Narrowing of Balance Function and Hadronization Ti
me at RHIC EnergyDu Jiaxin, and Liu Liansho
uInstitute Of Particle Physics,
Huazhong Normal University (CCNU)
[email protected] 2/13
Outline
About Balance Function
A Brief Introduction to AMPT Model
The Time Evolution in AMPT
Our Result of Balance Function
Summary
[email protected] 3/13
Why (changed) balance function?
Clocking HadronizationClocking Hadronization
QGP SignalQGP Signal
BF is expected to be narrower for a scenariowith delayed hadronization, due to the formation of a quark-gluon plasma.
Early Hadronization
Large y
Late Hadronization Small y
y
Bass, Danielewicz, and Pratt, Phys. Rev. Lett. 85, 2689 (2000).
Charge-anticharge pairs are correlated in rapidity. Those who created earlier can separate further in rapidity.
[email protected] 4/13
})()()()(
{2
1)|(
n
ynyn
n
ynynYyB W
21 yyy Relative rapidity
All the particles are within the rapidity window WY
Charge Balance Function in Yw
The width of the BF is defined by:
( | )
( | )W
i W iiY
i Wi
B y Y yy
B y Y
In our calculation [ 3.0,3.0]WY
[email protected] 5/13
Result given by STAR
The narrowing of balance function as the increase of multiplicity is clearly discovered by experiments.
STAR, QM04.
AuAu @ 200GeV
[email protected] 6/13
A brief Introduction to AMPT Modelinitial state
pre-equilibrium
QGP and hydrody- namic expansion
hadronization
hadronic phaseand freeze-out
Characteristic:
Quark-Parton phase included
Complete time evolution after parton produced
Two versions are available, we use the default version(v1.11).
[email protected] 7/13
Four main components :
Initial Conditions: HIJING model
Partonic Interactions: ZPC model
Hadronization: LUND string fragmentation mechanism (PYTHIA).
Hadronic Interactions: ART model
Zi-Wei Lin, Che Ming Ko, Bao-An Li and Bin Zhang, Phys. Rev. C72 064901 (2005).
[email protected] 8/13
AMPT is based on non-equilibrium dynamics. No equilibrium phase transition from parton phase to hadron phase.
A parton comes to hadronization only when it cease to interact with other partons.
Hadronization time in AMPT Model
No unique hadronisation time for the whole system. Each parton has its own hadronisation time.
[email protected] 9/13
We defined:
ifr fr0
1 partonN
iparton
t tN
as the characteristic hadronization time for an event. Where is the number of partons in the event, is the freeze out time of the parton.
thiparton
Nifrt
Fig.2 distribution for b>7 and b<7 correspondinglyfrt
10mb g
[email protected] 10/13
Two preliminary questions :
Balance Function in AMPT
BF become narrowing
Multiplicity increase
BF become narrowing
Delayed hadronization?Is the narrowing of Balance Function only caused by the multiplicity increase or really due to delayed hadronization?
How does the hadronization time vary as the multiplicity increase?How does the BF width vary when hadronization time increase but the multiplicity keep constant?
[email protected] 11/13
Fig.3. .vs. for b>7 and b<7 correspondinglyfrt chN
Two centrality samples:Each centrality sample is divided into sub-samples according to multiplicity intervals;The resulting sub-samples are further divided into sub-samples by different mean hadroniztion time intervals.
[email protected] 12/13
FIG. 3: for different and Au-Au@ 200 GeV.
wYy
frt chn
Our result:The width of BF decreases with the increasing of multiplicity.
In the same multiplicity interval, the width of BF is consistent of being constant, independent of the hadroni-zation time.
Using the narrowing of BF as a measure of hadroniza-tion time and as a signal of QGP is doubtful.
[email protected] 13/13
Summary We use the average of hadronization time as the unique hadr
onization time of the whole system.
We calculate the width of BF in different multiplicity interval and hadronization time interval.
The width of BF decreases with the increasing of multiplicity.
In AMPT model, the width of balance function is consistent with being independent of hadronization time in a fixed multiplicity interval.
Based on our calculation of AMPT model, We concludes that using the narrowing of balance function in RHIC as a measure of hadronization time and as a signal of QGP is doubtful.