# Presentation: 013101

## Femtoscopy in p+p vs heavy-ions in STAR

**Zbigniew**** Chaj****ę****cki** *The Ohio State University*
- for the **STAR** Collaboration

- Hot Quarks 2006 - Zbigniew Chajęcki for the STAR Collaboration

## Outline and motivation

**Multidimensional analysis in ****STAR**** **
**R(√S****NN****, ****m****T****, ****b, N****part****, A, B****, PID) **

- Beyond „simple” geometry – physics of spacetime *dynamics* (mT)
- Vary spatial scales (b, Npart, A, B)
- Scaling variable?  (Which „geometrical quantity” drives the radii?)
**p+p ******** Au+Au**** **
** **Onset of bulk behaviour?
** ****New (changing) physics**? ____________________________________________________
**Low-multiplicity collisions****  **
-  Shape analysis of correlation function

- the same _**experiment**_, collision _**energy**_, detector _**acceptance**_** !**

- Hot Quarks 2006 - Zbigniew Chajęcki for the STAR Collaboration

## „Universal” scaling ?

**„****Universal” scaling ?**

**Radii**** scale ****with ****multiplicity**
**Forget A,B,√s, N****part****...****dN/d******** determines ****HBT ****radii,****at all ****m****T**** ****(!!!!)**
**Is it trivial?**

- Lisa, Pratt, Soltz, Wiedemann, RNPS (2005) 55:357

**STAR DATA**** (pp,dAu,CuCu,AuAu@62GeV - prelim.) QM06**

- Hot Quarks 2006 - Zbigniew Chajęcki for the STAR Collaboration

## System expansion: Initial vs Final Size

**System expansion: ****Initial vs Final Size**

- Proton initial size = 0.89 fm from e-scattering

- 	Smooth expansion of the system from p+p to Au+Au... but not trivial

**AuAu: system expands **
**p****p (dAu): no or less expansion**

**STAR**     Collisions at 200GeV only

- Hot Quarks 2006 - Zbigniew Chajęcki for the STAR Collaboration

## Transverse mass dependence in Au+Au

**Transverse mass dependence**** in**** Au****+****Au**

**Calc. with Blast-Wave -****Retiere, Lisa,** **PRC 70 (2004) 044907**

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- Hot Quarks 2006 - Zbigniew Chajęcki for the STAR Collaboration

## Transverse mass dependence: p+p, d(p)+Au

-  p+p: HBT radii decrease with increase of mT
-  mT dependence in elementary collisions has been observed e.g. in OPAL, DELPHI, E735

**Transverse mass dependence: p****+****p, d(p)****+****Au**

- Note y-scale change!

**STAR preliminary**

**1. String fragmentation**

**2. Resonance contribution**

**3. Heisenberg uncertainty**

**4.Hydrodynamical expansion in pp?**

- G. Alexander, hep-ph/0302130

**DELPHI** - e+e- annihilation

**p+p treated as a bulk system!**

- Hot Quarks 2006 - Zbigniew Chajęcki for the STAR Collaboration

## Surprising („puzzling”) scaling

**Surprising („puzzling”) scaling**

-  All pT(mT) dependences of HBT radii observed by STAR scale with pp although it’s expected that different origins drive these dependences

**HBT radii scale with pp**
**Scary coincidence ****or somethi****n****g deeper?**

**pp, dAu, CuCu - ****STAR preliminary**

**Ratio of (AuAu, CuCu, dAu) HBT ****radii by pp**

- Hot Quarks 2006 - Zbigniew Chajęcki for the STAR Collaboration

## Non-femtoscopic correlations in low mult.collisions

**Non-femtoscopic correlations in low mult.collisions**

- 1D projections of 3D CF
-  the tail of the CF should go to unity for large Q !

**Do the projections provide us enough information about the shape of the CF?**
**No**, to make a projection one has to constrain non-projected Q-components  part of the information about 3D space is lost

**Q****x****< 0.08 GeV/c**

- Hot Quarks 2006 - Zbigniew Chajęcki for the STAR Collaboration

## Decomposition of CF onto Spherical Harmonics

- Hot Quarks 2006 - Zbigniew Chajęcki for the STAR Collaboration

## Decomposition of CF onto Spherical Harmonics

**Decomposition of CF onto ****Spherical**** Harmonics**

- Z.Ch., Gutierrez, Lisa, Lopez-Noriega, *nucl-ex/0505009, *
- Z.Ch., *nucl-ex/0510014*

**Q****x****< 0.08 GeV/c**

- Hot Quarks 2006 - Zbigniew Chajęcki for the STAR Collaboration

## Scaling (fit w/ baseline param.)

**Ratio of (AuAu, CuCu, dAu) HBT ****radii by pp**

**Fit w/o baseline parameterization**

**NEW**** fit w/ baseline parameterization**

**STAR preliminary**

- Hot Quarks 2006 - Zbigniew Chajęcki for the STAR Collaboration

## Baseline in p+p, d+Au and Au+Au

**Baseline in p+p, d+Au and Au+Au**

-  Some coefficients don’t vanish for large Q
-  Bias from zero is larger for more peripheral    collisions
-  This problem is getting more significant for small    systems (pp & dAu)
-  It can be due to
-  an experimental artifact ?
-  long range correlations (e.g. jets) ?
-  problem with momentum conservation ?
-  or ?

**Q****TOT**** [GeV/c]**

**Q****TOT**** [GeV/c]**

**Q****TOT**** [GeV/c]**

- Hot Quarks 2006 - Zbigniew Chajęcki for the STAR Collaboration

## Summary

- mT dependence of HBT radii for Au+Au, Cu+Cu, d+Au and p+p seems to be  the same although it’s expected to have different origins
- „universal scaling” of HBT radii with dNch/d1/3  from RHIC to AGS/SPS
- System expands x2 in Au+Au collisions and no or little expansion is p+p
**Importance of non-femtoscopic correlations in low multiplicity collisions**
-    Decomposition of CF in terms of spherical harmonics
-  new efficient diagnostic tool
-  Use symmetry of the Q-space
-  Pratt and Danielewicz [*nucl-th/0501003*] : connection of one-to-one CF and spatial anisotropies

- More on these analyses:STAR: PRC 71 (2005) 044906, nucl-ex/0505009, nucl-ex/0510014, nucl-ex/0511035

- Hot Quarks 2006 - Zbigniew Chajęcki for the STAR Collaboration

## .

**SUPPORT SLIDES**

- Hot Quarks 2006 - Zbigniew Chajęcki for the STAR Collaboration

## Pion Interferometry in STAR

- the same _**experiment**_, collision _**energy**_, detector _**acceptance**_** !**

- Hot Quarks 2006 - Zbigniew Chajęcki for the STAR Collaboration

## Consistency check on flow – kaons

**K**

**p**

****

**Consistency check on flow – kaons**

**Au+Au 62GeV – STAR preliminary **

******x******

******x******

- Hot Quarks 2006 - Zbigniew Chajęcki for the STAR Collaboration

## More confirmation

**More confirmation**

**STAR preliminary**

- Hot Quarks 2006 - Zbigniew Chajęcki for the STAR Collaboration

## Decomposition of CF onto spherical harmonics

- Cartesian-space (out-side-long) naturally encodes physics, but is poor/inefficient representation
- Recognize symmetries of Q-space -- decompose by spherical harmonics!
- Direct connection to source shapes [Danielewicz,Pratt: nucl-th/0501003] – *decomposition of CF on cartesian harmonics*
- ~immune to acceptance
**full information content at a glance**[thanks to symmetries]

-  : [0,2]
-  : [0,]

**Z.Ch., Gutierrez, Lisa, ****Lopez-Noriega, nucl-ex/0505009**

- Hot Quarks 2006 - Zbigniew Chajęcki for the STAR Collaboration

## Some properties of Alm coefficients

-  Alm = 0 for l *or* m odd – identical particle correlations
-   (for non-id particles, odd l encodes shift information)
-  A00(Q) ≈ one-dimensional “CF(Qinv)”  (bump ~ 1/R)
-  Alm(Q) = l,0 where correlations vanish
-  Al≠0,m(Q) ≠ 0  anisotropy in **Q** space
-  Im[Alm] = 0

- Hot Quarks 2006 - Zbigniew Chajęcki for the STAR Collaboration

## Long-range correlations : JETS ?

**Long****-****range correlations : JETS ?**

**Jets as a origin of ****the baseline problem ??**
- The idea was to try to eliminate pions coming from jet fragmentation from data sample. It can be done by applying an event cut which accepts only events that have no high-pt tracks. HBT analyses where done for three classes of events
-    **all** - all events accepted – as a reference
-    **soft** – only events without high-pT tracks               ( highest-pT < 1.2 GeV/c was chosen)
-    **hard** - only events with least one                track with pT >  2 GeV/c

- Hot Quarks 2006 - Zbigniew Chajęcki for the STAR Collaboration

## NA22 parametrization of CF

- ?

- Hot Quarks 2006 - Zbigniew Chajęcki for the STAR Collaboration

## NA22: 1D projections of 3D CF

**NA22, Z. Phys. C71 (1996) 405**

- Hot Quarks 2006 - Zbigniew Chajęcki for the STAR Collaboration

## NA22 parametrization of CF

- Hot Quarks 2006 - Zbigniew Chajęcki for the STAR Collaboration