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Prompt Photon Production from Proton - proton Collisions at √ s = 62.4 GeV in PHENIX ( PHENIX 実験における重心系 62.4 GeV での陽子 - 陽子衝突からの 直接光子の生成断面積の測定 ). JPS meeting March 26th, 2008 26pZF-11 Kohichi Sakashita ( Tokyo Tech ) for the PHENIX Collaboration. Contents. Introduction - PowerPoint PPT Presentation
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Prompt Photon Production from Proton - proton Collisions at √s = 62.4 GeV in PHENIX
( PHENIX 実験における重心系 62.4 GeV での陽子 - 陽子衝突からの
直接光子の生成断面積の測定 ) JPS meeting
March 26th, 2008
26pZF-11
Kohichi Sakashita ( Tokyo Tech )
for the PHENIX Collaboration
2
Contents
1. Introduction
2. PHENIX detector and data set
3. Method of prompt photon measurement
4. Result
5. Summary
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1-1. Introduction• Production of prompt photon
– Quark - gluon scattering is dominantsub-process at pp collision in√s = 62.4 GeV
• The related experiment– PHENIX √s = 200 GeV– R806, AFS, CCOR and CMOR using ISR collider at √s = 63 GeV in
CERN
• Test the applicability of perturbative QCD (pQCD)– Comparing the cross section of measurement to the one of pQCD calcul
ation• pQCD calculation in qg scattering :
– Once the applicable range of pQCD is determined, the framework of pQCD can be used to calculate other quantities of interest, in particular ALL
prompt photon
proton
gluon
quarkproton
€
dσ pp(qg )→γX
dpT
≅ dx1 ⋅dx2 ⋅q(x1)∫ ⋅g(x2) ⋅ ˆ σ qg →γX
q(x), g(x) : PDF for quark, gluon
: sub-process cross section
€
ˆ σ
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1-2. Introduction• Double helisity asymmetry ( ALL )
• Comparing to ALL in 200 GeV, large Bjorken’s x can be reached at 62.4 GeV
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
0.02 0.04 0.06 0.08 0.1 xT
€
xT =pT
s /2→ x
√s = 200 GeV
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Proton beam
2. PHENIX Detector and Data Set • PHENIX central arm detector
= 90° x 2, || < 0.35
• Data set – 2006 pp run– Integrated luminosity : 0.065 pb-1
• Basic analysis cuts• EMCal&BBC trigger • Vertex cut |z| < 30 cm• Remove 2 edge towers, dead and hot
towers
– Event selection• pT > 2 GeV/c• Shower shape cut• Charge veto with PC3
prompt γ
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3-1. Method of Prompt Photon Measurement
• Main issue of prompt photon measurement– Evaluation of systematic uncertainties
0 extraction and so on
– Prompt photon yields is small signal of all photon
• About 10 % at 3 GeV/c
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3-2. Method of Prompt Photon Measurement
N prompt γ = Nall γ- (1+A)*(1+R)*Nγ tag
By measuring Nall γand Nγtag, one can extract small Nprompt γsignal
( tagging method )
detecting two photon from pi0 decaymissing one photon from pi0 decay eta, eta' and omega decay photonprompt photon
Nγ tag
N prompt γ
Nall γ
x R* Nγ tag
x A*(1+R)* Nγ tag
’ ωdecay photon– The ratio of ’and ω0 production to
production – The ratio of branching ratio of photon of
’and ω0 to the branching ratio of photon of
• A = Σσiσ Br i γ / Br -> γγ
i : ’ ω
decay photon– Detecting two photon ( N
γ tag )• Reconstruction invariant mass
– Missing one photon• Evaluated by fast MC simulation• The ratio ( R ) of the missing one ph
oton to detecting two photon
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are needed to see this picture.
4-1. Result - cross section
• Cross section :
• pQCD calculation with NLO and CTEQ6M PDF agrees with experiment within theoretical uncertainty and experimental uncertainty
€
Ed3σ
dp3=
1
2πpT
⋅1
L⋅
ΔNγcorr
ΔpTΔη
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4-2. Result - comparison of PHENIX √s = 200 GeV and ISR experiments
• Results of ISR agree with this result within the experimental uncertainty
• Cross section slope at √s = 200 GeV is gentler than one at √s = 62.4 GeV
Open black circle : PHENIX at √s = 200 GeV ( 2005 year )
The others : ISR experiments at √s = 63 GeV
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5. Summary• Test the applicability of pQCD calculation
• Data set– pp collision at 2006 year √s = 62.4 GeV– Integrated luminosity : 0.065 pb-1
• Prompt photon yields as a function of pT are extracted by the 0 tagging method ( N prompt γ = Nall γ- (1+A)*(1+R)*N
γ tag ) with PHENIX central arm detector ( = 90° x 2, || < 0.35 )
• pQCD calculation with NLO and CTEQ6M PDF agrees with experiment within theoretical uncertainty and experimental uncertainty
• Results of ISR agree with this result within the experimental uncertainty
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Back up
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QuickTime™ and aTIFF (LZW) decompressor
are needed to see this picture.
3-1. Method of Prompt Photon Measurement
• Main issue of prompt photon measurement– Evaluation of systematic
uncertainties0 extraction and so on
– Prompt photon yields is small signal of all photon
Pro
mp
t p
hot
on /
All
ph
oton
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4. Result - systematic errors
• Error in Nγ tag
– Fit ( Gauss + pol.3 ) to the region of pi0 mass peak to extract 0 photon with 3 ( 105 < Mγγ < 165MeV/c2 )
– Difference of between Nγ tag with pol.2 and N
γ tag with pol.3 and between N
γ tag with 3 and Nγ tag w
ith 4 is assigned as the error
– 3.4 % to the Nγ tag with pol.3 and 3at 2 Ge
V/c
2.8 % to the Nγ tag with pol.3 and 3 at 3.75
GeV/c
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€
Nγcorr =
N promptγ
ε acceptance ⋅ε energysmering ⋅ε conversion ⋅ε BBCtrigger ⋅ε EMCaltrigger
Ed3σ
dp3=
1
2πpT
⋅1
L⋅
Nγcorr
dpT
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4. Result - systematic errorsNeutral hadron contamination
Secondary origin
Error in 1+A
Dalitz decay pi0 partner photon conversion loss
Error in Nγtag
1+R (acceptance)
1+R (Minimum E cut)
1+R (Pi0 cross section slope)
Energy scale uncertainty
Luminosity uncertainty
Conversion error
BBC bias uncertaintyQ
uick
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W = prompt / inclusive Error of C is scaled by 1/W - 1
16x
xDG (x)
present x-range
GS-C
GS-C, ΔG = 1
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