Exclusive Pion Electroproduction in the Resonance Region: Study of Nucleon Excitations

1. Exclusive π0 electroproductionin the resonance region. NikolayMarkov, Maurizio Ungaro, KyungseonJoo University of Connecticut Hadron spectroscopy meeting September 26, 2009

2. Outline • Motivation • Experiment • Analysis • Results • Conclusion

3. Motivation • 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 pionelectroproduction 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. e’ p, h, pp,.. γv e N*,△ N’ N A3/2, A1/2, S1/2 Ml+/-, El+/-, Sl+/-

4. E1e run Beam energy: 2.039 GeV Beam polarization: ~ 70% Current: 10nA Target: Liquid Hydrogen, thickness 2 cm, radius 0.2 – 0.6 cm Torus current: 2250 A Mini-torus current: 6000 A Data taking period: 12.2002 – 1.2003 Number of triggers: 1.5*109

5. Data analysis: procedure • Normalization • Elastic process • Inclusive process • Particle ID • Electron ID • Proton ID • Good runs selection • Electron momentum correction • Proton momentum correction • π0 selection: BH subtraction • Cherenkov cut efficiency • Simulation and acceptance correction • Radiativeand bin centering correction • Systematic studies

6. Particle ID Electron ID X versus Y cut Minimum momentum cut Pel > 0.461 GeV Sampling fraction cut Number of photoelectrons E inner > 50MeV Y, cm X, cm Etot/P 25 NPE P, GeV 0.461

7. Particle ID Electron fiducial cut Momentum and sector dependent The regions of uniform acceptance: θ θ 50 40 30 20 50 40 30 20 -30 -15 15 30 -30 -15 15 30 φ φ TOF inefficiencies θ Sector 5 θ φ P, GeV

8. Particle ID Proton ID Based on the ΔT =Tmeasured-Ttheoretical -2ns < ΔT < 4ns Timing correction For the loosely identified protons Tmeasured- Ttheoretical for each scintillator calculated M2,GeV2 ΔT, s ΔT, ns 4 2 0 -2 -4 Pp,GeV Pp,GeV P, GeV Resulting correction is then applied to the events. M2,GeV2 β Pp,GeV Pp,GeV

9. Particle ID Proton fiducial cut 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 20θ bins 0.4 < P < 0.6 GeV, Sector 1

10. Momentum correction Electron momentum correction Overview and reaction selection Electron kinematics coverage in case of Elastic events BH events π0 events BH selection, pre- and post-radiativeprocesses θ Preradiative BH selection, emitted photon is aligned with the beam direction. P, GeV • 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. ep -> epX all BH pre-radiative post-radiative mm2 -0.02 0 0.02 0.04

11. Momentum correction Electron momentum correction 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. Correction applied Coefficients of the polynomial fit are interpolated as a function of W, giving as a correction to be applied. Elastic events BH events Peak position σ Peak position σ Data Corrected Data Corrected

12. Data set selection 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.

13. Proton momentum correction Energy loss Based on the ep->epπ0 kinematics. Based on the ratio of generated and reconstructed proton momentum. Result, peak position Uses electron momentum and angles and proton angles Before correction Before correction ΔP/P ΔP/P 0.04 0.02 0 -0.02 -0.04 Result, σ P, GeV After correction -30 -20 -10 0 10 20 φ After correction ΔP/P 0.04 0.02 0 -0.02 -0.04 ΔP/P Data | Corrected -30 -20 -10 0 10 20 φ P, GeV

14. BH separation φe-φp All events π0 events φe – φp θ2p – θp θ1p – θp θ2p – θp φe-φp mm2, GeV2 Θ1p – θp φe-φp

15. Binning and kinematical coverage Binning: ΔW = 25 MeV ΔQ2 = 0.1 GeV2 Δcosθ = 0.2 Δφ = 300[15o]

16. Simulation Overview • Using MAID 2007 model with radiative effects, 130M events were generated (10M data events) • GSIM processing was based on e1e configuration • GPP 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

17. Simulation GPP simulation TOF mass σ TOF mass2, GeV2 TOF mass2, GeV2 simulation mm2, GeV2 mm2, GeV2

18. Cherenkov cut efficiency Problem: Electrons Efficiency distribution for Sector 2 NPE Events with identifies electron (no CC cut) divided in the bins of Pe, θe and φe, ←θ→ Fit the npe spectrum with the Poisson function. ←φ→ NPE

19. Normalization 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. Cross-sections comparison to Bostedparametereization Cross-sections ratio to Bosted parameterization Electron detection only Electron and proton detection Bostedparameterezation Electron detection only Electron and proton detection

20. Normalization 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 Brasseparametrization Radiative correction Bin centering correction Result μB/GeV3 Data Brasse Keppel

21. Corrections 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 Acceptance

22. Corrections Radiative correction Radiative processes: exclurad code MAID 07 model as an input Bremmstrahlung Vacuum polarization 1.225 < W < 1.250 GeV 0.5 < Q2 < 0.6 GeV2 Vertex correction

23. Corrections Bin centering correction Each W-Q2-θ-φbin is divided in 10 sub-bins leave the value, shift the point 1.225 < W < 1.250 GeV 0.5 < Q2 < 0.6 GeV2 MAID 2007 leave the point, shift the value

24. Results Cross-section μb Preliminary φ Data MAID 03 MAID 07 1.225 < W < 1.250 GeV 0.6 < Q2 < 0.7 GeV2 Statistical error only

25. Results Structure functions extraction μb Preliminary Very preliminary φ Data MAID 03 MAID 07 1.225 < W < 1.250 GeV 0.6 < Q2 < 0.7 GeV2 Statistical error only

26. Results Structure functions μb Preliminary Data MAID 03 MAID 07 1.225 < W < 1.250 GeV 0.6 < Q2 < 0.7 GeV2 Statistical error only

27. Systematics Overview Sampling fraction Electron fiducial cut Vertex cut Proton timing Proton fiducial cut Missing mass cut

28. Systematics Electron fiducial cut μb φ Preliminary θ Data regilar cut Dat strict Cut Data strictest Cut MAID 03 MAID 07 1.225 < W < 1.250 GeV 0.6 < Q2 < 0.7 GeV2

29. Systematics Missing mass cut 29 μb Preliminary mm2, GeV2 Data regular cut Data strict Cut Data strictest Cut MAID 03 MAID 07 1.225 < W < 1.250 GeV 0.6 < Q2 < 0.7 GeV2 N. Markov

30. Conclusions • 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.

31. More details http://www.jlab.org/~markov/ 31 N. Markov

32. Narrow φ* binning No BC and radiative corrections μb/sr*GeV3 Data MAID 03 MAID 07 1.225 < W < 1.250 GeV 0.6 < Q2 < 0.7 GeV2 φ bin size 15o Statistical error only

33. backup Elastic generated events Data 100% elastic events 90% elastics events