# Presentation: 659627

## Particle Ratios at Mid-rapidityin          = 130 GeV Au+Au collisions

- Gene Van Buren
- Brookhaven National Lab
- for the STAR Collaboration
- ThermalFest - July 20, 2001

## What are we looking for?

- What is the initial environment like for particle production?
- Net baryon density
- What happens during the initial particle production?
- Strangeness production
- Quark coalescence?
- Are re-interactions significant?
- Rescattering of hadrons
- Equilibration of strangeness

**Baryon / antibaryon ratios**

**Strange hadron / h- ratios**

**Quark-counting ratios**

**Strange baryon ratios**

**Hadron ratios vs. p****t**

## p/p  Ratios

**Ratio = 0.65 ±0.03(stat) ±0.03(sys)**

**Ratio is flat as function of p****t**** and y**

**Slight fall with centrality**

**PRL 86 p4778 (March 2001)**

## / Ratios

**Flat as a function of p****t**

**Central events**

**|y|<0.5**

**1**

**N****ch****/N****max**

**Slightly decreasing with centrality**

- Averaged over experimental acceptance in pt

**STAR Preliminary**

## Energy Evolution of B/B Ratio

*STAR preliminary*

**Production of baryons through pair processes increases dramati-cally with ********s – still not baryon free**

**Pair-process production is larger than baryon transport**

**2/3 of protons from pair processes , yet pt dist. the same as antiprotons**

**(ISR)**

- Thermalization?

## The  and  Baryons

- High quality data for strange and doubly strange baryons!

## The  Baryon

- The  Baryon

**15% Most Central**

- Peaks are evident, but statistics are low.
- Ratio on the order of 1 with large stat. errors presently.

## STAR B/B Ratios

**Ratio approaching 1.0 as strangeness content increases**

- Ratios calculated for central events at mid-rapidity, averaged over experimental acceptance in pt

## K+/K- versus Centrality

**K****+****/K****-**** constant over measured centrality**

- Nch/NMAX

## K+/K- versus Pt

**K****+****/K****-**** ratio consistent with being flat over pt**

## Energy Evolution Revisited

*STAR preliminary*

**(ISR)**

## Quark-Counting Ratios

- Phys. Lett. **B**347 (1995) p6

## Quark-Counting Ratios

**Quark-counting ratios are consistent with each other**

- Measured

- Predicted

- Statistical errors only

- Will change slightly with feeddown corrections (not included here)

- STAR Preliminary

##  fractions of h-

**Note: spectra are not **
**feed-down corrected**

****** ****yields are from fits to Boltzmann; h****-**** yields are power law fits**

## K0*, K0* Ratios

- 20% systematic error from assuming 300 MeV inverse slope in efficiency calculations.

- K*: |y| < 0.5,
-       0.2 < pt < 2.0 GeV/c
- h- : || < 0.5,
-       pt > 0.1 GeV/c

## K0*, K0* Ratios

- nucl-ex/0104001

**K*/h****-****  ****compatible with K*/********-**** from elementary particle collisions**

##  Ratios

- Relative production of  increasing with collision energy in heavy ion collisions.

## What were we looking for?

- What is the initial environment like for particle production?
- Net baryon density
- What happens during the initial particle production?
- Strangeness production
- Quark coalescence?
- Are re-interactions significant?
- Rescattering of hadrons

**Still a significant amount of baryon number around**

**Increasing fraction of particle production with energy, but not centrality?**

**Reasonable predictor**

**Little p****t**** dependence, significant rescattering?**

## Slide 19

## Baryon-Antibaryon Ratios

-  p/p
-  
-  
-  