Data Analysis - Timing Windows and Reference Times

Reference Times

Selecting Proper Reference Times

Reference times are a copy of the pre-trigger that is distributed to all read-out controllers (ROCs), which subsequently read out the detector signals associated with the signal. Hall C uses multi-hit TDCs and ADCs, so there can be multiple hits within the match window width of the TDC or within the programmable trigger window of the ADC. The reference time is subtracted from the detector signals within hcana, and hcana uses the first hit within the window if multiple hits are present. The number of hits within a TWW or PTW is dependent on the physics data rate, the TWW or PTW length, and the number of pre-triggers required to fire the DAQ. Refer to accidental rate exercise below to understand this more. In order to subtract the correct reference time from all detectors, we must set the reference time, which decreases the probability hcana chooses the incorrect hit in the ADC or TDC of the reference time (copy of the pre-trigger). This type of data analysis procedure is generally considered a 'Cut' because we are restricting ourselves to the data that falls after or within a range that is motivated by physics. Carlos Yero has created an Analysis Notes document, which contains important information about the possible reference times in different trigger configurations. Most of the information in this section is based on that document.

Carlos Yero DocDB ref. 1032 v1.

Accidental Rate Example

Within the hallc_replay_XEM framework I have added DEF-files that ignore any set reference time cuts for each trigger configuration expected in the XEM analysis (SHMS singles, HMS singles, COIN). There is a corresponding SCRIPT that uses these DEF-files based on the type of trigger being analyzed. I have grouped the reference time cuts and timing window cuts portion of analysis into the general activity of TIMING because we are looking at the timing of incoming detector signals and ignoring accidental signals based on those TIMING cuts.

Location of DEF-files

DEF-files/<trig>/TIMING/no_reference_times.def, <trig> = (SHMS,HMS,COIN)

Location of SCRIPTS

SCRIPTS/<trig>/TIMING/replay_no_timing_windows_<det>.C, <trig>=(SHMS,HMS,COIN), <det>=(shms,hms,coin)

Output ROOTfiles

ROOTfiles/<trig>/TIMING/<det>_noReferenceTime_runNo_Nevents.root, <trig>=(SHMS,HMS,COIN), <det>=(shms,hms,coin)

Post-replay script

The output histograms are checked by a trained eye.

Place reftime cut rootfile in online location run script over

Online Running Information
Responsibility	Check Frequency	Reporting Sections
Casey Morean	Every kinematic change	Commissioning Activity
	Every trigger change	Page on XEM Web JSROOT

Timing window Calibration

Online Running Information
Responsibility	Check Frequency	Reporting Sections
Casey Morean	Every kinematic change	Commissioning Activity
	Every trigger change	Page on XEM Web JSROOT