Narrowing of Balance Function and Hadronization Time at RHIC Energy

1. Narrowing of Balance Function and Hadronization Time at RHIC Energy Du Jiaxin, and Liu Lianshou Institute Of Particle Physics, Huazhong Normal University (CCNU)

2. Outline • About Balance Function • A BriefIntroduction to AMPT Model • The Time Evolution in AMPT • Our Result of Balance Function • Summary dujx@iopp.ccnu.edu.cn

3. Early Hadronization  Largey Late Hadronization  Smally Why (changed) balance function? Bass, Danielewicz, and Pratt, Phys. Rev. Lett. 85, 2689 (2000). • Clocking Hadronization Charge-anticharge pairs are correlated in rapidity. Those who created earlier can separate further in rapidity. • QGP Signal BF is expected to be narrower for a scenario with delayed hadronization, due to the formation of a quark-gluon plasma. dujx@iopp.ccnu.edu.cn

4. Relative rapidity All the particlesare within the rapidity window In our calculation The width of the BF is defined by: Charge Balance Function in Yw dujx@iopp.ccnu.edu.cn

5. Result given by STAR STAR, QM04. The narrowing of balance function as the increase of multiplicity is clearly discovered by experiments. dujx@iopp.ccnu.edu.cn

6. hadronic phase and freeze-out QGP and hydrody- namic expansion initial state pre-equilibrium hadronization A briefIntroduction to AMPT Model • Characteristic: • Quark-Parton phase included • Complete time evolution after parton produced Two versions are available, we use the default version(v1.11). dujx@iopp.ccnu.edu.cn

7. Zi-Wei Lin, Che Ming Ko, Bao-An Li and Bin Zhang, Phys. Rev. C72 064901 (2005). • Four main components : • Initial Conditions: HIJING model • Partonic Interactions: ZPC model • Hadronization: LUND string fragmentation mechanism (PYTHIA). • Hadronic Interactions: ART model dujx@iopp.ccnu.edu.cn

8. Hadronization time in AMPT Model • AMPT is based onnon-equilibrium dynamics. No equilibrium phase transition from parton phaseto hadron phase. • A parton comes to hadronization only when it cease to interact with other partons. • No unique hadronisation time for the whole system. Each parton has its own hadronisation time. dujx@iopp.ccnu.edu.cn

9. Fig.2 distribution for b>7 and b<7 correspondingly We defined: 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. dujx@iopp.ccnu.edu.cn

10. Multiplicity increase Delayed hadronization BF become narrowing BF become narrowing Balance Function in AMPT Is the narrowing of Balance Function only caused by the multiplicity increase or really due to delayed hadronization? Two preliminaryquestions : • 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? dujx@iopp.ccnu.edu.cn

11. Fig.3. .vs. for b>7 and b<7 correspondingly • 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. dujx@iopp.ccnu.edu.cn

12. 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. FIG. 3: for different and Au-Au@ 200 GeV. dujx@iopp.ccnu.edu.cn

13. Summary • We use the average of hadronization time as the unique hadronization 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. dujx@iopp.ccnu.edu.cn