Two new items of physics news. First, NewScientist reports on possible evidence for a new generation of fundamental particles:
First a rundown on what we know already. Each of the three known generations of matter contains two types of fundamental particle – quarks and leptons. First generation leptons include the familiar electron and neutrino (see images, right).
The first generation of matter can explain everything we encounter in everyday life. Atomic nuclei are composed of protons and neutrons, which are in turn composed solely of “up” and “down” quarks.
The second and third generations were introduced to explain the dozens of varieties of short-lived, subatomic particles spotted in the debris of particle smashers. Each of these two generations contains a pair of quarks – much heavier than those of the first generation – as well as muons and taus, heavy versions of the electron. They also each have their own version of the neutrino.
New generations of matter have tended to show up every 30 or 40 years – the last time was in 1975, when the tau was discovered. “We’ve seen three generations, why not four?” says Amarjit Soni of Brookhaven National Laboratory in Upton, New York. A fourth generation would be “a very simple continuation of the trend we’ve seen”, he says.
Now hints of this fourth generation have turned up in data from the Tevatron accelerator, which smashes together protons and antiprotons.
And second, new developments in the long-looked for transformation between neutrino types, and new evidence that neutrinos do in fact have mass. From ScienceNews:
“Since the late 1990s, experiments such as Super-Kamiokande in Japan have indicated that neutrinos spontaneously transform themselves, or oscillate, among three varieties or “flavors”: the electron neutrino, the muon neutrino and the tau neutrino. Such oscillations indicate that neutrinos, long thought to be weightless, must have some small amount of mass.
Those experiments revealed a lower-than-predicted abundance of a certain type of neutrino compared with the number produced at the neutrinos’ source. The abundance of that type had clearly declined, but it wasn’t clear which type of neutrino they had transformed into.
The new experiment not only shows a strong hint of just such a transformation but also identifies tau neutrinos as the type produced.”
Over at First Things, Catholic physicist Stephen Barr provides some commentary:
This fact tells us that there is something going on that lies beyond the original Standard Model. The most likely possibility is that these neutrino masses come from processes that are predicted to exist in so-called “grand unified theories”—theories that unify the three non-gravitational forces. They are therefore windows onto a realm of phenomena that are very hard to get any direct information about. That is one reason why theorists are very interested in them.