Search for New Physics in Rare Higgs Boson Decays with the CMS Detector at the Large Hadron Collider

A new boson with a mass of 125 GeV was discovered at the large hadron collider (LHC) in July 2012. The properties of this particle are so far consistent with the standard model (SM) expectation. Differences in the Higgs boson decay rates and predicted by the SM might indicate the presence of new particles and forces between them. Particularly, rare exclusive decays of the Higgs boson are a promising laboratory to study physics beyond the standard model. Searches for decays of the Higgs boson into a Z boson and a J/ψ meson or into pairs of J/ψ or Υ mesons are performed for using a proton proton collision data set collected by the compact muon solenoid (CMS) experiment at the LHC at a center of mass energy of √s = 13 TeV that corresponds to an integrated luminosity of about 137 fb−1. This class of rare Higgs boson decays can challenge the SM of particle physics. The branching fraction of these decays can be enhanced by the beyond SM particles or phenomena such that they could be observed in the LHC. Higgs decay candidate events with Z bosons decaying into an electron or muon pair, or with quarkonium resonances decaying into muon pairs are selected using online event filters. Longitudinal polarization is expected for the Z boson and assumed for the decay mesons. As different polarization states affect the signal acceptance, scenarios with uniform and transverse polarization are considered. No significant excess is observed, and therefore upper limits at 95% confidence level are placed on the branching fractions of these decays. The observed upper limit branching fractions at 95% CL for the Higgs boson decaying into the final states under investigation range from 10−4 to 10−3. The decay of the Z boson into J/ψ or Υ pairs is also searched for and found to be 10.8 × 10−7 for Z → J/ψJ/ψ and 3.9 × 10−7 for Z → Υ(nS)Υ(mS) (n, m = 1, 2, 3). Furthermore, higher mass quarkonium decays are included in the searches via their inclusive decay into the reconstructed ground state quarkonia. The high luminosity LHC is expected to reach Higgs boson decay branching fraction upper limits at values of about 10−5, about factors of 1 to 10 above the SM predictions, but expected by several extension of the SM. Luminosity measurements are crucial for the physics program of the CMS experiment. The pixel luminosity telescope (PLT) provides input for integrated luminosity and real-time feedback on instantaneous luminosity. The instrument must maintain stable operational conditions over a long time period. This stability can be monitored with the measured position of the collision points or beamspot. From the raw data collected by the PLT, tracks are reconstructed from hits in the three silicon detector planes. Corrections for the alignment of the planes within the telescopes are applied. These tracks are extrapolated to the center of the CMS detector to obtain an estimate of the beamspot position. This beamspot position remained within a radius of 300 μm for most of the proton proton collisions recorded during the year 2016. Beamspot positions outside this circle are used as indicators for adverse beam conditions

Techno-economic comparison of standalone microgrids for rural electrification in South Africa

Rural electrification is a global problem that primarily affects developing countries. The people worst affected are people living in sub- Saharan Africa. There are number of reasons why rural electrification is generally low. People in rural areas generally live in small communities, located far away or from the grid or in geographically tough terrain. As a result, it is not financially viable to extend the grid to these areas and therefore they remain unelectrified. Another dictating factor, is the fact that people in these areas are generally poor, and therefore this discourages any investment from the private sector. This dissertation focuses on rural electrification in South Africa specifically. Most people in South Africa affected by not being electrified live in rural areas on the border between the Eastern Cape and Kwa-Zulu Natal. As it is too expensive to extend the grid to these areas, off-grid options, such as microgrids were investigated. A large amount of research has been carried out on hybrid microgrids as a solution to rural electrification. However, a limited amount of research has been carried out on single source microgrids. Furthermore, South Africa is fortunate to have an abundance of solar, wind and microhydro resources, however, it is unclear which resource would be cheapest based on the location of the rural area. As a result, the aim of thesis was to analyse the impact of the strength of the resource when implementing a microgrid and comparing the three different renewable resources systems against one another. In order to carry out this analysis, three unelectrified villages were selected with each village located in an area of a strong resource, whether it be wind, solar or microhydro. i.e. one village was selected in an area with a strong solar resource, the second in an area with strong wind resource and the third in an area with strong microhydro resource. Once selected, a load for each village was modelled and the resource data for each village was obtained using open source sites. Solar-battery, wind battery and microhydro-battery systems were modelled for each village using HOMER. From the results it was clear that when comparing the same resource in each of the villages, then the strength of the resource did affect the levelised cost of energy i.e. the stronger the resource, the less the lower the cost of energy which was as expected. However, when comparing the solar, wind and microhydro system in each village against each other, it was apparent that the strength of the resource did not dictate the type of technology to be used in that area. It was found that wind systems were not suited to small scale generation, whilst microhydro was the cheapest technology in each village, however, its implementation may be deterred by non-technical issues such as the social and environmental impacts of constructing a dam. The cost of the solar system was comparable to microhydro only when the irradiation was above a certain level. As solar systems are easier and quicker to implement it is possibly the best system in general for rural areas in South Africa. Implementation of off-grid systems for rural electrification in South Africa is a viable option however, as the private sector is not incentivised to implement these systems, then government back in the form of grants and subsidies are required to implement these systems. However, as renewable technologies improve and get cheaper with time, this option to electrify rural areas is always becoming cheaper

Full-Duplex Radio for Uplink/Downlink Transmission with Spatial Randomness

We consider a wireless system with a full-duplex (FD) access point (AP) that transmits to a scheduled user in the downlink (DL) channel, while receiving data from an user in the uplink (UL) channel at the same time on the same frequency. In this system, loopback interference (LI) at the AP and inter user interference between the uplink (UL) user and downlink (DL) user can cause performance degradation. In order to characterize the effects of LI and inter user interference, we derive closed-form expressions for the outage probability and achievable sum rate of the system. In addition an asymptotic analysis that reveals insights into the system behavior and performance degradation is presented. Our results indicate that under certain conditions, FD transmissions yield performance gains over half-duplex (HD) mode of operation.Comment: Accepted for the IEEE International Conference on Communications (ICC 2015

Wireless Information and Power Transfer in Full-Duplex Systems with Massive Antenna Arrays

We consider a multiuser wireless system with a full-duplex hybrid access point (HAP) that transmits to a set of users in the downlink channel, while receiving data from a set of energy-constrained sensors in the uplink channel. We assume that the HAP is equipped with a massive antenna array, while all users and sensor nodes have a single antenna. We adopt a time-switching protocol where in the first phase, sensors are powered through wireless energy transfer from HAP and HAP estimates the downlink channel of the users. In the second phase, sensors use the harvested energy to transmit to the HAP. The downlink-uplink sum-rate region is obtained by solving downlink sum-rate maximization problem under a constraint on uplink sum-rate. Moreover, assuming perfect and imperfect channel state information, we derive expressions for the achievable uplink and downlink rates in the large-antenna limit and approximate results that hold for any finite number of antennas. Based on these analytical results, we obtain the power-scaling law and analyze the effect of the number of antennas on the cancellation of intra-user interference and the self-interference.Comment: Accepted for the IEEE International Conference on Communications (ICC 2017

Development of High Conductivity Copper Coatings for SRF Cavity

The development of metallic coatings with high purity and high thermal conductivity at cryogenic temperature could be very important for application to the superconducting radiofrequency (SRF) cavity technology. The deposition of such bulk coatings on the outer surface of a niobium cavity could result in higher heat conductance and mechanical stiffness, both of which are crucial for enhancing the cavity performance at a reduced cost. Cold spray technology was used to deposit bulk coatings of pure copper and copper-tungsten alloys on the niobium substrate and the samples of size 2 mm × 2 mm cross section were cut and subjected to annealing at various temperatures ranging from 300 ◦C to 1000 ◦C. Thermal conductivity and residual resistivity ratio (RRR) were measured for various samples. A maximum RRR value of ∼130 and ∼40 was measured for pure Cu samples and CuW samples, respectively. Scanning electron microscopy was used to analyze the grain growth, grain distribution and presence of contaminant particulates

Beamforming in Two-Way Fixed Gain Amplify-and-Forward Relay Systems with CCI

We analyze the outage performance of a two-way fixed gain amplify-and-forward (AF) relay system with beamforming, arbitrary antenna correlation, and co-channel interference (CCI). Assuming CCI at the relay, we derive the exact individual user outage probability in closed-form. Additionally, while neglecting CCI, we also investigate the system outage probability of the considered network, which is declared if any of the two users is in transmission outage. Our results indicate that in this system, the position of the relay plays an important role in determining the user as well as the system outage probability via such parameters as signal-to-noise imbalance, antenna configuration, spatial correlation, and CCI power. To render further insights into the effect of antenna correlation and CCI on the diversity and array gains, an asymptotic expression which tightly converges to exact results is also derived.Comment: Accepted for presentation on IEEE International Conference on Communications (ICC 2012), Ottawa, Canada, June 201