10 - H1 - Desy

58 Event reconstruction and preselection
where z and r are impact cluster parameters. Since the H1 machine has been subject to
some major repair efforts, the trigger efficiency was studied as a function of time. It was
also evaluated in 16 φ sectors sensitive to the definition of LAr Big Towers. Figure 4.4
presents the example of a zr dependence of trigger efficiency for the 2006 year running period.
Shaded LAr calorimeter areas with significantly low trigger efficiency are considered
as unreliable and are removed from the selection. The same figure presents the efficiency
as produced by the MC simulation. One can note that the main hardware problems were
properly simulated but in general the simulation overestimates the s67 trigger efficiency.
s67 eff.
s67 eff.
s67 eff.
s67 eff.
1
0.5
1
0.5
1
0.5
1
0.5
0 200
0 200
0 200
1
1
1
0.5
1
0.5
1
0.5
1
0.5
0 200
0 200
0 200
0.5
1
0.5
1
0.5
1
0.5
0 200
0 200
0 200
0.5
φ1
φ2
φ3
φ4
1
0.5
1
0.5
0 200
φ5
φ6
φ7
φ8
0 200
φ9
φ10
φ11
φ12
0 200
0 200
0 200
0 200
0 200
zr [cm]
zr [cm]
zr [cm]
zr [cm]
1
0.5
φ13
φ14
φ15
φ16
Figure 4.4: The trigger efficiency for 16 φ sectors as the function of zr variable. Data
points are plotted together with the MC simulation of the trigger efficiency (blue histogram).
Shadowed areas indicate regions which are removed from the selection.
The trigger efficiency as a function of the cluster energy has been evaluated for each year
and for each LAr calorimeter wheel. An example of determined efficiency for the year
2006 is presented in figure 4.5. The step function has been fitted to the points for both
data and MC. One can see again that simulated MC trigger efficiency differs significantly
from the measured data efficiency. Therefore, for most H1 analyses, the simulated trigger
response is neglected. Instead, the trigger efficiency as determined from data is treated as
a separate correction. In this particular analysis though, trigger introduces a bias to the
vital variables (cluster shape variables - see section 6.1) and for this reason MC trigger