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DVCS-3 Calibration and Analysis by Salina Ali

Updates and Progress as of 8/5/2017

• Main goal is to determine the livetime/deadtime correction factor (LTCF), which is needed in order to extract DIS cross section.

• Take a trigger rate/live rate and normalize using the current and adjust to the prescale (so we can eventually apply to LTCF) Template:Check mark
• To make sure the deadtime is correctly computed, the deadtime, current and prescale factors should be in agreement within 1%, especially for the range of rates in which the deadtime is linear.

• Current issues, that are independent of one another (as of now):

• There is a mysterious current dependence of live scalers when looking at dvcs events S2M and Cherenkov detectors, despite normalization using currents (to get rid of the dependence). This may be due to random coincidences between the two detectors...but still need to find out.

• The master OR, which is one of the scalers/counters for the S2M and Cherenkov detectors (the main detectors that were responsible for detecting DVCS events during the experiment), seems to have different live/raw scaler rates when comparing to CODA rates. These should be the same, and we think that this happens because of random counting within the scalers. For example, random coincidences

• Currently analyzing run taken in April 2016, 13418 which was a dedicated run for the deadtime analysis, at three different currents (10, 15, 20 uA) using a liquid hydrogen target. This is a run in which

• There are other dedicated deadtime runs taken in February 2016 with a carbon target, 12471 to 12476 at a current of ~5 uA with different prescale factors

Brief Overview

Deeply Virtual Compton Scattering (DVCS)-3 was an experiment that ran from 2015-2016 in Hall A (E12-06-114) and is one of the first experiments of the JLab 12 GeV era. The method of DVCS is the cleanest way to access Generalized Parton Distributions (GPDs). More information can be found on the DVCS-3 wiki page.

Experimental Setup

Detector Packages

The detector package within the HRS (High Resolution Spectrometer) include scintillators S0 and S2, a Cerenkov gas detector, and Pb-glass calorimeter.

Deadtime Analysis

The deadtime is defined as the ratio of the number of "live" events going into the electronics or computers to the total number of events. The deadtime calculations are crucial for the calibration process after an experiment. The electronic and computer deadtime need to be quantified and applied in order to eventually extract precision measurements of the cross section.

Relevant Terminology

• Scalars - two types of scalars, internal and external to the trigger or detector. For each set of internal and external set of scalars, there are corresponding live and raw scalars. The livetime is then the ratio of the live scalar to raw scalar.
  • External Scalars (list borrowed from here). Note that blank spaces after numbers means that those channels were not being used.
  1. 512ns clock from DVCS trigger crate (1)
  2. DVCS cosmic trigger
  3. s0
  4. s2
  5. CER
  6. EDTM
  7. DVCS external clock or LED trigger
  8. ARS_stop
  9. ARS_valid
  10. DVCS calorimeter ADC_gate
  11. inverted S0
  12. inverted S2
  13. inverted CER
  14. L1A
  15. CaloBlock001
  16. External S2M_CER
  17. 64ns clock from DVCS trigger crate
  18. 512ns clock from DVCS trigger crate (2)
  25. Master_OR
  26. Master_OR_Live
  27. HRS_Single
  28. S2M_CER
  29. S2M_CER_Scaled
  31. 103kHz clock from spectrometer
  32. BCM signal
• Beam Current Monitor (BCM) - works to measure a stable and non-interfering beam current measurement.
• Beam Position Monitor (BPM) - used to determine the position and direction of beam at the target.
• Analog Ring Sampler (ARS) - consists of an array of capacitor cells that work to sample the signals coming from PMTs by storing them. Stop and valid signals are the two signals that control the behavior of the ARS. The valid signal instructs the charge of each capicitor to be digitized, and the stop signal instructs the ARS to stop sampling, which occurs when all the capicitor cells are in a "hold" state, or isolated state. The valid signals correspond to the ARS Valid Rate, which is used as the trigger rate in the calculation of the deadtime.
• S2M&&CER - S2M and Cherenkov gas are used in conjunction to form a trigger. Only coincidences taken into account for the deadtime, which means when both detectors send a signal to the Master OR, and ARS.

Plots from run 13418: dedicated deadtime analysis run

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Histogram displaying S0, S2 and the Cherenkov Detector's livetime. We can see that since the Cherenkov detector has the shortest livetime, its deadtime dominates compared to the other detectors.	xx
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Important ELog Updates

• Mongi's ELog update: DVCS ELOG LOGIN REQUIRED on May 1, 2017
• Mongi's ELog update: DVCS ELOG LOGIN REQUIRED on May 21, 2017

References

1. Munoz, Carlos. Ph.D. Deeply Virtual Compton Scattering in Hall A at Jefferson Lab. 2009.
2. Roche, Munoz, et al. Measurements of the Electron-Helicity Dependent Cross Sections of Deeply Virtual Compton Scattering with CEBAF at 12 GeV. arXiv:nucl-ex/0609015.