E07-007/E08-025 (DVCS status report)

1. E07-007/E08-025 (DVCS status report) J. Roche Ohio University Hall A collaboration meeting June 9-10, 2011

2. In a nutshell: Goals: -To measure the DVCS cross-sections as a function of Q2 and two different beam energies for both LH2 and LD2 -To perform an L/T separation of these as a function of Q2 • Data taking took place in the fall of 2010 (Oct-Dec) • 80% of the expected data were taken (though at modified kinematics) • Successfully used and read out the expanded calorimeter • (ready for 12 GeV experiments – C. Hyde’s talk this afternoon) • Analysis just started

3. PRL 97: 262002 (2006) Goal of E07-007 and E08-025: To separate the BH.DVCS interference contribution from the DVCS2 contribution Measure each Q2 point at two different beam energies. For LH2 measure 3 Q2 while for LD2 measure only 1 Q2. BH2, DVCS2 and BH-DVCS interference all contribute significantly to the total cross-section. x=0.36, Q2=2.3 GeV2t=-0.28 GeV2

4. Actual kinematics Proposal assumed a 6 GeV beam energy (at 5 pass). Actual kinematic had to be adjusted to accommodate the low energy requirement of QWEAK (5.5 GeV at 5 pass) Impact: • Reduced lever arm in Q2: 1.5- 2.0 GeV2(instead of 1.5-2.3 GeV2) • Thelowest Q2-setting (at 1.5 GeV2) will be closer to the nucleon resonance region W2=3.55 GeV2(instead of 3.78 GeV2) • Larger background noise => Poorer resolution, less statistic. A long commissioning period and trigger issues limited our DAQ rate at the beginning of the experiment. The problem was fully resolved by the end of the experiment.

5. Improved dedicated equipment: expanded calorimeter and ancillary electronics Expanded calorimeter (from 132 to 208 blocks) - less radiation damage than previously (selection of blocks and better shielding) 1 GHz sampling electronic (ARS) with better transfer speed - used VME320 protocol (16 times faster) and buffering of the FIFO New coincidence trigger module - reduces data rate by selecting clusters above a threshold in the calorimeter - ran successfully during the last 8 days of the experiment

6. Improved dedicated equipment: Coincidence trigger module For each LHRS trigger (S2L+Cer), the coinc-trigger module computes the signal amplitude of all 2*2 towers of the 208 blocks. A DVCS trigger is issued if one tower is above a given threshold. The DVCS trigger becomes operational We received a lot of help from the Jlab DAQ group during the experiment. Thanks to all and especially toD. Abbot and Ben Raydo.

7. Online Data quality

8. Thank you all for a successful data taking: • Hall A /Jlab engineers, techs and staff, • Run coordinators and • Shift workers. We have started the offline analysis. Collaboration meeting March 2011

9. Analysis just started: BCM calibrations We experienced two sudden jumps in the gain of the downstream BCM. So far the source of the jumps is unknown. * BCMs not thermally regulated : analysis still in progress

10. Analysis just started: Coincidence timing e (p, e’g) p 1 GHz ARS (Analog Ring Sampler) L-HRS DVCS calorimeter Analysis so far (LHRS side): -correct for paddle offsets -correct for hit position in the scintillator -correct for slewing as a function of amplitude Results so far: -sigma 1ns -for last experiment, it went down to 0.6 ns t (ns)

11. Analysis just started: Spectrometer pointing

12. Analysis just started: Polarimetry Run the g-detector Compton when tune allowed (~ 30% of the time)

13. Status of E07-007/ E08-025 in summary: Goals: -To measure the DVCS cross-sections as a function of Q2 and two different beam energies for both LH2 and LD2 -To perform an L/T separation of these as a function of Q2 • Data taking took place in the fall of 2010 (Oct-Dec) • 80% of the expected data were taken (though at modified kinematics) • Successfully used and read out the expanded calorimeter • (ready for 12 GeV experiments – C. Hyde’s talk this afternoon) • Analysis just started