GlueX Barrel Calorimeter

The GlueX Detector in Hall D at Jefferson Lab has at its "heart" the barrel calorimeter (BCAL), and the design and construction of this device was undertaken by our group. This device is responsible for the detection, identification and total energy measurement of both neutral (photons, neutrons) and charged (protons, pions) particles.

Specifically, the BCAL must provide excellent energy and timing resolution, low threshold of detection, and the ability to completely contain the electromagnetic showers resulting from the conversion of photons. The dynamic energy range for photons over the complete list of induced reactions in the liquid hydrogen target spreads from as low as 40 MeV to 3.5 GeV. At the higher end of this range, the BCAL must be at least 15 radiation lengths thick for normal incidence, in order to capture enough of the produced photon shower to allow the correct reconstruction of the photon's energy. This requirement is coupled to the minimum inner radius of the BCAL which will allow for the placement of the interior subsystems (chambers, start/vertex counter and target), in setting the radial dimensions of the BCAL. It's longitudinal dimension is largely dictated by the length of the solenoidal magnet, resulting in a length of 3.9 m.

A design that is particularly suited for this experiment, is one of a lead and scintillating fiber combination (Pb/SciFi), with the fibers embedded in lead sheets that have been plastically deformed ("swaged") and aligned parallel to the central axis of the Hall D detector. The plans are to push the state-of-the-art envelope and improve both energy and timing resolution of BCAL to make it the new benchmark of electromagnetic calorimeter. To this end, specialized Pb/SciFi design, construction and testing facilities have been set up at our university. Prototype modules have been constructed locally, leading to the production of the 48 modules needed to complete the BCAL.

The construction of the BCAL at the University of Regina was completed ahead of schedule, in December 2011, hailing a major milestone for the entire 12 GeV Upgrade at Jefferson Lab.  Follow the stories in our news.

The BCAL was shipped to Jefferson Lab and placed inside the magnetic field of a superconducting solenoid.  Its operation presents a challenge for the photo-sensors that detect and amplify the scintillation light created in the fibres of the BCAL for the electronics to process. Considerable R&D had been conducted by the GlueX groups at the U of R and JLab on solid state photo-sensors commonly referred to as Silicon Photo-Multipliers (SiPM's) of large enough area to be used instead of traditional vacuum tubes that cannot operate in such strong magnetic fields. The R&D has pushed industry to develop and market large area SiPM's and GlueX will be the first experiment that will utilize such sensors that have wide application in medical imaging and other photo-sensing applications in industry.

In 2013 the BCAL was commissioned and is now fully operational, with recent work focusing on its calibration.  More information is available on the Hall D BCAL Wiki page.