# Presentation: 614049

## PHENIX Results on Jet Correlations versus Reaction Plane

- David Winter
- 24th Winter Workshop on Nuclear Dynamics
- South Padre Island, TX
- 8 April 2008

## Outline

- Motivation
- Background/PHENIX
- Results
- Future/Summary

- D. Winter, PHENIX Jet Correlations v. Reaction Plane

- WWND2008

## Jet Correlations and the Medium

- Jet reconstruction in HI collisions is *hard*
- Extract jet physics from azimuthal correlations

- Fast partons lose energy due to gluon density, path length
- Where does the energy go?
- How do different E-loss mechanisms contribute?
- How does the medium respond to the deposited energy?

- D. Winter, PHENIX Jet Correlations v. Reaction Plane

- WWND2008

## The Reaction Plane (and Flow)

- Spatial anisotropy in colliding zone leads to pressure gradients and anisotropy in momentum space
- Additional source of two-particle correlations  one physicist’s signal is another physicist’s background

- D. Winter, PHENIX Jet Correlations v. Reaction Plane

- WWND2008

## Correlations and Multiple Sources

- Two sources of correlation:
- C() = J() + Flow()
- Extraction of J() requires careful subtraction of flow contribution (eg. ZYAM method)
- Pair yield near = 0 and  ≈ 2 (away-side modification)

-  PRL 98 232302 (2007)

**?**

- D. Winter, PHENIX Jet Correlations v. Reaction Plane

- WWND2008

## Sources of Away-side modifications

- Mach cone / sonic boom
- Cherenkov gluon radiation
- Coupling of jets and flow

**Casalderrey-Solana, Shuryak, Teaney, Nucl. Phys. A774 (2006) 577**
**H. Stoecker, Nucl. Phys. A750 (2005) 121**
**J. Ruppert & B. Mueller, Phys. Lett. B618 (2005) 123**

**Koch, Majumder, Wang, PRL 96 (2006) 172302**

**Armesto,Salgado,Wiedemann, PRC 72 (2005) 064910**

- D. Winter, PHENIX Jet Correlations v. Reaction Plane

- WWND2008

## Evolution of the (inclusive) Jet Shape

- Evolves from flat  concave  convex
- Suppression in HR, Enhancement in SR
- Reappearance of peak is not due to merging of side peaks. High pT is consistent with jet fragmentation.
- Current conjecture:
- Head region  jet modification (dominant at high pT)
- Shoulder region  medium response (dominant at intermediate pT)

- Au+Au & p+p s = 200 GeV

**PRC 77 011901 (2008)**
**arXiv:0801.4545v1 [nucl-ex]**

- Per-trigger yield vs. *** *for various trigger and partner *p**T** *(*p**A**T** ** p**B**T*), arranged by increasing pair momentum (*p**A**T** * + *p**B**T**)*

- Establish the punch-through jet component (“Head Region”)
- and the medium-induced component (“Shoulder Region”)

- D. Winter, PHENIX Jet Correlations v. Reaction Plane

- WWND2008

**Notes:**
Need to carefully explain what is in this plot.  Emphasize, maybe with an arrow, the progression from flat/concave/convex

## Going Beyond Inclusive Measurements

- RAA 0 in AuAu s=200 GeV vs. Reaction Plane

**PRC76, 034904 (2007)**

- Little/no energy loss for L< 2 fm

- L =  distance from edge to center of participants calculated in Glauber model

- Advantage of RAA over v2: relative nature of v2 hides the geometric dependence of energy loss.
- L Caveats – the result is tantalizing, but:
- Too simple a picture (!)
- Implies something other than radiative E-loss
- Blind luck, or some mechanism we don’t understand?
- Will apply analysis to higher pT data

- RAA() vs. centrality varies density of and distance through medium

**3 < p****T**** < 5 GeV/c**

- D. Winter, PHENIX Jet Correlations v. Reaction Plane

- WWND2008

## Jets: Controlling path length effects

- Fix the centrality
- Constrains energy density
- Orient trigger particle *wrt* reaction plane
- Varies effective path length of jet
- Constrain path length dependence of energy loss to untangle jet and medium response

- D. Winter, PHENIX Jet Correlations v. Reaction Plane

- WWND2008

## High-pT measurement with PHENIX

- Tracking and Matching (DC, PC)
- charged hadrons

- EMCAL (PbSc + PbGl)
- ,0,Ks

- EMCAL --- measure energy deposit of electrons and gammas
- DC --- obtain momentum of charged particles

- PC --- measure hit position of charged particles

- h+

- h-

- h+

- h-

- D. Winter, PHENIX Jet Correlations v. Reaction Plane

- WWND2008

## Reaction Plane Measurement with PHENIX

- _Reaction Plane Detector_
- plastic scintillators @ 38<|z|<40cm
- 12 segments in 
- 2 segments in 
- 1.0 < || < 1.5
- 1.5 < || < 2.8
- Pb converter
- Run 7+

- _Beam-Beam Counters_
- Quartz Cherenkov radiators
- 64 elements in 3 rings
- 3.0 < || < 4.0
- All Runs

- _Muon Piston Calorimeter_
- PbWO4 PHOS crystals
- 192 towers
- 3.1 < || < 3.7
- Run 6+

- Multiple overlapping and complementary measurements

- D. Winter, PHENIX Jet Correlations v. Reaction Plane

- WWND2008

## Non-flow effects?

- Embed pythia events in HIJING
- Implement v2 modulation by weighting HIJING particles with v2(cent,pT)

- Measure “fake” v2 of jets
- Effect varies as function of  where v2 is measured

**arXiv:0801.4545v1 [nucl-ex]**

- BBC

- RXN

- Trigger relative to RP
- HIJING alone	HIJING+dijet

- D. Winter, PHENIX Jet Correlations v. Reaction Plane

- WWND2008

## Au+Au Correlation and Jet Functions

- Correlation functions: Significant RP-dependence (even in 0-5!)
- No RP-dependence in Jet functions

- Run 4 Au+Au 200 GeV
- 0-5 % Centrality

- D. Winter, PHENIX Jet Correlations v. Reaction Plane

- WWND2008

## Au+Au Correlation and Jet Functions

- Central and semicentral exhibit same trends

- Run 4 Au+Au 200 GeV
- 30-40 % Centrality

- D. Winter, PHENIX Jet Correlations v. Reaction Plane

- WWND2008

## Run7 Au+Au with Reaction Plane Detector

- Au+Au s=200 GeV 0-5% Centrality
- Left: Correlation functions
- Below: Jet Functions
- RP from Reaction Plane detector

- D. Winter, PHENIX Jet Correlations v. Reaction Plane

- WWND2008

## Run7 Au+Au Jet functions

- 0-5 %

- 30-40 %

- Head region sensitive to path length variation
- Consistent with energy-loss expectation
- Shoulder region insensitive to path length
- Inconsistent with jet-flow coupling
- NOT inconsistent with mach cone scenarios

- D. Winter, PHENIX Jet Correlations v. Reaction Plane

- WWND2008

## Cu+Cu Correlation and Jet Functions

- _Within a centrality_:
- Correlation functions: clear angular dependence
- Jet functions: no RP dependence within errors

- 0-10%

- 60-94%

- 0-10%

- 60-94%

- D. Winter, PHENIX Jet Correlations v. Reaction Plane

- WWND2008

## Shape Parameters Review

- Characterize peak shape:
- RMS
- Kurtosis
- Away-side double Gaussian fit: Offset ±*D*
- Saturates for *N*part>100
- Disfavors certain models
- Eg. Cherenkov gluon radiation
- Constrains others
- Eg. Non-Cherenkov gluon radiation at large angles

-  PRL 98 232302 (2007)

- D. Winter, PHENIX Jet Correlations v. Reaction Plane

- WWND2008

## Shape Parameters vs. RP (Cu+Cu)

- RMS, Kurtosis, and D all exhibit same trend as inclusive data
- No discernible dependence on angle of emission wrt reaction plane

- D. Winter, PHENIX Jet Correlations v. Reaction Plane

- WWND2008

## Medium effects w/o subtraction?

- Inclusive correlation Au+Au – Example: 0-5%
- Modest flow in this bin
- Background subtraction can only make effect more pronounced
- Choose a trigger orientation with minimal impact from modulated background
- 4th bin: ~ /4 (grey circles)
- Example: Au+Au in 4th RP bin, several centralities
- “mach cone”(?) effect clear without any subtraction
- Need to focus on source of shoulder!

- D. Winter, PHENIX Jet Correlations v. Reaction Plane

- WWND2008

## But... what about outside PHENIX?

- A. Feng, QM08
- STAR sees similar behavior

- D. Winter, PHENIX Jet Correlations v. Reaction Plane

- WWND2008

## The Future

- _Vertex and Forward Vertex Detectors_
- Study production and flow mechanisms of heavy quarks
- Measure reaction plane
- Improve *p* resolution
- Improve high-*p*T tracking

- _Nose Cone Calorimeter_
- 0.9 < || < 3.0
- Electromagnetic and shallow hadronic compartment
- Expand kinematical coverage for jets, neutral pions, electrons, and photons to forward rapidity

- D. Winter, PHENIX Jet Correlations v. Reaction Plane

- WWND2008

## Summary

- Heavy Ion data have displayed a fascinating evolution of the away side peak(s) with pT
- Jet Observables *wrt* the reaction plane offer a further insight into energy loss of fast partons and medium response
- The shoulder region:
- Just won’t “go away”, no matter what angle we look at it.
- Appears at the about the same location, independent of:
- Centrality
- System size
*Orientation of the trigger particle*
- PHENIX jet studies vs. trigger particle’s orientation tend to:
- Disfavor Cherenkov gluon radiation and jet/flow coupling models
- Support mach cone models
- Provide constraints for large-angle radiation models

- D. Winter, PHENIX Jet Correlations v. Reaction Plane

- WWND2008

*Backup Slides*

- D. Winter, PHENIX Jet Correlations v. Reaction Plane

- WWND2008

## Future PHENIX Acceptance for Upgrades  

**-3              -2             -1                 0                1               2               3    rapidity**

****** ****coverage                 2******

**EMCAL**

**EMCAL**

**(i) ********0**** and direct ******** with combination of all electromagnetic calorimeters**
**(ii) heavy flavor with precision vertex tracking with silicon detectors **
**	****combine (i)&(ii) for jet tomography with ********-jet **
**(iii) low mass dilepton measurements with HBD + PHENIX central arms**

- Future PHENIX Acceptance for Upgrades

- D. Winter, PHENIX Jet Correlations v. Reaction Plane

- WWND2008

## Reaction Plane Resolution

- Measure reaction plane orientation using angular distribution of particles
- Finite multiplicity limits resolution of measured angle
- Correction factor extracted from comparison of independent subevents (eg. North/south detectors).
- Sub-event approach assumes:
- Both sub-events contain the same number of particles
- Degree of flow is the same in each sub-event
- Any particle correlations other than flow are negligible

- Unity = perfect resolution

- Au+Au s=200 GeV

- D. Winter, PHENIX Jet Correlations v. Reaction Plane

- WWND2008