e07-007/e08-025 (dvcs status report)
DESCRIPTION
E07-007/E08-025 (DVCS status report). J. Roche Ohio University Hall A collaboration meeting June 9-10, 2011. In a nutshell:. Goals: -To measure the DVCS cross-sections as a function of Q 2 and two different beam energies for both LH2 and LD2 - PowerPoint PPT PresentationTRANSCRIPT
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E07-007/E08-025 (DVCS status report)J. Roche
Ohio University
Hall A collaboration meeting June 9-10, 2011
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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
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d5σ = |BH |2 +(BH • DVCS)+ |DVCS |2
x=0.36, Q2=2.3 GeV2 t=-0.28 GeV2
PRL 97: 262002 (2006)
BH2, DVCS2 and BH-DVCS interferenceall contribute significantly to the totalcross-section.
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.
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Actual kinematicsProposal 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)
• The lowest 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.
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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
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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.
We received a lot of help from the Jlab DAQ group during the experiment.Thanks to all and especially to D. Abbot and Ben Raydo.
The DVCS trigger becomes operational
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Online Data quality
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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
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Analysis just started: BCM calibrations
Run range U10 U3 U1 D10 D3 D1
6960-8334* 1.5 1.5 1.5 1.5 1.5 1.5
8334-8665 1 1 1 1 1 1
8667-9454 1.01 1.01 1.01 0.91 0.92 0.92
9456-9869 1.01 1.02 1.02 0.96 0.97 0.98
9456-9869 1.02 1.02 1.02 0.95 0.96 0.98
* BCMs not thermally regulated : analysis still in progress
We experienced two sudden jumps in the gain of the downstream BCM.So far the source of the jumps is unknown.
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Analysis just started: Coincidence timing
e (p, e’ g) p
L-HRS DVCS calorimeter
t (ns)
1 GHz ARS(Analog Ring Sampler)
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
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Analysis just started: Spectrometer pointing
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Analysis just started: Polarimetry
Period Horizontal Wien Angle Equivalent (estimated)
A 29B 5C 26.8D 29
Run the g-detector Compton when tune allowed (~ 30% of the time)
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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