Higgs Spin (Is It really a Higgs then, finally?)

CERN have a new press release out today while latest results are being presented at the QCD part of the Moriond conference. There are further updates since last week including the long awaited CMS results for the diphoton decay channel. The diphoton rate relative to standard model is now 0.8 +- 0.3, much lower than before and a huge disappointment for hopes of beyond-standard-model physics.


In the press release the CMS and ATLAS spokespeople are quoted as follows

The preliminary results with the full 2012 data set are magnificent and to me it is clear that we are dealing with a Higgs boson though we still have a long way to go to know what kind of Higgs boson it is.” said CMS spokesperson Joe Incandela.

“The beautiful new results represent a huge effort by many dedicated people. They point to the new particle having the spin-parity of a Higgs boson as in the Standard Model. We are now well started on the measurement programme in the Higgs sector,” said ATLAS spokesperson Dave Charlton.

So does this mean that they have officially conceded that it really is the Higgs boson and not some HHiggs-like imposter? The official line is now that “they find that the new particle is looking more and more like a Higgs boson, the particle linked to the mechanism that gives mass to elementary particles. It remains an open question, however, whether this is the Higgs boson of the Standard Model of particle physics, or possibly the lightest of several bosons predicted in some theories that go beyond the Standard Model.”

It’s a bit meally mouthed but nevertheless, most c0mmentators are interpreting this to mean that they have agreed that it is a Higgs boson of some sort.

The crux was the spin measurements which both teams agree disfavours spin 2 with positive parity at a 2 to 3 sigma level. The real Higgs boson has spin zero with positive parity and all other spin possibilities are directly ruled out by the fact that  it decays to two spin-one photons. Negative spin zero is not quite so strongly ruled out but this is not being billed as such an important observation.

particle propertty Can it be determined with LHC run 1 data? Does CERN think it is deterministic for a Higgs boson? current status
Decay modes YES YES WW,γγ,ZZ,ττ observed, bb,Zγ,μμ etc ongoing
Other Production modes NO NO gluon fusion OK, VBF, VH and ttH ongoing
no exotic decay modes NO NO preliminary results from ATLAS
Spin = 0 YES YES spin zero verified to about 2 or 3 sigma in each experiment
Parity = positive NO NO negative parity is disfavoured but not ruled out
W fusion NO NO nothing yet reported
Higgs self-coupling NO NO nothing yet reported

In summary, the things that CERN has decided are crucial for determining that this is a Higgs boson are thankfully exactly the things that can be determined from run 1 but there are plenty of other observations to keep them busy for run 2 and beyond.

20 Responses to Higgs Spin (Is It really a Higgs then, finally?)

  1. […] ¿Qué ha pasado hoy en Moriond QCD con el canal difotónico en CMS? Pues muy sencillo, el exceso observado en julio ha desaparecido por completo. El cociente entre la tasa de eventos en este canal predicha por el modelo estándar y la observada es μ = 0,8 ± 0,3 (para el modelo estándar μ = 1). La gran desviación (a más de dos sigmas) observada con anterioridad ha desaparecido por completo. ¿Por qué no se proclama entonces el descubrimiento de “el” Higgs en lugar de “un” Higgs? Porque ATLAS sigue mostrando un exceso en este canal (que está disminuyendo) y además porque podría ocurrir que “el Higgs” descubierto sea el primer miembro de una familia de Higgs. Hasta que no se descarte que “el Higgs” no corresponde a las predicciones de la supersimetría o de los modelos 2HDM, la dirección del CERN seguirá siendo reticente a hablar en público de “el Higgs” (aunque los demás, yo mismo incluido, podemos hacerlo desde hace mucho tiempo). En mi opinión, hasta que no se combinen los datos de CMS y ATLAS duplicando la estadística, el CERN no dará su brazo a torcer y hablará abiertamente de “el Higgs” (comparte mi opinión Philip Gibbs, “Higgs Spin (Is It really a Higgs then, finally?),” viXra blog, Mar 14, 2013). […]

  2. Lubos Motl says:

    “…or possibly the lightest of several bosons predicted in some theories that go beyond the Standard Model.”

    As many recent papers showed, this is really a misleading sentence because there may still be Higgses, such as the other one in MSSM, which are lighter than this 126 GeV one.

  3. Ervin Goldfain says:

    Phil, thanks for the report.

    Your table shows that run 1 has given us compelling answers on two out of seven properties of the Higgs-like resonance. But there are five entries with no answer yet and the expectation is that run 2 (and beyond) is going to seal the deal.

    How confident shall one be that no anomalies on gluon fusion, Higgs self-coupling or rare decays will surface in run 2? Are the CERN leaders ready to declare that this is very unlikely to happen, based on current results? And where does this leave us in terms of the unresolved fine-tuning problem, among other open issues?

    • Mr. Day says:

      I suspect that CERN leaders will declare that they require more data to answer your questions. Then, it’s just a matter of how much data. Run 2 is expected to produce 300 fb^-1 over several years (as opposed to about 25 fb^-1 over two). Then, the HI-LHC is expected to produce 3000 fb^-1 over several years, after the injector complex is upgraded.

      For the Higgs self-coupling, my guess is that you need enough energy to pair produce Higgs bosons, and plenty of them. A simple search seems to confirm this[1]. These guys estimate that you need around 1000 fb^-1 at 14 TeV to pin this down.

      I’m not going to comment on other aspects, as I’m not sure why they were included. I thought that gluon fusion and VBF were “obviously” occuring and were “obviously” available as production modes for the Higgs.

      As for fine-tuning, the Higgs reduces the fine tuning problems of the masses of many particles down to a single fine tuning problem. I’d be interested to know if people believing knowing the mass of the Higgs settles anything about this problem, but I really doubt it. You’d need a much more detailed account of the coupling properties of the Higgs to extrapolate backwards to the masses of the elementary particles.

      [1]: http://arxiv.org/pdf/1206.5001v2.pdf

      • Ervin Goldfain says:

        Knowledge of the self-coupling is essential in confirming that the Higgs mechanism is the true source of electroweak symmetry breaking. It is also a critical piece of the fine-tuning and vacuum stability problems, along with an in-depth knowledge of physics that may surface above the low TeV scale. With so much unknown territory and so many surprises possible, I have the feeling that CERN leaders are only selling half of the story to the general public.

    • Philip Gibbs says:

      We should not be at all confident that there are no anomalies in Higgs properties. CERN would obviously be the last to declare such a thing and it will require an ILC to get at all the details. At this point I cant even say if I think that such anomalies are likely or unlikely to be found. It could go either way.

      • Ervin Goldfain says:

        Well said.

      • carla says:

        OT, but will you be doing a post on the latest 113th LHCC Meeting that looked at 2012 performance?

      • mfrasca says:

        I see anomalies already now in their data. CMS presented a more precise cross section for WW decay. They get a smaller value with respect to the Standard Model and is an evident clue for an impostor. ZZ decay, even if is more fluctuating due to a reduced dataset for this channel, is perfectly consistent with the WW case. These are golden channels for the discovery of non-standard behaviors of this Higgs particle and if there exist other heavier excitations as their data seem clearly hinting to. They see such excited states as fluctuations because they are evaluating them using the “glass” of the Standard Model but these states are simply strongly depressed with respect the observed ones. So, I am somewhat optimistic about this situation and I would not tear my hairs off for the current outcomes from CERN. In any case, we can have variations as large as 20-30% with respect to the cross sections of the Standard Model and we are not able to appreciate them yet with the given data.

  4. Tony Smith says:

    As mfrasca said “… we can have variations as large as 20-30% with respect to the cross sections of the Standard Model and we are not able to appreciate them yet with the given data …”.

    That is clear from the CMS High Mass Higgs to ZZ to 4L / 2l2tau plot shown on this blog at vixra.files.wordpress.com/2013/03/mzzcms2.png
    in which the Brazil Bands have not yet been pushed down by data accumulation to be well below 20 per cent.
    That plot shows 3 possible peaks (around 200 GeV, 270 GeV, and 320 GeV) that might either go away with more data or remain as real higher-mass Higgs states with cross sections as described by mfrasca.

    All that is consistent with the CERN press release statement that the observed 125-126 GeV Higgs might be
    “… possibly the lightest of several bosons predicted in some theories …”.


  5. Do you guys *really* believe that Higgs boson gives mass to other particles? Based on my theory you don’t need any high energy boson to do that. Current particle physics is went all wrong. Bold claim but so true… and I can prove it.

  6. mike says:

    They can’t have it both ways, either its standard model Higgs and there is no reason to build the ILS (what justification would you use to fund it if there are no indications beyond the standard model) or you have BSM and a reason to spend new money (probably wouldn’t be funded in this climate anyway)

    • Philip Gibbs says:

      They dont know if it is SM or BSM which is why they may need an iLS. The ILS would be a top/Higgs factory measuring their properties to high precision, The question is over whether it could do significantly better than the LHC and HL-LHC can do.

  7. Orwin O'Dowd says:

    1. TOE = {TOE} or there could be no TOE.
    2. Hence there are not Cartesian brackets { ,{}} and no dimensions.
    3. Importantly, this means (semantic inference) that TEO must be discontinuous: only discontinuous mappings of plane onto line etc. exist.
    4. It follows that we have to integrate gravity *across* quantum jumps, which then requires a statistical construal, in Banach space, not Hilbert space.
    5. No amount of gawking at the odd logic of superposition etc. will ever do anything for TOE, nor will any continuum theory.

    Hypothesis: there exists somethign like N-4 SYM in the vacuum, which gives that sort-of gluino trace from the last LHC1 report. The Higgs is then the heaviest resonance in nature, and must be breaking the symmetry of matter and anti-matter.

    Thanx to Pappus of Aleandria for the method of analysis and synthesis (hypothesis). And that classical paper On the Wisdom of Bees, which gave us…uh, Intelligent Design.

    I’m out of here, before the D-brain (Dennet, Dummett, Dawkins) brigade hear about this….

    • My dad has kept bees for as long as I can remember…They are interesting creatures…sometimes people would walk up quietly to my cubicle and then set there for a minute and then say “It’s like being gently set down by an angel…” and then someone would say “Shhh you’re not supposed to talk about that..” and I would be like, “what, did I miss some joke?” and then a boss would walk by screaming about Stephen Hawking and gravity… and I’m just a programmer, trying to survive… is a theory necessary? Is it scary without one?

  8. Orwin O'Dowd says:

    Norbert Weiner, of cybernetics fame, used to bust in on his graduate students at MIT, smoking a cigar, and intone: “Information is entropy!” which is untrue, of course, and was then disproved three times in the literature, but the myth had taken root, and is still alive. It sounds like Stephen Hawking got his message mixed up with the Big Bang deregulation in finance, which was bankrolling a new wave of merchant adventuring into space. Google’s Larry Page speaks of a lifetime commitment to it.

    My worry now is that Georg Cantor tried to interest theologians in his transfinite arithmetic, and ran smack into a theological prejudice against the “actual infinite”. The conjecture about dimensions is due to Dedekind, who was more diplomatic, and proven correct. But the professional philosophy of the Theory Age was finitist, and is now closed in on itself in a private conversation. That set me muttering about taking them to court under Anti-Trust legislation…

    • Stephen Crowley says:

      This was at my old job working for that dumbass group of privacy invading excuse making billegerant assholes known as Yahoo , they had a deal with Fox News and were doing some very nefarious things with satellite feeds, but that is in the past, I know now that when that boss tried to “name drop” the show “Big Bang Theory” in my vicinity as if something amazing was happening was just an attempt to try to relate to me, and so in retrospect is endearing but still insulting and presumptive that I even watch television or approve of their function and status as a cultural symbol. My new job is mostly over the internet so I don’t have to worry about peoples weirdness as much.

  9. Orwin O'Dowd says:

    Ten Myths of Modern Analysis: http://arxiv.org/abs/1202.4153

    All very well, gives you the story of model theory, but what we face now interpreting these LHC results is Galois’ blessed Absolute Group taking its slow revenge an all unbelievers…

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