arXiv subjects

William Murray

Publications and source records attributed to William Murray.

7 recordsLinked to original sources

arXiv2025

Biased rate estimates in bump-hunt searches

The cleanest way to discover a new particle is generally the "bump-hunt" methodology: looking for a localised excess in a mass (or related) distribution. However, if the mass of the particle being discovered is not known the procedure of quoting the most significant excess seen is "greedy", and random fluctuations from the background can be merged with the signal. This means that an observed 3{\sigma} evidence probably has the rate over-estimated by of order 10% and the mass uncertainty underestimated by more like 20%. If the width of the particle being discovered is also unknown, or the experimental resolution uncertain, the effect grows larger. In the context of LHC, the data-doubling period is now measured in years. If evidence for a genuine signal is obtained at the 3{\sigma} level, the true signal rate probably corresponds to a lower significance. The additional data required to produce a 5{\sigma} discovery may be hundreds of inverse femtobarn more than might be naively expected.

hep-ph↗

arXiv2019

Electric field induced metallic behavior in thin crystals of ferroelectric {\alpha}-In2Se3

Ferroelectric semiconductor field effect transistors (FeSmFETs), which employ ferroelectric semiconducting thin crystals of {\alpha}-In2Se3 as the channel material as opposed to the gate dielectric in conventional ferroelectric FETs (FeFETs) were prepared and measured from room to the liquid-helium temperatures. These FeSmFETs were found to yield evidence for the reorientation of the electrical polarization and an electric field induced metallic state in {\alpha}-In2Se3. Our findings suggest that FeSmFETs can serve as a platform for the fundamental study of ferroelectric metals as well as the exploration of the integration of data storage and logic operations in the same device.

cond-mat.mtrl-sci↗

arXiv2019

Electroweak-QCD interference in hadronic vector bosons at LHC

The analysis of hadronic vector boson decays at LHC does not normally allow for interference with QCD production. These effects are studied here using the Sherpa package and can move by several GeV/c 2 the peak positions experiments would reconstruct. However, their impact depends strongly on the kinematics involved. The shifts expected in boosted W and Z bosons, which have been the subject of experimental study, are explored for the first time. The effects in the channels examined are all very small or negligible, but this may not true if lower transverse momenta are analysed, for example in the experimental trigger systems.

hep-ph↗

arXiv2016

The sensitivity of the Higgs boson branching ratios to the W boson width

The Higgs boson branching ratio into vector bosons is sensitive to the decay widths of those vector bosons because they are produced with at least one boson significantly off-shell. Gamma(H to V V ) is approximately proportional to the product of the Higgs boson coupling and the vector boson width. Gamma Z is well known, but Gamma W gives an uncertainty on Gamma(H to W W ) which is not negligible. The ratio of branching ratios, BR(H to W W )/BR(H to ZZ) measured by a combination of ATLAS and CMS at LHC is used herein to extract a width for the W boson of Gamma W = 1.8+0.4-0.3 GeV by assuming Standard Model couplings of the Higgs bosons. This dependence of the branching ratio on Gamma W is not discussed in most Higgs boson coupling analyses.

hep-ph↗

arXiv2012

LHC Higgs Boson searches

A summary of the Higgs boson searches by the ATLAS and CMS collabrations using 1 f b-1 of LHC data is presented, concentrating on the Standard Model Higgs boson. Both experiments have the sensitivity to exclude at 95% CL a Standard Model Higgs boson in most of the Higgs boson mass region between about 130 GeV and 400 GeV. The observed data allow the exclusion of a Higgs Boson of mass 155 GeV to 190 GeV and 295 GeV to 450 GeV (ATLAS) and 149 GeV to 206 GeV and 300 GeV to 440 GeV (CMS). The lower limits are not as constraining as might be expected due to an excess in both experiments of order 2-3σ which could be related to a low mass Higgs boson or to a statistical fluctuation.

hep-ex↗

arXiv2009

Reducing multi-dimensional information into a 1-d histogram

We present two methods for reducing multidimensional information to one dimension for ease of understand or analysis while maintaining statistical power. While not new, dimensional reduction is not greatly used in high-energy physics and has applications whenever there is a distinctive feature (for instance, a mass peak) in one variable but when signal purity depends on others; so in practice in most of the areas of physics analysis. While both methods presented here assume knowledge of the background, they differ in the fact that only one of the methods uses a model for the signal, trading some increase in statistical power for this model dependence.

physics.data-an↗

arXiv2003

Using Artificial Intelligence for Model Selection

We apply the optimization algorithm Adaptive Simulated Annealing (ASA) to the problem of analyzing data on a large population and selecting the best model to predict that an individual with various traits will have a particular disease. We compare ASA with traditional forward and backward regression on computer simulated data. We find that the traditional methods of modeling are better for smaller data sets whereas a numerically stable ASA seems to perform better on larger and more complicated data sets.

cs.AI↗