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LHC experiments see first evidence of a rare Higgs boson decay

164 points by bluish29 3y ago

rickreynoldssf 3y ago
I'm an airchair physics person so I'm curious how close my layman understanding of this matches reality... So Higgs particles don't exist under normal conditions, they're just proof that the Higgs field exists and explains how mass exists. When the energy that's perturbing the Higgs field dissipates it does so through other fields perturbing them to create one of their particles and so on. Sci-Fi or Fact or somewhere in the middle?
- HPsquared 3y ago
  I'm another armchair physics layman, I'd thought it was something like a "virtual particle" which gets created and destroyed so quickly in the process of performing its very important duties (that is, making sure things act as if they have mass). The hard part being to isolate it and get it in an "observable" condition where you can actually see it.
  - m3kw9 3y ago
    I’m an arm chair “arm chair physics layman”, it seems like this will help with defining the meaning of the universe, and will await till this observation is useful enough to have real physicists explain this in layman terms
- tux3 3y ago
  Also a countertop swivel chair physicist, my understanding is that Higgs bosons are recruited as virtual particles all the time to bestow other particles their mass. So everything is able to consort with the Higgs field at any time without expending energy, because those are only background virtual Higgs, not full fledged particles with a sense of self You can also create bona-fide Higgs particles, but you have to put in a lot of energy to do it (like the LHC does), and it will proceed to immediately disintegrate into lighter particles, which is what the LHC is observing in detectors I think that when particles use the Higgs field to get their mass, the virtual particle is only a temporary ripple living on borrowed time, so it can interract with other fields but has to go back to nothing when the interaction is over, like a local variable in a function. When you have a real Higgs, if it decays into say two photons, then yes you have a wave in the Higgs field dissipating, while equal energy/charge/<other conserved quantities...> waves replace it in other fields (IANAP. This does not constitute physical advice.)
  - lanza 3y ago
    > Also a countertop swivel chair physicist, my understanding is that Higgs bosons are recruited as virtual particles all the time to bestow other particles their mass. Physicist here: nope. The coupling between the Higgs field and other particle fields is what creates the phenomona of mass. The Higgs particle is just an excitation of that field. Virtual particles aren't "real" in the same way that the first order Taylor series of sin(x) being x doesn't max x a real sinusoidal wave. All it does is let you make your calculations "close enough" for your accepted definition of "close enough."
    - borissk 3y ago
      Aren't both virtual and non-virtual particles non-real - in the sense that they are both excitation/waves of/in a field. With virtual particles just being smaller waves.
    - tux3 3y ago
      Thanks! So if I understood you right, whatever coupling does to the fields, it's something doesn't involve virtual Higgs, is that right? Is it fair to say that both virtual Higgs and 'real' Higgs are two types of excitations of that field, except that virtual particles can't be directly observed? I find the name virtual particles interesting, since they don't seem to be exactly the same kind of ripples as particles, and physicists frequently seem to disagree on how 'real' they are as a matter of interpretation
      - lanza 3y ago
        Virtual particles are calculational tools. They aren’t concrete things the way you’re proposing them to be. They are closer in character to “completing the square” than they are a an actual physical object. They are great for trying to help human brains make concrete the details of the process. But again they are just artifacts of the way we do our computations. And the Higgs field is a particularly great example of this. If you shift a sin wave 90 degrees it becomes a cosine wave. If you don’t expand about the lowest energy of the Mexican top hot potential for the Higgs field it creates an entirely different description of the physical phenomena and virtual particles.
- cwillu 3y ago
  This correlates very well with what Matt Strassler says: https://profmattstrassler.com/articles-and-posts/particle-physics-basics/virtual-particles-what-are-they/ https://profmattstrassler.com/articles-and-posts/particle-ph... https://profmattstrassler.com/articles-and-posts/the-higgs-particle/the-higgs-faq-2-0/ https://profmattstrassler.com/articles-and-posts/the-higgs-p...
- lanza 3y ago
  > So Higgs particles don't exist under normal conditions Eh. That's like saying fully constructed lego kits don't exist under normal conditions. Yea sure, my normal life conditions don't entail me having just finished putting together a lego rollercoaster. But calling that "normal conditions" is a weird way of describing the situation. I'm being kinda nitpicky, but as a physicist who understands the phenomena I'd just definitely never say "under normal conditions" here. The LHC just provides more potential interactions in a highly regular way and thus more opportunities to measure it. The Higgs boson is just heavy and unstable and less probabilistic to be created via most particle interactions. > So Higgs particles don't exist under normal conditions, they're just proof that the Higgs field exists and explains how mass exists This Higgs particle doesn't explain how mass exists. The construction that explains how mass works predicts that a Higgs boson exists.
- RickyS 3y ago
  Experimental particle physicist here. What you say about Higgs particles "they don't exist under normal condition" is loosely true of all particles in nature in the sense that a particle is nothing but a "quantum" of a "field". Fields pervade all physical space and can vary in time. Particles (or quanta) simply represent a local state of observable things. A field can only do certain things to certain physical states and at a probabilistic level. Notice that fields do things even with the vacuum which is just another state from which particles can be "extracted". The peculiar experimental challenge about the Higgs field is that it can extract its quanta from certain physical states (certain initial conditions in a particle physics reaction) only at very high energy and with low probability, but that is true also for other particles. Its truly peculiar thing is that the presence of the Higgs field, in addition to the fields of all other particles that we know of, explains why quanta in general have a mass (although this is not clear for neutrinos) through a mechanism where the Higgs field interacts with the quanta of other particles.
  - polishdude20 3y ago
    Can you think of quanta in a field as like knots in a string?
    - dist-epoch 3y ago
      The usual metaphor is springs in a mattress: https://www.ribbonfarm.com/2015/08/20/qft/ https://www.ribbonfarm.com/2015/08/20/qft/
      - jvanderbot 3y ago
        That excellent writeup reinforced something I've become convinced of: decades of "shut up and calculate" have created gobs of contradictory analogies and false intuitions that pedagogy hasn't caught up to. When I hear: "In the jargon of field theory, physicists often say that “virtual particles” can briefly and spontaneously appear from the vacuum and then disappear again, even when no one has put enough energy into the field to create a real particle. But what they really mean is that the vacuum itself has random and indelible fluctuations, and sometimes their influence can be felt by the way they kick around real particles." I can't help but immediately question every jargon word I see, especially "random", "particle" and "wave".
- FranchuFranchu 3y ago
  Arm chair physicist however I know how this data is analyzed, so I have something to say: I think there's a better and perhaps clearer to understand interpretation here: All particles have an invariant mass, inherent to the particle itself, and a momentum, which is, roughly related to velocity in matter and frequency in photons (but not quite!). These together determine the energy a particle has. Some particles are long-lived and some are short-lived. The Higgs boson is short-lived. In these collisions, it really does exist for a period of time, however, it decays to smaller particles with an total energy that equals the energy of the original Higgs boson. The ATLAS detector detects these long-lived stable particles. The phenomenon you are attempting to explain is particle decay (why the Higgs boson decays into other particles). I never heard of inter-field energy dissipation as a cause for particle decay, but it seems really interesting. However, I don't really understand what "inter-field energy dissipation" means. They are all very theoretical terms to me. I am comfortable with hand-waving it as "particles decay because they decay, because that's the way the laws of physics work, and it's allowed because the resulting state is of higher entropy". It seems like it is a phenomenon that is very hard to explain.
- VyseofArcadia 3y ago
  IIRC the Higgs mechanism only explains some mass, and most of the rest is binding energy at the quark level.
dist-epoch 3y ago
I've once read that almost every electro-magnetic interaction involving a photon also involves a Z boson, but given that it's massive, it decays very quickly. Is this true?
- cwillu 3y ago
  https://profmattstrassler.com/articles-and-posts/particle-physics-basics/fields-and-their-particles-with-math/8-how-particles-and-fields-interact/ https://profmattstrassler.com/articles-and-posts/particle-ph... has some understandable math showing how this happens, more or less. Note that it's at the _end_ of a series called “Fields and Their Particles, With Math”, so you may want to skim it and then skip back closer to the beginning.
gary_0 3y ago
Cool research, but it's only 3.4σ so far and this decay is already predicted by the Standard Model.
- Kye 3y ago
  I thought the whole point of the LHC was to confirm the Standard Model.
  - codeflo 3y ago
    That's the new, after-the-fact justification for the project after the original goal, finding new physics, didn't happen. But to be fair, there was no way to new whether new physics would be found without looking.
    - atoav 3y ago
      I mean at this point in physics everything new has to be a variation of the classical rabbit/duck picture: Essentially the same data points but a different way to explain them that doesn't invalidate the existing findings. This means we can use any knowledge we can find and we definitly should continue testing promising alternatives — either we find something or we reduce the size of the white spots on the map — which makes exploring them easier.
  - rdedev 3y ago
    While that is true afaik a lot of scientist were hoping to find something that is not predicted by the standard model to get new ideas. I don't think that has planned out yet
  - gary_0 3y ago
    The point of an experiment is to find out what you don't already know. The LHC has previously shown low-sigma hints of non-SM physics but nothing has panned out yet. At any rate, the Standard Model has clear gaps in it (quantum gravity, dark matter, etc) so the hope is that the LHC will show hints towards filling them--although it's a long shot. 27 kilometers long, ha!
efitz 3y ago
Why should I, as a taxpayer, want to my government to subsidize this research? I haven’t seen anything useful come out of high energy particle physics in decades. This is an honest question, not a troll. I see lots of spin-off technologies coming out of other “big science”. Consider space programs. We see materials technology coming out of space programs. I can even see the PR value in the space program as it appeals to our imagination and sense of exploration. I can even buy into the “time to make sure all our eggs aren’t in one basket” theory of Musk et al for colonization of other planets. And I love that companies are commercializing it rather than leaving it just to governments. But as a layperson, high energy particle physics seems like (figuratively and literally) pouring money down large holes to satisfy the curiosity of a few researchers. While it’s mildly interesting it’s practically inscrutable and very hard to connect to anything that normal people care about.
- paddw 3y ago
  Well, I think that trying to understand fundamental physics questions contains some value at large for society which is hard to quantify. But even if you don't believe in that, you could think of this research as buying an option on the case that one of these experiments does end up revealing something that's revolutionary.
- bradrn 3y ago
  Fundamental research has a funny way of producing results in other areas. To name just one example, the World Wide Web was developed at CERN. The other thing is that you never know exactly what will and won’t have applications later on. General relativity seemed pretty useless until we had GPS; number theory had no practical use for thousands of years until asymmetric cryptography was invented. Even within particle physics, neutron scattering is now a fundamental part of material science, and I’m sure there are many more similar examples. I can’t tell you exactly what CERN’s current research will result in, but I wouldn’t be at all surprised if it eventually finds a use. (Or has already, in fact.)
  - efitz 3y ago
    I hate the “web was invented at CERN” trope. Yes, it’s trivially true, but TBL was standing on the shoulders of giants. When HTTP came along, we already had gopher. We already had HyperCard. SGML was already a thing. We already had FTP. Lots of us already had shell internet accounts; many more had CompuServe or AOL. The web was inevitable at that point in time, and would have taken a similar shape and happened in very short order regardless of whether CERN ever existed.
dguest 3y ago
Direct link to papers: https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/CONFNOTES/ATLAS-CONF-2023-025/ https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/CONFNOTES/ATL... https://weblib.cern.ch/record/2859713/files/HIG-23-002-pas.pdf https://weblib.cern.ch/record/2859713/files/HIG-23-002-pas.p...
borissk 3y ago
Fun fact: the Higgs boson is the only particle in the Standard Model that has inherent mass.
- liamwire 3y ago
  Practically by definition, no?
tarruda 3y ago
Reminded me of one of my favorite kurzgesagt videos, "Vacuum decay": https://youtu.be/ijFm6DxNVyI https://youtu.be/ijFm6DxNVyI
ChrisArchitect 3y ago
Aside: what is the shared url doing with 3 slashes? https://www.interactions.org/press-release/lhc-experiments-see-first-evidence-rare-higgs-boson-decay https://www.interactions.org/press-release/lhc-experiments-s...

164 points by bluish29 3y ago

I'm an airchair physics person so I'm curious how close my layman understanding of this matches reality... So Higgs particles don't exist under normal conditions, they're just proof that the Higgs field exists and explains how mass exists. When the energy that's perturbing the Higgs field dissipates it does so through other fields perturbing them to create one of their particles and so on. Sci-Fi or Fact or somewhere in the middle?

HPsquared 3y ago
I'm another armchair physics layman, I'd thought it was something like a "virtual particle" which gets created and destroyed so quickly in the process of performing its very important duties (that is, making sure things act as if they have mass). The hard part being to isolate it and get it in an "observable" condition where you can actually see it.
- m3kw9 3y ago
  I’m an arm chair “arm chair physics layman”, it seems like this will help with defining the meaning of the universe, and will await till this observation is useful enough to have real physicists explain this in layman terms
tux3 3y ago
Also a countertop swivel chair physicist, my understanding is that Higgs bosons are recruited as virtual particles all the time to bestow other particles their mass. So everything is able to consort with the Higgs field at any time without expending energy, because those are only background virtual Higgs, not full fledged particles with a sense of self You can also create bona-fide Higgs particles, but you have to put in a lot of energy to do it (like the LHC does), and it will proceed to immediately disintegrate into lighter particles, which is what the LHC is observing in detectors I think that when particles use the Higgs field to get their mass, the virtual particle is only a temporary ripple living on borrowed time, so it can interract with other fields but has to go back to nothing when the interaction is over, like a local variable in a function. When you have a real Higgs, if it decays into say two photons, then yes you have a wave in the Higgs field dissipating, while equal energy/charge/<other conserved quantities...> waves replace it in other fields (IANAP. This does not constitute physical advice.)
- lanza 3y ago
  > Also a countertop swivel chair physicist, my understanding is that Higgs bosons are recruited as virtual particles all the time to bestow other particles their mass. Physicist here: nope. The coupling between the Higgs field and other particle fields is what creates the phenomona of mass. The Higgs particle is just an excitation of that field. Virtual particles aren't "real" in the same way that the first order Taylor series of sin(x) being x doesn't max x a real sinusoidal wave. All it does is let you make your calculations "close enough" for your accepted definition of "close enough."
  - borissk 3y ago
    Aren't both virtual and non-virtual particles non-real - in the sense that they are both excitation/waves of/in a field. With virtual particles just being smaller waves.
  - tux3 3y ago
    Thanks! So if I understood you right, whatever coupling does to the fields, it's something doesn't involve virtual Higgs, is that right? Is it fair to say that both virtual Higgs and 'real' Higgs are two types of excitations of that field, except that virtual particles can't be directly observed? I find the name virtual particles interesting, since they don't seem to be exactly the same kind of ripples as particles, and physicists frequently seem to disagree on how 'real' they are as a matter of interpretation
    - lanza 3y ago
      Virtual particles are calculational tools. They aren’t concrete things the way you’re proposing them to be. They are closer in character to “completing the square” than they are a an actual physical object. They are great for trying to help human brains make concrete the details of the process. But again they are just artifacts of the way we do our computations. And the Higgs field is a particularly great example of this. If you shift a sin wave 90 degrees it becomes a cosine wave. If you don’t expand about the lowest energy of the Mexican top hot potential for the Higgs field it creates an entirely different description of the physical phenomena and virtual particles.
cwillu 3y ago
This correlates very well with what Matt Strassler says: https://profmattstrassler.com/articles-and-posts/particle-physics-basics/virtual-particles-what-are-they/ https://profmattstrassler.com/articles-and-posts/particle-ph... https://profmattstrassler.com/articles-and-posts/the-higgs-particle/the-higgs-faq-2-0/ https://profmattstrassler.com/articles-and-posts/the-higgs-p...
lanza 3y ago
> So Higgs particles don't exist under normal conditions Eh. That's like saying fully constructed lego kits don't exist under normal conditions. Yea sure, my normal life conditions don't entail me having just finished putting together a lego rollercoaster. But calling that "normal conditions" is a weird way of describing the situation. I'm being kinda nitpicky, but as a physicist who understands the phenomena I'd just definitely never say "under normal conditions" here. The LHC just provides more potential interactions in a highly regular way and thus more opportunities to measure it. The Higgs boson is just heavy and unstable and less probabilistic to be created via most particle interactions. > So Higgs particles don't exist under normal conditions, they're just proof that the Higgs field exists and explains how mass exists This Higgs particle doesn't explain how mass exists. The construction that explains how mass works predicts that a Higgs boson exists.
RickyS 3y ago
Experimental particle physicist here. What you say about Higgs particles "they don't exist under normal condition" is loosely true of all particles in nature in the sense that a particle is nothing but a "quantum" of a "field". Fields pervade all physical space and can vary in time. Particles (or quanta) simply represent a local state of observable things. A field can only do certain things to certain physical states and at a probabilistic level. Notice that fields do things even with the vacuum which is just another state from which particles can be "extracted". The peculiar experimental challenge about the Higgs field is that it can extract its quanta from certain physical states (certain initial conditions in a particle physics reaction) only at very high energy and with low probability, but that is true also for other particles. Its truly peculiar thing is that the presence of the Higgs field, in addition to the fields of all other particles that we know of, explains why quanta in general have a mass (although this is not clear for neutrinos) through a mechanism where the Higgs field interacts with the quanta of other particles.
- polishdude20 3y ago
  Can you think of quanta in a field as like knots in a string?
  - dist-epoch 3y ago
    The usual metaphor is springs in a mattress: https://www.ribbonfarm.com/2015/08/20/qft/ https://www.ribbonfarm.com/2015/08/20/qft/
    - jvanderbot 3y ago
      That excellent writeup reinforced something I've become convinced of: decades of "shut up and calculate" have created gobs of contradictory analogies and false intuitions that pedagogy hasn't caught up to. When I hear: "In the jargon of field theory, physicists often say that “virtual particles” can briefly and spontaneously appear from the vacuum and then disappear again, even when no one has put enough energy into the field to create a real particle. But what they really mean is that the vacuum itself has random and indelible fluctuations, and sometimes their influence can be felt by the way they kick around real particles." I can't help but immediately question every jargon word I see, especially "random", "particle" and "wave".
FranchuFranchu 3y ago
Arm chair physicist however I know how this data is analyzed, so I have something to say: I think there's a better and perhaps clearer to understand interpretation here: All particles have an invariant mass, inherent to the particle itself, and a momentum, which is, roughly related to velocity in matter and frequency in photons (but not quite!). These together determine the energy a particle has. Some particles are long-lived and some are short-lived. The Higgs boson is short-lived. In these collisions, it really does exist for a period of time, however, it decays to smaller particles with an total energy that equals the energy of the original Higgs boson. The ATLAS detector detects these long-lived stable particles. The phenomenon you are attempting to explain is particle decay (why the Higgs boson decays into other particles). I never heard of inter-field energy dissipation as a cause for particle decay, but it seems really interesting. However, I don't really understand what "inter-field energy dissipation" means. They are all very theoretical terms to me. I am comfortable with hand-waving it as "particles decay because they decay, because that's the way the laws of physics work, and it's allowed because the resulting state is of higher entropy". It seems like it is a phenomenon that is very hard to explain.
VyseofArcadia 3y ago
IIRC the Higgs mechanism only explains some mass, and most of the rest is binding energy at the quark level.

dist-epoch 3y ago

I've once read that almost every electro-magnetic interaction involving a photon also involves a Z boson, but given that it's massive, it decays very quickly. Is this true?

cwillu 3y ago
https://profmattstrassler.com/articles-and-posts/particle-physics-basics/fields-and-their-particles-with-math/8-how-particles-and-fields-interact/ https://profmattstrassler.com/articles-and-posts/particle-ph... has some understandable math showing how this happens, more or less. Note that it's at the _end_ of a series called “Fields and Their Particles, With Math”, so you may want to skim it and then skip back closer to the beginning.

gary_0 3y ago

Cool research, but it's only 3.4σ so far and this decay is already predicted by the Standard Model.

Kye 3y ago
I thought the whole point of the LHC was to confirm the Standard Model.
- codeflo 3y ago
  That's the new, after-the-fact justification for the project after the original goal, finding new physics, didn't happen. But to be fair, there was no way to new whether new physics would be found without looking.
  - atoav 3y ago
    I mean at this point in physics everything new has to be a variation of the classical rabbit/duck picture: Essentially the same data points but a different way to explain them that doesn't invalidate the existing findings. This means we can use any knowledge we can find and we definitly should continue testing promising alternatives — either we find something or we reduce the size of the white spots on the map — which makes exploring them easier.
- rdedev 3y ago
  While that is true afaik a lot of scientist were hoping to find something that is not predicted by the standard model to get new ideas. I don't think that has planned out yet
- gary_0 3y ago
  The point of an experiment is to find out what you don't already know. The LHC has previously shown low-sigma hints of non-SM physics but nothing has panned out yet. At any rate, the Standard Model has clear gaps in it (quantum gravity, dark matter, etc) so the hope is that the LHC will show hints towards filling them--although it's a long shot. 27 kilometers long, ha!

efitz 3y ago

Why should I, as a taxpayer, want to my government to subsidize this research? I haven’t seen anything useful come out of high energy particle physics in decades. This is an honest question, not a troll. I see lots of spin-off technologies coming out of other “big science”. Consider space programs. We see materials technology coming out of space programs. I can even see the PR value in the space program as it appeals to our imagination and sense of exploration. I can even buy into the “time to make sure all our eggs aren’t in one basket” theory of Musk et al for colonization of other planets. And I love that companies are commercializing it rather than leaving it just to governments. But as a layperson, high energy particle physics seems like (figuratively and literally) pouring money down large holes to satisfy the curiosity of a few researchers. While it’s mildly interesting it’s practically inscrutable and very hard to connect to anything that normal people care about.

paddw 3y ago
Well, I think that trying to understand fundamental physics questions contains some value at large for society which is hard to quantify. But even if you don't believe in that, you could think of this research as buying an option on the case that one of these experiments does end up revealing something that's revolutionary.
bradrn 3y ago
Fundamental research has a funny way of producing results in other areas. To name just one example, the World Wide Web was developed at CERN. The other thing is that you never know exactly what will and won’t have applications later on. General relativity seemed pretty useless until we had GPS; number theory had no practical use for thousands of years until asymmetric cryptography was invented. Even within particle physics, neutron scattering is now a fundamental part of material science, and I’m sure there are many more similar examples. I can’t tell you exactly what CERN’s current research will result in, but I wouldn’t be at all surprised if it eventually finds a use. (Or has already, in fact.)
- efitz 3y ago
  I hate the “web was invented at CERN” trope. Yes, it’s trivially true, but TBL was standing on the shoulders of giants. When HTTP came along, we already had gopher. We already had HyperCard. SGML was already a thing. We already had FTP. Lots of us already had shell internet accounts; many more had CompuServe or AOL. The web was inevitable at that point in time, and would have taken a similar shape and happened in very short order regardless of whether CERN ever existed.

dguest 3y ago

Direct link to papers: https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/CONFNOTES/ATLAS-CONF-2023-025/ https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/CONFNOTES/ATL... https://weblib.cern.ch/record/2859713/files/HIG-23-002-pas.pdf https://weblib.cern.ch/record/2859713/files/HIG-23-002-pas.p...

borissk 3y ago

Fun fact: the Higgs boson is the only particle in the Standard Model that has inherent mass.

liamwire 3y ago
Practically by definition, no?

tarruda 3y ago

Reminded me of one of my favorite kurzgesagt videos, "Vacuum decay": https://youtu.be/ijFm6DxNVyI https://youtu.be/ijFm6DxNVyI

ChrisArchitect 3y ago

Aside: what is the shared url doing with 3 slashes? https://www.interactions.org/press-release/lhc-experiments-see-first-evidence-rare-higgs-boson-decay https://www.interactions.org/press-release/lhc-experiments-s...