10 - H1 - Desy

4.3 Triggering 59
simulation is used. Additionally efficiency correction is introduced:
w Trigger (t, η γ , E γ T ) = effdata s67
, (4.4)
effs67
mc
where effs67
data is the measured s67 trigger efficiency and effs67 mc is simulated s67 trigger
efficiency. The application of the w Trigger variable is given in section 8.2.2.
s67 efficiency
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0
Data
Mc
CB1
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IE1
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[GeV]
Figure 4.5: S67 trigger efficiency for the year 2006 and for six LAr calorimeter wheels.
The measured trigger efficiency is compared to the MC simulation.
4.3.3 Level 4 trigger
Events triggered by s67 subtrigger are subject to event classification on trigger level four
(L4) 3 and events not classified as any of the hard physics classes are highly prescaled.
The great majority of events triggered by s67 enable L4 HS ET CLUST statement on
trigger level four. The condition for L4 HS ET CLUST is the existence of an electromagnetic
cluster with transverse energy larger than 5 GeV. Events with L4 HS ET CLUST
enabled are classified as class 4 (”High Q 2 ”) events. Figure 4.6 presents the run averaged
L4 rejection rate for events triggered by s67 in the example period of 2006/07 e + p data.
The average rejection rate is about 10%. Here, also the additional L1 trigger requirement
described above, being in force starting from day ∼ 400 of the visualised period may be
noted. It greatly improves the quality of s67 triggered events. which is reflected in the
drop of the L4 rejection rate.
Trigger level four, is working on fully reconstructed event and thus LAr calorimeter clusters
are already formed. The clusters on this level are subject to a rough online energy
3 L2/L3 trigger level is not used in the main selection for this analysis.