# Presentation: 232250

## Punch-through Jets in A+A Collisions at RHIC/LHC

**Han-Zhong  Zhang**
**Institute of Particle Physics, Huazhong Normal University, China**
**Collaborators: J. Owens,  E. Wang and  X.-N. Wang**

**Quark**** ****Matter**** ****2008**

**Feb. 4-10 , 2008**

## Introduction

**Fragility of single/dihadron suppression factors**
**Single/dihadron spectra at RHIC/LHC**
**IV. Azimuthal angle anisotropy of single/dihadron spectra at RHIC/LHC**
**V.   Conclusions**

**Outline**

## I.    Introduction

**What happens for a jet propagating inside QGP?**

**Jet quenching:**

**The hard jet loses a significant amount of its energy **
**via radiating gluon induced by multiple scattering.**

## Jet Quenching effect in AA is incorporated 

**via modified fragmentation functions.**
** **

**Nuclear **
**geometry**

**A NLO pQCD parton model with jet quenching in A+A**

**Parton**
**distribution**
**functions**

**NLO cross sections**

**(****X. -N. Wang , PRC70(2004)031901)**

**Jet energy loss **

## Parton jet energy loss per unit length:

**E. Wang , X. -N. Wang , PRL87(2001)142301)**

**B. B. Back for PHOBOS, nucl-ex/0604017v1**

**(a parameterization form of theory calculations)**

## Slide 6

## II. Fragility of single/dihadron suppression factors

**Simultaneous fit of single/dihadron spectra**

**In most central Au+Au** ** **

**dihadron**

**single hadron**

## in most central Au+Au  

**     ****for single**

**     ****for dihadron**

**H. Zhang, J.F. Owens, E. Wang and **
**X.-N. Wang , PRL 98(2007)212301**

**Iaa robust when Raa fragile at RHIC**

**Sharp concave **
**Flat concave**

**in most central Au+Au** ** **

## dihadron

**Surviving jets:**** ****close and perpendicular to**** ****the surface**

**Surviving dijets:**** ****close and tangential to**** ****the surface + ****punch-through**** dijets**

**dihadron**

**Color strength: yield per unit area**

**Thickness of the outer corona**

**single hadron**

## HIJING shadowing + JQ

**HIJING shadowing + JQ**

**EKS98 shadowing + JQ**

**Energy loss parameter**

## III. Single/dihadron spectra at RHIC/LHC

**punch-jets**

**Surface emission bias**

**dihadron**

**single hadron**

**At LHC**

##    Comparisons for shadowing in single hadron spectra in p+A

**   ****Comparisons for shadowing in single hadron spectra in p+A**

**At RHIC**

**At LHC**

**4 kinds of shadowing parameterizations, ****(1)HIJ ****(S.-Y. Li and X.-N. Wang, PLB527(2002)85-91)****(2)EKS**** ****(K.J. Eskola, V.J. Kolhinen and C.A. Salgado, Eur. Phys. J.,  C9 (1999) 61)****(3)nPDF ****(M. Hirai, S. Kumano, and T.-H. Nagai, PRC70, (2004) 044905) ****(4)nDS**** ****(D. de Florian, R. Sassot, PRD69(2004) 074028)**

**No Quenching!  Only shadowing!**

**Shadowing depends on impact parameter in pA collisions.**

##  Single/dihadron spectra with different shadowing in A+A at RHIC

**Single/dihadron Raa/Iaa are all **** insensitive to**** different shadowing ****at RHIC**

**dihadron**

**single hadron**

**At RHIC**

## Single/dihadron spectra with different shadowing in A+A at LHC

**Single/dihadron spectra with different shadowing in A+A at LHC**

**Single hadron Raa ****insensitive**** to different shadowing.**

**Dihadron Iaa ****sensitive to**** different shadowing.**

**At LHC**

**dihadron**

**single hadron**

## 1) Initial partons participating in strong interaction in central region should be associated with stronger shadowing effects than those initial partons in the outer layer of the system.2) Because of surface emission bias, single hadron Raa is insensitive to shadowing at RHIC/LHC.3) Punch-through jets are created from central system region, and where the shadowing is stronger. 4) Punch-through jets at RHIC are greatly suppressed, so dihadron Iaa is also insensitive to shadowing at RHIC.5) Punch-through jets at LHC are released to dominate dihadron, so dihadron Iaa is sensitive to shadowing at LHC. 

## IV. Azimuthal angle anisotropy of single/dihadron spectra at RHIC/LHC

** ****v2 definitions in single/dihadron spectra**

**Azimuthal anisotropy is **
**probed by “single jets”****.**

**For dihadron,**

**Azimuthal anisotropy is **
**probed  by “dijets”****.**

**Trig**

**Asso**

**For single hadron,**

##  Azimuthal angle anisotropy manifested by jet quenching in high p_T single spectra 

** ****Azimuthal angle anisotropy manifested by jet quenching ****in high p_T single spectra **

**jets**

**single hadron at RHIC **

##   Dihadron v2  >  single hadron v2 

**  ****Dihadron v2  >  single hadron v2 **

**single hadron v2**

**dihadron v2**

**For single hadron, the anisotropy is ****probed by quenched single jets ****which have a bias of surface emission.**** ****For dihadron, the anisotropy ****is probed by quenched dijets ****which have a bias of tangential surface emission.**** **

##    v2@LHC  >  v2@RHIC

**   ****v2@LHC  >  v2@RHIC**

**RHIC**

**LHC**

**single hadron v2**

**dihadron v2**

**LHC**

**RHIC**

**Initial gluon density at LHC > RHIC**

## V. Conclusions

**1)    -fit to both single and dihadron suppression factors**
**provides a convincing evidence for the jet quenching**
**description.  I_AA is robust to probe the dense matter **
**when R_AA is fragile.**
**2) Punch-through jets are found to dominate high p_T **
**dihadron production in Pb+Pb at LHC. **
**Dihadron Iaa at LHC is able to distinguish different **
**shadowing parameterizations.**
**3) Dihadron v2  >   single hadron v2 at RHIC/LHC,**
**and v2@LHC  >  v2@RHIC for both single/dihadron. **

## Thank for your attention!

-   谢谢!

## PHOBOS , nucl-ex/0510042v1, nucl-ex/0604017v1

**PHOBOS , nucl-ex/0510042v1, nucl-ex/0604017v1**

## Slide 23

## Surviving jets contributing to hadron at RHIC

**Surviving jets contributing to hadron at RHIC**

** ****Only ****vertical surface emission**
** ****for single hadron**

**b=0 AuAu****at RHIC**

** ****Tangential surface emission**
** ****+ ****punch-through**** for dihadron**

## 2) Suppression factors vs centrality

**0-10%**

**10-20%**

**20-30%**

**30-40%**

**40-50%**

**50-60%**

**2) Suppression factors vs centrality**

**0-5%**

**60-70%**

**70-80%**

**single hadron**

## nuclear  modification  factor

## Invariant mass:

**(****X. –N. Wang , PLB 595(2004)165**

##  The dihadron azimuthal distributions

## The ratio between the yield/trigger in AA and in pp:

## Slide 30

## Slide 31