# Presentation: 499930

## Reaction features in  
   65 AGeV Au + 65AGeV Au

Electromagnetic dissociation
dN(ch)/d distribution -4<<4                                vs. Collision Centrality
Production of charged particles, N(ch)/pr.participant 
Bjorken limit attained ? Transparency or Stopping
p-bar/p vs y, b, pt
Strangeness vs y
Future...

**   ****65 AGeV Au + 65AGeV Au**
**Electromagnetic dissociation**
**dN(ch)/d******** distribution -4<********<4                                vs. Collision Centrality**
**Production of charged particles, N(ch)/pr.participant **
**Bjorken limit attained ? Transparency or Stopping**
**p-bar/p vs y, b, p****t**
**Strangeness vs y**
**Future...**

**BRAHMS Y2000 run ****@ RHIC: ********s****nn****=130 GEV**

- APS-Wash-DC, Jens Jørgen Gaardhøje, Niels Bohr Institute

- April 29, 2001

##        I.G. Bearden7, D. Beavis1, C. Besliu10, Y. Blyakhman6, J. Bondorf7, J.Brzychczyk4, B. Budick6,     H. Bøggild7, C. Chasman1, C. H. Christensen7, P. Christiansen7, J.Cibor4, R.Debbe1,                  J. J. Gaardhøje7, K. Grotowski4, K. Hagel8, O. Hansen7, H. Heiselberg7, A. Holm7, A.K. Holme12, H. Ito11, E. Jacobsen7, A. Jipa10, J. I. Jordre10, F. Jundt2, C. E. Jørgensen7, 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. Murray8, J. Natowitz8, B.S.Nielsen7, K. Olchanski1, D. Ouerdane7, R.Planeta4,    F. Rami2, D. Roehrich9,  B. H. Samset12, S. J. Sanders11, I. S. Sgura10, R.A.Sheetz1, Z.Sosin3,   P. Staszel7, T.S. Tveter12, F.Videbæk1, R. Wada8 and A.Wieloch3. 
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 

**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, Romania                                                      ****11****University of Kansas, Lawrence,USA                                                        ****12**** University of Oslo Norway **

**BRAHMS ****Intl. collaboration **

- APS-Wash-DC, Jens Jørgen Gaardhøje, Niels Bohr Institute

- April 29, 2001

## RHIC physicsAugust 2000

**2:00 o’clock**

**4:00 o’clock**

**6:00 o’clock**

**8:00 o’clock**

**10:00 o’clock**

_***STAR***_

_***PHENIX ***_

**RHIC**

**AGS**

**LINAC**

**BOOSTER**

**TANDEMS**

**9 GeV/u**
**Q = +79**

**1 MeV/u**
**Q = +32**

**HEP/NP**

** ******** ****g-2**

**U-line**

**BAF (NASA)**

- BRAHMS: Lpeak = 3.3   1025 cm-2 s-1
-                             Lave  =  1.7   1025 cm-2 s-1

- Rcoll= 350 Hz

_***PHOBOS***_

- 6 b-1

- 2 wks

- APS-Wash-DC, Jens Jørgen Gaardhøje, Niels Bohr Institute

- April 29, 2001

## BRAHMS in the 2’ hall      ...  in  1998

- APS-Wash-DC, Jens Jørgen Gaardhøje, Niels Bohr Institute

- April 29, 2001

## Forward & Midrapidity  spectrometers

**FS:**  2 TPC,  2 TOF, C,  3 Drift Ch. Mod., RICH, 4 Dipoles
- 2.5 - 30 deg.    ****** = 1.5 - 4**

**MRS****:** 2 TPC, 1 Dipole,  1TOF
- 30 - 90 deg.      ******= 0 - 1.5**

- APS-Wash-DC, Jens Jørgen Gaardhøje, Niels Bohr Institute

- April 29, 2001

## BRAHMS acceptanceAugust 2000

- APS-Wash-DC, Jens Jørgen Gaardhøje, Niels Bohr Institute

- April 29, 2001

## Global detectorsSiMA, TMA, BB

-  SiMA         (2.0< | |<2.0)
-  PTMA        (2.2< || <2.2)
-  Beam-Beam (3 < | | < 4)

- 97% (geom)

- APS-Wash-DC, Jens Jørgen Gaardhøje, Niels Bohr Institute

- April 29, 2001

## Centrality  determinationVertex distribution 

- 1m

- APS-Wash-DC, Jens Jørgen Gaardhøje, Niels Bohr Institute

- April 29, 2001

## Electromagnetic nuclear dissociation

**Electromagnetic nuclear dissociation**

- LO+NLO  Mutual EM

- Mutual Electromagnetic dissociation
- (Spectrum of virtual photons)  *                 (absorption cross section) = WW
- Multiphonon GDR excitation, abs
- EM vs Nuclear coll.
- => neutron (L*R) coincidences
- RELDIS. Pshenichnov et al.

- EM dissociation selected by ZDC coincidences
-  and TMA Veto in BRAHMS

- n

- n

- n

- 2n

- 1n

- LO

- NLO

- APS-Wash-DC, Jens Jørgen Gaardhøje, Niels Bohr Institute

- April 29, 2001

## Neutral Energy correlations (ZDC)

- C2(EL,ER)=P(EL,ER)/(P(EL)*P(ER))

- APS-Wash-DC, Jens Jørgen Gaardhøje, Niels Bohr Institute

- April 29, 2001

## dNch/dSiMA, TMA, BB, TPC

**N=********dE /<dE>**
**P(0)/P(n********1)**
**Background corr.due to secondaries (20-50%)**
**Consistency between several independent. detector systems **
** **
****** ****N(ch)d********= 4000±200**
**Central 0-5%**
**    ****dN(ch)/d******** (********=0) =550**
**FWHM of distribution **
**	********= 7.6 ******** 0.7**

- BRAHMS preliminary

- MTPC1 (CEJ)

- Yuri Blyakhman. BRAHMS Thesis

- APS-Wash-DC, Jens Jørgen Gaardhøje, Niels Bohr Institute

- April 29, 2001

## TPC tracks, Vertex reconstruction, Charged particle track density 

- MTPC1

- z

- y

- APS-Wash-DC, Jens Jørgen Gaardhøje, Niels Bohr Institute

- April 29, 2001

## Multiplicity of Charged Particle tracks in TPC’s 

- B = 0

- APS-Wash-DC, Jens Jørgen Gaardhøje, Niels Bohr Institute

- April 29, 2001

## Total production of Charged particles

**4000 charged part. observed**
**Nch ******** 23.5 pr. part. Pair**
**cf. Nch ******** 17 in p+p at ********s=130GeV**
**35-40% increase over p+p**** **

- Syst

**?**

- APS-Wash-DC, Jens Jørgen Gaardhøje, Niels Bohr Institute

- April 29, 2001

## Centrality and Number of Participants

| Cent %
 | b (fm) | HIJING | Fritiof | Glauber |
| --- | --- | --- | --- | --- |
| 0-10 | 0-5 | 329.2 | 321.7 | 316 |
| 10-20 | 5-7 | 233.8 | 230.0 | 223 |
| 20-30 | 7-8.5 | 163.3 | 162.9 | 154 |
| 30-40 | 8.5-10 | 108.6 | 111.8 | 102 |
| 40-50 | 10-11 | 70.0 | 72.9 | 63 |

- APS-Wash-DC, Jens Jørgen Gaardhøje, Niels Bohr Institute

- April 29, 2001

## NCharged vs. number of participant nucleon pairs 

**dN/d******** ********3 (********=0) pr.part pair.**
**Cf. HIJING, ****FRITIOF**** **
**No saturation effects observed**

- Claus Ekman Jørgensen. BRAHMSThesis

**FRITIOF **

**HIJING**

**MTPC1 CEJ**

**EKRT**

**2**

**2**

**2**

- APS-Wash-DC, Jens Jørgen Gaardhøje, Niels Bohr Institute

- April 29, 2001

## Hadron identification MRS (90, 40 deg)

- m2=p2( t2 / L2 -1)

- p-bar

- 

- K

- p

-  ******=0**

-  ******=3**

**p**

**K**

******0**

- p, pbar

- K±

- 

****

- APS-Wash-DC, Jens Jørgen Gaardhøje, Niels Bohr Institute

- April 29, 2001

## Hadron IdentificationFS (4 deg)

**Hadron Identification****FS (4 deg)**

- 

- p-bar

-  ******=3**

- C1,H1,T2

- +

- p

- m2=p2( t2 / L2 -1)

- +

- p

- K+

- APS-Wash-DC, Jens Jørgen Gaardhøje, Niels Bohr Institute

- April 29, 2001

## N(pbar)/N(p)Centrality and Pt dependence

**N(pbar)/N(p)****Centrality and P****t**** dependence**

**Antiproton absorbtion correction to pbar/p ratio:**
**    ****5 % for FS at 4 deg**
**    ****2 % for MRS at 90, 40  deg**
**10% corr. (low pt) p from Be-tube**
**Applied to data**
**Most pbar and p from Hyperon decays fall into spectrometer acceptance.**
**Correction factor depends on  H/B, H-bar/B-bar and T****B****/T****H**
**    ****For H/B < 0.5 systematic correction is < ******** 5% on ratio**
**Model dependent ******** not applied to data**

- APS-Wash-DC, Jens Jørgen Gaardhøje, Niels Bohr Institute

- April 29, 2001

## Bjorken limit reached for Au+Au s= 130AGeV?

**Bjorken limit reached ****for Au+Au ********s= 130AGeV?**

- ISR R803

- s=23

- s=63

**BRAHMS-RHIC**
- Subm. to PRL

- APS-Wash-DC, Jens Jørgen Gaardhøje, Niels Bohr Institute

- April 29, 2001

## P-bar/p ratioCentrality dependence

**P-bar/p ratio****Centrality dependence**

- BRAHMS

- APS-Wash-DC, Jens Jørgen Gaardhøje, Niels Bohr Institute

- April 29, 2001

## N(p-bar)/N(p) systematics vs CM energy

- STAR

- PHENIX

****

**BRAHMS**

- APS-Wash-DC, Jens Jørgen Gaardhøje, Niels Bohr Institute

- April 29, 2001

## N(pbar)/N(p)Au+Au s= 130AGeV

**BRAHMS**
- Subm. to PRL

- APS-Wash-DC, Jens Jørgen Gaardhøje, Niels Bohr Institute

- April 29, 2001

## StrangenessK-/K+ vs rapidity

**Strangeness****K-/K+ vs rapidity**

**Preliminary**

- CERN-SPS

- APS-Wash-DC, Jens Jørgen Gaardhøje, Niels Bohr Institute

- April 29, 2001

## How consistent are the models?

**How consistent are the models?**

- APS-Wash-DC, Jens Jørgen Gaardhøje, Niels Bohr Institute

- April 29, 2001

## Summary First Au+Au s=130 AGeV

**FUTURE**
**RHIC startup June 2001**
**Au+Au ********s=200 AGeV**
**Higher Luminosity**
**Narrower vertex distribution**
**p + p running**
**BRAHMS full forward spectrometer ready**
**Start full scan ********=0 to ********=4**
**High pt coverage (PID in FS to p=25 GeV/c)**

**RESULTS**
**Nch (0-5%) ******** 4000**
**dN/d******** (y=0) ******** 550. ********FWHM**** ******** 7.6**
**N(ch) ******** 23 pr. participant-pair**
**dN/d******** (y=0) ********  3 pr. part. Pair**
**AntiMeson/Meson close to unity**
**p-bar/ p vs y shows increased  but still incomplete transparency**
**Midrapidity Plateau?**
**y =0,0.7,2 : pbar/p ******** 0.64, 0.66, 0.41 (±0.05 ± 0.06)**
**Weak pt and centrality dependence**
**Bjorken limit not reached**
**Models inconsistent with data**

- APS-Wash-DC, Jens Jørgen Gaardhøje, Niels Bohr Institute

- April 29, 2001