HAPPEX/Lumi PMT Studies Luis Mercado UMASS 7/10/09

PMT Linearity Past tests have shown nonlinearities in PMT output dependant on input and gain. Want to study and document good linearity regions for Lumi and HAPPEX PMTs.

PMT Linearity (Formalism) A PMT’s non-linear response can be expressed as follows: Experimental asymmetry can be approximated:

Experimental Test Setup

Lumi PMT Linearity Input = 12nA HV = 370 Output = uA B*N_0 = -5.14%

Good Lumi PMT Linearity Input =~1nA HV = 690 Output ~ 7uA B*N_0 = 1.19%

HAPPEX PMTs Received one HAPPEX PMT last week. Re-built experimental setup with bigger box. Have done linearity tests at input photocathode currents of [ ] nA. Only good linearity region found was for an input of ~1nA at HV=1250.

Linearity of output signal breaks down with high enough HV. Signal becomes unpredictable in these regions.

HAPPEX PMT Linearity Input ~1nA HV = 1100 Output = 7uA B*N_0 = %

Good HAPPEX PMT Linearity Input ~ 1nA HV = 1250 Output~ 37 uA B*N_0 = 0.35%

Odd Pedestal Behavior The pedestal signal is huge for HV=1250. Huge signal with no light.

Odd Pedestal Behavior Also happens with Lumi PMT.

Ongoing Tests Need to track down the cause of the odd pedestal behavior. Study other available HAPPEX PMT. Finalize linearity mapping for all PMTs.

Acknowledgements Krishna Kumar Kent Pashke Dustin McNulty Robert Michaels Aimee Shore HAPPEX/PREX Collaboration