Marvelous mystery cosmic radiation.

Marvelous mystery cosmic radiation 

Over the decades, accelerator laboratoriesand cosmic radiation have tended to alternate as arenas in which new high-energy particle physics phenomena have been discovered. Right now, after a long stretch of time in which particle physics news usually came from accelerators, the cosmic rays are coming up with unusual effects. One of the most spectacular and controversial of these are what Gaurang Yodh of the University of Maryland in College Park calls "Marvin's marvelous muons.' Now Yodh is adding a few unusual muons of his own.

Marvin is Marvin Marshak of the Universityof Minnesota in Minneapolis, and the muons are particles that he and colleagues have been finding in a detector called Soudan buried deep in a mine in northern Minnesota (SN: 1/3/87, p.8). Presumably these muons are produced in the detector by some highly energetic, extremely penetrating radiation that comes from certain sources in the sky-- Cygnus X-3 and Hercules X-1 are among those implicated--and can penetrate the earth's atmosphere and several thousand feet of rock to reach the detector.

The existence of these strange, unidentifiedrays--which have been called cygnets because they were first seen coming from the direction of Cygnus X-3 --has been variously supported, denied and maybe-ed by other underground detectors around the world that are more or less similar to Soudan, but few other physicists have found the evidence convincing. Now, an experiment on the surface --at a high altitude, in fact--operated by Yodh and graduate student Brenda L. Dingus has found a similarly unusual production of muons associated with cosmic-ray air showers. In this case the source seems also to be Hercules X-1.

When an ordinary cosmic ray, whichcan be a gamma ray, a proton or an atomic nucleus, strikes the top of the atmosphere, it initiates a shower of particles, some knocked out of the atoms of the air, some created in the collision. On the ground, physicists customarily detect these showers by spreading large areas of particle-detecting material. The experiment of Yodh and Dingus, which is located at Los Alamos (N.M.) National Laboratory at an altitude of 7,000 feet, differs from most in having in its center a flash chamber, which is actually part of an accelerator laboratory there, and which can identify muons. Yodh told the Heavenly Accelerators workshop, which met recently at Johns Hopkins University in Baltimore, that just a few months ago a series of air showers initiated by gamma rays that seem to come from Hercules X-1 had "too many muons' associated with them--that is, more than known and accepted physics would expect--and therefore something strange is going on.

To a chorus of murmurs from theaudience, Yodh replied, "You are confused; we were surprised.' Marshak had suggested that his cygnets were some previously unknown kind of particle. Yodh suggests that the source to the anomalous muons may be known particles --neutrinos or perhaps those of the class called vector mesons--acting in previously unknown ways. A similar suggestion comes from Gabor Domokos and Susan Kovesi-Domokos of Johns Hopkins, who suggest that ordinary neutrinos could be doing it, provided they are not simple elementary particles but composites.

The most widely believed theory at thispoint holds that the elementary building blocks of matter consist of six quarks and six leptons. Neutrinos and muons are leptons and so are believed to be simple elementary particles. However, for reasons that seem good to them, some theorists have suggested that there may be a level of structure below that of quarks and leptons--that is, that the quarks and leptons are composites made of things called preons. If neutrinos are composites made of preons, Gabor Domokos told the workshop, then a neutrino striking the atmosphere might induce processes of preon exchange that could make numbers of muons that are impossible if preons don't exist.

"I hope we will see the signal again,'says Yodh. "If the data are good, it's up to the theorists.'