# Presentation: 887484

## Strangeness at RHIC: recent results from BRAHMS

-  Stopping
-  Pion and kaon production
-  Particle composition at 	intermediate pt
-  Nuclear modification factor

**Strangeness at RHIC: recent results from BRAHMS**

**Dieter Roehrich**
**UiB**
**for the BRAHMS collaboration **

**Au+Au****	****at ********s****NN ****= 130GeV**
**Au+Au****	****at ********s****NN ****= 200GeV**
**d+Au****	****at ********s****NN ****= 200GeV**
**p+p****	****at ********s****NN ****= 200GeV**
**Au+Au****	****at ********s****NN ****= 62.4GeV**

## The BRAHMS experiment

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

- Two small solid angle
- spectrometers (FS and MRS)

- provide excellent PID over
- a broad range in y-pT

**The BRAHMS experiment**

## Net-proton rapidity distribution

- BRAHMS, PRL, in print
- nucl-ex/0312023

- _dN_
- dy

- RHIC
- central Au+Au
- Npart=3578

## Stopping (1)

## Stopping (2)

**Stopping (2)**

- Net-baryon after
- feed-down & neutron corrections

- 6 order polynomial

**Gaussians in p****z**:

- Rapidity loss:
- (Npart= 357  10)

## Energy loss

**Energy loss**

- Upper limit to  rapidity loss?
- Energy loss:

- E = 25.7  2.1 TeV
- E/nucleon = 72  6 GeV

## Stopping summary

**Net-baryon poor midrapidity region**
**dN(net-protons)/dy = 7**
**Total-baryon rich midrapidity region**
**dN(all baryons)/dy  ******** 65**
**Largest observed rapidity loss**
**<********y> = 2**
**as large as in pA**
**Stopping power**
**central Pb+Pb at RHIC: 72%**
**central S+S at SPS: 58%**
**p+p collisions: ******** 50%**

## Rapidity distributions of identified hadrons 

**Produced particles:  ****	****   ****	****Gaussian shapes**
**Integrating the Gaussians gives****:**

|  | + | - |
| --- | --- | --- |
|  | 1780 | 1760 |
| K | 290 | 240 |
| p | (85) | 85 |
| ppart | (180) | -   |

**Notes:**
Get energy in lambdas.

## Energy dependence of widths

**Landau hydrodynamics**
**Gaussian rapidity distribution **
**Observed in hadron - hadron collisions**
**Width ******** depends only ****on c.m. energy:**

- L.D. Landau, Izv. Akad. Nauk SSSR 17 (1953)  52
- P.Carruthers, M.Duong-van, PRD 8  (1973)  859

**Finite boost-invariant region for thermodynamic variables**
**Boost-invariant region ******** < 2**
**Gaussian rapidity distribution**

- T. Hirano, Y. Nara, nucl-th/0404039

## Transverse Flow (1)

- y~0

- y~3

- y~2

- y~1

- pT (GeV/c)

- BRAHMS Preliminary

- Fix ,T

- Fix ,

**B****last ****W****ave**** ****f****its at**** ****y~0,1,2,3 ****(T,**** ********s****,**** ******** f****ree,**** R****max****=13fm****)**** **

## Transverse Flow (2)

**3D-Hydro**
-  CGC initial  condition
-  Ideal massless  QGP EoS

- nucl-th/0404039

## Corrections for feed-down from weak decays –  Towards 4 multiplicity

** ****Proton spectra contain ****   approx. 55% of all****   hyperon decays**
** ****Pion spectra contain****   approx. 35% of all K****0****S**
** **** ****Corrected ****4******** multiplicity**

|  | + | - |
| --- | --- | --- |
|  | 1709 | 1690 |
| K | 290 | 240 |
| p | (51) | 51 |
| ppart | (180) | -   |

**Pion contamination by neutral kaon decays**

** ****Integrating the Gaussians**** and adding unseen****  weak decay products**** gives N****ch**** = 4****62****0 ******** 50**
** ****Integrating the pseudo-rapidity spectra gives ****  ****N****ch**** = 4630 ******** 370**

**Notes:**
Get energy in lambdas.

## Strangeness production (1)

**Strangeness production (1)**

**Rapidity dependence of K/******** ratio**

**Energy dependence of K/******** ratio**

- Over the full phase space and corrected for weak decays:
- K+/+ = 17.0  1.5 % (syst)
- K/ = 14.2  2.0 % (syst)

- no change for +

- 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]

- Divergence
- at higher y

## Strangeness production (1)

**Weak decays ON**
**T              = 154.7 +- 2.6   MeV**
**muB/T     = 0.634  +-  0.028**
**gamma_S = 0.888 +- 0.017**
**Weak decays OFF**
**T = 164.6 +- 5.7 MeV**
**gS = 0.834 +- 0.015           chi2 = 5.4/2**
**muB = 91.4 +- 4.0 MeV**
**Realistics weak decay fraction**
**T = 153.4 +- 4.4 MeV**
**gS = 0.848 +- 0.018           chi2 = 0.97/2**
**muB = 96.4 +- 4.3 MeV**

## Strangeness production (2)

**Strangeness production (****2****)**

**Energy dependence of K/******** ratio**** at midrapidity**

** **Preliminary 63 GeV  data follow trend

**See ****Djamel Ouerdane****’s talk on Thursday afternoon**
**(Parallel session 2)**

## Strangeness production (3) 

- BRAHMS, PRL90 (2003) 102301
- T~constant, B varies with y

- Increasing y

**K****-****/K****+**** dependence on p/p**

**See Michael**** ****Murray’s talk on Friday afternoon**
**(Parallel session 4)**

## Particle Ratios in p+p interactions

##  Midrapidity

** ****p/******** ratio ******** 1**
** ****Enhancement compared to pp, d+Au**
** ****Forward ****	****rapidity**
** ****p/******** ratio ******** 0.5**
** ****Flow effect?**

- p+p

**Baryon enhancement at intermediate pt***** ***

##  Midrapidity & Forward rapidity

** ****K****/******** rati****o increases with transverse momentum**
** ****K****/******** ratio ******** ****0.7 at 2 GeV/c**

- p+p

**Kaons**** at intermediate pt***** ***

## Nuclear Modification Factor

**Transverse momentum spectra of charged hadrons and identified particles at ****different rapidities**** (0 < y < 3.2)**
**Nuclear modification factor**
**Rapidity dependence of R****dAu ****and R****Au  ****helps to distinguish final from initial state effects and to disentangle different initial conditions**

## Arsene et al. PRL2003

- Arsene et al. PRL2003

**Nuclear Modification Factor: Au+Au**

**Large high p****T**** suppression in central Au+Au**
** **
**Even larger suppression at forward rapidity**

## Are Pions and Protons suppressed?

**Protons are not suppressed up to pt = 3 GeV/c**
**Very strong pion suppression at forward rapidity **

**Are Pions and Protons suppressed?**

******=****0**

******=****2.2**

**preliminary**

## Nuclear Modification Factor: d+Au

**High p****T**** ****enhancement**** in d+Au collisions at ****s****NN****=200 GeV**
**Comparing Au+Au to   d+Au at midrapidity**
**    ******** ****Strong effect of dense medium**
**	******** ****Partonic energy loss**

**charged hadrons**

## Nuclear Modification Factor

**Midrapidity**
**d+Au**
**Central Au+Au**
**Forward rapidities****Where do ****shadowing/ ****gluon saturation effects come in? **

**“****Cronin effect”**
- Initial state multiple scattering
- leading to **Cronin** enhancement (RAA>1)

**Jet-quenching**

**Shadowing/saturation**
- depletion of low-x partons
- due to:
- - coherent multiple scattering
-  gluon saturation
-  e.g. Color Glass Condensate (CGC)

## RdAu at different Pseudorapidities

**BRAHMS: Submitted to PRL, March 2004**

**Cronin****-****like enhancement at ********=0**
**Clear suppression as ******** changes ****from 0**** to 3.2**
**But**: **ratio of dn/d******** exhibits similar trend**

## Centrality Dependence of Enhancement/Suppression in d+Au

**C****hange**** of R****CP**** ****from mid- to forward rapidities is stronger for central collisions than for semi-peripheral collisions**

## CGC Saturation Model (1)

- Nucl.Phys. A 730 (2004) 448

**CGC Saturation Model (1)**

**CGC describes dn/d******** and predicts**
**But HIJING and AMPT also do well**

## CGC Saturation Model (2)

**CGC model describes R****dAu**** and R****CP**
**Suppression comes in at y > 0.2**** **

- D. Kharzeev, Y.V. Kovchegov,
- K. Tuchin, hep-ph/0405054 (2004)

## BUT (1) - 

**BUT (1) - **
**Pseudorapidity Distribution in d+Au**

**Multiplicity in dAu scales with**** ****N****part**
**Enhanced production for ******** < 0**
**Suppression for ******** > 0**
**Modification effects for soft pions, not only for high p****T**
**Same observation at SPS (NA35, NA49)**

- PHOBOS data
- P. Steinberg, QM 2004

## BUT (2) -  RpA at SPS energies

**BUT (2) -  R****pA ****at SPS energies**

**NA49 data**
**200 GeV pPb**
**as we go forward ****R decreases**
- B. Boimska, PhD thesis
- Warsaw Institute forNuclear Studies, May04

## BUT (3) - pQCD Models (1)

**pQCD-improved parton model **
**Glauber-type collision geometry**
**Nuclear shadowing **
**Nuclear multiscattering **

**Increasing strength of standard nuclear shadowing with increasing ******
**Including nuclear multiscattering ******** reasonable agreement between data and pQCD**

- G.G. Barnafoldi, G. Papp, P. Levai,
- G. Fai, nucl-th/0404012 (2004)

- See also R. Vogt,
- hep-ph/0405060 (2004)

- See also
- R. Vogt, hep-ph/0405060 (2004)

## Summary

**Central Au+Au collisions**
**Stopping: rapidity shift of 2 units**
**72% of energy available for particle production**
**Gaussian rapidity distributions**
**Rapidity dependence of K/******** ratio**
**Energy dependence of K/******** ratio (total yields)**
**Baryon enhancement at intermediate p****T**
**Nuclear modification**
**Strong pion suppression at all rapidities - even stronger at large ******
**Protons are not suppressed up to p****T ****= GeV/c**
**d+Au collisions**
**Nuclear modification**
**Cronin****-****like enhancement at ********=0**
**Clear suppression as ******** changes ****from 0**** to 3.2**
**Indication of shadowing/saturation?**

## The BRAHMS Collaboration

**I.Arsene****10****,I.G. Bearden****7****, D. Beavis****1****, C. Besliu****10****, Y. Blyakhman****6****, J.Brzychczyk****4****,**
** ****B. Budick****6****,H. Bøggild****7 ****,C. Chasman****1****, C. H. Christensen****7****, P. Christiansen****7****,**
**J.Cibor****4****,R.Debbe****1****,J. J. Gaardhøje****7****,****M. Germinario****7****, K. Hagel****8****,**
** ****O. Hansen****7****, H. Ito****11****, E. Jacobsen****7****, A. Jipa****10****, J. I. Jordre****10****, F. Jundt****2,**** **
**C.E.Jørgensen****7****, E. J. Kim****5****, T. Kozik****3****, T.M.Larsen****12****, J. H. Lee****1****, Y. K.Lee****5****, **
**G. Løvhøjden****2****, Z. Majka****3****, A. Makeev****8****, B. McBreen****1****, M. Murray****8****, J. Natowitz****8****, **
**B. Neuman****11****,B.S.Nielsen****7****, K. Olchanski****1****, D. Ouerdane****7****, R.Planeta****4****, F. Rami****2****, **
**D. Roehrich****9****,  B. H. Samset****12****, S. J. Sanders****11****, I. S. Sgura****10****, R.A.Sheetz****1,**** Z.Sosin****3****, **
**P. Staszel****7****, T.S. Tveter****12****, F.Videbæk****1****, R. Wada****8**** ,A.Wieloch****3****,Z. Yin****9**
**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**** **

## Extra slides

## Kaon Spectra 

-  Wide acceptance  for kaons in y
-  Spectra: projection of rapidity intervals to pT axis

**See ****Djamel Ouerdane****’s talk on Thursday afternoon**
**(Parallel session 2)**

## Particle Spectra 

- Top 5% central collisions

## Outlook

**Preliminary**

**High pt suppression ****in Au+Au collisions at**** 62.4 GeV?**** **

## 62.4 GeV references

## pQCD models (3)

**pQCD **
**Different parametrizations of nuclear shadowing **
**No inclusion of Cronin effect **

**Fairly good agreement with R****dAu**** for the ******** dependence **
**Calculation underestimates centrality dependence of R****CP**
**R****dAu ****different for pions and protons**

- R. Vogt, hep-ph/0405060 (2004)

**p**

****

**K**

- FGS parametrization

## Suppression due to partonic Energy Loss

**Initial state parton saturation effects?**

**Suppression due to partonic Energy Loss**

******=****0**

**preliminary**

## Particle Identification

***Particle Identification***

*TIME-OF-FLIGHT*

- Particle Separation: pmax (2 cut)=

- TOFW

- TOF1

-  TOF2

-  / K

- 2 cut

- K / p

- 2 GeV/c

- 3 GeV/c

- 4.5 GeV/c

- 3.5GeV/c

- 5.5GeV/c

- 7.5GeV/c

## Kaons vs B

***Kaons vs ************B***

## High pT Particle Production in A+A 

**Fragmentation Function**

**High p****T**** Particle Production in A+A**** **

**(According to pQCD)**

- K. Filimonov, QM 2004