Resonance K* reconstruction and its role
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Resonance K* reconstruction and its role in heavy-ion collisions 相对论重离子碰撞中 矢量介子 K* 的重建及其应用. 唐泽波 中国科学技术大学近代物理系. Why do we need resonance How to reconstruct it What can it tell us. Kinetic Freeze-Out. Chemical Freeze-Out. Colliding. QGP evolution. What we can measure.

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唐泽波 中国科学技术大学近代物理系

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4470278

Resonance K* reconstruction and its rolein heavy-ion collisions

相对论重离子碰撞中

矢量介子K*的重建及其应用

唐泽波

中国科学技术大学近代物理系

  • Why do we need resonance

  • How to reconstruct it

  • What can it tell us

Zebo Tang, Lecture for Zhangbu's class


Qgp evolution

Kinetic Freeze-Out

Chemical Freeze-Out

Colliding

QGP evolution

What we can measure

  • How to study the property of the hot dense medium and its evolution?

  • What kind of probe we can use?

A time scale compatible to the lifetime of the medium is needed

Zebo Tang, Lecture for Zhangbu's class


Property of k

Property of K*

t=4 fm/c

Zebo Tang, Lecture for Zhangbu's class


Re scattering vs re generation

Re-Scattering vs. Re-Generation

K

K*

K

K*

Lost

Measured

K

K

K*

K

K

K*

t

Colliding

hadronization

begins

Chemical

freeze-out

Thermal

freeze-out

Resonances produced at chemical freeze-out stage

Daughter particle’s re-scattering effect destroys part of resonance signal

Re-generation effect compensates on resonance yield

Zebo Tang, Lecture for Zhangbu's class


Jet quenching

130 GeV nucl-ex/0206011

hadrons

q

q

hadrons

leading

particle suppressed

hadrons

leading particle

q

q

hadrons

leading particle suppressed

The high pT suppression behavior

is different for KS0 and 

Is this a mass effect or depending

on particle species (meson vs.

baryon) ?

Hydrodynamic Model

Quark Recombination Model

K* and : mesons but their masses

Close to 

K* at high pT ( > 2 GeV/c ) are the same as individual hadrons

K* RAA can distinguish this difference

p+p

Jet Quenching

Au+Au

9

Zebo Tang, Lecture for Zhangbu's class


A typical au au event at 200 gev

p

K

K

p

K*

K*

A typical Au+Au event at 200 GeV

Primary vertex

~1000 tracks/particles produced within STAR acceptance in a central Au+Au event

K* dN/dy ~ 10 in central Au+Au collisions at 200 GeV

Zebo Tang, Lecture for Zhangbu's class


K reconstruction

K* reconstruction

  • What we can detect is final stable particles

  • How to identify K*?

  • What properties does K* have?

Zebo Tang, Lecture for Zhangbu's class


Pion and kaon identification

Pion and Kaon Identification

|Nsp|<2 and |NsK|<2

Zebo Tang, Lecture for Zhangbu's class


Kaon pion paring

Nothing! Why?

Kaon Pion paring

How to find the K-p pair from the same parent?

No way! What should we do?

Pair every pion with every kaon in the same event

Zebo Tang, Lecture for Zhangbu's class


Random combinatorial bg reconstruction

Random Combinatorial BG Reconstruction

  • Like-sign technique

  • Mixed-event technique

  • Rotate technique

Zebo Tang, Lecture for Zhangbu's class


Like sign

K+

p-

K*

Like-sign

p+

uncorrelated

K-

uncorrelated

Zebo Tang, Lecture for Zhangbu's class


Rotate

K+

p-

K*

Rotate

p-’

Remove correlation

Zebo Tang, Lecture for Zhangbu's class


Mixed event

K+

p-

K*

Mixed-event

uncorrelated

p-’’

Zebo Tang, Lecture for Zhangbu's class


Invariant mass distribution

Invariant Mass Distribution

Zebo Tang, Lecture for Zhangbu's class


Combinatorial bg subtracted

Combinatorial BG subtracted

Zebo Tang, Lecture for Zhangbu's class


Bg reconstruction method comparison

BG reconstruction method comparison

Zebo Tang, Lecture for Zhangbu's class


Source of residual background

Y

K

K*

Y

K

X

K

K*

K*

K*

X

Source of residual background

  • Elliptic flow

  • Particle mis-identification

  • D0Kp etc.

Zebo Tang, Lecture for Zhangbu's class


K signal

K* signal

Zebo Tang, Lecture for Zhangbu's class

J.Adams et al., PRC71(2005)064902


K raw p t spectra

K* raw pT spectra

Branching ratio corrected

Zebo Tang, Lecture for Zhangbu's class


Efficiency acceptance determination

Efficiency×acceptance determination

  • Generate K*, flat y, f, pT distribution

  • Decay in GEANT, simulate STAR sub-detectors’ responses

  • Embed into a real event

  • Reconstruct embedded event

  • Associate MC tracks with reconstructed tracks

  • Run through embedded events, applied all of the cuts and get the counts of reconstructed K*, compare to MC K* counts

Zebo Tang, Lecture for Zhangbu's class


Efficiency acceptance vs p t

Efficiency×acceptance vs. pT

  • Increase as increasing pT

  • Decrease as increasing multiplicity

Zebo Tang, Lecture for Zhangbu's class


K p t spectra

K* pT spectra

Extract integrated yield dN/dy

and inverse slope T

Extrapolate to unmeasured

pT range

Exponential function:

Zebo Tang, Lecture for Zhangbu's class


Dn dy

dN/dy

  • Increase with increasing energy

  • No system size dependence

Zebo Tang, Lecture for Zhangbu's class


4470278

<pT>

Higher in central collisions

Re-scattering effect

Close to proton, higher than Pion and Kaon

Mass instead of particle type

Zebo Tang, Lecture for Zhangbu's class


K k ratio

K*/K- Ratio

  • K* and K- have same quark content

  • Ratio in Au+Au collisions smaller than that in p+p collisions (res-cattering dominant over regeneration)

  • Decrease as increasing system size (increasing fireball lifetime)

Zebo Tang, Lecture for Zhangbu's class


F k ratio

f/K* Ratio

  • K* and f have similar mass and same spin, different strangeness

  • K* re-scattering or strangeness enhancement or both

Zebo Tang, Lecture for Zhangbu's class


Nuclear modification factor

Nuclear Modification Factor

K* RAA @ pT<1.5 GeV/c  Lower than other particles

 Rescattering Effect

K* RAA @ pT>1.5 GeV/c  Close to KS0, different from 

 No strong mass dependence

Zebo Tang, Lecture for Zhangbu's class


Elliptic flow

y

Non-central Au+Au Collisions

coordinate space

x

z

x

y

Momentum space

py

px

Elliptic Flow

Reaction plane r

Fourier expansion for particle azimuthal

distribution in momentum space:

Elliptic flow carries information at initial

stage

Multiple interactions and pressure gradient lead

to the final observable elliptic flow

Elliptic Flow v2: second Fourier coefficient

10

Zebo Tang, Lecture for Zhangbu's class


V 2 vs p t

LOW

INTERMEDIATE

HIGH

STAR

PHENIX

v2 vs. pT

Low pT : affected by hydrodynamic flow

Intermediate pT : may be related to quark matter anisotropy

High pT : space emission

Zebo Tang, Lecture for Zhangbu's class


K v2 scaling

Y

K

K*

pY

K

X

K

K*

K*

K*

pX

Momentum phase space

Coordinate phase space

K* v2 scaling

Low pT:

Resonance daughter particles’ re-scattering and re-generation effects depend on the fire ball shape in the coordinate space

Resonance v2 compared to hadron v2 at low pT can tell the fireball shape in the coordinate space at late stage

Intermediate pT:

For directly produced K*, n=2

For regenerated K*, n=4

Zebo Tang, Lecture for Zhangbu's class


Event plane reconstruction

Event Plane Reconstruction

Zebo Tang, Lecture for Zhangbu's class


Event plane distribution

Event Plane Distribution

Zebo Tang, Lecture for Zhangbu's class


Extract v 2

Extract v2

  • In certain pT bin, get the same-event and mixed-event invariant mass distribution in several (f-y2) bins

  • Fit background subtracted invariant mass distribution, get K* yield N(f-y2,pT)

  • Fit N(f-y2,pT) with A*(1+2v2cos(2(f-y2))), get v2(pT)

Zebo Tang, Lecture for Zhangbu's class


V 2 results

v2 results

n=2.0±0.4, c2/ndf = 2/6

Zebo Tang, Lecture for Zhangbu's class


Spin alignment

Spin alignment

Zebo Tang, Lecture for Zhangbu's class


Global polarization in non central a a collisions

1. Z.T.Liang and X.N.Wang, PRL 94 102301 (2005), PLB 629 (2005) 20-26

2. S.A.Voloshin, nuch-th/0410089

Global polarization in non-central A+A collisions

In non-central A+A collisions

  • large initial orbital angular momentum of partonic system

  • quarks and anti-quarks will be polarized opposite to reaction plane

  • For vector mesons, spin density matrix elementρ00 should be 1/3 in unpolarized case. The deviation of ρ00 from 1/3 manifests the global polarization of vector mesons.

Zebo Tang, Lecture for Zhangbu's class


Vs hadronization mechanism

vs. hadronization mechanism

Two kinds of quarks and anti-quarks:

1) quarks and anti-quarks in QGP ---- Polarized;

2) created in accompanying process ----- higher pT and unpolarized.

Three different hadronization scenario :

1) recombine quark and anti-quark in QGP;

2) recombine in QGP with those from accompanying process;

3) fragmentation of a fast quark/anti-quark from the QGP.

Zebo Tang, Lecture for Zhangbu's class


Measurement

K* is relatively short-lived (~4fm/c)vector meson.

In the rest frame of K*, K/π distribute as:

Event plane

measurement

  • good Particle IDentification capability

  • large acceptance

  • uniform at both azimuth and polar directions

Zebo Tang, Lecture for Zhangbu's class


Extract r 00

Extract r00

Zebo Tang, Lecture for Zhangbu's class


R 00 vs p t

r00 vs pT

Consistent with 1/3, provide no evidence of global spin alignment

Zebo Tang, Lecture for Zhangbu's class


Summary

Summary

  • Resonance is a unique/important tool to probe the property of the hot dense medium and its evolution

Zebo Tang, Lecture for Zhangbu's class


Homework

Homework

  • 已知K*0Kp的分支比约100%,K*0K+p- 的分支比是多少?

  • 从RAA和v2的测量中我们可以看出在STAR中KS和L的测量要比K*要好得多,为什么?

Zebo Tang, Lecture for Zhangbu's class


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