Christina Markert SQM2007, June 2007, Levoča, Slovakia 1

Resonance production in heavy-ion collisions at STAR

Christina MarkertUniversity of Texas at Austin

• Motivation• Resonances Hadronic phase (system size/energy) Chiral symmetry restoration (jets)• Conclusion

Christina Markert SQM2007, June 2007, Levoča, Slovakia 2

Lifetime of nuclear medium 200 GeV Au+Au

TchemicalTchemical

t ~ 3-5 fm/cresonances

t ~ 10 fm/c2 particle correlation Partonic phase ~ 5-7 fm/c

Phys. Rev. Lett. 97 (2006) 132301

Christina Markert SQM2007, June 2007, Levoča, Slovakia 3

Hadronic re-scattering and regeneration

Life-time [fm/c] :K(892) = 4.0 =(1520) = 13 (1020) = 45

Depends on:• hadronic phase density • hadronic phase lifetime

time

signal lost

signal measured late decay

signal measured

signal measuredearly decay

che

mic

al fr

eeze

-o

ut

p

pp

kin

etic

fre

eze

-out

re-scattering

regeneration

e+

e-leptonic decay

hadronic decay

Christina Markert SQM2007, June 2007, Levoča, Slovakia 4

System size and energy dependence

increasing centralitylarger system size

Au 197

Cu 64

smaller nucleus Smaller system size

lower energy

200 GeV

62 GeV

compare to number ofproduced charged

particlesdN/dy

Christina Markert SQM2007, June 2007, Levoča, Slovakia 5

Resonance suppression (system size dependence)

Suppression scales with dNch/dy ~ system size

STAR preliminary

[1] P. Braun-Munzinger et.al.,PLB 518(2001) 41, priv. communication[2] Marcus Bleicher and Jörg Aichelin Phys. Lett. B530 (2002) 81. M. Bleicher and Horst Stöcker J. Phys.G30 (2004) 111.

Phys. Rev. Lett. 97 (2006) 132301 Phys. Rev. C71 (2005) 064902See S. Dash SQM2007 statistical errors only !

Regeneration/Rescattering cross section:p)

Life-time [fm/c] :K(892) = 4.0 =(1520) = 13 (1020) = 45

STAR Preliminary

A Lordanova SQM2007

[2][1]

Christina Markert SQM2007, June 2007, Levoča, Slovakia 6

Resonance suppression (energy dependence)

STAR preliminary

Phys. Rev. C71 (2005) 064902nucl-ex/0703033See S. Dash SQM2007

Life-time [fm/c] K(892) = 4.0 (1020) = 45

STAR preliminary

M. Bleicher et al.

statistical errors only !

Less re-scattering at lower energies in peripheral collisionsSame volume but,• Lower density smaller interactions cross section?• Shorter hadronic lifetime less hadronic interactions ?

Christina Markert SQM2007, June 2007, Levoča, Slovakia 7

Regeneration might increase elliptic flow

C. Nonaka, et al.,Phys.Rev.C69:031902,2004

Data suggest small regeneration for K* (need smaller errors !)

minbias 200 GeV Au+Au

Partonic resonance generation:Number of Constituent Quark (NCQ) scaling at intermediate pT (meson NCQ = 2)

Hadronic resonance (re)generation:Regenerated resonances–final state interactions NCQ = 4 (* = + =2+2)

Phys. Rev. C71 (2005) 064902

Recombination model

Christina Markert SQM2007, June 2007, Levoča, Slovakia 8

Mass shift and width broadenings are predicted as influence of medium on resonance spectral function, e.g.:

For baryonic and strange resonances

M.F.M Lutz (SQM 2001) J.Phys.G28:1729-1736,2002

M.F.M Lutz, E.E. Kolomeitsev, Nucl.Phys.A755:29-39,2005. hep-ph/0501224

For mesonic resonances Ralf Rapp (Texas A&M) J.Phys. G31 (2005) S217-S230

(1520) and (1385) resonances decay channel change

M. Kaskulov et al., nucl-th/0509088

Resonance in a medium (nuclear matter)

Christina Markert SQM2007, June 2007, Levoča, Slovakia 9

Resonances from jets

near-side

STAR Preliminary

near

away

Study Chiral Symmetry Restoration by comparing resonance production in event classes based on azimuthal distribution:

We expect high pT resonances from the away side jet to be medium modified due to the high density and temperature of the partonic and pre-equilibrium hadronic medium

arXiv:nucl-ex/0706.0724

Christina Markert SQM2007, June 2007, Levoča, Slovakia 10

Formation of hadronic resonances (from jets) in a chiral medium

side 1

side 2

near

away

Low pt High pt

Near side No medium or late hadronic medium

No medium

Away side Late hadronic medium Partonic or early hadronic medium (depend on formation time) CSR ?

Side 1 & 2 Late hadonic medium Early hadronic medium

Formation time arguments:a.) General pQCD:Formation time [fm/c] ~ pT [GeV]Formation time [fm/c] ~ 1/massb.) Specific string fragmentation (PYTHIA) formalism:Gallmeister, Falter, PLB630, 40 (2005)Intermediate pT resonances form earlyc.) Vitev et al. (hep-ph/0611109): High pT heavy particles and resonances form early

Need to determine the right momenta for trigger and resonance particle

Christina Markert SQM2007, June 2007, Levoča, Slovakia 11

First attempt(1020) reconstruction from jets

M inv (K+ K-)

M inv (K+ K-)

Trig

ger/

Eve

nt

Number of triggers

• Trigger particle: hadron pT > 4.0 GeV • Associated particle: resonance (1020) <pT>~ 0.9 GeV

~95% of events have on trigger particle

(1020)

charged hadrons200 GeV Au+Au

Christina Markert SQM2007, June 2007, Levoča, Slovakia 12

(1020) from same/away side in/out of plane

side1

side2

near

away

Systematic errors are ~ 10%

51385±2369

64498±2400 54893±2378

61043±2394

No mass shift or width broadening

visible

Yield away/same1.26±0.19

side2

side1 near - side

away- side

Christina Markert SQM2007, June 2007, Levoča, Slovakia 13

Hadron - resonance correlation in Au+Au

of h-(1020) – C • h-(1020) mixed event

Pythia 75M events p+p 200 GeV only phi (no background from K+K combinations)

QM2006 M.Horner

Pythia p+p

STAR preliminary

ZYAM = zero yield at minimum

Hadron trigger pT > 4 GeV (1020) <pT > ~ 0.9 GeV ( need higher pt )

Not corrected for acceptanceSystematic BG normalization error not included

Not corrected for v2

Christina Markert SQM2007, June 2007, Levoča, Slovakia 14

Time of Flight upgrade detector

STAR: Time of Flight detector upgrade:• PID at higher momentum • Electron hadron separation• Installation completed in 2-3 years

STAR Experiment

|1/β-1|<0.03

J.WU QM2006

TOF

Improves reconstruction of hadronic and leptonic decay channels:K* K+, p*p

ee

Christina Markert SQM2007, June 2007, Levoča, Slovakia 15

Conclusions

• Low momentum resonances provide information regarding the lifetime of hadronic stage.

• Re-scattering cross section scales with system size.• Lower collision energy results in less hadronic interactions.

• High momentum resonances from jets could be used as a tool to trigger on early produced resonances and test chiral symmetry restoration

• Need more quantitative theoretical description of formation time of hadronic resonances as a function of mass, momentum and medium density.

• First step: Untriggered 1020) correlation spectrum shows no

evidence of medium modification • Next steps:

• Trigger on high p T (1020)• Reconstruct resonances in jets with shorter lifetime as (1020)

but sufficient statistics (e.g. K*, ).

• New TOF detector will help to study higher pT resonance and leptonic decays.