Exclusive π 0 e lectroproduction in the resonance region.

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Exclusive π 0 electroproduction in the resonance region. Nikolay Markov, Maurizio Ungaro, Kyungseon Joo University of Connecticut Hadron spectroscopy meeting September 26, 2009

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Exclusive π 0 e lectroproduction in the resonance region. Nikolay Markov, Maurizio Ungaro , Kyungseon Joo University of Connecticut. Hadron spectroscopy meeting September 26, 2009. Outline. Motivation Experiment Analysis Results Conclusion. Motivation. - PowerPoint PPT Presentation

Transcript of Exclusive π 0 e lectroproduction in the resonance region.

Page 1: Exclusive  π 0  e lectroproduction in the resonance region.

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