# Presentation: 119298

## Sergey Panitkin

RHIC/AGS User Meeting
2006

**Sergey**** ****Panitkin**
**RHIC/AGS User Meeting**
**2006**

**Energy dependence of the Bose-Einstein Correlations**

## Outline	

**Introduction**
**Energy dependence of pion correlations**
**Azimuthally sensitive pion HBT**
**Summary**

## Two-particle Correlations

**Single particle spectrum is sensitive to momentum **
**distribution only**** **

**Relative momentum distribution of particle pairs**
** ****is sensitive to space-time information**

**Basis for Identical and Non-identical particle femtoscopy**

**Source function**

**FSI**** **

**System evolution encoded in S(r,q)**

## Hanbury Brown-Twiss interferometry

**Hanbury Brown-Twiss interferometry**

**Pratt-Bertsch parameterization**

## HBT for Gaussian sources

**HBT for Gaussian sources**

_**Decompose q into components:**_
- qLong	: in beam direction
- qOut 	: in direction of transverse momentum KT
- qSide 	:  qLong & qOut

_**Radii are related to source variances:**_

**In Longitudinally Co-Moving System (LCMS) ********l**** =0**** **

**Sensitive to emission time**

**Sensitive to transverse extent**

**Sensitive to longitudinal extent**

## Mt dependence 

**Charged pions, AuAu (PbPb) most central**

**Mt dependence is attributed to collective flow**

## Femtoscopic signature of QGP

- 3D 1-fluid Hydrodynamics

- “”

**Long-standing signature of QGP:**
**Lattice QCD**** -> Speed of sound goes to zero (pressure drop) at phase transition**
**increase in ********, R****OUT****/R****SIDE**** ****due to**** deconfinement ******** confinement transition**
**hoped-for “turn on” as QGP threshold is reached (“softest point”)**

- G. Boyd et al., , Nucl.Phys. B469 (1996) 419** **

## The HBT Excitation function circa 2001

- Compilation of world BP 3D -HBT parameters as a function of s

-  ~10% Central AuAu(PbPb) events
-  y ~ 0
-  kT 0.17 GeV/c
- no significant rise in spatio-temporal size of the  emitting source

- STAR Preliminary

**The HBT Excitation function circa 2001**

**QM 2001**

## Energy systematics 2006

- Many new measurements since 2001
- Same conclusions

## Kinetic freezeout from AGS->RHIC

- TKFO (RHIC)  =  100 ± 10 MeV

-  Rapid change in freeze-out temperature and flow velocity between 2-20GeV
-  Explosive Transverse Expansion
- at RHIC **** High Pressure
- Almost constant freeze-out temperature above 20 GeV

**Kinetic freezeout from AGS->RHIC**

**T. Nayak**

**Blast wave fits to spectra **

## Freeze-out volume vs. beam energy

-  non-monotonic behaviour
-  minimum between AGS and SPS
- Why there is a drop at AGS ?

** ****H. Appelshauser**

- Freeze-out volume **estimate**:

- Not a simple concept for  expanding sources with continuous emission

- Because of flow the best “total volume” estimate is at low Kt
- Ad hoc formula

## Freeze-out volume

**Freeze-out volume**

- Freeze-out volume **estimate**:

- CERES *Phys. Rev. Lett. 90 (2003) 022301*

- Centrality dependence:

- since

*only at given beam energy!!*

## Particle multiplicity vs. beam energy

- CERES *Phys. Rev. Lett. 90 (2003) 022301*

-  particle number increases monotonically
-    freeze-out at constant density excluded
-  chemical composition changes
-  cross sections are very different
-    try mean free path:

**√****s(GeV)**

## Mean free path

- in a *composed* medium:

- CERES *Phys. Rev. Lett. 90 (2003) 022301*

**√****s(GeV)**

-  also *N**σ** *shows non-monotonic behaviour
-  dominated by baryons at low energy and mesons at high energy

## Universal pion freeze-out

**Universal pion freeze-out**

- CERES *Phys. Rev. Lett. 90 (2003) 022301*

**√****s(GeV)**

- * **N**σ* follows *V**f*
-  data are consistent with constant
-     mean free path at freeze-out

- independent of beam energy and centrality

## Universal freeze-out II

- universal pion freeze-out:
- independent of beam energy and
- system size
-    in  A-A:  ***f** << R*
-  why no dependence on beam energy and system size?
-  why so small?

**sqrt(s****NN****) (GeV)**

******f**** (fm)**

- ..implies f.o. at constant density (*R~(dN**ch**/d****)**1/3*) if particle ratios are constant!

**H. Appelshauser**

## What is “true” scaling variable?

**STAR Preliminary**

**Nch seems to be better**

## Multiplicity scaling of radii

**STAR DATA**** (pp,dAu,CuCu,AuAu@62GeV - prelim.)**

- “Universal radii scaling”
- as a concequence of  volume scaling

- For different systems and
-  energies at RHIC physics
-  does not change!?

- Multiplicity scaling seems to work at all measured Kt

## HBT relative to reaction plane HBT() 

- “Standard” HBT provides direct access to **space-time** (size) information about source, "HBT radii"
- Additionally, HBT() provides direct access to **shape** and **orientation** of source
- Source shape at freeze-out  evolution of system*"How much of initial spatial deformation still exists at freeze-out?"*

- Heinz & Kolb, Nucl.Phys. A702 (2002) 269-280

- _collective expansion of system_

## Elliptic geometry leads to oscillations of the radii
For example Rside

**For example R****side**

- out-of-plane
- extended source

- p=0°

- p=90°

- Rside (large)

- Reaction
- plane

- Rside (small)

- _Naïve view with no flow_

**HBT with respect to reaction plane**

-  Heinz, Hummel, Lisa, Wiedemann PRC 044903 (2002)

## Predictions from hydro

- _Hydrodynamics_: initial out-of-plane anisotropy may become in-plane

- Teaney, Lauret, & Shuryak, nucl-th/0110037

- Heinz & Kolb, hep-ph/0111075

- _k__T__ dependence_

## Centrality Dependence of HBT()

**12 ********-bin analysis (kT integrated) **
- 15° bins, **72 CF's total**        **12**  bins      ×  **3** centrality bins      ×  **2** pion signs
- 0.15 < kT < 0.65
- Oscillations exist in transverse radii for all bins
- Amplitudes weakest for 0-10%

- Lines represent fits to allowed oscillations:

- out, side, long go as **cos(2********)**
- out-side goes as **sin(2********)**

**STAR**

## Estimate of initial vs F.O. source shape

**Estimate of initial vs F.O. source shape**

- estimate INIT from Glauber
- from asHBT:

- FO < INIT → dynamic expansion
- FO > 1 → source always OOP-extended
- constraint on evolution time

**Out of plane extended source**

**Short life time**

## Exitation function

- does it make sense?  Is it related to *bulk* dynamics?
-  **YES**

**Exitation function**

- AGS: E895, RHIC: STAR
- ~200 GeV Gap in measurements

**Notes:**
we finally see something that changes with energy!!  yay!

But does it make sense?   Yes!!

## Summary

**HBT is a valuable tool for studies of space-time structure of systems created in heavy ion collisions**
**Important additional constraint for spectra and v2 measurements**
**Large systematic datasets are already collected from AGS, SPS and RHIC**
**Non-trivial energy dependence of HBT radii is observed**
**No predicted signatures of 1****st**** order phase transition are not (yet?) observed**
**Non monotonic behaviour (dip) around 10 GeV **
**“****CERES hypothesis” is tempting: Universal mean free path at f.o.?**
**Similar dynamics, hence chemistry drives freeze-out**
**Multiplicity scaling at SPS and RHIC**
**Azimuthally sensitive HBT provides additional unique information about reaction dynamics**
**Detailed measurements at RHIC (and AGS), no measurements at SPS**
**Out of plain extended sources observed, imply short (~10 fm) source lifetime**
**More measurements are needed**
**Lower energy measurements around 10-20 GeV will be very interesting**