Number 299, December 13, 1996 by Phillip F. Schewe and Ben Stein
QUARKS ARE POINTLIKE AT THE 10**-19 METER LEVEL. Quarks, along with
leptons, are the most elementary things in the universe, as far as experiments
can tell. If quarks, which are the constituents of protons and neutrons,
had constituents themselves, how would we know? One way is to smash quarks
together and see what flies out. Physicists at Fermilab smash protons (which
can be thought of as delivery vehicles for quarks) and antiprotons with
one another and look at the outgoing jets of debris particles. Previously
(Update 258) an excess of events with high-energy jets shooting away from
the interaction at large angles was interpreted by some (although not by
the experimentalists themselves) as possible evidence for subquarks. The
latest word on the situation, as reported now by the CDF collaboration,
is that quarks do not have any apparent structure. One way of expressing
this is to say that if objects are hiding inside quarks, their energy would
have to be greater than about 1.6 TeV. A still more dramatic way of registering
this null result is to say that having trained their microscope on quarks,
the Fermilab scientists see no objects at the 10**-19--meter level, the
smallest distance scale inside quarks ever explored. (F. Abe et al. an
article on dijet angular distribution in Physical Review Letters, 30 December
1996; contact Robert Harris at Fermilab, rharris@cdfsga.fnal.gov; 630-840-4932.)
A few other experiments, such as those that search for proton decay, have
in effect probed even finer distance scales without finding any tiny lurking
things.
SONOLUMINESCENCE RESEARCH VIBRATES WITH ACTIVITY. At last week's joint
meeting of the Acoustical Societies of America and Japan in Honolulu, researchers
presented the latest results on sonoluminescence (SL), the mysterious phenomenon
in which acoustic waves aimed at a water tank create oscillating bubbles
which collapse and release ultrashort light flashes representing trillion-fold
concentrations of the original sound energy. Presenting new experimental
results, groups at Yale, the University of Washington (UW), and UCLA bolstered
the front-running explanation for SL, namely, that a collapsing bubble
creates an imploding shock wave which heats up gas inside the bubble and
generates light. The three groups all recorded sharp acoustical pops during
the SL process, suggesting the creation of shock waves. UW's Tom Matula
presented preliminary results of SL experiments on a NASA astronaut-training
plane showing that the same maximum light output was produced in high gravity,
microgravity, and normal gravity. These results weakened recent speculations
that SL occurs when an imploding bubble forms a needle-like spike or "jet"
on one side which punctures the other side of the bubble to produce a flash
of light, since different gravity conditions would surely vary the shape
of the bubble and the formation of any resulting jets.
HELIUM-3 CAN REMAIN SUPERFLUID IN AEROGEL , albeit at a lower temperature.
When He-3 was injected into a sample of aerogel, a wispy glass gel with
a density not that much greater than air, some expected the gel's filaments
to disrupt entirely the pairing of He-3 atoms necessary for superfluidity.
This didn't happen. A new surprise is the fact that an applied magnetic
field does have an effect on superfluidity in the aerogel; it depresses
the superfluid transition temperature further (Sprague et al., Physical
Review Letters, 25 November). Research on superfluid He-3 in aerogel may
have implications for the study of superconductivity since the pairing
of He-3 atoms in superfluids is analogous to electron pairing (the BCS
mechanism) in some superconductors. (Science News, 7 December 1996.)
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