Post on 20-Dec-2015
transcript
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!!!!