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