Multiple Coulomb scattering in the MICE experiment

• Main Author: Nugent, John Columba
• Published: University of Glasgow 2017
• Subjects: 539.7; QC Physics
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.705611

The International Muon Ionisation Cooling Experiment (MICE) aims to give the first demonstration of ionisation cooling. MICE will use a low Z absorber to first reduce the momentum of a muon beam; then use a series of radio-frequency (RF) cavities to restore its longitudinal momentum. This action will reduce the overall phase-space volume of the muon beam. The goal of MICE is to reduce the emittance of a muon beam by 5\% and to measure the change in emittance to a precision of 1%. In 2011 MICE took data in its Step I configuration with the goal of understanding the muon beam that will serve the MICE experiment. In order to evaluate the expected performance of the beam using extensive simulation data the MICE user software had to be installed on the Grid. A G4beamline model of the MICE muon beam was updated and validated with Step I data and used for production jobs on the Grid. The results presented in this thesis demonstrate that the simulation is in good agreement with data. These data were also used to determine the pion contamination in the MICE muon beam using the Time-Of-Flight (TOF) and Kloe-light (KL) detectors. The measurement of ionisation cooling in MICE relies on the selection of a pure sample of muons that traverse the experiment. To make this selection, the MICE Muon Beam is designed to deliver a beam of muons with less than ~1% contamination. The upper limit for the pion contamination measured in this thesis is less than 1.4% at 90% C.L., including systematic uncertainties. A similar procedure applied to the G4Beamline and MAUS Monte Carlo simulation yields a pion contamination of less than 1.7% at 90\% C.L., including statistical and systematic errors. The expectation from the simulated MICE Muon Beam is for a contamination of (0.22 +/- 0.01)%. Therefore, the MICE Muon Beam is able to meet the stringent pion-contamination requirements for the study of ionisation cooling. In 2015 and 2016, MICE took data in its Step IV configuration giving the first measurement of multiple scattering with the MICE apparatus. In this thesis the results of the measurement of the scattering of muons in gaseous xenon and lithium hydride are reported. The motivation for the gaseous xenon measurement is to benchmark Multiple Coulomb Scattering (MCS) in a high-Z material, in order to perform further measurements of MCS in the MICE experiment. From this baseline the same analysis was applied to the lithium hydride data, a material for which it is essential to accurately model the MCS for the demonstration of ionisation cooling for muon acceleration. Results from this analysis are compared to GEANT4 simulations and to predictions from an analytical formula advocated by the Particle Data Group (PDG).