Tamara
showed some plots of the normalized energies measured in the EMEC
and HEC versus time.
In order to produce these plots, she took the time-intervals covered by various
runs and aligned them such that for each run the `time' is from 0 to 22 ns.
The normalized energies are obtained by dividing the measured energy for
a particular bin in time by the energy averaged over all time bins for
a particular run.
She plotted the results of a number of runs into the same histogram
and finds that the shape of the time-dependence is independent of
the beam energy. This means, that a global correction can be performed,
regardless of energy!
Tayfun
reported that he created a list of runs that are tagged `good' or `bad',
depending on the global timing and the beam-chamber reconstruction.
If a run is has more than 60% bad global time or bad beam chamber reconstruction
he classifies it as `bad'.
Michel pointed out that it would be useful of he would add
the good/bad acceptance/rejection criteria into the list to
form a table or a poor man's data-base. This would make it easier
to study variation on the criteria and to select for different
criteria.
Margret
showed some plots of her longitudinal shower shape analysis.
She now used the approach, where she fits for the shower-shape
parameters in the EMEC and for the amount of material that is always
in front of the EMEC. These fits are done runs that have no additional
material in front.
Then she fixes all shower shape parameters and fits for the
amount of material in front. This results in somewhat poor and
inconsistent fits. The thickness of the individual Pb plates of extra material
is known to be about 0.45 Xo. With that, the fit-results indicate either
less and less material that is always in front of the EMEC or a
plate-thickness that is significantly less than the one given.
Neither case is very likely.
So, instead of fitting for the material thicknesses, Margret fixed
all shower shape parameters to the ones obtained with the runs that
have no additional material in front, and she also fixes the amount of
material in front to be the amount of material obtained in the initial fits
plus the known material of the additional plates. Then she overlays
the measured EMEC energies from the first, second and third EMEC compartment
with the theoretical energies, obtained from the initial shower-shape
parameters. She finds that there is good agreement in the
second and third compartment of the EMEC. She also finds that for the runs
with lots of additional material in front, the energy measured in the
first compartment tends to be significantly lower than the energy
that should have been measured, if the theory is correct.
The conclusion that was reached by everyone is that the most
likely scenario is, that in a significant number of events the shower
start early and radiates energy far off to the side, where it is not
detected. It was suggested that Margret should look at the lateral
shower size, and, if possible see whether there are any hits in the front
veto wall. Michel pointed out that without MC studies it will not
be possible to obtain any further understanding on this.
Richard pointed out that the understanding of the longitudinal
shower shape might be useful to separate em showers from pion showers
e.g. in tau analyses in ATLAS. Furthermore the shower-shape might help
to assign depth-weights to cells that are used in position resolution studies.
Michel
reported that he talked to Rob on the phone and learned the very important
information that
Naoko now uses FFT to obtain the digital filtering weights for the
EMEC. After she obtained the new weights, she finds that the need for
timing corrections goes away!