Strong field QED in lepton colliders and electron/laser interactions

Studies of strong field particle physics processes in electron/laser interactions and lepton collider interaction points are reviewed. These processes are defined by the high intensity of the electromagnetic fields involved and the need to take them into account as fully as possible. The main theoretical framework considered is the Furry picture. In this framework, the influence of a background electromagnetic field in the Lagrangian is calculated non perturbatively, involving exact solutions for quantised charged particles in the background field. These "dressed" particles go on to interact perturbatively with other particles. The background field starts to polarise the vacuum, in effect rendering it a dispersive medium. Particles encountering this dispersive vacuum obtain a lifetime, either radiating or decaying into pair particles at a rate dependent on the intensity of the background field. In fact, the intensity of the background field enters into the coupling constant of the strong field QED Lagrangian, influencing all particle processes. A number of new phenomena occur. Particles gain an intensity dependent rest mass shift that accounts for their presence in the dispersive vacuum. Multi photon events involving more than one external field photon occur at each vertex. Higher order processes which exchange a virtual strong field particle, resonate via the lifetimes of the unstable strong field states. Two main arenas of strong field physics are reviewed; those occurring in relativistic electron interactions with intense laser beams, and those occurring in the beam beam physics at the interaction point of colliders. This review outlines the theory, describes its significant novel phenomenology and details the experimental schema required to detect strong field effects and the simulation programs required to model them.Comment: Review article, 56 pages, 29 figures. Version 2 has corrected errata, 1 new reference, 5 updated figure

A closer look at the beam-beam processes at ILC and CLIC

The strength of the electromagnetic fields in the bunch collision at a linear collider will have a significant effect, yielding large numbers of beamstrahlung photons and associated coherent pair production. These effects are limited in the proposed ILC beam parameters which limit the strength of the bunch field to $\Upsilon_{\text{ave}}=0.27$. The CLIC 3 Tev design by comparison has a $\Upsilon_{\text{ave}}=3.34$ yielding huge number of coherent pairs. In terms of the precision physics programs of these proposed colliders there is an imperative to investigate the effect of the strong bunch fields on higher order processes. From the exact wavefunctions used in the calculation of transition rates within the Furry interaction picture, and using appropriate simplifications, a multiplicative factor to the coupling constants was obtained. This indicates a significant variation to the transition rate near threshold energies. Further studies are in progress to calculate the exact effect on expected observables.Comment: 7 pages, 3 figures, LCWS11 (Granada) Proceedings, v

Enhanced, high energy photon production from resonant Compton scattering in a strong external field

A theoretical and phenomenological consideration is given to higher order, strong field effects in electron/laser interactions. A consistent strong field theory is the Furry interaction picture of intense field quantum field theory. In this theory, fermions are embedded in the strong laser field and the Volkov wavefunction solutions that result, are exact with respect to the strong field. When these Volkov fermions interact with individual photons from other sources, the transition probability is enhanced in a series of resonances when the kinematics allow the virtual fermion to go on-shell. An experiment is proposed in which, for the first time, resonances could be used to generate high energy photons from relativistic electrons at rates orders of magnitude in excess of usual mechanisms.Comment: 4 pages, 4 figure

Methods for evaluating physical processes in strong external fields at e+e- colliders: Furry picture and quasi-classical approach

Future linear colliders designs, ILC and CLIC, are expected to be powerful machines for the discovery of Physics Beyond the Standard Model and subsequent precision studies. However, due to the intense beams (high luminosity, high energy), strong electromagnetic fields occur in the beam-beam interaction region. In the context of precision high energy physics, the presence of such strong fields may yield sensitive corrections to the observed electron-positron processes. The Furry picture of quantum states gives a conceptually simple tool to treat physics processes in an external field. A generalization of the quasi-classical operator method (QOM) as an approximation is considered too.Comment: 14 pages, 6 figures, to appear in the conference proceedings of the Corfu Summer Institute 201

The Stimulated Breit-Wheeler Process as a Source of Background e+e- Pairs at the ILC

Passage of beamstrahlung photons through the bunch fields at the interaction point of the ILC determines background pair production. The number of background pairs per bunch crossing due to the Breit-Wheeler, Bethe-Heitler and Landau-Lifshitz processes is well-known. However, the Breit-Wheeler process also takes place in and is modified by the bunch fields. A full QED calculation of this stimulated Breit-Wheeler process reveals cross-section resonances due to the virtual particle reaching the mass shell. The one-loop electron self-energy in the bunch field is also calculated and included as a radiative correction. The bunch field is considered to be a constant crossed electromagnetic field with associated bunch field photons. Resonance is found to occur whenever the energy of contributed bunch field photons is equal to the beamstrahlung photon energy. The stimulated Breit-Wheeler cross-section exceeds the ordinary Breit-Wheeler cross-section by several orders of magnitude and a significantly different pair background may result

Strong field effects on physics processes at the Interaction Point of future linear colliders

Future lepton colliders will be precision machines whose physics program includes close study of the Higgs sector and searches for new physics via polarised beams. The luminosity requirements of such machines entail very intense lepton bunches at the interaction point with associated strong electromagnetic fields. These strong fields not only lead to obvious phenomena such as beamstrahlung, but also potentially affect every particle physics process via virtual exchange with the bunch fields. For precision studies, strong field effects have to be understood to the sub-percent level. Strong external field effects can be taken into account exactly via the Furry Picture or, in certain limits, via the Quasi-classical Operator method . Significant theoretical development is in progress and here we outline the current state of play.Comment: 6 pages, ICHEP 2012 Proceeding

Do first and second year teachers feel prepared? : an evaluation of a standards based teacher preparation program

The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file.Title from title screen of research.pdf file (viewed on August 12, 2009)Thesis (M.A.) University of Missouri-Columbia 2008.The purpose of this study was to serve as a program evaluation and investigate how first and second year teachers felt their teacher preparation program prepared them according to state standards for teacher education preparation. Results of 2 (teacher year: 1st or 2nd year teachers) X 4 (survey year: 2004-7) analysis of variance revealed that perceptions of preparedness between teacher year differed based on the year surveyed for several standards. Results of 2 (teacher year: 1st or 2nd) X 5 (certification level: early childhood, elementary, K-12, middle school, or secondary) analysis of variance revealed significant differences in perceived level of preparedness according to certification level for several standards. To some extent, whether or not there were differences between teacher year depended upon certification level. Regardless of teacher year, the participants of this study felt less prepared in the areas of learner differences, assessment, and technology. These findings suggest that the institution needs to re-evaluate how the content in these areas is delivered. Additionally, these results might suggest school districts would benefit by offering professional development opportunities in these areas for beginning teachers.Includes bibliographical reference

Differences in pre-service teachers' epistemological beliefs : a cross-sectional study

Title from PDF of title page (University of Missouri--Columbia, viewed on December 7, 2010).The entire thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file; a non-technical public abstract appears in the public.pdf file.Dissertation advisor: Dr. Roberta Scholes.Vita.Ph. D. University of Missouri--Columbia 2010.This study investigated the differences in epistemological beliefs of pre-service teachers in relation to their level of education and their certification area. While there has been little research done on pre-service teachers' and epistemology, it is important to understand the beliefs pre-service teachers hold regarding the nature of knowledge construction as their beliefs will influence their teaching practices. For this study, pre-service teachers were asked to complete the Epistemological Beliefs Survey (EBS) which examined their epistemic beliefs on five sub-scales: Speed of Knowledge Acquisition, Structure of Knowledge, Knowledge Construction and Modification, Characteristics of Successful Students, and Attainability of Objective Truth. Two series of ANOVAs were conducted to examine differences in pre-service teachers' levels of epistemic sophistication on these scales. While differences were found for education level (with more advanced students generally holding more sophisticated beliefs), there were no differences found in relation to certification area. This was one of the first studies in the United States to specifically investigate pre-service teachers as a unique population.Includes bibliographical reference