Yu. Guz 08/02/20121 HCAL 2011/2012 shutdown activities

Yu. Guz 08/02/ The HCAL maintenance was performed on Dec (side C) and Jan (side A). This time it was decided to replace: dead dark current > 50 nA rate effect > 0.2 (abnormally high rate effect was seen with the LED system for many HCAL PMTs, reported several times at CALO meetings, see also next slides). Replaced only the most unstable ones, mainly for studies. Total of 59 PMs replaced !!! 2x more than in 2010/2011. The replaced PMT/CWs side C were briefly studied with LED pulses at the pit. Few observations: 1) the rate effect in replaced PMTs a) is visible also with oscilloscope on LED pulses b) is a feature of PMT itself and not of CW: an attempt made to replace the CW board c) to some extent, observed also in all “leaking” PMTs Why this abnormal rate effect is absent at all in ECAL? Studies will be continued, after the RP clearance of PMTs. PMT replacement > 200 nA (13) nA (14) nA (20) rate effect > 0.2 (11) dead CW (1)

Yu. Guz 08/02/ The HCAL 137 Cs run was performed on 26-Jan Three source passages, in order to determine the PMT slope parameters. A preliminary HV recipe (for E T max=15 GeV) prepared. To be done: check the contact in ATI connectors with CAT using the reflection test. Are we going to work at E T max = 30 GeV in 2012? If yes: 1.a HV recipe should be produced (based on the last 137 Cs run; one more Cs run may be useful to verify it). 2.L0 recipe for E T max = 30 GeV should be produced 3.not to be forgotten: recover the energy scale in the reconstruction (Conddb?) Preparations for the 2012 run

HCAL PMT rate effect Larger than in ECAL! To be understood. The PMTs with high rate effect look distributed randomly, so not related to the average anode current. In some PMTs, the gain stabilizes rather slowly, at few hours time scale. In several cells the instability is high, suspect malfunctioning CW base, to be replaced / repaired during the winter shutdown. (shown for 07-Sep – 05-Oct) 4Yu. Guz 2011/11/23

Yu. Guz 09/02/ There were few dead and unstable PMTs to replace. In addition, it was decided to replace also those with anode leakage >40 nA, with the following motivation: 1) the leakage current tends to grow (reported several times at CALO meetings in 2010), it reached ~ nA in few cells, starting from ~10 nA in October 2009; 2) although a moderate leakage is not a problem for HCAL, at >1000 nA the 137 Cs calibration may fail : the calibration current itself is up to 700 nA in some cells, and the sum may saturate the integrator (the limit is ~1500 nA) 3) the replacement therefore makes sense to avoid (or at least reduce number of) channels with nA by the end of 2011; Total of 25 PM/CWs replaced: dead : 3 unstable, intermittent 5 anode leakage /2011 – a reminder dead (3) unstable (5) nA (2) nA (6) nA (9)

Yu. Guz 08/02/ September 2009: leakage < 5 nA over the whole HCAL Present situation: 17 PMTs with 40…900 nA replaced + 30 PMTs with 10…40 nA left on HCAL Features of the leakage current: - surprisingly, appeared 5 years after the production; - increases with time; - “ohmic” (proportional to HV rather than to PMT gain); - the PMTs with high leakage showed also high long-term gain variation: 10…40% drop from to PMs with maximal leakage currents were studied. In each of them a dynode exists for which the resistance to anode is ~ GΩ. The conductive path is situated inside the PMT bulb and not on its outer surface. In principle, there can exist PMTs with high conductivity between two dynodes, but they are not detectable with integrators. PM anode leakage The leakage seems to be intrinsic for our PMTs, we cannot do much about it.