# Presentation: 656464

##  Evidence from d+Au measurements for final-state suppression of high pT hadrons in Au+Au collisions at RHICThe STAR Collaboration

*Peter Jacobs*
*Lawrence Berkeley National Laboratory*

- nucl-ex/0306024

- d+Au and final-state suppression in Au+Au

## The STAR detector

**     ****E-M Calorimeter**

**Time of          Flight**

**Projection               Chamber**

- d+Au and final-state suppression in Au+Au

## Partonic energy loss in dense matter

-  Multiple soft interactions:

- Strong dependence of energy loss on gluon density glue
- measure  color charge density at early hot, dense phase

- Gluon bremsstrahlung

- Opacity expansion:

- Bjorken, Baier, Dokshitzer, Mueller, Pegne, Schiff, Gyulassy, Levai, Vitev, Zhakarov, Wang, Wang, Salgado, Wiedemann,...

- d+Au and final-state suppression in Au+Au

## Jets at RHIC

- p+p jet+jet (STAR@RHIC)

- Au+Au ??? (STAR@RHIC)

- Find this..........in this

- d+Au and final-state suppression in Au+Au

## Partonic energy loss via leading hadrons

- Energy loss   softening of fragmentation  suppression of leading hadron yield

- d+Au and final-state suppression in Au+Au

## Au+Au and p+p: inclusive charged hadrons

- PhysRevLett 89, 202301

- nucl-ex/0305015

- p+p reference spectrum *measured* at RHIC

- d+Au and final-state suppression in Au+Au

## Suppresion of inclusive hadron yield

-  central Au+Au collisions: factor ~4-5 suppression
-  pT>5 GeV/c: suppression ~ independent of pT

- nucl-ex/0305015

- Au+Au relative to p+p

- Au+Au central/peripheral

- RAA

- RCP

- d+Au and final-state suppression in Au+Au

## Jets and two-particle azimuthal distributions

- p+p  dijet

-  trigger: highest pT track, pT>4 GeV/c
-   distribution: 2 GeV/c<pT<pTtrigger
-  normalize to number of triggers

- N.B. shifted horizontally by /2 relative to previous STAR plots!

- Phys Rev Lett 90, 082302

- d+Au and final-state suppression in Au+Au

## Azimuthal distributions in Au+Au

- Au+Au peripheral

- Au+Au central

- Near-side: peripheral and central Au+Au similar to p+p

- Strong suppression of back-to-back correlations in central Au+Au

- pedestal and flow subtracted

- Phys Rev Lett 90, 082302

- d+Au and final-state suppression in Au+Au

## Is suppression an initial or final state effect? 

- Initial state?

- Final state?

- partonic energy loss in dense medium generated in collision

- strong modification of Au wavefunction (gluon saturation)

- d+Au and final-state suppression in Au+Au

## Inclusive suppression: theory vs. data

- pQCD-I: Wang, nucl-th/0305010
- pQCD-II: Vitev and Gyulassy, PRL 89, 252301
- Saturation: KLM, Phys Lett B561, 93

- pT>5 GeV/c: well described by KLM saturation model (up to 60% central) and pQCD+jet quenching

- Final state

- Initial state

- d+Au and final-state suppression in Au+Au

## Is suppression an initial or final state effect? 

- Initial state?

- gluon saturation

- Final state?

- How to discriminate? Turn off final state  d+Au collisions

- d+Au and final-state suppression in Au+Au

## d+Au vs. p+p: Theoretical expectations 

- All effects strongest in central d+Au collisions

- d+Au and final-state suppression in Au+Au

## d+Au event selection

- Centrality tags:
- 1. FTPC-Au: charged particle multiplicity in -3.8<<-2.8
- 2. ZDC-d: neutron spectator from deuteron

- Minimum bias trigger: ZDC-Au (953% of hadronic)

- d+Au and final-state suppression in Au+Au

## Centrality tags

- FTPC-Au cut selects more *central collisions*

- Modeling FTPC-Au multiplicity: convolute Au-participant (Glauber) with UA5 mult. distribution (pbar+p @ 200 GeV, 2.5<<3.5)

- min. bias <Nbinary>=central 20% <Nbinary>=12.91.0

- ZDC-d neutron spectator tag:
-  measured: 191% of hadronic
-  Glauber: 183% of hadronic
- peripheral events

- d+Au and final-state suppression in Au+Au

## Inclusive charged particle spectra

- d+Au and final-state suppression in Au+Au

## Inclusive yield relative to binary-scaled p+p

- Suppression of the inclusive yield
- in central Au+Au is a final-state effect

-  d+Au : enhancement
-   Au+Au: strong suppression
-  pT=4 GeV/c:
- cent/minbias = 1.110.03
-  central collisions enhanced wrt minbias

- d+Au and final-state suppression in Au+Au

## Azimuthal distributions

- Near-side: p+p, d+Au, Au+Au similar
- Back-to-back: Au+Au strongly suppressed relative to p+p and d+Au

- Suppression of the back-to-back correlation in central Au+Au is a final-state effect

- d+Au and final-state suppression in Au+Au

## The strong suppression of the inclusive yield and back-to-back correlations at high pT previously observed in central Au+Au collisions are due to

- final-state interactions with the dense medium generated in such collisions.

- d+Au and final-state suppression in Au+Au

## Have we found the Quark Gluon Plasma at RHIC? 

- We now know that Au+Au collisions generate a medium that
- is dense (pQCD theory: many times cold nuclear matter density)
- is dissipative
- exhibits strong collective behavior

- Not yet, there is still work to do

- We have yet to show that:
- dissipation and collective behavior both occur at the partonic stage
- the system is deconfined and thermalized
- a transition occurs: can we turn the effects off ?

- We have developed the tools necessary to complete this program

- This represents significant progress in our understanding of strongly interacting matter

- d+Au and final-state suppression in Au+Au

## The STAR Collaboration

**Russia:**
- MEPHI - Moscow
- LPP/LHE JINR - Dubna
- IHEP - Protvino
**U.S. Lab****oratories****:**
- Argonne
- Berkeley
- Brookhaven
**U.S. Universities: **
- UC Berkeley
- UC Davis
- UC Los Angeles
- Carnegie Mellon Creighton University
- Indiana University
- Kent State University
- Michigan State University
- City College of New York
- Ohio State University
- Penn. State University
- Purdue University
- Rice University
- Texas A&M
- UT Austin
- U. of Washington
- Wayne State University
- Yale University

**Brazil: **
- Universidade de Sao Paulo
**China: **
- IHEP – Beijing
- IMP - Lanzou
- IPP – Wuhan
- USTC
- SINR – Shanghai
- Tsinghua University
**Grea****t Britain****:**
- University of Birmingham
**France:**
- IReS Strasbourg
- SUBATECH - Nantes
**Germany: **
- MPI – Munich
- University of Frankfurt
**India:**
- IOP -  Bhubaneswar
- VECC - Calcutta
- Panjab University
- University of Rajasthan
- Jammu University
- IIT - Bombay
- VECC – Kolcata
**Poland:**
- Warsaw University of Tech.

- d+Au and final-state suppression in Au+Au

## Extra slide

- d+Au and final-state suppression in Au+Au

## Two-particle azimuthal distributions

-  near-side and back-to-back peaks seen in minbias and central d+Au
-  p+p d+Au minbias  d+Au central:
-  growth of off-jet pedestal
-  small, if any, growth of back-to-back width

- d+Au and final-state suppression in Au+Au