STAR STRANGENESS!

K0s

K+

(Preliminary)

What do we measure?

K+ (us) 494MeV ++ccm

K0s (ds) 498MeV ++ ccm

uds) 1116MeV p+- ccm

(dss) 1321MeV +- ccm

(sss) 1672MeV +K- ccm

0 (ss) 1020MeV K++K+ ccm

+ anti-particles + other more exotic resonances ((1520)!)

What do we measure (2)?

Particle yields

How much is created?

Spectra (dN/dy, dN/dpt, d2N/dydpt)

Where and when are they created and what are the dynamics?

Particle ratios

What are the chemical potentials?

Interferometry

How large is the source and how long did it exist?

Tfireball < Tc Hadron gas

Hard to make S 0 particles

+ N + K (Ethresh 530MeV) + K + (Ethresh 1420MeV)

Mtm phase space suppressedNeed to create 3 qq pairs

(initially there are no q) with similar momenta in a region already containing many quarks.

Why are we interested in Strangeness production?

Tfireball >Tc QGP

Easy to make s quarks E=2ms ( 300MeV)Free gluons

g-g fusion - dominate s s creation faster reaction time than qq

Pauli blocking may aid creation of s s quarks

( probably not true at high T, too many states).

¯

¯¯

¯

¯

¯

What is the best thing to measure?

While K’s carry ~70% of the strangeness they are easily produced in the final stage reactions as the hadrons in the expanding gas interact and

already show an enhancement over N-N collisions at energies too low

to form a QGP.

Want to look at the yields of multi-strange (anti-)baryons

production suppressed in Hadron Gas because

a) need large energy to create

b) need to create u d s where there are already many ud

c) need to create them in the same mtm phase space

Looking at the particle ratios ptells you the s/u ratio -> 1 if there is chemical equilibration

¯

¯¯¯

¯ ¯ ¯¯

Evidence for Strangeness Enhancement - WA97 results

Strange particle ratios

AGS > 1 and is higher than SPS.

Seems to be a clear strangeness enhancement between pA and AA

collisions at the SPS

Where are the strange particles produced?

If heavy ion collisions were just N-N reaction superpositions

(uds) concentrated in the baryon rich projectile regions

(uds), K0s(ds) peaked at mid-rapidity

due to their sea-quark content

PROBLEM!

What if there is any stopping?

Baryon-rich projectile and baryon-free

“fire-ball” region become merged

Have to separate fire-ball creation from that merely due to associated production

Stopping and the net distribution

We expect that the net

yield should follow the net p yield.

However there is a distinct “bump” about mid-rapidity in the

distribution that is not observed in the p.

Is this NEW physics?

Or is it evidence of feed-down into the channel that has yet to be corrected properly. NA49 have

recently obtained and results

which may help answer this question

Freeze out “Temperature” vs Mass

From two particle correlation studies you can extract 2/T from R.

~50% transverse kinetic energy goes into radial flow.

-> Very important for any global thermo-chemical analysis

Tprop = 120 ±10MeV

= 0.5

N.B

(Na49) T=305 MeV

(Na50) T=213 MeV

Also 3x smaller yield

K+/- +/- +

K+, K- High Pt identification via “Kink”Analysis

Finding V0s

STAR TPC Acceptance for B=0.25T (Half Field)

—

The peaks in their glory

332K Events |z|<50cm, |y|=0.5, GeV/c

0.16/event 0.13/event

154K MinBias Events |z|<50cm, |y|=0.5, GeV/c

And there’s more

0.0009/event0.2/event

STAR STRANGENESS!

K0s

K+

(Preliminary)

In case you thought it was easy…

Before

And Voila!!!!

After

• Large peaks at 2 o’clock and 8 o’clock

• TPC pad row “floating”

Fine way to calibrate a detector..

Now in ExB “Hell”

• Baryons distributions carry information related to– stopping and particle production– baryon chemical potential– thermal equilibrium

• p/p ratio should be sensitive•

• Last call for RHIC predictions (nucl-th/9907090) at sNN = 200 GeV :– Quark Coalescence: p/p = 0.6– Fireball: p/p = 0.9 - 1.0– Hijing: p/p = 0.8– RQMD: p/p = 0.5

p/p: centrality and pt dependence

• No strong pt dependence• Weak centrality dependence

more stopping and/or other process ?

85% centrality 6% Ratio for 0.3 < |y| < 0.4

/ preliminary

= 4 MeV

332K min bias Events0 < pt < 2.3 GeV/c0.5<y<0.5

¯

p/p

@AGS

@SPS

p/ p E866

+

+

p/ p NA49

WA97

p/ p STAR

STAR-

---

-

AGS SPS RHIC

STAR Preliminary

/

ratio

Anti-Baryon/Baryon Ratio

Preliminary: / = 0.70 0.05 (stat) 0.2 (syst)

p/p = 0.65 0.03 (stat.) 0.06 (sys.) ¯

Conclusion

Stay tuned for QM2001!!!!