Transversity at STAR

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Transversity at STAR

• Akio Ogawa
• Penn State Univ
• for collaboration
• 2000 Sep 19
• Future Transversity Measurements

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Spin Physics at STAR
Gluon Polarization Direct Photon Direct
Photon jet Jet Jet Jet Quark /
Anti-Quark Polarization W production Transve
rsity Pion pair correlation Dijet?
Parity Violating Asymmetry Search for New
Physics
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Nucleons Transversity
Leading twist quark distribution
Longitudinal Spin Distribution
Transversity
No gluon contribution Helicity flip Soffer
Inequality Last missing piece at leading twist
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Need mass to have helicity flip Need chiral odd
interaction to observe
Experimentally, free from false asymmetry
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Two meson production
f
mass
z
Pt,h
Phase Shift
is known
Fragmentation function
unknown
Interference fragmentation function
Schwartz Inequality
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Asymmetries predicted by Jian Tang for
pp at sqrt(s) 200/500 GeV
This model is an optimistic estimation
saturate Soffer Schwartz inequality, mass0.8
(at max asymmetry)
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STAR detector
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STAR detector for Transversity measurement
Wide acceptance Jet measurements
25-30 Et resolution check Z dependence
check Pt Rapidity dependence Good invariant
mass resolution 2-5 at 800MeV check
invariant mass dependence STAR is a working
detector! But slow Need good
triggers at high luminosity TPC has 40usec drift
time pile up events STAR-RCF
bandwidth (20Mb/sec) L3 data volume
reduction No PID at high pt 10
Kaon/proton
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A factor from Phase Shifts as function
ofinvariant mass
Invariant mass resolution of STAR for Pt 2-10
GeV pair around mass 0.8 GeV
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STAR Trigger
Level 0 Trigger EMC 1.0(h) x 0.8(f) trigger
patch see
only 1/3 of total energy at L0 trigger
bias
towards EM rich events
Look at the other side of triggered jet
CTB/MWC
multiplicity trigger
Level 3 Trigger TPC tracking
available DAQ
to tape speed depends on data size
Data size reduction at
L3 Possibly selecting invariant mass
, z , cosf
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Signal Estimation
Cuts Find jets (EMcharged hadrons) in -0.3
lthlt 0.3 Any 2 opposite charged particle pairs
within a jet Pt gt 0.3GeV -1 lt h lt
1 0.5 lt mass lt 1.0GeV
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Number of pairs / Event vs Z
In average 1.2 pairs within the mass
range There are 2 jets events
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1
z
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A scenario
Year 2002 or 2003 L 8 1031 /cm2/sec 1 week
run, 50 machine time 32/pb L0 (EMC Jet)
Trigger with threshold 10GeV Only using
north/south (not top/bottom) With L3 data size
reduction 15Hz to tape 300K
sec Hz Total Jet Events 15 4.5M Beam
Polarization 0.7 ptlt10 2M cosf integral
0.5 10ltptlt20 2M dilution
factor 0.35 20ltpt 0.5M 82K events 1
error on A 2M events 0.2 error on
A Study dependence on cosf, mass , z, Pt_jet ,
h _jet
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Does it make sense to run in year 1?
Year 2001 (Numbers here are even more
rough) L 1.25 1030 /cm2/sec 2 week run, 50
machine time CTB multiplicity trigger Only
using north/south (not top/bottom) 30Hz(?) (L3
event selection on Jets / high z ? /mass ?)
10Hz to tape(?) 600K sec Hz Total Min
bias 30 Jet Events 3 1.8 M Beam
Polarization 0.5 5ltptlt10 2.5 1.8 M cosf
integral 0.5 10ltptlt20 0.4 240K
dilution factor 0.25 20ltpt 0.02 12K 160K
events 1 error on A 4M events 0.2
error on A Single spin transverse spin / false
asym free / EMC is not must If we measure
non-zero, its already something We should start
looking at it, when we get collisions But
require good polarization luminosity to have
real physics data
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Conclusion
STAR can measure 2 pion asymmetry Can see
dependence on mass , cosf, z, Pt_jet , h
_jet Many handles to check models Fragmentatio
n function is needed to extract
transversity Analysis on LEP data is going on