5 ms·

Not long after the initial discovery, we had enough data for everyone at the experiments to simply run a basic invariant-mass calculation and see the mass peak

Not long after the initial discovery, we had enough data for everyone at the experiments to simply run a basic invariant-mass calculation and see the mass peak popping up. Once I could "see" the peak, without having to conduct statistical tests against expected background, it was "real" to me. In these cynical times, it may be that everything is relative and "post-modern subjective p-hacking", but sufficient data usually ends these discussions. The real trouble is that we have a culture that is addicted to progress theater, and can't wait for the data to get in.

louthy 2y ago
> run a basic invariant-mass calculation and see the mass peak popping up. For the idiots in this post (me), could you please explain what that entails and why it helps confirm the discovery?
- deleted 2y ago
  [deleted]
- fnands 2y ago
  Not the original commenter, but also ex-HEP person: The invariant mass is the rest mass of the particle (i.e. it's "inherent" mass). You can calculate it by taking the final state decay products of the original particle (i.e. the particles that are actually observed by the detector) and summing up their four-vectors (squared). You can plot the invariant mass calculated from any particular final state, and for a rare particle like the Higgs the majority of the contributions to your plot will be from background processes (i.e. not Higgs decays) that decay into the same final state. If you have a lot of Higgs decays in your sample you should be able to see a clear peak in the distribution at the invariant mass of the Higgs boson, a clear sign that the Higgs (or something with the same mass) exists. Often by the time the discovery has reached statistical significance, you might not really be able to see such a clear sign in the mass distribution. I.e. the calculations are telling you it's there but you can't see it that clearly. I wouldn't really say this helps confirm the discovery in a scientific sense, just that it's reassuring that the signal is so strong that you can see it by eye.
  - nick3443 2y ago
    Like this one? https://cds.cern.ch/record/1546765/files/figs_gamma_gamma_mass.png https://cds.cern.ch/record/1546765/files/figs_gamma_gamma_ma...
  - exmadscientist 2y ago
    > just that it's reassuring that the signal is so strong that you can see it by eye It's really something when this happens. I worked on a big neutrino experiment searching for theta_13, where our goals were to (a) determine if theta_13 was dead zero or not (being truly zero would have a Seriously Major Effect in theories) and then (b) to measure its value if not. Our experiment was big, expensive, and finely tuned to search for very, very small values of theta_13. We turned the thing on and... right there there was a dip. Just... there. On the plot. All the data blinding schemes needed to guarantee our best resolution kind of went out the window when anyone looking at the most basic status plot could see the dip immediately! On the one hand, it was really great to know that everything worked, we'd recorded a major milestone in the field (along with our competition, all of whom were reading out at basically the same time), and the theorists would continue to have nothing to do with their lives because theta_13 was, in fact, nonzero. On the other hand... I wasted how many years of my life dialing this damned detector in for what now? (It wasn't wasted effort, not at all... but you get the feeling.)
  - Filligree 2y ago
    Squared four-vectors? I'm only an amateur, but wouldn't that give different results depending on choice of units? I.e, I usually use C=1.
    - dguest 2y ago
      the math is m^2 c^4 = E^2 - p^2 c^2 where m is mass, E is the total energy in the decay products and p is the 3-vector sum of the momentum. Those units should work out (they certainly do if you set c = 1).
      - Filligree 2y ago
        Ah, I see. I was assuming you meant the 4-momentum. Though I'm not sure this doesn't come out to the same thing.
thaumasiotes 2y ago
> In these cynical times, it may be that everything is relative and "post-modern subjective p-hacking", but sufficient data usually ends these discussions. I don't think that's right. I think having an application is what ends the discussions. If you have a group of people who think CD players work by using lasers, and a rival group who think they do something entirely different, and only the first group can actually make working CD players, people will accept that lasers do what group #1 says they do.
- dspillett 2y ago
  > people will accept that lasers do what group #1 says they do Most people. Some fringe groups will believe it is all a front, and they are only pretending that so-called “lasers” are what make the CD player work when in fact it is alien tech from Area 51 or eldritch magics neither of which the public would be happy about. What else would CDDA stand for, if not Compliant Demon Derived Audio? And “Red Book”. Red. Book. Red is the colour of the fires of hell and book must be referring to the Necronomicon! Wake up sheeple!
- biofox 2y ago
  Counterpoint: Vaccines work, but far too many people think that COVID vaccines contain Jewish-made GPS tracking devices that act as micro-antennae to allow Bill Gates to sterilise them using 5G.
  - thaumasiotes 2y ago
    [flagged]
    - roywiggins 2y ago
      It's not hard to find people who are germ theory truthers. They have alternative "explanations" for why nobody gets polio or smallpox anymore.
      - otabdeveloper4 2y ago
throwawaymaths 2y ago
Yeah. The higgs evidence is pretty convincing visually. Not so sure about LIGO. There is an extraordinary claim of noise reduction that requires extraordinary evidence and it's all obfuscated behind adaptive machine learning based filtering, and the statistical analysis on that is unparseable to a non-expert (that is worrisome). The pulsar timing network though is easily believable. Luckily, there's pretty simple statistics that one can throw at that once the third detector comes online. Hopefully that comes in before we spend too much money on LISA. It's basically this, from the article, but from astro: > Particle physics does have situations where the hypothesis are not so data driven and they rely much more heavily on the theoretical edifice of quantum field theory and our simulation of the complicated detectors. In these cases, the statistical models are implicitly defined by simulators is actually a very hot topic that blends classical statistics with modern deep learning. We often say that the simulators don't have a tractable likelihood function. This applies to frequentist hypothesis testing, confidence intervals, and Bayesian inference. Confronting these challenging situations is what motivated simulation-based inference, which is applicable to a host of scientific disciplines.
- maxnoe 2y ago
  How do you explain the LIGO detection of a neutron neutron star merger that was at the same time observed as GRB by many, many other telescopes? https://en.m.wikipedia.org/wiki/GW170817 https://en.m.wikipedia.org/wiki/GW170817
  - throwawaymaths 2y ago
    That's an n of one (I could be wrong but its the only multi messenger GW event we've seen, with how many events are being generated, you'd have expected more). Could be a coincidence. The angular resolution of LIGO is not exactly amazing, and we don't have a real estimate of the distance to the source of the GW? In fact, IIUC the event could be exactly in the opposite direction too. 1 for 29 by 2019: https://scholarcommons.sc.edu/phys_facpub/164/ https://scholarcommons.sc.edu/phys_facpub/164/
- polyphaser 2y ago
  There's no fancy machine learning needed to detect some "bright" LIGO signals (some of the first blackhole-blackhole mergers). Given a set of template signals, a matched filter tries to find the one that best matches the noisy signal your instrument recorded. In order for a MF to work, what you really need is a good understanding of the noise in your instruments observations -- and there're very few people in the world better at that than LIGO folks. LIGO spent almost 20 years in construction and R&D, and almost 30 in planning. When you hear stories about how they can detect trucks miles away, and detect the waves crashing on the coast, it's possible because of scores of PhD students' who spent years characterizing each and every component that affects LIGO's noise levels. All of this to say that it's possible to download their data online and do a quick MF analysis (I did that), and with a little bit of work you get a blindingly bright statistical significance of 20-sigma or so. The actual result quoted in the papers was a bit higher. That's a testament to how well the instrument was built and its behaviour understood.
dguest 2y ago
I think the gigantic bumps that Kyle pointed to "discovered" the higgs. The statistical interpretation showing a 5 sigma signal was certainly essential, but I suspect it would have taken the collaborations much longer to publish if there wasn't a massive bump staring them in the face.

louthy 2y ago

> run a basic invariant-mass calculation and see the mass peak popping up. For the idiots in this post (me), could you please explain what that entails and why it helps confirm the discovery?

deleted 2y ago
[deleted]
fnands 2y ago
Not the original commenter, but also ex-HEP person: The invariant mass is the rest mass of the particle (i.e. it's "inherent" mass). You can calculate it by taking the final state decay products of the original particle (i.e. the particles that are actually observed by the detector) and summing up their four-vectors (squared). You can plot the invariant mass calculated from any particular final state, and for a rare particle like the Higgs the majority of the contributions to your plot will be from background processes (i.e. not Higgs decays) that decay into the same final state. If you have a lot of Higgs decays in your sample you should be able to see a clear peak in the distribution at the invariant mass of the Higgs boson, a clear sign that the Higgs (or something with the same mass) exists. Often by the time the discovery has reached statistical significance, you might not really be able to see such a clear sign in the mass distribution. I.e. the calculations are telling you it's there but you can't see it that clearly. I wouldn't really say this helps confirm the discovery in a scientific sense, just that it's reassuring that the signal is so strong that you can see it by eye.
- nick3443 2y ago
  Like this one? https://cds.cern.ch/record/1546765/files/figs_gamma_gamma_mass.png https://cds.cern.ch/record/1546765/files/figs_gamma_gamma_ma...
- exmadscientist 2y ago
  > just that it's reassuring that the signal is so strong that you can see it by eye It's really something when this happens. I worked on a big neutrino experiment searching for theta_13, where our goals were to (a) determine if theta_13 was dead zero or not (being truly zero would have a Seriously Major Effect in theories) and then (b) to measure its value if not. Our experiment was big, expensive, and finely tuned to search for very, very small values of theta_13. We turned the thing on and... right there there was a dip. Just... there. On the plot. All the data blinding schemes needed to guarantee our best resolution kind of went out the window when anyone looking at the most basic status plot could see the dip immediately! On the one hand, it was really great to know that everything worked, we'd recorded a major milestone in the field (along with our competition, all of whom were reading out at basically the same time), and the theorists would continue to have nothing to do with their lives because theta_13 was, in fact, nonzero. On the other hand... I wasted how many years of my life dialing this damned detector in for what now? (It wasn't wasted effort, not at all... but you get the feeling.)
- Filligree 2y ago
  Squared four-vectors? I'm only an amateur, but wouldn't that give different results depending on choice of units? I.e, I usually use C=1.
  - dguest 2y ago
    the math is m^2 c^4 = E^2 - p^2 c^2 where m is mass, E is the total energy in the decay products and p is the 3-vector sum of the momentum. Those units should work out (they certainly do if you set c = 1).
    - Filligree 2y ago
      Ah, I see. I was assuming you meant the 4-momentum. Though I'm not sure this doesn't come out to the same thing.

thaumasiotes 2y ago

> In these cynical times, it may be that everything is relative and "post-modern subjective p-hacking", but sufficient data usually ends these discussions. I don't think that's right. I think having an application is what ends the discussions. If you have a group of people who think CD players work by using lasers, and a rival group who think they do something entirely different, and only the first group can actually make working CD players, people will accept that lasers do what group #1 says they do.

dspillett 2y ago
> people will accept that lasers do what group #1 says they do Most people. Some fringe groups will believe it is all a front, and they are only pretending that so-called “lasers” are what make the CD player work when in fact it is alien tech from Area 51 or eldritch magics neither of which the public would be happy about. What else would CDDA stand for, if not Compliant Demon Derived Audio? And “Red Book”. Red. Book. Red is the colour of the fires of hell and book must be referring to the Necronomicon! Wake up sheeple!
biofox 2y ago
Counterpoint: Vaccines work, but far too many people think that COVID vaccines contain Jewish-made GPS tracking devices that act as micro-antennae to allow Bill Gates to sterilise them using 5G.
- thaumasiotes 2y ago
  [flagged]
  - roywiggins 2y ago
    It's not hard to find people who are germ theory truthers. They have alternative "explanations" for why nobody gets polio or smallpox anymore.
    - otabdeveloper4 2y ago

throwawaymaths 2y ago

Yeah. The higgs evidence is pretty convincing visually. Not so sure about LIGO. There is an extraordinary claim of noise reduction that requires extraordinary evidence and it's all obfuscated behind adaptive machine learning based filtering, and the statistical analysis on that is unparseable to a non-expert (that is worrisome). The pulsar timing network though is easily believable. Luckily, there's pretty simple statistics that one can throw at that once the third detector comes online. Hopefully that comes in before we spend too much money on LISA. It's basically this, from the article, but from astro: > Particle physics does have situations where the hypothesis are not so data driven and they rely much more heavily on the theoretical edifice of quantum field theory and our simulation of the complicated detectors. In these cases, the statistical models are implicitly defined by simulators is actually a very hot topic that blends classical statistics with modern deep learning. We often say that the simulators don't have a tractable likelihood function. This applies to frequentist hypothesis testing, confidence intervals, and Bayesian inference. Confronting these challenging situations is what motivated simulation-based inference, which is applicable to a host of scientific disciplines.

maxnoe 2y ago
How do you explain the LIGO detection of a neutron neutron star merger that was at the same time observed as GRB by many, many other telescopes? https://en.m.wikipedia.org/wiki/GW170817 https://en.m.wikipedia.org/wiki/GW170817
- throwawaymaths 2y ago
  That's an n of one (I could be wrong but its the only multi messenger GW event we've seen, with how many events are being generated, you'd have expected more). Could be a coincidence. The angular resolution of LIGO is not exactly amazing, and we don't have a real estimate of the distance to the source of the GW? In fact, IIUC the event could be exactly in the opposite direction too. 1 for 29 by 2019: https://scholarcommons.sc.edu/phys_facpub/164/ https://scholarcommons.sc.edu/phys_facpub/164/
polyphaser 2y ago
There's no fancy machine learning needed to detect some "bright" LIGO signals (some of the first blackhole-blackhole mergers). Given a set of template signals, a matched filter tries to find the one that best matches the noisy signal your instrument recorded. In order for a MF to work, what you really need is a good understanding of the noise in your instruments observations -- and there're very few people in the world better at that than LIGO folks. LIGO spent almost 20 years in construction and R&D, and almost 30 in planning. When you hear stories about how they can detect trucks miles away, and detect the waves crashing on the coast, it's possible because of scores of PhD students' who spent years characterizing each and every component that affects LIGO's noise levels. All of this to say that it's possible to download their data online and do a quick MF analysis (I did that), and with a little bit of work you get a blindingly bright statistical significance of 20-sigma or so. The actual result quoted in the papers was a bit higher. That's a testament to how well the instrument was built and its behaviour understood.

dguest 2y ago

I think the gigantic bumps that Kyle pointed to "discovered" the higgs. The statistical interpretation showing a 5 sigma signal was certainly essential, but I suspect it would have taken the collaborations much longer to publish if there wasn't a massive bump staring them in the face.