# Presentation: 575016

## Recent Results from BRAHMSfrom y=0 to y=3

- I. G. Bearden

- Niels Bohr Institute
- University of Copenhagen, Denmark

- Quark Matter 2002, July 18-24, Nantes, France

-                       *for the*
- BRAHMS COLLABORATION

## The BRAHMS Collaboration

- I.G. Bearden7, D. Beavis1, C. Besliu10, Y. Blyakhman6, J.Brzychczyk4, B. Budick6,
- H. Bøggild7 , C. Chasman1, C. H. Christensen7, P. Christiansen7, J.Cibor4, R.Debbe1,
- E. Enger12, J. J. Gaardhøje7, M. Germinario7 , K. Grotowski4 , K. Hagel8, O. Hansen7,
- A.K. Holme12, H. Ito11, E. Jacobsen7, A. Jipa10, J. I. Jordre10, F. Jundt2, C.E.Jørgensen7,
- R. Karabowicz4 , T. Keutgen9, E. J. Kim5, T. Kozik3, T.M.Larsen12, J. H. Lee1, Y. K.Lee5,
- G. Løvhøjden2, Z. Majka3, A. Makeev8, B. McBreen1, M. Mikkelsen12, M. Murray8,
- J. Natowitz8, B.S.Nielsen7, K. Olchanski1, D. Ouerdane7, R.Planeta4, F. Rami2,
- D. Roehrich9,  B. H. Samset12, D. Sandberg7, S. J. Sanders11, R.A.Sheetz1, Z.Sosin3,
- P. Staszel7, T.S. Tveter12, F.Videbæk1, R. Wada8, A.Wieloch3 and I. S. Zgura10
- 1Brookhaven National Laboratory, USA, 2IReS and  Université Louis Pasteur, Strasbourg, France
- 3Jagiellonian University, Cracow, Poland, 4Institute of Nuclear Physics, Cracow, Poland
- 5Johns Hopkins University, Baltimore, USA, 6New York University, USA
- 7Niels Bohr Institute, Blegdamsvej 17, University of Copenhagen, Denmark
- 8Texas A&M University, College Station. USA, 9University of Bergen, Norway
- 10University of Bucharest, Romania, 11University of Kansas, Lawrence,USA
- 12 University of Oslo Norway

## The BRAHMS Experiment

## Determination of Collision Vertex, Centrality

**Determination of Collision Vertex****, Centrality**

## Multiplicity density @ 200GeV

**Multiplicity density @ 200GeV**

-  100AGeV+100 AGeV:
-  N(ch)d=
-        4630
- Central 0-5%
-     dN(ch)/d (=0) =632
- FWHM of distribution
- 	= 7.5 0.5

- For details, see the BRAHMS poster by S. Sanders, H. Ito.

## Limiting fragmentation

**Limiting fragmentation**

- Shift data to beam frame of reference

- PRL 88 (2002) 2002301 BRAHMS

- PLB 523 (2001) 227 BRAHMS

- Phys Rev C (2000)62 014903

**Moving away**
**from midrapidity particle production**
**looks like SPS**

## dNch/d: Comparison to Models

******S****NN****=200GeV**

**AMPT**
**High density QCD**
**gluon saturation**
**Kharzeev and Levin,**
**PLB523(2001)79**

**Differences for**
**Peripheral Collisions **
** ****but Small effect !**

## MRS

- 

- FORWARD
- 

## PID in BRAHMS

- MRS
- TOF

- FS
- TOF

- FS
- TOF
- +C1

- RICH

## Ratios are (relatively) easy...

- Ratios could vary in pt, and in y
- Narrow y bins, look vs pt

- geometric acceptance same for
- particles and antiparticles, so correction is not needed.

- For given B field, angular setting,
- compare (+) and (-) polarity

- Normalize to number of triggers,
- and --bingo!-- ratios....

- No dependence on transverse momentum or centrality
- See poster for details of the analysis!

## Particle/Particle vs rapidity

**Particle/Particle vs rapidity**

- BRAHMS, submitted to PRL
- 12/07/02 nucl-ex/0207006

## Becattini: T=170, s=1

- BRAHMS, submitted to PRL
- 12/07/02 nucl-ex/0207006

**Becattini: T=170, ********s****=1**
**PBM (PhysLettB518**
**(2000)41) predicts  y=0**
**ratios almost exactly**
**K****-****/K****+****=**
**exp(2********s/T)(pbar/p)****1/3**
**K****-**** /K****+****=(pbar/p)****1/4**** is **
**a fit to the data points**

## Slide 13

## Not surprisingly, the antiparticle spectra don’t look much different...at y=0!

## Only small part of high rapidity data analyzed...so far.

## Inverse pT Slope vs. mass...

- Nb: all fits are in pt, over
- same range for all particles,
- at all rapidities

## Strangeness : ratio K/

## Strangeness : K/ systematics

**Strangeness : K/******** systematics**

## Slide 20

## p and pbar yields

**0-10%:  BRAHMS Preliminary  ********SNN=200 GeV: 0-10% Central**

- y = 0

- y=0.8

## p and pbar at y=2.9

**BRAHMS Preliminary**

**antiproton**
**Yield =10.5 ******** ****0.8 ********1.6**
** ****(Inverse pt slope =325.5********17.****3****)****  **

**proton**
**    ****Yield = 33.7 ********1.8 ******** 5.1**
**    ****(Inverse pt slope**
**    ****= 341.8 ******** ****13.8**

## Net protons, first shot...

**BRAHMS Preliminary**

- d2N/dpTdy

## Net protons vs Rapidity!

## Can we kill models?

- Points scaled by 2

## Q’

- AMPT

##  High pt  y=0

**y=0   High p****t     ****y****=2.2**

-  **C.E.Jørgensen **
**Parallel session I **
**today.**

## Future plans...

**Analyze complete data set at high rapidity **
**Better pt coverage**
**(slightly) higher y**
**Spectra, yields for 1<y<3**
**Source size at mid, forward rapidity**
**p+p data **
**Longer term...**
**Upgrades better high pt PID in MRS**

## Summary

**K-/K+, pbar/p ratios fall off with rapidity**
**Universal correlation between K-/K+ and pbar/p**
**K-/********-  decreases from 0.15 (y=0) to 0.1(y=3)**
**Inverse slope decreases with rapidity**
**Measured dN/dy over 3 units of rapidity.**
**Dramatic increase in net protons at y=3**
******Low to high chemical potential from y=0 to y=3**
******Net  baryon central plateau (y=0 to almost y=2)**
******Significant transparency**

## Radius versus Momentum

- RICH used for PID
- p>15GeV/c
- K>8 GeV/c
- >4 GeV/c