CERN's Large Hadron Collider Makes Its First Observations of Neutrinos (phys.org) 35
Physicists have observed neutrinos originating "from the sun, cosmic rays, supernovae and other cosmic objects, as well as particle accelerators and nuclear reactors," writes Phys.org. But one remaining goal was observing neutrinos inside "collider" particle accelerators (which direct two particle beams).
It's now been accomplished using neutrino detectors located at CERN's Large Hadron Collider (LHC) in Switzerland by two distinct research collaborations:
- FASER (Forward Search Experiment)
- SND (Scattering and Neutrino Detector)@LHC
Phys.org argues the two achievements "could open important new avenues for experimental particle physics research. " The results of their two studies were recently published in Physical Review Letters. "Neutrinos are produced very abundantly in proton colliders such as the LHC," Cristovao Vilela, part of the SND@LHC Collaboration, told Phys.org. "However, up to now, these neutrinos had never been directly observed. The very weak interaction of neutrinos with other particles makes their detection very challenging and because of this they are the least well studied particles in the Standard Model of particle physics...."
"Particle colliders have existed for over 50 years, and have detected every known particle except for neutrinos," Jonathan Lee Feng, co-spokesperson of the FASER Collaboration, told Phys.org. "At the same time, every time neutrinos have been discovered from a new source, whether it is a nuclear reactor, the sun, the Earth, or supernovae, we have learned something extremely important about the universe. As part of our recent work, we set out to detect neutrinos produced at a particle collider for the first time...
"Because these neutrinos have high fluxes and high energies, which makes them far more likely to interact, we were able to detect 153 of them with a very small, inexpensive detector that was built in a very short time," Feng explained. "Previously, particle physics was thought to be divided into two parts: high energy experiments, which were required to study heavy particles, like top quarks and Higgs bosons, and high intensity experiments, which were required to study neutrinos. This work has shown that high energy experiments can also study neutrinos, and so has brought together the high-energy and high-intensity frontiers."
The neutrinos detected by Feng and the rest of the FASER collaboration have the highest energy ever recorded in a laboratory environment.... Cristovao Vilela, part of the SND@LHC Collaboration, said "The observation of collider neutrinos opens the door to novel measurements which will help us understand some of the more fundamental puzzles of the Standard Model of particle physics, such as why there are three generations of matter particles (fermions) that seem to be exact copies of each other in all aspects except for their mass. Furthermore, our detector is placed in a location which is a blind spot for the larger LHC experiments. Because of this, our measurements will also contribute to a better understanding of the structure of colliding protons."
It's now been accomplished using neutrino detectors located at CERN's Large Hadron Collider (LHC) in Switzerland by two distinct research collaborations:
- FASER (Forward Search Experiment)
- SND (Scattering and Neutrino Detector)@LHC
Phys.org argues the two achievements "could open important new avenues for experimental particle physics research. " The results of their two studies were recently published in Physical Review Letters. "Neutrinos are produced very abundantly in proton colliders such as the LHC," Cristovao Vilela, part of the SND@LHC Collaboration, told Phys.org. "However, up to now, these neutrinos had never been directly observed. The very weak interaction of neutrinos with other particles makes their detection very challenging and because of this they are the least well studied particles in the Standard Model of particle physics...."
"Particle colliders have existed for over 50 years, and have detected every known particle except for neutrinos," Jonathan Lee Feng, co-spokesperson of the FASER Collaboration, told Phys.org. "At the same time, every time neutrinos have been discovered from a new source, whether it is a nuclear reactor, the sun, the Earth, or supernovae, we have learned something extremely important about the universe. As part of our recent work, we set out to detect neutrinos produced at a particle collider for the first time...
"Because these neutrinos have high fluxes and high energies, which makes them far more likely to interact, we were able to detect 153 of them with a very small, inexpensive detector that was built in a very short time," Feng explained. "Previously, particle physics was thought to be divided into two parts: high energy experiments, which were required to study heavy particles, like top quarks and Higgs bosons, and high intensity experiments, which were required to study neutrinos. This work has shown that high energy experiments can also study neutrinos, and so has brought together the high-energy and high-intensity frontiers."
The neutrinos detected by Feng and the rest of the FASER collaboration have the highest energy ever recorded in a laboratory environment.... Cristovao Vilela, part of the SND@LHC Collaboration, said "The observation of collider neutrinos opens the door to novel measurements which will help us understand some of the more fundamental puzzles of the Standard Model of particle physics, such as why there are three generations of matter particles (fermions) that seem to be exact copies of each other in all aspects except for their mass. Furthermore, our detector is placed in a location which is a blind spot for the larger LHC experiments. Because of this, our measurements will also contribute to a better understanding of the structure of colliding protons."
Re:Hardon Collider (Score:2)
Ha*DR*on Collider (Score:2)
Thanks dyslexia.
Re: (Score:2)
I once had the same problem. We were in a physics TA recitation and the girls giggled every time I spoke. I had no idea why they thought physics was funny.
After the class, my friend told me I was saying it wrong over and over.
I never made the mistake again.
Re:Ha*DR*on Collider (Score:5, Funny)
Thanks dyslexia.
Oh, if you haven’t, pop on over to scholar.google.com and search for ‘large hardon collider’. The sheer number of legitimate misspellings in the actual literature is hilarious.
Re: (Score:2)
Re: (Score:2)
Re: Ha*DR*on Collider (Score:2)
Re: (Score:2)
The sheer number of legitimate misspellings in the actual literature is hilarious.
legitimate? Is it really surprising that plenty of physicists have a juvenile sense of humour?
Closely related, witness SpaceX's internal name for the Starship: BFR.
High energy neutrinos (Score:3)
How do you measure the energy of a neutrino?
In fact what aspect of a neutrino gives it more energy than another neutrino?
I thought that neutrinos went at c like photons. The energy level of a photon varies with the frequency.
Whereas heavy particles like protons and neutrons move slower than c , and the energy and momentum vary by their velocity.
Re:High energy neutrinos (Score:5, Insightful)
We can measure the energy of a neutrino by the "kick" it delivers to other particles when either emitted or absorbed.
Neutrinos do not travel at c. Neutrinos sometimes morph from electron-neutrinos to either muon or tau-neutrinos, and the number observed to have morphed increases with distance. That would be impossible if they were traveling at c because no time passes: At c, the time contraction is infinite.
Since they don't travel at c, neutrinos have rest mass.
Charged Leptons and No (Noticeable) Oscillations (Score:5, Interesting)
We can measure the energy of a neutrino by the "kick" it delivers to other particles when either emitted or absorbed.
That's partly correct - when a neutrino interacts it does kick a lot of energy into a nucleus - often shattering it and creating a shower of what are called hadronic particles. However, in the process the neutrino itself is usually converted into a charged lepton of the same flavour as the neutrino - and electron, muon or tau - and we see that as well. This is important because if we can see and identify the charged lepton we then know what flavour of neutrino interacted and that can be important for testing some models of physics.
Neutrinos sometimes morph from electron-neutrinos to either muon or tau-neutrinos, and the number observed to have morphed increases with distance.
Not the ones at FASER - the oscillation probability grows with the distance travelled (L) but decreases with increasing energy (E) - which is why we see oscillations at low energies (GeV or less) and long baselines (Earth-Sun and diameter of the Earth depending on the dominant oscillation). FASER is ~400 metres away (IIRC) from the collision point and looks at neutrinos with energies much above a GeV in energy.
Since they don't travel at c, neutrinos have rest mass.
That argument is backwards: we know that they have rest mass because they oscillate therefore we know they do not travel quite at 'c'. However, experimentally nobody has been able to measure any neutrino as having a speed different from 'c' because the mass is so tiny that we only have an upper limit on the mass and no actual measurement of the mass. Oscillations only let us measure the difference in the square of the masses which means that so far we don't even know which neutrino is most massive! There are two possible arrangements: the "normal" and the "inverted" mass heirarchies and the next generation of neutrino experiments should definitively tell us which one is correct, but still not what the absolute masses are.
Re:High energy neutrinos (Score:5, Informative)
I thought that neutrinos went at c like photons.
Not quite. Their speed is very very nearly c (something like 99.9999%), but it's not exactly c. Neutrinos actually have mass, so their energy and momentum depends on speed almost exactly like any other massive particle (I say "almost" because their relationship with mass is complicated, and a bit different from most other particles).
As far as detecting their energy, it's hard. You can't directly observe the neutrino. You instead have it hit a target and produce a secondary charged particle (usually an electron it knocks off an atom, although in these experiments though it produces a muon). That particle can then be tracked and measured pretty easily. This doesn't give you the energy of the original neutrino, but it gives you a minimum energy at least, and if you collect enough statistics you can reproduce the spectrum of the incoming neutrinos.
Re: High energy neutrinos (Score:2)
How many muons spontaneously move without neutrinos even present, and do they just throw that data out because ?
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Muons by themselves are very short lived, hence neutrino detectors are deep underground and in many cases actually "looking" through the whole Earth to minimize background particles' noise.
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There are actually quite a few: muons are produced in the upper atmosphere from cosmic rays hitting the atmosphere (the rate at sea level is about 1 per square cm per minute, much higher than the LHC rate). But they're pretty easy to filter out: they're going downwards, the muons they're looking for are going sideways. A few can make it though from the horizon, but since those muons have a lot more atmosphere/earth to travel though, they're a fairly small (and extremely well measured) background. The LHC ne
Re:High energy neutrinos (Score:4, Interesting)
It's also worth noting that neutrinos do not literally "hit" other particles, all particles just interact through quantum fields they're sensitive to, and as neutrinos are only sensitive to gravity and the weak nuclear force, and since the weak nuclear force particles are relatively heavy the interactions are very very ... rare (requiring neutrinos to "pass" very very close to a particle it can interact with). Interactions are not through "bumping", but through exchange of specific quantum field force carriers, and things get only more interesting from that (as particles themselves are just energy waves propagating through their quantum fields).
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Re: High energy neutrinos (Score:2)
Arguably, no. What we traditionally refer to as âoebumpingâ is repulsion through the electromagnetic force. We wouldnâ(TM)t for example call a very heavy rock being held down onto the earth âoebumpingâ because the interaction is attraction through gravity.
Our colloquial name for weak force interactions is usually âoedecayâ.
Re:High energy neutrinos (Score:5, Interesting)
They do not, at least not all of them. At least one of the three flavours of neutrino must have mass, and probably they all do. For any particle with mass, the energy is a combination of their "rest mass" and their kinetic energy.
It's all the same though. Massive particles have a wavelength just like the massless ones and it's related to their momentum, i.e. their mass and speed, i.e. their energy. The equation for the wavelength of any particle is wavelength = h / momentum.
There Can be Only One Zero (Score:5, Informative)
At least one of the three flavours of neutrino must have mass
Actually, at least two of the three neutrino mass states must be non-zero. We only know the mass-squared differences between the mass states which is enough to know that there are three different masses, so only one of these can be zero. Also, technically the flavour states of the neutrinos do not have a well-defined "mass" since they are each a mixture of the three mass states which have three different masses. It is only the mass eigenstates themselves that have a well-defined mass.
Re: There Can be Only One Zero (Score:2)
Vacuum Stability (Score:2)
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Quite correct.
Re:High energy neutrinos (Score:4, Funny)
I thought that neutrinos went at c like photons.
Neutrino velocity is like having sex on a boat. It's fucking close to C.
No super-symmetric partners though (Score:2)
Not an Issue for String Theory (Score:4, Interesting)
That's the problem with String Theory - its energy scale is so high that it is easy to just put whatever physics they need at a sufficiently high energy that it would never be seen in today's experiments. This is also why it is impossible to experimentally constrain String Theory.
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That's the problem with String Theory - its energy scale is so high that it is easy to just put whatever physics they need at a sufficiently high energy that it would never be seen in today's experiments. This is also why it is impossible to experimentally constrain String Theory.
So, it is an unfalsifiable physical theory. Or, in one word, an oxymoron.
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So, it is an unfalsifiable physical theory.
No, it is falsifiable but you just need a much, much higher energy collider than anything we have managed to build with our technology so far. Think of the ancient Greeks. They made measurements that suggested that the world should be a sphere but lacked the technology at the time to actually circumnavigate it to prove that was the case. String Theory is like that - a theory that could explain how GR and quantum unify but which we lack the technology to currently test.
This reminds me of a joke (Score:5, Funny)
The bartender says, "We don't serve faster than light neutrinos here."
A faster than light neutrino walks into a bar.
Re: This reminds me of a joke (Score:2)
Not if the birds stop it again : ) (Score:2)