# Presentation: 782337

## The BRAHMS _x0005_HI and Spin Programs

**B**road **RA**nge **H**adron
**M**agnetic **S**pectrometers

**The BRAHMS ****_x0005_HI and Spin Programs**

- S. J.  Sanders
- U. Kansas

## Particle Identification

***Particle Identification***

*TIME-OF-FLIGHT*

- Particle Separation: pmax (2 cut)=

*CHERENKOV *

- (2 settings)

- C4 Threshold (MRS):
-  / K separation 9 GeV/c

- RICH (FS):
-  / K separation 20 GeV/c
- Proton ID up to  35 GeV/c

- MRS

- FS

## BRAHMS studies the properties of the produced medium as a function of its longitudinal expansion...

- What is the energy available for particle production?
- What is the longitudinal extent of the created medium?
- How does the “chemistry” of the medium change with rapidity?
- Are small-x effects (saturation) evident in the forward direction?
- Are there characteristic differences seen at large rapidity between AA and pp collisions?

- PRL 94, 032301(2005)

- PRL 88, 202301(2002)

**Nucl-th/0108056 Polleri and Yuan**

**Beam**
**Rapidity**

## Particle Spectra (200 GeV Au+Au)

- PRL 94, 162301(2005)

- 5% central

## Energy Balance (200 GeV Au+Au)

**Starting with ********35 TeV **
**(E****beam********N****part****), **
******25 TeV carried away by produced particles.**

## Bjorken vs. Landau

- PRL 94, 162301(2005)

- |y|<1 plateau?

**Bjorken:**
- Boost invariance of central region.
**Landau:**
- Isentropic expansion of 3D relativistic pion gas.
- P.Carruthers, M.Duong-van, PRD **8**, 859  (1973).

- Gaussian fit width

## K/ Ratios 

- 200 GeV Au+Au (5% central)

- Y < 1 : consistent with
- Hadron Gas Stat. Model
- K+/+ : 15.6   0.1 % (stat)
- K/ : 14.7   0.1 % (stat)
-  [Phys. Lett. B 518 (2001) 41]

- 62.4 GeV

- PRL 94, 162301(2005)

**Is forward BRAHMS at 62.4 GeV going to approach SPS?**

## BRAHMS particle ratiosAu+Au and pp compared (200 GeV)

***BRAHMS particle ratios******Au+Au and pp compared (200 GeV)***

- Phys. Lett. B 607, 42(2005)

**AuAu ≈ pp**

- (20% central)

## Particle Ratios (AuAu and pp) continued...

- Heavy ion

- pp

## d+Au at 200 GeV.   Initial state effects at forward rapidity? RdAu and Rcp  

- PRL 93, 242303(2004)

- Both saturation and recombination models can reproduce behavior!

**Notes:**
We multiply pp by N_col.

## RdAu rises faster for pbar than -

- Preliminary

- d Au

- p p

**p**** ****shows little p****T**** dependence...**

**...****while pp reference falls.**

**Min-bias**

## What about forward Au+Au?Identified particle RAA.

- No p suppression!

- Preliminary

## What about forward Au+Au? (cont.)Rcp (AuAu)

**Little ******** dependence at 200 GeV...**

**...****but greater suppression approaching beam rapidity at 63 GeV.**

- kinematic
- limit

- Preliminary

## RAA(62.4 GeV Au+Au)

**(pp reference is based on ISR collider data)**

- Preliminary

- Peripheral Au+Au is not pp!

## Azimuthal (Elliptic) Flow

- An asymmetric reaction region leads to asymmetric particle production:

**What happens at forward rapidity?**

- Laboratory horizontal

- Reaction plane

## BRAHMS Azimuthal Flow

***BRAHMS Azimuthal Flow***

- Flow Ring 3
- Z = -11 cm

- Flow Ring 2

- Si Ring 1

- Tile Ring 1

**Identified particle v****2****(p****T****) over an extended ******** range, 0<********<3.2,  will be presented at QM2005...**

- BRAHMS Preliminary

**h****+/-****, ********=0**

## Single Transverse Spin Asymmetry

- An = (+ - -) / (+ + -)
- With spin direction defined by

- Low energy data (FNAL E704 ) show clear differences between  +- and 0.

- D.L.Adams (E704) Phys.Lett B264,462(1991); Phys.ReV D53, 4747 (1996).

- +

- -

- 0

**Early pQCD calculations predicted effect to be small.**

- Several models:
- Sivers effect (initial state).
- Collins effect (final state).
- Qui and Sterman (twist-3 pQCD)

## Kinematic Variables and Measurement

- The kinematic variables of interest are Feynman x (xF) and pT.
- Shown is the BRAHMS acceptance for the data taken at  = 2.3o and the maximum field setting (7.2 Tm).

- p/p~1% at 22 GeV/c)

## AN for +  and - (2004 run) 

**Also find A****N****≈0 for protons.**

- (BRAHMS Preliminary)

- Qui & Sterman
- Twist-3 pQCD
- extrapolation

- (Use yellow beam pattern for -xF.)

## With 2005 pp data, BRAHMS will be able to explore pT-xF dependence...

## Summary

- With a focus on the forward region, the BRAHMS heavy-ion program includes studies of a rich variety of topics:
- Nuclear stopping and energy balance.
- Low-x saturation effects.  Relative importance of initial state (saturation) and final state  (recombination, etc.) effects in the forward region.
- Longitudinal extent of produced medium.
- Nuclear chemistry of produced medium as a function of rapidity.
- Radial and azimuthal flow.
- Initial state *vs*. final state questions of a very different type arise with the study of single transverse spin alignment of pions in  polarized pp measurement.  Extensive new results will become available with the analysis of the 2005 pp data.

## The BRAHMS Collaboration

**I.Arsene****10****, I.G. Bearden****7****, D. Beavis****1****, S. Bekele****11****, C. Besliu****10****,**
** ****B. Budick****6****, H. Bøggild****7 ****, C. Chasman****1****, C. H. Christensen****7****, P. Christiansen****7****,**
**J.Cibor****4****, R.Debbe****1****, E.Enger****12****, J. J. Gaardhøje****7****, K. ****M. Germinario****7****, K. Hagel****8****,**
**  ****H. Ito****1****, A. Jipa****10****, E. Johnson****11****, J. I. Jordre****10****, F. Jundt****2****, C.E.Jørgensen****7****, R.Karabowisz, E. J. Kim****11****, T. Kozik****3****, T.M.Larsen****12****, J. H. Lee****1****, Y. K.Lee****5****, S.Lindahl, R.Lystad, **
**G. Løvhøjden****2****, Z. Majka****3****, M. Murray****11****,**
** ****J. Natowitz****8****, B. Neuman****11****,B.S.Nielsen****7****, D. Ouerdane****7****, R.Planeta****4****, F. Rami****2****, **
**D. Roehrich****9****, C.Ristea, O.Ristea, B. H. Samset****12****, S. J. Sanders****11****, R.A.Sheetz****1,**** **
**P. Staszel****7****, T.S. Tveter****12****, F.Videbæk****1****, R. Wada****8****, H. Yang****9****, Z. Yin****9****,**** ****I. S. Zgura****10**
**1****Brookhaven National Laboratory, USA, ****2****IReS and  Université Louis Pasteur, Strasbourg, France**
**3****Jagiellonian University, Cracow, Poland, ****4****Institute of Nuclear Physics, Cracow, Poland**
**5****Johns Hopkins University, Baltimore, USA,**** 6****New York University, USA**
**7****Niels Bohr Institute, Blegdamsvej 17, University of Copenhagen, Denmark**
**8****Texas A&M University, College Station. USA, ****9****University of Bergen, Norway **
**10****University of Bucharest, Ro****mania,**** ****11****University of Kansas, Lawrence,USA   **
**12**** University of Oslo Norway **

- - 12 institutions-

## Strangeness—Kaon Spectra 

- Top 5% central collisions

- AuAu 63 GeV

- AuAu 200 GeV

- y0

- y3.5