Trigger efficiencies
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This page is considered done. It been reviewed by Dominik. There may be missing elements, but they are all flagged and the text has no errors. |
Intro
Our dedicated DIS trigger is Trigger 21, separated into a TOP trigger (Trigger 24) and a BOTTOM trigger (Trigger 25) after year 1997. Each of these triggers is obtained from the combined responses of some detectors, and as such its efficiency depends on the efficiencies of these detectors.
- Asymmetries.
When one is analysing asymmetries, the trigger efficiencies (T.E.) at numerator and denominator cancel, as they do not depend on the specific target material, or target polarization. They do depend, instead, on the kinematics (eg. momentum) and spacial configuration of the event (eg. ). It has to be noted that the statement that the T.E. cancel is only valid in the case of target asymmetries. For beam asymmetries, when the data sets in the two helicity states have been taken in two separate time periods this is no longer true, as T.E. depend on time.
- Absolute cross-sections.
The analyser has to pay attention to trigger efficiencies in the case of absolute cross-sections since the measured cross section contains the effect of the various inefficiencies. If a large enough number of triggers is available (made of various combinations of detectors), 'most likely' for each event there will be some trigger firing; in this case one does not need to ask for a specific 'trigger 21' cut. This assumption has to be proven valid, and one has to make sure that there is at least one trigger with very high efficiency. If, on the other hand, one is applying a cut on 'Trigger 21' events, then the efficiency of such a trigger has to be applied on an event-by-event basis. This is the case of high-density running, where many triggers were prescaled, and, to obtain the real absolute cross sections a cut on Trigger 21 has to be applied.
Essentials
Let us consider Trigger 24 (=Trigger 21 TOP):
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where H0T, H1T, H2T and CALOT are the top H0,H1, H2, CALO. Its efficiency Fehler beim Parsen (MathML mit SVG- oder PNG-Rückgriff (empfohlen für moderne Browser und Barrierefreiheitswerkzeuge): Ungültige Antwort („Math extension cannot connect to Restbase.“) von Server „https://wikimedia.org/api/rest_v1/“:): {\displaystyle \varepsilon(Tr24)} is given by
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To obtain the efficiencies of each detector one has to use a trigger that is similar to Trigger 24 and contains all detectors except the one under study. So, for example, to obtain the efficiency of H1, one can use Trigger 19:
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so that
Fehler beim Parsen (Konvertierungsfehler. Der Server („https://wikimedia.org/api/rest_“) hat berichtet: „Cannot get mml. Server problem.“): {\displaystyle \varepsilon (H1T)={\frac {N_{19.AND.24}}{N_{19}}}}
where Fehler beim Parsen (MathML mit SVG- oder PNG-Rückgriff (empfohlen für moderne Browser und Barrierefreiheitswerkzeuge): Ungültige Antwort („Math extension cannot connect to Restbase.“) von Server „https://wikimedia.org/api/rest_v1/“:): {\displaystyle N_{19}} is the number of events in which Trigger 19 fires, while Fehler beim Parsen (MathML mit SVG- oder PNG-Rückgriff (empfohlen für moderne Browser und Barrierefreiheitswerkzeuge): Ungültige Antwort („Math extension cannot connect to Restbase.“) von Server „https://wikimedia.org/api/rest_v1/“:): {\displaystyle N_{19 .AND. 24}} is the number of events in which Trigger 19 and 24 fire at the same time. The efficiency so built measures the number of times when H1 should have fired and hasn't.
For more details the reader is referred to the two notes written on the subject. [1] [2]
Dependencies
Efficiencies have a strong dependence on time (due to voltage changes or aging of the detector), on Fehler beim Parsen (MathML mit SVG- oder PNG-Rückgriff (empfohlen für moderne Browser und Barrierefreiheitswerkzeuge): Ungültige Antwort („Math extension cannot connect to Restbase.“) von Server „https://wikimedia.org/api/rest_v1/“:): {\displaystyle \theta_x-\theta_y} (due to the fact that at small angles the hit rate is much larger than at large angles, thus giving a larger aging and then a lower efficiency), momentum. They also depend on the number of tracks in the event, as more tracks give a higher probability of triggering.
The bottom H0 detector showed in 1998 an efficiency for DIS leptons as low as 95% from radiation damage. It was then replaced. In later years its performance was around 97% for 2005 and 2006. The figure shows the trigger efficiency of H0 for the 2004 H running and displays the typical circular shape of trigger efficiencies, with lower efficiencies towards the beam center.
The efficiencies for H1,H2 and CALO were always above 99% for DIS leptons.
Codes
A subroutine that calculates the correction for trigger efficiencies is available in [3] (subroutine) [4] (include file).
Please note that this subroutine was obtained during a specific study (inclusive measurement of Fehler beim Parsen (MathML mit SVG- oder PNG-Rückgriff (empfohlen für moderne Browser und Barrierefreiheitswerkzeuge): Ungültige Antwort („Math extension cannot connect to Restbase.“) von Server „https://wikimedia.org/api/rest_v1/“:): {\displaystyle F_2} ), and uses specific cuts on data.
For any other analysis, please check with the author if you can use it.
NEEDTEXT on cuts used in this subroutine and Francesca's subroutine