HCal Overview

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The SBS Hadron Calorimeter is a transversely segmented sampling calorimeter designed to detect several GeV protons and neutrons. HCal sits behing the SBS dipole magnet which separates protons and neutrons on the surface of HCal by their charge. HCal was designed to have time resolutions as good as 0.5 ns, position resolution of 3-4 cm, and has an energy resolution of around 30%.

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HCal is comprised of 288 individual detector modules. These modules are arranged in 24 rows and 12 columns. Each module is composed of 40 layers of iron alternating with 40 layers of scintillator. The iron causes the hadrons to shower and then scintillator then samples the energy. The light produced by the scintillator passes into a wavelength shifter at the center of the modules to shift the light into the sensitive region of the PMTs. This light then passes through a light guide into the PMTs. Each HCal module has six LEDs pointing into the PMT that can be illuminated for calibrations and things like gain monitoring.

HCal has three triggers available. They are the sum trigger, the LED pulser, and the cosmic paddle coincidence. The sum trigger is the primary HCal production trigger. The PMT modules on HCal are grouped in 4x4 clusters of adjacent PMTs which have their energies summed by summing amplifiers modules. These clusters energies are then summed in groups of 4 adjacent clusters to make 10 overlapping super clusters (8x8 PMTs). These 10 super cluster energies are sent to discriminator and if any of the 10 super cluster energies exceeds the threshold a sum trigger will be produced.

The LED pulser trigger is programmable to allow the user to illuminate different LEDs in different patterns. This pulser is then used as the DAQ trigger and will often be run in conjunction with the sum trigger to monitor PMT gains. The cosmics paddle trigger is a coincidence of a scintillator paddle above and below HCal where each scintillator paddle triggers on a coincidence of the 2 PMTs on either end of the paddles.

The DAQ of HCal is composed of 19 16-channel fADCs (18 for the PMTs and 1 for a reference time, the 10 supercluster sums, and the cosmic paddles) and 5 F1 TDCs. The fADCs measure energy in 4 ns bins and the full waveform of the PMT signal is recorded. The TDCs measure the timings of hits in the PMTs.