# Presentation: 336675

## Systematics of identified particle spectra

- Levente Molnar, Purdue University
- For the STAR Collaboration

- Outline:
-  Physics motivation
-  Particle spectra and properties at 62.4GeV and beyond ...
-  Resonance effect on extracted freeze-out parameters
-  Summary, outlook, ...

- Levente Molnar, Purdue University

## Motivation

-  New data set: 62.4GeV Au-Au collisions,
-  first step in the energy scanning program at RHIC.
-  Bulk particles are the ‘final’ dynamic thermometers of the collision system:
-  Identified particle spectra at low pT
-  Study particle production vs. psNN , centrality, ...
-  Particle ratios → chemical freeze-out properties
-  Shape of the spectra → kinetic freeze-out temperature and transverse radial flow: dynamics of the collision.
-  Study of resonance decay effect on the extracted freeze-out parameters.

- Levente Molnar, Purdue University

## Identified particle spectra in AuAu at 62.4GeV

-  Spectra evolution with centrality is similar to that observed at 200GeV.
-  Particle spectra are fitted with Blast-Wave model (thermal source + flow )
- ( E. Schnedermann *et* al. PRC**48**, 2462, (1993) )

**STAR Preliminary**

**STAR Preliminary**

**STAR Preliminary**

- Levente Molnar, Purdue University

## Particle - antiparticle ratios

-  / - 1⁄4 1.
-  K- / K+ ratio is smaller at 62.4GeV.
-  Significant drop in antiproton to proton ratio!
-  Statistical models are very successful describing ratios from AGS-RHIC.

**STAR Preliminary**

- Errors shown:
- 200GeV systematic errors
- 62.4GeV stat. errors

- BRAHMS, nucl-ex/0410020

**STAR Preliminary**

- Levente Molnar, Purdue University

## Unlike particle ratios vs centrality

- Errors shown:
- 200GeV systematic errors
- 62.4GeV stat. errors

**STAR Preliminary**

- Levente Molnar, Purdue University

## Average transverse momenta

**Nch**

- STAR: 200GeV AuAu: Phys. Rev. Lett. **92** (2004) 11230

-  <pT> follows the
- same trend in Nch
- < pT >K,p is extracted
- from Blast-Wave fit.
-  < pT >π  is extracted
- from Bose-Einstein fit.

- Errors shown:
- 200GeV systematic errors
- 62.4GeV stat. errors

**STAR Preliminary**

- Levente Molnar, Purdue University

## Freeze-out parameters I.

- Errors shown:
-  200GeV systematic errors
-  62.4GeV stat. errors

**STAR Preliminary**

**STAR Preliminary**

**STAR Preliminary**

- <β>

- Levente Molnar, Purdue University

## Freeze-out parameters II.

****

- Errors shown:
-  200GeV systematic errors
-  62.4GeV stat. errors

- Nch

- Nch

**STAR Preliminary**

**STAR Preliminary**

**STAR Preliminary**

- Becattini, hep-ph/0202071

- Levente Molnar, Purdue University

## Estimate of Resonances and Method

- The blast wave model study shown so far treated particles as if they were primordial. Systematic errors include resonance effects studied by a stand alone MC.
- A more complete study of resonance effects based on code from ref.: U.A.Wiedemann, U.Heinz, Phys.Rev. C56 (1997) 3265-3286.
- Improvements:
- Increase the number of resonances included: , , ’, , K*, KS, , 1520, , 1385, , .
- Implementation of two freeze-out temperatures
- Chemical model fit provides Tchem, B, S and 
- Calculate primordial particle yields
- Blast wave model; shape of particle spectra including  resonances. (Ref.: E. Schnedermann *et* al. PRC48, 2462, (1993) , ... )
- Resonance decay channels, ref. see above
- Addition of decay channels ! Inclusive spectra.
- The inclusive simulated spectra then are fitted to the measured , K, p spectra.
- Extract Tkin and  for which the 2/ndf is minimum.

- Levente Molnar, Purdue University

## PiMinus Spectra 

- PiMinus Spectra

-  Note: pion spectra (data) are corrected for weak decays, no  and K0Scontributions..

**STAR Preliminary**

**T****kin****=90MeV**
******0.6**
**n=0.8**

- Levente Molnar, Purdue University

## KMinus Spectra 

**STAR Preliminary**

**T****kin****=90MeV**
******0.6**
**n=0.8**

**STAR Preliminary**

- Levente Molnar, Purdue University

## Proton Spectra 

- Proton Spectra

**T****kin****=90MeV**
******0.6**
**n=0.8**

**STAR Preliminary**

**All Protons**
**Thermal protons**
**Lambda**
**Delta**
**Xi**
**Sigma**
**Omega**
**Sigma1385**
**Lambda1520**

**STAR Preliminary**

- Levente Molnar, Purdue University

## Fit I.

-  Pion spectra can be reproduced, kaons and protons are less well described .

**STAR Preliminary**

**STAR Preliminary**

- /ndf=1.547

**T****kin****=90MeV**
******0.6**
**n=0.8**

- pT (GeV/c)

- pT (GeV/c)

- Levente Molnar, Purdue University

## Fit II.

-  Kaons and protons agree well, pions are less well described.
-  Short lived resonances, eg.: 

**STAR Preliminary**

**STAR Preliminary**

**T****kin****=90MeV**
******0.64**
**n=0.8**

- /ndf=1.396

- Levente Molnar, Purdue University

## Rho contribution

- It is an open question what flow velocity and temperature should be assigned to short-lived resonances such as , , ...
- They decay and are regenerated constantly during the system evolution:
- assume  decay pions and other pions are in equilibrium and behave similarly ( similar temperature and flow velocity ).
- the  does not gain stronger flow due to its large mass during its short lifetime.
- Assume  does not contribute to spectral shape change, i.e. we take primordial pion shape for the  decay pions as well.  decays are still included but their contribution is small.

- Levente Molnar, Purdue University

## Fit III.

-  With the contribution as described before, blast wave describe all spectra well. The parameters agree with published values within syst. errors.

**STAR Preliminary**

**STAR Preliminary**

**T****kin****=90MeV**
******0.64**
**n=0.8**

- /ndf=0.305

- Levente Molnar, Purdue University

## Summary and Outlook

- Summary and Outlook

- Levente Molnar, Purdue University

## Slide 18

## PiMinus Spectra No Rho

- Levente Molnar, Purdue University

## Paper plots

-  Pion spectra – with the decay channels – as  in paper can be reproduced.
-  Note: linear transverse flow **rapidity** profile is used in paper: t= f r, where r=0-4.
-  In the following calculations “regular” flow is used =S (r/R)n=0.8

- Levente Molnar, Purdue University