Searches for Fractionally Charged Particles: What Should Be Done Next? Page: 2 of 4
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4. ACCELERATOR AND COLLIDER
SEARCHES
General accelerator and collider detectors can-
not be used to find particles with - < s be-
cause track reconstruction is uncertain. With
this constraint no fractional charge particles have
been found up to masses of about 200 GeV/c2 in
searches using hadron collisions and up to about
100 GeV/c2 in searches using electron-positron
collisions.
5. SEARCHES FOR FRACTIONAL
CHARGE PARTICLES COMING
FROM OUTSIDE THE EARTH
The possible sources are:
" The particles may have been produced in
the early universe and still be a stable com-
ponent of the present material in the uni-
verse.
" The particles may be produced in the
present era in violent astrophysical pro-
cesses .
" The particles may be produced in the in-
teraction of ordinary cosmic rays with the
Earths atmosphere.
No fractional charge particles have been found
and search sensitivities have reached down to
fluxes of less than 10-15 cm-2s--1sr-1. Reference
[3] describes the most sensitive search by the MI-
CRO experiment.
6. SEARCHES FOR FRACTIONAL
CHARGE PARTICLES IN BULK
MATTER
Two methods have been used to search for frac-
tional charge particles in bulk matter. The lev-
itometer method was developed and used by the
Smith and Jones group [4] and by Marinelli and
Morpurgo [5].
The modern Millikan liquid drop method was
pioneered by the Bland group at San Francisco
State University [6]. The Millikan liquid drop
method was then further developed and used atthe SLAC National Accelerator Center from 1994
through 2007 with the initial paper by Charles
Hendricks, Klaus Lackner, Gordon Shaw and my-
self [7]. Our final experimental paper, P. C. Kim
et al. [8], reported null results on both meteoritic
material and on the largest sample of bulk matter
in the form of mineral oil ever studied.
The methods are both described in [1].
Searches have been carried out in the following
materials: sea water, residues from evaporation
of sea water, mercury, iron, niobium, silicone oil,
mineral oil, and meteoritic material from aster-
oids.
There were no confirmed discoveries of frac-
tional charged particles. Table 1 lists the major
searches and [1] gives references and details.
7. MILLICHARGED PARTICLES
Millicharged particles are hypothetical elemen-
tary particles with small 2, usually 2 < 0.1, and
extending down to 2 < 10-8 or lower.
There have been many limitations on the exis-
tence of such particles from considerations such
as energy loss in stars [9].
But there has been only one experimental
search, by Prinz et al. [10]. No millicharged par-
ticles were found.
8. WHAT SHOULD BE DONE NEXT?
Thus the physics world has seen 50 years of fail-
ures in searches for fractional charge elementary
particles. What should be done next?
First, some history of the searches that have
been made by my colleagues and myself using
the Millikan liquid drop method, searches from
1994 to 2007. Over the years we have been a cre-
ative, happy, and efficient band of experimenters
consisting for various lengths of time of Gordon
Shaw, Charles Hendricks, Klaus Lackner, Howard
Rogers, Eric Lee, Nancy Mar, George Fleming,
Brendan Casey, Edward, Garwin, Peter Kim, Se-
wan Fan, Irwin Lee, Valerie Halyo and myself.
We ranged from undergraduate students to fac-
ulty. We had a wonderful time.
But what now? The funding for our group has
changed and our group is dispersed; only Peter
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Perl, Martin L. Searches for Fractionally Charged Particles: What Should Be Done Next?, article, January 15, 2009; [Menlo Park, California]. (https://digital.library.unt.edu/ark:/67531/metadc897321/m1/2/: accessed April 25, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.