To say that neutrinos aren’t the easiest particles to study would be a bit of an understatement. Outside of dark matter, there’s not much in particle physics that is as slippery as the elusive “ghost particles” that are endlessly streaming through you and everything you own. That’s why its exciting news that JUNO is now taking data as the world’s largest detector.
First, in case you’re not a physics geek, let’s go back to basics. Neutrinos are neutral particles (the name was coined by Fermi as “little neutral one”) with very, very little mass and a propensity for slipping in between the more-common particles that make up everyday matter. The fact that neutrinos have mass is kind of weird, in that it’s not part of the Standard Model of Particle Physics. Since the Standard Model gets just about everything else right (except for dark matter) down to quite a few decimal points, well… that’s a very interesting kind of weird, hence the worldwide race to unravel the mysteries of the so-called “ghost particle”. We have an explainer article here for anyone who wants more background.
With JUNO, China is likely to take the lead in that race. JUNO stands for Jiangmen Underground Neutrino Observatory, and if you fancy a trip to southern China you can find it 700 metres under Guangdong. With 20,000 tonnes of liquid scintillator (a chemical that lights up when excited by a subatomic particle) and 43,200 photomultiplier tubes (PMTs) to catch every photon the scintillator gives off, it is the largest of its type in the world.
The liquid scintillator — linear alkyl benzene, for the chemists — is housed within an acrylic sphere surrounded by PMTs, suspended within an extra sixty thousand tonnes of ultra-pure water for radiation shielding. The arrangement is similar to the Sudbury Neutrino Observatory, but much larger. More PMTs point outwards to monitor this water jacket to serve as coincidence detectors for things like muons. With all of those PMTs, we can only hope everyone has learned from Super-K, and they don’t all blow up this time.
Assuming no catastrophic failure, JUNO will have great sensitivity in particular to antineutrinos, and will be used not just for astroparticle physics but as part of a beam experiment to study neutrino oscillations from neutrinos emitted by nearby nuclear reactors. (Virtually all nuclear reactions, from fusion to fission to beta decay, involve neutrino emission.) Neutrino oscillation refers to the strange ability neutrinos have to oscillate between their three different ‘flavours’ something related to their anomalous mass.
While JUNO is the biggest in the world, it won’t be forever. If everything goes according to plan, Japan will take the crown back when HyperKamiokande comes online inside its 258,000 tonne water vessel in 2028. Of course the great thing about scientific competition is that it doesn’t matter who is on top: with openly published results, we all win.
I would not call reactor neutrinos a beam. They are emitted into all directions (isotropically). There are other experiments like T2K that use an accelerator to create a directed beam of neutrinos.
You’re not wrong, but what would you call it? It seems like “beam experiments” is the term used, even if the “beam” is a purely notional slice of a sphere.
Juno is not the world’s largest neutrino detector. IceCube is much larger, as is rno-g
Somebody’s going to have to explain to me how IceCube, the KM3NeT observatories, and Baikal are smaller than this. Last I checked, a billion tons of water is somewhat bigger than 20,000 tons of fancy oil.
Largest in its energy range. Detectors like SuperK/JUNO/SNO/etc. are lower energy neutrino detectors.
If you’re going for pure detector volume, even IceCube/KM3NeT aren’t biggest: there have been experiments which look for interactions in lunar regolith, so “the limb of the moon” wins, but only at extreme energies. In between there are other experiments like ANITA/PUEO/ARA/RNO and others which have large effective volumes over certain energy ranges.
I get that, but our author and the linked article call it the “Worlds [sic] Largest Neutrino Detector” and “World’s Largest Neutrino Lab” respectively, without qualification, which is bullshit.
I expect jingoistic distortion ranging from puffery to fabrication from a state-controlled media outlet. I expect, perhaps without justification, Hackaday authors to be knowledgeable enough to not credulously repeat it.
It’s common even in the science community. It’s also partly the difference between “this is the whole detector” and “we spread detectors out over this volume.”
There was going to be a paragraph to answer just that question, but I cut it out because I thought it was being pedantic. I should have known better!
Largest in its energy range, as Pat says, is one way to count it. The other is largest of its type, which is underground liquid scintillation detectors. The fact that it uses “fancy oil” as you say, is key– detections in water come from chekernov radiation, which makes those big’uns both less sensitive and less discriminating than those using “fancy oil”.
No, it’s not the largest by mass or volume, by far. OTH, IceCube, KM3NeT and Baikal aren’t just neutrino detectors. They all have copy on their websites (and grant applications!) talking about how they’re also being used for dark matter searches and studying high-energy cosmic rays. That’s arguably a good thing! But it also arguably means this is the largest detector only aimed at neutrinos. (Like SNO+, JUNO may be repurposed at the end of its run for a double-beta-decay search, but otherwise isn’t good for much other than neutrinos.)
A third way to count it is “largest in number of neutrinos detected”– neutrinos have an energy distribution, and it’s by no means even. By dipping down to lower energy levels from fusion, fission, and even crustal beta events, you get a LOT more neutrinos than you do at the high energy levels the ice/water detectors you mention are stuck with. I haven’t crunched the numbers to see if they can expect more events than KM3NeT or IceCube, but I’d bet on it.
Plus, nobody built the Mediterranean or Lake Baikal, so they’re just cheating. ;)
“how they’re also being used for dark matter searches and studying high-energy cosmic rays.”
All neutrino detectors are used for alternate stuff as well. It’s just a question of how you present it. Graduate students need a dissertation topic, so you try to figure something out.
“A third way to count it is “largest in number of neutrinos detected””
Oh, no, definitely not. While JUNO is expected to be sensitive to very low energy neutrinos, it definitely won’t be fully efficient (they produce a ridiculously tiny signal), and the interaction length at those energies is so low that even though the flux is high, you don’t get many of them.
IceCube is much more efficient at detecting atmospheric neutrinos because the interaction length is shorter and the signal is significantly cleaner and stronger. For reference IceCube’s atmospheric neutrino rate is like 100k/yr: SuperK’s is like a few thousand/yr (and JUNO will be scale-wise similar).
interaction length at those energies is so long not so low, friggin autocorrect
Would be more interesting still if someone could figure a better way to detect them.
But publishing would be troublesome, you’d have to not get killed first.
Alright I’ll bite, who is the shadowy cabal trying to suppress neutrino knowledge
The ‘Treacherous French’.
Same as always.
I fart in your generoll directión!
So the funny thing about this is that there is a better way to detect neutrinos, called coherent scattering (where the neutrino scatters elastically off of the entire nucleus) – it’s just really hard to do because you’re picking up this super-small nuclear recoil (the example they usually use is a mosquito hitting an elephant).
It only works for low energy neutrinos, though (MeV and less scale), and one of the main applications would be… reactor monitoring. Which… y’know, kinda does have people trying to prevent you from studying them.
The existential question of our time is, what are the Chinese going to do with all these neutrinos they are catching and what do they have to do with Chemtrails and GMO foods?