Search

A search for new physics with a signature of missing energy in events with high pT jets is presented. The analysis is performed with 1.1 fb-1 of 7 TeV data taken using the Compact Muon Solenoid detector at the Large Hadron Collider in 2011. The kinematic variable α T is used to control the dominant QCD background that exhibits fake missing energy originating from mismeasurment. The remaining electroweak backgrounds are estimated using data-driven techniques through the use of two control samples. The background from boosted W decays is estimated with the use of a dedicated µ + jets control sample, while the irreducible background from Z → [Symbol appears here. To view, please open pdf attachment] is estimated using a γ + jets control sample. A shape analysis is performed across eight bins in HT , with the signal selection and the two control samples treated simultaneously in a likelihood fit. The data was found to agree very well with the Standard Model only hypothesis with a p-value of 0.56, which indicates no evidence of new physics. The results are interpreted in the scope of a possible new physics model, the Constrained Minimal Supersymmetric Standard Model. Exclusion limits are set at the 95% confidence level on the parameters m0 and m1/2 that set the mass hierarchies of the sparticles. An extension is also presented allowing additional signal into the muon control sample. The effect on the limit is negligible, although adopting a leptonic variable of the αT variable increases the ratio between signal and background events significantly. This approach is recommended for searches with higher statistics in 2012.

The International Muon Ionization Cooling Experiment (MICE) is designed to demonstrate the currently untested technique of ionization cooling. Theoretically, this process can condition the high quality muon beams required to build a neutrino factory or muon collider which will be the next generation of machines for the study of Particle Physics. The beam line to transport muons into the MICE cooling channel lattice cell was installed in December 2009. Step I of the experimental programme, whose goal was to demonstrate that the beam line can generate beams similar to those expected in a neutrino factory cooling channel, was completed in August 2010. Methods were developed to use time difference measurements in the MICE time of flight counters (TOFs) to obtain a transverse spatial resolution of approximately 10 mm and to track muons through the focusing elements of the beam line, thus allowing the trace space vectors of individual muons to be reconstructed and their integrated path length to be calculated. The TOFs were used to make an absolute measurement of the momentum of muons with zero bias and a systematic error of less than 3 MeV/c. The measured trace space vectors of single muons were used to estimate the emittances and approximate optical parameters of eighteen muon beams. The results of beam line simulations were compared with the measurements and, once the effects of experimental resolution had had been included, found to be in good agreement. A sample of individual muons whose phase space vectors had been measured was injected into a simulation of the full MICE cooling channel; the beam was found to be suitable for demonstrating muon cooling, although some fine tuning of the cooling channel optics will eventually be required.

The purpose of this thesis is to study the electron spin relaxation (eSR) in small organic molecular semiconductors using the muon spin relaxation (MuSR) technique. One of the inherent problems in utilising the spin degree of freedom is the lack of understanding of the fundamental mechanisms behind spin relaxation. Two interactions have been proposed as the dominant mechanisms behind the spin relaxation, the Hyper ne interaction (HFI) and the Spin Orbit (SO) interaction. There remains much debate over the models for these interactions and their exact role, a contention that drives the work carried out in this thesis. The MuSR technique is utilised providing a novel molecular scale probe sensitive to relaxation rates in the range of 0.01-10 MHz. The Avoided Level crossing (ALC) MuSR application is useful in accessing the spin relaxation information. Temperature dependent ALC-MuSR measurements are performed for a selection of functionalised acenes and Quinolate molecules. Transverse eld MuSR measurements are also taken to determine the Hyper ne coupling constants present. DFT and semi-empirical computational methods are employed to determine theoretical values for the isotropic and anisotropic terms and the suitability of these methods was discussed. It is concluded that an intra-molecular eSR is present in all small organic molecular semiconductors. The mechanism behind this eSR was found not to be the HFI but in fact the SO interaction. It is also determined that the eSR is coupling to the vibrations in the molecule and a possible theory based on the curvature of the molecule from the vibrational modes inducing an enhanced SO coupling is proposed, which results in the eSR. The nal part of this thesis looks at the future experiments that have been initiated or can be conducted to further the understanding of spin relaxation and determine the role of a vibrationally enhanced SO coupling.

The Main Injector Neutrino Oscillation Search (MINOS) project is a long baseline neutrino oscillation experiment, consisting of a beam of mainly muon neutrinos measured by two steel-scintillator calorimeters. The Near Detector will measure the beam spectrum before oscillations have a had a chance to occur significantly, with the Far Detector measuring the spectrum 735 km away. MINOS has been designed to achieve a relative energy scale calibration between the detectors to 2% and an absolute calibration to 5%. The relative calibration is performed using muons and the absolute using measurements from testbeams, taken with the purpose built Calibration Detector (CalDet). Results are presented from tests of the MINOS calibration chain, carried out using data from the CalDet and Far Detector. A strip to strip calibration of both the CalDet and Far Detector has been carried out using muons and the light injection system. This calibration has been performed to the 2% level at the CalDet. Results are shown of a cross detector calibration using beam related and cosmic ray muons, with momenta selected through range. Studies of the charge distribution of upward-going muons, which come from atmospheric neutrino interactions in the rock beneath the Far Detector, are presented. MINOS will be the first experiment that has been able to measure the charge of muons produced from atmospheric neutrinos.