# Presentation: 895545

## BRAHMS Scanning the phases of QCD

**I. Arsene, I.G. Bearden, D. Beavis, C. Besliu, B. Budick, H. Bøggild, C. Chasman, **
**C. H. Christensen, P. Christiansen, J. Cibor,  R. Debbe, E. Enger J. J. Gaardhøje, **
**M. Germinario, ****K. Hagel, O. Hansen, A. Holme,  A.K. Holme, H. Ito,  A. Jipa, **
**J.I.  Jørdre, F. Jundt,  C.E.Jørgensen, R. Karabowicz,  E.J. Kim, T. Kozik, **
**T.M. Larsen, J.H. Lee, Y. K.Lee, S. Linda, G. Løvhøjden, R. Lystad, Z. Majka, **
**A. Makeev, M. Mikelsen, ****M. Murray****, J. Natowitz, B. Neumann, B.S. Nielsen, **
**K. Olchanski, D. Ouerdane, R.Planeta, F. Rami, C. Ristea, O. Ristea, D.Röhrich,**
**B. H. Samset, D. Sandberg, S. J. Sanders, R.A.Sheetz, P. Staszel, T.S. Tveter, **
**F.Videbæk, R. Wada,Z. Yin  and I. S. Zgura**
**Brookhaven, Strasbourg, Krakov, Johns Hopkins, NYU, Niels Bohr.**
** ****Texas A&M, Bergen, Bucharest, ****Kansas,**** Oslo**

**Notes:**
Corner Claus: More visually appealing Brahms Logo: Name on it. Each slide part of same presentation: 
Muddled skip back and forth between things that are easier, don’t require PID, then real stuff. First 5 or 6 slides nothing about BRAHMS. Make a group for p bar. 

## Identifying high rapidity particles

## Why study rapidity dependence?

**For AuAu we want to understand the limits of jet quenching?**
**We also hope to understand the longitudinal dynamics of the source and measure  the total energy loss, multiplicity strangeness etc.**
**We may find that there is more than one source, i.e. different parts of the system lose causal contact. **
**For dAu  high rapidity allows us to study the Au nucleus with a faster probe x = e****-y ****m****T ****/********S**

**Notes:**
Here x = exp-y

## 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

## A possible time line for Au+Au collisions.

**A possible time line for Au+Au collisions.**
**This curve itself is a function of rapidity.**

- dAu at forward rapidity

- Hi PT

- Chemistry,
- Multiplicity,
- Fluctuations

- Transverse Flow
- Coalescence

**This talk will try to  run time backwards**** **

**Phys. Today 10/03 McLarren+Ludlum **

- Jet
- Quenchng

**Notes:**
This is a cartoon of how the energy density of the system might evolve in time 
Redo Axis by hand to make clearer

## What questions can we attack?

**How much energy is available for particles?**
**How many particles?**
**What is the volume?**
**How do particles flow in the transverse & longitudinal  direction?**

**What is the chemistry of the system?**
**What is the rapidity dependence jet quenching **
**What is the nature of the Au wave function at small Feynman x?**

## Spectra vs. Pt and  rapidity

- PT

**D. Ouerdane**
**Hadron Spec.**
**Thursday **

**AuAu 10% Central**

## Spectra vs. Rapidity

**Spectra vs. Rapidity**

## Where do the protons go?

**25 ******** 1 TeV is liberated  for particle production**

**Rapidity Loss**

**Beam Rapidity**

**BRAHMS: nucl-ex/0312023**
** “****Nuclear stopping in Au+Au **
**collisions at ********S****NN**** = 200 GeV**”

- Similar effect for pA, see
- Buzza *et al* ARNS 88 150

- _dN_
- dy

**Notes:**
Start top right data. Peaked is gaussian, black gaussian. Don’t talk about assumptions. Sum = Npart=175

## What can you buy for 25TeV? 

|  | + | - |
| --- | --- | --- |
|  | 1780 | 1760 |
| K | 290 | 240 |
| P | 85 | 85 |

**Integrating the energy seen in ********, k & P and estimating other particles gives 25 ******** 5 TeV**

**AuAu 5%**

**Notes:**
Get energy in lambdas.

## dAu Multiplicity

- HIJING, & AMPT do well. Saturation model has problems.

**Notes:**
Too many words

## dAu dN/d v √S 

**H. Ito Poster**
**Spectra 18** :

**Gold Frame**

**Deuteron Frame**

- AuAu

**NA35 √S****NN  ****=20GeV**

- BRAHMS √SNN  =200GeV

**Notes:**
Mention different scale on right

## Coalescence vs. Rapidity

**Compare p, d at  same velocity**
**Deuterons coalescence from nearby nucleons**
**B****2**** = d/p****2**
**B****2**** ******** 1/volume**

**Gemanio +**
**Bearden **
**Poster S27**

***BRAHMS preliminary***

- x10

## Flow vs. Centrality

**Fit AuAu spectra to blast wave model:**
******S ****(surface velocity) drops with dN/d******
**T (temperature) almost constant.**

- T

- Blue y=0
- Red  y=1

**E.J. Kim Poster Spectra 19**

- T

**p****T ****(GeV/c)**

- 1 and 3  contours

**y= 0**

**Notes:**
Get better plot from Eun-Joo, put equqtion down. 

## Flow vs. Rapidity

******S**

**Flow parameters have a stronger dependence on rapidity than on centrality**

****** ****drops and T rises as y increases**

**Notes:**
Claus doesn’t understand insert, flip it over.

## Landau hydrodynamics along beam axis 

**Isentropic expansion driven by equation of state**
**Mass-less particles**
**Pt and rapidity**** factorize**

**Assumptions:**

**Implications:**

-  **dN/dy Gaussian **
** ******** ****= log (√S****NN****/2m****p****)**
**   ≈ ****log (********beam****)**
** ****Model consistent with “limiting fragmentation”**

**Notes:**
First time wider than prediction.

## Chemical analysis vs. rapidity

- 4π result

- Assume that at each rapidity we have zero net strangeness. Fit data to Becattini model
- .

**The system may have fewer degrees of freedom at high rapidity**

**J.I ****Jørdre****, **** **
**Poster**
**Strange 15**

**1 ******** contour**

**Notes:**
4pi mu_b=98+-3, 154+-2 Note gamma s= 1 for curves, get systematics on plot

## Particle ratios in pp vs. AuAu

**pbar/p higher than**
**AuAu while k****-****/k****+**
**and ********-****/********+**** are**
**lower in pp**
**Conservation of**
**isospin and  **
**strangeness more**
**important for pp.**
**Stopping different.**

**B. H. Samset**
**Poster Spec. 34**

*BRAHMS Preliminary*

## Rapidity dependence of jet quenching

**R****AuAu ****< 1 for central collisions **
**R****AuAu ****at ********=0 and  ********=2.2 are similar**

**BRAHMS: PRL 91072305 (2003).**

## RAuAu for π - at =2.2

**pp reference**
**built from  PHENIX π****0**** at y=0 and Pythia **

**p****T**** (GeV/c)**

- C.E. Jørgensen
- Poster
- High pT 16

***BRAHMS preliminary***

**Notes:**
Hint of drop at higher pt

## Ratios: anti-protons to pions

**Z. Yin Tuesday High p****T ****parallel **

**Notes:**
Hadronization in vacume, there is less of it at eta=2.2, LEP = max .2 

## Deep inelastic scattering at HERA

**Deep inelastic scattering at HERA**

**Gluon Density**

**Momentum Fraction x**

**HERA measures the density of gluons as a function of the** **momentum transfer Q**** and the gluon’s **
**momentum fraction x****.**** **
**For small x there is a universal density  function **
**D = D (x, Q/Q****S****)**
**Q****S ****is the saturation scale below which gluons fuse.**

**Notes:**
Saturation at small Q

## Look at a nucleus at high speedTake the normalized ratio of dAu and pp spectra

**R. Debbe**
**Tuesday morning**

**Notes:**
Cronin peak at eta = 0. 

## Moving Forward

**Keep pushing to higher p****T  ****and rapidity with more data and better particle identification.**
**Add reaction plane as another “axis” to each measurement.**
**Extend coalescence to higher rapidity**
**Get more data for dAu (and Au - d) ASAP**
**Design new experiment for forward region.**

## What has rapidity taught us?

******E = 25********1 TeV in AuAu, broken scaling. **
**dAu multiplicity follows beam participant scaling**
**Landau hydrodynamics gives rough rapidity dependence of particle production.**
**Chemical + kinetic temperatures increase slightly with y, maybe fewer degrees of freedom.**
**Jet quenching persists at least to ******** = 2.2.**
**R****dAu ****at y:0 => 3 suggests gluon saturation.**

**Notes:**
Evolution

## Backups

## Systematics of thermal fits