MINOS experiment sheds light on mystery of neutrino disappearances

British scientists are joining colleagues from around the world today (Thursday March 30th 2006) at Fermi National Accelerator Laboratory (Fermilab) in the USA to share the first results from a new neutrino experiment. The Main Injector Neutrino Oscillation Search (MINOS) is designed to study ghostly particles called neutrinos and in particular to study how the three different types are able to transform one into the other. In their first data release, the MINOS team has already reached the sensitivity of previous experiments and provides independent confirmation that neutrinos have mass.

Professor Jenny Thomas, from UCL, said “The first MINOS result is a totally independent confirmation of the surprising fact that neutrinos are not massless. It opens up a whole field of study to understand why this is true and what it means to our understanding of the universe.”

Neutrinos are vital to our understanding of the Universe. Nature provides for three types of neutrinos, yet scientists know very little about these ghost particles, which can traverse the entire Earth without interacting with matter. But the abundance of neutrinos in the universe, produced by stars and nuclear processes, may explain how galaxies formed and why antimatter has disappeared. Originally neutrinos were thought to have no mass, but previous experiments suggested that they can oscillate between the three types – a phenomenon which is only possible if they do have mass.

MINOS is designed to measure a stream of muon neutrinos where they are produced at Fermilab and again 450 miles (735 km) later. As neutrinos pass easily through the Earth, researchers can measure how many muon neutrinos were lost through oscillating into another type. With their first few months of data alone (a small fraction of the information the experiment will gather) MINOS has improved on the world data and confirmed that a significant number of muon neutrinos are disappearing in a manner consistent with oscillation between neutrino types. This observation has been used to measure the mass difference between two of the neutrino types to be 0.056 eV, just 0.00001% of the mass of the electron, a tiny but very significant difference. MINOS will take 15 times more data than this and will be able to determine categorically whether the disappearance is indeed due to oscillations or whether alternative explanations, such as neutrino decay or extra dimensions, are required.

Dr Geoff Pearce of CCLRC Rutherford Appleton Laboratory, UK spokesperson for the project said “To have an initial result from such a complex experiment so soon after starting to take the data is very exciting for the whole team. UK scientists and engineers have been central to the construction and operation of these massive neutrino detectors and UK physicists have played a leading role in analyzing and interpreting the data. It is an achievement that has only been possible because all aspects of the experiment have converged successfully in a short period of time. ”

Dr Lisa Falk of the University of Sussex is anticipating further results from MINOS “Neutrino oscillations are thought to be able to manifest themselves in three different ways, two of which have been observed. The next task for MINOS will be to pin down the details of one of these, in a measurement of unprecedented precision. MINOS will also make the world’s most sensitive search for the third, hitherto unobserved, manifestation. Our results will set the scope for further studies of neutrinos for years to come, ultimately helping us to understand the formation of the universe.”

Professor Keith Mason, CEO of the Particle Physics and Astronomy Research Council that funds UK participation in MINOS said, “The MINOS experiment is a hugely important step in our quest to understand neutrinos-we have created neutrinos in the controlled environment of an accelerator and watched how they behave over very long distances. This has told us that they are not totally massless as was once thought, and opens the way for a detailed study of their properties. UK scientists have taken key roles in developing the experiment and in exploiting the data from it, the results of which will shape the future of this branch of physics.”

The MINOS experiment includes about 150 scientists, engineers, technical specialists and students from 32 institutions in 6 countries, including Brazil, France, Greece, Russia, the United Kingdom and the United States. The institutions include universities as well as national laboratories. The U.S. Department of Energy provides the major share of the funding, with additional funding from the U.S. National Science Foundation and from the United Kingdom’s Particle Physics and Astronomy Research Council.

The Fermilab side of the MINOS experiment consists of a beam line in a 4,000-foot-long tunnel pointing from Fermilab to Soudan. The tunnel holds the carbon target and beam focusing elements that generate the neutrinos from protons accelerated by Fermilab’s Main Injector accelerator. A neutrino detector, located 350 feet below the surface of the Fermilab site and called the MINOS near detector, measures the composition and intensity of the neutrino beam leaving the lab. The Soudan side of the experiment features a huge 6,000-ton particle detector that measures the properties of the neutrinos after their 450-mile trip to northern Minnesota. The cavern housing the detector is located half a mile underground in a former iron mine. A 60-foot mural, painted on the wall of the cavern by Minneapolis artist Joe Giannetti, shows highlights of neutrino research from across the world. (Details available at http://www.symmetrymag.org/cms/?pid=1000118)