Researchers at IceCube detect record energy neutrinos

Apr 26, 2013 by Bob Yirka report
The two observed events from August 2011 (left panel) and January 2012 (right panel). Each sphere represents a DOM (digital optical module). Colors represent the arrival times of the photons where red indicates early and blue late times. The size of the spheres is a measure for the recorded number of photoelectrons. Credit: arXiv:1304.5356 [astro-ph.HE]

(Phys.org) —Researchers at the Antarctic research station IceCube are reporting that they've detected the highest ever energy neutrinos ever observed. In their paper they've uploaded to the preprint server arXiv, the team describes how in analyzing sensor data over the period 2010 to 2012 they found evidence of two neutrino induced events that were on an order of ten times the energy of any previous event.

Neutrinos are of particular importance to researchers because they have no charge and very little mass. This means they are free to travel through space without having their paths changed due to gravitational or , a trait that makes them very valuable for one day locating their source. The two neutrinos recorded at IceCube (dubbed Bert and Ernie) are of particular relevance because the odds are very good that they came from the far reaches of space, rather than as a by-product of a collision between and Earth's atmosphere—the researchers give it a confidence level of 2.8 sigma—meaning that the two neutrinos are very likely the first detected from outside the solar system since 1987, when detectors recorded neutrinos believed to have come from a supernova in the .

The IceCube research station records collisions between neutrinos and ice particles via an array of tied together with strings beneath the ice—such collisions are recorded roughly every six minutes—they can be observed because the collisions release enough Cherenkov radiation to be measurable for an area as large as 6 city blocks. Generally such collisions register energies in the 100 tera-electronvolt range—Bert and Ernie in contrast came in at approximately 1000 tera-electronvolts.

Researchers at the IceCube station and elsewhere are hoping that finding neutrinos that originate from outside the solar system will help explain where high energy cosmic rays that reach our planet come from—their source has baffled scientists for nearly a century. If researchers can eventually trace back to their source, they might find that doing so also reveals the source of the cosmic rays.

Because all data from IceCube is recorded, the researchers are able to go back and take a closer look at neutrino events over time using different criteria. Because of this new find, that's exactly what they plan to do next, using a lower threshold to determine if other similar events might have been recorded, but missed due to preconceived notions of what they were supposed to be looking for.

Explore further: Ultrafast imaging of complex systems in 3D at near atomic resolution nears

More information: First observation of PeV-energy neutrinos with IceCube, arXiv:1304.5356 [astro-ph.HE] arxiv.org/abs/1304.5356

Abstract
We report on the observation of two neutrino-induced events which have an estimated deposited energy in the IceCube detector of $1.04 pm 0.16$ and $1.14 pm 0.17$,PeV, respectively, the highest neutrino energies observed so far. These events are consistent with fully contained particle showers induced by neutral-current $nu_{e,mu,tau}$ ($barnu_{e,mu,tau}$) or charged-current $nu_{e}$ ($barnu_{e}$) interactions within the IceCube detector. The events were discovered in a search for ultra-high energy neutrinos using data corresponding to 615.9 days effective livetime. The two neutrino events are observed over an expected atmospheric background of $0.082 pm 0.004 text{(stat)}^{+0.041}_{-0.057} text{(syst)}$. The resulting p-value for the background-only hypothesis is $2.9times10^{-3}$ ($2.8sigma$) taking into account the uncertainty on the expected number of background events. Though the two events could be a first indication of an astrophysical neutrino flux, the moderate significance and the uncertainties on the expected atmospheric background from neutrinos produced in the decay of charmed mesons do not allow for a firm conclusion at this point.

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tpb
5 / 5 (4) Apr 26, 2013
"Neutrinos are of particular importance to researchers because they have no charge and very little mass. This means they are free to travel through space without having their paths changed due to gravitational or magnetic forces"

Is this true, photons have no charge or mass but they're affected by gravity?
Gravitational lensing is used all the time.
Why would photons be affected by gravity, but not neutrinos?
Mike_Massen
4.5 / 5 (4) Apr 26, 2013
tpb brought up an interesting point
Is this true, photons have no charge or mass but they're affected by gravity?
Gravitational lensing is used all the time.
Why would photons be affected by gravity, but not neutrinos?
As you correctly point out the comparative issue, photons are affected by gravity fields but (so far) it appears neutrinos might not, well we can't be 100% sure of the latter because they 'might' be so little affected its difficult to measure...

Given the wikipedia quote
"Neutrinos are affected only by the weak sub-atomic force, of much shorter range than electromagnetism, and gravity, which is relatively weak on the subatomic scale."
It does seem the gravity claim in the article above is wrong !

Given a photon is considered a magnetic field at right angles to an electric field and a neutrino is not, then one wonders the basis of the neutrino's structure or rather, its essence.

Reasonable link, see references at bottom
http://en.wikiped...Neutrino
vacuum-mechanics
1 / 5 (8) Apr 26, 2013
Because all data from IceCube is recorded, the researchers are able to go back and take a closer look at neutrino collision events over time using different criteria. Because of this new find, that's exactly what they plan to do next, using a lower threshold to determine if other similar events might have been recorded, but missed due to preconceived notions of what they were supposed to be looking for.

It is interesting to note that because neutrino cannot directly observed, so there are a lot of questions involved, maybe this physical view could help getting some idea.
http://www.vacuum...=9〈=en
Ober
2.3 / 5 (3) Apr 26, 2013
I picked up on the same point, RE Gravity and magnetism NOT affecting the trajectory of a Neutrino!! I thought that the better description of Gravity, is that Gravity affects objects that have MOMENTUM!! Hence a photon is affected due to it having momentum. I'd say a Neutrino also has momentum, as it is moving!!! Anyway, if it were true that a Neutrino is NOT affected by Gravity and Magnetism, then how would this help them work out where it came from? The rest of the universe is constantly moving under the above two forces, and the movement becomes HUGE over vast time frames. So an accurate knowledge of where the Neutrino came from would require a very accurate knowledge of winding back the cosmos. The further away the source, the far grater the uncertainty.
Doesn't make sense to me!!!!! How can a Neutrino travel through space without being affected by the shape of the space-time continuum. Perhaps the little bugger really does oscillate through other dimensions.
vpoko
2 / 5 (1) Apr 27, 2013
Neutrinos are only weakly affected by gravity, but they are affected by it. There no known particles that are completely unaffected by gravity. Photons don't have a rest mass, but they do have an effective mass due to their momentum (since they have energy, it reasons they have mass per the famous E=MC^2), hence they're also affected by gravity.
tkjtkj
not rated yet Apr 28, 2013
Re: vpoko ..
"Photons don't have a rest mass, but they do have an effective mass due to their momentum (since they have energy, it reasons they have mass per the famous E=MC^2), hence they're also affected by gravity."


so, neutrinos must have a large mass ?
1000Tev's are 1000Tev's , no?

This isnt passing the famous 'Nose Test'
;)
Apparently, it must 'boil down' to 'how small is small' ...
Fleetfoot
5 / 5 (3) Apr 29, 2013
Re: vpoko ..
"Photons don't have a rest mass, but they do have an effective mass due to their momentum (since they have energy, it reasons they have mass per the famous E=MC^2), hence they're also affected by gravity."


All particles follow the curvature of spacetime hence they are equally affected by gravity regardless of their mass, the article is simply wrong on that point.

so, neutrinos must have a large mass ?
1000Tev's are 1000Tev's , no?


No. The individual masses of the three flavours cannot be measured but an upper limit can be set for the sum of the three masses from a number of experiments and that is currently around 0.4eV. The lower limit for the most massive neutrino is 0.04eV.

http://en.wikiped...ino#Mass

The TeV values in the above article refer to kinetic energy due to their very high speed.
tkjtkj
not rated yet Apr 29, 2013
FleetFoot :
"The TeV values in the above article refer to kinetic energy due to their very high speed."


Yes .. i see .. 'small IS small ..' as described here for the photon:
""The Charge Composition Explorer spacecraft was used to derive an upper limit of 6 × 10−16 eV with high certainty. This was slightly improved in 1998 by Roderic Lakes in a laboratory experiment that looked for anomalous forces on a Cavendish balance. The new limit is 7 × 10−17 eV. Studies of galactic magnetic fields suggest a much better limit of less than 3 × 10−27 eV, but there is some doubt about the validity of this method"

http://math.ucr.e...ass.html

Fleetfoot
5 / 5 (1) Apr 30, 2013
FleetFoot :
"The TeV values in the above article refer to kinetic energy due to their very high speed."


Yes .. i see .. 'small IS small ..' as described here for the photon:
""The Charge Composition Explorer spacecraft was used to derive an upper limit of 6 × 10−16 eV with high certainty. This was slightly improved in 1998 by Roderic Lakes in a laboratory experiment that looked for anomalous forces on a Cavendish balance. The new limit is 7 × 10−17 eV. Studies of galactic magnetic fields suggest a much better limit of less than 3 × 10−27 eV, but there is some doubt about the validity of this method"

http://math.ucr.e...ass.html


Yes, but even 3*10^-27 is still an upper limit. Theory suggests, and all observations to date are consistent with the photon mass being identically zero. Not so for the neutrino where we also have lower limit.
tkjtkj
not rated yet May 01, 2013
FleetFoot :

Re: vpoko ..
"Photons don't have a rest mass, but they do have an effective mass due to their momentum (since they have energy, it reasons they have mass per the famous E=MC^2), hence they're also affected by gravity."


I'm sensing that I and perhaps others are laboring under this incorrect even subliminal perception: i.e. , that 'kinetic energy' as in the relationship E=mc*2 , *IS* mass .. and can be treated as such in calculations. Now I realize the error, as it is mass IF CONVERTED to mass by some process. The baseball sitting on my desk represents an enormous amount of energy, yet yields submissively to my baseball bat, swung with gazillions less energy. Mass is energy only when converted to to BE energy, and vice versa ... yielding the truth that 'zero mass' is alway the case when the item IS pure energy .. .. Hence we have the concept of 'zero rest mass' which only makes sense to me now.
Your lucid arguements have made my day ;)
Fleetfoot
not rated yet May 01, 2013
I'm sensing that I and perhaps others are laboring under this incorrect even subliminal perception: i.e. , that 'kinetic energy' as in the relationship E=mc*2 , *IS* mass .. and can be treated as such in calculations. Now I realize the error, as it is mass IF CONVERTED to mass by some process....
Your lucid arguements have made my day ;)


You are right, many people treat it too simply. There's a more detailed explanation here:

https://en.wikipe...relation

Think of mass as a number defined by

m^2 = E^2 - p^2

It is qualitatively the amount by which the total energy exceeds the momentum though quantitatively you need to use the squares. The amount by which E at speed v exceeds the value of E when p=0 is what we call kinetic energy.

For a photon, E=p hence m=0 (note I am assuming c=1 in these units as it makes the underlying connections clearer).
Q-Star
2.3 / 5 (3) May 01, 2013
@tkjtk

Ya are on the correct track. E = mc^2 is probably the best known and least understood formula in all of science. It's so simple that "everyone" who memorizes it, thinks that's all there is and it explains all things worth knowing.

Most people think it is a measure of kinetic energy. Not so. It is a measure of the theoretical maximum that any massive particle can obtain. Only two known particles can achieve the velocity "c", the photon, and gluons, and only because they are massless. A third particle is inferred or predicted, the hypothetical graviton.

But ya are on the right road to being able to intuitively understand it. Think: "kinetic energy" particles moving, the function of their mass & velocity,,,, momentum.

Think "potential energy" the energy from E = mc^2. They momentum they would possess only when they obtain a velocity of "c".

Remember, "c" is a just a speed-limit, it's just as correct if ya leave "light" out it altogether.
Fleetfoot
not rated yet May 01, 2013
Remember, "c" is a just a speed-limit, it's just as correct if ya leave "light" out it altogether.


c has the value 1 if you measure distance in light seconds ;-)

If we measured distance north in inches and distance east in millimetres, you would need to use the constant 25.4 when applying Pythagoras' Theorem and c plays the same role in relativity, it just corrects the odd historical relationship between metres and seconds.
Q-Star
2.3 / 5 (3) May 01, 2013
Remember, "c" is a just a speed-limit, it's just as correct if ya leave "light" out it altogether.


c has the value 1 if you measure distance in light seconds ;-)


That's true what ya say. I was trying to help him understand that "c" is the conceptual speed limit, a universal constant. Ya can give it the value "1", but if ya do that then ya also have to stick with velocities that are measured as something less than unity. That is a very hard thing for most of the visitors on these pages to "feel". Most of them still refuse to except the fact that E = mc^2 by itself is incomplete, approximate, and only theoretical.

That little formula has done more harm than anything else in propagating misconceptions and misunderstanding in some very elementary physics. In my opinion all physics should be taught from a momentum perspective rather than mass, but alas, mass is something that is easy to intuit at an early age, but it usual equated wrongly,,,, referenced to weight.
Fleetfoot
5 / 5 (1) May 02, 2013
Remember, "c" is a just a speed-limit, it's just as correct if ya leave "light" out it altogether.


c has the value 1 if you measure distance in light seconds ;-)


That's true what ya say. I was trying to help him understand that "c" is the conceptual speed limit, a universal constant. Ya can give it the value "1", but if ya do that then ya also have to stick with velocities that are measured as something less than unity.


Indeed, but I was trying to go a little deeper and show the cause of the limit. They say you can't add apples and pears, but you can apply Pythagoras to durations and distances. Seeing 'c' as nothing more than conversion of units emphasises that.

When you then look at a Lorentz boost on a spacetime diagram, if the space axis rotates clockwise, the time axis rotates anti-clockwise and they meet at 45 degrees. That angle is obviously the maximum and the slope is 1, hence c=1 is the maximum velocity before the axes become degenerate.
tkjtkj
5 / 5 (1) May 07, 2013
Re: FleetFoot , for whom I have the highest regard .. :

"it is qualitatively the amount by which the total energy exceeds the momentum though quantitatively you need to use the squares. The amount by which E at speed v exceeds the value of E when p=0 is what we call kinetic energy.


Once again I thank you for clarity, even in the face of these gut-feelings: 1) just why must the variables be ^2 ..

and 2)assumming your reply will demonstrate your truth, why is the exponent not 2.001 , for example ..?

Fleetfoot
5 / 5 (1) May 07, 2013
Re: FleetFoot , for whom I have the highest regard .. :

"it is qualitatively the amount by which the total energy exceeds the momentum though quantitatively you need to use the squares. The amount by which E at speed v exceeds the value of E when p=0 is what we call kinetic energy.


Once again I thank you for clarity, even in the face of these gut-feelings: 1) just why must the variables be ^2 ..

and 2)assumming your reply will demonstrate your truth, why is the exponent not 2.001 , for example ..?


That's a great question and one I find hard to answer (I even wrote a web page on it in an introduction to SR about 15 years ago). All I can say is that the reason is that spacetime exhibits a particular geometry and the reason is presumably the same as that which requires the exact squares to appear in Pythagoras' Theorem:

en.wikipedia.org/wiki/Pythagorean_theorem

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