Effect of dead material in a calorimeter Page: 4 of 14
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One, two, or three contiguous layers were then dropped from the energy sum at
various locations within the HCAL compartment. The resulting distributions were
then characterized by their means and second moments, the r.m.s. The first and
second moment were scaled to those for no dead material anywhere.
A first attempt to correct for the dead layer was made. The first active layer was
given a weight so as to compensate for the dead material. For example, for 1 dead
layer the next layer in the stack contributed to the energy sum with weight 2,
while for 2 dead layers the weight was 3. This scheme gives a uniform samping
fraction throughout the calorimeter. If the hadronic shower is uniform on the
scale of the dead material, then this method will restore the spread seen in the
energy sum. In contrast, if there are fluctuations on the scale of 2.5, 5, or 7.5 cm,
then the distribution will indicate poorer measurement capability.
The results for 2.5, 5.0, and 7.5 cm unsampled ( or "dead" ) Fe are shown in
Figs. 1, 2 and 3 respectively. The 2 sets of data points correspond to no
corrections, o , and a correction which restores uniform sampling fraction, *.
The magnitude of the loss of energy depends on the location of the of the dead
material. Basically, it corresponds to the mean energy deposition "profile". The
peak loss is ~ 4%, 8%, and 12% for 2.5, 5.0, and 7.5 cm dead fe respectively.
That peak occurs at - hadronic shower maximum, or layer 5 to 10 in HCAL.
Since ECAL is - 0.74 absorption lengths, the location of maximum sensitivity to
dead material is - 1.5 - 2.6 absorption lengths.
The weighting correction restores the unsampled energy to the sum so as to
restore the average response. For 2.5, 5.0, and 7.5 cm dead Fe, the mean is
restored to 1%, 2%, and 4% respectively, as seen in Figs. 1, 2, and 3. It is clear
that the average response can be restored by adjusting sampling.
The Increase in the r.m.s.
The question remains as to the effect of dead material on the spread of the energy
measurements. In Figs. 4, 5, and 6 we show the ration of rms/mean , normalized
to the case of no dead material, for dead material of 2.5, 5.0, and 7.5 cm of Fe
respectively as a function of the location within HCAL of the dead material. The 2
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Green, D. Effect of dead material in a calorimeter, report, October 1, 1995; Batavia, Illinois. (digital.library.unt.edu/ark:/67531/metadc628213/m1/4/: accessed September 21, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.