Data Analysis - Overview

Calibration and Passes

Overview

The XEM2 analysis can be broken into two major parts; online and offline data-taking. Online data-taking leverages the online GUI, and the 50k replays. These will be discussed below. Timing windows and reference times must be set for each trigger type that will be used in an experiment. Additionally, for online analysis 'okay' calibrations need to be made for the hodoscopes, calorimeter, drift chamber, and noble gas cherenkov detectors. These calibration coefficients typically roll over from the previous experiment and are determined using cosmic ray scans and/or early commissioning beam.

The offline analysis is comprised of all the same steps, but the level of detail is increased to understand the systematic uncertainties, optimal calibration parameters, cut quantities. This process typically takes several iterations as detector calibrations depend on one another in some cases. For instance, the drift chambers are used to construct tracks, which can be used in the calorimeter calibration code to sum energy deposition in clusters of blocks around projected electron hits. Most importantly, the hodoscope needs to be properly calibrated for almost all detector calibrations.

The analysis is generally broken up into passes. In each pass, a specific set of calibrations and corrections are applied and the data is replayed. Each set of data in a pass is typically saved to /cache/ to save for comparisons between passes.

Carlos Yero made an amazing analysis note based on his thesis experiment, which can be accessed by logging into the private Hall C DocDB and searching for entry 1032.

Pedestal Defaults

The FADC250 modules used for data analysis automatically determine the pedestal by looking at the first 4 samples of the programmable lookback (PL), which corresponds to the same four samples of the programmable trigger window (PTW). The average of the fisrt four samples is saved as the Pulse Pedestal, which is saved in the EVIO file and used inside hcana to calculate the pulse integral PulseInt = PulseIntRaw - PulsePed. When any of the first four samples are above threshold of the PTW, the FADC250 sets the Pulse Pedestal to zero. Prior to April 2020 hcana would throw out events, which had a PulseAmpRaw==0. In an April 2020 update, Mark Jones added 'cut' parameters to set a default pedestal for all ADCs that are not the hodoscope. The change for the hodoscope is outlined in the below for the ScintillatorPlane::ProcessHits function of the THcScintillatorPlane Class.

THcScintillatorPlane.cxx Changes

ScintillatorPlane::ProcessHits

• Selects first TDC PMT hit within the TDC_min and TDC_max windows.
• Old code
  • If Raw ADC Amp = 0 , then do not use hit.
  • First ADC hit within ADCTDC_min < TDC_time – ADC_time < ADCTDC_max
  • If no ADC hit is found then PMT hit is not “good”. Need both ADC and TDC info for “good” PMT hit.
• New Code
  • If Raw ADC amp = 0, then use hit and test ADC hit setting ADC Amp =200.
    • Adc Amp=200 sets the timewalk correction to zero.
  • First ADC hit within ADCTDC_min < TDC_time – ADC_time < ADCTDC_max with largest ADC value
  • If none found then selects one with smallest TDC_time – ADC_time .
  • So if there is an ADC hit for paddle PMT, then it will set “good” PMT hit if there is TDC PMT hit.

Mark Jones DocDB ref. 1055 v2.

hcana April-2020 Changes to Other Detectors

• The FADC uses the first four samples of the FADC time window to determine the pedestal.
• In a pulse is detected in the first four samples
  • FADC sets the raw pulse amp for all pulses in the window to zero
  • The pedestal is not the true pedestal for later pulses in the window.
• Old Code : Throw out the detector hits when found PulseAmpRaw ==0
• New Code: When PulseAmpRaw ==0
  • Uses an average pedestal value, PedDefault, that is a parameter for each detector PMT.
  • Calculates the PulseInt = PulseIntRaw – PedDefault
  • Set PulseAmp=0. Can be used as tag to look for these events.
  • Hodoscope detector is special. It does not use PedDefault. The PulseAmp is used for time walk correction. So when PulseAmpRaw==0, set PulseAmp=200.

Mark Jones DocDB ref. 1056 v1.

Pedestal defaults are read directly from the fADC250 and are typically 4 samples long. In some cases, a pulse can occur when the fADC is attempting to determine the pedestal. In this case we need to give hcana a default pedestal, which is determined from the same PMT. Pedestals tend to be stable, so setting pedestal defaults at the beginning of the run and checking periodically is probably enough.

• Check: Every 100 runs
• Responsibility: Casey Morean
• Commissioning, overview GUI added to web

Hodoscope Changes HCANA-April2020

Reference Times

The reference times must be determined before moving onto the timing windows. We use multihit TDCs and ADCs, which can have multiple hits recorded. Given the rate of physics triggers, and the wide width of the drift chamber reference time, it is quite likely the wrong hit is taken. We shrink the timing windows by cutting on the raw adc or tdc spectra

• Check: Every kinematic, every change of trigger
• Responsibility: Casey Morean
• Commissioning, overview GUI added to web

Timing window Calibration

• Check: Every kinematic, every change of trigger
• Responsibility: Casey Morean
• Commissioning, overview GUI added to web

Hodoscope Calibration

Drift Chamber Calibration

Noble Gas Cherenkov Calibration

Heavy Gas Cherenkov Calibration

Calorimeter Calibration

Online Monitoring

Runlist Aggregation

Deadtime Monitoring

Good electron rate / Rate Information

Charge Monitor

Spectrometer Angle Monitor

Studies

Beam Current Studies

Optics Studies

Open Trigger Study