# Presentation: 223372

## Strangeness Report

- Federico Antinori
- INFN Padova - Italy

## Contents

- 	 I concentrate on strange particle abundances (yields and ratios)
- QGP predictions
- Enhancement pattern
- Hadronic transport
- Thermal models
- Beyond equilibrium?
- The Φ
- Extras
- Conclusions
- not covered: 	Resonances (Fachini), Spectra (Velkovska), Flow (Retiere), 		Pentaquarks (Jaffe), HBT (Magestro)

## Two historic QGP predictions

- restoration of  symmetry -> increased production of s
- mass of strange quark in QGP                                              expected to go back to current                                                        value
- mS ~ 150 MeV ~ Tc
- copious production of ss pairs,                                                 mostly by gg fusion
- 	[Rafelski: Phys. Rep. 88 (1982) 331]
- 	[Rafelski-Müller: P. R. Lett. 48 (1982) 1066]
- deconfinement  stronger effect for multi-strange
- can be built using uncorrelated s quarks produced in independent microscopic reactions
- strangeness enhancement increasing with strangeness content
- 	[Koch, Müller & Rafelski: Phys. Rep. 142 (1986) 167]

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## @ top SPS (NA57, √sNN = 17.3 GeV)

- @ top SPS (NA57, √sNN = 17.3 GeV)

- and (yesterday’s news) @ low E SPS (NA57, √sNN = 8.8 GeV)

- and indeed...

- qualitatively similar picture emerging from 8.8 to 200 GeV

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## Alternative definition of pA enhancement?

- e.g.: [Fischer: Nucl. Phys. A 715 (2003) 118]
- two-component model of particle production:
- 	 in pA:  YpA = [/2 + 1/2] Ypp               ( = number of collisions)
- 			  = Npart Ypp/2
- enhancement “blamed” on projectile component only:

- 	_alternative enhancement_: F
- 	       YpA = [/2 + F/2] Ypp
- 	reasonable for baryon number transfer, but do e.g. strange quarks know if they come from projectile or target ?

- 	_usual enhancement_: E
- 	(Y/Npart)pA = E · (Y/Npart)pp
- 	 YpA = E [/2 + 1/2] Ypp

- then: (F – 1) = (E – 1) Npart
- 	 enhancement within pA appears even if pA yields  Npart

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## Hadronic transport

- Hadronic transport codes:
- do reasonably well on singly strange particles
- but fail to reproduce the production of multi-strange particles at SPS and RHIC
- see for instance:
- [Soff et al.: Phys. Lett. B471 (1999) 89],
- [C.Greiner: nucl-th/0208080 and references there],
- [STAR: nucl-ex/0307024],
- [Huovinen & Kapusta: nucl-th/0310051]
- they get closer if:
- masses are reduced towards chiral values
- 	or string tension is enhanced with respect to ee/pp/pA
- enhanced contribution from inelastic scattering during expansion
- Activity is still ongoing:
- e.g.: [Capella: nucl-th/0303045; Subrata Pal et al.: nucl-th/0106074]
- hadronic models are getting more and more exotic...

- [Huovinen & Kapusta: nucl-th/0310051]

- [Huovinen & Kapusta: nucl-th/0310051]

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## Meanwhile at the AGS...

- Nice new measurement: _Ξ__-__ production close to threshold_,                     Au-Au @ 6 A GeV (E895) [P.Chung et al.: nucl-ex/0302021]
- At this energy RQMD works fine!

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## Thermal fits

- Thermal fits don’t do too bad!
- e.g.: brand new @ RHIC 200
- Tch = 160  10 MeV
- μB  =  24  5 MeV
- 	(STAR Preliminary)

- relative particle abundances ~ as expected at thermodynamical equilibrium for grand-canonical system, _even for rare, multi-strange particles_

## T systematics

- it looks like Hagedorn was right!
- 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
- indeed, we don’t seem to be able to get a system of hadrons with a temperature beyond Tmax ~ 170 MeV!

- filled: AA
- open: elementary

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

## T vs μB systematics

- the extracted freeze-out points at SPS and RHIC lay very close to the predicted QGP phase boundary

## Canonical vs Grand Canonical

- Energy penalty to create a strange particle:
- _Canonical_:
- 	computed taking into account also energy to create companion to ensure conservation of strangeness
- _Grand Canonical limit_:
- 	just due to creation of particle itself. The rest of the system acts as a reservoir and “picks up the slack”

- removal of canonical suppression
- increases with strangeness
- ~ observed enhancements
- detailed centrality dependence not reproduced (very crude modelling)
- [Hamieh et al.: Phys. Lett. B486 (2000) 61]

- @ RHIC:
- decrease of enhancements from SPS predicted
- order of magnitude of enhancements close
- again, model for Vcorr vs Npart seems to be inadequate

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## Does this explain the observed enhancement pattern?

- a system _in eq._, if it is large enough, is in GC eq.,                         but being large in itself is not a sufficient condition for    being GC!
- if AA colls. were just a superposition of pp, they would have to be treated canonically all the same!
- the system must also know it is large...
- it must know that an Ω+ generated here can be compensated by, say, an Ω- on the other side of the fireball!
- what counts is the *correlation volume*
- “Canonical Suppression is removed!”
- an *observation*, not an *explanation*

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## How is Canonical Suppression removed?

- how does the system know it is large?
- how can information travel so quickly through the system?
-  not by conventional hadronic transport (no time!)
- natural if the system is coming                                      back from deconfinement
- two recent ideas:
- quantum coherence in the fireball [Stock: hep-ph/0312039]
- can it be developed into testable model?
- what about pA?
- multi-particle interactions [Braun-Munzinger et al.: nucl-th/0311005]
- only important close to phase boundary
- if true, we are actually *measuring* Tc
- microscopic mechanism to restore abundances to hadronic eq.

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## mid-rapidity multi-strange/Λ @ 40 GeV SPS 
	NA57 vs [Becattini: private communication]
s = 1, T from 4π fit to NA49 40 GeV [Becattini et al.: hep-ph/0310049]
using π±, K±, φ, Λ and Λ
Λ and Λ dN/dy from NA57 fix μB and normalization
Prediction of Ξ- Ξ+ Ω- and Ω+ dN/dy
total 2/dof = 1.4    against values measured by NA57 
No parameter for multi-strange
	again, not bad...

- 	NA57 vs [Becattini: private communication]
- s = 1, T from 4π fit to NA49 40 GeV [Becattini et al.: hep-ph/0310049]
- using π±, K±, φ, Λ and Λ
- Λ and Λ dN/dy from NA57 fix μB and normalization
- Prediction of Ξ- Ξ+ Ω- and Ω+ dN/dy
- total 2/dof = 1.4    against values measured by NA57
- No parameter for multi-strange
- 	again, not bad...

- An equilibrium *pre-*diction

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## Physics beyond equilibrium? look at fine details

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## Λ(1520)

- Λ(1520) deviates from sistematics (~ 1/2)
- e.g.: [Markert: J. Phys. G 28 (2002) 1753]
- we look for in-medium
- 	effects
- 	we take fits very seriously!

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

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## Resonances @ RHIC

- new: Λ(1520), K*(892), Δ(1232) in STAR at 200 GeV

- resonances show larger deviations from statistical fit
- rescattering vs regeneration?
- see talk by P. Fachini

## Non equilibrium: s

- 4π yield ratios sometimes preferred for thermal fits
- to be safe in case strangeness ends up too far away in rapidity from where originally produced
- (but can one assume global equilibrium with same T and _same μ__B_ at different rapidities?)
- in this case s ~ 0.7 - 0.8 must be introduced
- strangeness undersaturation factor:
- 	for each particle, a factor sN(s+s)
- 	e.g.: [Becattini et al.: hep-ph/0310049]
- could it also mimic residual canonical suppression?

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## Non equilibrium: s & q

- see e.g.: [Rafelski & Letessier: hep-ph/0309030]
- q controls overall abundance of qq
- olds becomes s/q
- w.r.t. previous, additional factor qB   for baryons
- fits get beautiful        e.g.: @ RHIC 
- 	[see also Becattini et al.: hep-ph/0310049]
- 	(but additional parameter)
- @ RHIC 130:
- q = 1.6 ± 0.2       s q = 1.3 ± 0.1
- strangeness actually enhanced  _above hadronic equilibrium values_?

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- pentaquark production (if statistical) would be particularly sensitive to need for q!
- additional q2 factor for Θ+ w.r.t. other models
- e.g.: [Letessier et al.: hep-ph/0310188, Becattini et al.: hep-ph/0310049]

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## Hyperon enhancements at 40 GeV

- enhancements vs Nwound steeper at 40 than at 160
- C to GC predicts a factor 4 - 5 larger Ξ- enhancement at 40 GeV than at 160, not seen in the data
- perhaps yields trying to shoot up but don’t go all the way?
- on the other hand, equilibrium fit not too bad... [Becattini: priv. comm]

- [Tounsi & Redlich: hep-ph/0111159]

- [Bruno (NA57): yesterday]

## Marek’s Horn

- Change of behaviour of K+/π+ in A-A around 30 GeV
- K-/π- has a smooth behaviour with energy
- Could this signal chiral transition?

## Brahms: K± vs y

- caution! K± sensitive to baryon density...

- [D. Ouerdane, PhD Dissertation, Copenhagen University, Aug. 03]

-         [Brahms: Phys. Rev. Lett. 90 (2003) 102301]

- ... and s [ = 2<ss>/(<uu>+<dd>) ] max. around 30 GeV:

- [Braun-Munzinger et al.: NPA697(2002)902]

- thin:   iso-s
- thick: freeze-out

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- so one expects a broad maximum in K+/π+ about there...
- but nothing so sharp!
- it looks like we have some anomaly...

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## Absolute values of hyperon dN/dy

- absolute values of Λ and Ξ+ dN/dy go up with √s...
- absolute values of Λ and Ξ- dN/dy               ~ constant from √sNN = 8.8 to 130 GeV !
- Statistical fits: T and μB only sensitive to particle ratios
- overall normalization of yields controlled by fitted V parameter
- T, μB and V all vary with energy, but in such a way as to ensure Λ, Ξ- yields stays constant ...
- there must be a simple reason ...

- see talk by D.Elia, Friday, P2

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## The mysterious Φ

- s2, but no C suppression

- the NA49 – NA50 discrepancy is still with us...
-  NA60 should provide           high stats, low pT Φ  μμ

- The mysterious Φ

- NA49: small deviation from PDG mass seen in all three Pb+Pb data sets, but not in pp

- K+K-

- μ+μ-

- see [NA49 (Friese): SQM 03]

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## First Φ signal from NA60

- First Φ signal from NA60

- peripheral In-In
- expected > 100k Φ  μ+μ-
- expected mass resolution:
- 	~ 20 MeV
- also looking at Φ  K+K-

- 

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## Φenix

- Φ  K+K- (min bias 200 GeV)
- Mass and width agree    within errors with             PDG values

**Yield**

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

- Φ  e+e- (min bias 200 GeV)
- _Preliminary yields_:

- see [Phenix (Maguire): SQM 03]

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## Extras...

- some results on spectra that I could not resist showing...

## Very low pT π, K, p from Phobos !

- tracks characterized by range and energy loss in Si layers
- particle id.
- momentum within 5%
- unique constraints for transport, hydro, thermal models

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## Rcp for multistrange !

- Φ seems to follow K0s more than Λ
-  meson-baryon, not mass?

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## v2 for multistrange !

- scaling seems to work
- (not for pions...)
-  parton recombination?

- scaled with n(quarks)

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## mT scaling in pp...

- not absolute...

- ...but if one rescales:

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## ... but not in Au-Au

- _data_

- _data / power law_

## Conclusions

- Evidence for high degree of chemical equilibration
- even for rare, multistrange particles
- QGP prediction !
- freeze-out curve traces expected phase boundary at SPS - RHIC
- hadronic transport does not seem to be able to do it   (no time!)
- RHIC opening up exciting new windows for strangeness !
- elliptic flow, high pT, high statistics reference data (pp, dAu)
- Strangeness perhaps enhanced above hadronic equilibrium !
- stand-alone smoking gun?

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- we must understand (non-)equilibrium
- we need highest possible precision data on yields and ratios (RHIC!)
- (we need theory to provide agreed statistical approach)
- we need to understand the Φ
- precision data from NA60 and Phenix
- we must understand what’s going on in the region          √sNN = 5 - 10 GeV
- low E SPS ?
- SIS 200 @ GSI !

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## Credits

- Many thanks for discussions and material to:

- Carlos Lourenço
- Djamel Ouerdane
- Emanuele Quercigh
- Jan Rafelski
- Karel Šafařík
- Reinhard Stock
- Julia Velkovska

- Francesco Becattini
- Rene Bellwied
- Giuseppe Bruno
- Helen Caines
- Domenico Elia
- Marek Gazdzicki
- Adam Jacholkowski

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