1. E07-007 & E08-025 status report Maxime DEFURNE CEA-Saclay/Irfu/SPhN 1

2. Goals Measure DVCS and   electroproduction cross sections at different Q² off proton and neutron. Two beam energies: - Separate DVCS.BH and |DVCS|² terms. - Separate σ L /σ T of   cross sections. t=(p-p’)² GPD    Q2Q2 p p’ xBxB Q² (GeV²)Energie faisceau (GeV) 0.361.5(3.355 ; 5.55) 0.361.75(4.455 ; 5.55) 0.362(4.455 ; 5.55) 2

3. Experimental Setup Data taken from October to December 2010. Calorimeter 208 PbF 2 blocks 3

4. Data analysis Beam line - Polarimetry (Compton + Moller) data (FINISHED), E. Fuchey - Beam charge monitors (BCM) calibration (FINISHED), J. Roche HRS - Optics and mispointing checks (FINISHED), P. Bertin - Drift chambers time offsets (FINISHED), C. Munoz - Trigger/ detectors efficiency (FINISHED), M. Defurne, C. Hyde, M. Mazouz - Normalization : DIS cross section (IN PROGRESS), M. Defurne Calorimeter - Calibrations ( FINISHED ), A. Marti, C. Desnault, M. Ben Ali - Waveform analysis of PMT pulses (FINISHED), A. Marti - Timing corrections (FINISHED), M. Mazouz MC simulation - GEANT4 written from scratch based on previous GEANT3 and their comparison, (FINISHED) R. Paremuzyan, M. Defurne Physics analysis (IN PROGRESS) - DVCS off proton, A. Marti - DVCS off neutron, C. Desnault, M. Ben Ali -   electroproduction cross section, M. Defurne 4

5. G3 counts G4 counts G4/G3 counts R. Paremuzyan G3-G4 in relatively good agreement G4 Simulation package 5

6. Calorimeter calibration First step: block calibration coefficients are determined using elastic runs (proton in HRS, electron in the calo). (A. Marti) Second step: gain variations can be monitored and corrected day-by-day using e N -> e N   (C. Desnault – M. Ben Ali) Missing mass eN->e   X and invariant mass of the two photons in the calorimeter (GeV²) 6

7. C. Desnault * Before calibration * After calibration Calorimeter calibration Missing and invariant mass much more stable after calibration!! 7

8. Normalization Normalization studies through Deep Inelastic Scattering cross section extraction. -> Quality control, run-by-run -> Quality of the normalization (corrections, charge calculation,…) Upstream BCM Downstream BCM 2% 8

9. Pion rejector spectrum of single and multitrack events Energy (GeV) Multitrack events in HRS 9 Multitrack events contribution

10. Multitrack events in HRS Between 5 and 10% of multitrack events Failure of the tracking -> remove them and apply a correction BUT they are not all electron events: down to a 3% correction (max) E<2GeV: Only pions ≥ 2 tracks 2 tracks 3 tracks 4 tracks 5 tracks E>2 GeV in 2 tracks: Electrons 10

11. HRS acceptance First kinematics was run without collimator. 5 other kinematics were run with the collimator. Collimator at the wrong position ? R-function> 0.005 ……. Monte Carlo ……. Experimental data IN PROGRESS… 11

12. 12 M. Defurne BCM problem Cerenkov Threshold IN PROGRESS…

13. 13 1 week BCM problem

14. Next … Adapt the R-function and/or find a suitable set of cuts to compute the HRS acceptance. Compare DIS results with theoretical value (F2 parametrization). First DVCS cross sections off proton for late Fall 2013.(A. Marti) First DVCS off neutron (C. Desnault – M. Ben Ali) and   electroproduction cross sections (M. Defurne) for 2014. 14