Probing cosmic neutrinos with a giant 200000 km2 detector
Neutrinos are the most elusive particles of the Standard Model of particle physics. Some of them, with enormous energies, are once in a while able to reach Earth. To make it clear from the beginning, by ‘high energies’, I really mean it. We consider almost massless particles that have about 100–10.000 times the energy of the protons collided at the Large Hadron Collider at CERN, the largest and most powerful particle collider in the world (see here).
Until very recently, these super energetic cosmic neutrinos were a real puzzle for us. We did not know much about them, including the mechanism behind their production.
[image credits: WISE @ NASA (public domain)]
Last year, things have started to change thanks to the IceCube collaboration who was at the source of a breakthrough in astrophysics in this context.
The IceCube experiment has pointed out the existence of a cosmic engine capable of producing those neutrinos and accelerate them to crazy energies.
This engine consists in a giant galaxy with a rotating black hole in its center. Such galaxies are known as blazars.
From there, physicists are already thinking about the next steps: trying to detect even more of those highly energetic neutrinos, so that we could catalogue more sources and understand them better.
One potential project as a really great name, and is called GRAND, an acronym standing for the Giant Radio Array for Neutrino Detection. With such a giant detector, a 200.000 km2 array of radio-antennas to be located in China, the physics possibilities are extremely appealing.
But before digging further, let me briefly recapitulate some basic facts about neutrinos and cosmic rays, to make this post somewhat self-consistent.
MORE ABOUT NEUTRINOS
In the picture below, we can see the Sun (yeah no kidding :p), one of the many places where weak interactions are taking place for billions of years. Neutrinos are heavily connected to those weak interactions, and the Sun is one great source of (however low-energetic) neutrinos…
[image credits: NASA/SDO ]
About 100 years ago, radioactivity was the novelty of the moment. Physicists were studying the decays of given atomic species into other ones.
There was an intriguing on-going phenomenon: in many of these decays, the results where showing that some energy (and momentum) was missing.
Of course, this missing component was nothing but an invisible neutrino flying away. But this was not known in the 1910s.
100 years later, this invisible stuff is much more well-known, well embedded into the Standard Model of particle physics. Physicists are moreover able to see the invisible, at colliders or in dedicated neutrino experiments for instance, by relying energy and momentum conservation. From the properties of the visible, one can reconstruct what is missing and measure the properties of the invisible.
COSMIC RAYS AND NEUTRINOS
Cosmic rays are also 100 years old… I promise that I am almost done with the old stuff.
Victor Hess discovered at that time that our good old planet was bombarded by particles originating from space, the so-called cosmic rays.
[image credits: NASA/D. Berry (public domain)]
Cosmic rays can be made of a lot of stuff, like charged particles, photons or even neutrinos. They are traveling through space and those arriving on Earth can be detected (with appropriate detectors of course).
One interesting of their features consists in the energy of these particles. Their energy range spans tens of orders of magnitude, and big questions arise with the very energetic guys.
Where do high-energy cosmics come from? How are they accelerated to crazy energies?
To answer these questions, cosmic neutrinos have a great advantages over all the other cosmic species. They are very weakly interacting, so that they can travel from the source to Earth almost undisturbed, following a straight line. This contrasts with any other particle whose trajectory is bended, for instance, by all magnetic fields present in the Universe.
FROM ICECUBE TO GRAND
Some time ago, the IceCube collaboration discovered a source of highly energetic cosmic rays, this blazar I was mentioning in the introduction of this post that is nothing but a giant galaxy containing a rotating black hole in the middle.
This rotating black hole emits jets of very highly-energetic particles from its poles. This is where the super-energetic neutrino event detected by IceCube was initiated. After this observation, IceCube sent an alert to all telescopes around the world and gamma rays, X-rays, light and radio-waves (i.e. cosmic photons) have been observed as originating from the very same location.
We have thus convincingly discovered a cosmic engine capable of emitting and accelerating very-highly energetic cosmic rays! This was the breakthrough of the year.
[image credits: Greg Goebel (CC BY-SA 2.0)]
But life does not end there. We need to continue the searches and GRAND is a potential next step. The idea is to move on with even more energetic neutrinos.
GRAND, the Giant Radio Array for Neutrino Detection is a huge 200.000 km2 array of about 100.000 cheap radio-antennas (about 500 bucks each) to be located in China.
The core idea is to rely on one specific species of neutrinos, namely tau neutrinos. Tau neutrinos with energies 100–1000 times larger than what has been observed by IceCube emit radio waves that can be detected by simple radio antennas.
This contrasts with all existing experiments that focus on the light emitted by the neutrinos, and that are thus more limited in energy and necessitate more complex and expensive apparatus.
For now, a small set of 35 antennas will be deployed as a test case, to show that it works and that the radio background noise can be controlled. One of the key point is also to demonstrate that the budget can be kept under good control!
TLDR - SUMMARY
In this post, I addressed one option for what concerns the future of neutrino physics. Highly-energetic cosmic rays are observed by some time, and the IceCube collaboration has recently discovered one cosmic object, a distant galaxy with a rotating black hole in its center, capable to generate those very energetic cosmic rays.
It is however the first and so far sole observation of such an object capable to produce very energetic cosmics. The GRAND experiment is one option for the next steps, focusing once again on neutrinos (like IceCube). The idea is to focus on very (very very) energetic tau neutrinos that once in a while produce a huge shower of radio waves that can be recorded. As the shower is huge, we need a huge detector to get it. The proposed solution consists in building a 200.000 km2 array of radio-antennas in China.
A first prototype of 35 antennas will be deployed, and the future of GRAND will be decided from there. Can we make it, and at the same time controlling the budget of the entire experiment? This is the main question to answer by now!
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I've been thinking; these cosmic rays entering the earth, do they pose any serious effect to the inhabitants of the earth?
Or rephrasing it: Is there a limit to how much our bodies can absorb these radiations without being relatively affected by them?
The very energetic cosmic rays interact with the atmosphere of the planet and produce secondary particles, that produce tertiary particles when interacting, and so on. One gets a shower of particles that are less and less energetic, and humans are then safe and won't get hit by a very energetic particle in their face.
Note that cosmic rays may be responsible for being at the origin of life, by causing DNA mutations in the early days ;)
Wow! I've been wondering how the origin of life came to be; now I know better. Thanks for the insight sir.
PS: If the cosmic rays could cause DNA mutation, doesn't it also mean it could have effects on the human body?
PS 2:
Sounds like chain reaction to me :D
Note that this is one option for the origin of life. If I remember well, there is no certainty here.
Yes, but the probability is small.
This is correct! :)
Exactly sir. I once read a funny myth about the creation of life (from the Fulanis) - which stated that life originated from a big drop of milk.. I couldn't help laughing my arse out :D
I thought it was a big drop of turtle poo :D
Lol. Do turtles poo? :D
I don't want to check manually ;)
well, considering they have probably been there a bit longer than humans i'd say it looks pretty safe but the sensei can most likely explain it better than me
Why is China the location of choice? Any thing to do with their cheap labour and technology in terms of the building of the 200km2 antenna? The last question is why do the detection of this neutrinos require such a humongous antenna size? Interesting article.
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China has space. We don't talk about 200 km2 but 200.000 km2. It is for instance 1/3 of France. The cheap part is to keep the full budget of the experiment under control. For now, one must proof that one can produce an antenna that does the job for 500 USD. This is a challenge, but not that crazy as well.
Why do we need such a big detector. The answer is partly given in the answer to @samminator. Very energetic cosmic rays interact with the Earth atmosphere and produce secondary particles, that produce tertiary particles when interacting, and so on. This shower takes space, and we thus need a widely spread detector to detect it entirely.
Oh, I see where the confusion came from. I'm more familiar with the use of comma as delimiter of choice instead of a dot. Hence I confused 200,000 to be 200 :)
Both are huge. Thanks for the clarification as I now understand the need for both choice of location and size of the antenna.
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Ah yeah. sorry about that. I have removed the dot from the title to make it clearer! :D
It is now as clear as day. Thank you :)
I guess that explains the question I had as to why it was harder to detect higher energy neutrino than lower one which seemed counter-intuitive at first. They interact with the upper atmosphere while the lower energy one won't or not as much.
Tau neutrinos does sound Chinese.
Real astrophysics here Lemouth. There's a lot out there that we have yet to discover. But all in time.
We have electrons and their two big brothers: muons and taus. They are all alike electrons, but in a heavier version. Similarly that electrons are often accompanied by electronic neutrinos, taus and muons are accompanied by tau and muon neutrinos. More information can be found here.
Excellent @lemouth !
Regards.
Thanks a lot for reading my post!
so here i am (after six days, i know, sorry) almost at the third paragraph gaping in awe at this thing sitting at a nice 2.5 km deep into the arctic ice , making it another modern world wonder like CERN (and there people say it's just not like the old days and the pyramids ain't coming back , as i start talking in brackets i'll leave out the rant and dissertation on why there is not a floating hangar in space, a factory and warehouse that could basically save zounds on cost as a supply line to wherever , the moon ? mars ? the gas mines of uranus (pun not intended) could be set up, i see THIS, i see the LHC and i ask myself why havent they done that yet, there's so many resources out there and so few here ... yes i know, always do that don't i)
as i find out Einstein has been misquoted all along :
FTL is possible if you go through matter ?
i read about the Chinese detector quite a while ago but afaik their biggest problem was not building it (yes another world wonder) or the operating cost but finding people to work in it ? Is that solved yet ? seems like a bit of a waste and Trump will probably strongarm his MIT-ians to not do it.
Chopin is 208 years old btw and i still think he's not old but more like a classic when i'm in the mood for that.
I like the idea of creative use of resources very much, setting up a massive project at minimal cost, especially in these days. Even if mister Donald has promised to vamp up the space program i havent seen liftoff to the moon yet so any and all results, especially at lower cost will be beneficial to the future of us all.
Leaves me just one question : How hard do i have to run into a wall so i travel through matter fast enough to end up at proxima centauri within my lifetime ? :D
@lemouth
you know me by now ofcourse, i think its time i update that one too
Which Chinese detector? The one I am discussing in the post? A small-scale part will be developed and deplyed to test the viability of the project. There is an international team behind it and thy work hard to make it happen.
Budget is a crucial issue in fundamental science. We have very limited resources those days.
My answer: don't try! :)
PS: glad to still see comments on my rarer and rarer physics posts ^^
the one i read about :)
[here] we are, took almost five google searches to find that back
if my last name was Gates i'd sponsor one to Proxima Centauri you know that
how come you post less on physics then ? its the most interesting part to me ?
trying to deviate traffic to the new app ?
The reason is simple: steemstem takes all my time and I have less time for my own blog. But I finally managed to write something today. Dark matter is back :)
dark matter is back lol
it must be nice to be able to work on a project like #steemstem at high level like that, even if i dont think id be the person to handle something like that , figuring it out seems like a mighty fine puzzle :p
i had a weird idea last time after watching that video on cherenkov shiney lights, like if particles can travel through matter FASTER than light wouldnt that distort the whole vision of the "observable" universe then ? i mean everything that goes through matter might suddenly not adhere to common formulas if it goes FTL, you take some beam from somewhere or you take the time it take light to reach the telescope or whatever and its assumed that lightspeed is the top speed but that woman in that video was like "o but they always leave something out, it CAN , if it goes through matter", so neutrinos and dark matter might be moving ? faster than light, which sets off every calculation since einstein, right ?
or is that all incorporated?
@lemouth i'll just mention, in case, but please take your time, there's no expiry date on comments or replies
That is easy to answer. I will do it immediately :)
The key point is that the speed of light in the vacuum is the largest possible speed. However, the speed of light in matter may be slower. Therefore, when a particle leaves a given a medium (where the speed of light is larger) and enters another medium (where the speed of light is smaller), it can get faster than the speed of light. It then generates Cerenkov radiation (in the same way an airplane traveling above the speed of sound generates a bang).
oh ...
i see ...
it's a trick question :) so ... the constant "c" is not a constant ? the only letter i remember, ever since its only three actually
'c' is constant: it is the speed of light in the vacuum. Not in any other medium :)
actually, before i switch off, as i was eating i was thinking, if this means the speed of light is variable and also since an absolute vacuum is mostly something that exists only in theory as there's always some kind of matter present, does that mean a foton shooting from "the center" towards earth would have a variable speed, like if it has to go through a place with more matter like on of those nebulae,
cosmic sized gas clouds other particles could (in theory) move faster through that part of space ? (yea i get weird thoughts at the funniest moments, but the fries and stew was good :)
just one last edit, i already turned it off but the word hit me : refraction ! spending all that time in blender lately and not even coming up with the word, assuming (by my limited knowledge fotons wont just shoot through the iron core of a planet but refraction is a fenomenon not just limited to liquid, its about matter, right ? so gas is matter (just trying to plot out my train here) so if gas is matter and light shoots through it you get this refraction just like you would get in liquid / water.
how do you factor in refraction across lightyears ? i know its off-topic to the post but it just popped into my head here and i can't imagine a better person to ask this :)
or is that all part of how gravity bends light since the force is related to the amount of matter (mass?) that's around
The intergalactical medium is a good vacuum. There is very little matter in there. In fact, the universe is mostly empty, except at very well located points so that light travels at 'c'.
Concerning refraction, it always occur at the interface of different media. Since there is not that many of such interfaces in the universe, we are save. Gravity is what bends the trajectory of light.
Fingers crossed for GRAND. Is there some timetable when thing are expected to develop? Is this something we can look forward to in 2019 or is that too unreali/optimi stic?
I would say if GRAND happens, it is more for the next couple of decades. So not for tomorrow, but almost.