HAPPEX/ Lumi PMT Studies

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# HAPPEX/ Lumi PMT Studies - PowerPoint PPT Presentation

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).

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### HAPPEX/Lumi PMT Studies

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:
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 [0.06-6.0] 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 = -15.69%

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