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Could the Standard Model Be Wrong? Exploring Lepton Universality

Could the Standard Model Be Wrong? Exploring Lepton Universality


What is lepton universality? Now there aren’t many different types of particles
that make up matter. There are six types of quarks. Up. Down. Strange. Charm. Top and bottom. And six types of leptons. Three of these leptons are charged. Three
of them are neutral. Electrons are the most common charged lepton. But there are two others – the muon and the
tau lepton that behave in a similar way to the electron but they’re just progressively more massive. Now our theory of particle physics, the standard
model, assumes that the behaviour of electrons, muons
and tau leptons are identical to each. And that means that if a quark decays to a
lepton, which it can do sometimes under one of the
fundamental forces, then all things being equal it should decay into electrons, muons and taus equally often. And this assumption is the one that goes by
the grand title – lepton universality. Now it is just an assumption. And because it’s an assumption, it’s really
important to test this. Because if the assumption is wrong, then so
is the standard model, and so is our understanding of particle physics. So we really have to make sure about it. Now one way that lepton universality can be
tested is to look how often particles called B mesons, these are particles that contain bottom quarks, decay to kaons and either an electron and
anti-electron pair, or a muon, anti-muon pair. If lepton universality holds we should see
B meson decaying to electron pairs as often as B mesons
decay to muon pairs. If they don’t, then something weird is happening. LHCb can make measurements of lepton universality. And that’s because when the large hadron collider collides its beams 40 million times a second
inside the experiment it generates huge data sets of quarks and
anti quarks. Amongst which are bottom quraks and anti-bottom
quarks that form the B mesons we want to study. By analysing all LHC collision data, we can record collisions that contain B mesons decaying to a kaon and a pair of
electrons or a pair of muons. And then, simply, we count how many of each
type we have. And compare one to the other. And see whether we have any differences or
not. Now LHCb first made a measurement of this
back in 2014, a really preliminary measurement. However,
a measurement that was interesting. Because it seemed to show that muons were being produced 25% less often than electrons. However, it was a really preliminary measurement and it definitely wasn’t significant enough
to really get excited about. Since that time we’ve been analysing all of
our data. And what we’ve measured now with higher precision is that muons seem to be produced in B meson
decays 15% less often than electrons are produced. This is a tantalising result because it’s
not yet definitive. There’s still a chance, a small probability,
1:100, that what we’re seeing could just be a fluctuation from B mesons decaying to electrons and muons
at the same rate. So in order to be absolutely sure, we’re going
to have to analyse more data. To get that final significance. But the reason why this is so interesting
and thrilling is that besides being unexpected, this could genuinely be the first sight of
something new. Because if, when we’ve analysed more data, this difference between muons and electrons
stays, and lepton universality seems to be violated. Well, what that means is, there’s something
wrong with the standard model. We found the crack, finally, in our understanding
of particle physics. There’s absolutely no way that we can explain this observation with our current understanding. In fact the only way we think we can explain
what’s going on is if there are new particles in the universe associated with new physics processes beyond
those that we understand. And that these new particles are interfering
with the B mesons as they decay. And suppressing the decay to muons compared
to electrons. Now if that turns out to be the case that
will truly be momentous. Forget the Higgs, this will be the first sign
of physics beyond the standard model. And it’s what we’ve built the LHC to find
out.

76 comments on “Could the Standard Model Be Wrong? Exploring Lepton Universality

  1. probably we don't understand nature at all since so many newly minted PhD folks always coming up with new ideas, job security…

  2. Are we in a massive game of grand theft auto 😃
    Scientist in one thousand years will laugh at today’s theories 😊
    And what happens when the smashing of particles is not observed ?
    Interesting times .

  3. A day after I got lambasted for suggesting there's a crisis in cosmology this turns up, thank you universe.

    Didn't take long for an argument to break out in this thread, what a shame 🙁

  4. Thank you I know everything now. Apart from the god particle. The more you look the more you see .be it small micro or universal. But it's best to look than sit back and think wow god is real and controlling everything…..keep looking and be brave ❤

  5. I long for the days of the Plum Pudding model…sigh…physics left me behind when I graduated in 1966…or was it 1866, so long ago…

  6. she seems to be speaking to the camera and not to an audience. are there going to be more bite-sized snippets like this in the future from the RI channel?

  7. Why should leptons that have different masses be produced with equal probabilities? Intuition suggests lighter particles should be easier to produce, thus higher probability. I'm just an ignorant layman, just asking, since the reason for equal probability wasn't explained in the video.

  8. I'm still waiting for something useful to come out of sub-particle physics. I'm all for it, but what difference does it make if you refine the standard model? "Hey, we discovered there are likely 13 dimensions instead of 12…cool, can we make fusion work now?" Where is all this going? Not really joking though, does understanding these things really help on some applicable real life thing?

  9. I am no scientist, but a question seems in order about Lepton Universality …….

    How could you get decay into dissimilar mass particles without also having the ratio of that decay have relevance to that mass?

  10. I just heard yesterday a rabbi speak about how scientists are scared little children who make assumptions, think they know everything, and shut out any information that is contrary to their understanding. I'd like to see what he has to say about this. I haven't met him personally yet, but I'm going to make sure that I will.

  11. I love the excitement – When you're pushing the edge of knowledge, finding out you were wrong about something is exciting*. It means you get to learn *new stuff about the world that you didn't know before, or couldn't accurately explain before. And when the model at issue is the Standard Model, to this point the most stable and well-tested model ever devised, finding a crack where new knowledge can expand understanding is super exciting.

    Naturally, any revisions will have to take into account all of the existing observations that made the current Standard Model so successful, so a revised model probably won't look too different, at least on the surface – but who knows what we'll end up finding under the hood when it all shakes down. ^_^

  12. OK, comment from the peanut gallery (that would be me in the cheap seats) is the Muon around 15% more massive than the Electron? Could this be explained by Newtonian Physics? (this question was asked by a person that failed Calculus at ISU so if someone responds, please keep it at the See Jane Run level of math and physics)
    Tara is a wonderful presenter. Love the smoothness of her voice. Very interesting, love learning new things.

  13. The switching of camera angles is disconcerting. The first camera angle makes it seem as though she's talking to us, the viewers watching through the camera, but the second angle makes it seem as though she's talking to a live audience, and we're the interlopers.

  14. Electric Universe fixes all this. …. There's only ONE fundamental force in the universe. Electromagnatism.

  15. How can the standard model be right as long as it is not complete? As long as we have no clue about dark matter and dark energy, a lot of things remain to be discovered, altered, completed, reviewed, etc.

  16. Please! May this have anything to do with the new found in Hungary? https://bigthink.com/surprising-science/fifth-force-nature

  17. May I ask a simple question?

    Your LHC is built to understand the physics of the universe, it is made of metal and uses electricity, why have you excluded life energy from your investigations?

    Hint: "The Einstein Affair"

    I just think this life energy stuff, due to its nature of always trying to accumulate to higher concentrations of itself when possible, might help fill in a gap or two in equations, and ideally simplify many of the things you are struggling to understand. Currently scientists are clearly feeling stuck, with no other route than to keep adding more complexity, but going down this path instead might be what you need for some aha moments and clarity to be able to move forward. What if the life energy described is the same as Higg's boson and aether and exists all throughout the universe perhaps even as dark matter? Well then it has a property, and that characteristic is currently missing from all of the equations.

    Another thing you can consider just dawned on me in viewing time lapse video of a plant growing in constant light, not night/day. Even with continuous light, it stretches, grows, then relaxes for a bit, as the leaves droop, rinse, repeat. That might be the nature of this life energy. In equations, we look for constant values but one element of an equation might be cycling over time, pulsating, almost like breathing. The rate in various situations could be interesting, for example there could be one or more very slow frequencies to our solar system, because frequencies can make standing waves which result in order. Think physical material, or stasis or simply stability on both large and small scales. If it were me, I would assign a willing undergrad to investigate with an open mind and see what they can come up with, at the hint above, even quietly behind the scenes examining for example whether the life energy accumulator at the hint above can be verified. If so, then try one in the LHC around the point of collision to see if anything different happens. You might wind up replacing lepton universality with life universality.

  18. Please NO SIDE_CAMERA – I beg you! Side camera makes sense in a lecture, but is utterly nonsensical in a one-on-one delivery. PLEASE!

  19. wtf is a quark and a lepton?

    Secondly, why do you expect the decay of a bigger particle to yield equal number of daughter particles? there might be many reasons as to why some particles are yielded more than others

  20. Very interesting news! I have a question though. Are these interactions that require the higher energy levels that can only be created in the LHC? This is the first I have heard of this purpose for the LHC, but this sounds very important.

  21. Maybe the assumption "that quarks should decay 'equally' into each category of leptons" is not correct. Maybe equitable distribution is not part of nature 🙂

  22. Tara / RI: I have a totally irrelevant question relating to Einstien's theory of space-time fabric. We are always shown in graphics that space-time bends 'downwards'? Why it bends downwards? Why not 'upwards'? Because if you look at things from space's perspectives, there are no East-West-North-South. So why downwards?

  23. You guys, we're so glad you're loving this video. One of you total legends has even provided Spanish language subtitles! Gracias! If anyone else feels like flexing their language muscles in addition to their physics ones, you can do so here – http://www.youtube.com/timedtext_video?ref=share&v=VQjXHoZitU0

  24. Scientists locked themselves in a world of bumping particles. Now, deal with it 😀 Everything around sounds different but they still insist we are made of particles. Why? When we are getting close enough, all particles suddenly disappear in a mist.

  25. Remember kids, the scientific model by definition demands direct observational data, transparancy, objectivity and repeatability. LHC lack all of these.

  26. Isn't the standard model by definition wrong since we don't know everything about the universe yet?
    It's more right than the newtonian physics, but it can't not also be wrong?

  27. The standard model is obviously incomplete because of the unexplained masses etc but couldn't bias in the reaction because by some kind of field effect instead of a 'particle'? or are there no fields without particles. Perhaps it could be some bias in the fabric of space, akin to how mass is currently in the lowest quark family. Or how particles have the masses they do. Something must be enforcing those 'biases' as it seems unlikely to have a neat underlying mechanism without constants. Some constellation of intrinsic resonant frequencies.

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