End of Year Higgs Roundup

It has been a sensational year for particle physics with the discovery of the Higgs”-like” boson making front page news and cash stuffed awards going to some of the deserving scientists at CERN who made it possible. Congratulations to them and sympathies to the many people at CERN who were overlooked from the likes of Steve Myers and John Ellis down to the humble post-grad who was pictured falling asleep at the July announcement after having queued all night for his place.

Reuters reports that they will (maybe) finally be able to remove the “-like” at Moriond in March when the analysis of the full dataset is presented. With alternative spin and parity possibilities already ruled out with low to medium confidence many of us have already reached that conclusion. Serious doubters will wait for the self-couplings to be measured in twenty years time before conceding.

In the same Reuters report it is claimed that CERN scientists have “dismissed suggestions circulating widely on blogs and even in some science journals that instead of just one type of the elementary particle they might have found a pair (of particles)” Of course the truth is that every independent blog that has been following the developments has debunked the two-Higgs claim. This is the kind of no-thanks we have become used to for our efforts, Merry Christmas (Update: see comments). To add a little more credance , here is a plot made by merging two plots from the ATLAS conference note on the ZZ analysis.

ZZobsvs125

This shows the observed signal best fit for Higgs to ZZ decays (black dotted line) overlaid on the simulated one-sigma bands for a 125 GeV Higgs boson. This makes it clear that the observed signal is perfectly consistent everywhere with a 125 GeV Higgs within about one-and-a-bit sigma. It is only when they try to do a fit to this data that they get a discrepancy with other observations. Obviously the right conclusion is that it is too soon to do the fit because the error bands below 125 GeV are still widening too rapidly.

All the channels are now giving signals close to the standard model prediction for a Higgs around 125 to 126 GeV. Most of the new data is loaded into the Unofficial Higgs Combination Applet so you can roll your own, but here are the combined signals by channel at 126 GeV on a scale where 1.0 is the standard model cross-section, with statistical only errors

bb  :  1.24 +- 0.40

ττ :  0.4 +- 0.40

WW :  0.63 +- 0.21

ZZ : 0.99 +- 0.16

γγ : 1.77 +- 0.24

All of these are close enough to the standard model signal except perhaps the γγ where the discrepancy appears to be about 3.2 sigma but with systematic errors included this will drop to about 2.5 sigma. CMS have not yet updated this channel and rumours are that they see less excess. It seems daft that they have not released the results yet especially after the ATLAS delay turned out to be a fuss over nothing. Show us what you’ve got, please.

Here too is the unofficial global combination of high-resolution channels (ZZ, γγ) showing an impressive 9.4 sigma signal at 125.5 GeV and just noise everywhere else.

HiggshiresDec2012

Where does this leave us? Everything looks standard-model-like except the diphoton over-excess which may go away. If it stays there is a good chance that it will be explained by new particles such as a charged Higgs or vector-like fermions waiting to show up in other searches. If it goes we have the possibility of split SUSY or perhaps just the standard model at the LHC scale. Many models have been swept away leaving us to contemplate the implications of an unnatural little mass hirearchy. In one year our view of particle physics has moved on a long way. It’s just not clear which direction yet.

31 Responses to End of Year Higgs Roundup

  1. Bob Evans says:

    As the author of the Reuter piece mentioned above, I would like to apologise via viXra and courtesy of Philip to all those bloggers who had already poured scorn on the “Higgs Twins” theory, for unintentionally leaving the impression that all you good folk were as off-the-wall as a certain leading scientific journal. It seems clear that it was the SciAm blog that sent the twins whizzing around cyberspace — and planted them in some newspapers — over the past few days. If I had had more space in what was essentially a catch-up, year-end, look-forward piece for the non-scientific reader I would have quoted a few of you too, honest! Onward to Moriond!

    • Philip Gibbs says:

      Bob, Thanks for clearing that up

    • Ervin Goldfain says:

      Bob, your report says:

      “The latest data we have on this thing we have been watching for the past few months show that it is not simply ‘like a Higgs’ but is very like a Higgs,” said Oliver Buechmuller of the CMS team at CERN’s Large Hadron Collider.

      “The way things are going, by the Moriond meeting we may be able to stop calling it Higgs-like and finally say it is the Higgs,” he told Reuters”

      Is Buechmuller speaking on behalf of the ATLAS team too? Does his statement imply that the twin-peaks result and the diphoton excess are under control now?

      Cheers,

      Ervin

    • Philip Gibbs says:

      I dont think a diphoton over-excess will stop them calling it a Higgs boson. It will just mean that it is either a non-standard Higgs or Higgs plus other particles. To declare it a Higgs they are just seeking to confirm that it has spin zero and plus parity to some unspecified levels of certainty. It is an arbitrary finish line determined by the need to satisfy the Nobel Committee in time for the 2013 awards. If they could determine the quartic coupling this year then that would be made the deciding factor but that will require an ILC

      • Ervin Goldfain says:

        Quoting Matt Strassler:

        “It is correct, however, that the evidence, while very strong, is still not at the point of being so overwhelming that all uncertainties are gone. And no one is afraid to say that. There is clearly something new in the data; exactly what it is, time will tell. We have a strong prejudice as to what it is; if that turns out to be wrong, that will be very exciting. And there’s not much to worry about, since the LHC has still only produced 5% or so of its total data set, and at less than its maximum energy. We will learn a great deal more over coming years.”

        It seems to me that this position makes the most sense at the moment.

      • Philip Gibbs says:

        Obviously it will never be the case that all uncertainty is gone but the evidence *is* overwealming that they have detected a scalar boson that is responsible for electroweak symmetry breaking along the lines of some variant of the Higgs mechanism. It could still be a Higgs doublet or even a pseudoscalar Higgs or (at a stretch) a composite Higgs but that does not stop it from being a Higgs boson. You can argue that this conclusion makes use of theoretical prejudice but it is impossible to interpret any experimental result without applying your prior probabilities for each theoretical model. You would have to have a very strong prejudice against the Higgs mechanism not to accept the evidence at this point.

        Somebody could keep saying that its nature has not been proven until its self coupling is checked to show that it is sitting at the bottom of a Mexican hat potential. They could even say that they need to see the unbroken electroweak phase and check that. The LHC will never be able to do that. The line has to be drawn somewhere. CERN are drawing it where it best suits them as experimenters with a machine of certain capabilities and a long period of shutdown looming. Theorists find it suits them better to accept the clear evidence already collected and move on to the next likely refinement so that they can make further predictions. That is more about the different jobs they have to do than different prejudices.

        If I were being really pedantic I would say that it is not the experimenters right to decide when the Higgs boson has been discovered. They should just keep giving cross-sections and p-values for observations according to various hypothesis. It is up to the theorists to draw conclusions and each theorist may draw different conclusions based on different assumptions.

      • Lawrence B. Crowell says:

        I am pulling for continued diphoton excess. This may indicate charged Higgs, which is a signature of supersymmetry. I have a hard time imagining the world is not supersymmetric. If it is not then there must be some really bizarre structure at work.

        LC

  2. Lubos Motl says:

    …who were overlooked from the likes of Steve Myres and Jon Ellis…

    And whose names were misspelled and mispronounced, right? ;-) I suppose you meant Steve Myers and John Ellis.

    • Philip Gibbs says:

      You have probably noticed by now that I have a little dyslexia and rely on the spelling checker, which does not always help with names. Steve commented here just once, to complain about me misspelling his name. Ellis is actually a Jonathan so it is not clear that Jon is really the wrong shortening even though most people write his name as John. I will correct anyway thanks.

      • Lubos Motl says:

        I’ve never noticed any dyslexia of yours! News to me. Ellis may be a Jonathan but he never uses the shortened first name Jon while he uses John almost everywhere.

  3. Orwin O'Dowd says:

    So Sciam is in a flat isospin… seriously, here’s a neat “isospin symmetric” solution from Japan, and guess what? It predicts a gamgam excess of 56%!

    arxiv:1208.1305v2 [hep-ph]

    I notice, though, a semantic slippage in the usage of the term isospin, which is now assimilated to the symmetry-breaking paradigm.

    Also, they predict a Higgs-top binding, or “heavy top”: now is that the slippery source of these “stop” rumours?

    I still say, no normal Higgs without an isospin solution!

  4. Robert L. Oldershaw says:

    If anyone gets desperate enough to consider a radically different way to quantify the Planck scale, let me know.

    I have one the gives MLT values closely associated with the proton, and therefore avoids the most severe mass hierarchy problem.

    As a bonus, it explains the physical meaning of the fine structure constant.

  5. Ervin Goldfain says:

    @ Phil

    “You would have to have a very strong prejudice against the Higgs mechanism not to accept the evidence at this point.”

    This is a biased viewpoint. It is not about having strong prejudice against the Higgs mechanism. It is ONLY about demanding due dilligence which takes lots of time and patience.

  6. […] have survived problems the absence of the Higgs Boson would have caused, although issues with the Higgs are still causing apocalyptic reactions from some physicists. At least news today is that other […]

  7. Tony Smith says:

    Phil you said “… The LHC will never be able to …
    see … the unbroken electroweak phase …”.

    What are the plans of the physics community
    to see “the unbroken electroweak phase” ?

    Tony

  8. Tony Smith says:

    If the Standard Model holds up as well as it seems to be doing,
    and if the Higgs, Higgs VEV, and all SM particles are below around 250-300 GeV or so,
    then
    why wouldn’t
    “the unbroken electroweak phase” begin to appear
    around 500 GeV or a few TeV ????

    Is the idea of requiring
    “a hundred or even a thousand fold increase in energy”
    based on
    high-energy models like conventional supersymmetry, GUT, superstrings, etc., for which there is no experimental evidence
    but
    which postulate phenomena with energies beyond the reach of the LHC in order to survive in the face of lack of experimental evidence ???

    If so, then why is there no excitement among plain-vanilla Standard Model people about proposals to look for “the unbroken electroweak phase” in the 2015-2020 run of the LHC
    ???

    Does the plain-vanilla Standard Model have no influential advocates ???

    Tony

    • Marc Sher says:

      Tony—-In order to see the unbroken phase, you don’t just need a few hundred GeV of energy, but you need a few hundred GeV of temperature. This means heating up some region of space to a huge temperature. RHIC heats up nuclei to about 1 GeV, but remember that the energy density goes like T^4, so you’d need energy densities 10^10 times those produced by RHIC. Even high energy cosmic rays, which do reach 10^11 Gev, don’t get to high temperatures since there is not enough time for equilibration in a collision. I don’t see any practical way to produce the unbroken electroweak phase in the next century.

      The physics of this is nothing more than the thermodynamics of an ideal Bose gas. No high energy models are needed. One just adds the free energy density of an ideal gas at nonzero temperature to the Higgs potential, and analyzes the resulting potential.

      • Tony Smith says:

        Marc, what you say may be correct but I am having trouble understanding, so please forgive the naivete of these questions:

        It may be beyond this century to produce a RHIC-type heavy nucleus-size region up to a temperature of a few hundred GeV,
        but
        would the LHC produce a proton-size region of that temperature
        and
        would the proton-proton collisions at energies of a few TeV produce events occurring as unbroken electroweak phenomena ?

        As to the time for equilibration in an LHC quark-quark collision,
        even if the unbroken EW phase had not reached equilibrium,
        would there be observable nonequilibrium processes that might be an identifiable signature of unbroken EW phenomena ?

        Thanks for your discussion. It is very helpful in my efforts to understand.

        Tony

      • Marc Sher says:

        Tony, your questions are good. It is actually more complicated. In order to restore the electroweak symmetry, one must heat the background Higgs field to a temperature of a TeV, and the region of high temperature be coherent over a size which must exceed the critical bubble size. A long time ago, I wrote a paper with John Ellis and Andrei Linde looking at whether a high energy cosmic ray collision could touch off the decay of a metastable vacuum (as they can in bubble chambers). It’s at Phys.Lett. B252 (1990) 203-211. Doing the same analysis for the Standard Model symmetry restoration shows that you need a LOT more energy than 1 TeV, since you must produce a cascade of Higgs bosons….anyway, the paper was pre-arxiv, so you might need a library to get behind the firewall…

      • Tony Smith says:

        Marc, thanks for the reference to your paper Phys.Lett. B252 (1990) 203-211.
        I found it available (for free) on CERN CDSweb and here are some quotes from it, followed by some questions:

        “… Arnold … show[ed] that the number of quanta required to be produced …[to]… induce the transition if our vacuum was unstable … was large: N greater than 100

        In order to get a more precise idea of a possible spatial distribution of the Higgs bosons produced in the cosmic ray collisions … Let us consider ultra high energy quark-antiquark annihilation with Higgs boson production …
        this reaction … looks like a chain reaction q + qbar to PHI to 3 PHI to 3^2 PHI to 3^3 PHI …
        The first scalar particle produced has a very big energy E equal to the sum of energies of the two quarks, but zero momentum (… c.m.s. …).
        Therefore the cross-section of the multiple Higgs boson production is sphereically symmetric.
        This symmetry is spontaneously broken since each decaying HIggs boson produces three bosons moving away from the enter with energy ((E/3). Each of such bosons produces 3 new bosons with energy O(E/9), etc.
        This process goes on until N = O(E/mH) nonrelativistic Higgs particles are produced. …
        At the last stage the decaying Higgs particles are nonrelativistc, so they move in all directions and collide with each other in a small domain of size O((1/3)(1/mH)) …”.

        Question 1: Is the following a reasonable application of the ideas in the paper ?

        If mH = 125 GeV, then the size of the small domain is O(1 / 375 GeV).

        In order to get up to N = 100,
        the energy of quarks in the collider needs to be roughly 100 x 375 = 37,500 GeV
        which would have been in range of the SSC if it had been built for 40 TeV.

        With LHC maximum energy of 14 TeV,
        the number N of Higgs would be roughly 14,000 / 375 = 37.

        Looking to the future, Philip Gibbs estimated (on his blog):
        “… If they could revive the tunnel of the abandoned SSC collider in Texas and use niobium-tin magnets it would be possible to build a 100 TeV collider, but the cost would be enormous. …”.
        That would give N roughly 100,000 / 375 = 266 Higgs in the small domain.

        Question 2: Is the 125 GeV Higgs mass state too far from the vacuum instability region for the circumstances of Question 1 to be effective ?

        LHC analysis of the ZZ to 4l channel shows a peak around 270 GeV with cross section somewhat over 20 per cent of that expected for a Standard Model Higgs (see the viXra unofficial HIggs Combo in this blog entry)
        It is only an almost-3-sigma peak now and may go away with further data around 2015,
        but If that peak persists and turns out to be a 270 GeV mass state of the Higgs
        then
        the chart in the Phys.Lett. paper indicates that such a heavy Higgs might live in a region of vacuum instability.

        Questions 3-4: Applying the above reasoning to a 270 GeV Higgs state
        would give N = 100,000 / 810 = 123 Higgs in the small domain.
        Could that produce interesting vacuum phenomena ?

        Would that make building a new SSC for 100 TeV a good idea,
        both as physics
        and
        as a big public works project that could give jobs to lots of USA workers ?

        Tony

      • Marc Sher says:

        Tony–brief response here (you can email me for more discussion, although the paper was 23 years ago). 1. At a pp collider, the average quark energy is about 1/6 of the total energy, so 37.5 TeV quarks would need a collider well over 100 TeV. 2. Instability issues arise if it is ONLY the standard model up to a high scale – 125 GeV is right on the edge (note that the 1990 paper was before the top discovery). If there’s another Higgs at 270, all of the instability issues change dramatically, since it’s a two-Higgs model. 3. Again, the factor of 6 hurts. 4. I’m not willing to say whether a 100 TeV hadron collider is worth the investment until we have more LHC data.

  9. Sankaravelayudhan Nandakumar Nandakumar says:

    New Pauli exclusion principle observed from ejection of blackhole regions out of colloding galaxies:

    Modification is required in atomic structure formulated by Neil Bohr based on colliding galaxies that provides the direction of ejection of blackhole dots as the electron spin in opposite directions for a merger and blackhole dot production for transfer of energy in between orbits that really for tractor waves in between electron orbits and even cooper electron pair merging is always ejecting a blackhole dot for energy trnasfer based on Hubble telescope observer Astrogeneticist Sankravelayudhan Nandakumar.

    Tractor beams are a well-known concept in science fiction. These rays of light are often shown pulling objects towards an observer, seemingly violating the laws of physics, and of course, such beams have yet to be realised in the real world. Haifeng Wang at the A*STAR Data Storage Institute and co-workers have now demonstrated how a tractor beam can in fact be realized on a small scale. “Our work demonstrates a tractor beam based only on a single laser to pull or push an object of interest toward the light source,” says Wang.

    Based on pioneering work by Albert Einstein and Max Planck more than a hundred years ago, it is known that light carries momentum that pushes objects away. In addition, the intensity that varies across a laser beam can be used to push objects sideways, and for example can be used to move cells in biotechnology applications. Pulling an object towards an observer, however, has so far proven to be elusive. In 2011, researchers theoretically demonstrated a mechanism where light movement can be controlled using two opposing light beams — though technically, this differs from the idea behind a tractor beam. Your recent email to Professor Hawking [Incident: 121224-000008 news@nature.com

  10. Frank Close says:

    I hope the digamma excess holds up, as any new heavy charged particles will occur in the loop at the same order as t and W. I note that charged Higgs is mentioned. However, the Bs to 2mu decay, which isnt mentioned here (maybe Ive missed it) fits with W+W- loop so perfectly (Gilman and Wise predicted it decades ago, so its a remarkable result) that it suggests either no charged Higgs, or one very far away, or some conspiracy. Whats the consensus on the implications of the Bs data on the status of BSM?

    • Marc Sher says:

      Frank—in the type II 2-Higgs model, there is already a lower bound of 340 GeV on the charged Higgs mass from b –> s gamma, and that is high enough to make bounds from Bs to 2mu relatively unimportant (slight slices of parameter space). In the type I model, the charged Higgs can be lighter, but is also somewhat fermiophobic, so no bounds can be reached.

  11. Robert L. Oldershaw says:

    New rumors: 5-sigma mystery bump at 105 GeV, and another excess at 60 GeV.

    No doubt particle physicists have many explanations ready to roll out if these bumps hold up.

    Are there any conceivable phenomena for which particle physicists could not manufacture =/> 5 unique explanations?

  12. […] Higgs because CMS and ATLAS have already set lower limits around 300 – 400 GeV for H++. In a comment here yesterday on the digamma excess Frank Close pointed out that if a doubly charged Higgs is responsible for the […]

    • Frank Close says:

      My comment was for H^+ not H^++ and the role of Bs to mu mu in (e)limi(na)ting this. Thanks to Marc Sher for pointing out b to s gamma limits M>340Gev already. Ive always felt there is wriggle room in the b to s gamma but if limits are similar to Bs to mu mu I am happy to stop wriggling :)

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