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A NLO Analysis on Fragility of Dihadron Tomography in High Energy AA CollisionsPowerPoint Presentation

A NLO Analysis on Fragility of Dihadron Tomography in High Energy AA Collisions

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### A NLO Analysis on Fragility of Dihadron Tomography in High Energy AA Collisions

Han-Zhong Zhang

Institute of Particle Physics, Huazhong Normal University, China

Co-authors: J. Owens E. Wang X.-N. Wang

- Introduction
- Numerical analysis on single hadron and dihadron production
- Conclusions

QuarkMatter2006

Nov. 18 , 2006

leading

particle

hadrons

q

q

hadrons

leading particle

Leading particle suppressed

hadrons

q

q

hadrons

N-N collision

A-A collision

leading

particle suppressed

QM 2006 Shanghai

Han-Zhong Zhang IOPP

Hard Probe Signal of QGP in RHIC and LHC

Jet quenching:

Induced by multiple scattering in QGP medium, a parton

jet will radiate gluon and lose its energy.

2

Han-Zhong Zhang IOPP

LO analysis of jet quenching in AA:

2→2 processes (tree level)

Jet quenching in 2→2 processes

A factor K=1.5-2 was put by hand to account for higher order corrections

3

Motivation :1) contribution for higher order correction?

2) find a robust probe of dense matter

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NLO (Next to Leading Order ) corrections:

K is absent

One-loop corrections

Jet quenching in 2→3 processes

2→3processes (tree level)

(Jeff. Owens , PRD65(2002)034011;

B.W. Harris and J. Owens , PRD65(2002)094032)

4

Han-Zhong Zhang IOPP

Modified Fragmentation Function (FF)Jet Quenchingeffects lead to the modification of FF

KKP

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

where

and the averaged scattering number,

It determines the thickness of the outer corona where

a parton jet survives in the overlapped region.

5

Han-Zhong Zhang IOPP

In 1-demension expanding medium, the total energy loss:

The energy loss with detailed balance:

(Enke Wang and Xin-Nian Wang, PRL87(2001)142301)

An energy loss parameter

proportional to the initial gluon density

6

Han-Zhong Zhang IOPP

II. Numerical analysis on single hadron and dihadron production

1) fix scales and energy loss parameter

2) the centrality dependent of the

suppression factor

3) hadron contour plot

4) fragility of single and dihadron tomography

7

Han-Zhong Zhang IOPP

The invariant p_T spectra of single hadronp-p data at 200GeV are used to fix scales,

8

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0-10% AuAu data at 200GeV are used to fix the energy loss parameter (proportional to the initial gluon density):

9

Single hadron is dominated by surface emission

y

emission surface

Single hadron

x

parton jet

coronathickness

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Han-Zhong Zhang IOPP

completely suppressed

Color strength =single hadronyield from partons in the square

11

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is a fragileprobe of dense matter.

loses its effectiveness

as a good probe of dense matter

Similar to the study by K. J. Eskola , H. Honkanen, C. A. Salgado,

U. A. Wiedemann, NPA747 (2005) 511-529

12

of dihadron in Au+Au collisions

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No jet quenching in d+Au,

Fit dAu data by pp result to fix scales,

Invariant mass

0.3

13

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

If no jet quen-ching,

0.3

15

Dihadron is from surface emission + punch-through jets

N

y

triggered hadron

x

associated hadron

partonic di-jet

tangential

S

punch-through jets

25% left

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Color strength =dihadronyield from partons in the square

16

is a robust probe of dense matter.

1.68

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at 200GeV

Trigger:8GeVat RHIC

17

is a robust probe of dense matter.

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at 5.5TeV

LHC

Trigger:20GeVat LHC

18

Because of the stronger quenching effects,

the single hadron is dominated by surface emission;

the dihadron is from surface emission + punch-through jets.

2)

The dihadron is more sensitive to the initial gluon density

than the single hadron . When becomes fragile in

higher energy AA, is a robust probe of dense matter.

3)

Without inputing K factor by hand, NLO results fit data well.

Because of the additional 2→3processes, NLO contributions

behave with stronger quenching effect than LO contributions:

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III. Conclusions19

is the differential 2-body or 3-body phase space element

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The inclusive cross sections for single hadron production:

The inclusive cross sections for dihadron production:

is the squared matrix elements

(Shi-Yuan Li and Xin-Nian Wang , PLB527(2002)85)

(Enke Wang and Xin-Nian Wang, PRL87(2001)142301)

(B. B. Back et al. [PHOBOS collaboration], PRC70(2004)021902)

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Han-Zhong Zhang IOPP

Nuclear shadowing

effects only

in small pT region

So in large pT,

medium effects

only come from

Jet Quenching !!!

Invariant mass:

How to fix scales:

If no medium effects,

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(X. –N. Wang , PLB 595(2004)165

increases while decreases with collision energy.

RHIC

LHC

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There are much more punch-through jets in higher energy AA

collisions,

is a robust probe of dense matter.

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at 5.5TeV

Trigger:20GeVat LHC

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