/Energy photon cluster triggered correlation with
-     mid-rapidity  charged hadrons
-  Mid-rapidity charged hadron triggered correlation with photon
-     clusters in PMD

## What we learn’t from the Photon Multiplicity Distribution in Au+Au Collisions

- Scaling energy independent for both photons and charged hadrons
- Scaling centrality independent for photons and dependent for charged hadrons
- Difference  due to baryons

- STAR : PRL 95 (2005) 062301

- Longitudinal Scaling

- STAR : PRC 73 (2006) 034906

## Want to see how the scaling works for d+Au data

- Given : Scaling centrality independent for photons and  dependent for charged hadrons
- How does d+Au photon distribution fit into the picture of longitudinal scaling ?

- PHOBOS : PRC (2005)

- Already studied for charged
-  hadrons in  d+Au collisions
-  by PHOBOS

## d+Au photon data a reference for Au+Au 

- Reference data to understand the mechanism of photon production  in
-  high energy collisions

## Expected Multiplicity, Feasibility, Events required

- Feasibility : We have reconstructed
-  such multiplicity in Cu+Cu and
- peripheral Au+Au collisions

- In PMD coverage

- Events required  : For a statistical
-  error of  1%, we require 300 K
-  useable PMD events with minimum
-  bias trigger

- d+Au Collisions at 200 GeV  Minimum bias HIJING Simulation

## Photon-Charged hadron correlation

- Majority of the photons are from 0 decay

- Physics issues :
- To understand correlation between charged hadron and photon production in d+Au collisions.
- Charged hadron - Photon correlations in forward-backward can help understand effects of  short and long range correlations.

- Two points to keep in mind :
- The energy deposited by photons in the detector (Cluster ADC) roughly proportional to photon energy.

- HIJING
- PMD-FTPC
- same coverage

- HIJING
- PMD-FTPC (west)

- Reference studies in STAR for Au+Au :
-  http://www.star.bnl.gov/protected/ebye/tjt/LRC_Paper/lrc.html
- http://www.star.bnl.gov/protected/ebye/sunil/correlation/charge-neutral_corr.html

## Motivation for triggered photon-charged hadron correlation

- Taking high pT 0 in forward rapidity - allows
-  probing high-x valence quark correlations with
-  low -x gluons : A probe of low-x gluons

- Kharzeev, Levin, McLerran NPA748, 627

- STAR : PRL 97 (2006) 152302

- Signature of CGC

## Triggered photon cluster in PMD - charged hadron correlation

- STAR : PRL 97 (2006) 152302

- Want to investigate correlations with triggered
-  high ADC/Energy photon cluster in PMD
- coverage and mid rapidity charged hadrons.
- Note PMD is on the Au going side

- HIJING Simulations are underway for such  a study.
- Preliminary estimate shows for a correlation signal of 1%
- Level  above background we need of the order of 1 million
- events

## Triggered mid-rapidity charged hadron - photon cluster in PMD correlation - d+Au collisions

- Want to investigate correlations similar to those carried out below with FTPC-TPC

- |trig|<1, 2.7<|assoc|<3.9

- Jet correlation dAu at  forward rapidities
- Not a simple recombination
-    (Hwa, Yang, nucl-th/0605037)
- Hierarchy in the away side yields:  CGC?

- Trigger part. : 3<pTtrig<4 GeV/c
- Assoc. FTPC: 0.2<pTassoc< 2 GeV/c
- Assoc. MTPC: 0.2<pTassoc< 3 GeV/c

- Away-side correlations are
- very similar in MTPC and FTPC!

- Reference : L. Molnar - QM2006