We observe two classes of anomalous signals in
We observe two classes of anomalous signals in HCAL 1) Electronics noise from the Hybrid Photo Diode (HPD) and Readout Bo. X (RBX) used for the Hadronic Barrel (HB), Outer (HO), and End. Cap (HE) calorimeters HV gap ~8 k. V The HPD has 18 channels/device There are 4 HPDs in a RBX 2) Cherenkov light produced by interactions in the window of the Forward Calorimeter PMTs Glass window thickness in the center is ~1 mm increasing to ~6. 1 mm on the edges
HPD and RBX Noise HPD Ion Feedback (~1 HPD channel) CMS Preliminary Photoelectron induced liberation of ions from the silicon diode which accelerate across the HV gap and interact with the photocathode freeing additional photoelectrons HPD Discharge (up to 18 HPD channels) With the HPD operating at ~8 k. V in the CMS magnetic field, dielectric flashover from the wall can produce large signals in many channels RBX Noise (up to 72 channels) Source unknown, possibly due to external noise coupling to HV of many channels across the whole RBX For the HB and HE the total rate of HPD and RBX noise is 10 -20 Hz for E>20 Ge. V which includes the contribution from the OR of 288 HPDs HPD and RBX noise is random and the overlap with physics is very low HPD/RBX noise produce distinct patterns in HCAL Filters have been developed making use of hit patterns, timing, pulse shape, and EM fraction
Signals from interactions in the HF PMT windows and in the fiber bundles were observed in the testbeam and published in: Eur. Phys. J. C 53, 139 -166 (2008) 2004 Test beam Long fibers: extends for the full length of HF Short fibers: start at a depth of 22 cm from the front of HF Fiber Bundles PMT Window Rates in 2009 minimum bias data (~1720 PMTS) ~6 x 10 -3 per event identified for 900 Ge. V data ~8 x 10 -3 per event identified for 2. 36 Te. V data Dominant sources are muons from decays in flight and hadron shower punch through EL (Ge. V) Most of the HF PMT hits can be identified based on the energy sharing between the Long and Short fibers using R = (EL-ES)/(EL+ES). Filters have been developed to effectively remove anomalous signals with little impact on real energy deposits. CMS Preliminary PMT Hits More details on the filtering and characteristics of the noise has been published in: JINST 5 T 03014 ES (Ge. V)
Notes to the Presenter These are technical slides intended for HCAL experts Contacts: Frank Chlebana (chlebana@cern. ch) Vladimir Gavrilov (gavrilov@cern. ch) Reference Material: The material has been discussed in the HCAL DPG and the ASCTF meetings. Results have been published in: Eur. Phys. J. C 53, 139 -166 (2008) JINST 5 T 03014
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