10 - H1 - Desy

4.3 Triggering 57
energetic tracks in the tracker. Subtriggers s82 and s83 were used. The exact definition
for the s82 subtrigger has been changed in the year 2006 from demanding at least 3 tracks
with p T > 400 MeV to at least one track with p T > 900 MeV. The change has been
in charge from run 488289 on. The subtrigger s83 has been additionally verified by L2
topological finder in order to detect D ∗ or di-jet events and was available until run 487915.
Since the statistics of the alternative monitor sample is insufficient for a reliable determination
of the trigger efficiency, the subtrigger s61, based on both SPACAL energy deposition
(including the inner part of the calorimeter) and the tracker, has been included.
Table 4.2 summarises the subtriggers used to determine the efficiency of s67. The overlap
between two samples amounts to 50% of the main monitor sample.
Subtrigger L1 Condition L2/L3 Condition
Monitor
Sample
s0 E IET (outer) > 6 GeV R Spacal > 20 cm
s3 E IET (outer) > 9 GeV R Spacal > 30 cm
s9 E IET (outer) > 2 GeV R Spacal > 30(40) cm
E ET6 > 3 GeV
s82
NTrack 400MeV > 2
−
Alternative
Monitor
Sample
s83
(NTrack 900MeV > 0)
E ET6 > 3 GeV
NTrack 400MeV > 2
D ∗ or di-jet
s61
E IET (all) > 6 GeV
NTrack 900MeV > 0
−
Table 4.2: Subtriggers definitions used for monitoring s67 trigger efficiency.
The trigger efficiency has been evaluated for clusters passing the same cluster selection
as used later in the main selection with the sole exception of the isolation criteria, which
has been skipped altogether. A consistent usage of only highly isolated clusters decreases
the statistics of monitor sample overall by 70% and particularly in forward direction by
85% introducing a high error on fitted trigger efficiency. The possible bias due to missing
isolation criteria has been studied and the results are compatible within statistical errors.
The LAr trigger suffered during the HERA II running period from various localised hardware
problems. In order to restrict the measurement to the well triggered events the
trigger efficiency has been studied as a function of the variable zr defined as
zr =
{
z
r + 300 cm
for CB1, CB2, CB3, FB1, FB2 LAr wheels
for IE1 LAr wheel.
(4.3)