# Presentation: 694612

## Two- and three particle azimuthal correlations

**Stefan Kniege **
**Johann Wolfgang Goethe Universität Frankfurt a.M.**

**For the  CERES collaboration**

**Two- and three particle azimuthal correlations**
**@ SPS energy **

**ISMD 04-09.08.2007 Berkeley, USA**

## Outline

**Outline**

**High-pt correlation measurements @ SPS**

**  ****	********Motivation for the measurement**
**  ****	********Previous correlation measurements at RHIC and  SPS**
**	**
**	********High-pt hadron correlations at CERES (****preliminary****)****  ****           **
** ****	**
**	****	********  ****CERES detector setup**
**	****	********  ****analysis method and results for **
**                   ****two particle correlations**
**           ****	********  ****model studies to estimate systematic errors**
**           ****	********  ****analysis method and results for **
**                   ****three particle correlations**** **

## High- pt hadron correlations

**     ****Possibilities for measuring ****jet**** properties:**

** ****Measuring ****transverse angular**
**  ****	****correlations**** with respect to a trigger**
**  ****	****	************ ****distributions : ****same event ****/mixed events**

** ****Full reconstruction**** of a jet**
**   ****drawback: large background in A+A collisions**

**Study of the ****fragmentation pattern**** of ****jets****  produced in hard ****parton-parton**** scatterings in heavy ion collisions**

**High- pt hadron correlations**

## Motivation / earlier measurements

******Vanishing of the away- ****	****side in case of high ****	****trigger/associate pt**
******Non Gaussian structure   ****	****on the away side**

**Motivation / earlier measurements**

** ****centrality and  **
** ****pt dependence of the yield/shape on the away side**

**nucl-ex/**
**0612019**

**nucl-ex/**
**0510060**

## Centrality and energy dependence

**RHIC**

**SPS**

**RHIC**

**CERES Collaboration, G. Agakichev, et al. **
**Phys. Rev. Lett. 92 (2004) 032301**

******Centrality depencence of shape of the away side **
**    ****( ****!non triggered**** correlations of pions with  p****t**** > 1.2 GeV/c )**

** ****CERES:**

**non Gaussian shape also visible at SPS energies**

**Key features also observable **
**at SPS energies !?**

**PHENIX**
**nucl-ex/0611019**

**Motivation / earlier measurements**

## CERES Detector setup and data sets

**	****SDD****:**
** ****	****Silicon Drift Detector**
**	****RICH****: **
**	****Ring Imaging Cherenkov **
** ****	****Counters****	**
**	****TPC**** : **
** ****	****Time Projection Chamber**
**	****Acceptance  ********	****: (****8-15****)°**
**                       ****	********	****: (****0-360****)°**

**CERES Detector**

** ****Data set:**

**  ****3****·****10****7**** ****Pb-Au**** events **

** ****Components**

**CERES Detector setup and data sets**

##   2-particle correlations

## Measurement: 2 particle correlations

**Measurement: 2 particle correlations**

_**Construction of the correlation function**_** **

**Investigation of different**
** ****charge combinations**

**Measured at different centralities:**
******geom ****:(****0-5****)%, (****5-10****)%,(****10-20****)% **
**determined by track multiplicity **

## Measurement: 2 particle correlations

**: elliptic flow in trigger- (****A****) and associate (****B****)  p****t **** ****range**
**   ****determined with CERES reaction-plane analysis **

**Measurement: 2 particle correlations**

**ZYAM  (Zero Yield At Minimum)   ****J(********min****) = 0****  :  **
**	****   **
**     ******** ****Subtract flow from C(********)  to get Jet correlations**

**Removing flow contribution**

**Conditional yield**

**Jet- associated particles**
** ****per trigger**

**flow-like**

**let-like**

## Results: Conditional yield

**Results: Conditional yield**

**all charge combinations**

**      ****flow contribution**
**    ****(stat. unceratinties in v****2****)**

**Conditional yield  ****Correlation function**

**p****t****: trigger :(****2.5-4.0****) GeV/c  ; associates : (****1.0-2.5****) GeV/c**

## Results:  charge selection

**Results:  charge selection**

**Raw Correlation**

**Conditional yield**

**flow contribution**

******/********geom**** = 10 - 20 %**

******/********geom**** = 5 - 10 %**

******/********geom**** = 0 - 5 %**

**Charge dependence: properties of initial state and fragmentation process    **

**For all ****centralities****: **
**Yield on the ****near side**** more pronounced for ****unlike sign  ****particles**
** ****	****	******** ****charge correlation in the fragmentation process**
**Yield on the ****away side**** is higher for ****like sign**** particles**
**  ****	********initial collisions**

## Detailed view on charge combinations 

**Detailed view on charge combinations **

******/********geom**** = 0 - 5 %**

******triggers sample dominated by positive triggers**

** **

- +/+                      +/-                         -/+                       -/-

**Trigger sample dominated by  ****positive**** triggers**

**              ****Away side yield higher for positive associates**
**                            ******** ****Initial state dominated by ****positives**** **

**Near side yield higher for **
**  ****unlike sign particles**

**Trigger and associates (initial state) **
**dominted by positive paritles**

## Summary of  

**results on two particle correlations**

**Trigger and away side yield**** dominated by positive particles**
**                     ******** ****Initial state dominated by positive particles**
**Near side****:  Higher yield for ****unlike ****than for ****like sign**** pairs**
**                     ******** ****charge correlations in fragmentaion process**
**Away side****: Non gaussian shape for central collisions**
**                     ******** ****Final state interactions with the medium**
**     **

## Interlude : Systematic studies

**Interlude : Systematic studies**

**Current analysis (ZYAM): **
**flow + jet**

**      **_**Jet-trigger events:**_
**trigger + jet associates**
**trigger + flow associates **
**   ******** ****random component**

**Toy model : **
**Two uncorrelated sources: jet-trigger random to reaction plane **

_**Flow-trigger events:**_
**trigger and**_** **_**associates**
** ****flowing**

**Input:   ****v****2trig****  = 0.03**** ;   ****v****2asso****  = 0.02****;               ****	****     ****yield/trigger       **
**              ****number of flow associates <n****flow****> ********15****          ****probability for a jet trigger  :p****jet****   =0.1**

**n****flow**** >> y****trig**** ******** random component ****~ p****jet**

## Interlude : Systematic errors

**Generate correlation function and apply ZYAM to extract yield:**

**Extracted yield in good agreement to input**

**ZYAM**

**Signal components**

**Input and extracted yield**

**jet events**

**flow events**

**Random component leads to overestimated **
**flow modulatoion in ZYAM **
**( small v****2**** ******** not visible) **

## Interlude : Systematic errors

**ZYAM**

**Signal components**

**Input and extracted yield**

**Increase of v2 :  ****v****2trig****  = 0.1**** ; ****v****2asso****  = 0.07****  corresponding to **

******/********geom**** = 10 - 20 %**

**Interlude : Systematic errors**

**jet events**

**flow events**

**Significant difference of the extracted yield**
****** ****Shape and yield**

**Same relative overestimation of v****2**
**has large impact due to subtraction**

**Relative change in v****2****  :     p****jet*****v****2**** **

******    ****Can ****p****jet**** ****this quantity bedetermined?**

## Determining jet trigger probability pjet 

**Pairs of jet associates:**

**Jet associate particles****:**

**unknown**

**Determining jet trigger probability p****jet **

**particle yield/trigger**
**pair yield(projection)/trigger**

**Comparison of number of ****jet**** ****associates**** to ****pairs of associates**

**known from two/three **
**particle analysis**

**Possibility to determine yield per jet ?**

**: <n jet-asso.> / trig.(jet)**

**( poissonian distribution **
**  ****of associates )**

**: <n jet-asso. ****pairs****> / trig.(jet)**

##   3-particle correlations

**the away side**

**  ****3-particle correlations**

## 3 particle correlations

**Impact of  jet topologies on the 2 particle correlation function**

**Non gaussian shape on the away side**

**Event by event**** **
**deflection of jets**

**Cone like**** structure **
**in one event**

**3 particle**** correlations**

**Trigger     p****t  ****:  (****2.5-4.0****) GeV/c   **
**Associate  p****t**** :  (****1.0-2.5****) GeV/c**

******geom ****:(****0-5****)%**

**p****t  ****:  (****2.5-4.0****) GeV/c     (****1.0-2.5****) GeV/c**** **

## Toy Model : Cone vs. Event by Event

**Toy Model : ****Cone**** vs. ****Event by Event**

## Contribution to 3-particle correlations

**Contribution to 3-particle correlations**

**Two particle correlation:**

**Three particle correlations:**

**1. jet-jet**

**2. hard*soft**

**3.   soft soft (mixed events) **
**      ****+flowing trigger**
**      **

**measured !**

- (**J. G. Ulery and F. Wang, nucl-ex/0609016**)

- flow

**+**

##    Three particle correlation functions

**   ****Three particle correlation functions**

**unlike**
**sign**
**assoc.**

**Preliminary**

**all charge combinations**

**C****3**

**C****3**

**C****3**

**like**
**sign**
**assoc.**

## Background contributions

**Background contributions**

-  **- (..+..+.. )  =**

**yield**

**offdiogonal **
**components**

**correlations function**

**yield**

**a.u.**

**ZYAM**

**preliminary**

**preliminary**

## Charge dependence of Yield

**Charge dependence of Yield**

**Different charge combinations of ****associate**** particles**** **

**Yield**

**Correlation function**

**              ****all                                 unlike sign                           like sign **

**charge **
**correlations**

**a.u.**

**a.u.**

**a.u.**

**preliminary**

**preliminary**

**preliminary**

## Summary

-  **Non gaussian shape**** on the away side of **
**  ****2 particle correlation function **

-  **Shape of the correlation function for different charge**
** ****combinations indicate **
**charge ordering in the fragmentation process**

**Shape of the 3 particle correlations indicate cone like structure **
**on the away side of the jet**

**Further investigations are needed to draw final conclusions**

## The CERES collaboration

**V. Belaga, J. Bielcikova, P. Braun-Munzinger, O. Busch, A. Castillo, A. Cherlin, **
**S. Damjanovic, T. Dietel, L. Dietrich, A. Drees, S. Esumi, K. Filimonov, K. Fomenko,**
**Z. Fraenkel, C. Garabatos, P. Glässel, G. Hering, J. Holeczek, S. Kniege, V. Kushpil, B. Lenkeit, **
**W. Ludolphs, A. Maas, A. Marin, J. Milosevic, A. Milov, D. Mi****ś****kowiec, R. Ortega, **
**Yu. Panebrattsev, O. Petchenova, V. Petracek, A. Pfeiffer, ****M.P****ł****osko****ń****, S. Radomski, **
**J. Rak, Ravinovich, P. Rehak, W. Schmitz, J. Schukraft, H. Sako, S. Shimansky, **
**S. Sedykh, J. Stachel, M. Sumbera, H. Tilsner, I. Tserruya, G. Tsiledakis, T. Wienold, **
**B. Windelband, J.P. Wessels, J.P. Wurm, W. Xie, S. Yurevich, V. Yurevich**

**NPI ASCR, Rez, Czech Republic**
**GSI Darmstadt, Germany**
**Frankfurt University, Germany**
**Heidelberg University, Germany**
**JINR Dubna, Russia**
**Weizmann Institute, Rehovot, Israel**
**SUNY at Stony Brook, USA**
**CERN, Switzerland**
**BNL, Upton, USA**
**Münster University, Germany**
**MPI Heidelberg, Germany**

**The CERES collaboration**

**Thank you for your attention**

## Backup

## Alternative: correlations among the associates 

**trigger**

**S: ****trigger**** and ****accociates**** from the same event**

**B: ****trigger****, ****accociate1****, ****associate2****  from different events**

**Orientation of angles with **
**respect to the trigger **
******steeply falling ********  distribution**

**cut on associate ******
**with respect to trigger**

******trig<->ass****> 1.0**

**trigger**

****** ****(rad)**

**a.u.**

## Monto Carlo studies of the background

**Monto Carlo studies of the background**

**flow*flow**

**flow*****jet ****+**
**flow*flow**

**data**

**flow comp.**
**subtracted**

**Monte Carlo construction of ****non jet-jet**
** ****contributions to the measured data **
**based on the 2 particle conditional yield **
** ****and measured elliptic flow.**

**normalized by**
**steeply falling **
******  ****distribution**

**Yield of away side pairs**

**Indication of cone structure on the **
**away side ******** needs further investigation**

- C(****

**Preliminary**

**Preliminary**

**Preliminary**

**No trigger separation cut**

******geom**** : (0.0-5.0)%**

**Trigger     p****t  ****:  (****2.5-4.0****) GeV/c   **
**Associate  p****t**** :  (****1.0-2.5****) GeV/c**

- C(****

## Sructure on the away side also seen with

**Sructure on the away side also seen with**
** ****cut around the trigger region**

- T

**Preliminary**

**Indication of cone structure on the **
**away side ******** needs further investigation**

## Three partile correlations

**all   **

**unlike sign**
**associates**

**like sign**
**associates**

**corr              hard soft            soft soft          trigger flow          yield                 **

## Misc.

## Determining jet trigger probability pjet 

**Pairs of jet associates:**

**Jet associate particles****:**

**unknown**

- Possibilily to determine yield per jet ?

**Determining jet trigger probability p****jet **

**particle yield/trigger**
**pair yield(projection)/trigger**

**Comparison of number of ****jet**** ****associates**** to ****pairs of associates**

**known from two/three particle analysis**

**Possibilily to determine yield per jet ?**

**: mean number of associates **
**  ****(pairs)  per  trigger (jet****)**

**Poissonian distribution **
**of associates**

## Slide 34

## Jet- Jet yield

******geom**** : (0.0-5.0)%**

**Trigger     p****t  ****:  (****2.5-4.0****) GeV/c   **
**Associate  p****t**** :  (****1.0-2.5****) GeV/c**

**Jet- Jet yield**

**raw correlations**
**(all charge combinations)**

**Subtraction of two particle correlations ****( soft*soft , hard*soft )**
-  (**J. G. Ulery and F. Wang  nucl-ex/0609016**)

**Off-diagonal components remain**

**Preliminary**

**Yield (Preliminary)**

## Background contributions

**Background contributions**

-  **- (..+..+.. )  =**

**yield**

**correlations function**

**soft*soft **

**trigger flowing **

**hard*soft **

**Backgr.:**

**clear offdiogonal **
**components**