# Presentation: 862755

## Trigger Particle Correlation Results from PHENIX

- Paul ConstantinLos Alamos National Laboratory

## Hadronic Jets in Cold and Hot QCD matter (I)

- Medium effects on jets can be studied using dihadron angular correlations:

** ****Cronin** (***multiple scattering***) modification of kT in cold QCD medium –
- away side shape in dAu (vs. pp and centrality)

** ****Monojet dominance** (***gluon saturation***) at low x in nuclear media –
- transition from dijets to monojets in dAu and AuAu at low x

-  Partonic transverse mometum **k****T** – away side (Δφ~π) shape in pp
-  Parton FF **D(z)** – away side conditional yields pp and dAu

- RHIC/AGS Users Meeting

- 21 June 2005

## Hadronic Jets in Cold and Hot QCD matter (II)

** ****Jet broadening** (***gluon radiation***) in hot QCD medium – away side shape
- in AuAu (vs. dAu and centrality)
** ****Jet suppression** (***gluon radiation***) in hot QCD medium – away side
- conditional yield in AuAu (vs. dAu and centrality)

** ****Conic flow** (***sonic waves in liquid QGP***) – away side shape in AuAu

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## PHENIX Detector

- Beam-Beam Counters (3<|η|<4)
**centrality**: Npart, Ncoll
**reaction plane orientation**: v2 of particles at η~0 (central arms)
- Central Arms (|η|<0.35)
- charged hadrons **h****±****:** DC, PC1, PC3
- neutral pions **π****0**: PbSc, PbGl
- high pT charged pions **π****±****:** DC, PC1, PC3, RICH, PbSc, PbGl
- identified charged hadrons **π****±**** ,K****±****, p/pbar**: DC, PC1, PC3, TOF
- Muon Arms (1.4<|η|<2.2)
- charged hadrons **h****±**: MuTr, MuID

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## Dihadron Angular Correlations 

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- 21 June 2005

## Calibrating Dijets – pp and dAu Collisions

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## Dijet Parameters

- Parton FF **D(z)** from away conditional yield with fixed trigger:

- Parton fragmentation transverse momentum **j****T** - constant value independent on
- fragment’s pT is characteristic of jet fragmentation (jT-scaling): it is directly related to the
- near side (Δφ~0) Gaussian width: ******N**** ********  ********|j****Ty****|******

- Parton transverse momentum **k****T** –
- (intrinsic+NLO radiative corrections+multiple
- scattering)*** ***carries the information on the
- parton interaction with the QCD medium:
- it can be extracted from the near side (Δφ~0)
- and away side (Δφ~π) Gaussian widths
- and <z>: A  |jTy|  |kTy| z

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## kT in pp and dAu

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## Parton FFs in QCD Vacuum

- Red data
- Blue pythia

- 5<p**T,trig**<6

- PHENIX Preliminary

- p+p

- Near Side

- Away Side

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## Parton FFs in cold QCD matter

- we do not see the factor of two larger
- conditional yields in dAu compared to
- pp predicted by the recombination model:
- Hwa and Yang nucl-th/0407081

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## High-x and Low-x Triggers in dAu (and pp)

- Trigger on hadrons from the low-x north muon arm (1.4<η<2.2) or from the high-x south muon arm (-2<η<-1.4) and associate
- with hadrons in the central arm (|η|<0.35):

- Since |Δη|>1rad between central and muon
- arms, there is *no near side correlation*:
- it is driven by fragmentation which has a 1D
- opening angle of ~0.7rad.

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## Muon Arms – Central Arms Dihadron Correlations

- PHENIX preliminary

- Unnormalized correlation functions between trigger hadrons in the muon arms
- and associated hadrons in the central arms: pT,trig>2GeV/c, 0.5<pT,asso<1GeV/c

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## Dijets in Hot QCD Matter – AuAu Collisions

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## Subtraction of the Underlying Event

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## Dihadron Correlation Functions

- Extraction of dijet correlations
- is done under the ZYAM
- (“Zero dijet Yield At Minimum”)
- assumption: dijet yield is zero
- at some (variable) Δφ0.
- This fixes the value of B:
- B=C(Δφ0)/(1+2v2cos(2Δφ0))

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## Dijet Correlation Functions

- Strong modification of the away side dijet correlation: local minimum at Δφ~π
- and local maximum at |Δφ-π|~1rad...

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## Conditional Yields and RMS

-  Small enhancement with centrality of both near/away conditional yields
-  Recovery of the jet remnants from high pT?
- 	(considering STAR away suppression at larger momenta)
-  Large broadening away dijet RMS with centrality

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## Sonic shock waves, sound speed, and viscosity in liquid QGP

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## However...

**I. Vitev** also gets a dip at θ*~0 rad in the spectrum of radiated gluons,
- but when he translates to Δφ, it is gone! Effects of acoplanarity, projection to
- η~0, fragmentation of quenched parton should be included in the calculation.

- hep-ph/0501255

**Δφ**** [rad]**

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## Identified Trigger Correlations (I)

- Method:
-  Identify trigger hadrons with TOF
- detector and count associated h±
-  Use the v2 with respect to BBC
- reaction plane (as above)
-  Calculate the combinatorial background level B: nta=nt**.**na(1+ξ) where ξ is the correction for residual multiplicity correlation
-  Integrate over 55o and extract near/away conditional yields

- identified trigger hadron in (2.5-4)GeV/c
- unidentified associated hadron in (1.7-2.5)GeV/c

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## Identified trigger correlations (II)

**nucl-ex/0408007**

**Jet partner likely for trigger baryons as well as mesons.**
**Same side: slight decrease with centrality for baryons.**
**Away side: partner rate as in pp/dAu confirms jet source of baryons.**
**Modification of fragmentation by hard-soft recombination**

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## Identified Associated Correlations (I)

**Associated**
**Mesons**

**Associated**
**Baryons**

- PHENIX Preliminary

- Dijet term is stronger with associated mesons than with associated baryons

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## Identified Associated Correlations (II)

- Observed baryon to meson ratio is higher for away-side jets

**1 < p****T,asso ****< 2.5 < p****T,trig ****< 4 GeV/c**

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## Conclusions

- Dijets in pp and dAu collisions:
- kT measured in 3-15GeV/c pTtrig range in both pp and dAu. *No significant broadening in dAu with respect to pp*.
*FFs in both pp and dAu scale with x**E** and p**Ttrig*. They also agree with Pythia.
- correlation functions in dAu collisions triggered on low-x and high-x hadrons from the muon arms.
- Dijets in AuAu collisions:
- strong modification of away side shape: *presence of local maximum at |**Δφ**-**π**|**~1rad*. Indication of sonic shock waves in the liquid QGP?
- small enhancement of near/away conditional yields, indicative of the *recovery of jet remnants*.
*jet source for baryons at intermediate p**T*. Jet partner is as likely to be found if we trigger on baryon as on meson.
- more associated mesons than baryons per trigger hadron; more baryons per trigger in the away side than in the near side.

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## Looking Forward to QM’05...

- Finalized dihadron correlations between central and muon arms in pp and dAu
- Electron triggered correlations with charged hadron in central arm in pp, dAu and AuAu
- Detailed study of dihadron correlations in AuAu in the central arms: centrality, momentum, reaction plane dependence (Run4 AuAu data set: ~1.5 Billion events)
- Higher statistics identified dihadron correlations
- Direct photon tagged jets

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## Backup Slides

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## Recombination

- nucl-th/0407081

- Ratios of conditional yields vs. pT of associated meson

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## Absolute normalization

- In the example of Npart scaling the pair rate always exceed the combinatoric rate, by an amount which increases with the width of the Npart distribution relative to its mean.

- For an event sample with a finite spread in centrality the background pair rate will always exceed the combinatoric rate; but we can estimate by how much:

- If we assume that the rate of singles in background pairs are uncorrelated except for common centrality, then we can estimate the background rate “blind”, without any distributions.

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- 21 June 2005

## Simulation Test of Jet Recovery : Normal Shapes

**Simulation Test of Jet Recovery : Normal Shapes**

**Di-jet faithfully recovered**

**Normal Jet Shape**

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## Cronin from correlations at Fermilab

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