# Presentation: 170609

##  Overview of Strangeness Production for the STAR Experiment... 

*Anthony Timmins for the STAR Collaboration*

## Contents

- Bulk Strangeness Production...
- Thermal Model Comparisons...
- Mid-*p**T* Particle Spectra...
*v**2* Measurements...
- Low Energy Scan...
- Fragmentations Functions in p+p...
- Summary...

## Canonical formalism (Phys. Lett. B 486 (2000) 61) reproduces various features...
Thermal model for hadron gas
Insists strangeness conservation strictly met 
Strangeness production more suppressed in smaller system
Assumes system volume  Npart

Observed strangeness enhancement not unique to QGP formation...

What can the data at RHIC tell us?

**Canonical formalism** (*Phys. Lett. B 486 (2000) 61*) reproduces various features...
- Thermal model for hadron gas
- Insists strangeness conservation strictly met
- Strangeness production more suppressed in smaller system
- Assumes system volume  ***N**part***
- Observed strangeness enhancement **not unique to QGP formation...**
- What can the data at RHIC tell us?

**Bulk Strangeness Production***What did we learn at the SPS?*

**CERN Press statement:** "The combined data coming from the seven experiments on CERN's Heavy Ion programme...  **We now have evidence of a new state of matter where quarks and gluons are not confined**. There is still an entirely new territory to be explored concerning the physical properties of quark-gluon matter. **The challenge now passes to the Relativistic Heavy Ion Collider at the Brookhaven National Laboratory** and later to CERN's Large Hadron Collider."

**CERN Press statement:** "The combined data coming from the seven experiments on CERN's Heavy Ion programme...  **We now have evidence of a new state of matter where quarks and gluons are not confined**. There is still an entirely new territory to be explored concerning the physical properties of quark-gluon matter. **The challenge now passes to the Relativistic Heavy Ion Collider at the Brookhaven National Laboratory** and later to CERN's Large Hadron Collider."

**CERN Press statement:** "The combined data coming from the seven experiments on CERN's Heavy Ion programme...  **We now have evidence of a new state of matter where quarks and gluons are not confined**. There is still an entirely new territory to be explored concerning the physical properties of quark-gluon matter. **The challenge now passes to the Relativistic Heavy Ion Collider at the Brookhaven National Laboratory** and later to CERN's Large Hadron Collider."

**Notes:**
1)One of the major findinngs in the SPS progrmams
	Led to statement....
2) Enhancement factor = yields/Npart divided by yields/Npart PP  at 17.3 GeV 
	Lagre deviations observed from pp
		Factor of 20 for Omega,
3) Finish on 3rd point....

## Bulk Strangeness Production Cu+Cu and Au+Au 200 GeV...

**Bulk Strangeness Production ***Cu+Cu and Au+Au 200 GeV...*

**Enhancement** in strangeness production has been established for Au+Au at 200 GeV
- Canonical formalism again reproduces various features...
- AGS and SPS showed **strangeness** systematics **don’t scale** with ***N**part*** in **light** and **heavy** systems
- Does this apply to Cu+Cu and Au+Au at 200 GeV?
- Higher yields in (mid) central Cu+Cu at given ***N**part***
**Inconsistent** with Canonical formalism...
- Also applies to **non strange  sector**...

*arXiv:0809.0823v1  [nucl-ex]*

**Notes:**
3) Will see this later....

## Bulk Strangeness ProductionCu+Cu and Au+Au 62 GeV...

- What about Cu+Cu and Au+Au 62.GeV?
-  and K0S exhibit **similar** patterns as **200 GeV**..
**Same** applies to **multi-strange** sector...

*Marcelo Gameiro Munhoz, SQM 2008*

*STAR Preliminary*

## Bulk Strangeness Production The  particle...

** particle shows **above unity enhancement** for Cu+Cu and Au+Au 200 GeV
- Contrary to naive interpretation of the Canonical model...
**Enhancement=1** for particles with **closed strangeness**...
*** *enhancement sits **between ******** and ******
- Dynamical effect boosting ** yield*?*
- Core/Corona effect?
*arXiv:0805.0098v2*
- Differences between Cu+Cu Au+Au not observed within errors for 62 and 200 GeV...

* **J. Phys. G. Nucl. Part. Phys. 35 (2008) 044031*

## Bulk Strangeness ProductionEPOS and AMPT comparisons...

**EPOS** (*Phys. Rev. Lett. 98 (2007) 152301*)
**Core** hadron production
- Aims to mimic QGP
- High density region follows statistical emission...
- Upon hadronization, strangeness oversaturated with ***s*>1
**Corona** hadron production
- Superposition of p+p collisions
- Strangeness under-saturated with s<1
- Strangeness **conservation** precisely met...
**AMPT** (*Phys.Rev. C72 (2005) 064901*):
- HIJING based model
**Soft** hadron production is from by nucleon excitation and string breaking..
**Hard** hadron production from (mini) jets
- Mini-jet partons and newly produced hadrons allowed to **rescatter**...

*STAR Preliminary*

*arXiv:0810.0017v1 [nucl-ex]*

## Bulk Strangeness Production EPOS and AMPT comparisons...

**Bulk Strangeness Production ***EPOS and AMPT comparisons...*

*STAR Preliminary*

**Model Comparisons**
- Both models reproduce key qualitative features for , anti- and K0S
- Rising per participant yields for a given system
**Higher** yields at given ***N**part**** *for* *Cu+Cu
**EPOS** does **better** for strange **baryons**...
- Multi-strange predictions?

*arXiv:0810.0017v1 [nucl-ex]*

## Bulk Strangeness Production Mid-rapidity s+s rates...

- Approximate **total** strangeness production at* y*~0 at 200 GeV
- Add yields from single and multi-strange particles
**AMPT shows...**
- If main **s+s** production is from string fragmentation in **initial collisions**
- Mechanism **sufficient** in producing **s+s** yield for Cu+Cu and Au+Au...
**EPOS** **shows...**
- Hadronization of **s+s** quarks may require core+corona mechanism
- Gives better description of strange baryon yields compared to AMPT

*arXiv:0810.0017v1 [nucl-ex]*

*STAR Preliminary*

**Notes:**
mod

## Thermal Model ComparisonsChemical freeze out...

**Thermus** package (*hep-ph/0407174*) used to extract statistical parameters from particle ratios ...
**Canonical** and **Grand** **Canonical** implementations compared to data
- Chemical freeze-out temperature constant of over all systems and centralities...

*Jun Takahashi SQM 2008*

## Thermal Model ComparisonsStrangeness saturation...

*Jun Takahashi SQM 2008*

*STAR Preliminary*

***S* indicates **deviation** for strangeness production from **equilibrium** expectations
- Despite **higher** strangeness production for Cu+Cu at given *<N**part**>*
- Cu+Cu and Au+Au lie on the **same** trend...
***S* controlled by K/ ratio?
- Also lies on **same** trend for Cu+Cu and Au+Au...

## Mid-pT  SpectraRCP in Cu+Cu 200 GeV...

***R******CP*** contrasts production per binary collision in central and peripheral collisions
- Systematic **differences** found for mid-*p**T* **baryons** and **mesons** in Au+Au 200 GeV
**Interpretation**: Production  from coalescence more favorable for baryons
- Such **differences** apply to Cu+Cu collisions...
*R**CP* < 1 at *p**T *>~ 5 GeV:* * **Jet quenching** occurs in **central Cu+Cu...***** ***

*STAR Preliminary*

* **J. Phys. G. Nucl. Part. Phys. 35 (2008) **104074*

## Mid-pT  SpectraRCP in Cu+Cu 62 GeV...

*Marcelo Gameiro Munhoz, SQM 2008*

**Mid*****-p******T  *****Spectra***R**CP** in Cu+Cu 62 GeV...*

- How Does*** R******CP*** **change** with **energy** for Cu+Cu 62 and 200 GeV collisions?
-  and K0S lie on the **same** curve
- Same pattern observed for Pb+Pb 17.4 GeV, Au+Au 62.4 GeV 200 GeV
-  **Coalescence** in all systems?

**Notes:**
2) Animate the 200 GeV particles in after 62.....

## Mid-pT  SpectraParticle ratios...

- Previous Au+Au data shows / ratio consistent with coalescence predictions
- Applies to Cu+Cu...
- Anti-Baryon/Baryon ratios **constant** for all *p**T* in central Cu+Cu collisions
- / and / **ratios** lie on the **same** trend
- May have some relevance in the coalescence framework (*nucl-th/0801.2265*)

* **J. Phys. G. Nucl. Part. Phys. 35 (2008) **104074*

## v2 MeasurementsProbe of initial conditions...

- Characterizes the conversion from **initial** **spatial** anisotropy to **momentum** anisotropy...
- Initial **hydrodynamic** predictions appeared to **describe** mass and *p**T* dependence for Au+Au 200 GeV collisions
- What is observed for Cu+Cu?

*Hiroshi Masui, SQM 2008*

## v2 MeasurementsQuark scaling...

**Quark v****2**** **(*v**2**/n**q**) vs ***Quark*** ***Kinetic Energy***** ****(m**T** - mass)/n**q*
- Scaling expected in coalescence framework where kinetic energy is conserved (*Phys. Rev. C 75 (2007) 03190*)
- Au+Au 200 GeV results showed this scaling applied across full *p**T* for minbias collisions...
- Cu+Cu 200 GeV collisions show..
- Particles lie on same curve for 0-60%
- Also applies to 0-20% and 20-60%....

**Notes:**
1) Indrioduce plot after first after first point 

## v2 MeasurementsHydro-limit not reached at RHIC?

***v******2***** Measurements***Hydro-limit not reached at RHIC?*

**Transport theory**
- Gives v2/ as a function of system density...
- Finite Knudsen number ***K*** indicates **deviation** from ideal hydro
*K*=0 Ideal hydro, *K* > 0  Non-ideal hydro
- Curve shows **decreasing** ***K*** with increasing system density...
- Hydro limit not reached for Cu+Cu and Au+Au strange particle *v**2*?

*Yuting Bai**, SQM 2008*

**Notes:**
Right panel: Transport model fits v2 to data; division of v2/epsilon-hydro tells you how far the system 

## Low Energy ScanMotivation...

- Various lattice QCD calculations prediction a thermodynamic **critical point**
- QGP  hadron gas **phase transition** becomes **first order** at the higher values of ***B*
- RHIC has the capability to provide heavy-ion collisions with sNN ~ 5  50 GeV
- Large acceptance detector (**AKA STAR**) best placed to investigate...
- Proposed **scan** aims to cover all **predicted critical points with respect to ***********B***

*Lokhesh Kumar, SQM 2008*

**Notes:**
Very much the future of RHIC program...

## Low Energy ScanMultiplicity distributions...

- 3000 Au+Au 9.4 GeV collisions recorded early 2008 in 4 hours
- Measured** multiplicity distribution **well** reproduced **by** simulation**:
- Monte Carlo Glauber + Kharzeev-Nardi

*Lokhesh Kumar, SQM 2008*

## Low Energy ScanK/ ratios...

- STAR’s K+/+ and K-/- and ratios sit on world trend
- Same applies to K-/K+, -/+ and p-/p+ ratios
- Year 1’s **Au+Au 19 GeV** results also consistent..
**STAR detector** very much **ready** to take more data...

## Fragmentation Functions in p+pCharged hadron and strange meson and baryon...

**Fragmentation Functions in p+p***Charged hadron and strange meson and baryon...*

*arXiv:0809.3769v1*

- Full **jet reconstruction** in p+p 200 GeV allows for measurement of **fragmentation functions**
- Number density of given hadron with given ***p******T*** **per jet** with energy ***E******jet***
- Expressed in terms of*** *********
- Charged hadron fragmentation functions compare well with **PYTHIA**...
- True for all jet energies..
- What happens for strangeness?
- QCD models predict mass ordering of ********* ***
*Phys. Lett. B 273 (1991) 319*
**Not reproduced** **by data!**
- Errors still under study...

**Notes:**
This is somethinh a little, but in my view this reasserts the importantance of strangeness production in our understanding of QCD....
Logarithmic measure of momentum...
2) 

## Fragmentation Functions in p+p/K0S as a function of  and pT...

- What about the /K0S ratio in jets?
- Approaches **one** at **mid-*****p******T**** *from high-*p**T *..
***<N******charge******>*** dependence observed for  **inclusive** mid-*p**T** *ratio
- Higher *<N**charge**>* in p+p event, higher probability of hard parton scatter...

**10< E****jet****< 15 GeV**

## Summary

**Bulk Strangeness Production in Heavy-ion Collisions **
- Yields do not scale with <Npart> in Cu+Cu and Au+Au: reproduced by AMPT and EPOS at 200 GeV
- Processes in initial collisions appear sufficient in producing bulk strangeness, core-corona needed to get better agreement for strange baryon yields
*T**ch *and* ****S* lie on same trend for Cu+Cu and Au+Au as a function of *<N**part**>*
**Mid-*****p******T***** Spectra **
- Baryon-meson RCP differences apply to Cu+Cu collisions
- Cu+Cu / ratios described by coalescence predictions
**v****2**** Measurements**
- Quark scaling holds for strange meson and baryon v2 vs pT in Cu+Cu
- Transport theory indicates hydro limit may not be reached in heavy-ion collisions
**Low Energy Scan**
- STAR has collected first data
- Global consistency already achieved with other experiments
**Fragmentation Functions in p+p**
- Observed mass ordering of 0 contrary to QCD expectations
- /K0S ~1 at *p**T* 2-3 GeV/c for jets

## Summary

**Thermal production of particles at RHIC**
- 	*Jun Takahashi*
**S****trange and multi-strange hadron production in **
**Cu+Cu collisions at 62.4 GeV at RHIC **
**	***Marcelo Gameiro Munhoz*
**System size, energy and centrality dependence **
**of strange hadron elliptic flow at STAR **
- 	*Hiroshi Masui*
**Anisotropic flow: indications for incomplete **
**thermalization**
- 	*Yuting Bai*
*	*
**First results from Au+Au collisions at 9.2 GeV in **
**STAR **
- 	*Lokesh Kumar*

**

*K*

**