High Energy Frontier

Pions, muons and positrons

Pions, muons and positrons: The M11 beam channel provides low intensity beams of pions, muons and positrons for testing and calibrating detectors for particle physics experiments world-wide.  Three notable examples from the period 2013-2018 are described here. TREK The TREK experiment is searching for new physics beyond the standard model in the rare decay modes of kaons. In November 2013 and June 2014, a group led by Mike Hasinoff (UBC) tested the scintillating fibre target to establish the bias voltage offsets for each individual MPPC detector/scintillating fibre combination. Muon and positron tracks through the detector were measured to compute individual fibre efficiencies. This target was subsequently used for data taking in Experiment 36 at J-PARC in Tokai, Japan. Previous to this, in November 2012, the TREK group tested TOF counter time resolution and e-mu discrimination using a polyethylene block placed in front of a Lead-Glass-Counter to change the shower development. ATLAS Polycrystalline chemical vapor deposition (pCVD) diamond detectors are a candidate for forward calorimetry in the high luminosity environment of the CERN LHC.  One such detector was exposed to particles delivered by M11 to quantify the variation in signal response across the surface of such a detector. A discrepancy was observed in the diamond detector’s response to beam particles at different bias polarities.  This study was documented in a Carleton MSc thesis, "Characterization of diamond sensors for use in ATLAS calorimetry upgrades", by Joshua Turner, 2012, Super-B and BELLE The Super-B drift chamber group undertook two tests of drift chamber prototypes in the M11 beam line in 2013. These tests were the first to demonstrate that the particle identification capabilities of drift chambers could be significantly improved by counting individual ionization events in the gas (“cluster counting”), rather than just measuring the total energy deposited in each cell. The results were published as NIM A735, 169-183 (2014), and formed a key component of the PhD thesis of Jean-Francois Caron (UBC, 2015). After the merging of the Super-B and BELLE-II collaborations, the Belle II Canada group used the M11 beamline to test pure and thallium CsI crystals with various readout options in the summer of 2015. The group subsequently decided not to pursue pure CsI. The thallium-doped CsI data have been used, along with data collected at the proton irradiation facility at TRIUMF, to develop a new method of distinguishing hadronic from electromagnetic energy deposits using pulse shape discrimination. This technique is being implemented for the Belle II calorimeter, and will form an important component of the PhD thesis of S. Longo (Victoria).