Neutrino Oscillations Confirmed 122
mfg writes "The Sudbury Neutrino Observatory has found evidence that neutrinos can change type between the Sun
and Earth. See the
BBC news story for more details."
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Neutrino Oscillations Confirmed
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Re:Why are the neutrinos interesting? (Score:5, Informative)
They beat em (Score:5, Informative)
For the people who have no idea what neutrinos oscillating is about - try here. [fnal.gov] It gives a good overview, made so someone like me could even understand it.
for those too slow to avoid the slashdotting (Score:4, Informative)
Experiment confirms Sun theories
The SNO was constructed to solve a mystery
By Dr David Whitehouse
BBC News Online science editor
Neutrinos - some of nature's most elusive sub-atomic particles - do change their properties as they travel through space.
We are much more certain now that we have really shown that solar neutrinos change type
Prof Dave Wark, University of Sussex New evidence confirms last year's indication that one type of neutrino emerging from the Sun's core does switch to another type en route to the Earth.
This explains the so-called solar neutrino mystery, which has had scientists puzzled for 30 years - why so few of the particles expected to emerge from the nuclear furnace in our star can actually be detected.
The new data mean the reactions put forward by physicists to describe how the Sun works are correct.
The data were obtained from the underground Sudbury Neutrino Observatory (SNO) in Canada.
Going underground
Neutrinos are ghostly particles with no electric charge and very little mass. They are known to exist in three types related to three different charged particles - the electron and its lesser-known relatives, the muon and the tau.
Electron-neutrinos are created in the thermonuclear reactions at the solar core. Because these reactions are understood, it has been possible to estimate the number of electron-neutrinos that should emerge from our star.
But it has baffled scientists for decades as to why just a third of this expected number could actually be detected.
Using the underground Sudbury neutrino detector, an international group of researchers has been able to determine that the observed number of electron-neutrinos is only a fraction of the total number emitted from the Sun - clear evidence that the particles change type en route to Earth.
SNO Project Director, Dr Art McDonald, of Queen's University, Canada, said the number of electron-neutrinos detected combined with the numbers of other types picked up at Sudbury gave a total that was consistent with scientists' understanding of the nuclear reactions occurring at the Sun's core.
All types
The Sudbury Neutrino Observatory is a unique neutrino telescope, the size of a 10-storey building, two kilometres underground, down a mine in Ontario.
The SNO detector consists of 1,000 tonnes of ultrapure heavy water, enclosed in a 12-metre-diameter acrylic-plastic vessel, which in turn is surrounded by ultrapure ordinary water in a giant 22-metre-diameter by 34-metre-high cavity.
The observatory detects about one neutrino per hour
Outside the acrylic vessel is a 17-metre-diameter geodesic sphere containing 9,600 light sensors or photomultiplier tubes, which detect tiny flashes of light emitted as neutrinos are stopped or scattered in the heavy water.
At a detection rate of about one neutrino per hour, many days of operation are required to provide sufficient data for a complete analysis.
Because SNO uses "heavy" water - the hydrogen atom in the water molecule has an extra neutron - it is able to detect not only electron-neutrinos through one type of reaction, but also all three known neutrino types through a different reaction.
Very accurate
Dr Andre Hamer, of the Los Alamos National Laboratory, US, said: "In order to make these measurements, we had to restrict the radioactivity in the detector to minute levels and determine the background effects very accurately to show clearly that we are observing neutrinos from the Sun."
The research not only improves our understanding of the Sun but of the elusive neutrinos as well.
The latest results, entirely from the SNO detector, (and which have been submitted to Physical Review Letters) are said to be 99.999% accurate.
Dr MacDonald said: "The SNO team is really excited because these measurements enable neutrino properties such as mass to be specified with much greater certainty for fundamental theories of elementary particles."
Mass differences
This announcement is confirmation of indications released in June 2001 that suggested that it was highly likely that neutrinos changed type on their way from the Sun.
However those conclusions were always tentative because they were based on comparisons of results from SNO with those from a different experiment, the Super-Kamiokande detector in Japan.
Professor Dave Wark, of the University of Sussex and the Rutherford Appleton Laboratory, UK, commented: "Whenever a scientific conclusion relies on two experiments, and on the theory connecting them, it is twice as hard to be certain that you understand what is going on.
"We are therefore much more certain now that we have really shown that solar neutrinos change type."
Professor Hamish Robertson of the University of Washington, US, added: "There's absolutely no question the neutrino type changes and now we know quite precisely the mass differences between these particles."
Not at all (Score:5, Informative)
In fact, there is a large quantity of work going on in this field. Current experiments include KamLAND, Borexino, Opera, NuMI-MINOS, Super-Kamiokande (when they finish their repairs in a year or so), K2K (KEK to Super-K), MiniBOONE the new JHF facility, plus a bunch more I'm forgettting.
There are several reasons for all this activity. First, there are at least two different types of oscillaitions. (The naive and over-simplified theory is that there is nu-electron to nu-mu oscillation, and nu-mu to nu-tau oscillation, the first of which is seen by SNO, the second of which is seen by atmosphereic neutrinos and by the beam experiments). There may be a third mode, which implies a new variety of neutrino (nicknamed 'sterile' for various reasons).
In addition, we're looking to prove that our theory about the oscillations is correct; that they really oscillate in the way we think they do (i.e. change back and forth between flavours on a given time scale that is dependent on energy and suchlike). We want to know the exact parameters in the theory, so the theorists have some hard numbers to much on to make better overarching theories. And, there's always the possibility that something entirely new will crop up in these studies.
(A note on that last: modern neutrino detectors were born out of eariler attempts to build proton decay experiments... but the neutrinos kept getting in the way! On the 'don't beat 'em, join 'em' approach, people started looking at the neutrinos themselves with more interest.)
--Nathaniel, prowling his favourite topic.
SNO / Laurentian Press Release from 18 April (Score:3, Informative)
New scientific results from the Sudbury Neutrino Observatory to be announced
April 18, 2002
(Sudbury, Ontario) - Scientists from Canada, the United States and the United Kingdom, working at the Sudbury Neutrino Observatory (SNO), a unique underground laboratory built to provide insights into the properties of neutrinos and their emission from the core of the Sun, will submit a scientific paper with important new results later this week. They will announce these research findings in a scientific presentation by Dr. Andre Hamer on Saturday, April 20, at the Joint Meeting of the American Physical Society and the American Astronomical Society in Albuquerque, New Mexico. A copy of the first scientific paper and news release summarizing SNO's findings and their importance will be posted on the SNO website (www.sno.phy.queensu.ca) at 1:20 p.m EDT (10:20 a.m. PDT) on Saturday, April 20. A summary talk on the implications of these neutrino measurements will be presented by Dr. John Wilkerson on Monday, April 22, at the same conference.
"We look forward to this opportunity to share these new findings with the scientific community and the general public," says Dr. Art McDonald, SNO Project Director and member of the Department of Physics at Queen's University. "For the first time, we are reporting on an important neutrino reaction in the SNO detector - a reaction in which all known neutrinos participate, regardless of their type. The successful observation of these neutrino signals has been a chief goal of the years of intense work by a collaboration of close to 100 scientists at 11 universities and national laboratories in Canada, the United States and the United Kingdom, and we are very pleased with the quality of the data obtained."
In June 2001, the SNO scientific collaboration announced definitive results based on two other reactions seen in the SNO detector, and on measurements at the SuperKamiokande neutrino detector in Japan, establishing that neutrinos from the Sun change from their original electron neutrino type, to a mixture of electron and other (mu or tau) neutrino types. The new data from the Sudbury Neutrino Observatory to be announced on April 20, enables this question to be addressed accurately from data obtained entirely from SNO, and is expected to enhance significantly our understanding of these important properties of neutrinos from the Sun and of the Sun itself.
Additional information about the conference presentations, the SNO laboratory, the neutrino measurements being made and the participating institutions can be found at www.sno.phy.queensu.ca [queensu.ca].
Re:They beat em (Score:2, Informative)
This is not a pointless experiment. In both experiments that the article mentions (SNO and SuperKamiokande) neutrinos are produced by a natural process (either nuclear reactions in the Sun or cosmic rays in atmosphere). There is always a possibility that we don't understand these natural processes good enough and that we misinterpret the data.
In these planned terrestrial neutrino oscillation experiments (such as NOMAD [nomadinfo.cern.ch], K2K [neutrino.kek.jp], OPERA [web.cern.ch], MINOS [fnal.gov], etc.) neutrinos will be produced in controlled reactions on Earth, making interpretation and measurements easier, more precise and more model-independent.
Re:So what are the implications? (Score:2, Informative)
Of course, this is only the mass _difference_. There's very little direct mass evidence, so the maxixum mass could still be up high enough to be more interesting, but it's viewed as unlikely.
---Nathaniel
Re:Why are the neutrinos interesting? (Score:5, Informative)
No. This is probably the single most common misconception about physical science; but a misconception it is.
A physical "law" is not a "theory that has been proven". The word "law", in physical science, is used to describe relations between independently observable properties of systems that have been detected through experimentation or observation. Thus we have Newton's Law of Gravitation, which relates an external observable property of an object (the force upon it) to intrinsic but observable properties of that object (its mass, the masses of other objects, and the distances between them); this is a physical law even though, strictly speaking, it isn't true (as we now know that it provides only an approximation, which holds reasonably well over certain domains of length and mass scale).
The fact is that theories are never proven to be true in science. A theory can be falsified, but can never be proven true. This is because no matter how much evidence you have collected in favor of a theory, it is always imaginable that tomorrow, someone will observe some phenomenon that contradicts it. We have tons and tons of evidence supporting conservation of momemtum in systems isolated from external forces; but no matter how much evidence we have, it is logically impossible for me to guarantee that tomorrow someone won't do a robust experiment that shows violation of conservation of momentum. I'll bet all the money in the world that won't happen, I'm confident it won't happen; but I cannot logically assert with 100% confidence that it cannot happen. You can never say with logical certainty what will happen in an experiment until you do the experiment; and because of this, scientific theories are not proven true. Instead of being "proven to be true," scientific theories are "supported by the weight of accumulated evidence"; it is the degree to which that accumulates evidence is convincing that determines the statue of the theory it supports.
Neutrino interactions and ball bearings (Score:2, Informative)
"It all depends on what you mean by 'hit' of course, seeing as matter consists almost entirely of nothing at all. The chances of a neutrino actually hitting something as it travels through all this howling emptiness are roughly comparable to that of dropping a ball bearing at random from a cruising 747 and hitting, say, and egg sandwich."
Also incidently, the neutrino toaster is not an invetion, it's a discovery: being close to a supernova would make you feel mighty warm, even if you did have shielding to protect you from the light and the matter shockwaves. Supernovae release 90% of their energy as neutrinos.
---Nathaniel, on the Neutrino Prowl, co-author on the recent SNO papers.
Re:Acutely interesting, but where's the detail??? (Score:2, Informative)
Re:Acutely interesting, but where's the detail??? (Score:3, Informative)
Actually the day/night ratios detected at SNO
is more complex than this, the neutrino capture
cross section in matter is so small that the
even the whole mass of the earth doesn't block
a signicant fraction of the neutinos, the detected
flux of 1 neutrino per hour at SNO as a testament
to the vest number of neutrinos emitted by the
sun.
Instead what is happening is that (according
to theory), the neutrino oscillation rate becames
signicantly increased while the neutrino is
travelling through matter, so that at night
detented particles contains less electron neutrinos and more of the other types.
Oh, and finally, the neutrino captured in SNO emit a cone of UV light (checknov radition), and
the cone points in the direction the neutrino
came from, so scientist at SNO can have a good
idea weather the neutrinos came from the sun or
from deep space.
Local Colour (Score:2, Informative)
Stompin' Tom Connors even wrote a song [geocities.com] to prove it!
There are occasional tours of the SNO site (usually for academics and visiting dignitaries) but you have to set aside a large block of time just to allow for transit time down and back up.