exclusive π 0 e lectroproduction in the resonance region
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Exclusive π0 electroproductionin the resonance region.
Nikolay Markov, Maurizio Ungaro, Kyungseon Joo
University of Connecticut
Hadron spectroscopy meetingSeptember 26, 2009
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Outline
Motivation Experiment Analysis Results Conclusion
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• The experimental N* program has as main component the accurate measurements of transition form factors (A3/2, A1/2, S1/2) of known states as function of the photon virtuality (Q2) to probe their internal structure and confining mechanism
• Exclusive pion electroproduction from protons is proven to be an especially sensitive tool for the study of the transition from the hadronic picture to the quark-gluon picture of nucleon resonance excitations.
Motivation
e
e’
γv
N N’
N*,△
A3/2, A1/2, S1/2
Ml+/-, El+/-, Sl+/-
p, h, pp,..
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E1e run
Beam energy: 2.039 GeVBeam polarization: ~ 70%Current: 10nATarget: Liquid Hydrogen, thickness 2 cm, radius 0.2 – 0.6 cmTorus current: 2250 AMini-torus current: 6000 AData taking period: 12.2002 – 1.2003Number of triggers: 1.5*109
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Data analysis: procedure
Particle IDElectron IDProton ID
Good runs selectionElectron momentum correctionProton momentum correctionπ0 selection: BH subtractionCherenkov cut efficiencySimulation and acceptance correctionRadiative and bin centering correctionSystematic studies
NormalizationElastic processInclusive process
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Electron IDX versus Y cutMinimum momentum cut Pel > 0.461 GeVSampling fraction cutNumber of photoelectronsE inner > 50MeV
Particle ID
NPE
X, cm
Y, c
m
P, GeV
Eto
t/P
25
0.461
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Electron fiducial cut
Momentum and sector dependentThe regions of uniform acceptance:
TOF inefficiencies
)sin( min4
6
21min
CCp
CC
Particle ID
Sector 5
φ
θ
θ θ
-30 -15 15 30φ -30 -15 15 30φ
50
40
30
20
50
40
30
20
P, GeV
θ
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Proton IDParticle ID
Timing correctionFor the loosely identified protons
Tmeasured- Ttheoretical
for each scintillatorcalculated
Resulting correction is then applied to the events.
Based on the ΔT =Tmeasured-Ttheoretical -2ns < ΔT < 4ns
Pp,GeV
M2 ,G
eV2
P, GeV
ΔT, ns
4 2 0-2-4
Pp,GeV
M2 ,G
eV2
Pp,GeV
ΔT, s
Pp,GeV
β
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Proton fiducial cutParticle ID
0.4 < P < 0.6 GeV, Sector 1
8 bins in momentum
0.0 GeV < P < 0.4 GeV
0.4 GeV < P < 0.6 GeV
0.6 GeV < P < 0.8 GeV
0.8 GeV < P < 1.0 GeV
1.0 GeV < P < 1.2 GeV
1.2 GeV < P < 1.4 GeV
1.4 GeV < P < 1.6 GeV
1.6 GeV < P < 1.8 GeV
20 θ bins
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Electron momentum correctionMomentum correction
Kinematical coverage of elastic events is quite different from π0,while BH lies in similar region;Since we have good statistics in the elastic region, they will be used as additional W bin with its own kinematics.
Overview and reaction selection
BH selection, pre- and post-radiative processesPreradiative BH selection, emitted photon is aligned with the beam direction.
θ
P, GeV
ep -> epXall BHpre-radiativepost-radiative
-0.02 0 0.02 0.04mm2
Elastic events BH events π0 events
Electron kinematics coverage in case of
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Electron momentum correctionMomentum correction
Elastic events BH eventsPeak position σ
Data Corrected
Peak position σ
Data Corrected
data
theordata
PPP
is calculated for each event and stored in sector - W - θe - φe bins.Gaussian fit to obtain a peak position is performed and peak positions are fitted with 2nd order polynomial a + bx + cx2 as a function of φe.
Coefficients of the polynomial fit are interpolated as a function of W, giving as a correction to be applied.
Correction applied
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Based on the ratio of the number of events in the specific reaction in the run to the faraday cup charge for this run, 4 runs were excluded from the further consideration.
Data set selection
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0.040.02 0-0.02-0.04
Proton momentum correction
Based on the ep->epπ0 kinematics.Based on the ratio of generated and reconstructed proton momentum.
Energy lossResult, peak position
Result, σ
Data | Corrected
Before correction
After correction
Uses electron momentum and angles and proton angles
Before correction
After correction φ
φ
ΔP/P
ΔP/P
P, GeV
P, GeV
ΔP/P
0.040.02 0-0.02-0.04
ΔP/P
-30 -20 -10 0 10 20
-30 -20 -10 0 10 20
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BH separation
φe – φpθ1p – θpθ2p – θp
φe-φp
φe-φp
φe-φp
θ2p – θp
Θ1p – θp
mm2, GeV2
All eventsπ0 events
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Binning and kinematical coverage
Binning:ΔW = 25 MeVΔQ2 = 0.1 GeV2
Δcosθ = 0.2Δφ = 300[15o]
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Overview
Using MAID 2007 model with radiative effects, 130M events were generated (10M data events)
GSIM processing was based on e1e configurationGPP was used to include effects for:
DC wire inefficiency TOF smearing and DC smearing
Same reconstruction code was used for both data and simulation
Same cuts applied to data and simulation
Simulation
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TOF
mas
s σ
GPP
TOF mass2, GeV2 TOF mass2, GeV2
mm2, GeV2mm2, GeV2
simulation
simulation
Simulation
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Cherenkov cut efficiency
Events with identifies electron (no CC cut) divided in the bins of Pe, θe and φe, Fit the npe spectrum with the Poisson function.
400
0
400
25
)(
)(
dxxf
dxxfE
Electrons
Problem:
Efficiency distribution forSector 2
NPE
NPE ←φ→
←θ→
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Elastic
-Elastic events with realistic radiative tail were generated-Momentum correction was applied to the simulation;-Electron or both electron and proton were detected in the final state.
Normalization
Electron detection onlyElectron and proton detection
Cross-sections comparison to Bosted parametereization
Cross-sections ratio to Bosted parameterization
Electron detection onlyElectron and proton detection
Bosted parameterezation
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Inclusive
• Events were generated using keppel_rad generator;•Momentum correction, which uses the generated events as a precise measurements, were applied•Radiative correction based on the ratio of keppel_rad/keppel_norad was applied;•Bin centering correction based on the keppel_rad model was applied;•Data is compared to the Keppel and Brasse parametrization
Normalization
Bin centering correctionRadiative correction
Result
DataBrasseKeppel
μB/G
eV3
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Acceptance correction
1.2 < W< 1.225 GeV, 0.4 < Q2 < 0.5 GeV2
1.2 < W< 1.225 GeV, 0.8 < Q2 < 0.9 GeV2
1.525 < W< 1.55 GeV, 0.5 < Q2 < 0.6 GeV2
1.725 < W< 1.75 GeV, 0.4 < Q2 < 0.5 GeV2
Corrections
Acceptance
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Radiative correction
Bremmstrahlung
Vertex correction
Vacuum polarization
Radiative processes:exclurad codeMAID 07 model as an input
1.225 < W < 1.250 GeV 0.5 < Q2 < 0.6 GeV2
Corrections
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Bin centering correction
leave the point,shift the value
leave the value,shift the point
1.225 < W < 1.250 GeV 0.5 < Q2 < 0.6 GeV2 MAID 2007
Each W-Q2-θ-φ bin is divided in 10 sub-
bins
Corrections
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Cross-section
DataMAID 03MAID 07
1.225 < W < 1.250 GeV 0.6 < Q2 < 0.7 GeV2
Statistical error only
φ
μb
Results
Preli
minary
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DataMAID 03MAID 07
Structure functions extraction
)cossin)1(22cossin(2 222
*
*
0
0 p
p
LTTTLTpmW
Wpdd
2sin
)1(2sin
2coscos
c
ba
cbay
TT
LT
LT
Very
preli
minary
Statistical error only
φ
1.225 < W < 1.250 GeV 0.6 < Q2 < 0.7 GeV2
Results
μb
Preli
minary
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Structure functions
LT
TT
LTPreli
minary
DataMAID 03MAID 07
Statistical error only 1.225 < W < 1.250 GeV 0.6 < Q2 < 0.7 GeV2
Results
μb
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Overview
Sampling fraction Electron fiducial cut
Proton fiducial cut Missing mass cutProton timing
Vertex cut
Systematics
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Data regilar cutDat strict CutData strictest CutMAID 03MAID 07
1.225 < W < 1.250 GeV 0.6 < Q2 < 0.7 GeV2
Electron fiducial cut
θ
φ
Systematicsμb
Prelim
inary
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N. Markov
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Data regular cutData strict CutData strictest CutMAID 03MAID 07
1.225 < W < 1.250 GeV 0.6 < Q2 < 0.7 GeV2
Missing mass cut
mm2, GeV2
Systematicsμb
Prelim
inary
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Preliminary cross-sections and structure functions were obtained in wide kinematic range with high statistics.
Systematic studies are partially finished.Detailed partial wave analysis combined with
other channels using JANR will be performed.
Conclusions
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N. Markov31
http://www.jlab.org/~markov/
More details
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Narrow φ* binning
No BC and radiative corrections
DataMAID 03MAID 07
Statistical error only 1.225 < W < 1.250 GeV 0.6 < Q2 < 0.7 GeV2
φ bin size 15o
μb/s
r*G
eV3
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backup
Data100% elastic events90% elastics events
Elastic generated events
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