# Presentation: 265571

## Using intermediate pT measurements as a probe for investigating hadron production mechanisms

**Boris Hippolyte, YALE University**

- Baryon/meson ratios: only radial flow effect or      **other mechanisms needed ?**
- Identify particles using the STAR detector
- 	for Au+Au collisions at sNN = 200 *GeV**.*
- Particle identification with STAR RICH
- 	(p, K-,  and c.c.) for pT  [1-5 GeV/c].
- Access intermediate physics region (difference between
- 	baryon and meson production, coalescence models).

- Hot Quarks - Taos Valley

## Particle production vs PT for Au+Au @ 200 GeV

- Particle production vs PT for Au+Au @ 200 GeV

- pT

- pQCD

- Hydro

- 2-3 GeV/c

- 6-7 GeV/c ?

- Soft

- Fragmentationand quenching of jets

- 0

- Mechanism(s) atintermediate pT?

**Spectra, identical & mixed ratios, R****cp**

**What we know for sure... **

- Hot Quarks - Taos Valley

- 23/07/2004

## Baryon/Meson ratios in heavy ion collisions

**Success of coalescence and reco models to reproduce mixed ratios for RHIC most central data...**

- PHENIX data and Texas A&M model

**Charged particles identification at intermediate p****T**** from STAR (humility!)**

- Hot Quarks - Taos Valley

- 23/07/2004

## STAR Detectors @ intermediate pT

- r ~ 235cm, s~1.1m2
- ||<0.3 and 

**STAR Ring Imaging Čerenkov Hodoscope**

- STAR Detectors @ intermediate pT

**Prototype (ALICE, small acceptance)**

**STAR Time Projection Chamber**

**run II Au+Au @ 200 GeV**

**dE/dx PID range: **
****** ****(dE/dx) = .08]**
**p ******** ~ 0.7 GeV/c for K****/******
**   ******** ****~ 1.0 GeV/c for ********p/p**

- ||<1.5 and 

**+ Topology analysis (V0s,Cascades)**
**no limitation in p****T ****but stat.**

**run IV  STAR  TOF (less humble!)**

- Hot Quarks - Taos Valley

- 23/07/2004

## RICH  Identification

- Charged particle through radiator
- MIP and photons detection

- 3) Ring reconstruction

**RICH PID range:**
**1 ~3 GeV/c ****for Mesons**
**1.5 ~4.5 GeV/c**** for Baryons**

**STAR preliminary**

- Hot Quarks - Taos Valley

- 23/07/2004

## Event Selection

**Au+Au @ 200 GeV: data taken in 2001**

- statistics:
- 1.8M central
- 2.0M minbias

** ****Space charge distorsions induce a**
** ****correction for momentum determination**

- Hot Quarks - Taos Valley

- 23/07/2004

## Track Selections and Reconstruction with RICH

| Selections | Range |
| --- | --- |
| Residual (local x and y) | < 0.5 cm |
| DCA (primaries) | < 0.5 cm |
| TPC track fit point | > 20 |
| Minimum # of photons | > 1* |

**Cluster charge: separating ******** and mip**

| Selections | Range |
| --- | --- |
| Last TPC point radial distance | > 140 cm |
| Minimum pt | > 1.5* GeV/c |
| Pseudorapidity of the track || | < 0.15 |
| Minimum MIP deposit | > 150 ADC |

**STAR preliminary**

- Hot Quarks - Taos Valley

- 23/07/2004

## Cherenkov distribution and Fitting: integrated method

- Cherenkov angle distribution in momentum bins

- 3 Gaussians fit:
-   8 (= 9-1 constraint) parameters.
- constraint: integral = entries.
- fixing parameters with simulation

- Condition: low background

-  Separate species for each momentum slice:

- Hot Quarks - Taos Valley

- 23/07/2004

## Efficiency Calculations with Embedding technique

** ****No strong species dependence, centrality dependence (TPC multiplicity)**

**STAR preliminary**

- Hot Quarks - Taos Valley

- 23/07/2004

## Identified particle pT spectra :p,p, K-,+, -,+, K0s and 

-  Baryon Spectra over Meson Spectra for most central data...

- Hot Quarks - Taos Valley

- 23/07/2004

## Identified particle pT ratio: B/B

- This pQCD calculation fails : wrong regime, uncertainties in PDFs and fragmentation functions ?
- Both the ‘Soft+Quench’ and recombination model predictions are consistent with the data.

- Soft+Quench (130 GeV) : Nucl. Phys. A**715** 779-782 (2003)
- Recombination (200 GeV) : Phys. Rev. C**68** 044902 (2003)

- Hot Quarks - Taos Valley

- 23/07/2004

## Identified particle pT ratio: p/-

- Reco : Phys. Rev. C**68** 044902 (2003)
-   Coal  : Phys. Rev. C**68** 034904 (2003)

- Hydro: Phys. Rev. C**67**, 044903 (2003)
-  S+Q: 130 GeV data - Phys. Rev. C**65**, 041902

- Same than P. Jones talk !
- _Soft+Quenching:_ agreement +peripheral events...
- _Coalescence:_ amplitude...
- _Reco:_ Shape and turnover...
- _QGP+minijets:_ agreement but peripheral events ?!

**STAR preliminary**

- Hot Quarks - Taos Valley

- 23/07/2004

## Conclusion and Outlook

- Baryon/meson ratios with STAR detector
- Access intermediate physics region: good qualitative agreement for central data and for most of the models but time to look into  details!
- Spectra: centrality, energy & system dependence
- centrality then Rcp
- energy: fresh data Au+Au @ 62 GeV (Rcp, V2)
- SPS: well... what about /K0s ?!
- Run IV at 200 GeV: more stat and STAR TOF to probe this intermediate pT domain.

**STAR preliminary**

- Hot Quarks - Taos Valley

- 23/07/2004