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."

Comments

bragging time

[phlegmofdiscontent]

I've actually seen the detector at the Soudan Mine. Pretty impressive. Kinda hard to get to (300 mile drive into the middle of nowhere followed by a half mile trip underground).

Re:bragging time

[Trelane]

Yeah, the universe ran out of vanilla, so it's substituting a rich, creamy chocolate.

Yeah, but they both have up- and downsides. While the vanilla is extremely common and thus is not as strange as the chocolate flavour, it still has its charm. But the chocolate is packed with more calories (being more fudge than chocolate) and hence will pack on pounds to your top and bottom.

But the staunch advocates of vanilla aren't at all mute. They've been quite vocal in support of their flavour of choice and have even proposed creating a new sub-flavour, the electric vanilla. Unfortunately for them, however, due to the long legacy of having only vanilla, people have been taught to expect vanilla to be boring. Therefore, the electric vanilla is expected to flop.

Temporarily relieving the boring-vanilla problem, however, someone long ago discovered vanilla in red, green, and blue colours (as well as in cyan, magenta, and yellow, but those are really just the opposite of the other colours). One would hope that the new chocolate flavour would also come in similar colours and--thus far--this seems to be the case.

My humblest apologies for this post; I've been learning particle physics by grading homework in it, and I suspect it's driven me quite mad.

Soudan, US

[Wyatt Earp]

Thats is sloppy on the BBC's part, they should have put the State in there. In this case it is Minnesota.

http://www.dnr.state.mn.us/state_parks/soudan_unde rground_mine/physicslab.html

Re:Soudan, US

[Bonker]

The US is a federation of 50 sovereign states (each with the size and economy to match), and saying "Foo City, US" would be like saying "Foo City, EU" (though Europe has the advantage of many languages to broaden the name space).

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:Soudan, US

[node 3]

Thats is sloppy on the BBC's part, they should have put the State in there.

Why? They don't care anymore than we (Americans) care that Tijuana, Mexico is more appropriately, "Tijuana, BC, Mexico".

To us, the state is important, but to the British, it's really not that pertinent. The point is that the detector is in the US, not what particular state it's in.

Given how awful most Americans are at geography, your complaint comes off trite and arrogant, sort of like you require people to call you by your full name and title, yet you don't really care whether you get anyone else's name right at all.

*shakes head*

[Monkeys!!!]

You know you are a serious geek when you read the headline and say 'YES!' out loud.

Re:*shakes head*

[MeanMF]

You're ok as long as you didn't have that reaction to the "OMG BARBIE LINUX LOL!!1!!!!" headline...

Re:*shakes head*

[barefootgenius]

And you know you are a sceptic when your next thought is,"hold on, they sent these particle's through an object they know next to nothing about and then use the fact that some of them didn't turn up as proof".
Then you read more and you get,"Of course, most of them travel right through our detectors as well, but once in a blue moon one of them will interact - about one or so per day."

I suppose I am being pedantic, but can anybody explain to me why I should believe their explanation that their not turning up in such large numbers is proof?

Re:*shakes head*

[honkycat]

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.

Already Known

[physicsphairy]

Neutrino mass has been an established fact since 1998 (courtesy work at the Super-Kamiokande).

Would slashdot also be interested in posting my own confirmations that light has a finite speed?

Re:Already Known

[rewinn]

... as claimed in 1998 Scientific American article

Re:Already Known

[n0mad6]

Perhaps simply reading the title would give a hint as to why this is important (i.e., note the word "confirmed"). Experimental results aren't really useful unless its a result that can be reproduced. The MINOS result is simply the first confirmation of the earlier Super-K result.

Re:Already Known

[Firehed]

Actually, I think it's been an established fact since the beginning of universal existance (quite possibly predating the Big Bang, if possible, and assuming that it did actually occur). It's been a known fact since 1998.

Re:Already Known

[habig]

Not quite - the SK result has been confirmed several times (to less precision) by other atmospheric neutrino experiments.

And once before by the K2K accelerator experiment, which was (like MINOS) a controlled, make-your-own-neutrinos, measured-before-and-after sort of experiment. Although one might argue since that used SK as a far detector that it might not be as independant a confirmation as you might like.

The MINOS result is nice because in the first 6 months of a multi-year run, we already have the precision of the K2K results, and that all the experiments point to a similar number. Which makes us feel good that after a few more years work we'll have accomplished the goal of measuring these oscillations way more precisely than ever before, and will have a shot at uncovering more subtle things going on with the neutrinos.

But, that doesn't make good headlines, so you won't read that take on things in the popular press. Same reason as we get a rash of "black holes finally discovered" articles every six months when someone presents some new black hole observations at an AAS meeting.

Fox News had a fun headline though, something like "Feds lose neutrinos, gain knowledge".

PS - note that I'm on both Super-K and MINOS, in fact I created my slashdot account in 1998 to respond to comments about that first SK result. It's pretty neat that doing the experiment a completely different way still shows the same thing happening - so Mother Nature must be up to something real here.

PPS - if you're up in Northern MN for some reason (likely canoeing or fishing) do stop by the Soudan Underground State Park on your way to Ely to take a tour of our lab (and the historic mine). Add a proper geeky component to your otherwise dangerously outdoorsy vacation.

Re:Already Known

[Goldsmith]

Which is why Slashdot for once had the right headline:

Neutrino Mass Confirmed

I know plenty of people who work on Super-K and I'm sure they're as glad as anyone their work has been found accurate. The fact that it took almost a decade to confirm this shows how amazing that first measurement is.

In other news today

[edwardpickman]

New evidence has confirmed that the Universe does in fact have mass. Science advisor for the Bush administration was quick to point out that this is a theory and there was still no hard evidence. "The Bible makes no mention of the Universe having mass so we'll have to wait until a method is devised for weighing the Universe. We don't want any more psedoscience like that Darwin character was spreading."

Dark Matter

[ruiner13]

Could these particles having mass explain the "missing matter" that scientists formerly attributed to dark matter? I wonder what other particles are there taking up space that we never thought had mass, either.

Re:Dark Matter

[syntaxglitch]

http://en.wikipedia.org/wiki/Dark_Matter#Compositi on
http://en.wikipedia.org/wiki/Hot_dark_matter

...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).

Meet the new boss

[pdq332]

Although the article implies that the Standard Model will have to be revised as a result of this experiment, this result does not really change the Standard Model all that much. The theoretical method used to establish neutrino mass, ie- that neutrino oscillations imply neutrino mass, is itself a Standard Model prediction. Rather the results fixes some of the unbound parameters of the theory. In other words, the arguments are better known now, but the method signatures remian the same.

Re:Pardon me, but. . .

[bcrowell]

A hundred years ago, physicists generally classified things like this:

• 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?

[TechnoGuyRob]

This is a very interesting conclusion. I am currently taking a modern physics II class at a college in my town, and I live 15 minutes away from Fermilab. In fact, our professor is a scientist at Fermilab that only comes in this term to teach our class. The interesting question, though, is (and I know it's small), what is the exact mass that they obtained (if any so far)? Of course, this would have to be given in eV (electron volts), but assuming it's very small (~E-3 eV) (EDIT: I just looked at the press release linked to at the end of this post, and indeed, it is on that scale!), this could prove to have some interesting conclusions. I actually found this passage in the article that explains it better than I could:

"In particle physics there is the Standard Model which describes how the fundamental building blocks of matter behave and interact with each other," explained Dr Falk Harris.

"And this model tells us that neutrinos should have no mass. So the fact that we have now got independent measurements of neutrinos saying that they must have mass, means that this Standard Model is going to have be revised or superseded by something else."

This is very interesting because of its possible re-affirmation of Wikipedia. I'm not going to take out my string theory book right now to see if calculations of a positive neutrino mass correspond to any viable conception in string theory, but a re-affirmation and eventual proof of string theory could spur as great of an innovation as the concept of an atom.

We'll have to wait and see, but for anyone who would like more information, Fermilab's website has an article about the discovery.

Re:Implications regarding the Standard Model?

[honkycat]

Basically, at this point, they've got measurements of the difference between the masses of the three flavors of neutrinos. They also have an upper bound of, IIRC, around 0.7eV (not from this experiment) for the absolute value of the neutrino mass. The delta sets the lower bound (if one flavor were at zero mass, the heavier ones must be at least the delta heavier).

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.

Re:This is new?

[bcrowell]

Yes, this is a confirmation of something that had already been shown by one experiment.

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.

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.

Re:explanation about oscillation/mass relationship

[Anonymous Coward]

Okay, as a particle physicist, I learned about this in terms of the Hamiltonian evolution of a wavefunction, and some analogy to neutral kaons, and a page of math. But thats not what you wanted to hear.

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.

It was a long haul ....

[rhatcher]

Boy, was it great to see our result presented on Thursday. Though I'm a little disappointed that the story here didn't link to, say, our press release or even to the Fermilab or MINOS experiment home pages.

I joined the experiment in 1995 soon after the collaboration came together and created the proposal. In that time I've written simulation ("Monte Carlo"), reconstruction and framework code for the experiment. It's been a pretty exciting 10 years. The push to get everything together this last month has been exhausting. But after presenting the results on Thursday do we physicists take a well deserved break and party like 1999? Well, noooo. We spend Friday, Saturday and Sunday IN MEETINGS! Today (Saturday) we were there from 8:30am to 7:00pm discussing how further to proceed. We've got 50% more data "in the can" that we didn't yet present (cross checks to perform, fits to perform). Plus plans for more data taking after the accelerator comes up again in June. Plus other physics results we're still trying to extract. Plus more improved simulations to do in order to yield improved limits. Such is the life of a physicist.

Obligatory-

[capz loc]

Neutrinos have mass? I didn't even know they were Catholic!

A Sad note

[stox]

This may be one of the last discoveries at Fermilab. As it stands now, Fermilab, SLAC, and Brookhaven's future is in severe doubt.

http://www.sciam.com/article.cfm?chanID=sa006&arti cleID=00080A6A-C9C7-1419-89C783414B7F0101&colID=2

Umm...a couple of corrections

[kf6auf]

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.

simple explanation

[alexander m]

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 ;)