# Presentation: 862976

## Recent Results from BRAHMS  

**Recent Results from BRAHMS**

**J.H. Lee**
**Physics Department**
**Brookhaven National Laboratory**
**For the            Collaboration**
**March 27 2006**

**Mostly Strangeness**

**  **

## Short Introduction

**Short Introduction**
**BRAHMS in “1 page”**
**What have we learned so far? **
**  ****Selected Published + Preliminary Results**
**Outlook/Summary**

##    Forward Physics in R.H.I. Collisions: Mapping Space-time Evolution

**Formation of Hot Matter, QGP?**
**  ****-**Identifying and Characterizing the Hot Matter
**  **- How does the system extend/develop? Transverse and longitudinal dynamics
-    - Strong constraints for theoretical modeling/interpretation
-  Initial Conditions/Partonic Dynamics: High-pT vs y
-  Collective Hydro-dynamics: Flow (radial and elliptic) vs y: “Viscometer”
-  Thermodynamic and freeze-out properties: Temperatures, Ratios, HBT vs y
-  Baryon Transport: Net-baryon vs y
-  Bulk Properties: multiplicity, dN/dy

-                            **B**raod **RA**nge **H**adron **M**agnetic **S**pectrometers
- Designed to study nuclear reactions in broad kinematic range (y-pT)
- 2 movable spectrometers with small solid angle measuring charged identified hardrons precisely
- Centrality detectors (Si+Scintillator Tiles) to characterize events
- 53 people from 12 institutions from 5 countries

**FS PID using RICH **

**Multiple settings**

## Baryon Transport: How much energy available from the collision?

**Baryon Transport: How much energy available from the collision?**

- AGS->RHIC : Stopping -> Transparency
- Rapidity Loss <y>: 2±0.4: not linearly increase with ybeam
- Energy loss <E> per nucleon: 73±6 GeV
- Available energy for excitation: ~3/4 of total energy

-  PRL 93 102301 (2004)

**Net-proton in p+p**

**H. Yang, Symposium**

## Rapidity Dependent Kaon Balence: “Net”-kaon (K+-K-)

**Rapidity Dependent Kaon Balence: “Net”-kaon (K****+****-K****-****)**

- longitudinal net-kaon evolution similar as net-proton
-      in |y|< 3 at RHIC (AuAu @ 200 GeV)
- strong “association”: net-kaon / net-lambda /net-proton?

## Baryon/meson (p/+,pbar/-) at √s = 200 GeV

- Scale with <Npart>, independent of system at =0 and 3.2
- Decrease with rapidity and increase with <Npart> and pT
- (flow , medium effect)
- Ratio independent of centrality

- proton dominates at y~3: R(p/y~3 ~ 2* R(p/y~0
-      for central AuAu, CuCu and pp: baryon transport
-  pbar at y~3: R(pbar/y~3 ~ 0.5* R(p/y~0

## Limiting Fragmentation: Longitudinal Scaling

- d+Au sNN=200GeV sNN=19.4GeV
- Au+Au sNN=200GeV

**Limiting Fragmentation: Longitudinal Scaling**

- PRL 94 (2005)

-  **PRL 88 (2002)**

- Particle production independent of beam energy
-      near beam rapidity: Limiting fragmentation behavior
- “Crucial Observation” (L.M.) for universal QCD

## Limiting Fragmentation of pion and Kaon

**BRAHMS/RHIC + SPS + AGS**

******-**

## “Extended” Longitudinal Scaling for <mT>  for K- 

**PHOBOS PRL 94 (2005)**

**BRAHMS Preliminary**

**BRAHMS Preliminary**

- K- <mT> decreases with rapidity
- Longitudinal Scaling in all available rapidity ranges
- <pt> driving Hydro

## Energy dependent K/for central AuAu

- 200GeV

- 63 GeV

**Energy dependent K/********for central AuAu**

- K/: No surprises at 63 GeV
- 200 and 63 GeV: Similar rapidity dependence

## K/ vs pT at ~3.2 at √s = 200 GeV

- K/ increase with system size
- K/ increase with pT (~ < 2GeV/c) at forward

## Flowing at Forward

**Flowing at Forward**

**v2 for pion**

- Understanding missing low-pt fraction is important for integrated v2 from FS
- Kaon and proton v2 will come: Statistically Challenging
- v2(y~0) ~ v2(y~3) for 0.5<pT<2 GeV/c

## Rapidity Dependent High-pT Measurement

- Partons are expected to loose energy in the dense matter
- Different rapidities provide different densities of the medium: Sensitive to the dynamics
- “Dialing” initial condition channel
- Largest medium effect  at mid-rapidity (“Scale” to multiplicity)?
- Rapidity dependent high-pT suppression factors: provide information on dynamical medium effect

- at fixed time

- y~0

- high-y

**Rapidity Dependent High-p****T**** Measurement**

## pp at forward : more then  reference spectra 

- NLO pQCD describes data at forward rapidity at 200 GeV
- K- are described best by KKP (Kniehl-Kramer-Potter) than Kretzer
-      (NLO pQCD Calculations done by W. Vogelsang)

- pT (GeV/c)

**BRAHMS Preliminary**

## Energy and System Dependent Nuclear Modification Factors at ~0 and 1

**Energy and System Dependent ****Nuclear Modification Factors at ********~0 and 1**

- R AuAu (200 GeV) < RAuAu(63 GeV) <  RCuCu(63 GeV) for charged hadrons
- Pp at 63 GeV is ISR Data (NPB100), RHIC-Run6 will provide better reference

## Nuclear Modification Factors (Rcp, RAuAu) for ,K,p at y~3.1

- Suppression for pions and Kaons: RAuAu: <K<p
- RAuAu ≠ Rcp (<Ncoll>,<Npart> for 40-60% ~ 70,56)

## RAuAu(Y=0) ~ RAuAu(y~3) for 0-10% Central at √s = 200 GeV 

- R AuAu (Y=0) ~ RAuAu(y~3) for pions and protons: Accidental?
- Rapidity dependent interplay of Medium effect + Hydro + baryon transport

## RdAu Update: Identified Particle RdAu at y~3

- RdAu of identified particle consistent with published h- results
- dAu(-)/dAu(+): Valance quark isospin dominates in pp?

**BRAHMS Preliminary**

**+ blue**
**- red**

## 
System, Energy dependent 
    - Strangeness production
    - Freeze-out chemistry
Turning off the medium effect in Rapidity, Energy, Species?
    - Rcp, RAA at higher-rapidity ~3.5 for Kaon 
Universal (QCD) property at forward?
     Saturation – Fragmentation
   - “Complete” rapidity and pT-dependent kaon measurement for pp, dA, AA 
Longitudinal (partonic) dynamics of strangeness:
   - rapidity, pt, centrality, reaction-plane dependent kaon yield,ratios
   - v2 vs y for kaons
pQCD vs forward kaons in pp 
Strangeness spin physics also: 
   - Transverse single spin Asymmetries for K at “high”-xF

- System, Energy dependent
-     - Strangeness production
-     - Freeze-out chemistry
- Turning off the medium effect in Rapidity, Energy, Species?
-     - Rcp, RAA at higher-rapidity ~3.5 for Kaon
- Universal (QCD) property at forward?
-      Saturation – Fragmentation
-    - “Complete” rapidity and pT-dependent kaon measurement for pp, dA, AA
- Longitudinal (partonic) dynamics of strangeness:
-    - rapidity, pt, centrality, reaction-plane dependent kaon yield,ratios
-    - v2 vs y for kaons
- pQCD vs forward kaons in pp
- Strangeness spin physics also:
-    - Transverse single spin Asymmetries for K at “high”-xF

**Strangeness Physics from 5 years of BRAHMS running**

## Summary

-  Non-hadronic energy loss through the medium in |y|<3:

- High energy density >> nuclear density

-  **- ********y******** ******** 2 **
** ****- 25 TeV left for particle production**

- Strong transverse/elliptic flow in y<3

- (local) Chemical equilibration

-  Onset of gluon saturation?

**Summary**

- Limiting
- fragmentation

## BRAHMS White Paper

## The BRAHMS Collaboration

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

**The BRAHMS Collaboration**