1. PEPPo Weekly Meeting February 23, 2011 PEPPo Electromagnetic Calorimeter First measurements Jean-Sébastien Réal, Eric Voutier Laboratoire de Physique Subatomique et de Cosmologie Grenoble, France

2. Experimental setup Light tight crystal box Optical coupling with gel or silicon cookie Crystals are illuminated with 22 Na or 137 Cs radioactive sources for the measurement of their energy resolution in self-triggering mode. The influence of the wrapping material and of the optical coupling are of interest, as well as a relative comparison of the crystals performance.

3. Sodium source spectra Pedestal 0.511 MeV 1.275 MeV Discriminator threshold effect HV = 1200 V  t = 2.0 µs Th. = 7 mV

4. Cesium source spectra Compton edge region 0.662 MeV HV = 1200 V  t = 2.0 µs Th. = 7 mV

5. Experimental data CsI Crystal Resolution HV = 1200 V Th. = 7 mV Crystal 5 Background correction Statistics + Background Systematics Crystal 3 Original Tyvek wrapping gives 4.01% Mylar wrapping gives 7.90% Optical gel coupling gives 3.82% Opical cookie coupling gives 4.18% Operating time gate The E166 wrapping configuration (Tyvek+Copper) will be preserved.

6. Experimental data CsI Crystal Resolution Source data from E166 Source data from PEPPo The observed resolution dispersion for the PEPPo configured crystals is ±8%, as compared to ±9% for the photon yield measured by E166. HV = 1200 V  t = 2.0 µs Th. = 7 mV

7. Experimental prospects Experimental Plan  Visual characterization (optical transmission) and carefull cleaning (optical coupling) of each crystal for final measurements of the resolution.  Evolution of the resolution along the crystal (optical transmission).  Characterization of each PMT (quality check).  Integration and test of the LED monitoring system. To be done with radioactive sources Data collection and analysis by the end of march

8. Cosmic Bench Test Experimental prospects A new cosmic trigger is under construction for the complete characterization of the crystals in Grenoble, and will also be used at JLab. The characterization of the final assembly (crystals + PMTs + custom bases) with cosmic will be the last measurement before shipping. The combination of an up-down coincidence with a crystal raw and the anti-coincidence of the other crystals define a track. At JLab, additionnal lead shielding between cosmic scintillators and the crystals will select minimum ionizing muons with a well-defined energy deposit.