yin@sri-unix (09/07/82)
I understand that Cabrera, the researcher at Stanford who came up
with the recent candidate monopole event, has a new detector about
to come on-line. This one consists of 3 superconducting loops, of about
30x(?) the original area, arranged so that the loops are orthogonal.
This should give greater sensitivity, allow the detection of monopoles
passing through a space rather than a plane, give some indication of
the path and make event detection independent of fluctuations within
individual loops.
The original loop had a detection area of 20 cm^2. With this set-up
an event occured after 151 days, giving an upper limit to the isotropic
distribution of moving particles of 0.53 /m^2/sr/d. If certain assumptions
are made wrt grand unified theories, the actual value might be as much
as 0.3 /m^2/sr/d. The event that was detected looks very convincing,
judging by the details given in a preprint to Phys Rev Letters. The set-up
was designed so that a monopole event would induce a current equivalent
to 8 superconducting flux quanta. The detected event had a value of about
7.5 flux quanta. No other event, including known disturbances (liquid
helium, liquid nitrogen transfers, power fluctuations, rfi, etc), exceeded
values of 2 flux quanta, with the exception of impulses to the set-up.
These sometimes approached 6 flux quanta, however, there were no seismic
disturbances recorded on the day of the event and the laboratory was
unoccupied. External magnetic fields were attenuated 180 dB by shielding.
Btw, should be interesting if monopoles are confirmed. If grand unified
theories are right, a magnetic monopole will have a mass of about
10^16 Gev, something like a small paramecium. (Of course there is still
the intermediate vector baseball with a mass of about 10^18 Gev .) The
familiar Maxwell's equations will also have to add on some terms:
div B = 4 * pi * rho
m
1 dB 4 * pi
- curl E = - * -- + ------ * J
c dt c m
Yin Shih
Megatest, Santa Clara