First Glimpse of the Higgs Boson: Guest post from Jack Gunion

By John Conway | December 13, 2011 3:59 pm

Perhaps best known in the field of particle physics as the co-author of the Higgs Hunter’s Guide, Jack Gunion has been in the theoretical trenches of the search for the Higgs boson for several decades now. He is a senior professor and leader of the theoretical particle physics group at UC Davis, where he has been a member of the faculty for over 25 years. Here is a guest post from him on today’s big news from CERN.


Tuesday December 13 has been a very exciting day for particle physics. The ATLAS and CMS experiments at the Large Hadron Collider (LHC) announced today that they are both seeing hints of a Higgs boson with properties that are close to those expected for the Standard Model (SM) Higgs boson as originally proposed by Peter Higgs and others. While the “significance” of the signals has not yet reached “discovery level” (5 sigma in technical language) the two experiments both see signals that exceed 2 sigma so that there is less than a 5% chance that they are simply statistical fluctuations. Most persuasively, the signals in the channels with excellent mass determination (the photon-photon final decay state and the 4-lepton final state) are all consistent with a a Higgs boson mass of around 125 GeV IN BOTH EXPERIMENTS. This coincidence in mass between two totally independent experiments (as well as independent final states) is persuasive evidence that the photon-photon and 4-lepton excesses seen near 125 GeV are not mere statistical fluctuations.

Observation of the Higgs with approximately the SM-like rate suggests that to first approximation the Higgs is being produced as expected in the SM and that it also decays as predicted in the SM. Many theorists, including myself, have suggested that a Higgs might be produced as in the SM but might have extra decays that would have decreased the photon-photon and 4-lepton decay frequencies to an unobservable level, making the Higgs boson much harder to detect at the LHC. The level of the observed excesses argues against such extra decays being very important. The photon-photon and 4-lepton detection modes were originally proposed and shown to be viable for a SM-like Higgs boson by myself and collaborators (in particular, Gordy Kane and Jose Wudka) way back in 1986-1987. It has taken a long time (25 years) for the technology and funding to reach the point where these detection modes could be examined. I often joked that I was personally responsible for forcing each of the LHC collaborations to spend the 30 million dollars or so needed to build a photon detector with the energy resolution required. Fortunately, it seems that the money was well-spent and the ATLAS and CMS detectors both found ways to build the needed detectors, a real triumph of international collaboration and technical expertise. Also key is the very successful operation of the LHC that has produced the enormously large number of collision events needed to dig out the Higgs signal from uninteresting ‘background’ events. Until this summer produced the first very weak signs of the Higgs, I was beginning to wonder if the Higgs would be discovered during my lifetime. Fortunately, simplicity (i.e. a very conventional SM-like Higgs boson) seems to have prevailed and ended my wait.

Going forward, by the end of 2012 the levels of these excesses should reach the 5 sigma “discovery” level if the SM-like Higgs really does have the mass and decays indicated by current results. Further, we will begin to have some moderately precise (20%-30% or so?) measurements of the individual decay modes of the Higgs boson that might indicate just how precisely SM-like it is. Many theories beyond the Standard Model predict the possibility of deviations from the predictions of the purely SM Higgs boson. As data accumulate, looking for such deviations will be a major focus. Current data (weakly) hint at the possibility that the Higgs production rate might turn out to be modestly larger than predicted if the Higgs is that of the Standard Model and has mass of 125 GeV — the best-fit ATLAS cross section is about 1.5 times as large as the SM prediction, whereas the best-fit CMS cross section is very close to the SM prediction. Time (i.e. more accumulated data) will tell.

Of course, the current run of the LHC will be halted at the end of 2012, followed by a lengthy shut down for upgrades to the accelerator and to the detectors. After this upgrade, the LHC will operate at a much higher energy (14 TeV) compared to the current energy of 7 TeV, and, if all goes according to plan, have a much higher collision rate. At this point, precision studies of the Higgs boson will certainly be possible. If deviations are observed, then we will strongly suspect that the SM is incomplete. Even before that time, we are hoping that by the end of 2012 we will have seen new types of particles that do not fit into the Standard Model. This, for example, is predicted if the universe is supersymmetric. Supersymmetric models tend to predict a light Higgs boson that is fairly, but not completely, SM-like with mass in the range 110 GeV to 140 GeV and so are very consistent with what is being observed. If some supersymmetric particles (so called sparticles) are observed then their masses and properties constrain the Higgs mass in a given model and consistency of the entire theory can be nicely tested. Hopefully, some version of physics beyond the Standard Model will be directly observed at the LHC, in which case there will be at least a decade of exciting observations and analyses to determine the precise beyond-the-Standard-Model theory.

Still, the pure Standard Model with no new physics cannot be totally discarded. Although this would not allow a so-called “natural” explanation of the Z boson and Higgs boson masses, the pure SM is still internally consistent even at energies close to the Planck scale for a Higgs mass greater than or equal to about 125-130 GeV. In other words, the observed Higgs mass is on a borderline. Above 125-130 GeV, new physics below the Planck mass scale is not required for internal consistency of the SM. But, had the Higgs boson mass been significantly below this (the precise border being somewhat uncertain theoretically), the SM would necessarily break down at some energy scale below the Planck scale and at this lower energy scale new physics would have to enter. In short, a SM-like Higgs boson with mass near 125 GeV is maximally interesting from many theoretical perspectives.

In any case, theorists and experimentalists are all very relieved that the LHC appears to be observing a Higgs boson thereby ensuring an extremely interesting program of physics at the LHC for decades to come. Further, such a light SM-like Higgs boson provides strong motivation for a linear electron-positron collider of low center-of-mass energy. Studies suggest that only such a collider can easily measure the properties of such a light Higgs boson at the few percent level, although the LHC might not do that much worse depending upon future improvements and upgrades.

CATEGORIZED UNDER: Guest Post, Higgs, Science, Top Posts
  • anon

    Generally this is an excellent post. However, I’ve got to quibble with this phrasing: “Still, the pure Standard Model with no new physics cannot be totally discarded.” This gives the impression that there were actual significant evidence for any physics beyond the SM (other than neutrino oscillations). There isn’t. We are not even close to discarding the pure SM without SUSY, and in fact all of the data from LHC so far points at this being the most likely scenario: SM higgs and little else.

  • dan

    @anon:
    “This gives the impression that there were actual significant evidence for any physics beyond the SM (other than neutrino oscillations). There isn’t.”

    Dark matter doesn’t count as physics?

  • anon

    Fair enough, I’ve got no issue with dark matter (or dark energy for that matter). But there is no guarantee, and not even a hint yet, that LHC will see such a thing. I’m putting my money on axions to be honest rather than WIMPs.

  • http://gbruno2@blogspot.com g bruno

    I love the language in this Romanian report on B-mode polarisation
    http://www.infim.ro/rrp/2009_61_3/art17Stefanescu.pdf

    Planck apparently reports on this in Feb 2012 (coolant gas has already run out?)
    which we assume will nail inflation to the door.

    And all the physicists take up the many-worlds cry, somehow seems like an abandonment…

  • Albert Z

    We have seen 3 sigma “hints” disappear in particle physics.

    We have seen 4 sigma “hints” disappear in particle physics.

    “First Glimpse of the Higgs Boson”? Possibly.

    But the long string of false positives in recent years would argue powerfully for a bit more scientific objectivity and a lot less wishful thinking.

    No need to be so desperate. Nature will reveal the correct answers in due time.

    Albert Z

  • Pingback: Sigma: così buoni, così vicini « Tutti a Zanzibar

  • http://www.flisser.com Bob F.

    Great post. How long will the shut-down be for the 14 TeV upgrade?

  • http://www.astro.multivax.de:8000/helbig/helbig.html Phillip Helbig

    It is not absolutely certain that dark matter must be some sort of elementary particle. Most of the other candidates (such as primordial black holes—formed before nucleosynthesis, they are non-baryonic) have been ruled out, but that doesn’t prove conclusively that dark matter is some sort of elementary particle (though now that primordial black holes—excellent theory, shame about the observations—are ruled out, it is looking more likely).

  • http://www.astro.multivax.de:8000/helbig/helbig.html Phillip Helbig

    The Higgs has other properties besides its mass. How many of these have been measured and what, if any, is the uncertainty?

  • TJR

    Is the comparison to sigmas being done within the standard statistical hypothesis testing approach? As in, you assume a null hypothesis (no Higgs particles here) and then work out how many standard deviations (sigmas) away from the mean it is?

    If so, then it is not correct to say that with a 2-sigma result “there is less than a 5% chance that they are simply statistical fluctuations”, i.e. random variation. What it actually means is that IF the null hypothesis is true (no Higgs) THEN the chance of observing something as extreme, or even more extreme, as we did, is less than 5%. Not the same thing. We can’t claim it as an unconditional probability, as we don’t know if the null hypothesis is true or not.

    This is the correct interpretation in standard statistical hypothesis testing, but if the setup is different here then my comment may be irrelevant. For example, if the analysis is Bayesian the interpretations are quite different.

    Asked out of genuine interest, not as a criticism.

  • http://www.astro.multivax.de:8000/helbig/helbig.html Phillip Helbig

    A related problem: distinguishing between the probability of the data, given the model, on the one hand, and on the other hand the probability of the model, given the data. My model (hypothesis) is that the person I am talking to is female. The data are that this person is pregnant. Probability of the data, given the model: about 3 per cent. Probability of the model, given the data: 100 per cent.

  • Pingback: CERN Reports 'Hints' of Higgs Boson - But No Discovery Yet - Forbes

  • Neil

    Nice piece. If Jack Gunion ever discovers a particle, it will be easy to name.

  • http://coraifeartaigh.wordpress.com Cormac

    A lovely post, exemplary. Many thanks

  • Noel25

    Have we not learned anything from the past year or so with several other “hints” of important particle physics discoveries that never panned out? The same thing has been true of the dark matter searches in which several “hints” have turned out to be mirages e.g CDMS II, Pamela, LEP Higgs c. 2000, etc.

    My speculation is that since many of the breakthrough confirmations that many physicists have been hoping for a long time have yet to occur, there is a sort of desperation kicking. Hopefully the desperation will end soon so a refocusing of efforts in other theoretical directions can more easily occur.

  • et

    @Noel25: ” in which several “hints” have turned out to be mirages e.g CDMS II, Pamela, LEP Higgs c. 2000, etc.”

    How do you figure these first two are mirages? They are definitely real results, just not fully conclusive. They certainly are giving direction to other experiments and theory… And anyway, everyone I’ve ever talked to who worked with these experiments knew very well that they were not going to have major breakthroughs at 10sigma. They’re all extremely hard measurements that are intended to explore parameter spaces – after all, the analysis generally focuses on *ruling-out* possible dark matter particles rather than actually detecting them. In science, a non-detection is often as interesting as a detection (although the press usually doesn’t communicate that fact very well…).

  • Mass

    finally, the masterpiece, that is the Standard Model is complete….

  • Mass

    Noel25 has no clue what he is talking about.
    The reason those other PAMELA etc things went away is because those “excesses” were apriori unlikely. There’s no clear expectation for them to have been there, and so it was most likely statistical noise.
    On the other hand, the Higgs is the centerpiece of the Standard Model – a theory that has been confirmed 100000 times. It requires a Higgs particle, and so we strongly, strongly expect that it exists – and now the data seems to confirm it. So the 2, or 3, or 4 sigma excesses carry much more significance.

  • Albert Z

    Mass: “finally, the masterpiece, that is the Standard Model is complete….”

    Oh the credulity is impressive, but see below.

    1. The Standard Model is primarily a heuristic model with 26-30 fundamental parameters that have to be “put in by hand”.

    2. The Standard Model cannot predict the masses of the fundamental particles that make up all of the luminous matter that we can observe.

    3. The Standard Model did not predict the existence of the dark matter that constitutes the overwhelming majority of matter in the cosmos. The Standard Model describes heuristically the “foam on top of the ocean”.

    4. The vacuum energy density crisis clearly suggests a fundamental flaw at the very heart of particle physics. The VED crisis involves the fact that the vacuum energy densities predicted or measured by particle physicists (microcosm) and cosmologists (macrocosm) differ by up to 120 orders of magnitude (roughly 1070 to 10120, depending on how one estimates the particle physics VED).

    5. The Planck mass is highly unnatural, i.e., it bears no relation to any particle observed in nature, and calls into question the foundations of the quantum chromodynamics sector of the Standard Model.

    6. Many of the key particles of the Standard Model have never been directly observed. Rather, their existence is inferred from secondary, or more likely, tertiary decay products. Quantum chromodynamics is entirely built on inference, conjecture and speculation. It is too complex for simple definitive predictions and testing.

    And so on, if we care to be honest and scientific.

    Rant on now,
    Albert Z

  • http://www.astro.multivax.de:8000/helbig/helbig.html Phillip Helbig

    I agree with all of Albert’s points, especially #4, with the exception of #5. The Planck mass involves gravity. Standard particle physics does not. Why is it unnatural if it is not related to any particle in nature and what does it have to do with QCD?

  • pah

    Thank god we have Albert Z around to restore honesty and integrity in science! The standard model is not a theory of everything and so we should throw it in the bin. That’s how science works.

  • James

    Nonsense. Clearly (and fortunately) there is still much work to be done and many physical mysteries to be resolved, but Mass is quite right to call the Standard Model a “masterpiece” – it is one of (if not the) supreme intellectual achievements of mankind, and should rightly be celebrated.
    To demur in the way Albert Z is simply churlish. It’s like pooh-poohing the Moon landings because they didn’t go to Mars.

    (Edit: I was partly addressing Pah@21 until I re-read the post).

  • Shantanu

    anon, non-0 neutrino mass is not evidence for physics beyond standard model. The PDG lists it
    as part of standard model.

  • Torbjörn Larsson, OM

    Good article. Combined with Jester’s short description on the several agreeing channels and experiments, I now believe I see the tempered excitement.

    #19:

    I like how #4 claims unnatural vacuum energy vs Planck energy (and calls it a crisis, when for example environmental selection nicely predicts it), then turns around in #5 and claim unnatural Planck energy vs inhabitants of said vacuum. You can really turn that gear to count if you crank it twice every count.

    Then “honesty and integrity” seems an inept description – nothing personal, mind. How about “irrelevant digging for details outside of the theory as is (i.e. complete)” and “counting twice”?

  • Torbjörn Larsson, OM

    Speaking of unnaturalness, as a layman I hear that a 125 GeV standard Higgs is marginally stable (fresh arxiv papers). The universe will then end, not because protons decays (GUTs), not because spacetime “decays” (Big Rip), but because the vacuum decays.

    Who ordered that?

    Assuming a standard Higgs comes through as the simplest theory, at a guess that cries out for environment selection again. Mirroring #4, multiverses seems popping up many times over…

  • Albert Z

    The Standard Model of Particle Physics has some good parts and some very good parts.

    We cannot throw it in the dust bin until we have something better to replace it.

    The Standard Model is model-building effort to fit the observations, and as I said above, it does a creditable job in many sectors. However, it is heurisitc and incomplete. Provisional.

    It should not be treated as dogma, as some (many) do.

    What we need is a new unified paradigm that can explain nature at all scales without tooth-fairies and ad hoc epicycles.

    The new paradigm already exists and has been published repeatedly in many forums, but it is almost completely ignored because its author is a “nobody”. To those who are steeped in the old paradigm, it sounds more than a bit strange, but it extends nature’s fundamental symmetries in an amazing and beautiful way. It is conceptually, and in principles, very simple but very complex in detail.

    What is this new paradigm, you ask? Well, you must ask my somewhat dim student. Although the fellow is a bit of a slow study and mathematically unsophisticated, he has laser-like instincts when it comes to nature because of his obsession with knowing the observational properties of nature at all scales – particles to galaxies and and then some. Not many people do this, being focused in their one limited and rarefied sector. It has been interesting to work with him. Seek and ye shall find.

    Best,
    Albert Z

  • http://www.astro.multivax.de:8000/helbig/helbig.html Phillip Helbig

    “The new paradigm already exists and has been published repeatedly in many forums, but it is almost completely ignored because its author is a “nobody”. ”

    Has it been published in a refereed journal? If so, please give a reference. If not, why not? Wherever it has been mentioned (forums? which ones?) please give a reference so that we can check it out. Otherwise: I was thinking of a plan to die my whiskers green but always use so large a fan that they cannot be seen. In other words, what’s the point?

    Talks of “paradigm” usually gains one points on the crackpot index.

    I don’t know which, if either, of you I insult if I mention that this sounds rather like RLO.

    Note that there is another Albert Z who often comments on blogs who usually uses his full surname. If you are not he (and I suspect that you are not), I suggest using a less confusing moniker.

    Has this new paradigm made any testable predictions? If so, what are they?

  • Albert Z

    Phil Helbig: “Has this new paradigm made any testable predictions? If so, what are they?”

    The new paradigm makes a virtually unlimited number of predictions that are testable and are of the make-or-break kind. They cannot be altered or fudged.

    The dim bulb (and don’t worry, he refers to me as “fossil”; it’s just our form of sarcastic fun) has published somewhere in the range of 10-15 such predictions.

    Two have been vindicated already, but the big one is yet to be fully tested. Should be soon.

    In the 1980 the dim bulb went to a party of grad students and profs and someone brought a psychology text showing a picture with much visual information subtracted out. The test was to see if you could figure out what the “chaotic” array of dots, lines and weird shapes actually represented. 60% eventually figured it out, 20% did so with help, and 20% even had trouble when helped.

    The dim bulb solved it in an order of magnitude less time than the second fastest.

    The party-goers at first thought he was just saying he knew what it was, but in truth he did (a Dalmation walking in a woods); black+white photo made it a real challenge.

    When asked how he could solve it so fast, the dim bulb said the critical thing is identifying the crucial clues that are always there waiting. Then someone with exceptional pattern recognition let’s their mind fill in the missing parts of the underlying fundamental pattern.

    So it is with paradigms and nature . Some will get lost in the infinite details and end up with complicated and strained theories of little real explanatory power. Others see the underlying physical principles. It appears that you are going to have a very difficult time, my friend. To others it will come with little effort, like it did with the dim bulb. Five years from no science at all to the new paradigm, at least in crude outline. Exceptional!

    Good Luck,
    Albert Z

  • Roman

    A bit off topic (or maybe not) – are there any crackpot “experimentalists” out there or only crackpot “theoreticians”?

  • John R Ramsden

    @Albert Z (#26)

    Sounds like some joke I’m missing, but in case not ..

    I’d be interested in a reference to somewhere your student’s theories are outlined, refereed or not. It would be interesting to compare them with my ideas, such as these are.

    I really don’t understand why you are so coy about giving a reference here though. If you fear someone might pinch this student’s ideas and run with them, you can be reassured by the fact that professionals are amazingly (although understandably) resistant to ideas which deviate much from their preconceptions!

    j h n r m s d n @ y a h o o . c o . u k

  • Albert Z

    No one could “pinch” the dim bulb’s new paradigm for physics because he has scores of published papers about it already in is name.

    However, if somone should try to steal the idea, the dim bulb would only be too happy. That is because he is not looking for money, fame or power, or access to pretty young women. No, his only motivation is to teach people this new way of seeing nature that has always been staring them in the face.

    Mandelbrot got the ball rolling but then everyone settled for the easily reached fruit and did not pursue the fractal paradigm far enough.

    Phil Helbig did corrctly identify the dim bulb, but he has no idea who I am and I prefer to keep it that way so as not to excercise undue influence one way or the other.

    Just search on Discrete Scale Relativity or “discrete fractal cosmology” and you are off and running.

    Unlike string theory, it does not take 16-20 years of drudgery to learn the new paradigm. With an hour or two a day, one could be one of the world’s leading experts in about a month, at least that is the case at this point.

    Caveat: no pain – no gain. If you want to understand nature in the elegantly unified way, you must commit to putting in some sustained and sincere effort. The principles upon which nature is based are not back-of-the-cereal-box affairs that can be mastered with one skim through a website.
    One must think, think, think. And study the empirical properties of nature assiduously. Expect a few upsetting changes to previous assumptions. Well, what did you expect? That has to be so.

    Lucky for you, the dim bulb has broken the one path (out of thousands of false starts) that leads to the top of the mountain. At least that is the way I see it, after putting in a lot of effort to understand is paradigm and how it can stand up to all attacks. Believe me I have tried my best to shoot it down, and the best I could get on any issue was a draw. He turned out to be right in virtually every aspect that can and has been tested so far. My bet is that the new paradigm will have the integrity of general relativity, only it will now include the Standard Model and Quantum Mechanics (suitably reinterpreted), because it is in essence an extension of GR and EM using more sophisticated geometrical symmetries.

    Very easy to understand conceptually, analytically a real bear, fully testable.

    Good Luck,
    Albert Z

  • Albert Z

    Apparently the dim bulb is blocked from posting to this site, so he asked me to post this for him.
    ————————————————————

    “How can physics live up to its true greatness except by a new revolution in outlook which dwarfs all its past revolutions? And when it comes, will we not say to each other, ‘Oh, how beautiful and simple it all is! How could we ever have missed it for so long!’.”

    John Archibald Wheeler, 2000
    —————————————

    Amen,

    The new fundamental symmetry is global discrete cosmological self-similarity, which yields an infinite discrete fractal cosmos.

    RLO
    Discrete Scale Relativity

  • http://www.onlyspacetime.com John Macken

    I want to return to basics and discuss the origin of inertia (rest mass). A photon is always described as an example of a massless particle. However, a photon is only a massless particle when it is freely propagating. If it is confined in a hypothetical 100% reflecting box, then it is forced to have a specific frame of reference and it exhibits inertia (rest mass). When the box is accelerated, then there is unequal photon pressure on the reflecting walls of the box. There is a net force on the box that is the photon’s inertial force. This force is analyzed on the website:
    http://www.onlyspacetime.com/
    and shown to exactly equal the inertia exhibited by a fundamental particle of equal energy. Also, when the box is traveling at a constant relative velocity, the confined photon is perceived to undergo a bidirectional Doppler shift that results in a net increase in energy that exactly equals the kinetic energy expected of an equal energy fundamental particle.

    It can be shown that the conservation of momentum would be violated if the inertial force were not the same for the confined photon and fundamental particle of equal energy. The point of this is that the Higgs mechanism supposedly gives inertia to fundamental particles. However, the amount of inertia given to an electron, for example, must exactly equal the amount of inertia exhibited by 511 KeV of confined photons. If a Higgs field is required to externally supply inertia to an electron (which would otherwise have no inertia), how does the Higgs field give exactly the correct inertia to preserve the conservation of momentum? The above website examines the question of how fundamental particles acquire the correct inertia.

  • martenvandijk

    Inertia is a matter of time. Particles do not exist. Time rules the waves. There are waves only (Stephen Hawking’s supposition in “A brief history of time” is true). Do you want to know why? Search for my arguments on WordPress.com and have a Wonderful Christmas and a Happy New Year without Higgs bosons or any other particles or any strings attached.

  • Pingback: Wo die Jagd auf’s Higgs Ende 2012 angekommen ist « Skyweek Zwei Punkt Null

  • GDubya

    Nice exchange of thoughts as regards Higgs boson research, even for a novice reader.

  • Prentice

    Looks like mass is the one who doesn’t know what he’s talking about. I have a down to earth question for anyone who wishes to give a straight answer. When does a theory cease being a theory and become real? If a theory is confirmed to be real one time, seems to me, it then should be real, period. If it has to be confirmed again then the first proof of confirmation wasn’t proof at all. Unless the word proof means different things to theorists than it does to the rest of the world. Mass says the standard model theory has been confirmed 100,000 times. Why does it take so many confirmations to prove it’s real?

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