Missing: Electron antineutrinos and Understanding matter-antimatter imbalance

An international particle physics collaboration has announced its first results toward answering a longstanding question - how the elusive particles called neutrinos can appear to vanish as they travel through space.

The result from the Daya Bay Reactor Neutrino Experiment describes a critical and previously unmeasured quality of neutrinos, and their antiparticles, antineutrinos, that may underlie basic properties of matter and explain why matter predominates over antimatter in the universe.

Embedded under a mountain near the China Guangdong Nuclear Power Group power plant about 55 kilometers from Hong Kong, the Daya Bay experiment used neutrinos emitted by powerful reactors to precisely measure the probability of an electron antineutrino transforming into one of the other neutrino types.

The results, detailed in a paper submitted to the journal Physical Review Letters, reveal that electron neutrinos transform into other neutrino types over a short distance and at a surprisingly high rate.

"Six percent of the electron antineutrinos emitted from the reactor transform over about two kilometers into another flavor of neutrino. Essentially they change identity," explains University of Wisconsin-Madison physics professor Karsten Heeger. Heeger is the U.S. manager for the Daya Bay antineutrino detectors.

Coincident with presentations by other principal investigators in the Daya Bay collaboration, Heeger is describing the results in a talk at the Symposium on Electroweak Nuclear Physics, held at Duke University.

Neutrinos oscillate among three types or "flavors" - electron, muon, and tau - as they travel through space. Two of those oscillations were measured previously, but the transformation of electron neutrinos into other types over this distance (a so called "mixing angle" named theta one-three, written ?13) was unknown before the Daya Bay experiment.

"We expected that there would be such an oscillation, but we did not know what its probability would be," says Heeger.

The Daya Bay experiment counted the number of electron antineutrinos recorded by detectors in two experimental halls near the Daya Bay and Ling Ao reactors and calculated how many would reach the detectors in a more distant hall if there were no oscillation. The number that apparently vanished on the way - due to oscillating into other flavors - gave the value of theta one-three.

After analyzing signals of tens of thousands of electron antineutrinos emitted by the nuclear reactors, the researchers discovered that electron antineutrinos disappeared at a rate of six percent over the two kilometers between the near and far halls, a very short distance for a neutrino.

CERN Declare Antimatter Bombs Impossible

A graphic showing a collision at full power is pictured at the Compact Muon Solenoid experience control room of the Large Hadron Collider at CERN in Meyrin, outside Geneva, on March 30 of last year.

Scientists at CERN, the European Organization for Nuclear Research have been experimenting with particles that may seem esoteric to the layman.

One of these mysterious particles being studied by the physicists at CERN is antimatter, the twin to matter particles that make up everything in the universe.

Antimatter particles are sub-atomic particles that have the opposite properties of those found in normal matter particles. An electron's antimatter equivalent is the positron.

Scientists have theorised that the universe had the same amount of matter and antimatter in the first moments after the Big Bang but over 14 billion years most of the antimatter was destroyed.

Scientists have never been able to explain why the antimatter disappeared but one theory points out that there could have been more matter than antimatter in the beginning.

Matter and antimatter annihilate each other when they meet so if there were more matter than antimatter, there would have been enough normal matter to form the stars.

Ever since the scientists at CERN reported that they were successful in creating antimatter using the Large Hadron Collider there have been some concerns among the general public about the implications of the discovery.

Could antimatter be used to make bombs as popularised in Dan Brown's book "Angels and Demons" where a secret society used an antimatter bomb?

To allay those fears CERN actually released a disclaimer on its site about antimatter and the possibility of an antimatter bomb.

"It would take billions of years to produce enough antimatter for a bomb having the same destructiveness as 'typical' hydrogen bombs, of which there exist more than ten thousand already," the group responsible for creating the antimatter explained at their website.

There is also not enough antimatter created by CERN to annihilate the Earth or even use for anything other than for pure research. Creating enough antimatter to build a bomb is also very inefficient since CERN can only create miniscule amounts of antimatter by colliding particles at very high energies.

"Thanks to the inefficiency of the transformation process of energy into antimatter we are safe," CERN physicist Rolf Landua explained on the institute's website. "We do not have to worry about military applications."

"Take Dan Brown's hypothetical 1 gram of antimatter," he continued. "With present CERN technology, we would be able to produce about 10 nanograms of antimatter per year, at a cost of about $10-20 million.

Then we would have to deal with the problem of how to store so many particles (about 10,000,000,000,000,000 antiprotons).

Obviously, it would take 100 million years - and $1,000 trillion - to make 1 gram. This appears ambitious even for the US military."

ALPHA stores antimatter atoms for nearly 17 minutes

The ALPHA Collaboration, an international team of scientists working at CERN in Geneva, Switzerland, has created and stored a total of 309 antihydrogen atoms, some for up to 1,000 seconds (almost 17 minutes), with an indication of much longer storage time as well.

ALPHA announced in November, 2010, that they had succeeded in storing antimatter atoms for the first time ever, having captured 38 atoms of antihydrogen and storing each for a sixth of a second. In the weeks following, ALPHA continued to collect anti-atoms and hold them for longer and longer times.

Scientists at the U.S. Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab) and the University of California at Berkeley, including Joel Fajans and Jonathan Wurtele of Berkeley Lab's Accelerator and Fusion Research Division (AFRD), both UC Berkeley physics professors, are members of the ALPHA Collaboration.

Says Fajans, "Perhaps the most important aspect of this result is that after just one second these antihydrogen atoms had surely already decayed to ground state. These were likely the first ground state anti-atoms ever made." Since almost all precision measurements require atoms in the ground state, ALPHA's achievement opens a path to new experiments with antimatter.

A principal component of ALPHA's atom trap is a superconducting octupole magnet proposed and prototyped in Berkeley Lab's AFRD. It takes ALPHA about 15 minutes to make and capture atoms of antihydrogen in their magnetic trap.

"So far, the only way we know whether we've caught an anti-atom is to turn off the magnet," says Fajans. "When the anti-atom hits the wall of the trap it annihilates, which tells us that we got one. In the beginning we were turning off our trap as soon as possible after each attempt to make anti-atoms, so as not to miss any."

Says Wurtele, "At first we needed to demonstrate that we could trap antihydrogen. Once we proved that, we started optimizing the system and made rapid progress, a real qualitative change."

New Anti-matter Exotic Particle Found

In a single collision of gold nuclei at the RHIC particle accelerator, many hundreds of particles are emitted.

The particles leave telltale tracks in the STAR detector (shown here from the end and side).

Scientists analysed about a hundred million collisions to spot the new antinuclei, identified via their characteristic decay into a light isotope of antihelium and a positive pi-meson. Altogether, 70 examples of the new antinucleus were found. Credit: BNL

Scientists have created a never-before seen type of exotic matter that is thought to have been present at the earliest stages of the universe, right after the Big Bang.

The new matter is a particularly weird form of antimatter, which is like a mirror-image of regular matter. Every normal particle is thought to have an antimatter partner, and if the two come into contact, they annihilate.

The recent feat of matter-tinkering was accomplished by smashing charged gold atoms at each other at super-high speeds in a particle accelerator called the Relativistic Heavy Ion Collider at the U.S. Department of Energy's (DOE) Brookhaven National Laboratory in Upton, N.Y.

Among the many particles that resulted from this crash were bizarre objects called anti-hypertritons. Not only are these things antimatter, but they're also what's called strange matter. Where normal atomic nuclei are made of protons and neutrons (which are made of "up" quarks and "down" quarks), strange nuclei also have so-called Lambda particles that contain another flavour of quark called "strange" as well. These Lambda particles orbit around the protons and neutrons.

If all that is a little much to straighten out, just think of anti-hypertritons as several kinds of weird.

Though they normally don't exist on Earth, these particles may be hiding in the universe in very hot, dense places like the centers of some stars, and most likely were around when the universe was extremely young and energetic, and all the matter was packed into a very small, sweltering space.