[Hps-ecal] Today's meeting canceled

[Garcon Michel]

HI Andrea,

Two quick remarks on your slides:

Slide 11: we have not started mounting the LED holders at JLab. Currently, we think it will be done after testing individual crystals with glued APDs.

Slide 18: somehow, will have to set a threshold in an apparent gain shift (from LED run) before taking any action. For DVCS/IC, we saw a decrease of about 10% in the LY from the laser system, only for the innermost crystals (layer closest to beam). But the calibration with physics events (pi0-> gamma gamma) did not show any of this shift. That could be due either to the fact that only the first mm of the crystals were being radiation damaged, or that the calibration does not work too well for crystals on an edge, or else ? In any case, I don't know how to quantify it, but a LY decrease from the LED system should be used as a warning to trigger more in depth calibration with physics events.

Regards,
Michel.

_______________
Michel Garçon
Irfu/SPhN                                               
CEA-Saclay, bât. 703                               
91191 Gif-sur-Yvette cedex        
France                                           
Tél.: +33 1 69 08 86 23

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