# Presentation: 119277

## Patricia Fachini
Brookhaven National Laboratory

***Brookhaven National Laboratory***

- Motivation
- Measurements
- Results
- Summary

- Resonance Production

- Recent Results

## In-medium modification of mass and/or width  Chiral Symmetry Restoration, Collision Broadening or Phase Space?

 ρ0(770)  Leptonic decay channel  probes all stages of the collision. Hadronic decay channel  probes only late stages of the collision
Φ  Information from early time ? 
K*0(892)  Regeneration and daughter rescattering  time scale ?

- In-medium modification of mass and/or width **** Chiral Symmetry Restoration, Collision Broadening or Phase Space?
-  ρ**0**(770) ****** **Leptonic decay channel ****** **probes all stages of the collision. Hadronic decay channel ****** **probes only late stages of the collision
- Φ ****** **Information from early time ?
- K***0**(892) ****** **Regeneration and daughter rescattering **** time scale ?

- ρ**0** c**** = 1.3 fm

- Φ c**** = 44 fm

## Motivation - II 

- If resonance decays before kinetic freeze-out **** not reconstructed  due to rescattering of daughters
- K***0** (c****** **= 4 fm) survival probability ****** **time between chemical and kinetic freeze-out, source size and p**T** of K***0**
- Chemical freeze-out **** elastic interactions πK **** K***0****** πK regenerate K***0**(892) until kinetic  freeze-out
- K***0**/K may reveal time between chemical and kinetic freeze-out
- Λ*****/Λ, Δ**++**/p, ρ**0**/π, f**0**/π ?

**Chemical freeze-out**

**Kinetic freeze-out**

## Motivation - III 

- K***0** regeneration ****** **σ(Kπ)
- K***0**** **daughter rescattering** ******** **σ(ππ)
- σ(ππ) >>>> σ(Kπ)
- σ(pπ) > σ(ππ)
- Hadronic cross-sections ****** **Change yields of K*****, Λ*****, Δ**++**, ρ**0**, f**0**

****** ****Probe dynamics between chemical and kinetic freeze-out**

**Chemical freeze-out**

**Kinetic freeze-out**

## Resonance Production – Hadronic Channel

- Δ**++**(1232) ****** **p π**+  **B.R. ~1     	c****** **= 1.6 fm
- f**0**(980) **** π**+ **π**-** 	     B.R. 2/3		c****** **= 2.6 fm
- K***0±**(892)** ******** **π** **K   B.R. 2/3	         c****** **= 4 fm
- Σ(1385) ****** **Λ π     B.R. 0.88         c****** **= 5.5 fm
- Λ(1520)** ******** **p K**    **B.R. 0.45	c****** **= 12.6 fm
- Φ(1020)** ******** **K**+ **K**-****  **B.R. 0.49  	c****** **= 44 fm

- Life Time

## Raw Invariant Mass Distribution from Data -I

**Invariant Mass (GeV/c****2****)**

- Statistical error only

- STAR Preliminary

- STAR Preliminary

- Invariant Mass (GeV/c2)

- Invariant Mass (GeV/c2)

- Φ****K**+**K**-**

- Φ****K**+**K**-**

- Φ****K**+**K**-**

- Φ****K**+**K**-**

- NA49 Preliminary

- NA49 Preliminary

- |y|<0.5

****sNN = 200 GeV

- Minimum bias
- p+p

- 0-7% Pb+Pb

- Minimum bias
- Au+Au

- 0-7% Pb+Pb

- |y|<2.0

****sNN = 12.3 GeV

****sNN = 8.76 GeV

- Minimum bias
- Au+Au

- Φ****K**+**K**-**

- PHENIX

- |y|<0.5

****sNN = 200 GeV

## Raw Invariant Mass Distribution from Data -II

- Invariant Mass (GeV/c2)

****sNN = 200 GeV

- |y|<0.5

- STAR Preliminary

- STAR Preliminary

- STAR Preliminary

- STAR Preliminary

- STAR Preliminary

- Λ(1520)

- Λ(1520)

- Minimun bias
- p+p

- Minimun bias p+p

- Minimun bias
- p+p

- 0-10% Au+Au

- 30-50% Au+Au

- 0.9 **≤** p**T** **<** 1.5 GeV/c

- 0.8 **≤** p**T** **<** 1.4 GeV/c

- 0.8 **≤** p**T** **<** 1.3 GeV/c

- Statistical error only

- 0.4 **≤** p**T** **<** 2.0 GeV/c

- Δ**++**

- Δ**++**

- Invariant Mass (GeV/c2)

- Invariant Mass (GeV/c2)

- Invariant Mass (GeV/c2)

- Invariant Mass (GeV/c2)

## Raw Invariant Mass Distribution from Data -III

- STAR Preliminary

- STAR Preliminary

- K***0**

- K***±**

- Minimun bias
- p+p

- Minimun bias
- p+p

- 0.8 **≤** p**T** **<** 3.5 GeV/c

- 0.1 **≤** p**T** **<** 1.5 GeV/c

- STAR Preliminary

- 0.0 **≤** p**T** **<** 3.2 GeV/c

- 0-10% Au+Au

- K***0**

- |y|<0.5

****sNN = 200 GeV

- Statistical error only

- 40-80% Au+Au

- 0.6 **≤** p**T** **<** 08 GeV/c

- Minimun bias p+p

- 0.6 **≤** p**T** **<** 08 GeV/c

- STAR Preliminary

- STAR Preliminary

## Phase Space

- P. Braun-Munzinger *et.al.*, CERES Int. Note, March 2000, unpublished; E.V. Shuryak and G.E. Brown, Nucl. Phys. A 717 (2003) 322; P.K. Kolb and M. Prakash, nucl-th/0301007; H.W. Barz *et al.*, Phys. Lett. B 265, 219 (1991); R. Rapp, hep-ph/0305011.

- M = Invariant Mass; pT = transverse momentum; T = Temperature
- pp ****** **particle composition reasonably reproduced by statistical model ****** **T = 160 MeV
- 	F. Becattini, Nucl. Phys. A **702**, 336 (2002); Z. Phys. C **69**, 485 (1996); F. Becattini and U. Heinz, Z. Phys. C **76**, 269 (1997)
- Au+Au ****** **between chemical and kinetic freeze-out ****** **resonances formed until particles too far apart** ******** **resonances emitted**        **T = 120 MeV
- 	E.V. Shuryak and G.E. Brown, Nucl. Phys. A 717 (2003) 322

##  K*0 Mass and Width

- K***0** mass **** shifted in p+p and Au+Au at low pT
- K***0** width **** agrees with the MC (GEANT) calculation
- Systematic and statistical error added in quadrature

- STAR Preliminary

- STAR Preliminary

- |y|<0.5

****sNN = 200 GeV

- PDG value

- PDG value

- pp

- pp

- AuAu

- AuAu

##  Δ++ Mass and Width

- p+p at ****s = 27.5 GeV ****** **M**Δ****++** = 1225 ± 2 MeV/c2
- Δ**++**** **mass **** lower in p+p and Au+Au at low N**ch**
- Δ**++**** **mass ****** **increases with increasing N**ch **
- Statistical errors only

- PDG value

- Δ**++** Mass GeV/c**2**

- Δ**++** Width GeV/c**2**

- dNch/dη

- dNch/dη

- STAR Preliminary

- STAR Preliminary

- pp

- 0.6 ≤ pT < 1.6

- 0.6 ≤ pT < 1.6

****sNN = 200 GeV

- |y|<0.5

- pp

- pp

- AuAu

- AuAu

##  ρ0 Mass

-  p+p at ****s = 27.5 GeV ****** **M**** = 762.6 ± 2.6 MeV/c2
-  PDG average hadroproduced ρ**0** ****** **M**** = 769.0 ± 0.9 MeV/c2
- PDG average e+e- ρ ****** **M**** = 775.9 ± 0.5 MeV/c2
- ρ**0**  mass p**t**** **dependent and lower than previous p+p measurement in both p+p and peripheral Au+Au collisions
- ρ**0**  mass high multiplicity** **p+p** **lower than minimum bias p+p ****** **multiplicity dependent
- Systematic errors ****** **common and correlated between p+p and peripheral Au+Au
- ρ**0**** **width **** no sensitivity for systematic study

- 10% of minimum bias p+p for |η|<0.5

****sNN = 200 GeV

- |y|<0.5

- STAR Preliminary

##  Possible Explanations for Mass Shift - I

- nucleons, hyperons and baryon resonances
- pions, kaons and ρ**0**-mesons
- t-channel exchanges
**** Distortion of the ρ**0** spectral shape **** mass shift and/or broadening

- -23 MeV/c2 shift in the ρ**0 **mass

- -38 MeV/c2 shift in the ρ**0** mass
- due to t-channel attraction

- R. Rapp, hep-ph/0305011

- E.V. Shuryak and G.E. Brown, Nucl. Phys. A 717 (2003) 322

-  Possible Explanations for Mass Shift - I

- Δ**++** ****** **different from** **ρ**0** ****** **mass should increase!** **(prediction)

##  Possible Explanations for Mass Shift - II

- 3. Bose-Einstein correlations between ρ**0**** **decay daughters and pions in the surrounding matter can also distort the resonance shape                                                                                  G.D. Lafferty, Z. Phys. C 60, 659 (1993); R. Rapp, hep-ph/0305011; S. Pratt *et al*., nucl-th/0308087.

-  Possible Explanations for Mass Shift - II

- Interference

##  Spectra - I

- Au+Au and K***0**, Λ(1520)** ** p+p **** spectra fit to exponential in m**T**-m**0**
- p+p** ****** spectra fit to power-law

- K***0**

- K***±**

****sNN = 200 GeV

- STAR Preliminary

-  pp minbias

- |y|<0.5

- STAR Preliminary

- STAR Preliminary

-  ρ**0**
-  f**0**

- Statistical error only

- K***0**

- Λ(1520)

-  pp minbias

- STAR Preliminary

- Au+Au

- p+p

- p+p

- Au+Au

##  Spectra - II

- Δ**++**

- Statistical error only

- Central Pb+Pb

- NA49 Preliminary

- Φ

- Φ

****sNN = 200 GeV

- |y|<0.5

- Au+Au and Σ(1385) p+p **** spectra fit to exponential
- p+p** ****** spectra fit to power-law

- Σ(1385)

- STAR Preliminary

****sNN = 200 GeV

****sNN = 200 GeV

-  pp minbias

- STAR Preliminary

- Au+Au

- Au+Au

- p+p

- p+p

##  Particle Ratios – Beam Energy Dependence

**** No strong energy and system size dependence (except K***0**/K**-**)

- STAR Preliminary

- STAR Preliminary

- STAR Preliminary

- STAR/NA49 Preliminary

##  Particle Ratios – Multiplicity Dependence

- Φ/K- independent of centrality ****** **Φ not produced via kaon coalescence ?
- Cross-section ****** **regeneration or rescattering ?

-  M. Bleicher *et al.* J. Phys. G 25 (1999) 1859

-  Particle Ratios – Multiplicity Dependence

- Statistical and systematic errors added in quadrature

-  σ(Kπ)

-  σ(ππ)

-  σ(πp)

##  Time between Chemical and Kinetic Freeze-out

- If rescattering is the dominant process,
- And the time between chemical and kinetic freeze-out should be Δt ~ 3 fm
- If regeneration is the dominant process, Δt > 3 fm

##  Thermal Models - I

- Chemical freeze-out

- Kinetic freeze-out

- Chemical = Kinetic
- freeze-out

-  m**ρ**=770MeV

-  m**ρ**=700MeV

- Statistical and systematic errors added in quadrature

****sNN = 200 GeV

- Au+Au

##  Thermal Models - II

- Statistical and systematic errors added in quadrature

- Chemical freeze-out

- Chemical freeze-out = Kinetic freeze-out

****sNN = 200 GeV

- Thermal calculations **** Do not reproduce ratios of short-lived resonances

- Au+Au

## Summary

- ρ**0**, K***0**** **and** **Δ**++**** ******** **mass shift observed in p+p and Au+Au collisions even after phase space correction
- Δ**++**** ******** **width broadening in central Au+Au collisions
- Mass shift expected due to in-medium modifications, interference and Bose-Einstein correlations ?
- Φ/K- independent of centrality ****** **Φ not produced via kaon coalescence ?
- Short-lived resonances ****** **Regeneration and daughter rescattering ****** **driven by hadronic cross-sections ?
- Resonances can provide information on the collision dynamics

## Outlook

- What’s next?
- We need:
- Systematic study of K***0** and Δ**++**** **mass and width** **in Au+Au
- ρ**0** in central Au+Au
- Λ(1520), Σ(1385), Ξ(1530)... Other higher state resonances...
- High-p**T** and v**2** measurements of resonances
- Leptonic Channel
- Φ, ρ, ω...
- Φ, ρ ****** **Comparison between leptonic and hadronic channels in Au+Au!!!
- Requires
- Large statistics **** RUN 4 @RHIC
- RHIC Upgrades
- Low mass dileptons **** PHENIX
- TOF **** STAR

## Experimental References

- H. Zhang** ******** **ρ**0**(770) , K*****(892)**, **Δ**++**(1232) STAR ****** **Poster QM2004
- S. Salur ****** **Σ(1385) STAR ****** **Poster QM2004
- C. Markert ****** **Λ(1520) STAR ****** **Talk QM2004
- J. Ma ****** **Φ(1020)** **STAR ****** **Poster QM2004
- L. Gaudiche ****** **Λ(1520) STAR ****** **SQM2003
- P. Fachini** ******** **f**0**(980) STAR ****** **SQM2003
- R. Seto ****** **Φ(1020)** **PHENIX ****** **Talk QM2004
- D. Mukhpadhyay ****** **Φ(1020)** **PHENIX ****** **QM2002
- C. Maguirre ****** **Φ(1020)** **PHENIX ****** **Poster QM2004
- Marek Gazdzicki ****** **Φ(1020)** **NA49 ****** **Talk QM2004
- V. Friese ****** **Φ(1020)** **NA49 ****** **SQM2003