1. Considerations for Distinguishing Between Soft- and Hard-Component by Multiplicity Correlation
Na Li
Huazhong University of Science and Technology
7th International Workshop on CPOD,
November 2011

2. Motivation Particle production soft particles: from hot dense medium
Mixed when measured in experiment
Particle
production
jets:
beginning of the collision
hard process
Particles produced in different processes carry different information of the collisions.
It is important to distinguish the contribution of hydro part and non-hydro part, especially in the intermediate pT region.
Na Li, CPOD,

3. … F-B Elliptic Correlation Function
Requirement: ● Jet randomly falls into one region in a single event.
J. Liao and V. Koch, Phys. Rev. Lett. 103, (2009) η …
forward
backward
Assumption:
the multiplicity of flow particle in each side fluctuate independently -> <ηFηB>=0
g->0, (hydro dominance) CFB->1
g->1, (jet dominance) CFB->0
Na Li, CPOD,

4. More measurement needed!
Unsolved Problem
2 equations with 3 unknown variables!
More measurement needed!
Na Li, CPOD,

5. … Multiplicity Correlation Function Definition: η
forward
backward η
The effect of <ηFηB> is small when g is relative large.
FB correlation of flow multiplicity
jet contribution
Na Li, CPOD,

6. AMPT string melting model
In A Multi-phase Transport Model (I)
AMPT string melting model
At low pT :
With the assumption of no jet contribution at low pT, we may obtain
Although the flow multiplicity exponentially decreases with pT , little pT dependence has been observed for <ηFηB>.
Na Li, CPOD, 6
Na Li, Hangzhou,

7. In A Multi-phase Transport Model (II)
At intermediate pT :
The tail of hydro particle distribution may also caused the decreasing of FB multiplicity correlation function.
The data points from AMPT are lower than the hydro-only simulation.
The jet contribution can not be neglect in intermediate pT range.
Na Li, CPOD, 7
Na Li, Hangzhou,

8. Non-hydro Contribution in v2
If: the multiplicity of flow particle
in each side fluctuate correlated
L. X. Han, Phys.Rev.C 83, (2011)
jet contribution
correlation of flow multiplicity fluctuation
Na Li, CPOD,

9. Elliptic Correlation in AMPT
Results of AMPT model
L. X. Han, Phys.Rev.C 83, (2011)
CFB is about 2 in central collisions.
<ηFη B> is close to 0.25 at low pT.
Inconsistent with the result from multiplicity correlation ?
Na Li, CPOD,

10. v2 fluctuation For the flow dominate case: Particles produced in
in-plane and out-of-plane may fluctuate, thus ηF and ηB are the functions of φ, which may cause the fluctuation of v2!
For the flow dominate case:
Larger v2 fluctuation in central collision causes the larger CFB at low pT. 10

11. Pure flow and jet v2 are expected to be extracted!
Observables
Constant at low pT
Neglectable at large g
Pure flow and jet v2 are expected to be extracted!
Na Li, CPOD,

12. Summary
A multiplicity correlation is proposed to measure non-hydro contribution.
The forward-backward multiplicity correlation <ηFηB> is small in the transport model.
The jet contribution is significant in intermediate pT.
The elliptic anisotropy correlation is proposed to measure the non-collective contribution from elliptic flow.
Thank You!
Na Li, CPOD,
Na Li, CPOD, 12

13. Multiplicity Correlation Simulation
Inputs:
Mflow and Mjet are constrained by g
(Mflow +Mjet ) fluctuates ±20%
φflow randomly generated between [0, 2π]
φjet randomly generated between [0, 2π] , and associated particles are generated within ±π/16 according to jet direction
CFB is consistent with the theoretical value.
The method is not very sensitive with the pure multiplicity fluctuation.
The effect of <ηFηB> is small when g is relative large.
No correlation in the simulation
Real case?
Na Li, CPOD, 13

14. Non-hydro Contribution in v2
If: the multiplicity of flow particle
in each side fluctuate correlated
L. X. Han, Phys.Rev.C 83, (2011)
jet contribution
correlation of flow multiplicity fluctuation
Na Li, CPOD,

15. Elliptic Correlation Simulation
Inputs:
Nflow and Njet are constrained by g
(Nflow +Njet ) fluctuates ±20%
Add in v2 signal
Associated particles are
generated within ±π/8
according to jet direction
grey markers: jet corn = π/4
A. M. Poskanzer, Phys.Rev.C 58, 1671(1998)
The pure jet elliptic anisotropy v2 could be extracted from when g≥0.3
Na Li, CPOD,