# Presentation: 303765

## Why would I want to look at strange particle production?

- “Truth is **ALWAYS** strange”
- Lord Byron (1788-1824)

## Strangeness enhancement    

- General arguments for enhancement:
- 1. Lower energy threshold
- 	         *T**QGP* > *T**C* ~ *m**s **= *150 MeV
- Note that strangeness is conserved in the strong interaction
- 2. Larger production cross-section

- Strange particles with charged
- decay modes

- Enhancement is expected to be more pronounced for
- multi-strange baryons and their anti-particles

- Arguments still valid but now use strange particles for MUCH MORE.

## A theoretical view of the collision

- Tc – Critical temperature for transition to QGP
- Tch– Chemical freeze-out (Tch  Tc) : inelastic scattering stops
- Tfo – Kinetic freeze-out     (Tfo  Tch): elastic scattering stops

-  Hadronic ratios.
-  pT spectra.
-  Resonance production.
-  Partonic collectivity.
-  High pT measurements.

- 3

- 2

## The search

**proton**

**pion**

**Primary**
**vertex**

## PID over large pT range

***STAR Preliminary***

***STAR Preliminary***

- K

- 

- K*

- STAR Preliminary

- K0s

- 

- 

- Preliminary

- STAR Preliminary

- 

## Collective motion in Au-Au

**Collective motion in Au-Au**

- _data / power law_

- not absolute
- mT scaling...

- but if you rescale

- not in Au-Au

- _data_

**Kinetic Freeze-out**

-  Large flow, lots of re-interactions, thermalization likely
-   ,K,p: Tkin decreases with centrality , : Tkin = const.

- Hydro does not need different T for multi-strange
- Freeze-out T different  – Is blastwave realistic?

- Are re-interactions till freeze-out realistic either?

- Blastwave parameterization

- STAR Preliminary

## Strange baryon production at SPS

- A clear evolution of shape of  is visible.
- No big change of shape of  and  with energy.

- 158 AGeV

- 80 AGeV

- 40 AGeV

- 30     AGeV

-    

- preliminary

- preliminary

- preliminary

- NA49 Pb-Pb Collisions – C.Meurer QM2004

- Due to baryon transport from beam to mid-rapidity

**Baryon transport to mid-rapidity**

-  Clear systematic trend with collision energy

-  Very similar trend between heavy ion and p-p

-  62.4 GeV data fits into pattern

- E866 -

-  At RHIC top energies ~25 TeV is stopped for particle production
- That’s ~75% of the beam energy – plenty around for making strangeness

## Energy (in)dependence of yields

- *Refs: Physical Review Letters 89 (2002), 092301
-             nucl-ex/0206008, nucl-ex/0307024

**               ****Centrality regions: ****	****NA57:****   ****0-5% (********K), 0-12% (********)**
**	****	****      ****	****STAR*:**** ****0-5% (********), 0-6% (K), 0-10% (********)**

- T, μB and V can all vary with energy, but in such a way as to ensure Λ, Ξ- yields stays constant
- Change in baryon transport reflected in anti-particles and K

## What can Kaons tell us?

- Kaons carry large percentage of strangeness content.
- 	K- = us
- 	K+ = su
- Ratio tells about baryon
- transport even though not a baryon.

- By varying rapidity range can study many different physics regions – Especially at RHIC

**Statistical hadronic models**

- Assume thermally (constant Tch) and chemically (constant ni) equilibrated system at chemical freeze-out
- System composed of non-interacting hadrons and resonances
- Given Tch and  's (+ system size), ni can be calculated in a _grand canonical ensemble_
- Obey conservation laws: Baryon Number, Strangeness, Isospin
- Short-lived particles and resonance feed-down need to be taken into account

*Minimization of difference between calculated ratios and experimental data*

- Tch, B

**Constraining the parameters**

## Works very well

- Fit to NA49 data
- [Becattini et al.: hep-ph/0310049]

- STAR Preliminary
- Au-Au 200 GeV

**T****ch**** =  160********5 MeV **
******s****  =   0.99********0.07**

******B****  =  24 ******** 5 MeV**
******s****  =  1.4 ********1.4 MeV**

******B****  =   247******** 8MeV**

**T****ch**** =  158********2 MeV **
******s****  =   0.84********0.03**

## Tch systematics

**T****ch**** systematics**

- Hagedorn (1965):
- If the resonance mass spectrum grows exponentially
-     (and this seems to be the case):
- There is a maximum possible temperature for a system of hadrons.

- [Satz: Nucl.Phys.
-  A715 (2003) 3c]

- filled: AA
- open: elementary

- Blue – Exp. fit
- Tc= 158 MeV

- r(m) (GeV-1)

- Green - 1411 states of 1967
- Red – 4627 states of 1996

- Seems he was correct – don’t get above Tch ~170 MeV

- m

## This exercise in “hadro-chemistry”
Applies to final-state (ordinary) hadrons
Does not (necessarily) indicate 
Deconfinement
Says nothing about how
 or when the system got 
 there or its dynamical
 properties
A smooth continuation of trends seen 
at lower energies
in p-p, even e+e-

- Applies to final-state (ordinary) hadrons
- Does not (necessarily) indicate
- Deconfinement
- Says nothing about how
-  or when the system got
-  there or its dynamical
-  properties
- A smooth continuation of trends seen
- at lower energies
- in p-p, even e+e-

**Limits of thermodynamics**

## Wroblewski factor

- P. Braun-Munzinger, J. Cleymans, H.Oeschler, K. Redlich, NPA 697(2002) 902

- Produced strange quarks to light quark ratio

## Elementary collisions thermal?

**Elementary collisions thermal?**

*Beccatini, Heinz, Z.Phys. C76 (1997) 269*

- Also Seems to work well ?!

**Statistics ******** Thermodynamics**

- Ensemble of events constitutes a statistical ensemble
- “Phase Space Dominance”

- A+A

- One (1) system is already statistical !
-  We can talk about pressure
-  T and μ are more than Lagrange multipliers they have physical meaning

- p+p

## How do we know when its thermal?

**How do we know when its thermal?**

-  Canonical suppression
- increases with decreasing energy

-  Canonical suppression increases with increasing strangeness

- σ(Npart) / Npart = ε σ(pp)         ε > 1 Enhancement!

-  When reach grand  canonical limit strangeness will
-  saturate.

- _Canonical (small system i.e. p-p)_:
- 	Quantum Numbers conserved exactly.
-     Computations take into account energy to create companion to ensure conservation of strangeness.
- 		Relative yields given by ratios of phase space volumes
- 				Pn/Pn’ =n(E)/n’(E)
- _Grand Canonical limit (large system i.e. central AA)_:
- 	 Quantum Numbers conserved on average via chemical potential Just account for creation of particle itself.
-    The rest of the system “picks up the slack”

- Not new idea pointed out by Hagedorn in 1960’s

## SIS energies

- Pion density
- n() = exp(-E/T)* *
- Strangeness is conserved!
- Kaon density – need to balance strangeness
- NN     N Λ K+
*   **n(K**+**) = exp(-E**K+**/T)**
*     **(g**K**V**  ∫ ... exp[-E**K**/T] + *
*g******V** ** **∫** ... exp[-(E**Λ**-**μ**B**)/T])*

- KaoS ( Au-Au 1 GeV)  M. Mang et al.

- J. Cleymans, H. Oeschler, K. Redlich, PRC 59 (1999)

- C:    N ~ V2 (V 0)
- GC: N ~ V  (V )
- Assume V ~ Npart
- Pions/Apart   constant
-           grand-canonical!
- Kaons/Apart   rising
-           canonical!

- In agreement with T=60 MeV

## Top SPS energies

- We seem to understand what is happening

**Top SPS energies**

## But then at √s= 8.8 GeV

- C to GC predicts a factor 4 - 5 larger Ξ- enhancement at √sNN =8.8 GeV than at 17 GeV

- Perhaps yields don’t have time to reach limit – hadronic system?
-          Need to see thermal fit.  (word is it is not too bad)

- NA57 (D. Elia QM2004)

## And then at 200 GeV...

- But does it over saturate or ONLY just reach saturation?

**And then at 200 GeV...**

## What happens to other particles?

-    – show Npart scaling
- p – show slight increase
- 	phase space suppression
- of baryons?
-  K0s – show increase
- only small phase space
- suppression of strange
- mesons?

- What about the 

- Contains s and s quark, so not strange
- should show no volume dependence

##  Can we find a scaling?

- The larger strangeness content scales better with Nbin
- Still not perfect
- Scaling dependant on pT?

- The more strangeness you add to the baryon the less it scales with Npart

- 100    200    300  Npart

**R****AA ****of strangeness**

- Phase space suppression of strangeness in p-p
- plus other effects all pT dependent – need to disentangle

- STAR Preliminary

## Summary 

- The more we learn the less we know!
- Seems that  and  freeze-out differently as a function of centrality – except at SPS...
- Net baryon density depends on collision energy not system
- Appear to have strangeness saturation at most central top RHIC but not before
-  What happens at SPS?

- Seems our simple thermal pictures are only approximately correct.
- The devil is in the details but we have the data to figure it all out.

## Backup and stuff

- That’s really the end