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