SiPM Readback Noise Tagging & HCAL Calibration Dayton Thorpe July 8, 2010

CMS Hadron Calorimeter (HCAL) HCAL sits outside of the tracker and electromagnetic calorimeter (ECAL). HCAL uses steel and brass plates to detect muons that do not interact with ECAL. In the central region, ECAL and the Hadron Barrel alone are insufficient to contain hadron showers. An additional layer outside the solenoid, the Outer Calorimeter (HO), is used to stop high energy hadrons.

Silicon Photomultipliers CMS HCAL group plans to replace over 2,000 Hybrid Photodectors with Silicon Photomultipliers (SiPMs) during 2012 shutdown. In April 2009, 144 SiPMs were installed for testing. SiPM gain varies significantly with temperature (8-10 percent per degree C), so frequent temperature and voltage readbacks are needed for Peltier coolers to maintain a constant temperature (de Barbaro & Vishnevskiy, 2009). Recently discovered that temperature readback induces a large signal. This “feature” will be eliminated in SiPM readout electronics to be installed in Need a software solution for 2010/2011. Objective is to develop a simple algorithm for tagging noise events due to temperature readback without tagging collision data.

There are 132 channels which record ADC counts for 10 time slices per event. The above data are from cosmic rays when triggers from several subdetectors are combined to verify that a muon is actually present which should give a low noise/signal ratio due to temperature readback.

The above data are from a run with an HO trigger: whenever HO records a large value the event is recorded. This should capture all of the temperature readback data to give a higher noise/signal ratio. There are two extra patches of data with more than 6 ADC counts below 0 and more than 15 ADC counts above 20.

Time series of this data is also nonphysical. Two patches of data are distinct in the ADC>20 data. Possibly due to succession of temperature and voltage readbacks.

Conclusion Proposed algorithm would tag events with more than 6 ADC counts below 0 and with more than 15 ADC counts above 20. In the process of developing the code. Next project: redo CMS HCAL calibration report. Conditions such as temperature and voltage of SiPM’s and HPD’s have changed since it was last done one year ago.

Acknowledgments Pawel de Barbaro Dmitry Vishnevskiy Paolo Rumerio John Paul Chou