Of Particular Significance

First News from Kyoto Conference

POSTED BY Matt Strassler

POSTED BY Matt Strassler

ON 11/12/2012

The HCP [Hadron Collider Physics] 2012 conference in Kyoto is underway.  After opening talks laying out the field’s future, the main topics today have been

  • Collisions of heavy ions (specifically of lead or gold nuclei) and generic proton-proton collisions
  • Processes involving “heavy flavor” (meaning in this case the properties of hadrons containing bottom and charm quarks.)

Although there were a number of interesting new results from several experiments, today’s highlight so far has been a presentation on a new measurement by the LHCb experiment, one of the special-purpose experiments at the Large Hadron Collider [LHC], of a rare decay of a B_s meson to a muon and an antimuon.  I described this process in some detail, and claims and counterclaims about it, in the first portion of an article last year; the details of the measurements are out of date, but the physics process is, of course, the same.

Today the LHCb experiment, for the first time, announced evidence for the existence of this process, using their data collected in both 2011 and 2012.  In the Standard Model (the equations that describe the known particles and forces), it is predicted that about one in about 300,000,000 B_s mesons (hadrons containing a bottom quark and a strange anti-quark, or vice versa) should decay in this fashion.  The measurement that LHCb has made is completely consistent with this prediction.

[In detail, the Standard Model predicts (3.54 ± 0.30) × 10-9 {including mixing effects} and LHCb measures (3.2 +1.5[−1.2])× 10-9.]  The measurement is at the level of 3.5 standard deviations — evidence, but not yet a convincing observation.  LHCb excludes a rate of zero at much better than 95% confidence; their 95% confidence lower bound on the process is 1.1 × 10-9.]

The detailed implications of this result will take a while to work through, but the general implication is easy to state: the Standard Model has survived another test.  And the constraints from LHC data on speculative ideas that predict particles and forces beyond those of the Standard Model have become tighter.  Many variants of these speculative ideas would have affected this process, and the more precisely the data matches the Standard Model prediction, the more of these variants are excluded by the data.

Note Added: CMS says they a very good chance of being able to confirm LHCb’s result using the full 2012 data; not sure what ATLAS says about their chances.

2nd Note Added: Gino Isidori, in his talk on the theoretical perspective on heavy flavor physics, emphasized that a future high-precision measurement of this process will be very important; it can be predicted with high precision, and interesting variants of speculative ideas often have effects on its rate that are between 10% and 100%.

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26 Responses

  1. Sorry Professor, the hierarchy problem is fine tuned for Z and W bosons or the discrepancy is appears negligible under LHC, SM. Even after fine tuning, the discrepancy is apparent in the case of Higgs boson- may be due to frequency difference(mass) between them?. I have said Iam a layman.

    The Dirac Lagrangian for a fermion in terms of left and right handed components; we find none of the spin-half particles could ever flip helicity as required for mass, so they must be massless. Therefore it seems that none of the standard model fermions or bosons could “begin” with mass as an inbuilt property except by abandoning gauge invariance.

    “If that angular distribution of the stuff it breaks into is totally spherically symmetric, that would be spin zero. The Higgs boson has “zero spin”, otherwise it would be all over the place and therefore probably some other particle- it finally disappears, The Higgs particle has a trick up it’s sleeve that the other particles in the Standard Model do not. In the language of Feynman diagrams, a Higgs line can terminate: The line just ends; there are no other particles coming out. Very peculiar! We know that ordinary particles don’t do this… we don’t see matter particles disappearing into nothing, nor do we see force particles disappearing without being absorbed by other particles.

    Sir, mass could be understood as a particle “bumping up against the Higgs boson’s vacuum expectation value (vev).” Because of low frequency(unlike known particles like W and Z bosons) of Higgs boson on SMs PE(vev), it is impossible to differentiate “chiralities”- same or no chirality, required for HP mass. If it spin twice(Stroboscopic effect), also spin zero- but with different “space time” ?. sorry… I stop my postings.

  2. Current data show that the four forces do look more and more alike at
    very high energies. Standard Model: while it perfectly describes
    most things at earthly energies, without something Higgs-like, its predictions for very high-energy events degenerate into nonsense. Thus if the universe is hot enough (approximately 1015 K, a temperature exceeded until shortly after the Big Bang) then the electromagnetic force and weak force will merge into a combined electroweak force. We cannot create high enough temperatures to “see” what is really going on at those scales.

    SM(the equations that describe the known particles and forces) is a huge observable puzzle joined together within earthly energies or simple(local) symmetry. Even this decay of a B_s meson to a muon and an antimuon is within LHCs zero value(at broken electroweak symmetry). Broken symmetry is necessary for observations and experiment, but symmetry created at high temperature is necessary for mass or existance of matter(atom bag, super bag of SMs PE).

    This discrepancy adjusted by Higgs field in SM, thus clearing the mass of Z and W bosons – but chirality of Higgs boson is inherent, intrinsic property, it is inconsistant within SM(adjusted only to helicity)?- the helicity change may heightened to Stroboscopic effect- thus creating Cherenkov effect within LHC and SM?- making either one of them as illusion at observable level?.

  3. Thanks, Tim, for the link. I feel like I’ve entered Particle Physics Heaven, there’s so much to read on that, and other links too. I just finished reading Tommaso Dorigo’s post “Who Has the Best Limit on Bs Mesons?”.

  4. SUSY will not explain rotation, curvature of spacetime. I believe we are looking in the wrong places from the wrong parts, at LHC and in colliders in general. We cannot create high enough temperatures to “see” what is really going on at those scales. The setup we are using in colliders will lead to nowhere.

    In contrast to creating a high energy collision event(s), we need to create a furnace that we can a) create very high temperatures b) maintain the temperatures stable long enough to measure properly and c) keep increasing the temperatures / stable setup until we hit the “Holy Grail”.

    If we cannot create this setup here on earth then we should search the Heavens. I don’t believe the amount of particles in the universe is fixed, there are particles still seeping into existence all the time and need to find where and at what temperatures (and mechanism).

    What is energy? … If temperature is a property of motion then energy must have a quanta, a stable state that confines energy in a fixed (constant) volume.

    How does it coalesce? … How does energy get confined in such a volume? Is it analog or is it like a switch turning on and off in a constant frequency, the fundamental frequency of Nature?

    How does it curve spacetime? … Fields are the forced curvatures of spacetime, the harmonics of the fundamental frequency mentioned above. So if we can understand how the coalescing of energy curves spacetime we should be able to figure out unification of all the fields. I do believe the fields are composites that each harmonic, type, settle in a stable conduit confined by a similar mechanism as the quanta volume itself, a transition from close (singularity) to open (equilibrium).

  5. This is a fascinating post. I’ve been focused on genetic genealogy for the last few years, so am only just getting back into particle physics, which I’ve had a lifetime interest in. But I have one question. What factors contribute to the very low probability of the muon/antimuon decay channel for the B_s?

    1. I think what BBC article should state more correctly is that new limits have been imposed on SUSY models and some of those can be discarded. I do not see that as blow to SUSY at all. There are SUSY models out there compatible with current findings.

      1. Although the fact a mainstream broadcaster like the BBC should cover this story at all, let alone linking it from it’s news front page (and so very quickly) is highly commendable. It seems the science journalists on the BBC are some of the best.

        The story does strike a balance by asking for opinions from supersymmetry supporters ( that is John Ellis ).

      2. I’m not sure if mainstream broadcasters reporting about particle physics is a good thing, if they do it in a misleading manner. For example by claiming that some latest results are a deadly blow to supersymmetry etc if this is not true is rather damaging I think …

  6. Thank you, professor. May I pose another “what-if”? Suppose the standard model keeps holding up, beyond all expectations. What would we do with Gravity?

    1. Well, wait a second; your statement is far too strong. It has never been “beyond all expectations” that the Standard Model would describe all physics at the Large Hadron Collider. The best *bet* among most theorists has long been that the Standard Model would be supplemented by something that would be detected by the LHC, but the bet is based on an apparent paradox (the “hierarchy problem”, http://profmattstrassler.com/articles-and-posts/particle-physics-basics/the-hierarchy-problem/), not on a clear contradiction.

      You should contrast this with the argument in favor of the existence of the Higgs particle (or something else to take its place) at a scale that the LHC could discover. In that case, there was a clear contradiction in the equations that had to be resolved.

      When I and many of my other colleagues teach students about these things, we are always very careful to draw the distinction between these two examples. Before we discovered the Higgs particle, we knew there had to be something new for the LHC to find — maybe a Higgs particle, maybe something more complicated. Now that we’ve found the Higgs particle, one that so far looks like it is of the type predicted by the Standard Model, there is no way to be sure that the LHC will discover anything else.

      Howeve, we already know the Standard Model isn’t the whole story for nature, because there are dark matter, dark energy and gravity to account for. And also the Standard Model doesn’t explain many of its own features, including the pattern of particle masses, the number of particles, the number and the nature of the nongravitational forces, etc.

      *But* the Standard Model might be the whole story at the LHC. Other, more powerful experiments, or more clever experiments — ones that will not be done for decades or even centuries — may be needed to figure out the larger story, of which the Standard Model is only a part. And gravity will have to fit into the larger story.

      So keep in mind: the only thing we’re doing right now is testing whether the Standard Model describes all the physical processes at the LHC. We already know that it certainly does not describe all the physics of nature.

  7. Hello Prof,
    About the SM, we seemed to have a fairly good handle on it which is clear from the very good predictions thus far.

    I was wondering, is there any perceivable pattern between type of decays and quantum numbers … and specifically quantum numbers and temperature (mass energy, MeV’s levels)?

  8. Brilliant info as always, but the link to process details on: “rare decay of a B_s meson to a muon and an antimuon” seems broken.


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