IN THE TANK: The Daya Bay experiment currently employs six detectors, with a total of 120 metric tons of liquid detector material, to register passing neutrinos.
Image: Roy Kaltschmidt, Lawrence Berkeley National Laboratory
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Gravity's Engines
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Neutrinos are devious little particles. Only in the late 1990s were they shown to have mass, after decades of head-scratching hints to that effect. They can oscillate between three neutrino types, or "flavors," changing their identity on the fly. And, perhaps most famously, they were accused just last year of breaking cosmic law by traveling faster than light. (The jury is out, but an acquittal appears imminent.)
Now investigators are just a bit closer to figuring out the neutrino's modus operandi. A collaboration of physicists says it has measured one of the key descriptors of the neutrino's flavor-changing behavior—a number called theta 13 (pronounced "theta one three"). That number, known as a mixing angle, describes the probability that an electron neutrino's antiparticle, the electron antineutrino, will oscillate into another flavor over a relatively short distance. (Each of the three neutrino flavors—electron, tau and muon—has its own antiparticle partner.) Two other neutrino oscillation parameters, or mixing angles, have already been measured, but theta 13 is relatively small compared with the other two and has proved harder to pin down.
Since last year a group of physicists has been trying to measure theta 13 by tracking antineutrinos given off by a large Chinese nuclear power plant. The Daya Bay Reactor Neutrino Experiment collaboration built a series of six detectors, some near the reactors and some more than a kilometer farther away, to track how electron antineutrinos morph into other flavors as they travel through space. Because the detectors are tuned to identify only electron antineutrinos, any oscillation means that the neutrinos will escape detection—that is, they will seem to disappear. Other experiments have taken the opposite tack, looking for the appearance of electron neutrinos in a beam carrying other types of neutrinos.
In just two months of data, the distant set of detectors registered more than 10,000 hits by electron antineutrinos. But that is only 94 percent as many as would be naively expected by extrapolating from the detectors closest to the nuclear reactors. That means that a substantial fraction had oscillated to another flavor on their relatively short journey. "What we're seeing now is this disappearance of [electron antineutrinos] is at the 6 percent level," says neutrino physicist Karsten Heeger of the University of Wisconsin–Madison, a member of the Daya Bay collaboration. "It's a fairly large effect." Heeger presented the experimental results March 8 at a symposium at Duke University, and the group has submitted its study to Physical Review Letters.
The experiment is not even fully built yet—a seventh and eighth detector are in the works—but already the Daya Bay team has observed enough disappearances to quantify how the process works. The new estimate, which falls within previous limits set by other experiments, establishes that theta 13 is not equal to zero, and in fact is relatively large compared with what was plausible in light of other recent results. A zero value for theta 13 would mean that electron neutrinos would not appear in beams of muon neutrinos or, in the Daya Bay case, that electron antineutrinos would not disappear by the time they reached the far detectors. Another reactor experiment, called KamLAND, has also registered the disappearance of antineutrinos over much larger distances, where the oscillation is described by the mixing angle theta 12, rather than theta 13.
"We are the first experiment that measures it and shows that it is nonzero," Heeger says of theta 13. "There have been recent indications, but none of the other results were significant enough to match what we physicists call a discovery." The Daya Bay group claims better than 5-sigma evidence in support of a nonzero value for theta 13. 5 sigma, or five standard deviations, implies that the finding has only a one-in-several-million chance of being caused by a statistical fluke.
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16 Comments
Add CommentThese experiments' failure to detect the emitted quantities of electron antineutrinos does not offer confirmation that they have oscillated into other flavors that are also not detected. IMO, only detection of the other flavors in the missing quantities would establish positive evidence of neutrino oscilation, allowing measurement of mixing angles and other characteristics.
Reply | Report Abuse | Link to thisThe failure to detect could be produced by detector failure or excessive dispersion of inadequately focused beams, for example.
IMO, the experiment should include muon and tau neutrino detectors so that their oscillation assumptions and therefore their results can be confirmed.
Could anti-matter simply be matter with a reversed time arrow? And if so, how would this play spatially? Another question, may time have a relative angle with respect to our observed timeline, if so, how would the basic set of particles appear at different angles, spatially, relative to our time line? Also, if neutrinos are there own anti-particle, would this infer some sort of symmetry with time. Note that it may be true that time is simply an abstract concept, therefore these perusings may be valid questions.
Reply | Report Abuse | Link to thisThe thought of a reversed time arrow has occurred to me. It seems to me that if this were the case, a complete universe would exist heading in the opposite way, time-wise, from the Big Bang. In other words... this universe would be existing "before" the Big Bang.
Reply | Report Abuse | Link to thisIf matter is condensed energy and energy has no mass in itself, there must be some other factor for mass other than energy itself: back to field theories of gravity.
Reply | Report Abuse | Link to thisAs I understand, if E=mc^2 then m=E/c^2. In effect, mass is decelerated or localized [kinetic] energy; it is potential energy.
Reply | Report Abuse | Link to thisIt seems to me that the gravitational effect, expressed by through contraction of the dimensional coordinates of spacetime, must draw external kinetic energy from spacetime, directed to an aggregated source of potential energy or mass. This is not the pseudo-material ether, IMO.
"The failure to detect could be produced by detector failure"
Reply | Report Abuse | Link to thiswhich may be a great part of the reason why they have several detectors at each site,
"or excessive dispersion of inadequately focused beams, for example."
Even if neutrino beams could somehow be focused and dispersed, it isn't relevant, as the neutrinos are not emitted in a beam. They're from fissions in a nuclear reactor and are emitted in all directions.
As for E=mc^2, it is an equation. It describes the relationship between using some unit of mass or using some unit of energy to describe the same thing. It does not imply that mass can turn into energy or vice versa, it implies that mass and energy is the same, merely with - for historical or practical reasons - different units depending on what we're calculating.
Mass is not a special form of energy, it IS energy. Energy can not take form as mass or not, it IS mass, whatever kind of energy it is. "Rest mass" is a special form of energy, and quite a lot of energy is bound in the form of "rest mass," though at a more fundamental level, this may well not be so restful.
So much is bound in the form of rest mass, that in our daily lives it's usually easier to use different units for rest mass and other forms of energy/mass. The conversion between these units is what E=mc^2 describes.
Since rest mass can turn into other forms of energy/mass and vice versa, the equation is often used to convert between the units in such processes, and this can give the impression, when E=mc^2 is misunderstood, that a certain amount of mass becomes a certain amount of energy. What happens is that a certain amount of energy in one form becomes the same amount of energy in another form, and we convert the units to the ones we usually use for the form in question.
Perhaps there is no arrow of time. Perhaps it flows forward and backward from any selected point. If it is flowing 'backward', then we cannot know it because we are losing memories and growing younger until we enter our mother's womb and are slowly absorbed into her body through the umbilical cord. Bodies are dug up inside boxes to be brought to life, or spring from the oceans, or just the dirt, or the river Ganges, (which flows up the Himalayas to for glaciers and snow). In the reverse universe the sun absorbs light and heat from surrounding space and will someday de-coalesce along with the planets, to form a nebulae of gases and dust. Sometime in the 'future'(past) all of the matter in the universe will come together to form a singularity, and then explode outward again. Because there is a continuous stream of time, flowing in both directions, there is a continuous 'big bang', existing forever, as well as a continuous expansion and contraction. All exist simultaneously.
Reply | Report Abuse | Link to thisCaution: getting your head around this thought can be hazardous.
I stand corrected regarding my assumption that a neutrino beam was employed in the Daya Bay experiments. However, neutrino beams are used in other experiments. Please see: http://en.wikipedia.org/wiki/Neutrino_oscillation
Reply | Report Abuse | Link to thisThe point remains that there could be unidentified causes, other than neutrino oscillation, for the discrepancy in the actual number of electron neutrino detections by the far detector and the number projected from the number of detections by the near detector.
Positive confirmation of results can only be ensured by direct detection of muon and tao neutrinos ant both near and far detector sites. While this would be more expensive and difficult, it is possible to achieve even with a single detector. Please see: http://en.wikipedia.org/wiki/Sudbury_Neutrino_Observatory
I don't really follow your discussion of E=mc^2, but in the real world I think the equation applies to explosive devices employing nuclear fission to directly convert the potential energy of a relatively unstable heavy element's mass into kinetic energy.
May be the right place to look at is plutonium's core. What makes it unstable may explain how the mass came into being.
Reply | Report Abuse | Link to thisPerhaps. I'm just guessing, but I think the instability of massive nuclei is just the product of the short range strong nuclear force's weakness over the large diameter of large numbers of aggregated nucleons.
Reply | Report Abuse | Link to thisIf anti-neutrinos are reversed in time, then they are those produced by the nuclear reactor a fraction of a second from now. We will get the same information from them.
Reply | Report Abuse | Link to thisHowever, antimatter does not go backwards in time. Otherwise it would not work in particle accelerators.
The formula e=Mc^2 works with protons and electrons. If a proton and an electron come together they lose mass and create a hydrogen atom. The difference in mass between the masses of the free proton and the free electron and the hydrogen atom, become energy. Plug the difference into the formula and you have your calories. It is there in the Coulombic section of the Theory of Relativity.
CERN's neutrinos exceeding the speed of light @ v-c/c=2.48 sec in 453.6 miles is an exact match to Stanford's SLAC E158 weak force asymmetry value showing the cause of 2.48e-5 is not the politics of a "loose fiber optic cable" checked countless times with the same "gain in space" shown by FERMI Lab's neutrinos supporting an observation that goes back to 1947 and is summed up in 2007 by G. Nimtz and A. A. Stahlhofen who believe it occurs outside the bounds of SR [arXiv:0708.0681v1] not aware of the simple explanation I showed E158 data provides with direct proof provided by SLAC's E158 data exposing a gain in time/space in 453.6 miles also @ 2.48e-5 with a .20 harmonic comma as I predicted for the needed asymmetry in the reverse arrow/phase of time the calculations reveal changing physics. SLAC's data comes from the distance light travels in 1000 years at the speed of light in a ratio to a 1 hour SOL gain making this comparative measurement the most spectacular ever made in physics and does so in regard to the most important observation in the History of Man.
Reply | Report Abuse | Link to thisWhat this means is E=m+{a}c2 outside the weak force where E=mc2 because that equation does not include the neutrino's space needed for the photon via the neutrino (force carrier space) to exit the weak force to create the strong force. This changes physics far more that E=mc2 did due to the infrastructure in place to take advantage of the energy tap {a} provides. It brings back real time by adding past time putting us back in sync with Newton's time but armed with E=mc2 corrected as well as Newton's law by adding the second reverse phase held by "imaginary" numbers in physics that never add up correct without {a} added to expose the second "real" reverse phase in time. And one more thing, it shows we live in a world of only 3.6 seconds a year due to time dilation and that's why atoms hang out so long but not their anti-matter reverse phases. This is what happens when you look at the Sun: a thousand years in the inertial frame of the week force is an hour of a day at the speed of light in time equal to distance at the speed of light relative to our body’s inertial frame of reference. Theata 13 shows there 3 points of observation within the weak force as I showed Erin Edwards in demonstrating the chemical source timing relative to a true inertial frame of reference and Mass location within the DNA’s Gene Ensemble Instance Location. When you move the speed of light remains constant....so where in time do you think the distance comes from? Hint: Not from future time.
I felt easy after knew about the faulty optical fibre of CERN, however, i still wonder about the finding of ICARUS that neutrinoes were travelled at the same speed of light. I believe a mass should not travel at the same speed with light as it will violate the theory of relativity too. I tried my best to understand it and think about an explaination. I assume neutrinoes are existing and decaying simultaneously and what we detected is actually the sum of neutrinoes’ decaying vectors but not the real particles of tiny mass.
Reply | Report Abuse | Link to thisYou are mistaken if you think time travel backward is possible. Just because time appears to slow down as you approach light speed does not mean it will completely stop and go backwards if you exceed it. According to the laws of thermal dynamics and conservation of energy, there is only one direction that time can flow. You may have an "event horizon" as a border but from a single point a cone of probability (less than 180 degrees max.) radiates out in a number of directions necessary according to the elements and conditions of that point in space time. However it is still, and always will be in one direction, never going back on itself.
Reply | Report Abuse | Link to thisAs I recall, in the OPERA experiment a proton beam is directed towards a filter that produces proton decay into muon particles and neutrinos. The decay occurs along the length of this filter; then muon particles are detected and a time stamped record is produced representing a proxy record of a neutrino emission. Basically, it is not possible to precisely determine the neutrino emission points in space or time.
Reply | Report Abuse | Link to thisLater neutrino detections are similarly but more precisely time stamped. Since the actual number of proxy records (from muon detections near the emission location) for emitted neutrinos far exceed the number of subsequent actual neutrino detections, the propagation time for any detected neutrino can only be statistically determined.
From this 'measurement' methodology (along with many other potential geodesic and relativistic effects that may affect the actual traversal time and distance of neutrinos), there is a fairly significant uncertainty regarding the actual speed attained by neutrinos. I notice that the OPERA experiments refer to their current results as being 'consistent with the speed of light' (in a vacuum over the estimated traversal distance) rather than being an actual precise measurement of the speed of neutrinos.
I suspect that the tiny mass of neutrinos produces a similarly scaled deficit in their actual propagation speed, although their may be some relativistic effects in some potential experimental conditions that might affect the actual speed of light vs. neutrinos.
I'm no physicist, but I certainly agree philosophically - just as directional velocity and momentum have no reverse or 'anti' direction, at least in the physical universe.
Reply | Report Abuse | Link to thisI suspect that some other readers have had PET scans as I have, in relation to some medical procedure. As stated by http://en.wikipedia.org/wiki/Positron_emission_tomography
"Positron emission tomography (PET) is a nuclear medicine imaging technique that produces a three-dimensional image or picture of functional processes in the body. The system detects pairs of gamma rays emitted indirectly by a positron-emitting radionuclide (tracer), which is introduced into the body on a biologically active molecule. Three-dimensional images of tracer concentration within the body are then constructed by computer analysis."
I don't think there's any real question about the temporal sequence in detection events of decay products in these procedures...