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Photons at low energies? [message #4986]

Tue, 28 August 2007 17:19

StefanoSpataro
Messages: 2736
Registered: June 2005
Location: Torino

first-grade participant

From: *physik.uni-giessen.de

Hello,
Chris has found a particular behaviour of the cluster response for low energy photons...

If you run the EMC simulation (G3) with photons at 200 MeV in the theta range of [40°-140°], and then you perform the full recontruction, this is the plot you get as cluster energy:

index.php?t=getfile&id=3812&private=0

(the plot was made with 10k events, but even with 1k events you can see the same). I check with the stable version 1_0_0 and with the last svn update. It seems that the energy response is discrete, with an energy spacing of ~ 3 MeV. I checked with 400 MeV or higher energies but it seems it is not present there, neither increasing the binning (so it is not an effect of the histogram).

Maybe some problem with digitization?

Attachment: emc_clu_200MeV.gif
(Size: 10.92KB, Downloaded 602 times)

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Re: Photons at low energies? [message #4987 is a reply to message #4986]

Tue, 28 August 2007 18:25

Dima Melnychuk
Messages: 213
Registered: April 2004
Location: National Centre for Nucle...

first-grade participant

From: *fuw.edu.pl

Hi,
This behaviour is really connected with digitization.

Now digitization is implemented in the way that energy range from 0 to 15 GeV digitized with 12 bits. I.e. with step 15000/2^12=3.7 MeV. And it results in such a discrete response.

May be this is not realy realistic and low energy will be digitied with higher precision.

I would propose to put at the moment 14 bits in emp.par file for NBits and update this number when final emc readout will be known in more details.

Dima

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