arXiv subjects
Publications and source records attributed to S. Reucroft.
We investigate the hypothesis that the core of a galaxy has a positive electrical charge with an equal and opposite negative charge distributed over the galactic periphery. We present a determination of the amount of charge needed to explain the apparent anomalous rotation behaviour.
The limited number of active pixels in a Geiger-mode Avalanche Photodiode (G-APD) results not only in a non-linearity but also in an additional fluctuation of its response. Both these effects are taken into account to calculate the amplitude resolution of an ideal G-APD, which is shown to be finite. As one of the consequences, the energy resolution of a scintillation detector based on a G-APD is shown to be limited to some minimum value defined by the number of pixels in the G-APD.
We describe a new technique to look for evidence of the Higgs mechanism. The usual method involves seeking evidence for the Higgs boson either directly or via the indirect effect that a virtual Higgs boson would have on a variety of Standard Model parameters. The new technique looks for Higgs field effects that are predicted to reduce the masses of heavy particles when they are in the presence of other heavy particles.
A consequence of the Higgs mechanism is that high mass particles, such as the Z-boson, the W-boson and the t-quark, are predicted to have masses that depend on the process by which they are produced. Thus, for example, particles produced singly are predicted to have higher masses than those produced in a pair near threshold. Quantitative details of this prediction are presented and discussed within the context of the current experimental situation.
In the Standard Model, all massive elementary particles acquire their masses by coupling to a background Higgs field with a non-zero vacuum expectation value. What is often overlooked is that each massive particle is also a source of the Higgs field. A given particle can in principle shift the mass of a neighboring particle. The mass shift effect goes beyond the usual perturbative Feynman diagram calculations which implicitly assume that the mass of each particle is rigidly fixed. Local mass shifts offer a unique handle on Higgs physics since they do not require the production of on-shell Higgs bosons. We provide theoretical estimates showing that the mass shift effect can be large and measurable, especially near pair threshold, at both the Tevatron and the LHC.
In nuclear physics, it is well known that the electromagnetic (Coulomb) interaction between final state products can drastically effect particle reaction rates. Near thresholds, for example, nuclear alpha decay is suppressed while nuclear beta decay is enhanced by final state Coulomb interactions. Here we discuss high energy physics enhancement and/or suppression of reactions wherein the potentials must include weak and strong as well as electromagnetic interactions. Potentials due to the exchange of gluons and the exchange of a hypothetical Higgs particle are explicitly considered.
We report on our studies of applying novel detector technologies developed for LHC-era experiments to cosmic ray detection. In particular, we are investigating usage of scintillating tiles with embedded wavelength-shifting fibers and avalanche photodiode readout as part of a robust, inexpensive cosmic air shower detector. In the near future, we are planning to deploy detector stations based on this technology at area high schools and colleges as part of an outreach and education effort, known as SCROD.
A re-examination of the atmospheric cascade profile of the highest energy cosmic ray is presented. The study includes air-shower simulations considering different cross sections, particle multiplicity and variation of the hadronic-event-generator to model interactions above 200 GeV. The analysis provides evidence that a medium mass nucleus primary reproduces the shower profile quite well. This result does not support the idea, increasingly popular at present, that the highest energy particles are protons, derived from the decay of supermassive relic particles. On the other hand, we show that debris of relativistic super-heavy nuclei, which can survive a 100 Mpc journey through the primeval radiation are likely to generate such a kind of cascade.
We present an evaluation of a simulated cosmic ray shower, based on {\sc geant4} and {\sc top-c}, which tracks all the particles in the shower. {\sc top-c} (Task Oriented Parallel C) provides a framework for parallel algorithm development which makes tractable the problem of following each particle. This method is compared with a simulation program which employs the Hillas thinning algorithm.
{\sc top-c} (Task Oriented Parallel C) is a freely available package for parallel computing. It is designed to be easy to learn and to have good tolerance for the high latencies that are common in commodity networks of computers. It has been successfully used in a wide range of examples, providing linear speedup with the number of computers. A brief overview of {\sc top-c} is provided, along with recent experience with cosmic ray physics simulations.
We study the self-similar structure of electromagnetic showers and introduce the notion of the fractal dimension of a shower. Studies underway of showers in various materials and at various energies are presented, and the range over which the fractal scaling behaviour is observed is discussed. Applications to fast shower simulations and identification, particularly in the context of extensive air showers, are also discussed.
We present a detailed simulation of the performance of water Cerenkov detectors suitable for use in the Pierre Auger Observatory. Using {\sc geant4}, a flexible object-oriented simulation program, including all known physics processes, has been developed. The program also allows interactive visualization, and can easily be modified for any experimental setup.
We critically review the common belief that ultrahigh energy cosmic rays are protons or atomic nuclei with masses not exceeding that of iron. We find that heavier nuclei are indeed possible, and discuss possible sources and acceleration mechanisms for such primaries. We also show detailed simulations of extensive air showers produced by ``superheavy'' nuclei, and discuss prospects for their detection in future experiments.
A re-examination of the energy cosmic ray spectrum above $10^{20}$ eV is presented. The overall data-base provides evidence, albeit still statistically limited, that non-nucleon primaries could be present at the end of the spectrum. In particular, the possible appearance of superheavy nuclei (seldom discussed in the literature) is analysed in detail.
We report the results of exposing a Hamamatsu avalanche photodiode (APD) to a 7.9 Tesla magnetic field. The effect of the magnetic field on the gain of the APD is shown and discussed. We find APD gain to be unaffected in the presence of such a magnetic field.