Neutrino Mass Confirmed 318
biohack writes "BBC News reports that results from the MINOS experiment have confirmed that neutrinos have mass. To look for neutrino oscillations, scientists created muon neutrinos in a particle accelerator at the Fermi National Accelerator Laboratory (Fermilab). After passing through a particle detector at Fermilab, a high intensity beam of neutrinos travelled to another particle detector 724km (450 miles) away in a disused mine in Soudan, US. The set up established that fewer particles were being detected at the Soudan site than had been sent from Fermilab, which confirmed that some neutrinos changed their flavor on the way - an effect called neutrino flavor oscillation, which requires them to have mass. 'To put it simply, if they are heavy, it means that there is a lot more mass in the Universe than we thought there was,' said Professor Jenny Thomas from University College London."
Soudan, US (Score:3, Informative)
http://www.dnr.state.mn.us/state_parks/soudan_und
Creighton Mine (Score:3, Informative)
SNO Detector [queensu.ca].
This is new? (Score:2, Informative)
Re:bragging time (Score:2, Informative)
Re:Already Known (Score:5, Informative)
... as claimed in 1998 Scientific American article [hawaii.edu]
Re:Dark Matter (Score:5, Informative)
http://en.wikipedia.org/wiki/Hot_dark_matter [wikipedia.org]
Re:Pardon me, but. . . (Score:5, Informative)
- Matter has mass and is made of particles.
- Light has no mass and is made of waves.
Nowadays it's more like this:- Fermions are wave-particles that have half-integer spin. Atoms are made of fermions.
- Bosons are wave-particles that have integer spins. Bosons are the things that carry forces.
All the familiar, everyday fermions have nonzero rest mass, and the only familiar, everyday boson -- the photon -- has zero rest mass. However, there are bosons that have nonzero rest mass (e.g., gluons), and it's also possible that there are fermions that have zero rest mass. (Experiments so far only measure the differences between masses of different types of neutrinos, so it's still possible that the electron's neutrino has zero mass.)Implications regarding the Standard Model? (Score:4, Informative)
We'll have to wait and see, but for anyone who would like more information, Fermilab's website [fnal.gov] has an article about the discovery.
Re:Dark Matter (Score:3, Informative)
Re:Already Known (Score:1, Informative)
The experiment in this article has been designed to improve on these previous measurements, and as a first step there, they have presented initial results after only 8 months of operation.
(Didn't read the BBC article, but I do work in a mine.)
explanation about oscillation/mass relationship (Score:3, Informative)
I hate when people act as if a complicated issue is simply true. So, as a public service to the Slashdot community:
Here is a site that attempts to explain it. [uci.edu]
My quantum physics knowledge isn't teriffic. Any particle physicists know of a better source?
Re:This is new? (Score:5, Informative)
The experiment was similar and involved muon neutrinos changing flavors to electron neutrinos in a large particle accelerator.
No, it wasn't an accelerator, and the experiment wasn't similar. [wikipedia.org]
The real question is how many eV are the combined masses of the three flavors? The answer to that question portends much for the state of the universe.
No, not really. Not unless the mass of the electron's neutrino is surprisingly large compared to the mass differences among the different types of neutrinos.
It depends. (Score:1, Informative)
Yes, neutrinos are important in understanding the interior of the sun. They are not the only method, however, as "holes" do occur through which we can see very limited snapshots of segments of the interior. They are also not perfect, as less than half of the expected number of neutrinos ever reach the Earth, presumably through changes in flavour or through being absorbed.
Neutrinos are also very important in understanding the mechanics of radioactive decay. Remember, the entire premise from which neutrinos came from was that decay needed a massless particle that could carry with it rotational momentum. Since neutrinos have M amount of mass, then the sum of all other actual and effective masses being emitted must be reduced by M, for the calculations to still balance out.
(You're also much more restricted in the energy a neutrino can have, as you must now not only balance momentum but also kinetic energy. For things to equal out, this will place significant constraints on the state of a neutrino.)
All in all, this sort of work generally has massive repercussions and it will only be truly known what significance the mass has when ALL physical systems involving neutrinos have been adjusted accordingly. Again, the magnitude of the mass is totally unimportant. What matters is whether it breaks an existing model (eg: by violating the requirement for quantized states) or whether it eliminates any variables or constants (because they are no longer needed).
I am a great proponent of science, but I am getting tired of the complacency that has slowly been creeping in - the Victorian illusion that we are approaching the end of knowledge. If neutrinos having mass throws huge chunks of the physics community into disarray, I believe it will be a Good Thing and about time. We need something that will cause a major headache and a revolution in thinking.
Re:explanation about oscillation/mass relationship (Score:5, Informative)
A physicist on the recent Nova special "The Ghost Particle" (Maybe it was Boris Kayser) had a nice explanation. If neutrinos have no mass, then they travel at the speed of light. If they travel at the speed of light, then they would not experience "time". Since changing flavor is a process that takes time, or duration, or something like that (this previous clause is maybe a non-trivial thing to say), then if neutrinos change flavor, they must experience time, so they must travel slower than the speed of light, so they must have some mass.
Re:It depends. (Score:3, Informative)
Um, no, you're just completely wrong here.
Neutrinos are also very important in understanding the mechanics of radioactive decay. Remember, the entire premise from which neutrinos came from was that decay needed a massless particle that could carry with it rotational momentum. Since neutrinos have M amount of mass, then the sum of all other actual and effective masses being emitted must be reduced by M, for the calculations to still balance out.
No, the mass/energy scale -- eV -- is wrong for it to have any significant effect on nuclear beta decay, where the mass/energy scale is MeV.
Re:Soudan, US (Score:5, Informative)
While this is true, it's somewhat misleading, especially to those will limited knowledge of U.S. history or government. Even many Americans don't understand the difference between as state and a province.
State governments in the U.S. function approximately equally to provincial governments in countries that are not federations. Most of them were not originally independant countries, but were instead provinces and territories that were sponsored into statehood.
A significant fraction of the United States were indeed independant countries at one point. ALL U.S. states have significantly more rights than any given province. Each has its own constitution and government, and, contrary to popular opinion, the states elect the President and Senators. The U.S. president is *not* elected by a popular vote. (Although there have been calls to change this.) A few, most notably Texas, still claim the right to secede from the Union, although no state has really had this right since the end of the American Civil War in the late 1800s.
The U.S. constitution sets up the states as individual entities, unlike provinces. They can each impose their own taxes and own laws. In fact, this is one of the major contentions in our government to this day. States can theoretically impose any law that the constitution doesn't reserve for the Federal government. This causes a lot of conflict and consternation since States are also required to respect contracts formed in other states, frequently under a different set of laws and regulations.
The conflict over gay marriage contracts is one of the more recent flaps this has caused.
States can also each maintain their own militias. Many states have 'State Troopers', who usually do the same kind of jobs as normal policemen, albeit with greatly expanded jurisdiction. A few states have 'State Guards', although they usually don't server a military purpose. They usually come to the fore during natural disasters and the like.
While the U.S. is an extremely tight federation-- the word 'Union' is very accurate-- it is still a federation. Each state is indeed its own nation.
Re:It was a long haul .... (Score:2, Informative)
I haven't seen mentioned any of the news reports point out the, ah, irony [no pun intended, well, okay, yes it was] of the "coal to Newcastle" aspect of transporting 5.4 kilotons of steel into an iron mine. I just like to point that out..
A Sad note (Score:5, Informative)
http://www.sciam.com/article.cfm?chanID=sa006&art
Re:Soudan, US (Score:3, Informative)
"That kind of sloppiness is rare for the BBC"
The US is the country where 100 years is a long time. The UK is where 100 miles is a long distance. Even the British can be guilty of the ol' "Oh, you're from the US? Do you know $PERSON from $SIX_STATES_AWAY?"
The only countries bigger than the US are Russia and Canada, and I don't believe either has anywhere near the number of individual, named communities. And while it's rare for a story coming from Russia to mention what constituant part of the Russian Federation a particular town is in (forgivable, as the system of oblast, okrugs, etc. is truly byzantine), stories from Canada and China consistently mention what province the news come from. As for mentioning "department," most countries that subdivide themselves that way (e. g. France) are comparable in size to a single US state, so mentioning the department would make as much sense as mentioning what county in a state a city was in.
"It would sound weird/inaccurate to hear news about "San Francisco, USA" without mentioning California."
It would be ambiguous. There's a San Francisco in California, New Mexico and Texas. Depending who you talk to, "San Francisco, USA" may also refer to a city in Puerto Rico.
""CANCUN, Mexico (CNN) --" (Cancún is in the state of Quintana Roo)"
There is only one Cancun; the place isn't named after something so convenient as a Catholic saint. Besides, the typical Mexican state is considerably smaller than the typical US state: Quinas Roo is about the median for the area of a Mexican state at 19th, but it would fall between West Virginia (41) and Maryland (42) in the US. Chihuahua, the largest Mexican state, is a little smaller than Michigan.
"They didn't do their homework here. Yucatán is the state NW of Quintana Roo."
"Yucatan" refers to both a state and a geographical region. "St. Louis is a major Mississippi port" doesn't mean I believe that the city of St. Louis is in the State of Mississippi, and "Honolulu is a Hawaiian city" doesn't mean I believe Honolulu is on the same island as Hilo.
Re:bragging time (Score:3, Informative)
Umm...a couple of corrections (Score:4, Informative)
Bosons don't necessarily carry forces; in fact not all atoms are fermions. For example, the Helium-4 and Carbon-12 nuclei is a boson. See wikipedia [wikipedia.org]. Bosons are best defined as having integer spin and being capable of sharing the same quantum state while fermions have half-integer spin and obey the Pauil Exclusion Principle (cannot share the same quantum state). A composite particle of an even number of fermions (2 protons + 2 neutrons) is a boson (helium nucleus) but an odd number of fermions is always a fermion.
I also believe that physicists have determined that the electron neutrino has a mass of about 1meV-1eV (from a slide I saw in lecture a couple days ago).
In addition, physicists divide fermions into quarks and leptons, which are supersets of the elementary particles that make up nucleons and electrons.
Re:*shakes head* (Score:5, Informative)
They don't yet have enough data to rule out some alternative explanations. At this point, though, neutrino oscillation (and mass) would really be the simplest, least "out there" explanation. These experimenters would like nothing more than to find that even the oscillation theories don't explain the data. That would open a whole new field of inquiry and possibly lead to Nobel Prizes.
If you're techincally inclined, read about the Minos results [fnal.gov] straight from the horses' mouths.
The seminar talks go into a fair bit of detail about their data analysis, which included "blind analysis." In other words, they kept a significant (and unknown until the end) fraction of their data secret from those doing the analysis. Using the other fraction, they went through their testing procedures -- figuring out how to detect false events, how to deal with various , etc -- using a limited piece of the data. Once they were confident that they had done everything correctly, they opened the whole data set and ran their procedure without changing it.
This protected them from tainting their data by, e.g., throwing out data points that didn't match expectations. That is a common problem, even among good scientists. It's very easy to subconsciously make decisions that bias your results toward the expected answer.
Anyway, I am a physicist, and I think you should believe these guys. Everything I've seen indicates they've done a good, careful job with the experiment.
Re:Implications regarding the Standard Model? (Score:4, Informative)
The mass deltas are known as squared values -- the sign is unknown, so there's the question of overall mass scale plus the ordering of the various flavors.
simple explanation (Score:4, Informative)
Re:Already Known (Score:2, Informative)
For the oscillations, they are long known, and one of the most simple and exact explainations is that their eigenstate of mass are not the eigenstates of flavour, which in turn means that they have different mass, and at least one is different from zero. Neutrino Oscillation is not a proof for neutrino to have mass. Just a strong hint that they may have
Kinds of dark matter (Score:3, Informative)
When people talk about dark matter, they usually mean the exotic stuff, since there is a lot of evidence that the bulk of the universe's matter is exotic (look up "big bang nucleosynthesis" for details).
Neutrinos make up some of the exotic stuff, and how much depends on their mass. It turns out that they can't make up nearly enough of it, however. Furthermore, neutrinos are light particles which move at speeds near that of light. This means they don't clump together under their own gravity very easily, and tend to disrupt the formation of galaxy clusters. From looking at the distribution of galaxies in the universe, we can argue that most of the exotic dark matter must be slow-moving and "clumpable". The bulk of what people mean by dark matter is this stuff, which can't be neutrinos.
Mass and the speed of light (Score:3, Informative)
If photons (quanta of light) had mass, the world around us would be very different. Photons mediate the electromagnetic force, which is responsible for light, the pull of magnets, the fact that electrons stay in their orbits, etc. If the photon were massive this force would become short-range - its strength would decay exponentially with distance (like the weak nuclear force), rather than as an inverse-square law. We have done ridiculously precise tests of the inverse-square law, which translates into very tight constraints on photon mass.
Re:bragging time (Score:1, Informative)