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Neutrino Mass Confirmed
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."
Thats is sloppy on the BBC's part, they should have put the State in there. In this case it is Minnesota.
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http://www.dnr.state.mn.us/state_parks/soudan_und
SNO Detector.
This was proven in the late 90's in a Japanese lab. The experiment was similar and involved muon neutrinos changing flavors to electron neutrinos in a large particle accelerator. 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.
Making you think you're crazy is a billion dollar industry.
How did you like the elevator ride down? Dark and kinda clanky. I worked on this project when I was in school--good to see some results already!
... as claimed in 1998 Scientific American article
--- Attorneys Assisting Citizen-Soldiers & Families -
http://en.wikipedia.org/wiki/Dark_Matter#Compositi on
...short answer is: yes it has been considered, but current models of neutrino formation suggest they can't account for all dark matter (or even a significant component of it).
http://en.wikipedia.org/wiki/Hot_dark_matter
- 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.)Find free books.
We'll have to wait and see, but for anyone who would like more information, Fermilab's website has an article about the discovery.
They aren't really "point particles"; it's just mathematically easier to consider them such, for most problems.
"Confirmed" in this case should be taken to mean "Already known because Super-Kamiokande convinced us it was true in 1998, followed by more evidence from the Sudbury Neutrino Observatory and the K2K expeirment, and then also KamLand, but isn't it nice that this newer experiment sees (confirms) the same thing."
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.)
There is a large bit of hand waving here. Why are neutrino oscillations and neutrino mass inseparable?
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.
My quantum physics knowledge isn't teriffic. Any particle physicists know of a better source?
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.
It's a small world and it smells funny; I'd buy another if it wasn't for the money; Take back what I paid (SoM)
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..
This may be one of the last discoveries at Fermilab. As it stands now, Fermilab, SLAC, and Brookhaven's future is in severe doubt.
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http://www.sciam.com/article.cfm?chanID=sa006&art
"To those who are overly cautious, everything is impossible. "
Hmm...time to throw on that old, old song Little Neutrino
Light travels faster than sound. This is why some people appear bright until you hear them speak.........
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. 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.
They have two detectors. One very near to the source, one very far away. The near source measures many more hits than the far source does. Thus, they know they're being produced in larger quantities than they're being received in. Compared to a model of the test configuration assuming no oscillation, there are about 33% too few hits on the far detector as compared to the near. This amounts to a 4 or 5 sigma detection of the missing neutrinos (in other words, there is approximtely a 0.7%-1.8% chance that this is due to a statistical coincidence). It's typically at 2 or 3 sigma that you start making a confident announcement of a discovery, so a 4 or 5 sigma confirmation of an already reported result is very, very strong evidence.
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 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.
have a look at this. it's the transcript from the BBC's recent "horizon" show, called "project poltergeist", which is on precisely this topic (neutrinos having mass). very neatly explains to a lay audience what the mystery is, and also answers exactly your specific question. it's not a long read, maybe 10mins max, and as it's the transcript to the show it leads you through the topic in a well thought out manner http://www.bbc.co.uk/science/horizon/2004/polterge isttrans.shtml
and the short answer to your question is as follows: in order to undergo neutrino oscillation, the neutrino must be capable of change. to be capable of change it must experience a personal sense of time. if it was travelling at the speed of light, it would have no sense of time. objects with mass cannot travel at the speed of light (infinite energy required for objects with mass to do this). therefore, as we experimentally can confirm neutrino oscillation, we are also confirming that neutrinos have a sense of time, which implies they are not travelling at the speed of light, which implies they have mass.
hope that clears it up -- on a side-note my first degree was actually in astrophysics, at University College London (UCL), where the article's quoted scientist comes from... didn't have her for any of my lecures though ;)
Super-KamioKande didn't establish that neutrinos had mass directly. For that it needed the neutrinos from the nova to arrive spread over a time greater than that in which they departed. The duration of the beam on the nova was estimated about ten seconds, which is almost the same time spread of the revealed neutrinos.
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
Dark matter (mass we can't see) has several components: ordinary (protons, neutrons, electrons) matter we happen to be unable to see, exotic matter that we do understand, and exotic matter that we don't understand. You could go into a Rumsfeld-esque discussion of "known unknowns" and "unknown unknowns" at this point.
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.
A massless particle (like the photon) should move at exactly the speed of light, while a massive particle should always move slower than light. We always used to say that neutrinos move at the speed of light because we assumed they had no mass. Now that we know they are massive, they must be moving slower. They are so incredibly light, however, that we expect them to be moving extremely close to that speed - it takes very little force to accelerate them, so anything energetic enough to make them would make them go very fast.
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.
I was working at Fermilab when they made the Main Injector, a new ring whose job is to feed the Tevatron to improve it's luminosity. In part of the main injector (opposite the point where the protons are shaved off and sent across to the Tevatron if I remember correctly) they take some of the protons onto another path that dives down into the earth, hits a target to create nutrinos... just an huge tunnel heading down at a few degrees, aimed at the detector. It was very strange to think that those could go through the earth and show up at a mine so far away. There was a bit of a race with other detectors to be the first to detect nutrino mass... good to see that those guys have accomplished this.