Monday, May 31, 2010

Neutrinos have mass!

Scientists the INFN1’s Gran Sasso laboratory in Italy announced today that they have detected a muon neutrino spontaneously changing into a tau neutrino . This is exciting because the standard model of particle physics says that neutrinos don't have any mass, but in order to undergo this spontaneous change they must have a non-zero mass. So this means new physics could be at hand. It also means that neutrinos are a candidate explanation for dark matter.

From a philosophical point of view two things are worth noting. First, obtaining this result took years of painstaking work. And second, despite the fact that this result contradicts the orthodox view, it is being received with open arms, even excitement, but the scientific community. Contrary to the claims of creationists, scientists love it when experiments show that a theory is wrong because that is the only way that scientific progress is made. But nowadays, results of this magnitude are very hard to come by and they just don't happen very often.


[UPDATE:] Rob Warnock sent me an email that basically says that I have this all wrong. Rather than try to distill his critique at the risk of getting it wrong again, I'll just post what he sent me, edited for formatting only:


While this is indeed very interesting news, your article puts all the
emphasis on neutrinos having mass. But what was actuallyu announced by
CERN is simply that a muon neutrino was "caught in the act" of changing
into a tau neutrino, *not* that neutrinos change (oscillate) between
flavors nor that they have mass (which oscillation *requires*) -- that's
rather old news from the 1990s [with roots back to the 1950s]:
Neutrinos have a very small, but nonzero mass.
The solar neutrino number discrepancy problem
Starting in the late 1960s, several experiments found that the number
of electron neutrinos arriving from the Sun was between one third and
one half the number predicted by the Standard Solar Model (SSM). This
discrepancy, which became known as the solar neutrino problem, remained
unresolved for some thirty years. The Standard Model of particle
physics (SM) assumes that neutrinos are massless and cannot change
flavor. However, if neutrinos had mass, they could change flavor
(or oscillate between flavours).
Direct detection of flavor oscillation in solar neutrinos
Starting in 1998, experiments began to show that solar and atmospheric
neutrinos change flavors (see Super-Kamiokande and Sudbury Neutrino
Observatory). This resolved the solar neutrino problem: the electron
neutrinos produced in the Sun had partly changed into other flavors
which the experiments could not detect.
The Standard Model of particle physics assumed that neutrinos are
massless, although adding massive neutrinos to the basic framework is
not difficult. Indeed, the experimentally established phenomenon of
neutrino oscillation requires neutrinos to have nonzero masses.[11]
This was originally conceived by Bruno Pontecorvo in the 1950s.
In 1998, research results at the Super-Kamiokande neutrino detector
determined that neutrinos do indeed flavor oscillate, and therefore
have mass. While this shows that neutrinos have mass, the absolute
neutrino mass scale is still not known.
The initial results indicate |#m232| = 0.0027 eV^2, consistent with
previous results from Super-Kamiokande.[22] Since |#m232| is the
difference of two squared masses, at least one of them has to have a
value which is at least the square root of this value. Thus, there
exists at least one neutrino mass eigenstate with a mass of at least
0.04 eV.[23]

In 2009 lensing data of a galaxy cluster were analyzed to predict a
neutrino mass of about 1.5 eV.[24]

I don't know if it's hard to change articles once they're on Blogspot,
but you might want to shift the focus just a little bit, to put the
emphasis on the observation of the very specific flavor changing that
they saw. Muon neutrino <--> electron neutrino oscillation had been seen
[or at least inferred] before [in the context of the Solar "missing" neutrino
problem, as above], but direct observation of muon neutrino <--> tau neutrino
had never been seen before... which is the news here.

You might also be interested in comparing the coverage of this on
Tommaso Dorigo's excellent blog, which also has some background
on the history:
OPERA Sees Tau Neutrino Appearance!!
By Tommaso Dorigo | May 31st 2010 03:17 PM
In the late 1990s the Super-Kamiokande experiment in Japan proved that
neutrinos may "oscillate": they may change flavour, such that a muon
neutrino may turn into an electron neutrino, or vice-versa. But a muon
neutrino had never been directly seen turning into a tau neutrino yet.


XO said...

Most, but not all creationists. It's also worth noting (and well known) that continually fitting things to observed models/experimentation sometimes leads to subjective thinking and biased results. No fault to science for progressively seeking truth. But what perceived value do folks (presupposing no God) find in an extremely accurate (but completely wrong) alternative 2nd best guess? Logic is not without limitation cf. 1 Corinthians 1 16-30.

Ron said...

XO said...

I had Asimov's argument in mind while I was posting. Not sure if your response attempts to challenge or add to my post.

I find no fault with with progressively seeking truth. However, one can still move towards (and possibly end up) in a completely wrong place. This is not always bad...

We both appreciate good science. Its a tool used by humans with very specific motives to find answers to some long standing questions.

Like those before us --we stand on the shoulders of giants-- in pursuit of 'what appears to be' asymptotic truth. And like them, we'll also go to our graves.

As I pointed out in 1 Corinthians 1 16-30, God has introduced a dilemma to those who lean on logic alone.