# Presentation: 742114

## New Experimental Results from RHIC

- Mark D. Baker (BNL)

- Current and Future Directions at RHIC
-                  August 6, 2002

- Many thanks to: _Thomas Ullrich,_ _Sergei Voloshin,_
- _	_	     _Thomas Peitzmann_

## Organization

- Initial State
- “Bulk” Matter
- Boost (Non)-Invariance
- “Jet quenching”
- Or failure to scale with Ncoll...
- Opacity/Explosiveness
- High2002 pT puzzles
- Summary

## Multiplicity is a window on the initial state

**PRL 88 (2002) 022302**

- Start with low entropy
- Final state interactions just reshuffle

******s (GeV)**

## RHIC: Nch at mid-rapidity

**Consistency of RHIC results**
**PHENIX****:** PC, **STAR****:** TPC
**PHOBOS****:** Si  **BRAHMS****:** Si & Scint.

- A. Bazilevsky (PHENIX)

- Ratio R(200/130):
- BRAHMS:	1.14  0.05
- PHENIX: 	1.17  0.03
- PHOBOS: 	1.14  0.05
- STAR:		1.19  **(no sys. yet)**

** ****QM2002 summary slide (Ullrich)**

**Notes:**
Alexander (Sascha) Bazilevsky 

## Nch: Centrality Dependence at RHIC (SPS)

**PHOBOS Au+Au |********|<1**

- 19.6 GeV
- preliminary

**130 GeV**

**200 GeV**

**Au+Au**

**(preliminary)**

- M. Baker (PHOBOS)

- Everything counts:
-  Nch|=0 described nicely by KN (hard + soft)
-  Nch scales with Npart

** ****QM2002 summary slide (Ullrich)**

**Notes:**
pp not in fit   
 fix point 1.5 off beam-rapidity

## Nch(sNN) – Universality of Total Multiplicity?

- pQCD e+e- Calculation

- Total charged particle multiplicity / participant pair

- Total particle multiplicity reflects the initial state?
- Note: Still interesting dynamics in the final state interactions!

- (A. Mueller,
-  1983)

- Same for all systems at same s(seff for pp)

**Notes:**
1 free parameter in fit .... lambda_QCD = 225 
PYTHIA also gives s_eff = s/2

## More detailed comparison of AA, ee

**e****+****e****-**** measures dN/dy****T****(rapidity relative to****“thrust” axis)**

**200 GeV**

## Understanding “Bulk” Matter

- Studying Matter:
- Global Observables Nch, ET, pT
-  , S, ...
- Particle Yields & Ratios
-  Tch, B, S, ...
- Particle Spectra
-  Tfo, flow, stopping, ...
- Correlations
- ... and all that in pp, pA, AA

- STAR preliminary

** ****QM2002 summary slide (Ullrich)**

## Statistical Model: First Look at AuAu @ 200 GeV

**All 200 GeV data ta****k****en from QM tal****ks:**
- F. Wang (STAR)/G. Van Buren (STAR)/
- T. Chujo (PHENIX)/Ouerdane (BRAHMS)
- J. Lee (BRAHMS)/B. Wosiek (PHOBOS)
**New 130 GeV data are:**
- C. Suire (STAR)/J. Castillo (STAR)

- Predictions:
- phenomenologically:
- B ~ 1.3 GeV (1+s/4.5 GeV)-1
- assume unified freeze-out condition:
- E/N ~ 1.1 GeV  T

** ****QM2002 summary slide (Ullrich)**

**Notes:**
Caveat - BRAHMS: 10% effect on ratios when including feed-down

## K-/K+ and p/p from AGS to RHIC

- I. Bearden (BRAHMS)

- Becattini caluclation using
- statistical model:
- T=170, s=1 (weak dependency)
- vary B/T  K+/K- andp/p
- K- /K+=(p/p)1/4 is
- a empirical fit to the data points
- K****K****  driven by s
- ~ exp(2s/T)
- p/p   driven by  B
- ~ exp(-2B/T)
- s = s (B)   since <S> = 0

- BUT: Holds for y  0 (BRAHMS y=3)

** ****QM2002 summary slide (Ullrich)**

**Notes:**
Kristoph Redlich : two different curves: AGS K/K driven by associate production / RHIC pair production

## Radial flow

- M. Kaneta/N. Xu (STAR)

- <pT> prediction with Tth
- and <> obtained from
- blastwave fit (green line)

- <pT> prediction for
- Tch = 170 MeV
- and <>=0
*pp no rescattering, *
*no flow*
*no thermal equilibrium*

- STAR

- preliminary
- F. Wang

**Notes:**
fit k, pi, p only  ---- <pt> Boltzman for pion, K exp, p exponential, rest is exponential

## Identified Particle Spectra at RHIC @ 200 GeV

- Feed-down matters !!!

- BRAHMS: 10% central
- PHOBOS: 10%
- PHENIX: 5%
- STAR: 5%

** ****QM2002 summary slide (Ullrich)**

## Elliptic Flow

**V****2**

**Normalized Multiplicity**** **

**Particle **
**asymmetry**

**dN/d(********R ****) = N****0 ****(1 + 2V****1****cos (********R****) + 2****V****2****cos (2(********R****)) + ... ) **

**midrapidity : |********| < 1.0 **

## Centrality dependence @ RHIC.

- v**2**=0.05

- 130 GeV: 0.075< p**t **< 2.0
- 200 GeV: 0.150< p**t **< 2.0
- 4-part cumulants

- 200 GeV: 0.2< p**t **< 2.0

- 200 GeV: Preliminary

- Note possible dependence on low pt cut

- - Consistent results
- - At 200 GeV better pronounced decrease     of v**2 **for the most peripheral collisions.

** ****QM2002 summary slide (Voloshin)**

## v2 vs pseudorapidity

- PHOBOS:  No boost invariance !

** ****QM2002 summary slide (Voloshin)**

## Growth of Limiting Fragmentation Region

**p + p inel.**** **** **

- UA5, Z.Phys.C33, 1 (1986)

**dN/d******

**Systematic errors not shown**

**19.6 GeV is preliminary**

**PHOBOS Au+Au**

**dN****ch****/d********/<N****part****>**

- 6% central

## Interlude: Many ways to slice pz

_**Away from mid-rapidity:**_

**Rapidity: Generalized velocity**

**Pseudorapidity: ~y: easier to measure**

**Feynman x: scaled p****z**

## Rapidity dists.: Boost-Invariance at RHIC ?

- M. Baker (PHOBOS)

- D. Ouerdane (BRAHMS)

** ****QM2002 summary slide (Ullrich)**

## NEW: Rapidity dependence of ratios at RHIC

- I. Bearden (BRAHMS)

- BRAHMS 200 GeV

- At mid-rapidity:
- Net-protons: dN/dy  7
- proton yield: dN/dy  29
-  3⁄4 of all protons from pair-production

** ****QM2002 summary slide (Ullrich)**

**Notes:**
3x more protons produced than shifted in from beam

## Boost-Invariance at RHIC ?

-  Boost invariance only achieved in small region |y|<0.5

- 

- Thomas Ullrich,
- QM2002

**Notes:**
MB fits

## Suppression of Hadron Production (130 GeV)

- ratio of pT-spectra
- AA central / pp

- RAA < 1 for central Au+Aureactions at RHIC (130 AGeV)
- observed in neutral pions and charged hadrons (PHENIX and STAR)

- RAA =1 for scaling with number of binary collisions

**J.C. Dunlop et al. , Nucl. Phys. A 698, 515c (2002)**

**K. Adcox et al. , Phys. Rev. Lett. 88, 22301 (2002)**

** ****QM2002 summary slide (Peitzmann)**

## Energy Dep. of pT-spectra in pp and AA

- spectra in pp
- strong variationwith beam energy
- “flattening” of spectra
- power law
- influence of hard scattering

- K. Reygers et al., Hirschegg 2002

- spectra in AA
- little variation with beam energy
- almost exponential
- influence of thermal production?

** ****QM2002 summary slide (Peitzmann)**

## Charged Hadron Spectra

- C. Jorgensen, BRAHMS
- Parallel Saturday

- C. Roland,
- PHOBOS
- Parallel Saturday

- J. Jia, PHENIX
- Parallel Saturday

- J. Klay, STAR
- Parallel Saturday

- 200 GeV results from all experiments

** ****QM2002 summary slide (Peitzmann)**

## The 4 experiments

- Thomas Peitzmann,
- QM2002

**Notes:**
Show 130 GeV suppression in RAA plot.

## Participant scaling of AuAu vs. AuAu??

- Divide by the value at Npart=65

**PHOBOS Preliminary:**

**Au+Au 200 GeV**

**UA1 pp  (200 GeV)**

- C. Roland, QM2002

- S. Mioduszewski, QM2002

## Jet Evidence in Azimuthal Correlations at RHIC

- near-side correlation of charged tracks (STAR)
- trigger particle pT = 4-6 GeV/c
-   distribution for pT > 2 GeV/c
- signature of jets

- also seen in  (0) triggered events (PHENIX)
- trigger particle pT > 2.5 GeV/c
-   distribution for pT = 2-4 GeV/c

- M. Chiu, PHENIX Parallel Saturday

** ****QM2002 summary slide (Peitzmann)**

## Counter-Jet Suppression

- jet suppression measure as a function of centrality
- trigger-jet
- little modification(?)
- most trigger particles from jets!
- counter-jet
- strong suppression with increasing Npart
- jet quenching?
- inconsistencies for smallertrigger momentum
- to be investigated

- D. Hardtke, STAR Plenary Tuesday

** ****QM2002 summary slide (Peitzmann)**

## Surface Emission? 

- Jets ~ Npart??

- How about Ncoll  / V ?

- Future measurements may clarify this...

- Idea from X.N.Wang, QM2002

**Notes:**
Printed 

## Opaque expanding source would mean:

- Heiselberg, Levy,.PRC **59** (1999) 2716

**Notes:**
Printed 

## High pT v2 reaches geometric surface limit

** ****QM2002 (Voloshin)**

- E. Shuryak, nucl-th/0112042

** ****QM2002 (Filimonov, STAR)**

## Opaque, expanding source would mean:

- Opaque

- Expanding

- Rischke RIKEN workshop (2002):
- Such strong xt correlations probably
- require a lack of boost-invariance...

**Notes:**
printed

## kT dependence of Rout/Rside

- A. Enikizono
- QM2002

- C.M. Kuo, QM2002 poster (PHOBOS) 200 GeV:

- @0.25 GeV/c

## p/

- p/

-  Proton yield is comparable with pions @ 2 GeV in central collisions, less in peripheral

- Central

- p/

- Peripheral

- Tatsuya Chujo (PHENIX)

## High pT Puzzle I:

- T. Sakaguchi, PHENIX Parallel Saturday

- Important baryon and/or kaon contribution out to pT = 8 GeV/c?

- S. Mioduszewski, PHENIX

## High pT puzzle II:

- Adler et al., nucl-ex/0206006

- Still flowing at pT = 8 GeV/c?

## Our state is extreme

- Hot dense state
- Freezeout temperature near theoretical transition
- High Energy Density
- Very black source.
- v2 ~pT and ~ maximum allowed from surface
- HBT Ro/Rs
- Approximate Npart scaling of high pT particles
- Explosive source.
- Radial flow at roughly the speed of sound
- HBT Ro/Rs
- (Unlike 2-particle correlations)
- Alternatively (or additionally):
- Magic near-instantaneous freezeout
- Blast wave or Humanic model
- Puzzles left at high pT

## Oh, what one day can do...

**CERN baseline (17.3 GeV)**

**PHOBOS preliminary**
**                      ****& NA49**

**PbPb* WA98 (0-5%)**

**PbPb* NA50 (0-5%)**

**PbPb* NA50 (5-10%)**

**PbPb EMU13 (0-9%)**

**PbPb NA49 (0-5%)**

**PbPb 17.3 GeV (0-5%)**

**AuAu 19.6 GeV (0-6%)**

## Energy Density Estimate (Bj)

**formation time: 0.2 - 1 fm**

**PRL 87 (2001) 052301**