# Presentation: 093176

## Recent RHIC Results onBulk Properties

**Richard Hollis**

## The Road Ahead

- Bulk properties measurements at RHIC
- New measurements and expanded systematics
- Scaling with Npart, Nch or part
- Simple Scaling Rules

## Systematic Studies

- RHIC input
- Energy
- Collision system (species)
- Experimental input
- Rapidity
- Species
- System size/configuration

- Varied Cross-section
- esp. hard collisions
- Influence toward bulk properties
- Study dominating effect
- Npart or fractional cross-section
- Probe range of *x**F*
- Relative enhancement of baryons to mesons
- Path length and collective effects

- Do systematic studies paint a consistent picture of bulk particle production?

## Total Charged Hadron Distributions

- dN/d
- flow{v2,v1,(v2)/v2}

## Multiplicity

- Latest Results
- Au+Au (Peripheral)
- Cu+Cu (22.4 GeV)
- Mid-rapidity
- Factorization in energy and centrality
- 4
- Extended longitudinal scaling – factorizes in energy and centrality

- Factorization persistent across all systems

**QM2006**

## Elliptic Flow

- Similar systematic dependencies as multiplicity
- Mid-rapidity:
- v2/part scaling holds over a broad range of collision energy and system sizes
-  dependence
- v2/part holds over large  range
- Extended longitudinal scaling

**QM2006**

**Matched**
**N****part**

- Geometrical scaling with part

## Directed Flow

- v1 is found to scale with collision energy, not collision species
- Comparison of same overlap geometry
- Extended longitudinal scaling applies

**Relative shift**
**in y****beam**

## Elliptic Flow Fluctuations

- Large fluctuations in the v2 signal
- Geometrical Properties are imprinted on the data:
- Eccentricity via Flow

**arXiv:nucl-ex/0702036**

**Au+Au @ 200 GeV**

## Final Charged Particle Distribution Summary

- Final distributions provide a consistent picture of particle production driven by simple scaling laws:
- Energy, centrality factorization
- Detailed initial geometrical configuration (part)
- How do differential measurements compare

## pT Distributions

- pT Distributions

- Yield versus pT
- v2{pT}
- Freeze-out properties

## Yield versus pT

- Mid-rapidity yields versus pT
- Factorization in energy and centrality
- Similar behavior to bulk yields

**QM2006**

## Elliptic flow at mid-rapidity

- Latest Results:
- v2{pT} (200 GeV)
- v2{pT} *shape* independent of centrality and system size

**PRL 98, 162301 (2007)**

- v2{pT}: universal scaling?

## Kinetic freeze-out properties

**Kinetic freeze-out properties**

- Latest Results:
- Freeze-out properties
- Freeze-out temperature and flow velocity follow a common dependence with number of charged particles at mid-rapidity
- Mean-pT follow same trend

**QM2006**

- Scaling of low-pT properties with Nch

**Similar dependence noted by PHENIX (JPS 2007)**

## Chemical freeze-out properties

- Latest Results:
- Cu+Cu at 200 and 62.4 GeV
- Universal chemical freeze-out temperature, Tch, is observed for all studied systems

**QM2006**

## pT Distributions Summary

- First differential measurements:
- “Universal scaling” of elliptic flow versus pT
- Nch scaling of kinetic freeze-out properties

## Chemical properties

- Strangeness production
- Baryon enhancement
- v2{KE/nq,y}

## Strangeness production – K±

- Latest Results:
- 62.4 GeV Au+Au
- Charge “splitting” of K/ as observed at SPS
- “Chemical equivalence” with SPS energies

**QM2006**

## Strangeness production – 

- Latest Results:
-  scale reasonably with Npart for the same energy
- Enhanced strangeness production due to ***core*** of core/corona model
- More ***core*** per Npart in Cu+Cu collisions

**STAR Preliminary **

**QM2006**

**Phys. Rev. Lett. 98, 152301 (2007) **

## Recombination Model

- Describes the pT dependence of strange particles
- K,
- Fits provide good agreement with data
- Qualitatively reproduces /K0S ratio

**nucl-th/0602024**

******(STAR)**

**K****0****S****(STAR)**

## Baryon Enhancement

- Enhancement is maximal in the intermediate-pT region
- Cu+Cu data exhibit the same systematic trends as for Au+Au system

**QM2006**

**Illustrative p+p (not a fit)**

**Cu+Cu @ 200 GeV**
**STAR Preliminary**

## Baryon Enhancement

- Npart scaling for p/
- Integrated intermediate-pT region
- Moreover, ET scaling exists between 200 and 62.4 GeV (pbar/–)
- Baryon transport contributes at 62.4 GeV for protons

**JPS 2007**

**PHENIX preliminary**

- Scaling of intermediate-pT properties with ET

## Recombination Revisited

- Recombination predicts other B/M ratios
- Qualitative agreement.
- s-quark dependence on peak position is predicted
- But at higher-pT than data suggests

**QM2006**

## Recombination Revisited

- Validity test:
- ,
- A good description of the multi-strange spectra
- : dominated by thermal term
- Look at  correlations
- No near-side correlation expected
- Correlation observed
- Magnitude of near-side correlation is independent of strange-quark content

**QM2006**

**WWND 2007**

## Quark scaling of elliptic flow

- Latest Results:
- v2/nq scales with KET/nq
- Holds for Cu+Cu data
- Once  is accounted for

**PRL 98, 162301 (2007)**

**WWND2007**

## Identified v2

- For different centrality bins:
- No ***universal*** scaling

**←****Centrality Dependence**

**Min-bias, particle id’d****→**

## Elliptic flow versus rapidity

- Identified flow versus pT and rapidity
- No appreciable difference in shape
- cf. PHENIX flow at mid-rapidity
- No difference in magnitude

**BRAHMS**
**Preliminary**

- Systematics fit into existing data

**Xi’an 06**

- ≈0

- ≈3

## Chemical Summary

- Further differential measurements:
- pbar/ – Npart scaling
- Qualitative description of B/M ratios in the recombination picture
- But fails to describe the multi-strange correlations
- Universal scaling of identified v2{pT}
- Observed for min-bias across system size
- Not observed versus centrality

## Summary

- Bulk properties measurements at RHIC
- New measurements and expanded systematics
- Scaling with Npart, Nch or part
- For the bulk to intermediate-pT regions
- Simple Scaling Rules
- Applicable over a broad range of centrality, energy and colliding species

## Thanks!

- Credits:
- BRAHMS
- Flemming Videbaek
- PHENIX
- Barbara Jacak, Craig Ogilvie
- STAR
- Aihong Tang, Subhasis Chattopadhyay , Olga Barannikova, Rene Bellwied
- PHOBOS
- Wit Busza, David Hofman, Aneta Iordanova

- Evan, 6 weeks and 2 days

## Back-up Slides

- Core/corona
- Core – high density region
- Corona – low density region around the edge

- My own simulations
- Based on similar ideas

**Phys. Rev. Lett. 98, 152301 (2007) **

**Au+Au “core”**

**Cu+Cu “core”**

**Au+Au “corona”**

**Cu+Cu “corona”**

**Thesis (2005) **

## Particle Ratios versus system size

- Particle Ratios
- 200 and 62.4 GeV
- Au+Au and Cu+Cu
- Weak centrality dependence, no system size dependence of particle ratios

**Near**
**mid-rapidity**

**QM2006**