Techn. University, Diss., 2006--Darmstadt.

Heidelberg, Univ., Diss., 2005.

Univ., Diss., 2008--Frankfurt (Main).

Techn. Hochsch., Diss., 2003--Aachen.

Techn. University, Diss., 2006--Darmstadt.

This thesis presents details of the search for the Standard Model Higgs boson, in the low mass region (100 ≤ MH < 150 GeV), with the ATLAS detector at CERN. In this range, a Higgs boson may be produced in association with a W or Z-boson and decay predominantly to two b-quarks (H → b¯b). Specifically events having large Higgs boson transverse momentum (pT > 200 GeV) and large recoiling W- boson transverse momentum (pT > 200 GeV) are considered as a means to reduce the contribution from background processes. In this high pT (boosted) regime, novel jet-substructure techniques are applied to the reconstructed jets resulting from the Higgs boson decay. In order to use these jet-substructure techniques, b-tagging efficiency scale factors in the jet-substructure regime have also been derived for the first time. Details of their derivation are presented for many b- tagging algorithms, with 14.3 fb¯¹ of ATLAS proton-proton collision data in 2012 at √s = 8 TeV. These, and their associated systematic uncertainties, are then applied to the Higgs boson search. No significant measurement of Higgs boson production was made, based on 20.4 fb¯¹ of ATLAS proton-proton collision data in 2012 at √s = 8 TeV. For a Higgs boson mass of 125 GeV, an exclusion limit of 6.12 x σSM was found at the 95% confidence level, and a signal strength of 0:93 ± 2:63 was measured, consistent with both background-only and signal (Standard Model Higgs boson) plus background hypotheses.

3D silicon pixel detectors are a novel technology where the electrodes penetrate the sili- con bulk perpendicularly to the wafer surface. As a consequence the collection distance is decoupled from the wafer thickness resulting in a radiation hard pixel detector by design. Between 2010 and 2012, 3D silicon pixel detectors have undergone an intensive programme of beam test experiments. As a result, 3D silicon has successfully qualified for the ATLAS upgrade project, the Insertable B-Layer (IBL), which will be installed in the long-shutdown in 2013-14. This thesis presents selected results from these beam test studies with 3D sensors bonded to both current ATLAS readout cards (FE-I3) and newly developed readout cards for the IBL (FE-I4). 3D devices were studied using 4 GeV positrons at DESY and 120 GeV pions at the SPS at CERN. Measurements presented include tracking efficiency (of the whole sensor, the pixel and the area around the electrodes), studies of the active edge pixels of SINTEF devices and cluster size distributions as a function of incident angle for IBL 3D design sensors. A simulation of 3D silicon sensors in an antiproton beam test for the AEgIS experiment, with comparison to experimental results and a previous simulation, are also presented.

The neutron-deficient gallium isotopes down to N=32 have had their hyperfine structures and isotope shifts measured via collinear laser spectroscopy using the COLLAPS (COllinear LAser sPectroScopy) beam line. The ground-state spin of 63Ga has been determined as I = 3/2 and its magnetic dipole and electric quadrupole moments were measured to be µ = +1.469(5) µN and Qs = +0.212(14) b respectively. The nuclear moments of 70Ga were measured to be µ = +0.571(2) µN and Qs = +0.105(7) b. New isotope shift results were combined with previously measured values of the neutron-rich isotopes and the changes in mean-square charge radii of the entire gallium isotope chain were investigated. Analysis of the trend in the neutron-deficient charge radii demonstrated that there is no evidence of anomalous charge radii behaviour in gallium in the region of N=32. A sudden increase of the charge radii was observed at the N=50 shell gap and an inversion of the normal odd-even staggering effect was seen at N=40.The development of the CRIS (Collinear Resonant Ionisation Spectroscopy) beam line is reported, detailing the components that have been installed since its proposal in 2008. Results from the first experimental campaign on francium are discussed to present the current operational status of CRIS. Initial results demonstrate an experimental efficiency of 1:70, collisional background rate of 1:10^5 and a resolution of 1.5 GHz. Analysis of the 221Fr data provided an experimental accuracy of measurements using CRIS, with 44 MHz for the A(7s 2S1/2) hyperfine coefficients and 360 MHz for the isotope shifts. The A(7s 2S1/2) hyperfine coefficients and isotope shifts were measured for 207,211,220,221Fr and show good agreement with literature values. The isotope shifts were combined with literature values to determine the atomic factors for the 7s 2S1/2 to 8p 2P3/2 atomic transition so that changes in the mean-square charge radii could be extracted and compared with literature. The results demonstrate the successful commissioning of the CRIS experiment.

No description available.

<p>The high luminosity phase of the LHC, poised to start taking data in 2027, aims to increase the instantaneous luminosity of the machine to 7.5 x 10³⁴ cm^-2 s^-1. This will make it possible for experiments at CERN to make higher precision measurements on known physics phenomenon as well as to search for “new physics”. However, this motivates the need for hardware upgrades at the various experiments in order to ensure compatibility with the HL-LHC. This thesis describes some of the efforts to upgrade the inner-most layers of the Compact Muon Solenoid, namely the CMS silicon pixel tracking detector. </p> <p>Silicon sensors used to track particles are installed in the detector as part of a pixel sensor module. Modules consist of a silicon sensor-readout chip assembly that is wire-bonded to an HDI, or High Density Interconnects to provide power and signals. </p> <p>As part of the upgrade, 2,541 modules need to be assembled delicately and identically with alignment error margins as low as 10 microns. Assembly will be across three production sites in clean rooms to avoid dust and humidity contamination.</p> <p>In addition, the modules need to survive high magnetic fields and extended close-range radiation as part of the HL-LHC.</p> <p>In line with this effort, new materials and assembly procedures able to sustain such damage are investigated. Techniques to assemble modules are explored, specifically precision placing of parts with a robotic gantry and techniques to protect wirebonds. This is followed by a discussion of the accuracy and repeatability.</p>