NuTeV result disagrees with Standard Model

Trevor Johnson writes "New Scientist reports that physicists from the NuTev collaboration at Fermilab have announced a result on their Web page. Bombarding iron nuclei with high-energy neutrinos, they found a 99.75% chance that neutrinos interact slightly differently from the way the Standard Model (the reigning theory which describes the strong, electromagnetic, and weak forces, but not gravity) says they should. Even though the discrepancy is small, it is likely to be significant. There is no theory to explain the difference, but it could indicate a hitherto unknown force. NuTev has submitted a "Physical Review Letter" paper. There is a press release from Fermilab and a plain English version."

huh.

[Anonymous Coward]

Crazy. I'm still years away from understanding, but this sounds interesting. What's weird is that the measurements were from 1996 and 1997 and took a year to process. So why did it take so long to release the data?

Re:huh.

[rw2]

It's very common in high energy physics for it to take years to process the data. There is a very complex system in building the detector itself. This is not assembly line stuff. Once the detector is built and taking data it still takes a while to understand the behavior of the detector itself. There can be pieces broken (one trick I was just told about the other day is that a collision detector will have tubes run through it that a radioactive source is dragged through in order to create signal to different components in a controlled fashion as it moves through the tube) that need to be accounted for, manufacturing variance between different pieces of the same component and millions of other such details. Once that's done then 'real' data taking starts. The preliminary analysis starts immediately, but the reason these experiments run as long as they do is because they need that much data to produce solid results. Experiments are expensive to run and if they could run shorter they would.

Once the data is taken, the final analysis is begun in ernest. The data (petabytes for large collider experiments, but I don't know the size of nutev) is sent all around the world and scientists poke and prod it into shape. One thing that is easy for /.ers to appreciate is the software involved. There are millions of lines of code involved with a modern detectors controls systems and millions more with the analysis of the data the detector produces. Getting this stuff right and testing it to make sure is hard, time consuming work.

I know of at least one project that stopped taking data in '92 that is still be actively analyzed and has a chance of producing interesting results.

Look harder - there's probably more science here!

[wnknisely]

To explain the discrepancy between their very precise findings and their expectations, NuTeV experimenters wonder if their neutrinos have felt a new force previously unobserved in nature, or if there is some hitherto undiscovered particle influencing neutrino interactions.

It seems like there a whole bunch of weird shi^H^Htuff going on with Neutrinos. The Sudbury experiment [queensu.ca] this summer is starting to show non-zero neutrino mass, which I understood meant that oscillation between states was going to not happer - or be severely limited.

Now this experiment seems to show that not only is oscillation possibly happening but at a slightly greater rate than we expect.

Admittedly these are completely different effects - and on the surface aren't related but...

I agree with the quote above - my "spidey sense" is making me think that something really interesting is going on with Neutrinos, and perhaps the elementary particle types should start really focusing on getting some better data...

You know - there are going to be a number of vacant deep mine shafts coming vacant in Afgahnistan soon...

Just the Opposite

[Neil Rubin]

The Sudbury experiment [queensu.ca] this summer is starting to show non-zero neutrino mass, which I understood meant that oscillation between states was going to not happer - or be severely limited.

It's actually precisely the opposite. The modern way to understand this is in terms of quantum fields. The energy density of space depends on the values of these fields. In order for one neutrino to oscillate into another, the expression for this energy density must include a term which contains the anti-neutrino field of one flavor of neutrino and the neutrino field of another flavor (neutrinos come in three types, called flavors). This allows a neutrino of one flavor to be annihilated at the same time as another is created.

Now mass for a particular neutrino flavor comes mainly from a term containing the neutrino and anti-neutrino fields of the same flavor, but also those terms that mix it with other flavors. To be more precise, the measured masses of neutrinos are the eigenvalues of the matrix made up of these terms which multiply anti-neutrino and neutrino fields.

The only matrix with all eigenvalues zero is the zero matrix. Thus, if all neutrinos are massless, there is no mixing. The inverse is not necessarily true.

non-zero == oscillation

[rw2]

not non-zero != oscillation as I think you said.