# Presentation: 183780

- High-pT strange particle spectra and correlations in STAR

-                     Jana Bielcikova (Yale University)
-                         for the STAR Collaboration
-                        Hard Probes,  Asilomar, California
-                                        June 9-16, 2006

## Outline:

Baryon/meson enhancement and RCP at √sNN=200 GeV 
Azimuthal correlations of h, Λ, Λ and K0S  
    in d+Au and Au+Au collisions at √sNN=200 GeV
Test of recent ReCo model predictions 
            (Ω/ ratio, Ω triggered correlations) 
Conclusions

- Baryon/meson enhancement and RCP at √sNN=200 GeV
- Azimuthal correlations of h, Λ, Λ and K0S
-     in d+Au and Au+Au collisions at √sNN=200 GeV
- Test of recent ReCo model predictions
-             (Ω/ ratio, Ω triggered correlations)
- Conclusions

- Hard Probes 2006

- Jana Bielcikova (Yale)

##                Baryon/meson enhancement

-        a large enhancement of
-    baryon/meson  ratio in Au+Au
-  relative to p+p at √sNN=200 GeV
- Year2 data:
-    the enhancement reaches
-     maximum at pT~3 GeV/c
- Year4 data (high statistics) :
-  Λ/K0S ratio approaches p+p
-          for pT> 5 GeV/c
-    jet fragmentation is not a
-  dominant source of particle
-   production for pT=2-5 GeV/c

- Hard Probes 2006

- Jana Bielcikova (Yale)

##  Baryon/meson enhancement: model comparisons

-        Both, soft+quench and recombination type of models,
-        predict a peak in Λ/K ratio, however they can’t reproduce
-        the peak location in pT, its magnitude and shape in detail.

*SOFT+QUENCH: Gyullassy, Levai, Vitev,*
*                             **PRL 85 (2000),*
*                             **Nucl.Phys. A 715, 779 (2003) *

*TEXAS: Greco, Ko, Levai, PRL 90 (2003), *
*DUKE: Fries, Mueller, Nonaka, Bass, PRC 68 (2003)*
*OREGON: Hwa, Yang, PRC 67, 034902 (2003)*

- Hard Probes 2006

- Jana Bielcikova (Yale)

## RCP at √sNN=200 GeV

- Year2:
-      - baryon/meson difference
-      at intermediate pT = 2-5 GeV/c
- Year4:
-       - extends the RCP to higher pT
-       - strange and non-strange particles are consistent
-       - appear to show a similar suppression at pT> 5 GeV/c

- Hard Probes 2006

- Jana Bielcikova (Yale)

## Identified correlations at medium/high pT

- identified correlations at high-p**T**
-      can provide additional information on:
- jet quenching
- baryon/meson enhancement at RHIC
- particle production mechanisms
-      coalescence/recombination mechanisms
-                           and/or
-  (modified) fragmentation of high-p**T** partons?
- p**T** dependence of trigger particle species
-                    **Λ**** **from q-jet and g-jet**,**
**            ********Λ** from  g-jet only

- Hard Probes 2006

- Jana Bielcikova (Yale)

## Azimuthal correlations - method

-   near-side peak corresponds to intra-jet correlations
-   away-side peak corresponds to inter-jet correlations
-                    This talk is only about the near-side peak !

-    Jet+Ridge yield : Δɸ(J+R)
-    Jet yield	 : Δɸ(J)  = Δɸ(Δη < 0.5) –  Δɸ(Δη > 0.5)
-    Ridge yield	 : Δɸ(R)  = Δɸ(J+R) - Δɸ(J)

- Note: there are additional long-range η correlations (“ridge”)
-          in Au+Au collisions *(see talk by J. Putschke (STAR) ) *
*         *
*   *

- Hard Probes 2006

- Jana Bielcikova (Yale)

## Correlation functions for strange particle triggers in Au+Au at 200 GeV

- correlation functions
- before elliptic flow subtraction

- correlation functions
- after elliptic flow subtraction
- syst. error due to
- v2 uncertainty  ~ 25%

- Selection criteria:
-  3.0 GeV/c < pTtrigger < 3.5 GeV/c
-  1 GeV/c < pTassociated < 2 GeV/c
-  || < 1
- Corrections applied:
- reconstruction efficiency
-    of charged particles
- TPC sector boundaries

**STAR preliminary**

**STAR preliminary**

**STAR preliminary**

**STAR preliminary**

- trigger:   baryon/meson         baryon/antibaryon

- Hard Probes 2006

- Jana Bielcikova (Yale)

## Centrality dependence of near-side associated yield in Au+Au

- 	-> “jet” yield is independent on centrality
-  jet yield for Λ < K**0**S <~ h ?, ridge yield: h ~ K**0**S < Λ ?

- Centrality dependence of near-side associated yield in Au+Au

-             -> “ridge” yield rises with centrality

-   Near-side associated yield rises with centrality

- Hard Probes 2006

- Jana Bielcikova (Yale)

## pTtrigger dependence of associated yield:d+Au vs Au+Au   

- pTtrigger dependence of associated yield:d+Au vs Au+Au**   **

-  within errors no dependence on trigger species (d+Au and Au+Au)
-  yield is  ~ 3-4 times larger in Au+Au than in d+Au
-               Don’t forget: Au+Au is “ridge” dominated!
-                   Let’s look on the jet yield separately

**STAR preliminary**

**STAR preliminary**

- Hard Probes 2006

- Jana Bielcikova (Yale)

## pTtrigger dependence of jet and ridge yield   

- pTtrigger dependence of jet and ridge yield**   **

-   near-side yield is ridge dominated (~constant for p**T****trigger **> 2.5 GeV/c)

-   jet yield rises steeply with increasing p**T****trigger**
-   jet/ridge ratio varies between ~ 10-30% with increasing p**T****trigger**
-   Λ-trigger charged associations < for K**0****S**-triggers
-   Does baryon trigger take more energy away from jet than meson ?

- Hard Probes 2006

- Jana Bielcikova (Yale)

## pT distribution of associated particles

- pT distribution of associated particles

**STAR preliminary**

**Jet+ridge**

**Jet only**

**STAR preliminary**

| Trigger particle | T (jet+ridge) MeV | T (jet) MeV |
| --- | --- | --- |
| Charged | 450 ±   3 | 511 ±   6 |
| K0S | 456 ± 13 | 539 ± 58 |
| Λ | 430 ±   8 | 522 ± 84 |

**J/R~10-15%**

- Hard Probes 2006

- Jana Bielcikova (Yale)

## What does a parton recombination model predict?

**STAR preliminary**

-  central-to-peripheral ratio of near-side associated yield is:
-             -  ~ 3 at p**T****assoc **= 1 GeV/c
-             -   decreases slowly with p**T****assoc**
-  qualitative agreement between the parton recombination model and the data
-                                                   BUT!
-  a quantitative agreement requires same centrality and pT selection
-  check required on how well the “ridge” is reproduced by the model

*R. Hwa, Z.Tan: nucl-th/0503060*** **

**Au+Au @ 200 GeV**
**3GeV/c<p****T****trigger****<6GeV/c**

**STAR**

- Hard Probes 2006

- Jana Bielcikova (Yale)

## Recent ReCo Model Predictions

- The production of  and Ω is almost exclusively from thermal
- s-quarks even out to 8 GeV/c
- (shower ”S” contributions are
- strongly suppressed)

- Observables:
- 1. The ratio of Ω/ yields should rise linearly with pT
- 2. Ω or  di-hadron correlations should  be  swamped by the background and not observed

*R. Hwa , nucl-th/0602024*

- Hard Probes 2006

- Jana Bielcikova (Yale)

##   Ω/ ratio

- A qualitative agreement with model for pT < 4 GeV/c
- Need more data to draw conclusions for pT > 4 GeV/c

- QM’05

- SQM’06

- Hard Probes 2006

- Jana Bielcikova (Yale)

##   Ω-charged correlations

-   Ω-charged correlations

-       Not corrected for: efficiency, TPC sector boundaries, flow
- Within statistical errors we can’t exclude existence of
-                near-side peak in Ω triggered correlations.
-         We expect ~ 8-10 more statistics for Ω, so stay tuned .

- STAR preliminary

- Hard Probes 2006

- Jana Bielcikova (Yale)

## Conclusions 

- Azimuthal correlations of identified strange (Λ and K0s) trigger particles associated with charged particles at moderately high-pT show:
- 	      -  significant contribution from long range η correlations,
-            -  ridge yield is rising with centrality
-            -  jet yield is constant with centrality and rises with pTtrigger,
-            -  indication of a lower associated jet yield for baryon triggers
-                                       than for meson triggers.
-               **                           **

- Conclusions

- Within statistical errors, the Ω/ɸ ratio is consistent with
-      being constant and for Ω triggered correlations we can’t
-                     exclude existence of near-side peak.
-                                                                    (more data to come )
-               **                                      **

- Strong baryon/meson enhancement in Au+Au over p+p
-                   at √sNN=200 GeV observed for pT=2-5 GeV/c.
- Identified RCP shows a baryon/meson splitting for pT=2-6 GeV/c,
-      but for pT> 6 GeV/c baryons and mesons are similarly suppressed.
-               **                                      **

- Hard Probes 2006

- Jana Bielcikova (Yale)

## BACKUP

- Hard Probes 2006

- Jana Bielcikova (Yale)

## RCP at √sNN=200 GeV

- Identified RCP from Year2 shows a clear difference between baryons and mesons at intermediate pT = 2-5 GeV/c
- The Φ and K* clearly follow the mesons and not the baryons,
-       it is not a mass effect !

- 200 GeV

- 0-5%

- 40-55%

- Hard Probes 2006

- Jana Bielcikova (Yale)

## Identified correlations from PYTHIA

- Pythia 6.4 (untuned)

- Pythia 6.4 (K-factor=3)

- Default PYTHIA 6.4 is
- a leading-order calculation:
- does not describe well
- inclusive p**T**-spectra of
- strange particles (Λ,Ξ, Ω...)
- NLO contributions can
- be simulated by introducing
- a K-factor
-   the mixture of q+q, q+g and
- g+g processes is changed:
- -> it becomes more “gluon”-like

- Hard Probes 2006

- Jana Bielcikova (Yale)

## Comparison of pTtrigger dependence of jet yield in PYTHIA and d+Au

- Comparison of pTtrigger dependence of jet yield in PYTHIA and d+Au

-  near-side yield rises slowly with p**T****trigger**
-  default Pythia shows a different behaviour for anti-Λ,
-                        but yield agrees well with d+Au
-   Pythia with K-factor=3: all particle species behave similarly
-    as in the data, but the yield is a factor 2 higher
-    (because too many pions are generated with K-factor=3)

**STAR preliminary**

-  near-side yield rises slowly with p**T****trigger**
-  default Pythia shows a different behaviour for anti-Λ,
-                        but yield agrees well with d+Au

- Hard Probes 2006

- Jana Bielcikova (Yale)

## pT distribution of associated charged particles at near-side

- pT distribution of associated charged particles at near-side

-   spectral shape is similar for various trigger particle species
-                                           within  errors

**50% p+pbar**
**95% ****π**
**charged**

**1/N****trigger****dN/dp****T **

**p****T****associated****  (GeV/c)**

**STAR **Preliminary

*J. Ulery (STAR), QM2005*

**STAR preliminary**

- Hard Probes 2006

- Jana Bielcikova (Yale)

## Strange particle identification in STAR

-   Identification of strange particles:
-        V0-decay vertices:
**Λ**    ****** **p  + ******-**      BR 64%
**Λ**** **   **** p  + ******+**
- K**0****S**  **** ******+** + ******-**      BR 68%

- Cuts on dE/dx of daughter particles
- Topological cuts
-               -> a very good S/B ratio 

- Hard Probes 2006

- Jana Bielcikova (Yale)