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What do we learn from Resonance Production in Heavy Ion Collisions ?

Christina Markert, Yale University

Hot Quarks 2004, July 18-24, Taos Valley, New Mexico USA

Resonances

Heavy Ion Collisions

Analysis Techniques

Time Scale

Summary

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Sevil Salur (Yale):(1385) Resonance Studies and Pentaquark Search with STAR

Debsankar Mukhopadhyay (Vanderbilt U.): meson production in Au-Au collisions at sNN = 200 GeV

Gene van Buren (BNL):Reconstructing decays in the STAR detector ground state particle !

Hendrik van Hees (Texas A&M University ):Medium Modifications of the Delta Resonance at RHIC

Dipali Pal (Vanderbilt U.): meson production in d-Au collisions at sNN = 200 GeV

Talks in the Resonance Session

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What is a Resonance ?

uds ud ud uds

p K uud us uds

uds ud uus

Hadronic and leptonic decay:

K

e e

• Excited state of a ground state particle.• With higher mass but same quark content.• Decay strongly short life time (~10-23 seconds), width natural spread in energy: h/.• Broad states with finite and which can be formed by collisions between the particles into which they decay.

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Resonance Production and Observation I

Elastic and inelastic K-p cross section

Kp

Kbeam : plab= 395 MeV (

Data: Bubble chamber, Berkeley 1975T.S. Mast et at., Phys. Rev. D14 (1976) 14.

• Relativistic chiral SU(3) Lagrangian describe kaon-nucleon scattering M.F.M. Lutz and E.E. Kolomeitsev Nucl.Phys.A700 (2002) 193-308

---- only s-wave contribution contribution of s-, p-, d-waves

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Resonance Production and Observation II

K* from K-+p collision system

Invariant mass (K0+) [MeV/c2]

K*-(892)

640 680 720 760 800 840 880 920

Nu

mb

er o

f ev

ents

0

2

4

6

8

1

0

Bubble chamber, BerkeleyM. Alstone (L.W. Alvarez) et al., Phys. Rev. Lett. 6 (1961) 300.

Luis Walter Alvarez 1968 Nobel Prize for

“ resonance particles ” discovered 1960

Kp p K

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Resonance in Medium

• Different collision systems p+p and Au+Au, d+Au (p+p no medium, Au+Au extended medium, d+Au very small medium)

Hea

vy I

on R

eact

ion

Time,T, 0 Tch =160 MeV, 0 ~ 0.6

Tkin=100 MeV, 0 ~ 0.2I

I : early stage before chemical freeze-out mass and width II : late stage after chemical freeze-out yield and pT

mass and width

Survival probability of signals ?

mass and width shift: leptonic channel: particles interact less in hadronic phase hadronic channel: only if less rescattering of resonance or sensitivity to low density (T=100 MeV) yield and pT : leptonic channel: conditions at chemical freeze-out hadronic channel: chemical freeze-out and time scale

II

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Resonance in Medium I (nuclear matter)

(1520) and(1385) in medium0

(1520): ~100 MeV mass shift and (100 MeV width)(1385): ~40 MeV mass shift and (50 MeV width)

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

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Resonance in Medium II (nuclear matter)

STAR Preliminary

30-50% Au+Au

0.8 ≤ pT < 1.4 GeV/c

Δ++

Δ+

+ W

idth

G

eV

/c2

dNch/dη

STAR Preliminary

0.6 ≤ pT < 1.6

sNN = 200 GeV

AuAu

Hendrik van Hees Medium Modifications of the Delta Resonance at RHIC + nucleon propagation in medium + fireball conditions (T, ) (1232) inv. mass spectra at Tkin=100 MeV = 0.12 0 width increase

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1520)p

K

p

K

1520)

Rescattering

Between chemical and kinetic freeze-out Rescattering > Regeneration Resonance signal loss

time

chemical freeze out end of inelastic interactions

T~170 MeVparticle multiplicities

thermal freeze outend of elastic interactions

T~110MeVparticle spectra, HBT

Detector

Regeneration

Resonance Yields Rescattering and Regeneration)

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life time [fm/c]: < ++< K* < *< *(1520) < *(1530) < 1.3 <1.7 < 4 < 6 < 13 < 20 < 40

- all decay- measured

Survival probability in a Microscopic Model

(1385)

chemical freeze-out ~ 5fm/ckinetic freeze-out ~20-30 fm/c (long life time !)

Marcus Bleicher and Jörg Aichelin Phys. Lett. B530 (2002) 81-87. M. Bleicher and Horst Stöcker J.Phys.G30 (2004) 111.

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life time [fm/c]: < ++< K* < *< (1520) < 1.3<1.7 < 4 < 6 < 13 < 40

[MeV] T all T obs pT all pT obs pT

125 190 490 640 150

250 230 665 765 100

K(892) 160 230 550 690 140

(1385) 200 240 730 820 90

230 250 845 870 35

175 190 610 645 35

K(892) (1520)

pT changes due to Resonance Rescattering

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Meson at SPS

Hadronic channel: less signal in low pt lower yield E. Kolomeitsev, SQM2001

J.Phys.G28:1697-1706,2002

• Rescattering of secondary kaons• Influence of in-medium kaon potential

Talks :Debsankar Mukhopadhyay and Dipali Pal

meson production in Au-Au and d+Au collisions at sNN = 200 GeV

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Resonances at CERN SPS (NA49)

(1520) at SPS

Thermal model in Pb+Pb

Pb+Pb ratio = 0.03 T=125 MeV

Ratio = 0.07 for T=170 MeV

Thermal model calculations

T=170 MeV

Chemical feeze-out

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Energy loss in TPC dE/dx

momentum [GeV/c]

dE/dx

p

K

e(1385)

-

-

p

(1520)

K- p

K(892) + K

(1020) K + K

(1520) p + K

(1385) + +

End view STAR TPC

Resonance Reconstruction

• Identify decay candidates (p, dedx, E)• Calculate invariant mass

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(1520)

STAR Preliminary

(1520)

Invariant Mass Reconstruction

— original invariant mass histogram from K- and p combinations in same event.— normalized mixed event histogram from K- and p combinations from different events. (rotating and like-sign background)

Extracting signal:After Subtraction of mixed event background from original event and fitting signal (Breit-Wigner).

2212

21 ppEEminv

Invariant mass:

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STAR Preliminary

Statistical error only

K(892)

(1385)

STAR Preliminary

Resonance Signals in p+p

Talk by Gene van Buren(ground state particle)

Talk by Sevil Salur

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pT-coverage (yield) pT (integrated)K(892) 95% 680 30 30 MeV(1520) 91% 1080 90 110 MeV

(1520)K(892)

dN/dy at |y|<0.5

K(892) = 0.059 0.002 0.004

(1520) = 0.0037 0.004 0.006

Resonance pT Spectra in p+p at sNN 200 GeV at mid Rapidity

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Resonance Production in Au+Au Collisions at sNN 200 GeV

K*0

• K*0 peak invisible in the same event spectra before background subtraction due to huge combinatorial background.• Background comes from mis-identified correlated particles

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STAR Preliminary

Au+Au minimum biaspT 0.2

GeV/c

|y| 0.5

K*0 + K*0

Statistical error only

K(892)

(1520)

STAR Preliminary

dN/dy at y=0 central Au+Au

K(892)+Anti-K(892)/2 = 10.2 0.5 1.6

(1020) = 7.70 0.30 10%

(1520) = 0.58 0.21 40% (assuming T=350-450MeV)

(1020)

STAR Preliminary

Resonance Production in Au+Au Collisions at 200 GeV at mid Rapidity

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Time Scale H

ot a

nd d

ense

m

ediu

m

p+p

Au+AuAu+Au interactions:• Extended hot and dense phase• Thermalisation at chem. freeze-out• Kinetic freeze-out separated from chemical freeze-out

p+p interactions:• No extended initial medium• Chemical freeze-out (no thermalisation)• Kinetic freeze-out close to the chemical freeze-out

Tch, b Tkin,

Particle yields Particle spectra

time

p

K

p

K

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Statistical Model for Particle Production in p+p and Au+Au Collision

In pp particle ratios are well described with T=160 MeV

Resonance ratios in Au+Au are not are well described with

Tch = 16010 MeV, B = 24 5 MeV (Olga Barannikova)

Resonance Suppression

STAR Preliminary

p+p at 200 GeV Au+Au at 200 GeV

Also:

F. Becattini, Nucl. Phys.

A 702, 336 (2002)

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Thermal model [1]:T = 177 MeVB = 29 MeV

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

Rescattering and regeneration is needed !

UrQMD [2]

Life time [fm/c] :(1020) = 40 (1520) = 13 K(892) = 4 ++ = 1.7

p+p ratios are consistent with thermal model prediction T=160 MeV

F. Becattini, Nucl. Phys. A 702, 336 (2002)

Resonance Production in p+p and Au+Au

STAR Preliminary

K(892)

p+p

Au+Au

STAR Preliminary

K(892)

p+p

Au+Au

0.760 0.050

1.030 0.120

50% - 80%

0.620 0.040

0.680 0.040

pp

1.090 0.110

1.080 0.120

0% - 10%

pT (GeV/c)pT (GeV/c)Centrality

K(892) ProtonInverse slope increase from p+p to Au+Au collisions. UrQMD predicts signal loss at low pT due to rescattering of decay daughters. Inverse slopes and mean pT are higher.UrQMD has long lifetime ( 5-20fm/c)

Signal loss of ~70% for K(892)

[MeV] pT

100

K(892) 140

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Signal Loss in low pT Region

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Model includes: • Temperature at chemical freeze-out• Lifetime between chemical and thermal freeze-out• By comparing two particle ratios (no regeneration)

results between : T= 160 MeV => > 4 fm/c (lower limit !!!) = 0 fm/c => T= 110-130 MeV

(1520)/ = 0.034 0.011 0.013 K*/K- = 0.20 0.03 at 0-10% most central Au+Au

G. Torrieri and J. Rafelski, Phys. Lett. B509 (2001) 239

Life time:K(892) = 4 fm/c (1520) = 13 fm/c

preliminary

More resonance measurements are needed to verify the model and lifetimes

Temperature, Lifetime and Centrality Dependence from (1520)/ and K(892)/K

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t (Tch /Tkin –1) R/

Tch freeze-out

Tkin freeze-out

Tkin and from Blast-Wave-Fit to , K and p Tch from Thermal model

Lifetime nearly constant in

peripheral and central Au+Au collisions

Hhhff

Temperatures and lifetimes from Particle Spectra ,K and p

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• Resonances can be measured in heavy ion collisions

• K(892)/K and (1520)/ ratios are smaller in A+A than in p+p collisions (SPS and RHIC).

Thermal model predictions are higher than measured K(892)/K and (1520)/.

Rescattering and regeneration in hadronic source after chemical freeze-out

Results from leptonic channel from SPS gives same answer. RHIC ?

• Lifetime between chemical and thermal freeze-out > 4 fm/c

• Small centrality dependence in K(892)/K and (1520)/ratios. Suggest nearly same lifetime () for peripheral and central Au+Au collisions.

• Consistent with observation of stabile particle yields and spectra (,K,p)

Au+Au

Summary