Higgs Discovery on the Brink, but is it THE Higgs?

By now you should know that physicists working on the CMS and ATLAS experiments at the Large Hadron Collider are about to announce important new results in the search for the Higgs boson. The announcement will be made on the morning of the 4th July at CERN in advance of the ICHEP conference in Melbourne where more details may emerge. The expectation is that this update will actually be a discovery announcement for the Higgs Boson. This is based on vague rumours, plus the fact that CERN PR are not saying that it is not a discovery, plus the fact that it would make no sense to have such an update at CERN before a big conference unless it were a discovery, plus the fact that they would not have been so sure so soon that there was something big to say unless the signal had come through very clear and strong.

The details will have to wait for the day and of course I will be here to add my independent analysis and unofficial Higgs combinations as the story unfolds. Others will be live blogging including Tommaso Dorigo of CMS who says he will be in the auditorium. I hope he has a seat reserved for him so that he does not have to camp outside the door overnight to get in. I will be watching the live webcast from home instead.

How do they know it is the Higgs Boson?

This is now the most frequently asked question, how do they know it is the Higgs boson and not some other particle they are seeing? In the scientific papers we can expect that the physicists of the collaborations will be careful about how they word the discovery. They will say something like: “We have found a new resonance (i.e. particle) in the search for the Higgs boson which is consistent (or maybe not) with the standard model Higgs Boson. Further measurements will be needed to confirm that its properties are as predicted.” And of course they will quantify what they mean by this with a slew of numbers and plots. In the press you will simply hear that they have discovered the Higgs boson. Dont by upset by this, you can’t expect a report in the New York times to read like a paper in Physical Review D, but it is fair to ask to what extent its known properties so far indicate that it really is the Higgs boson.

What is the Spin?

The most distinctive characteristic of the Higgs Boson is that it is a scalar, i.e. it has no spin. Other elementary particles in the standard model are either fermions with spin one-half or gauge bosons with spin one. Particles with spin that is any multiple of one half are possible and it is a quantity that needs to be checked experimentally. The channel where they are seeing the signal for the Higgs boson most strongly is through its decay into two high energy photons. The photons have spin one but spin is conserved because the two photons take away spin in opposite directions that cancel. It is not possible for fermions that have a odd-integer spin to decay without producing at least one new fermion so we know already that the particle observed is a boson. By a theoretical result known as the Landau-Yang theorem it is not possible for a spin-one particle to decay into two photons either, but it is possible for a spin-two particle to decay into two photons with spins in the same direction.

So we know already that the new particle has spin zero or spin two and we could tell which one if we could detect the polarisations of the photons produced. Unfortunately this is difficult and neither ATLAS nor CMS are able to measure polarisations. The only direct and sure way to confirm that the particle is indeed a scalar is to plot the angular distribution of the photons in the rest frame of the centre of mass. A spin zero particle like the Higgs carries no directional information away from the original collision so the distribution will be even in all directions. This test will be possible when a much larger number of events have been observed. In the mean time we can settle for less certain indirect indicators.

In March the Tevatron presented their final observations in their search for the Higgs boson. Their detectors are more sensitive to the decay of the Higgs to two bottom quarks. A weakly significant signal was seen at the same mass of 125 GeV where the LHC is seeing its resonance. This too will be confirmed with more certainty by the LHC later.  This shows (or will show) that the particle can decay into two spin half fermions. This is certainly possible for a spin zero particle and also for a spin one particle but is it possible for a spin two particle? If not we would know that the spin must be zero by a simple process of elimination. In fact it is possible for a spin-two particle to decay into two spin halfs provided the extra spin one is carried away either as orbital angular momentum (p-wave) or as a soft photon that is not seen, but neither of these possibilities is very likely. We can therefore be reasonably sure already that the observed particle is indeed spin zero, but for absolute certainty we will have to wait for more detailed studies.

What about other quantum numbers?

As well as spin, any elementary particle is partially classified by other quantum numbers including electric charge, colour charge, baryon number,  CP, etc. The charges are strictly conserved due to gauge invariance and are zero in the decay products so we know for sure that the particle is neutral. We also know that the baryon number is zero otherwise the particle would provide a mechanism for baryon number violation that would probably destabilise the proton. The quantity CP can be either even or odd but it is hard to know for sure which it is because CP is known to be unconserved at an observable level. Given that the decay modes are predominantly into a particle and its anti-particle or into two particles that are the same, it is unlikely that the CP is odd, but we will have to wait for more carefull tests to be reasonably sure. In any case there are versions of the Higgs boson in theories outside the standard model that have odd CP so this question does not really affect whether or not they are seeing the Higgs.

What about other Higgs properties?

The mass of the Higgs boson is the last parameter of the standard model to be determined. With the imminent discovery we now believe it to be about 125 GeV. With this quantity known every other property of the standard model can in principle be calculated, but it is not always easy due to non-perturbative effects that are difficult to model. Uncertainty in other measurements also adds more uncertainty to any calculation. The decay time ( or width ) of the Higgs boson can be calculated but because 125 GeV is less than twice the W or Z masses, the boson is relatively stable and the width is a few MeV. This is far too narrow to be measured at the LHC where the mass resolution is in the order of a GeV.

However, the most distinctive characteristic of the Higgs boson is its coupling to massive particles. By the nature of the Higgs mechanism that gives mass to the fundamental particles in the standard model, the coupling is always proportional to the mass. according to the theory the fermions and gauge bosons do not have any mass in the unbroken electroweak phase due to gauge symmetry and chiral symmetry (however the fact that neutrinos have a small mass already takes us beyond the standard model)   This affects all the production rates and branching ratios for the decays so if these are measured and found to be in agreement with the standard model we will have a useful test that what we have found really is the Higgs boson. Only by producing the unbroken state can we get a clearer sign that it is the real Higgs mechanism that breaks electro-weak symmetry but that is not accessible to present day technology.

The decay rates for the Higgs to ZZ, WW and bb all go by direct couplings to the Higgs boson so these provide particularly good tests. We can’t measure them directly because the rates at which we see these processes also depend on the production rate for the Higgs boson. The predominant mechanism for Higgs boson production is gluon fusion. This can be calculated in the standard model to an accuracy of about 15%, but it can be suppressed or enhanced by physics beyond the standard model. This is because the process involves a quark loop that is dominated by the top quark in the standard model. In some SUSY theories it is enhanced due to the bottom quark getting a stronger role, or it can be suppressed if there is a stop quark with a mass near that of the top quark. Even if the production rate is unreliable the ratios of the decay rates to ZZ, WW and bb should be fairly robust and will make a good test of the Higgs mechanism.

What would enhance the diphoton channel?

In the 2011 data we saw an enhancement of the diphoton channel amounting to 80% above the standard model in the unofficial ATLAS + CMS combination. The local significance is about 1.6 sigma, so nothing special, but the fact that they have opted for a special update so soon after looking at the new 2012 data with perhaps only 3/fb revealed suggests that this enhancement could have persisted. Even the collaborations wont know for sure until the final results which will probably not be ready yet. However it is certainly something worthwhile for a blogger to speculate about. So what could cause such an enhancement and does it mean this particle may not be the Higgs boson?

The decay mode to photons is more interesting because it also involves a loop that is dominated by the W boson but which also has (negative) contributions from the top quark. This can also easily be suppressed or enhanced by new physics such as any new massive charged particle with mass near the electro-weak scale. A boson will tend to enhance it while a fermion has a negative sign in any loop so will tend to suppress it. Prime candidates for enhancement would be a scalar top (stop) or a scalar tau (stau) The stop also suppresses the Higgs production rate because it has colour so it works both ways, but the stau is pure enhancement.

The diphoton channel can also be enhanced indirectly along with the ZZ and WW if the dominant bb channel is suppressed, e.g. if the Higgs is partially fermiophobic. We can distinguish this from the direct enhancements by observing the ZZ and WW channels, especially through the ZZ to 4 leptons decays which is a very clean and predictable measurement.

Together, observations of these channels should add up to an excellent test for the presence of beyond standard model physics and will provide narrow clues as to what type of physics it is. However the Higgs boson will still be a Higgs boson even if it is not quite the standard model Higgs boson.

Can they say they discovered the Higgs boson then?

Once we have the data from the first 2012 run in our hands in ten days time we will already have enough data to say that the new particle looks like a Higgs boson. We may even be able to make some preliminary statements about any deviations from the standard model. These will improve in time.

There will always be those who say that we dont really know for sure that this is the Higgs boson rather than some other scalar neutral particle that happened to be around, but the fact is that this particle turned up just about where the Higgs boson was most expected and with the right properties. We already know from the discovery of the W and Z bosons and many other tests that the standard model is a good one and it is a model based on electroweak symmetry breaking. Something is required to break that symmetry and now we have found a particle that fits nicely the characteristics of such a particle. Only the most obstinate skeptic would complain if CERN claim to have discovered the Higgs boson given the evidence we expect to see very soon.

If it swims on a pond and quacks like a duck it is not unreasonable to say it is a duck, especially when you were expecting to find a duck. Further observations will just tell us more about what kind of duck it is.

50 Responses to Higgs Discovery on the Brink, but is it THE Higgs?

  1. neutrino14 says:

    Thanks for the info ;] Waiting impatiently for the news from the LHC.

  2. leo vuyk says:

    Could the result also com from TWO Higgs particles converting into two photons?

    • Philip Gibbs says:

      Creation of one Higgs is very rare so creation of two at the same time is virtually non-existent at the LHC

    • yes, you could have two Higgs bosons, for instance one with
      mass 125 GeV and the other with mass 125.02 GeV both with
      half the cross section of a standard model Higgs. This cannot be resolved by the LHC. This is the Hill model from 1986. It is
      the simplest (least extra parameters) extension of the standard model. There are also more interesting possibilities along these
      lines (HEIDI models). It shows why it is important to measure
      the width, more precisely the line-shape of the Higgs boson.

      • Philip Gibbs says:

        Sure, but to fit with what Leo was saying they would have to both be produced always at the same time and each would decay into a single photon (unless I misunderstood) . This would also be difficult because particles cannot decay into a single photon.

      • Leo Vuyk says:

        Yes Phil, Two Higgs into Two photons, why?
        In my Quantum Function Follows Form model (Q-FFF) the Higgs particle is interpreted as a massless transformer particle able to create the universe by transforming its shape after real mechanical collision and able to merge with other shaped particles into composite geometrical KNOTS called Quarks and some Leptons (Muons and Tauons). Singular particles are; the two Leptons: the Electron and Positron, different shaped Photons, Gluons and neutrinos all originated out of one single transformed Higgs. As a result, Q-FFF theory leads to a NON Standard Model of elementary particles, see

        Click to access 1112.0065v2.pdf

        In this letter I proposed that two gluon particles could present themselves as di-Photons.
        However two colliding Higgs could perhaps even change directly into two Photons.

  3. Thanks Philip, very clear explanation, even a layman like myself understands it perfectly.

  4. Robert L. Oldershaw says:

    Thanks! That discussion has been badly needed for some time. In science one must resist the human tendency of having one’s desires for a certain answer consciously or unconsciously manipulate the analysis of the observational results.

    The long battle over the value of the Hubble constant [Sandage 50; de Vaucouleurs 100; actual ~75] is a remarkable case in point.

  5. A “partially fermiophobic” Higgs is the 2nd best thing for the typical VIXRA contributor (the 1st being, surely, no Higgs). First, it implies that something is protecting the 84 fermionic states whose yukawa coupling is zero, and it makes more reasonable that the 16 top states have a “natural yukawa”, almost exactly equal to one. Crazyiness inspired in 11D SUGRA (and membranes) could surface here, as the bosonic sector of such theories has an object with 84 states too.

    Second, it should imply that the GUT point is not the one to look, directly at least, for the mass spectrum of fermions and then the door to low energy speculations –such as Koide waterfall, http://www.vixra.org/abs/1111.0062 ;-), which fixes all the masses from the one of the top quark– becomes officially open.

    • Philip Gibbs says:

      You should look at the earlier posting on Resanaances where jester explains a paper that shows that the pure fermiophobic limit with no coupling to fermions does not fit well, but one with reduced couplings is good. Significance is not high though http://resonaances.blogspot.co.uk/2012/04/what-is-higgs-telling-us-so-far.html

      • Thanks, I had missed that paper. It seems that, contrary to my comment, they favour the couplings of tau and bottom and prefer to play with top yukawa in a funny way. By the way. these negative signs reminder me of the negative sign solutions of de Vries proposal for Weinberg angle, which I looked in 2006; when the mass of Z squared was set to (91.1874)^2, de Vries method obtained a squared mass of (80.3717)^2 for W but there were also two negative sign partners, of respective mass squares of −(176.154)^2 and −(122.384)^2, which we left unexplained at that time.

  6. wl59 says:

    At the moment, we must wait what CERN will manifest. However, w.r.t. results based only on gammagamma, I would continue to be sceptical

  7. Anon says:

    The CERN press release says they will use data collected till June 18 2012 — so thats 6.6 /fb at 8TeV, which along with 5 /fb at 7 TeV shd be enough for 5 sigma discovery?

    • Philip Gibbs says:

      The press release mentions the data collected up to 18th June but it does not say they will use it all, If they do it is about 6.2/fb recorded per expt. The original plan was to use data collected until 10th June which was about 4.5/fb but they may use more if they have time. It would be enough to get 5 sigma in the ATLAS+CMS combination but they have decided to aim for discovery level in each experiment independently. They may now have enough data for that depending on luck with statistical fluctuations and other things.

  8. algernon says:

    “This is far too narrow to be measured at the LHC where the mass resolution is in the order of a GeV.”

    Give those limitations, would it make sense then to build a small dedicated collider fully designed and optimized to study a scalar boson of mass around 125 GeV, now that we know it is there?

    Perhaps that would take less time and money than running the LHC for 15 years just to improve our knowledge of the particle marginally…

    • anna v says:

      The LHC was not designed and built just to find the Higgs. It is a discovery machine for anything new at higher energies, and we expect many new things. It will be a great disappointment if nothing else is found even though that too will be a datum to consider.

      The International Linear Collider will be the machine which will aim for accuracies in widths, crossections and angular distributions. The analogue of LEP, which was the accuracy machine designed to solidify the discoveries of the antiproton proton collider.

    • yes, if this stays true a Higgs factory would be good.
      The question is which one and it will not be a small collider at all.
      I discussed this in Moriond, arXiv: 1204.3435

  9. amarashiki says:

    It can not be the SM Higgs if they got it now ( I have any other hints and information arriving to me now) with the data and specially IF the Higgs is fermiophobic. And if the Higgs is fermiophobic (partly or completely), that is really great news since it means BSM Physics!!!!! The next months are going to be fascinating!

    • Philip Gibbs says:

      That’s what I’d like to think too, but the results will be adjusted with more data being added and the analysis will evolve, so we should not be too sure of what early rumours suggest.

  10. amarashiki says:

    I agree Phil, but a SM Higgs, even being possible, offers more issues than answers. I have become more and more convinced of that after finishing my master degree the past year. The SM Higgs fixes everything and it closes the SM. It is possible and we could get the dessert up to Planck Scale. However, we have:

    1)Very serious hints of a light Higgs (precision data and 2011 LHC data, excesses around 126 GeV,…).

    2) Dark matter compelling evidences. A light SM Higgs gives no hint about the Nature of Dark Matter (the desert is a big issue). Modifed gravity related to Higgs? No clear way.

    3) Dark energy issues. SM Higgs does not answer it (even as an inflaton like mechanism).

    4) Neutrino masses. Forgetting the seesaw, you could adjust the supertiny neutrino masses with supertiny Yukawas. It can be done. But, why? SM Higgs does not answer it.

    5)The strong CP problem. No SM Higgs explains or suggest why something like a Peccei-Quinn like axion particle should exist.

    6)If the Higgs is 125 GeV, its mass suffers quantum.
    corrections…No SM symmetry protects the Higgs from that. Only a SM Higgs is not enough to understand why those corrections are low. SUSY?Extra Dimensions?

    7) Gravity. Does Higgs couple to (quantum) gravity?Does it modify gravity at some scale? The SM Higgs does not answer it.

    8) Is the SM Higgs fundamental or composite? The SM Higgs gives not hint about its origin, specially to its self-coupling.

    And many many others. I am just also wondering if maybe, the absence (although my spies said IceCube seems to have detected at last two astroneutrinos) of high energy neutrinos could be related to the fermiophobic Higgs somehow…

    • Ervin Goldfain says:

      It has been known for awhile now that discovery of the Higgs alone may spell theoretical troubles in the long run. Your list does not include the fermion flavor problem, discrepancies of the Higgs model with the observed magnitude of the vacuum energy density, the anomalous magnetic moment of leptons and the inability of SM to correctly account for the underlying mechanism of CP violation.

      One can only hope that we are just beginning to understand what is going on and Nature will be generous enough to show us the way.

      • amarashiki says:

        I said “many many others”…;) Thank you for the additional important unsolver problems you quoted…There are many issues that a SM HIggs leaves unsolved. That is why it can not be the final particle!

    • ohwilleke says:

      I would distinguish between Beyond The Standard Model physics, where a SM Higgs together with the absence of a detection of neutrinoless double beta decay that can be replicated, trashes BSM theory space, and Deeper Meaning Behind The Standard Model theories that try to look for deep reasons why the constants and equations have the form that they do.

      An example of a deeper meaning theory might be: “no force mediated by a massless boson can violate CP because the boson travels at the speed of light and does not experience time.” Any question about why neutrinos have the masses they do, is similarly a “deeper meaning” question. The SM answer for why there is no strong CP violation is that you omit the CP violating term from the equation in the SM.

      I’m also not convinced that “dark energy” needs any answer other than that it is the empirically determined value of the cosmological constant of general relativity which is an intrinsic property of space-time.

      The Standard Model doesn’t say anything about gravity, period, but GR absolutely adopts the position that gravitational mass and interial mass are the same, in which case the Higgs does couple to gravity. The Standard Model also adopts the position, as far as I can tell, that the Higgs boson is fundamental rather than composite – one can try to look for a composite non-SM Higgs boson, but the SM answer to the question is pretty straightforward.

      The Standard Model answer to dark matter is that there is no form of undiscovered particle out there so dark matter has to be made of something you’ve already discovered acting in some manner that you’ve failed to model properly, or that gravity equations are wrong in some respect (since they are part of the Standard Model so modifications of them can’t violate the Standard Model). This answer could be wrong, but there is a SM answer.

      • amarashiki says:

        About the strong CP problem. To be more precise in what I meant: the SM does not offer any explanation about why the Theta term piece in the QCD lagrangian is so tiny. Compare the almost absent CP violation from the pure QCD plus theta term with the electroweak source of CP violation. And that is weird. I am aware there has been some proposals to solve the strong CP problem in the SM context. I attended myself as an undergraduate student to a talk by M.GellMann about this kind of SM-solution to the strong CP problem, but I am not convinced it can work. Experiments will enlighten that. I wish.

        Dark energy: the SM does not explain yet why dark energy is so tiny compared with the vacuum energy of quantum fields. CC problem. There are lots of temptative solutions: nonperturbative “instanton-like” terms in the QFT calculation, extra dimensions, and so on. The most conservative solution is to include an instanton-like term in the QFT calculation, but its origin is yet unsolved as far as I know. Nonperturbative effects in QFT related to gravity are not in the SM till now. That is the sense I was meaning.

        ON your DM comment. Well, it is a nominal question. I don’t include DM candidates as SM physics, just in the same way, I don’t consider the inclusion of neutrino masses in the SM as the SM. They are pieces from an “extended” Standard Model we wil have to build in the next months/years. There is no alternative.

        About the Higgs and gravity. If Higgs exist, and since it has mass, I agree it couples to gravity. But how?Minimally?Softly?Non-trivially? I believe the Higgs self-interaction potential should be connected to gravity as well, but the way in which it will be done is essential. Indeed, the Higgs phase of the SM is important in Cosmology (inflation and related topics), so I am wishing what Planck probe is going to show us as well in the next months!

        In summary, I am not saying in any of my comments the SM fails to scales we have probed. Only, that it is not complete. DM or neutrinos are the most clear hints. Dark energy is just likely something related to the way we compute the vacuum energy and it matters as well at very large scales (but why?). The strong CP problem can not be naively solved simply plugging the theta term in the QCD lagrangian to zero, specially considering what CP violations in the electroweak sector do!Why are electroweak CP violations allowed while strong CP violations are so suppresed (sending the theta term to almost a null value)? The answer is not clear at all even if you try to guess a solution in the SM framework! And I don’t like anthropic arguments since they are not scientific!

      • Ervin Goldfain says:

        I fully agree with Amarshiki’s reply. These are serious challenges that cannot be brushed away with handwaving arguments.

      • ohwilleke says:

        My point is simply that a lot of these “deeper meaning” questions that ask “why” something is so, don’t necessary need or have an answer, and even iif they don’t, may not have any phenomenological consequences. The strong CP question is a “why” question, not a “what” question and physics isn’t necessarily about “why”.

  11. admin says:

    What does it taste like?

  12. Lubos Motl says:

    Concerning the 3quarks daily contest, I think we invested too much time into my avatar, Phil. Meanwhile, you forgot about your own name. Did you notice that your official name, Phil Gibbs, is neither Indian/Afghan/third-world nor female?


    How did you exactly want to win the contest? 😉 What you were thinking?

    • Philip Gibbs says:

      I think even if I had fixed all those things it would have been inappropriate for Sean to pick a winner in physics. It’s too close to his own field. 🙂 I suppose it could also be that the winners were better. It brought me 170 clicks. Every little helps.

      • carla says:

        I doubt you get enough clicks so you can give up your day job 😉

      • Lubos Motl says:

        Dear Philip, I share the sentiment that you shouldn’t feel indebted or corrupt because of 170 clicks. Their value is about $0.30 – and most of the people just randomly clicked and were not necessarily interested in anything. Based on the fact that Sean Carroll’s blog entry about the contest has 1 comment after 1 day, I would dare to guess that it is not a terribly serious matter, not even the main branch of it is serious.

        You may and you deserve to make an impact stronger by many orders of magnitude.

      • Dilaton says:

        I voted for Phil`s article but it obviously does not help if one can only do it once … 😛

        Learning about who the winners are by scrolling through the CV article made me turn away after 10s, because the results of the contest are now no longer interesting enough for me … 😉

        I`ve spotted the term “phase transition” in Sean Carroll’ s blog; that could be a valuable explanation why the level of the contest decayed … 🙂

      • Philip Gibbs says:

        I was happy to make the final. The ones that won were interesting and probably much better written than mine. It depends what you are looking for. If you were looking for a blog post that produced plots that would be shown later by a Nobel prize winner at a conference I would have won, but there were other criteria more relevant to what makes a good blog post that I am less good at producing. I wonder if the comic font was also a factor 🙂 and will it be used again at the next Higgs update?

      • wl59 says:

        I also voted for him, although that’s a cracpot blog because most people think there exist a Higgs …

  13. Phil, I found your post here inspiring and in synchronicity with what I was thinking about added five posts to my blog. Essentially I praise the discoveries as a victory for our LCH project of which your cautious questions on the nature of the so called Higgs and their press releases underestimate the significance of the results.

    Lubos posted it as a victory for string theory (if you believe string phenomenology while part of it all and accept statistical evidence) but close to nature where at the falsification its role in a new level of science is born.

    I see it as a victory for most all the issues at the frontiers now of all the things hoped to discover or surprises to encounter- and this will come out as you say eventually. I see Leo has a sense of this when it comes to the black hole like issues. There are alternatives that surpass our current physics but does not undermine the contributions.

    I wonder what the ducks look like to all the large frogs in such a small pond of our theoretical and experimental enquiry?

    Vojata, the strawberries came a little soon this year here but I am not sure if it can be explained by some sort of man made global warming or influences on our expected experiments.

    Perhaps in our useful diagrams of decay we may begin to ask what this Higgs (I suggest we keep the name anyway) may be a broken part from itself. As far as actual measures of some issues we should address this idea of evaporation (the wiki analogy to water) in terms of what is solid or mostly nodes in a vacuum and when the mass, that is at what existential time and point, some quantum leaves or merges with the more general states. Clearly some of it can be put into arithmetical concrete terms, and yes it can go beyond seven dimensions of semi-regular structures to perhaps a better understanding of 16 dimensions and not the 11 or 12 brane basis presented as really a stepping stone along the same lines of what amounts to our common knowledge of Euclidean geometry.

    It will be most interesting to see what they say they found, and caught in their nets, these God-particle butterfly hunters…\

    The PeSla pesla.blogspot. com

  14. WZ says:

    Are stau and stop predicted by SUSY? What SUSY tests exist with the data we will get from the potential Higgs this year (spin, charge, or other SM violations that translate into a SUSY success)? Finally, why no photon polarization filters at the LHC? I can get these at the local store (called sunglasses!). Just kidding – I am sure the wavelength, intensity or polarization resolution is not sufficient otherwise they would be part of the experiment.

  15. Murod says:

    Question related to spin: is it possible that two 1/2-spin fermions annihilate into two photons?Is this option excluded?

    • Leo Vuyk says:

      Electron positron annihilation into two photons is well known.
      In addition however, in my Q-FFF model two colliding Hiiggses are able to produce an electron and a positron, (e.g. at the black hole horizon) and combine into a Z particle or two photons…


    • Philip Gibbs says:

      A fermion and anti-fermion can give two photons. Happens all the time with electrons and positrons.But to expalin the observed results here you would need fermions with mass 63 GeV. You have to explain why these have not been seen before and why they dont show up in different ways, amongst other things.

      • Murod says:

        Maybe for the same reason why Higgs boson have not been seen before?

      • Tony Smith says:

        As to “you would need fermions with mass 63 GeV”
        why not
        decay of a fermion-antifermion pair forming a meson-type thing
        in which one has a mass of around 125 GeV and the other is light
        that decays like a Kaon ?
        My model is not the only such thing. For example, consider
        a technipion like that proposed by Eichten, Lane, Martin, and Pilon
        in arXiv 1206.0186 (in the context of the CDF Wjj bump).

        As to “why these have not been seen before”
        Eichten et al contend that they were seen in the CDF Wjj bump
        and that the ATLAS and CMS “refutations” of the CDF Wjj bump
        are invalid due to background issues,
        not to mention the fact that even CMS claims that its “refutation” is only at the 95 percent CL (which sounds impressive to the general public but is very unreliable in real life – see xkcd.com/882/ ).


      • Philip Gibbs says:

        I think a meson-like things would look a lot like a composite Higgs, so yes that is a possibility.

      • Dirk Pons says:

        ‘A fermion and anti-fermion can give two photons. Happens all the time with electrons and positrons.But to expalin the observed results here you would need fermions with mass 63 GeV. You have to explain why these have not been seen before and why they dont show up in different ways, amongst other things.’

        That was a helpful comment, thank you … obvious in hindsight but worth emphasising …please consider editing it into the main post.

  16. wl59 says:

    The problem however is, that in the gammagamma channel, photons don’t need to be produced to show such peaks. It’s enough if they are just a little frequence-shifted.

    And at least from the 2011 data, it appears that it’s this what happened. Because there are several peaks in the spectrum, and at the side of each peak is a valey. So that the total amount of photons in that interval seems to be the same as the predicted background, and there were not produced any photons, but just background photons shifted.

    Perhaps with the 2012 data it’s different, and they permit a better conclusion. However, for avaliate this, one would need to see these data. Anyway I would be sceptic to trust on the gammagamma data.

  17. Are the clouds a better place to search for the Higgs boson?

  18. amarashiki says:

    I am quite sure this week is going to be memorable and likely historical in the HEP community, and perhaps, one of the most trascendental moments in Science in the beginning of the 21st century. 101 years after the Rutherford’s experiment and the discovery of the atomic nuclei, we are going to explore one of the most enigmatic and mysterious aspects of the subatomic world: the scalar field (fundamental or composite). If some kind of non-standard Higgs boson (fermion-antifermion “preonic” state composite) is announced, it will boost theory and experiment in the next months/years. Moreover, it is quite probable, we are going to need the Linear collider and a muon collider to test the Nature of what that “non-standard” Higgs-like particle does …And too, we will need them to test the New Physics that hides inside the TeV scale and beyond…

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