# Presentation: 058520

## Back-to-BackCorrelations ofHigh pT HadronsFrom DynamicalModel Calculations

- _See also Poster “High p__T__ 19”_

## Tetsufumi Hirano1

- T.Hirano and Y.Nara,
- Phys.Rev. C**66**, 041901(2002);
- _Phys.Rev.Lett. __**91**__, 82301(2003)_;
- Phys.Rev. C68, 064902(2003);
- nucl-th/0307015.

_*OUTLINE*_
- Introduction
- Hydro+jet model
- Back-to-back correlations
-        of high pT hadrons
- Summary

- Tetsufumi Hirano1
-  and Yasushi Nara2

- 1RIKEN BNL Research Center
- 2University of Arizona

## 1. Introduction

- QGP?

_*1. Introduction*_

- 1. Jet quenching

- 2. Jet acoplanarity
- (transverse momentum imbalance)

- correlate ?

- Gyulassy, Plumer (’90)
- Wang, Gyulassy (’92)
- and a lot of work

- Bjorken (’82)
- Appel (’86)
- Blaizot, McLerran (’86)
- Rammerstorfer, Heinz (’90)

- g

- g

- g

## 2. Model

- Jet quenching
- Jet acoplanarity

- Interaction between soft and hard is *important!*

- Hydro + Jet model

- Soft (hydrodynamics)
- Space-time evolution of matter
- Phase transition between QGP
- and hadrons
- Particle spectra in low *p*T region

- Hard (mini-jets)
- Production of (mini-)jets
- Propagation through fluid elements
- Fragmentation into hadrons

- Interaction between fluids and mini-jets through parton energy loss

## 3. PYTHIA(+Hydro)

_*3. PYTHIA(+Hydro)*_

*N*

*N*

- 3

- 4

- Fragmentation:
- Independent
- Fragmentation
- Model

- PYTHIA

- 3D Hydro

- PYTHIA

- hadrons

- hadrons

- PDF:
- Collinear: CTEQ5LO
- kT: Gaussian

- Parton energy loss

- pQCD LO:

- *Initial and final state radiation are included.

## 4. Results from PYTHIA

- PHENIX 0
-  in *pp* collisions@200GeV,
- hep-ex/0304038.

- UA1 charged
- in *pp* collisions@200GeV,
- Nucl.Phys.B335, 261(1990).

## 5. Time Evolution in Hydro+Jet Model

- Free
- streaming

- Hydro evolution

_*5. Time Evolution in Hydro+Jet Model*_

**

**0

- Energy loss

- Fragmentation

**f

- =0.6fm/*c*

- ~10fm/*c*

- 0

- Formation time~0 fm
- For jets with *p*T>2GeV/*c*,
- 1/*p*T<0.1fm/*c*<<1fm/*c*
- Momentum dist. from
- PYTHIA ver. 6.2

- Thermalization time
- = Initial time of fluids
- Initial parameters in hydro have been already tuned.

- After hydro simulation, all survival jets fragment into hadrons.
- We neglect interaction of fragmented hadrons.

- Jets

- Full 3D
- hydro

- Particle spectra
- through Cooper-
- Frye formula

- CGC?
- Prethermaliztion?

## 6. Initial Condition in the Transverse Plane

- Initial configuration of mini-jets
- Prop. to # of binary collisions

- Au+Au 200*A*GeV, *b*=8 fm
- transverse plane@midrapidity

- Gradation
-  *Themalized* parton density
- Plot (open circles)
-  Mini-jets (*p*T>2GeV/*c*)

**(fm-3)

*x*(fm)

*y* (fm)

**0=0.6 fm/*c*

## 7. Parton Energy Loss

_*7. Parton Energy Loss*_

- Position of a jet

- Adjustable parameter

- Parton density
- from hydrodynamic
- simulations
- We have already
- had a solution!

- Initial
- 4-momentum
- of a jet in local
- rest frame

- M.Gyulassy *et al*. (2000)

- Simplified GLV formula 1st order in opacity expansion

- Relevant for
- heavy-ion
- collisions

## 8. Suppression Factor for 0

- GLV formula with
*C*=0.27 quantitatively
- reproduces the data

- Data from  S.S.Adler et al. (PHENIX),
- PRL91,072301(2003).

- Our starting point of
- the following discussion

- b=2.8fm

- Simplified GLV 1st order formula:

- M.Gyulassy *et al*., NP**B594**, 371 (2000).

## 9. Azimuthal Correlation Function

- Associated
- particles

- Trigger
- particles

_*9. Azimuthal Correlation Function*_

- p+p

- A+A

**

*p*T (GeV/c)

- 0.7

- -0.7

- 0

- 2

- 4

- 6

- STAR

- Strength of away-side peaks
- are the same in no jet quenching case

- Back-to-back correlations of high pT hadrons

## 10. Three Possible Effects on Back-to-back Correlations

| 1.Energy loss
of jets | 2. Primordial kT
of initial partons | 3. Broadening
of jets |
| --- | --- | --- |
| Final state | Initial state | Final state |
| 

Absorption | 

“Cronin effect” | 

Random walk
behavior |

- Nucleon
- inside a nucleus

- Target nucleus

- Beam direction

- Hot matter

- Hot matter

## 11. Effect of Parton Energy Loss

- Hot matter

- Simultaneous reproduction
- of *R*AA and *C*2 ?
- Another mechanism
-  is needed!

*C*=0.27 From fitting *R*AA

## 12. Effect of Intrinsic kT

- to the disappearance of
- back-to-back correlation!

- Primordial *k*T distribution

_*12. Effect of Intrinsic k*__*T*_

- collinear

- intrinsic kT

- Nucleon
- inside a nucleus

**Target nucleus**

- Beam direction

## 13. Effect of Broadening

- Transverse momentum
- orthogonal to its direction
- of motion

- Hot matter

- Model 1 (BDMPS):

- Model 2 (XNW):

## 14. Surface Emission Dominance ?

- Initial positions of jets which survive at final time

**Completely**

**Partially**

- No quenching

*C*=0.25

*C*=1.0

- An interesting signature may be events in which the hard
- collision occurs near the edge of the overlap region, with
- _one jet escaping without absorption and the other fully_
- _absorbed_.  --J.D.Bjorken, FERMILAB-Pub-82/59-THY (1982).

## 15. Centrality Dependence

- at **0 = 0.6 fm/c

## 16. Summary

_***Dynamical model***_** (hydro+jet) for heavy-ion physics**
**Soft: hydrodynamics **
**(**********-********** coordinate, full 3D, separate freezeout *****T*****)**
**Hard: PYTHIA**
**Parton energy loss: GLV 1****st**** order formula**
** ****Dominant effect of back-to-back correlations**
**Parton energy loss**
**The effects of intrinsic k****T**** and p****T**** broadening**
**are small.**
** ****Centrality dependence**
******Good description in b<~5 fm**