The Results of 10 Additional PMT Tests 1.Timing of afterpulse 2.ADC readout 3. Conclusion TTU HEP Group Meeting, Apr. 14, 2004

Test of R7525 PMT(CA1522) shows afterpulse. Need to confirm if afterpulse is general behavior in other PMTs. PMT serial # used in the test CA0066 CA0068 CA0405 CA0515 CA0874 CA1078 CA1313 CA1609 CA1817 CA2108 } } From batch 1~5 From batch 6~10

1. Timing of afterpulse a)b) c) a)0066, 0068, (1522) b)0405, 0515, 1609 c) 0872, 1078, 1313, 1817, 2108

Pulse height of afterpulse does not depend on main pulse (top). Afterpulse rate is higher in c) type, middle in b) and lower in a)(bottom). a) 0068b) 0405c) ADC readout

Most probable explanation of afterpulse Ionization of the residual gases in the tube gives rise to afterpulse. The usual ions are H 2 +, He + and CH 4 +. They cause afterpulses which have 0.3, 0.4 and 1  s transit times. -- photomultiplier tubes, Philips Photonics 3 peaks in timing distribution may be matched to ions. Test with type C) PMT under He abundant condition can be tried. -> expect that second peak will increase before/after He + blowing.

Energy estimations for the afterpulse Expect 0.25 p.e./ GeV for the HF calorimeter. (I) Based on ADC count of the afterpulse ~150 ADC count after 100 times amplified PMT output pC/count for Lecroy 2249W. 150 x 0.25 pC = 37.5 pC Since PMT output was amplified 100 times, it becomes pC. If we assume 10 5 gain for the PMT, the charge at the PMT cathode is 0.375x C. The number of p.e. at the cathode is (0.375x )/(1.6x ) = 23.5 p.e.  94GeV.

(II) Estimate base on pulse shape 500mV pulse height with 10ns width after 100 times amplification.  5mV PMT output I = Q/  t= V/R*1/2 (50ohm oscilloscope termination) Q = V/R*1/2*dt = (5x10 -3 )/50*1/2*10x10 -9 = 0.5x C = 0.5pC # of p.e. at PMT cathode = 0.5x /(1.6x x 10 5 ) =  125GeV

(III) If 10GeV is deposited in a tower, 10 x 0.25 p.e./GeV = 2.5 p.e. 2.5 x 1.6 x x 10 5 = 4 x = 0.04 pC After 100 times amplification, 4pC. Since 0.25pC/count in Lecroy 2249W ADC, 4pC => 16 ADC counts a)~0.06% b)~0.10% c) ~0.72% Afterpulse rate at 10GeV (main signal) cause ~100GeV afterpulses.

3. Conclusion & Plan *Test with another type of PMT -> We already know that there is afterpulse for other PMTs. -> Also need to quantify the level. *Operate PMT under He abundant condition. -> To understand(confirm) the source of afterpulse.