Identical charged pion correlations measured by PHENIX at sqrt(s NN )=200GeV
09/30/'06SPIN2006, T. Horaguchi1 Measurement of the direct photon production in polarized...
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Transcript of 09/30/'06SPIN2006, T. Horaguchi1 Measurement of the direct photon production in polarized...
09/30/'06 SPIN2006, T. Horaguchi 1
Measurement of the direct photon production in polarized proton-
proton collisions at s= 200GeV with PHENIX
CNS, University of Tokyo
Takuma Horaguchi
09/30/’06 for the RSC Meeting
09/30/'06 SPIN2006, T. Horaguchi 2
Contents
• Physics Motivation• Experimental Setup
– RHIC– PHENIX
• Direct Photon Production• Cross Section• Isolation Cut Method• Double Spin Asymmetry• Summary
09/30/'06 SPIN2006, T. Horaguchi 3
Physics Motivation
• Spin Puzzle from polarized DIS experiment
• Origin of proton spin– Gluon spin– Orbital angular momentum of quark and gluon
• RHIC-Spin– The first polarized proton-proton collider– Interaction of quark-quark, quark-gluon, gluon-gluon– Direct photon production (qg→γg)
gqLG 2
1
2
1ΔΣ~ 20-30%
09/30/'06 SPIN2006, T. Horaguchi 4
Relativistic Heavy Ion Collider• The first polarized proton-pr
oton collider• Beam energy:50-250GeV in
proton-proton collision • √s=200GeV (2005)• Beam polarization is 47%(2
005).• Luminosity is 3.8pb-1 (2005)• The beam polarization and l
uminosity will be improved in 2006 Run.– Beam polarization : 60%.– Luminosity : 7.5pb-1
PHENIX
STAR
Brahmspp2pp
09/30/'06 SPIN2006, T. Horaguchi 5
PHENIX Detector• ElectroMagnetic Calorimeter
(EMCal)– Measurement of photon & electro
n energy and position– Acceptance
• |η|< 0.35, Δφ=180 degree
– Distance from collision point : 5m– High pT photon trigger
• Beam-Beam Counter (BBC) & Zero Degree Calorimeter (ZDC)– Used for relative luminosity meas
urement
09/30/'06 SPIN2006, T. Horaguchi 6
Direct Photon Production
• A test of pQCD• Measurement of t
he polarized gluon distribution function
• Determination of the sign of the gluon distribution function
proton beam
proton beam
or
or
gluon
photon
Quark-Gluon Compton Scattering
09/30/'06 SPIN2006, T. Horaguchi 7
Direct photon cross section
To be submitted soon
• Obtained the final plot of the Run2003 data
• Direct Photon signal– Subtraction of backgro
und
• Evaluation of the photons from hadron decay
09/30/'06 SPIN2006, T. Horaguchi 8
Direct photon cross section
To be submitted soon
• pQCD calculation describes the our data
• The 4 orders of magnitude on
the cross section is obtained.• Systematic error is as follows
09/30/'06 SPIN2006, T. Horaguchi 9
Isolation-cut method
• Suppression of the photon from Jet
• Isolation Cut
– ΣEi : The sum of the energy within R<0.5
– ΣPi : The sum of the energy within R<0.5
EPER R
ii
1.05.0 5.0
Isolation cut
Rphoton
Direct photon
RPhoton in Jet
Photon in Jet
Photons and charged particles
Single photon
22 R
09/30/'06 SPIN2006, T. Horaguchi 10
Ratio of the direct photon• Theory curves
– Two fragmentation fuction – Three scale factors
• At high pT region (pT>7GeV/c)– The result shows many of dir
ect photons are isolated.– Theory predictions agree wel
l to the result• For low pT region
– The theory curve is higher. But the effect of underlying event is in the data
• Pi0 photons (from jet) are suppressed as we expected qualitatively.
09/30/'06 SPIN2006, T. Horaguchi 11
From Run5 dataX10 luminosity of Run3Cross Section in Run2005
• Pi0 tagging method and isolation cut method
• It is consistent to Run3 result
• Wider pT range
09/30/'06 SPIN2006, T. Horaguchi 12
Double longitudinal spin asymmetry
Rdd
Rdd
PPALL
21
1
ALL
qgqLLLL a
xq
xq
xg
xgA
)(
)(
)(
)(
2
2
1
1
• Double longitudinal spin asymmetry (ALL)– Measurement of the polarized gluo
n distribution
– dσ++ : Beam helicity is parallel.
– dσ+- : Beam helicity is unti-parallel
– P1,2 : Beam polarization
– R : Relative-Luminosity(L++/L+-)
• Direct Photon ALL
– Depend on the polarized gluon distribution function of the first degree.
– Determination of the sign of the gluon distribution function
09/30/'06 SPIN2006, T. Horaguchi 13
Effect of the Background• The effect of the backgro
und A_LL
• The assumption is– ALL
bg ~ ALL pi0 photon
• If GRSV-max is assumed– rALL
bg ~ 3% (pT=10GeV/c)
• Working on the measurement of the pi0 photon ALL from data
bgLL
isoLL
sigLL rAArA )1(
Pi0 A_LL (GRSV-max)
sig
bg
N
Nr
bgLL
isoLL
sigLL rAArA )1(
Isolation cutR=0.5, f=0.1minE=0.15GeVPmin=0.2GeVPmax=15GeV
09/30/'06 SPIN2006, T. Horaguchi 14
Outlook for the Future
• Run 2005– Luminosity:3.8pb-1– Polarization:47%
• Run 2006– Luminosity:7.5pb-1– Polarization:60%
• Working on the analysis of direct photon A_LL for the Run2005 data
09/30/'06 SPIN2006, T. Horaguchi 15
Summary
• We obtained the final result of direct photon cross section in Run2003. It was submitted to the PRL.
• We obtained the preliminary result of the direct photon cross section with pi0 tagging method and isolation cut method in Run2005.
• We are working on the analysis of the direct photon A_LL for the Run2005 data.
09/30/'06 SPIN2006, T. Horaguchi 16
09/30/'06 SPIN2006, T. Horaguchi 17
Outlook for the Future
• Run 2005– Luminosity:3.8pb-1– Polarization:47%
• Run 2006– Luminosity:7.5pb-1– Polarization:60%
• Working on the analysis of direct photon A_LL for the Run2005 data
09/30/'06 SPIN2006, T. Horaguchi 18
Signal fraction in the samplesubtraction method (pi0 partner Emin=0.5GeV)
all hadron
all pi0(tagged + missing partner)
green band shows systematic error size.Common parts are cancelled.(normalization, acceptance)
signal fraction in the sample.(Merged pi0 are already rejectedby the photon shape cut)
09/30/'06 SPIN2006, T. Horaguchi 19
(iso)Signal fraction in the sample
pi0 isolated photon (with partner)
isolated pi0 photon (missing partner)
Isolation cutR=0.5, f=0.1minE=0.15GeVPmin=0.2GeVPmax=15GeV
isolation cut method (pi0 partner Emin=0.5GeV)
The message: By applying a photon cut and an isolation cut, the purity is increased.
Isolated signal fraction in the sample.(Merged pi0 are already rejectedby the photon shape cut)
09/30/'06 SPIN2006, T. Horaguchi 20
Analysis methodDirect photon signal= All photon sample – photons from hadron’s decay (mainly pi0)
All photon sample
From EMCal clusters charge track veto Photon shape cut
Estimation of photons from hadron’s decay
Measurement of pi0 production cross sectionEstimate yield of photons based on pi0
Add other hadron’s (eta etc.) contribution
Cocktail method Pi0 tagging method
Tag pi0 photons with its partnerEstimate them bin by bin
Multiplied by the missing ratio to estimate the total
Add other hadron’s (eta etc.) contribution
Conventional method,It isn’t a direct count of the background
Newly appliedIt is a simple method.