Do Neutrinos Change Flavor at Night?
Kamioka Observatory, ICRR, University of Tokyo
SuperKamiokande engineers inspect the detectors as the as the huge cavern is filled with ultra-pure water.
Did you own a toy race-car track as a child? Ever crash your model trains into one another just to see what happened? If you did, then congratulations, you already know some of the basic principles behind the Large Hadron Collider (LHC). Built by the European Organization for Nuclear Research (CERN), the 27-kilometer tunnel buried in the Swiss countryside exists to smash particle beams into each other at velocities approaching the speed of light. The idea is to use the resulting data to better understand the structure and origins of the universe. We're talking heavy questions and even heavier answers. Perhaps it's understandable that some critics, conspiracy theorists, crackpots and (alleged) time travelers might fear something more substantial than the Higgs boson particle. In this article, we'll run through some of the more popular misconceptions about the LHC and how little you have to fear about it causing the end of the world as we know it.
5. CERN Is Making an Antimatter Bomb
The Dan Brown detective novel (and movie adaptation) "Angels and Demons" centers on a plot to steal an antimatter bomb from CERN and blow up the Vatican with it. While the blockbuster delivered its share of action and intrigue, it fell short on facts. Two of the film's biggest mistakes revolved around antimatter's potential use as both an energy source and a weapon. Yes, when an antimatter particle comes in contact with normal matter, the two particles destroy each other and release energy. But CERN is quick to point out that the energy payoff simply isn't there. In fact, the transaction is so inefficient that scientists only get a tenth of a billionth of their invested energy back when an antimatter particle meets its matter counterpart. As for developing an antimatter bomb, the same principles apply. CERN points out that, at current production rates, it would take billions of years for the organization to produce enough antimatter to generate an explosion equal to an atomic blast.
4. Fun-sized Black Holes
Some concepts don't become tamer when you tack a "micro-" or a "mini-" prefix in front of them. For example, a mini-stroke is still an excellent reason to visit the hospital, and you'd certainly be ill advised to question the power of a minigun. So when CERN scientists mention that they might create microscopic black holes in the midst of their particle smashing, it's easy to understand some of the ensuing panic. Based on Einstein's theory of relativity, a few speculative theories lend a sheen of possibility to micro-black hole creation. The good news is that these theories also predict the micro-black holes would disintegrate immediately. If these black hole welterweights did hang around a little longer, it would take billions of years to consume the mass of a tiny grain of sand. That means no reducing the European countryside to a singularity and certainly no destroying the planet "Star Trek" style.
3. Attack of the Strangelets
Read enough space publications and your perception of the universe changes pretty fast. Once you get beyond the absurd vastness of the cosmos, you encounter such mind-rending notions as black holes, antimatter and dark matter. After you've swallowed the notion of a gigantic star collapsing into something smaller than a pinhead, it's easy to get bowled over by the idea of universe-destroying strangelets. Strange matter is presumed to be 10 million times denser than lead and was birthed during the Big Bang from the hearts of dense stars. The fear, which originated with the start-up of the Relativistic Heavy Ion Collider (RHIC) in 2000, is that the LHC will inadvertently produce strangelets -- tiny particles of strange matter -- and that these particles will swiftly convert surrounding normal matter into even more strange matter. It only takes a thousand-millionth of a second for the chain reaction to convert the entire planet. Strangelets, however, are purely speculative, and haven't surfaced in over eight years of RHIC operation. CERN says that the RHIC was far more likely to produce the theoretical matter than the LHC, so there's really no chance of it consuming the planet.
2. Time Travelers Hate It
In "Bill & Ted's Excellent Adventure," the titular slacker duo wields time travel with the logic of a 12-year-old. When Bill and Ted need a cell key to bust a few historical figures out of a modern California jail, they simply make a mental note for their future selves to travel back in time and plant the key where they can find it. While the 1989 buddy comedy is pretty much the antithesis of hard science fiction, its view of time-travel logic is shockingly similar to a 2009 theory regarding the LHC. Danish string theory pioneer Holger Bech Nielsen and Japanese physicist Masao Ninomiya, in a series of posted physics articles, laid out their theory that the Higgs boson particle is so abhorrent to nature that its future creation will send a ripple back through time to keep it from being made. Naturally, this theory summons images of T-800s, Jean-Claude Van Damme and Hermione Granger all galloping back through time to prevent future disasters, but not everyone is busy cracking jokes and reminiscing about time-travel movies. The two scientists aren't even talking about shadowy strangers from the future, but merely "something" looping back through the fourth dimension. Imagine a poorly designed bomb that, upon creation, destroys half the bomb factory. Now expand that example out from the confines of linear time.
1. Gateway to Hell
Black holes, antimatter explosions and even strangelets all originate from scientific fact and theory (albeit with a bit of imagination thrown in). Forget all that for the moment and consider the "Satan's Stargate" theory, proposed by Chris Constantine, better known on the Internet as YouTube user gorilla199. Constantine charges that the LHC exists "to disrupt a hole in the Van Allen belt that surrounds the Earth" and "to allow the return of the Annunaki from the planet Nibiru in order that they can come here, corrupt the rest of the Earth and do battle with God at Armageddon." There's also some stuff in there about freemasonry, cosmic rays and the Old Testament offspring of humans and fallen angels. According to BBC News, Constantine received a suspended sentence for DVD pirating after his defense attorney charged that Constantine suffered from a serious psychiatric condition. The Antichrist could not be reached for comment.
A fascinating observation has been tentatively announced by scientists using the Japanese SuperKamiokande neutrino detector. After analyzing 18 years of data it appears that neutrinos generated by fusion in the sun’s core ‘flip’ flavors when detected on the night-side of Earth.
Neutrinos are the chargeless ‘ghosts’ of the quantum world. They have very little mass and travel near the speed of light. They are so weakly interacting with normal matter that they can blast through our entire planet, from one side to the other, without hitting a thing. The only force they interact with is the weak force.
Although they may seem impossible to detect, physicists have devised a means to snare stealthy neutrinos should they score a direct hit with terrestrial matter.
In the case of the SuperKamiokande detector, a vast cavern under a mountain 300 kilometers (190 miles) from Tokyo has been filled with 50,000 tons of ultra-pure water and thousands of detectors cover the cavern’s walls. Occasionally, should a direct collision between a neutrino and water molecule occur, high-energy electrons or muons are generated. These collision particles generate Cerenkov radiation, causing a brief flash that can be measured. If you have a big enough vat of water, it’s statistically likely that enough neutrino collisions can be spotted to create a kind of “neutrino telescope” (though, technically, it’s more of a particle detector than a telescope).
Although the Universe is swarming with a flood of these neutral particles, in our cosmic neighborhood the sun is the main neutrino generator.
Neutrinos can come in three different flavors — “electron,” “tau” and “muon” — and, through a quantum quirk, oscillate between these flavors. The nature of this oscillation has been the focus of physics studies for decades.
The fascinating thing about neutrino flavor is that only electron neutrinos are detected by SuperKamiokande. A longstanding mystery has been why far fewer than expected neutrinos are detected from the sun — it turns out that electron neutrinos (that can be detected) oscillate into muon and tau neutrinos (that can’t be detected) on their journey through interplanetary space, explaining the discrepancy.
As noted by Physicsworld.com, about half of the electron neutrinos with energies of less than 2MeV change flavor before reaching Earth. At higher energies, this oscillation rate is greater. There’s a trend; the higher the energy, the less likely the neutrino detection. This strange behavior is known as the Mikheyev–Smirnov–Wolfenstein (MSW) effect, named after the Soviet physicists Stanislav Mikheyev and Alexei Smirnov who, in 1986, built on 1978 work by US theorist Lincoln Wolfenstein. The MSW effect is also theorized to reverse this oscillation.
As muon and tau neutrinos travel through our planet, they can interact with the electrons contained within the dense terrestrial matter. This can cause the neutrinos to flip back to electron neutrinos. And it appears SuperKamiokande has detected observational evidence of this effect in action.
After analyzing 18 years of data, SuperKamiokande physicists noticed a 3.2 percent increase in neutrino detections at night than during the day. As the detector is facing away from the sun (at night), the neutrinos have to travel through the Earth before hitting the detector. During the day, the solar neutrinos hit the detector after traveling through space (and a few miles of atmosphere). This is a strong hint that after passing through our planet, muon and tau neutrinos are being influenced by the MSW effect, flipping them into electron neutrinos SuperKamiokande can detect.
However, the researchers urge caution. The statistical significance of this finding is not a “discovery” or definitive proof that the MSW effect is fiddling with neutrinos. This result has a statistical significance of 2.7σ, which is interesting, but cannot be considered a discovery. Only when the statistical significance reaches 5 σ can a discovery be announced. It seems we’re going to need a bigger detector for that to happen.
Fortunately, plans are afoot to build a HyperKamiokande that could possibly even use this strange neutrino flavor change to measure the different densities of rock within our planet.
“HyperKamiokande will be 25 times the size of SuperKamiokande, so we will get a much larger data set,” neutrino expert David Wark of the University of Oxford told Physicsworld.com (who was not involved in this study). “Whether it would be big enough to make measurements of the Earth’s density with interesting sensitivity, I am not sure, but we will certainly be looking at that as we further develop HyperKamiokande.”