Strange Baryons in the STAR Experiment

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Strange Baryons in the STAR Experiment

• Boris Hippolyte, IReS-Strasbourg
• For the STAR Collaboration

CRIS2002 - Catania - 06/14/02
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Outline
Boris Hippolyte

• Freeze-out
• Chemical
• Thermal
• Multi-strange ?
• H0 in STAR ?
• Simulation
• Real data
• Summary
• Prospects

• Motivation
• STAR experiment
• Particle reconstruction
• Selections
• Quality of the data
• Preliminary Results
• B/B
• Yields and Spectra

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Motivation
Boris Hippolyte

• Strangeness enhancement as a QGP signature ?
• Strange baryon production L, X and W
• chemical freeze-out particle yields and (mixed)
  ratios
• thermal freeze-out inverse slope parameters.
• How to study this ?
• STAR experiment large and full azimuthal
  coverage
• Extracting the signals
• Ratio,Yields and Temperature _at_130GeV
• Models and SPS comparisons
• Exotic Studies ?
• StrangeletsH0, L-L correlation
• Whats next ?
• Energy scan, lighter systems

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The STAR Detector (Year-by-Year)
Boris Hippolyte
Magnet
Coils
TPC Endcap MWPC
4m
ZCal
ZCal
2m
Central Trigger Barrel
RICH
yr.1 SVT ladder

• year 2000,

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Event (Centrality) Selection
Boris Hippolyte
PRL 86, (2001) 402
central collisions ?
nch primary tracks in ? lt 0.75
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Strange Baryon Selection
Boris Hippolyte
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Strange Baryon Invariant Mass Spectra
Boris Hippolyte
AuAu collisions at v sNN 130 GeV

• Event selection
• Central (11)
• 415k events

0.7 L/event
0.005 X/event
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Quality of the data W
Boris Hippolyte

• Kinematic check
• Armenteros-Podolanski
• Xi contamination
• Y,Pt window (ylt1, Ptgt0.5 GeV/c)

• No background subtraction
• 1672.4515 MeV/c2

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Anti-Baryon to Baryon Ratios
Boris Hippolyte

• Central (11), mid-y
• Feed-down correction

PRELIMINARY
FEED-DOWN CORRECTED
Almost baryon free
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Extracting Yields and Transverse mass Spectra
Boris Hippolyte

• Extracting raw yields
• only 4 bins in Mt !

Large Acceptance a
Corrections

• Pt dependent corrections!
• Integrated in ylt0.75

STAR Preliminary
Using Monte-Carlo particlesembedded in real
events
aExponential fit
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Extracting Yields and Transverse mass Spectra
Boris Hippolyte

• Mid-rapidity Yields
• Central events 0-14
• Stat. errors only !

dN(W-W) /dy 0.640.14 dNW-/dy
0.320.09 dNW/dy 0.340.09
Preliminary
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Do ratios agree with the statistical model
picture ?
Boris Hippolyte
Thermal statistical model fits well to particle
ratios

• Thermal fit prediction using all ratio except
• a X/h-, W/h-, W/X

Tch 17010 MeV mB4810 MeV mS2.35.1
MeV gS0.990.11
M.Kaneta (LBNL)
STAR Preliminary
W / W- (fit) 0.96 ? 0.07
W / W- (exp) 0.95 ? 0.15
W- / h- (fit) 0.00113 0.00091-0.00056
W- / h- (exp) 0.00127 0.0004
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Strangeness Excitation function
Boris Hippolyte

• Typical behavior
• Maximum (30GeV)
• then decrease

Preliminary
bvanishing baryonic potential bstable temperature
?
Again support statistical models
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Multi-strangeness Excitation function
Boris Hippolyte
Stat. Errors Only !
Preliminary
(W-/X-)RHIC (W-/X-)SPS (W/X)RHIC lt (W/X)SPS
(W-/h-)RHIC gt (W-/h-)SPS (W/h-)RHIC gt (W/h-)SPS
(sss/dss)
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Yield and temperature correlation
Boris Hippolyte
Stat. Error only !

• Fit a yield and inverse slope parameter
  simultaneously

Strong correlation
Preliminary
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Temperature and collective behavior
Boris Hippolyte

• Stronger radial flow at RHIC than SPS
• Strange baryons freeze-out earlier

STAR Preliminary
(stat. errors only)

• What is the W inverse slope parameter ?

a T 41146MeV(stat.)
Signature of flow in the partonic phase ?!
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Decay Modes
Boris Hippolyte
H0 a Lp p-
H0 a L L

• Reconstruction
• Simulation
• and Sensitivity

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How to reconstruct candidates
Boris Hippolyte
H0 aL p p-
W-
Same kind of selections
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Simulation Studies
Boris Hippolyte
H0 aL p p-
H0 hadronic cocktail
W-
Acceptance in STAR
Part mid-y p/- 300300 K/- 100100
p/p 5050 a/L 1520 h0 10
Not so different from W !
H0
10k events
Expected sensitivity
10-1
Low compared to coalescence prediction
but lets try !
10-2
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Real Data
Boris Hippolyte
yearI _at_ 130 GeV
H0 aL p p-
Preliminary
background
Xp
2L
H0 aL L
No signal seen
But Central events 500k only!
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Summary
Boris Hippolyte

• All strange baryons seen in YEARI
• B/B not yet baryon free at 130 GeV
• Yields chemical equilibrium ?
• Statistical thermal model picture ?
• a so far
• a need better stat. and full syst. understanding
• to add more constraints.
• Multi-strange baryons deviate from simple radial
  flow
• Search for H0 doable in STAR
• a weak decay mode not really different from W
• a strong decay mode (like resonance studies)

year I
STAR is a great apparatus for studying
strangeness production !
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Propects for multi-strange baryons
Boris Hippolyte
?SNN 200 GeV 10 times yearI stat. Silicon
Vertex Tracker in.

• Lower stat. Errors
• Syst. Errors
• System dependence
• Rapidity dependence
• Centrality dependence
• High pt studies
• Elliptic Flow
• Di-baryon search

year II
Preliminary 1/10 stat !
200 GeV
Christophe Suire (BNL)