Slashdot Mirror
Do Neutrinos Have Mass?
amyjigglypuff writes "MINOS, a joint project between Fermi National Accelerator Laboratory and the University of Minnesota, is going to attempt to uncover the mysteries of the neutrino. Scientists plan to study the mass of neutrinos, whether they are stable or oscillate, and their electromagnetic structure. If they are found to have mass, it could prove that neutrinos are responsible for the cosmic "dark matter" that has baffled scientists for decades. Here is a link for scientists and a summary for the general public."
Yes, Neutrinos have mass. This is old news dude.
Neutrinos, I believe, count as WIMPs (Weakly Interacting Massive Particles), the current prime candidate for just what makes up dark matter.
The other theory is that of MACHOs (Massive Compact Halo Objects) - large chunks of presumably baryonic material in a large halo orbiting the Milky Way.
The two theories are not exclusive, mind.
Soylens viridis homines es
I attended a seminar where one group was attempting to measure neutrino oscillations and found convincing evidence that this happens. In order for neutrinos to oscillate, however, they would have to have some mass. In the model that they proposed, some neutrinos may have mass and some may not. Also, if super symmetry comes into play, you could potentially have some very heavy neutrinos. For some cutting edge theories consult the archives.
The three neutrinos are each associated with a lepton (electron, tau, muon). The electron neutrino indeed has no charge. Electron neutrinos are typically emitted in beta+ decays or electron captues, both events involving a nucleus swallowing or spitting out an electron.
"I'm so moist I'm sticking to the leather." -Kermit the Frog on The Late Late Show
I remember at 117 Gev we had some higgs boson marks, but the results were just beneath the standard deviation. Now we have to wait till 2004 or 2005 till the commecement of the LHC to be sure.
But the LEP results were close, and many scientists and nonscientists like myself are convinced we have it in that range. At least some neutrinos do have mass.
"Give orange me give eat orange me eat orange give me eat orange give me you." -Nim Chimpsky
However, neutrinos are not sufficient to account for dark matter, and dark matter itself is not sufficient to account for the observed deviations of the shapes of galaxies from what is expected.
I've actually been working as an undergrad assistant in a lab at UT Austin that is very active in the MINOS consortium, so it's pretty cool to see the experiment getting some attention.
;)
There are some neat photos of the detector; the steel scintillator modules weigh about 5,000 tons (!), and you can see one as it is lifted into place. The detector uses something like 2000 16 channel photomultiplier tubes (I don't remember the exact number of tubes) to detect the showers of particles that are created as neutrinos interact with the steel scintillator plates, and the data from those tubes is processed to reconstruct events. Did I mention that the whole thing is in a cavern about 1/2 mile underground to reduce background noise from cosmic rays?
The detector is supposed to come online and start collecting real data in 2004.
Another very interesting neutrino experiment is SNO, the Sudbury Neutrino Observatory, which is in an underground mine in Canada. SNO resolved the solar neutrino problem; people previously couldn't explain why we weren't seeing the right number of neutrinos coming from the sun - it turns out that they "oscillate" and change into other types of neutrinos, and SNO verified this. The neutrino oscillations also imply that they have a non-zero mass (explanation beyond the scope of this comment
The point of MINOS is to observe neutrinos from a controlled high-energy accelerator beam, rather than whatever we get from the sun, to very accurately measure the oscillations.
It really gets cool in supernovae, because as much as 40% of a supernova's energy is in the form of neutrinos. I believe that this can be detected in theory, but I don't remember if it ever has been.
They have been.
The neutrino burst from Supernova 1987A was detected and found to coincide with the optical burst to within an hour (an hour before the optical burst, IIRC). This provided a direct demonstration that high-energy neutrinos travel at or extremely close to the speed of light, which in turn placed an upper limit on their mass (a very small value, but neutrino masses measured to date have been very small).
Another neat thing is that there may be a 4th neutrino that does not interact via the weak force. Imagine that!
No such neutrino exists, as far as anyone can tell. Neutrinos, leptons, and quarks are grouped into families. The first familiy - the up and down quarks, the electron, and the electron neutrino - are what normal matter is made of (or produces in nuclear reactions, in the case of the neutrino). The other two families contain much more massive particles, and so are only seen in exotic situations (high-energy collisions, and possibly as "strange matter" in neutron stars). The existence of higher-energy quark/lepton families has a measurable effect on lower-energy reactions (as the high energy flavours show up as virtual particles). All measurements to date indicate that there are only three families - the expected effects of higher families have not been seen.
Perhaps your source was confusing neutrino families with supersymmetric particles, which are strongly hinted to exist and which may qualify as weakly-interacting heavy particle candidates. None that I've heard of would have the properties you describe, however.