The electric neutrality of matter: A summary

Experimental particle physics without accelerators

In this paper we review the experimental and observational searches for stable, massive, elementary particles other than the electron and proton. The particles may be neutral, may have unit charge or may have fractional charge. They may interact through the strong, electromagnetic, weak or gravitational forces or through some unknown force. The purpose of this review is to provide a guide for future searches — what is known, what is not known, and what appear to be the most fruitful areas for new searches. A variety of experimental and observational methods such as accelerator experiments, cosmic ray studies, searches for exotic particles in bulk matter and searches using astrophysical observations is included in this review.

The search for stable, massive, elementary particles

Quark search experiments at accelerators and in cosmic rays

Since the initial measurements of the electron charge a century ago, experimenters have faced the persistent question as to whether elementary particles exist that have charges that are fractional multiples of the electron charge. In the standard model of particle physics the quarks are such particles, but it is assumed that quarks cannot be individually isolated, the quarks always being confined inside hadrons. This paper is a brief review of the present status of searches for isolatable fractional charge particles such as a lepton-like particle with fractional charge or an unconfined quark. There have been a very large number of searches but there is no confirmed evidence for existence of isolatable fractional charge particles. It may be that they do not exist, but it is also possible that they are very massive or that their production mechanisms are very small so that they have been missed by existing searches. Therefore the aim of this review is to urge (a) the invention of ways to substantially increase the range of known search methods and (b) to urge the invention of new search methods for isolatable fractional charge particles.

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A brief review of the search for isolatable fractional charge elementary particles

An experiment was performed to capture fractionally charged particles produced in heavy-ion collisions and to concentrate them in samples suitable for analysis by various techniques. Two of the samples so produced have been searched, with use of an automated version of Millikan's oil drop apparatus. The beam was /sup 56/Fe at 1.9 GeV/nucleon, incident on a lead target. Less than one fractional charge per 1.0 x 10/sup 4/ Fe-Pb collisions was found to be produced, and, with further assumptions, less than one per 2.0 x 10/sup 6/ collisions.

Alan A. Hahn

Papers

Search for Fractional Charges Produced in Heavy-Ion Collisions at 1.9 GeV/nucleon