New measurements from MINOS experiment suggest a difference in a key property of neutrinos and antineutrinos

Jun 14, 2010
Scientists know that there exist three types of neutrinos and three types of antineutrinos. Cosmological observations and laboratory-based experiments indicate that the masses of these particles must be extremely small: Each neutrino and antineutrino must weigh less than a millionth of the weight of an electron.

( -- Scientists of the MINOS experiment at the Department of Energy's Fermi National Accelerator laboratory today announced the world's most precise measurement to date of the parameters that govern antineutrino oscillations, the back-and-forth transformations of antineutrinos from one type to another.

This result provides information about the difference in mass between different antineutrino types. The measurement showed an unexpected variance in the values for neutrinos and antineutrinos. This mass difference parameter, called Δm2 ("delta m squared"), is smaller by approximately 40 percent for neutrinos than for antineutrinos.

However, there is a still a five percent probability that Δm2 is actually the same for neutrinos and antineutrinos. With such a level of uncertainty, MINOS physicists need more data and analysis to know for certain if the variance is real.

Neutrinos and antineutrinos behave differently in many respects, but the MINOS results, presented today at the Neutrino 2010 conference in Athens, Greece, and in a seminar at Fermilab, are the first observation of a potential fundamental difference that established physical theory could not explain.

“Everything we know up to now about neutrinos would tell you that our measured mass difference parameters should be very similar for neutrinos and antineutrinos,” said MINOS co-spokesperson Rob Plunkett. “If this result holds up, it would signal a fundamentally new property of the neutrino-antineutrino system. The implications of this difference for the physics of the universe would be profound.”

Neutrino oscillations depend on two parameters: the square of the neutrino mass difference, Δm2, and the mixing angle, sin22θ. MINOS results (shown in black), accumulated since 2005, yield the most precise known value of Δm2, namely Δm2 = 0.0024 ± 0.0001 eV2.

The NUMI beam is capable of producing intense beams of either antineutrinos or neutrinos. This capability allowed the experimenters to measure the unexpected mass difference parameters. The measurement also relies on the unique characteristics of the MINOS detector, particularly its magnetic field, which allows the detector to separate the positively and negatively charged muons resulting from interactions of antineutrinos and neutrinos, respectively. MINOS scientists have also updated their measurement of the standard oscillation parameters for muon neutrinos, providing an extremely precise value of Δm2.

Muon antineutrinos are produced in a beam originating in Fermilab's Main Injector. The antineutrinos’ extremely rare interactions with matter allow most of them to pass through the Earth unperturbed. A small number, however, interact in the MINOS detector, located 735 km away from Fermilab in Soudan, Minnesota. During their journey, which lasts 2.5 milliseconds, the particles oscillate in a process governed by a difference between their mass states.

“We do know that a difference of this size in the behavior of neutrinos and antineutrinos could not be explained by current theory,” said MINOS co-spokesperson Jenny Thomas. "While the and antineutrinos do behave differently on their journey through the Earth, the Standard Model predicts the effect is immeasurably small in the MINOS experiment. Clearly, more antineutrino running is essential to clarify whether this effect is just due to a statistical fluctuation.”

The MINOS experiment involves more than 140 scientists, engineers, technical specialists and students from 30 institutions, including universities and national laboratories, in five countries: Brazil, Greece, Poland, the United Kingdom and the United States.

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User comments : 9

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not rated yet Jun 14, 2010
So is this confirmation of Dirac's neutrino vs Majorana's?
not rated yet Jun 15, 2010
The lead paragraph is nuts ! Upper bounds for electron, muon, & tauon masses are: 2ev, 17Kev,
and 15 Mev, respectively. No way they are all 10^-6Me.
3 / 5 (2) Jun 15, 2010
So is this confirmation of Dirac's neutrino vs Majorana's?
Yes, this finding supports Dirac's model neutrino over the Majorana's one. The similar finding was done recently for matter-antimatter transitions for the B_s meson, where antimatter decay channel turned out to be slightly more probable. It means, antimatter appears slightly more lightweight and prone to decay - which could explain, we cannot observe it after Big Bang.

not rated yet Jun 16, 2010
Jimbo, I think the latest upper bounds for neutrino masses is around 0.2 ev compared to the electron mass of 0.511 Mev gives a mass ratio of roughly 2,5 millions.
1 / 5 (1) Jun 16, 2010
Took me time to read all the comments, but I really enjoyed the article. It proved to be Very helpful to me and I am sure to all the commenters here! It’s always nice when you can not only be informed, but also entertained! I’m sure you had fun writing this article.
Jun 16, 2010
This comment has been removed by a moderator.
1 / 5 (3) Jun 16, 2010
This model is only qualitative in this moment, but we can expect, the properties of particles and antiparticles would differ the more, the more their size/energy density scale would differ from human scale. Therefore the most heavy particles (top-quarks) or most lightweight ones (like the neutrinos) would differ more in their properties from corresponding antimatter, then the common atoms.

The slightly negative curvature of antiparticles would give them weak anti-gravity properties and lower stability, especially at the presence of gravity field of common particles due the their tendency to annihilate at distance. Such antiparticles would collect outside of this gravity field, where space-time curvature becomes negative, i.e. we can expect missing antimatter in dark matter streaks surrounding the observable matter, the very large of dense objects in particular.

1 / 5 (3) Jun 18, 2010
In my opinion, neutrinos do not oscillate.

MINOS spokesperson Rob Plunkett correctly describes the potential importance of this finding: “If this result holds up, it would signal a fundamentally new property of the neutrino-antineutrino system. The implications of this difference for the physics of the universe would be profound.”

I agree. If confirmed, this finding will undermine the foundation of physics.

With kind regards,
Oliver K. Manuel
not rated yet Jun 21, 2010
Need more data, 95% chance of changing deep physics is enough to pique my interest but not my belief. That's the same threshold the FDA uses and sure enough when you test enough drugs you will see a surprising number of false positives.

I expect the same in physics, we're exploring a lot of different things and a lot are at the 95% confidence interval. Many of these will be false positive, luckily in this case the side effects don't cause rash or bloating.
3 / 5 (2) Jun 21, 2010
In my opinion, neutrinos do not oscillate
The observed fact, mass of neutrino differs from anti-neutrino supports the nonzero mass of neutrino, therefore it supports the concept of neutrino oscillations.

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