Neutrino discovery—a step closer to finding charge-parity violation

June 6, 2017, University of Tokyo
The detected pattern of an electron neutrino candidate event observed by Super-Kamiokande. Credit: University of Tokyo

The different rates of neutrino and anti-neutrino oscillations recorded by an international collaboration of researchers in Japan—including from Kavli IPMU—is an important step in the search for a new source of asymmetry in the laws that govern matter and antimatter.

The Standard Model of particle physics describes the basic building blocks of and how they interact. It also makes a point that for every particle created, there is an anti-particle. However, the Standard Model does not explain why our Universe still exists today, since the matter and anti-matter symmetry implies that matter—including galaxies, stars, and even humans—should have been annihilated by the equal amounts of anti-matter.

This violation of symmetry, called the charge-parity (CP) violation, has been observed experimentally, but not enough to explain the large amount of matter existing in the Universe.

The international T2K (Tokai-to-Kamioka) collaboration is the first experiment in the world that can search for CP violation by studying neutrino and anti-neutrino oscillations. High intensity beams of muon neutrinos (or muon anti-neutrinos) are produced at J-PARC (Japan Proton Accelerator Research Complex) on Japan's east coast, and fired towards the Super-Kamiokande detector 295 km away in Gifu Prefecture. On the way, the neutrinos and anti-neutrinos spontaneously change 'flavor' from or anti-neutrinos, to electron neutrinos or anti-neutrinos. A difference in the rates of oscillations in separate neutrino and anti-neutrino beams would be proof of an imbalance between particles and anti-particles, and that there is new physics to be learned beyond the Standard Model.

The first data set by T2K was published in April, and detected 32 electron neutrinos and 4 electron anti-.

"While the data sets are still too small to make a conclusive statement, we have seen a weak preference for large CP violation and we are excited to continue to collect data and make a more sensitive search for CP violation," said T2K collaborator and Kavli IPMU Project Assistant Professor Mark Hartz.

Recently, the T2K experiment has finished collecting another set of data that has doubled the amount of data available in the electron neutrino configuration, and its results are expected to be presented later this year. Hartz has said they expect to continue to take data for another 10 years.

"If we are lucky and the CP violation effect is large, we may expect 3 sigma evidence, or about 99.7% confidence level, for CP violation by 2026," he said.

Details of T2K's most recent results using neutrino and anti-neutrino data were published in Physical Review Letters as an Editors Suggestion on April 10.

Explore further: LSU physicists collaborate on T2K CP violation results to explain workings of universe

More information: K. Abe et al. Combined Analysis of Neutrino and Antineutrino Oscillations at T2K, Physical Review Letters (2017). DOI: 10.1103/PhysRevLett.118.151801

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11 comments

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Seeker2
1 / 5 (2) Jun 07, 2017
"the matter and anti-matter symmetry implies that matter—including galaxies, stars, and even humans—should have been annihilated by the equal amounts of anti-matter."

Nyet, anyway. Conservation of energy at baryogenesis requires that in particle creation one of the particle pair must have negative energy if the other has positive energy, or so it seems. At least relative to the energy density of spacetime at the time of barygenesis. So one of the pair must have an effective negative mass and experience anti-gravity at the time of baryogenesis and for as long as the energy density of spacetime exceeds that of the negative mass particle. Like during inflation. After the energy density of spacetime decreases below that of the negative energy particle those particles then have effective positive energies and masses. So they will eventually gravitate like normal matter but with less gravitational force and eventually rejoin normal matter and then mutually annihilate. :-(
TimLong2001
5 / 5 (1) Jun 07, 2017
Pair-formation, as the only required matter creation mechanism, satisfies supersymmetry. Bound equal but opposite charges, forming photons, demonstrates that the charge amplitude determines its rotational radius, providing a stable wavelength. Threshold gammarays will decay into an electron and positron when influenced by an external field. If recombination (annihilation) occurs, two gammarays of one-half threshold energy are formed, traveling in opposite directions to satisfy conservation of energy.
AGreatWhopper
not rated yet Jun 07, 2017
Do these Russian trolls practice here? Thanx for the input, Tim.
Seeker2
not rated yet Jun 07, 2017
Yes Tim. Thanks for staying on topic and avoiding fake news.
Seeker2
not rated yet Jun 08, 2017
One can imagine in the final days one humongous black hole doing a death dance with a similar anti-matter black hole. When they merge it's sayanora, or maybe time for a new beginning, however you want to look at it. One could identify their meeting point as a singularity, or an area as small as you might imagine.
Da Schneib
not rated yet Jun 08, 2017
We'll see if the neutrino sector boosts the asymmetry enough to make the lepton sector account for it.
Seeker2
not rated yet Jun 12, 2017
"This violation of symmetry, called the charge-parity (CP) violation, has been observed experimentally, but not enough to explain the large amount of matter existing in the Universe."

Let me climb out on a great big limb on this one. Suppose the amount of matter is only 50% of what we see? That is because of random density distributions regions of equal amount of matter/antimatter annihilate during inflation - fueling more inflation actually. The end result is galaxies have to decide if they are matter or antimatter. Only those regions of one or the other survive. After all galaxies have collapsed to form black holes, the same winnowing process may continue with the black holes until there are only 2 winners left - one matter and the other antimatter. When they annihilate that provides enough energy for a new beginning.
Seeker2
not rated yet Jun 12, 2017
Found the key to build my case? - Tabby's star. An unstable region of our galaxy where this winnowing process is still going on.
Seeker2
not rated yet Jun 15, 2017
"matter and anti-matter symmetry implies that matter—including galaxies, stars, and even humans—should have been annihilated by the equal amounts of anti-matter."

It would seem the difference in energy between particle pairs created in baryogenesis would be one vacuum fluctuation at the time of creation. No idea what this fluctuation would be however. The result would be different mass values leading to slightly different accelerations and enough separation to prevent every particle pair from instant annihilation. Actually particle pairs would have to be accelerated in opposite directions to preserve total momentum anyway.
Seeker2
not rated yet Jun 15, 2017
cont
Note that spin orientations would have to be opposite to preserve angular momentum.
Seeker2
not rated yet Jun 15, 2017
cont
Also note that spin orientations of the last two remaining black holes would have to be opposite leading to conservation of total angular momentum =0 at the time of final annihilation and new beginning.

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