# Presentation: 786413

## Resonance Production in RHIC Collisions 

-  Kent State University

-      Motivation
-      Resonance in hadronic phase
-        Time
-        RAA  and  RdAu
-        Elliptic flow v2
-      Summary

**for the STAR Collaboration**

**Resonance Production in RHIC Collisions**

**Notes:**
I am going to talk about resonance production in heavy ion collisions. Let me stat with a motivation T

## Lifetime of Nuclear Medium

- t > 4 fm/c
- resonances

- Au+Au
- t ~ 10 fm/c
- (HBT)

**Partonic phase  ********  < 6   fm/c****  **

- C. Markert, G. Torrieri, J. Rafelski, hep-ph/0206260 + STAR   delta lifetime  > 4fm/c** **

## Time in Heavy Ion Reactions

- Hot and dense
- medium

**p+p**

**Au+Au**

**Au+Au interactions:**
-  Extended hot and dense phase
-  Thermalization at chem. freeze-out
-  Kinetic freeze-out separated from
-    chemical freeze-out

**p+p interactions:**
-  No extended initial medium
-  Chemical freeze-out (no thermalization)
-  Kinetic freeze-out close to the chemical freeze-out

- Particle yields

- Particle spectra

**time**

## Resonance Signals in p+p and Au+Au collisions from STAR

** ****K(892)**

****

******(1520)**

**p+p**

**p+p**

**Au+Au**

**Au+Au**

** ********(1385)**

**p+p**

**Au+Au**

******(1020)**

**p+p**

**Au+Au**

**p+p**

********

**K(892)    ********  K+ ********  **
******(1232)  ********  p+ ******** **
****** ****(1020)  ********  K + K**
******(1520)  ********   p **** ****+ K**
******(1385)  ********  ********+ ******

## Interactions of Resonance in Hadronic Nuclear Medium

- * and* show rescattering
- * shows regeneration
- _Regeneration/Rescattering cross section:_
******p)  ********  ******
- 

- Interactions of Resonance in Hadronic Nuclear Medium

- [1] P. Braun-Munzinger et.al.,PLB 518(2001) 41,
-       priv. communication
- [2] Marcus Bleicher and Jörg Aichelin
-        Phys. Lett. B530 (2002) 81.
-       M. Bleicher and Horst Stöcker
-        J. Phys.G30 (2004) 111.

**Life-time [fm/c] :**
********
********
****
********

**Preliminary**

**UrQMD******** =10****±3 fm/c**

****

## Regeneration Cross Sections 

- Regeneration Cross Sections

- 
- 
- 
- 

- _Regeneration/Rescattering cross section:_
****
- 

**Sascha Vogel, San Diego Winter Workshop 2006 **

- Production channel for measured resonances:

- UrQMD calculations

## RAA of Resonances (with rescattering)

-  K(892) more suppressed in AA than Ks0
-  K(892) are lower than Ks0 (and )
-    pt < 2.0 GeV factor of  2

## Nuclear Modification Factor RdAu

- K* is lower than  Kaons in low pt d+Au no medium  no rescattering why K* suppression in d+Au ?
- * follows h+- and lower than protons .

## Medium in d+Au ?

- *: No rescattering in hadronic d+Au medium
- K* : Rescattering in hadronic d+Au medium
**???**

## Low mean pT ≠ early freeze-out ?

- Resonance are regenerating close
- to kinetic freeze-out
-  we measure late produced (1385)
- How is elliptic flow v2 effected ?
- v2= signal for early partonic interactions

**Fit to ********and ******
**Higher T**** kin**** and lower <********T****>**

## Effects on v2 of and from Resonances 

-  v2 of pions:
- Primary produced (30%)
- Early resonance decay
- Late resonance decay
- v2 of resonances:
- Early resonances
- Regenerated resonances

**Notes:**
The main emphasis of research in the near future will be to study the hins of medium modification we found at SPS with the RHIC data.
Let me give you a little more detail. 

## Resonances v2 and NCQ Scaling Test

- Fluid dynamics calculations (zero viscosity)
-        describe data pT < 2 GeV
-        Do Resonances show same mass splitting ?
- Number of Constituent Quark (NCQ) scaling
-        at intermediate pT (2= mesons, 3= baryons)
-       indication of partonic degrees of freedom
- Regenerated resonances–final state interactions
-       NCQ =  5   (*  =  + =3+2)

**C. Nonaka, et al.,**
**Phys.Rev.C69:**
**031902,2004 **

**Notes:**
If the resonance in medium is mass modified, then collective medium properties such as the anisotropic flow v2 should be modified
As well for this resonance.
Here I show the mass dependency of v2 measured by phenix and sta. 
Cleary a mass modified resonance would resonance would exhibits a different pt dependency as the unmodified resonance.
Detailed measurements of v2 of resonances would be one of our future priorities.

##  elliptic flow v2 in minbias Au+Au 200 GeV

- 2(-)

- 2( -)

-    dN/d(-)

-   dN/d(-)

- signal

- Bg of  invmass

- v2=12±2%

- v2=16±0.04%

-   pT = 1.0-1.5 GeV

**Inv mass (K****+**** K****-****) **

**Inv mass (K****+**** K****-****) **

**Kaon p < 0.6 GeV**

## v2 of phi resonance in Au+Au 200GeV

- has long lifetime 45fm/c  less rescattering or regeneration
- Elliptic flow of Φ-meson is close to Ks      Delta resonance ?

**STAR Preliminary**

##  Summary

-  Hadronic resonances help to  separate hadronic  from partonic lifetime
-  Ranking of rescattering over regeneration cross section in medium.
- Low pt RAA behavior confirms rescattering hypothesis.  (RdAu puzzle?)
-  v2 of long lived resonances seems to follow stable particle trends (confirmation of NCQ scaling)

**Notes:**
The main emphasis of research in the near future will be to study the hins of medium modification we found at SPS with the RHIC data.
Let me give you a little more detail. 

## For Raymond 

**Notes:**
The main emphasis of research in the near future will be to study the hins of medium modification we found at SPS with the RHIC data.
Let me give you a little more detail. 

## Signal Loss in Low pT Region 

**Inverse slope increase from p+p to Au+Au collisions. **
- UrQMD predicts signal loss at low pT due to rescattering of decay daughters.
-   Inverse slopes T and mean pT are higher.
- Flow would increase pT of higher masse particles stronger.

|  |  pT UrQMD |
| --- | --- |
|  | 140 MeV |
|  | 90 MeV |
|  | 35  MeV |

**K(892)**

** ****flow**
- **p****T**** **

## Temperature and “Life-time” fromK* and *

- Temperature and “Life-time” fromK* and *

_**Model includes: **_
-   Temperature at chemical freeze-out
-   “Life-time” between chemical and
-     thermal freeze-out
-   By comparing two particle ratios
-    (no regeneration)
_** **__**Lambda1520**_
** ****T= 160 MeV ******** ********  > 4 fm/c  **
_**K(892)**_
** ****T = 160 MeV ******** ** ******  > 1.5 fm/c **** ****     **

******(1520)/******** = 0.039 ******** 0.015  at 10% most central Au+Au   **

**K*/K****- ****= 0.23 ******** 0.05  at 0-10% most central Au+Au**

- G. Torrieri and J. Rafelski,
- Phys. Lett. **B509** (2001) 239

**Life time:**
**K(892)   =  4 fm/c **
******(1520) = 13 fm/c**