J.W. Simpson

Bio: J.W. Simpson is an academic researcher from Stanford University. The author has contributed to research in topics: Bhabha scattering & Particle detector. The author has an hindex of 7, co-authored 13 publications receiving 123 citations.

Design and Performance of a Modularized NaI(Tl) Detector (The Crystal Ball Prototype)

Abstract: A prototye NaI(Tl) detector (the Cluster of 54) of spherical geometry subtending a solid angle of 7.5% of 4? at its center, has recently been assembled and tested. This detector consisted of 54 close-packed but optically isolated NaI(Tl) modules and the associated electronic circuitry. The Cluster of 54 is the predecessor of an almost complete spherical detector, the Crystal Ball, which will cover 94% of 4?. The latter detector is now under construction and is especially designed for the study of ?-rays produced in electron-positron collisions at colliding beam facilities. This article will outline the mechanical, optical, and electronic assembly of the prototype system. Cluster of 54 test data will be presented.

Measurements of the Reaction e + e − → e + e − at Center-of-Mass Energies of 7.0 and 7.4 GeV

Abstract: Measurements of the cross section for the reaction ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}{e}^{+}{e}^{\ensuremath{-}}$ (Bhabha scattering) at angles close to 90\ifmmode^\circ\else\textdegree\fi{}, relative to Bhabha scattering at 4\ifmmode^\circ\else\textdegree\fi{}, are reported at center-of-mass energies of 7.0 and 7.4 GeV. The results are in agreement with quantum electrodynamics, and new limits on cutoff parameters for the photon propagator are given.

The Observation of the Reactions e+ e- --> e+ e-, e+ e- --> gamma gamma and e+ e- --> mu+ mu- at a Center-Of-Mass Energy of 5.2-GeV

Abstract: We report measurements of e+e−→e+e−, e+e−→γγ, and e+e−→μ+μ− at angles close to 90°, relative to Bhabha scattering at 3.7°, at a center-of-mass energy equal to 5.2 GeV. The results are found to be consistent with the predictions of quantum electro-dynamics.

Measurements of e+e− → e+e− →, e+e− → μ+μ− and e+e− → γγ at Center of Mass Energies Close to 3105 MeV

Abstract: We report here independent evidence for the decay of the recently discovered ψ(3105) particle1–3 into electron-positron pairs and new evidence for the decay of this particle into muon pairs. We also report the results of a measurement of the reaction e+e− → γγ at center of mass energies in the vicinity of 3105 MeV. These measurements were begun immediately following the discovery of the ψ(3105) at SPEAR1. At that time an apparatus primarily designed for the study of quantum electrodynamics (QED) was operating in the second interaction region at SPEAR and was applied immediately thereafter to the study of the ψ(3105). This apparatus is very similar to that described recently by Beron, et al.,4 and is capable of identifying the reactions e+e− → e+e− →, e+e− → μ+μ− and e+e− → γγ. The detection apertures and procedures used to recognize each of these reactions are identical to those described by Beron et al.,4 except that the detection aperture for the reaction e+e− → μ+μ− is larger by a factor of 2.6. All of the measurements reported in this letter were made with the detection apparatus set to accept particles produced at angles 6 close to 90° with respect to the colliding beams.

The EGS5 code system

Abstract: In the nineteen years since EGS4 was released, it has been used in a wide variety of applications, particularly in medical physics, radiation measurement studies, and industrial development. Every new user and every new application bring new challenges for Monte Carlo code designers, and code refinements and bug fixes eventually result in a code that becomes difficult to maintain. Several of the code modifications represented significant advances in electron and photon transport physics, and required a more substantial invocation than code patching. Moreover, the arcane MORTRAN3[48] computer language of EGS4, was highest on the complaint list of the users of EGS4. The size of the EGS4 user base is difficult to measure, as there never existed a formal user registration process. However, some idea of the numbers may be gleaned from the number of EGS4 manuals that were produced and distributed at SLAC: almost three thousand. Consequently, the EGS5 project was undertaken. It was decided to employ the FORTRAN 77 compiler, yet include as much as possible, the structural beauty and power of MORTRAN3. This report consists of four chapters and several appendices. Chapter 1 is an introduction to EGS5 and to this report in general. We suggest that youmore » read it. Chapter 2 is a major update of similar chapters in the old EGS4 report[126] (SLAC-265) and the old EGS3 report[61] (SLAC-210), in which all the details of the old physics (i.e., models which were carried over from EGS4) and the new physics are gathered together. The descriptions of the new physics are extensive, and not for the faint of heart. Detailed knowledge of the contents of Chapter 2 is not essential in order to use EGS, but sophisticated users should be aware of its contents. In particular, details of the restrictions on the range of applicability of EGS are dispersed throughout the chapter. First-time users of EGS should skip Chapter 2 and come back to it later if necessary. With the release of the EGS4 version, a deliberate attempt was made to present example problems in order to help the user ''get started'', and we follow that spirit in this report. A series of elementary tutorial user codes are presented in Chapter 3, with more sophisticated sample user codes described in Chapter 4. Novice EGS users will find it helpful to read through the initial sections of the EGS5 User Manual (provided in Appendix B of this report), proceeding then to work through the tutorials in Chapter 3. The User Manuals and other materials found in the appendices contain detailed flow charts, variable lists, and subprogram descriptions of EGS5 and PEGS. Included are step-by-step instructions for developing basic EGS5 user codes and for accessing all of the physics options available in EGS5 and PEGS. Once acquainted with the basic structure of EGS5, users should find the appendices the most frequently consulted sections of this report.« less