Measuring elusive neutrinos flowing through the Earth, physicists learn more about the sun

Oct 07, 2011

Using one of the most sensitive neutrino detectors on the planet, an international team including physicists Laura Cadonati and Andrea Pocar at the University of Massachusetts Amherst are now measuring the flow of solar neutrinos reaching earth more precisely than ever before. The detector probes matter at the most fundamental level and provides a powerful tool for directly observing the sun's composition.

Pocar, Cadonati and colleagues report in the current issue of that the Borexino instrument has now measured with high precision the flux of the beryllium seven (7Be) solar neutrino, abundant, low-energy particles once below the observable threshold. With this advance, they can now precisely study the behavior of solar with kinetic energy below 1 megaelectron volt (MeV). Borexino scientists also recently reported the first observation of neutrinos produced in a little-studied solar nuclear process known as proton-electron-proton, or pep, and set of stringent limit on reactions involving carbon, nitrogen and oxygen (the CNO cycle) in the sun.

Cadonati says, "Borexino is the only detector capable of observing the entire spectrum of solar neutrinos at once. Our results, the culmination of 20 years of research, greatly narrow the observation precision. The data confirm the neutrino oscillations, flavor changes and flow predicted by models of the sun and particle physics."

Of particular interest, Pocar and Cadonati note, is the Borexino instrument's ability to more thoroughly test neutrino oscillation parameters, allowing an exploration of their characteristic non-zero mass, which does not fit the Standard Model of particle physics. "Our data can tell us about fundamental micro physics at the particle level," says Cadonati. "Borexino is using neutrinos to explore the interior of the sun, looking for new, exciting clues to the mysteries of the universe we cannot see." Pocar adds, "Our detector provides stringent tests of the three-neutrino oscillations model."

are produced in nuclear processes and radioactive decays of several elements during fusion reactions at the sun's core. As many as 65 billion of them stream out of the sun and hit every square centimeter of the earth's surface [or 420 billion every square inch] every second. But because they only interact through the nuclear weak force they pass through matter unaffected, making them very difficult to detect and to distinguish from the trace nuclear decays of ordinary materials. The weak force is one of the four fundamental forces of nature, with gravity, electromagnetism and the strong force. It is responsible for the radioactive decay of unstable subatomic particles, with a short range of influence, about 1 percent of the diameter of a typical atomic nucleus.

The Borexino instrument, housed far beneath Italy's Apennine Mountains, detects neutrinos as they interact with an ultra-pure organic liquid scintillator at the center of a large sphere surrounded by 2,000 tons of water. Its great depth and many onion-like protective layers maintain the core as the most radiation-free medium on the planet.

There are three neutrino types, or "flavors": electron, muon and tau. Those produced in the sun are the electron type. As they travel away from their birthplace, they oscillate, or change from one flavor to another. A detector like Borexino can observe all three types in real time and measures each one's energy, but it cannot distinguish between them. It's more sensitive to the electron type so they are more likely to be seen.

The 7Be neutrino flux now being detected by Borexino is predicted by the standard solar model to make up about 10 percent of solar flow, Cadonati says. Earlier instruments in Canada and Japan designed to detect higher-energy neutrinos had already observed evidence of their flavor oscillations, probing 1/10,000 of the solar neutrino flux and their oscillations as they travel through solar matter. However, without data in the low-energy range as scanned by Borexino, physicists were not able to confirm the specific energy-dependent effect of solar neutrino oscillations. Borexino has now filled this gap and for the first time observed evidence of neutrino oscillation in vacuum, as they travel between the sun and Earth.

Pocar says that from the astrophysics angle, Borexino's ability to conduct "precision physics" experiments and collect a large number of observations, with concomitant higher statistical power, is yielding data that show how our sun works. As for the possibility of discovering a new kind of neutrino coming from the sun, which is allowed by some theoretical extensions to the Standard Model of particle physics, he adds, "You always have the hope of seeing surprises, some small deviation from the expectations. And this you can only have if your accuracy and precision are good enough to see very small variations."

In a companion paper, the Borexino team says their 7Be solar neutrino flux measurements show no flow differences between day and night. Some had hypothesized that one might exist because neutrinos pass through the earth's bulk at night. But Pocar says, "The traverse through the earth seems not to change neutrinos' flavor."

In the future, the researchers hope to identify the origin of every neutrino type coming from the sun, particularly to assess the relative levels of carbon, nitrogen and oxygen there, to deepen understanding of how the sun evolved and how its workings are related to that of larger stars.

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Provided by University of Massachusetts at Amherst

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User comments : 10

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Nikola
5 / 5 (8) Oct 07, 2011
"As many as 65 billion of them stream out of the sun and hit every square centimeter of the earth's surface [or 420 billion every square inch] every second."

I've always found that to be utterly amazing - that we're living in a vast ocean of neutrinos moving through us at light speed.
yyz
4.3 / 5 (10) Oct 07, 2011
"The data confirm the neutrino oscillations, flavor changes and flow predicted by models of the sun and particle physics."

What, absolutely no evidence for a solar-mass pulsar??? Must have something to do with Henry Kissinger and Chairman Mao. They knew we couldn't handle the truth, I guess. I know the truth because I've seen the "secret" cables revealed at this very website!
rawa1
1 / 5 (3) Oct 07, 2011
What, absolutely no evidence for a solar-mass pulsar??
There is a weak evidence, the speed of decay of radioactive elements inside of spaceprobes around Sun is modulated with solar flares and rotational period of Sun core. IMO the Sun is surrounded with dense coat of primordial antineutrinos and the nuclear reaction at the Sun core are emanating the normal neutrinos in directional way: in polar jets, i.e. like the weak "pulsar", emanating neutrinos instead of gamma rays.

http://www.physor...660.html

Of course, such explanation doesn't requite the omatur's "neutron repulsion" hypothesis, as the Solar core generates the neutrinos with common nuclear reactions. I liked this model a lot - but the recent findings of superluminal neutrino speed violates it a bit. Why? The speed of primordial neutrinos shouldn't exceed the escape velocity from Sun (~ 570 km/sec), or these neutrinos couldn't form a dense coat around Sun. So I'm forced to rethink this model a bit.
rawa1
1 / 5 (3) Oct 07, 2011
IMO the primordial neutrinos are forming a missing antimatter, which the contemporary cosmology is looking for. These neutrinos are in thermal equilibrium with CMBR photons, so they cannot move with very high speed, because the upper limit of neutrino mass is just a few eV/c2. The neutrinos in OPERA experiment were high energy neutrinos instead.

IMO the neutrinos are behaving like tiny bubbles of space-time and they can influence the speed of nuclear reactions significantly. The nuclear fusion requires the temporal formation of thin neck with strongly negative curvature, which is thermodynamically unfavourable situation. When some neutrino will fly through such place, it could initiate the formation of such neck like the catalyst. The influence of neutrinos to the speed of nuclear reactions is surprisingly intensive, it could be even sensitive to neutrino oscillations inside of atom nuclei.

http://www.nature...64a.html
Pressure2
5 / 5 (5) Oct 07, 2011
Quote from article: "A detector like Borexino can observe all three types in real time and measures each one's energy, but it cannot distinguish between them. It's more sensitive to the electron type so they are more likely to be seen."

I find this statement a little puzzling. If it observes all three in real time and measures each one's energy, what other information would they need to distinguish between the three types?
yyz
5 / 5 (3) Oct 07, 2011
"There is a weak evidence, the speed of decay of radioactive elements inside of spaceprobes around Sun is modulated with solar flares and rotational period of Sun core."

What "spaceprobes" are you referring to? A 2008 study of the RTGs aboard the Cassini probe in route to Saturn found: "No significant deviations from exponential decay are observed over a range of 0.7 - 1.6 A.U. A 90% Cl upper limit of 0.84 x 10^-4 is set on a term in the decay rate of Pu-238 proportional to 1/R^2 and 0.99 x 10^-4 for a term proportional to 1/R."

http://arxiv.org/...48v1.pdf

Wouldn't it be more accurate to say that the reality of variable radioactive decay rates is in dispute and as of now no unequivocal evidence of such a decay mode exists (and several studies, including the one I noted above, find no evidence of it).

Even Fischbach et al conclude more study is needed to confirm or refute their controversial findings.
douglas2
5 / 5 (3) Oct 07, 2011
Quote from article:
I find this statement a little puzzling. If it observes all three in real time and measures each one's energy, what other information would they need to distinguish between the three types?

They measure energy, NOT flavor.
Callippo
1 / 5 (1) Oct 07, 2011
Even Fischbach et al conclude more study is needed to confirm or refute their controversial findings
Of course, single study means nothing - but there are many other studies, which found correlation of radioactive decay with neutrino flux.

The same applies to recent OPERA results: this study is indeed suspicios as such - but we have other (at least three) independent indicia. Mainstream science is strictly deterministic - if doesn't work well with distributed, emergent evidence. It tends to ignore, until it finds the strong reproducible connection - such connection indeed becomes often misleading and it cannot be extrapolated at the case of weak, emergent dependencies. I'd say, the physics at present stage of human understanding evolution should be handled rather like the detective story.
Callippo
1 / 5 (2) Oct 07, 2011
Once again: try to imagine, we are observing the water surface with its own ripples. At the proximity the determinism of surface ripples spreading increases with distance of observer. The close objects are often irregular and fuzzy, but the remote stars are all pretty spherical objects. In this stage of human evolution the deterministic approach based on reductionism brings a good results. This is why the recent century was a golden era of theoretical physics.

But with increasing distance from human observer scale the Universe isn't so regular anymore. The large stars are oval, the galaxies are flat or of irregular shape and the galactic cluster are completely random. The appearance of Universe changes into fuzzy quantum object again. Under such a situation the reductionist approach based on deterministic rigor doesn't work well anymore: the mainstream physics changes into landscape of many overlapping theories. A more reliable predictions would be based on distributed evidence there.
Skepticus
not rated yet Oct 08, 2011
The Borexino instrument, housed far beneath Italy's Apennine Mountains, detects neutrinos as they interact with an ultra-pure organic liquid scintillator at the center of a large sphere surrounded by 2,000 tons of water.


A Nobel Prize surely for anyone who comes up with a house-sized or smaller neutrino detector!