Feeds

Earth's night-side gets different kinds of neutrinos from day-side

Does your neutrino lose its flavour on the bed-post overnight?

5 things you didn’t know about cloud backup

A Japanese neutrino detector has provided experimental evidence for a prediction first made in the 1980s: that passing through something good and massive – like the Earth – will influence the flavour of neutrinos.

Analysing 18-years' worth of data collected by subterannean neutrino detector SuperKamiokande has shown that the detector observes more electron neutrinos (more on this in a moment) when it's night-time in Japan than during the day.

Neutrinos, which interact so weakly with normal matter that even the best detectors only manage to capture small handfuls of interactions, come in three “flavours”: electron, muon, and tau, and they oscillate between these flavours.

The SuperKamiokande detector, which comprises 50,000 tonnes of water and 11,000 photomultiplier tubes, is specific to electron neutrinos, spotting the tiny amount of Cherenkov radiation emitted when a neutrino scores a direct hit on an atom in the tank. These interactions are rare, which is why the experiments are so long-lasting.

With enough data, however, something interesting emerged: when it's night-time at SuperKamiokande, the detector observes 3.2 per cent more electron neutrinos than during the day. In other words, when the detector is on the sun-side of Earth, the neutrinos passing through it are very slightly skewed towards muon and tau flavours, while at night-time, there's slightly more electron flavours for the detector to observe.

The SuperKamiokande neutrino detector during construction

SuperKamiokande during construction. Image: Kamioka Observatory

The experimental data, it turns out, agrees with a prediction made in the 1980s called the Mikheyev–Smirnov–Wolfenstein effect. As Physicsworld explains, “At neutrino energies below about 2 MeV, about half of all electron neutrinos from the Sun change flavour before reaching the Earth. For neutrinos of higher energies, however, a larger fraction change, meaning that fewer electron neutrinos are detected.”

Neutrinos that haven't passed through the Earth are arriving at higher energies, meaning more of them arrive as muon or tau flavours and aren't spotted by SuperKamiokande. When the detector is night-side, the neutrinos have already interacted in some small way with Earth's mass, lost some energy – and because they arrive at the detector as electron neutrinos, they're spotted.

The researchers are still cautious: at a statistical significance of 2.7σ this falls under the heading of “observation” rather than “discovery”. However, the agreement between prediction and observation is encouraging, especially with plans afoot to build a larger detector.

The proposed HyperKamiokande would be 25 times as large as today's detector, the researchers say.

With a large enough data set, it's feasible that neutrino detectors could provide us with more information about the structure of the Earth. ®

Build a business case: developing custom apps

More from The Register

next story
Vulture 2 takes a battering in 100km/h test run
Still in one piece, but we're going to need MORE POWER
Boffins ID freakish spine-smothered prehistoric critter: The CLAW gave it away
Bizarre-looking creature actually related to velvet worms
TRIANGULAR orbits will help Rosetta to get up close with Comet 67P
Probe will be just 10km from Space Duck in October
CRR-CRRRK, beep, beep: Mars space truck backs out of slippery sand trap
Curiosity finds new drilling target after course correction
ANU boffins demo 'tractor beam' in water
The current state of the art, apparently
China to test recoverable moon orbiter
I'll have some rocks and a moon cheese pizza please, home delivery
What does a flashmob of 1,024 robots look like? Just like this
Sorry, Harvard, did you say kilobots or KILLER BOTS?
NASA's rock'n'roll shock: ROLLING STONE FOUND ON MARS
No sign of Ziggy Stardust and his band
Why your mum was WRONG about whiffy tattooed people
They're a future source of RENEWABLE ENERGY
prev story

Whitepapers

Endpoint data privacy in the cloud is easier than you think
Innovations in encryption and storage resolve issues of data privacy and key requirements for companies to look for in a solution.
Implementing global e-invoicing with guaranteed legal certainty
Explaining the role local tax compliance plays in successful supply chain management and e-business and how leading global brands are addressing this.
Top 8 considerations to enable and simplify mobility
In this whitepaper learn how to successfully add mobile capabilities simply and cost effectively.
Solving today's distributed Big Data backup challenges
Enable IT efficiency and allow a firm to access and reuse corporate information for competitive advantage, ultimately changing business outcomes.
Reg Reader Research: SaaS based Email and Office Productivity Tools
Read this Reg reader report which provides advice and guidance for SMBs towards the use of SaaS based email and Office productivity tools.