This year's HCAL test beam run in July was completely devoted to studies of hardware that will be used in the upcoming upgrades. During the course of the two weeks the detector was moved in two independent setups – HF and the combined EB+HB+HO – into various positions relative to the beam. Data were collected with pions, muons and electrons at various energies to study a variety of responses.

In the first of the two weeks, tests were done to qualify hardware to be installed during the 2013 shutdown. First on the list were the multi-anode photomultipliers (PMTs) that will replace existing forward calorimeter (HF) PMTs. After several years of R&D, Hamamatsu R7600U have been chosen in order to reduce background induced by anomalous signals in PMT windows. A highly realistic study was performed where photomultipliers were installed in the same kind of mechanical enclosure as in the experiment with all potential problems due to cross talk, grounding and electronic noise. Preliminary results were rather good and in October another round of tests will be performed to check the behaviour with the final set of signal cables that were not delivered in time for this test.

The other item was a similar, realistic study of behaviour of silicon photomultipliers (SiPM) that will replace hybrid photodiodes (HPDs) in the HCAL outer layer (HO) in 2013. The replacement is needed as the highly non-homogeneous magnetic field in the region where HO HPDs are housed causes discharges and rather strong non-physical signals. Like HF photodetectors, this project is in a mature stage where final tests were performed in conditions as realistic as possible outside the experiment.

The second week was devoted to R&D on silicon photomultipliers (SiPMs) to be installed in the HB/HE region during the Phase 1 Upgrade foreseen for the long LHC shutdown in 2016. Their small size and good performance allow us to envisage longitudinal segmentation of HB and HE. This will considerably improve performance of the whole CMS calorimetry system.

As an important part of jet energy is contained in the CMS electromagnetic calorimeter, the studies required the installation and use of the spare EB supermodule in front of the HCAL megatile. Timely installation and commissioning of SM36 by the ECAL team was highly appreciated, as was the generous and efficient help with its operation. These tests will continue in October as models of SiPMs from several manufacturers will have to be tested, with another set of more detailed measurements with a reduced set of models to follow in 2012.

Summer Students participation in the HCAL Test Beam Run

Princeton graduate student, Tatiana Medvedeva, connecting HO detector for tests.
Four undergraduate students from the University of Maryland (UMD) had the opportunity to come to CERN this summer to participate in the test beam efforts. Their tasks involved shifts to operate the data acquisition and data quality monitoring systems, and projects to modify and run analysis software on the data collected. They met with a UMD post-doc twice before coming to CERN to gain a general understanding of HCAL and to begin working with C++ and CMSSW (the software framework for CMS). Once in Geneva they met nearly daily with post-docs and professors to discuss analysis goals, coding techniques and general test beam knowledge.

There was a plethora of shift volunteers for the July test beam this year, mostly young students eager for experience in “real” science. A sense of camaraderie among many of the shifters was evident and contributed to the positive experience, which included the creation of a dance video entitled National Dance Day at CERN (available on YouTube).

Ultimately the ECAL+HCAL combined July test beam was declared a success, not only for the data collected for multiple HCAL improvements, but for the cultivation of the next generation of physicists. The four UMD undergrads returned home, full of a sense of accomplishment and with plans to show off to their jealous classmates.

— Submitted by Elizabeth Twedt and Dragoslav Lazic