Characterisation of the MICE experiment

Abstract

Muon beams of low emittance would deliver intense, well-characterised neutrino beams necessary to explicate the physics of flavour at a Neutrino Factory and for high-luminosity lepton-antilepton collisions at a multi- TeV muon collider. The International Muon Ionisation Cooling Experiment (MICE), based at the Rutherford Appleton Laboratory, aims to demonstrate ionisation cooling, the technique proposed to reduce the emittance of muon beams at such facilities. An ionisation cooling channel has been constructed. The muon beam traverses a low-Z absorber material, losing energy via ionisation. The phase space volume occupied by the beam is reduced, resulting in transverse cooling. This thesis presents two independent analyses accomplished through exploiting data obtained during the “Step IV” commissioning of MICE. Muons can decay within the cooling channel. The presence of electron contaminants within MICE will generate systematic uncertainties on the cooling measurement. The angular distribution of decay electrons is dependent upon the muon polarisation. It is, therefore, imperative to characterise the impact of depolariza- tion in the channel. Chapter 4 presents a unique measurement of the polarisation of the MICE muon beam at the downstream calorimeter. For an initially unpolarised muon beam a polarisation of: -0.021 ± 0.243 (stat.) ± 0.185 (sys.) ± 0.007 (depol.) ± 0.001 (det.) is obtained, appropriately identifying the polarisation of the beam at the point of decay, within acknowledged errors. MICE is devised to possess an on-axis magnetic field. It is paramount that misalignment in the cooling channel is characterised. Chapter 5 ascertains a measurement of the central Focus Coil’s transverse position using single particle transfer matrices. No misalignment of the Focus Coil’s magnetic axis, relative to the beam axis, is observed, within the limits of the analysis. This innovative technique can be employed by any multi-element accelerator system where particle co-ordinates are quantified upon entering and exiting a constituent magnet.