Transcript Document

-measurements
Saskia Mioduszewski
Martin Codrington
Texas A&M Group
Ahmed M. Hamed
BNL 10-17-07
-measurements
Table of Contents:
Motivatio
n oSingle particle spectra
oJet-like azimuthal correlations
o in Spin physics
o-measurements
Experimental Challenges
+nucleus
e+nucleus
e-+e++nucleus
e-++nucleus
oExperimental Technique
oPrevious -jet measurements at STAR
Preliminary Results of -triggered 2007 Data
o-trigger in Run 2007
oStatus and first look
Shower Shape Analysis
oComparison of shower shape in MC and Real data
oEffect of BSMD saturation on shower shape analysis
Summary
Texas A&M Group
Ahmed M. Hamed
BNL 10-19-07
Motivation
Why -measurements?
Single Particle Spectra-RAA?
p+p  jet+jet
Au+Au ???
QCD is written in terms of q&g degrees of freedom!
Study FF from ee+ collisions and PDF from pp collisions!
2 pT  y
x~
e
s
PDF in nuclear environment ! FF in medium!
NLO pQCD agrees with RHIC measurements for high pt particles at mid-rapidity.
oNuclear modification factor:
How to compare AA to pp?
Texas A&M Group
Ahmed M. Hamed
BNL 10-19-07
Why -jet measurements?
Motivation
<E>  sCxqL
Single Particle Spectra-RAA
“Static medium”
Mid-rapidity
Statistical Method
Heavy quarks suppress as much as light quarks in the medium.
No reduction is “as expected” observed in the baryon/meson ratio as in the
gluon dominance picture.
RAA
Forms of energy loss, s(T)?
exhibits only very limited sensitivity to the properties of the medium.
More differential observable is needed.
Texas A&M Group
Ahmed M. Hamed
BNL 10-19-07
Motivation
Why -jet measurements? Jet-like azimuthal correlations
?
Near-side: p+p, d+Au, Au+Au
is similar.
Back-to-back: Au+Au strongly
suppressed relative
to p+p and d+Au.
Surface bias for the trigger particle.
0
D
(
z
)

D
(
z
,
E
),
h
a
h
a
Suppression of the backto-back
correlation in central
Au+Au is a final-state
effect
Trigger particle with no surface bias is required for better
calibration of the away-side jet.
Texas A&M Group
Ahmed M. Hamed
BNL 10-19-07
Why -jet measurements?
Motivation
Spin Physics
• p+p
gluon density
Direct photons have the gluon distribution information
Texas A&M Group
Ahmed M. Hamed
BNL 10-19-07
Why -jet measurements?
Motivation
Summary
Four multipurpose experiments (BRAHMS, PHENIX, PHOBOS, STAR)
 Empirical lines of evidence:
Energy density well beyond critical value.
Large elliptic flow.
Jet quenching.
dAu control experiment.
Interpreted in terms of a strongly coupled QGP and a new QCD state (?)
Color Glass Condensate
Required:
Better understanding for the energy loss
mechanism!
oDirect Photons:
Doesn’t couple to the medium.
QGP thermal photons.
Elliptic flow.
Test for binary scaling for hard process.
Gamma-charged hadrons correlation.-jet measurements
Challengeable
measurements!
Texas A&M Group
Ahmed M. Hamed
BNL 10-19-07
Motivation
Why -jet measurements?
LO Direct photons
direct component
schematic view
thermal:
e
 E /T
Decay photons
Bremsstrahlung
fragmentation component
oGamma-charged hadrons correlation.
 Calibrated probe of the QGP – at LO.
 No Surface Bias
 Hard process
hard:
1
pTn
 Possible discriminator for quark/gluon jet at LO.
Texas A&M Group
Ahmed M. Hamed
BNL 10-19-07
Why -jet measurements?
Motivation
Spin Physics
-jet measurements on statistical basis
Inclusive -jet correlation function
0-jet (h-jet) correlation function
direct-jet = iclusive-jet-decay-jet
“taking into account decay kinematics”.
Texas A&M Group
Ahmed M. Hamed
BNL 10-19-07
Experimental Challenges
Is it possible to measure?
In medium:
0 –spectra are suppressed by a factor of ~5 relative to the
scaled p+p collisions.
The away-side in di-jet production is more suppressed.
Pythia v6.131 event
generator
pp-collisions at
√s=200 GeV,
|η|<1 (STAR
acceptance)
Background sources of direct photons suppressed in medium.
Texas A&M Group
Ahmed M. Hamed
BNL 10-19-07
Experimental Challenges
Inclusive -jet
Is it possible to measure?
in Au+Au at s=200GeV
SIMULATION (pp)
0 simulation
STAR Preliminary
Simulation shows no associated particles
in -charged correlation.
photon simulation
Away-side decreases with increasing centrality.
Decrease in near-side due to the increased
fraction of prompt photons.
Need /0 discrimination.
Texas A&M Group
Ahmed M. Hamed
BNL 10-19-07
Experimental Challenges
Is it possible to measure?
0 Bin
Mixed
Bin
Reduction in near angle peak
towards photon Bin.
Effect is more prominent
for larger Ettrigger .
More discrimination power is needed in the high multiplicity system
Texas A&M Group
Ahmed M. Hamed
BNL 10-19-07
Experimental Challenges
Is it possible to measure?
0 DECAY KINEMATICS
min= 2 Sin –1 (mInv /E),
 ~10-17 s
Towers (~0.05x~0.05),
Strips (~0.007x~0.007),
d ~2.2m at =0, l~2.93m.
-plane
Electromagnetic transverse
shower characteristics
0’s pT(GeV/c)
Texas A&M Group
High energy core.
Low energy halo.
Ahmed M. Hamed
BNL 10-19-07
L2 Gamma Trigger in Run 2007
oTower threshold
ET=5.76 [GeV]
oCluster threshold ET= 7.44 [GeV]
oCluster size is one or two tower.
L2gammaResult Contains: phi_bin,eta_bin, tower ET,
and Cluster ET.
~1.2M events. ~50% Reversed Full Field.
http://online.star.bnl.gov/L2gamma2007/l2gamma2007_bemc/
All runs after 8143* are in the reversed full field configuration.
Texas A&M Group
Ahmed M. Hamed
BNL 10-19-07
Preliminary QA of -trigger Data- BEMC
Texas A&M Group
Ahmed M. Hamed
BNL 10-19-07
Preliminary QA of -trigger Data- BSMD saturation
Texas A&M Group
Ahmed M. Hamed
BNL 10-19-07
Showers shape Analysis
Real data vs. Single particle simulation
pp@2006
Shower shape is wider in real data than in simulation!
Texas A&M Group
Ahmed M. Hamed
BNL 10-19-07
Shower Shape Analysis
Real data vs. pythia
Saturation parameters-Eta/Phi
[700,70,10]
oPythia doesn’t reproduce the shower
shape even with saturation!
oIn phi-plane the shower shape is
closer to the real data than in eta.
Texas A&M Group
Ahmed M. Hamed
BNL 10-19-07
Shower Shape Analysis
0 vs. electron
Saturation parameters-Eta/Phi
[700,70,10]
Texas A&M Group
Ahmed M. Hamed
BNL 10-19-07
Shower Shape Analysis
Texas A&M Group
0 vs. electron
Ahmed M. Hamed
BNL 10-19-07
Michael Betancourt
Pibero Djawotho
Single thrown γ and π0
75% eff @
75% rejection
Summary
-jet measurements are very promising tool for better understanding of
the medium.
Shower shape study is required for direct photons identification.
Promising study for transverse shower profile is undertaken.
Embedding request is still under processed.
Texas A&M Group
Ahmed M. Hamed
BNL 10-19-07