Fermilab experiment weighs in on neutrino mystery

Jun 24, 2011
The building blocks of matter include three types of neutrinos, known as electron neutrino, muon neutrino and tau neutrino. For more than a decade, physicists have seen evidence that these neutrinos can transform into each other. Credit: Fermilab

Scientists of the MINOS experiment at the Department of Energy's Fermi National Accelerator Laboratory announced today (June 24) the results from a search for a rare phenomenon, the transformation of muon neutrinos into electron neutrinos. The result is consistent with and significantly constrains a measurement reported 10 days ago by the Japanese T2K experiment, which announced an indication of this type of transformation.

The results of these two experiments could have implications for our understanding of the role that neutrinos may have played in the evolution of the universe. If muon neutrinos transform into electron neutrinos, neutrinos could be the reason that the produced more matter than , leading to the universe as it exists today.

The Main Injector Neutrino Oscillation Search (MINOS) at recorded a total of 62 electron neutrino-like events. If muon neutrinos do not transform into electron neutrinos, then MINOS should have seen only 49 events. The experiment should have seen 71 events if neutrinos transform as often as suggested by recent results from the Tokai-to-Kamioka () experiment in Japan. The two experiments use different methods and analysis techniques to look for this rare transformation.

The observation of electron neutrino-like events allows MINOS scientists to extract information about a quantity called sin2 2θ13. If muon neutrinos don’t transform into electron neutrinos, sin2 2θ13 is zero. The new MINOS result constrains this quantity to a range between 0 and 0.12, improving on results it obtained with smaller data sets in 2009 and 2010. The MINOS range is consistent with the T2K range for sin2 2θ13, which is between 0.03 and 0.28. According to the T2K data, the most likely value is 0.11. The MINOS result prefers a value of 0.04, and its data indicates that sin2 2θ13 is non-zero at the 89% confidence level. Credit: Fermilab

To measure the transformation of muon neutrinos into other neutrinos, the MINOS experiment sends a muon neutrino beam 450 miles (735 kilometers) through the earth from the Main Injector at Fermilab to a 5,000-ton neutrino detector, located half a mile underground in the Soudan Underground Laboratory in northern Minnesota. The experiment uses two almost identical detectors: the detector at Fermilab is used to check the purity of the muon neutrino beam, and the detector at Soudan looks for electron and muon neutrinos. The neutrinos' trip from Fermilab to Soudan takes about four hundredths of a second, giving the neutrinos enough time to change their identities.

For more than a decade, scientists have seen evidence that the three known types of neutrinos can morph into each other. Experiments have found that muon neutrinos disappear, with some of the best measurements provided by the MINOS experiment. Scientists think that a large fraction of these muon neutrinos transform into tau neutrinos, which so far have been very hard to detect, and they suspect that a tiny fraction transform into electron neutrinos.

The observation of electron neutrino-like events in the detector in Soudan allows MINOS scientists to extract information about a quantity called sin^2 2 theta-13 (pronounced sine squared two theta one three). If muon neutrinos don't transform into electron neutrinos, this quantity is zero. The range allowed by the latest MINOS measurement overlaps with but is narrower than the T2K range. MINOS constrains this quantity to a range between 0 and 0.12, improving on results it obtained with smaller data sets in 2009 and 2010. The T2K range for sin^2 2 theta-13 is between 0.03 and 0.28.

Neutrinos, ghost-like particles that rarely interact with matter, travel 450 miles straight through the earth from Fermilab to Soudan -- no tunnel needed. The Main Injector Neutrino Oscillation Search (MINOS) experiment studies a muon neutrino beam using two detectors. The MINOS near detector, located at Fermilab, records the composition of the neutrino beam as it leaves the Fermilab site. The MINOS far detector, located in Minnesota, half a mile underground, again analyzes the neutrino beam. This allows scientists to directly study the oscillation of muon neutrinos into electron neutrinos or tau neutrinos under laboratory conditions. Credit: Fermilab

"MINOS is expected to be more sensitive to the transformation with the amount of data that both experiments have," said Fermilab physicist Robert Plunkett, co-spokesperson for the MINOS experiment. "It seems that nature has chosen a value for sin^2 2 theta-13 that likely is in the lower part of the T2K allowed range. More work and more data are really needed to confirm both these measurements."

The MINOS measurement is the latest step in a worldwide effort to learn more about neutrinos. MINOS will continue to collect data until February 2012. The T2K experiment was interrupted in March when the severe earth quake in Japan damaged the muon neutrino source for T2K. Scientists expect to resume operations of the experiment at the end of the year. Three nuclear-reactor based neutrino experiments, which use different techniques to measure sin^2 2 theta-13, are in the process of starting up.

"Science usually proceeds in small steps rather than sudden, big discoveries, and this certainly has been true for neutrino research," said Jenny Thomas from University College London, co-spokesperson for the MINOS experiment. "If the transformation from neutrinos to electron neutrinos occurs at a large enough rate, future experiments should find out whether nature has given us two light and one heavy neutrino, or vice versa. This is really the next big thing in neutrino physics."

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User comments : 10

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Questionable
1 / 5 (7) Jun 24, 2011
Quote from article:
"For more than a decade, scientists have seen evidence that the three known types of neutrinos can morph into each other."

The article mentions about observing missing muon neutrinos that are believe to have oscillated into extra electron neutrinos. But there no mention of any observations of electron neutrinos morphing into muon neutrinos. Why?

Could it be because there is no neutrino oscillation going on here and that neutrinos are just a neutral form of radiation and some of this muon neutrino radiation is absorbed in transit and then detected as an electron neutrino?


Vendicar_Decarian
3.4 / 5 (10) Jun 24, 2011
"But there no mention of any observations of electron neutrinos morphing into muon neutrinos. Why?" - Questionable

Because it is being hidden by the Illuminati in their quest to destroy the universe through the establishment of a one world government.

Good God man... Don't you watch Faux news?
Pyle
5 / 5 (6) Jun 24, 2011
VD, not helpful and barely entertaining. You usually do so much better.

But there no mention of any observations of electron neutrinos morphing into muon neutrinos. Why?


Because they are sending a muon neutrino beam. There aren't any electron neutrinos to "morph" unless they had oscillated from muon neutrinos previously.

Your last point about muon neutrino absorption and subsequent detection as an electron neutrino isn't really possible. Muon nuetrinos that don't make it to the detector wouldn't have reactions that send electron neutrinos off towards the detector. If sufficient electron neutrinos are observed, flavor oscillation is almost certainly the mechanism.
Questionable
1 / 5 (1) Jun 24, 2011
This test is conducted with muon neutrinos and all the other test I have read about over the years are also done using muon neutrinos. Why don't they conduct a test using electron neutrinos, which are many times more plentiful, to see if any oscillate into muon neutrinos? After all don't they claim that is what happens to the missing neutrinos from the sun and the slight deficiency of electron neutrinos detected after they have traveled through the earth?
Questionable
2.5 / 5 (2) Jun 25, 2011
Can anyone explain exactly what is the difference between an electron and a muon neutrino other than their origin? We know that an electron neutrino can have many different energy levels, how is that possible if it is a particle that travels at the speed of light? Does the same apply to a muon neutrino? And how is energy and momentum conserved when a muon neutrino oscillates into an electron neutrino or visa versa? If it is conserved how can one tell the difference between the muon and electron neutrino?

Paul_Falk
not rated yet Jun 26, 2011
Seems to me they are looking for the connection to see if they translate to and fro from status to status. Although the particles tend to fuse back into matter before ideal data can be collected? Is what I'm getting more or less, wish we could see whats going on inside the darn things. . . darn lack of adequate diagrams.
Callippo
not rated yet Jun 26, 2011
Scientists think that a large fraction of these muon neutrinos transform into tau neutrinos, which so far have been very hard to detect, and they suspect that a tiny fraction transform into electron neutrinos.
I'd expect exactly the opposite result, i.e. large mixing angle for electron neutrino, small one for tauino.
Vendicar_Decarian
3.7 / 5 (3) Jun 26, 2011
"Can anyone explain exactly what is the difference between an electron and a muon neutrino other than their origin?" - Questionable.

Nope.
Eoprime
5 / 5 (1) Jun 27, 2011
Very interesting, looking forward to more experiments on neutrino oscillation. Would it be possible to send a beam directly through earth? And would this increase the possibility of changing flavor?

I'm wondering where our beloved omatur is hiding to not read this news.
Pyle
5 / 5 (1) Jun 27, 2011
Beloved? I certainly hope not. Also, he hasn't shown he understands what a neutrino is, nor any subatomic particle for that matter. Why exactly would you invite him to comment, and what, if any, relevance does neutrino flavor oscillation have to his NR? I can't think of a thing.

I think distance should improve chance of flavor oscillation. There probably is some equilibrium once you reach a certain number of oscillations too. It will be interesting to watch.