Of Particular Significance

Another Higgs Update from CERN

POSTED BY Matt Strassler

POSTED BY Matt Strassler

ON 12/13/2012

At the CERN laboratory today, there’s an ongoing report to the CERN council that oversees the lab, and this includes talks from the Large Hadron Collider [LHC] accelerator operators, and from the experimentalists who built and operate the detectors (ATLAS, CMS, LHCb, ALICE, TOTEM) that are designed to detect and interpret the debris from the LHC’s proton-proton collisions.  Among the results being presented today are some measurements of the properties of the Higgs-like particle whose discovery was announced in July, including ones that were notably missing from the HCP conference presentations in Kyoto last month.

Here are some highlights, to be fleshed out in more detail later, if warranted.

LHC accelerator operations report:

An excellent year.  In the best week the LHC produced 1.35 inverse femtobarn (fb) of data for both ATLAS and CMS; as of December 5, LHC produced 23.2 inverse fb for the year per experiment (note each experiment will have somewhat less recorded, due to normal losses), slightly above the target for the year.

Biggest problems: beam instability (much bigger problem in 2012 than 2011); stray high-energy particles affecting electronics in the tunnel; dust falling out of the beampipe into the beam, potentially a significant problem for 2015.

After the 2013-2014 shutdown, what will be the likely running conditions in 2015?  The current intention is to go to 25 nanoseconds between collisions (the design) rather than the 50 nanoseconds used in 2012, and to start at 13 TeV per collision.

ATLAS: New two-photon and four-lepton measurements; new spin and parity measurements.

Two photons: new categories of events added, with either 1 lepton or of two jets at low invariant mass, characteristic of production of a Higgs with a Z or W.

This channel now shows 6.1 standard deviation significance (3.3 expected) by itself: discovery of a Higgs-like particle in a single decay mode.  Mass 126.6±0.3±0.7 GeV/c²

Signal remains high: 1.8 ± 0.3 + 0.29 – 0.21 times the Standard Model expectation.  (But note the expectation depends somewhat on the assumed mass of the Higgs; not sure yet which mass was taken here.  126.6 GeV was assumed.)

Four leptons: 4.1 standard deviations, signal strength 1.3 ± 0.4 times Standard Model expectation. Mass 123.5±0.9+0.4-0.2 GeV/c² — notably lower than two photons.

The two mass measurements are 3 GeV apart (surprising but not impossible given the amount of data; or perhaps there is a technical problem somewhere, though I’m sure they looked very, very hard for one).  They are compatible only at 2.7 standard deviations.  Combined mass: 125.2 +- 0.3 +- 0.6 GeV/c²

Spin (from photons): spin 2 disfavored at the 91% level; compatible with spin 0.

Spin (from leptons): spin 2 disfavored only at the 85% level; compatible with spin 0.

Parity (from leptons): Exclusion of odd-parity spin-0 particle at 99%.


First limit on Higgs decay to Z + photon: although still ~20 times the Standard Model expectation, this limit is good enough to rule out various non-standard interpretations of the Higgs-like particle.

No update of Higgs decay to two photons.  This is too bad.  It’s somewhat exciting that ATLAS’s result on Higgs decay to two photons remains somewhat high compared to expectations.  But the excess is still not yet 3 standard deviations.  Deviations of this size do come and go.  And we don’t have confirmation from CMS.  So the situation remains tantalizing but unfortunately not yet very convincing.  We may not learn anything more from CMS or ATLAS til March, when they have analyzed the full 2012 data set.

I did not catch anything new from LHCb or ALICE; generally I haven’t had time to cover ALICE’s research program here.  TOTEM, a special purpose detector for measuring things I haven’t discussed on this website, is still getting rolling.

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58 Responses

  1. What’s up to every body, it’s my first go to see of this blog; this webpage includes
    awesome and truly fine data in support of visitors.

  2. If general relativity is applied in quantum gravity distance, there is change(or fluctuation) in spacetime metric at creation of mass by Higgs vev- is a pseudoscalar(in pion exchange) during Yukawa interaction- where graviton is scalar ? If there is no negative pressure of dark energy, improper rotation will not occur and combination of it with spin 2 will not be spin 0 ?
    So there is no conservation of energy(for a while) at quantum gravity distance – due to change in coupling constant of pions ?

      1. Thank you Professor for your tolerance and open mindness,
        my burst of intuitions could not find words and failed to ask sensible qustions.
        /It is a veritable cliche borne of quantum theory’s founding fathers that to utter an understanding of atomic reality based on quantum theory is to reveal one’s ignorance. Under such circumstances the most fruitful approach, it seems to me, is to be very receptive to new ideas. Possibly the ultimate explanation will be of a less mathematical character and a more artistic or intuitive character. Maybe all the baggage carried along with the word, “particle” is an obstacle to a deeper understanding. Maybe the problem has to do with our failure to fully understand gravity./ – Richard Benish | December 10, 2012.

  3. I see, thanks for clearing it up. It would still be interesting to know a little bit about what it does…
    (On the ILC suggestion: I was not intending that it be used to study p-p cross-section per se, rather to examine the internal structure of the proton with higher-energy electrons than ever before, assuming something would be lurking there).

    1. ILC will be uniquely designed for electron-positron collisions; it will not be useful for other purposes. Electron-proton colliders can study proton structure, and in a relatively clean fashion, but the ILC won’t be able to do this. And the last electron-proton collider, HERA at the DESY lab, http://www-zeus.desy.de/public/hera.php3, couldn’t go anywhere near as high in energy as the LHC — nor will any machine in coming decades. So for now the LHC is the place to be, for this particular investigation.

  4. I had not heard of TOTEM experiment before; I looked it up and it seems that in its simplicity (regarding the complexity and size of its detectors) it is measuring a fascinating and apparently unexplained phenomenon, namely the fact that the p-p cross section increases with energy. Apparently this is not predicted by SM.

    Have I misunderstood something, or could this be a hint of, if not “new physics” then at least a better understanding of the structure of the proton? Would this be something the ILC, if realized, could investigate?

    1. Yes, I’m afraid you’re mistaken — the increase in the proton-proton cross section that is observed in the data (and has been observed for decades) *is* predicted to occur within the Standard Model. The prediction is subtle and involves a phenomenon called “pomeron physics”, too complex to explain in a comment. But there’s nothing about it which poses a challenge for the Standard Model… and it reveals more about how protons interact with each other than it does about the structure of the proton. (Meanwhile the ILC is a bad place to study it — no protons!)

  5. Yes Professor, thank you.
    / In quantum computation, entangled quantum states are used to perform computations in parallel, which may allow certain calculations to be performed much more quickly than they ever could be with classical computers. So instantaneous wave function collapse does occur(keep locality)?
    If there is no continuous wave function field and phase transition, information can be transmitted faster than the speed of light – violating causality? . But the Schrödinger equation could not explain why this correlation occurs instantaneously even when the separation distance is large. Which shows, there’s no slower-than-light influence that can pass between the entangled particles./
    ‘Hidden’ variables are responsible for random measurement results in LHC?

    Please compare EPR paradox with the appeared two Higgs particles with 3Gev difference.

    1. I can compare them very easily; there’s no relation whatsoever. And by the way, the Schrodinger equation is not the equation used in quantum field theory; it is a non-relativistic equation, and relativistic equations have to be used if you are going to state the EPR paradox properly.

      1. I cannot understand difference between general relativity and Schrödinger equation. Schrödinger’s equation developed from classical mechanics(Newton’s second law), General relativity developed from Newton’s law of gravitation.

        Quantum field theory also developed from classical mechanics- in which Schrödinger’s equation is the analogue of Newton’s law for a quantum system. Without gravity(or quantum gravity) general relativity cannot be connected with QFT.
        The only problem is causality – which is absent both in Schrödinger’s cat and general relativity’s “c^2” ?
        Both of them only explain local realism(with imaginary constants). Experimental results always contradict with both of them ? – regardless it is Schrödinger’s equation or relativistic equations ?

        1. Your remark is very puzzling. You say : “Quantum field theory also developed from classical mechanics- in which Schrödinger’s equation is the analogue of Newton’s law for a quantum system.” That’s not true; it developed from Dirac’s (special-)relativistic quantum mechanics, and from Maxwell’s theory of electrodynamics, which was made (special-)relativistic by Einstein. [General relativity indeed has no role in this step.] Causality is encoded into the theory at the very outset.

          1. Thank you Professor, special relativity also developed from classical mechanics and electro magnetism – connected to quantum mechanics thru Dirac equation. It is relativistic but Schrödinger’s equation is not?
            The causality was encoded at Dirac’s resolute faith in the logic of mathematics as a means to physical reasoning – which had xenophobia with gravity by its own logic? Physical reasoning cannot avoid gravity, so it was included in general relativity?

            Experiments were made in local realism, so it can avoid gravity in mathematical models?
            If we believe bigbang, the temperature made to lock quarks inside hadrons(physical informations) can have quantum entanglement(boson level) with our piece of universe, if the informations travel more than “c” ?
            The fermion level(local realism) created by gravitons can interact with those physical informations thru Yukawa interaction. If the energy difference is considerable, then the experimental results in local realism will have different causality ? So the constancy of Heavens is changed ?
            Flying carpets and Moses split the Red Sea is not causal now. If you rewind to 17th century, Aeroplanes were not causal. May be anti gravity vehicles become causal in near future?
            There is anarchism in physical reasoning, but the theories are extremely good ?

            1. Try asking one sensible question at a time. Then maybe I can answer you. Right now, your logic does not make sense; you are connecting many things that are simply unrelated.

  6. When a wave front(or ripple) is reverberated upto rest mass, it is a stable particle(may be containing zillions of quark-antiquark pairs, dancing, bouncing and flailing to a DJ – like proton). They carry energy proportional to its frequency and its polarization as spin.

    If two of this wave front(protons) collide at high energy, like if you put your finger right on the edge of the water ripple, it dissipate suddenly.
    There is no analogy, at the point of collision, the water itself dissapear- means, the total energy(frequency) of so called decayed particles not equal to the energy of two protons. Something(ripple or vev) disappear as water(Higgs field) or nothing?
    Why there is two ripples(Higgh particles), did the explotion of proto-proton collision overcome the binding energy of Higgs(h) and in short while, it try to restore its energy conservation?

    1. I am not certain I understand your questions.

      When the two protons collide, and a Higgs particle is formed, the two protons do not disappear. A small portion of their collision energy is used to make the Higgs particle, but the remainder is used to make a large number of hadrons, which carry motion-energy as well as mass-energy. If you look at the picture which is at the upper left of my webpages, you will see this: there are two photons from the decaying Higgs, but there are also many particles (purple tracks) which are post-collision debris from the smashed protons.

      So the collision process is

      proton + proton –> Higgs + many hadrons (pions, protons, anti-protons, etc.)

      followed somewhat later, and completely independently, by the decay

      Higgs –> two photons.

      Have I answered your question?

  7. First Iam sorry and my tears for those beautiful and innocent children.

    Why we go to particle physics – mother of all basis?

    First our thanks to Professor Strassler – try to teach correct science. There is some answer…some not…may be never….

    Particles are reverberating(into energy) and dissipate(into nothing). This dance have a pattern, rhythm, follow some rule – we call it conservation law(Nature Believed (for deep reasons) To Be Exact), the three quarks rule(Rules of Nature Believed (for less deep reasons) To Be Very Nearly Exact). Some follow Bose–Einstein condensate, again dissipation become reverberation under absolute zero.

    We consider under Higgs world, all the particles are massless and Higgs vev gives mass – also answerable to this innocent children’s life. I mean the pattern must protect some ethic also- the question asked by Buddha also.

    why photons are stable
    why electrons are stable
    why protons are stable or very long-lived
    why at least one type of neutrino is stable or very long-lived
    Why neutrons are stable only in atomic nuclei?

    The dissipation of Higgs vev into nothing occur during proton-proto collision?.A particle is stable because it cannot decay further.

    The influence of gravity is very feeble. The effect of dynamite explosion is same under earth’s gravity and in outer space. There will be no effect of expansion of space even at the level of weakforce interaction distance of 3×10−17 during nuclear explosion(at zero gravity). The neutron decay cannot overcome the nuclear binding energy- but the proton decay can overcome both gravity and nuclear binding energy – so its decay is prominent than neutron.

    Why we call Higgs vev(resonance) as particle, if it dissipate at proton-proton collision. It is having intrinsic conservation, if it is not, it could not be transcendental. It is not following the rule of closed system of matter – formed during Big bang.
    It follows its own statistics at will, we call it as physical information. It does make physical paradox – having a long statistical pattern, we identify as different particles of different chiralities.

    This pattern is phenomenological, and vary according to the democracy???.

  8. What science behind this?: Elementary school schooting on Friday. Within minutes, 26 people were dead at Sandy Hook Elementary School — 20 of them children.

    1. No science involved in this at all, but my first response is why you brought this up in this forum and your question about science? It is a tragedy that has nothing to do with science. So what is your real question, or is it a sarcastic remark about science? What does a harmless forum on particle physics have to do with a tragedy of such porportions? We should be praying, and helping out, not boardening the spectre of it for no good reason.

  9. can the falling out of dust in the beam pipe have something to do with the use of the room in the tunnel close to the beam-pipe to shoot some low-budget horror movies?

  10. Discovery of radium paved the way for Gamma ray detection. It is photons of high frequency and resonance.
    When gamma energies exceeding 5MeV, intereacting with the electric field of nucleus, the energy of incident photon is converted into the “mass” of an electron-positron pair.
    A particle is a ripple in a field; its “mass” is a resonant frequency, and its decays are dissipation.

    If a photon or photon(s) atmosphere travel in opposite directions, roaring around or “returning around” in the closed system – at the point of “return” it LOSSES ITS KINETIC ENERGY, DUE TO BREMSSTRAHLUNG MECHANISM – due to conservation of energy it continues to travel at “c”- but the change in energy would have already emmited as radiation?.

    Where this black body radiation or dark matter particle go?. There is no difference in resonant frequency, but an unaccounted extra energy is involved from “zero rhythm” ?- I mean zero rhythm, will not change anything, but it will make Physical information enter into Physical paradox – because of arbitrary quantum phase(or resonance) transitions??

  11. dust falling out of the beampipe into the beam, potentially a significant problem for 2015.

    They should have gone with the Large Hamster Collider instead. That would have been self-cleaning.

    1. They did some trials but the experiments complained about the messy collisions. Also, PETA was a PITA.

    1. How would a dark matter particle cause some other particle to decay with one mass when it decays in one way, and to decay with a different mass when it decays another way? I don’t see any logical connection. Remember, a particle is a ripple in a field; its mass is a resonant frequency, and its decays are dissipation. Adding another particle is not going to cause the field to ripple with two resonant frequencies, one for one type of dissipation and one for another. How would you make a bell that has one tone when it loses energy to friction, and another tone when it loses energy to the air around it? A bell simply has a tone, period, even though its vibrations dissipate in many ways.


      1. Sorry my question was just dumb.

        I was thinking perhaps during the Higgs decay to two photons, if a light undetected DM particle was also being created then it might appear to the experiment that the Higgs was a little heavier than it really is.

        But with a little more thought on my part, I realize it was a silly question.

        1. Oh, *that’s* what you had in mind. It would go the other way, incidentally: if the Higgs decayed to four leptons + an additional particle, then the four leptons would have a lower mass than the two photons.

          But the real problem with the idea is that the invariant mass of the four leptons would not, in that case, form a peak. Instead it would form a broader distribution.

          The only way around that would be to have a second Higgs, call it H2, with a mass of 123 GeV, so that you have H1 –> H2 + X, where X is invisible, and then H2 decays to four leptons, giving a peak. However, with two Higgses, one that decays to photons and the other to four leptons (via Z particles), at that point you’d have mucked up the theory so thoroughly that nothing should look anything like the Standard Model at all.

  12. They are so coward at CMS,
    to not update the data about the decay to two photons 🙁
    I want to know this … !

  13. Does the 1.8 x signal strength for a 126.6 GeV Higgs in the diphoton channel work out to a roughly correct signal strength for a 125 GeV one? I thought that went the other way; lighter Higgs means weaker diphoton signal, right?

    1. No, you’ve got it backwards, I’m afraid. Around 126 GeV, lighter Higgs means greater production rate and almost the same diphoton decay probability; the probability is near its maximum here. So the product of the production rate and the probability to decay to two photons — which gives you the total size of the two photon signal — grows as you decrease the Higgs mass from 126 to 123. It doesn’t grow very fast though.

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