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CERN | Geneva | Switzerland

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It might look like a Higgs but does it really sing like one?

The special CERN seminar on recent Higgs boson results held yesterday was one of the most exciting presentations I ever attended. The ambiance was electricifying and the room was packed more than two hours before it even started.

Members of each collaboration working on this, namely CMS and  ATLAS, both knew their half of the story. But the two teams had worked independently and all the crucial details of the final results were not known outside the collaborations. Everybody wanted to see if the small excesses observed in their team coincided with similar findings from the other collaboration.

Physicists are notoriously cautious for good reason. To claim a discovery, we ask that if there is only background (and no Higgs), the odds of seeing an excess of event as large as the one observed be less than 0.00003% or 5-sigma.

In the case of the Higgs boson, if we find some signs of its possible presence, we will want it to do much more than just ”look like” a Higgs but also behave like one, smell like one, dance and sing like only that particle can do. As it is, it may look like a Higgs with a mass somewhere around 124-126 GeV but the level of confidence is way too low to draw conclusions. Each experiment has small signals at the 2-3 sigma level, which is what is expected if there is a Higgs boson given current data size. To reach the unambiguous 5 sigma-deviation level will require adding new data.

The higher the number of sigma, the more incompatible the data are with having only background and no Higgs.

Of course, it is encouraging that both groups find similar results, not only in one decay mode, but in multiple channels. A decay channel represents one of the many ways the Higgs boson can decay. As one of my colleagues put it, if the Higgs boson was a large coin, each decay channel would represent one way to break this coin to make small change. CMS and ATLAS collected all events corresponding to specific decay channels. The fact that they all point somewhere to roughly the same mass value is an indication they could all be coming from the same particle.

ATLAS spokesperson, Fabiola Gianotti, presented the ATLAS findings first.

Two separate decay channels both favour a mass value around 126 GeV: Higgs decaying into two photons and Higgs into two Z bosons, with each Z going into a pair of electrons or muons. A third channel with Higgs decaying into two W bosons, each W decaying into an electron or muon plus a neutrino is also consistent with this hypothesis but at a lesser level.

Guido Tonelli, CMS spokesperson, showed the combination of five different channels, adding the Higgs to two taus and Higgs to pairs of heavy quarks to those investigated by ATLAS. The combined results are compatible with a Higgs signal, the highest probability being found at 124 GeV, but not enough data were available to draw any definitive conclusions. The observed excess of events could be a statistical fluctuation of the known background processes, either with or without the existence of the Standard Model Higgs boson in this mass range.

The probability of obtaining an upward fluctuation as large or larger than that is observed if there is only background, prior to accounting for the look-elsewhere effect. As one can see, the excess falls in the same position for two different search channels and is also compatible with a much smaller excess in the third channel. The statistical significance is still modest but having three channels, especially two robust ones, is an indication this could be real. Nevertheless, this is a stronger signal than what was expected from a Standard Model Higgs boson with a mass of 126 GeV, which is shown by the black dashed curved.


The small excess of events observed by CMS in five different decay channels. The dotted line shows what was expected in the absence of a Higgs boson. The green and yellow bands represent the 1-sigma and 2-sigma error margin on this prediction. The black curve is the observed data. Excursions beyond the yellow band indicate where a Higgs signal is the strongest. The most significant value is found for a Higgs mass around 124 GeV.

When all their channels are combined, ATLAS obtains an excess of 2.3 sigma over background, while CMS gets 1.9 sigma, after taking into account the “look-elsewhere effect”, namely how often when looking at all the possible mass points under study would one point fluctuate that much. The chance of obtaining an upward fluctuation this large or larger if there is only background is 1% for ATLAS and about 2.9% for CMS.

Without the “look-elsewhere” correction, the ATLAS probability of such an excess of events if there is only background 3.6 sigma. This value can be compared to the 2.4 sigma deviation one would expect if the excess was due to a Higgs boson. So ATLAS sees slightly more events than what is expected from a Standard Model Higgs boson. Statistical fluctuations can happen in both directions, which is why caution is required until more data is analyzed.

Having already combined all data for 2010 and 2011 from more channels, CMS showed they now exclude all possible Higgs masses from 127 to 600 GeV with a 95% confidence level, leaving only a narrow window open between 114-127 GeV.  ATLAS excludes masses above 131 GeV up to 453 GeV with the same confidence level, but also between 114-115.5 GeV.

The exclusion limits presented by the CMS collaboration. The dotted curve shows what was expected while the black line with dots indicates what is observed. Whenever this curve falls below the red line is excluded. All masses above 127 GeV are now excluded at 95% confidence level.

Of course, everybody would love to be able to say: that’s it! We found it. But it is still premature despite encouraging signs. More data will be collected in 2012. The answer will then become unambiguous: we will either discover the Higgs or rule it out completely. If the small effects presented today keep growing, we will then see the Higgs do its little song and dance.

Pauline Gagnon

To be alerted of new postings, follow me on Twitter: @GagnonPauline or sign-up on this mailing list to receive and e-mail notification.

For more information, visit the CERN website or ATLAS and CMS websites

 

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20 Responses to “It might look like a Higgs but does it really sing like one?”

  1. gunn says:

    It is not Higgs ( http://arxiv.org/abs/physics/0302013v3 ) because every physics event is interpretted by particles which similar well-known elementary particles – leptons, quarks and gauge bozons. Therefore, if anybody will claim that he had found Higgs then not believe – this is not Higgs.

    • Folket says:

      Just because someone has a description of nature which does not require or allow higgs that is not a reason for it not to exists.

      Are you able to show me how your paper better explains the excess in the experiment?

    • gunn says:

      Dear Folket, similar excess since LEP was observed not less than three times – and what?
      And it is clear that all logically superfluous does not exist.

    • Xezlec says:

      gunn: Where are these “similar excesses” you speak of? Please point them out.

    • gunn says:

      Xezlec:
      September 2000, LEP,
      May 2011, Tevatron,
      July 2011, LHC,
      etc.

  2. nc says:

    “The answer will then become unambiguous: we will either discover the Higgs or rule it out completely.”

    That’s exactly the same two-hypothesis fallacy that “proved” the changing position of the sun across the sky is due to the daily orbit of the sun around the earth:

    (1) If the sun’s position in sky changes, it is orbiting the earth.
    (2) If the sun’s position in sky doesn’t change, it is not orbiting the earth.

    Collect as much “hard data” as you want and if you analyse it using fake two-hypothesis Popperian criteria, you can “prove” that the sun orbits the earth daily, no however many sigma you want. Not science!

    Science is not about fiddling your hypothesis testing to only two possibilities produce fake Popperian sigma “estimates”. Science must take account of all possibilities, not merely your contrived mainstream delusions, that the spin-0 boson must be the Higgs boson!

    Sorry to tell you this, but this is a fallacy: the “Higgs boson” is not any old electrweak symmetry breaking spin-0 boson. It’s defined as a particular part of the Standard Model. If you detect an an electroweak symmetry breaking spin-1 boson, there can be no evidence whatsoever that it is the “Higgs boson”. The “Higgs mechanism” is deeply flawed, it is a vague theory which doesn’t predict the mass quantitatively, and a non-quantitative theory is not science. In addition, it’s method of giving mass to weak bosons is intrinsically anti-quantum gravity. We proved in 1996 that the U(1) Abelian hypercharge gauge of the standard model is actually gravity, correctly predicting the cosmological acceleration of the universe two years before it was discovered: http://rxiv.org/pdf/1111.0111v1.pdf

    The electroweak theory of the standard model contains errors, and a spin-0 boson comes from an internal SU(2) electroweak symmetry breaking, not an U(1) X SU(2) Higgs mechanism symmetry breaking. The basic problems are not new:

    “One of us (Wilczek) recalls that as a graduate student he considered the now standard SU(2) x U(l) model of electroweak interactions to be ‘obviously wrong’ just because it requires such ugly hypercharge assignments. … it still seems fair to call the model ‘obviously incomplete’ for this reason.”

    - Savas Dimopoulos, Stuart Raby and Frank Wilczek, “Unification of Couplings,” Physics Today, Oct. 1991.

    “Stephen Weinberg and Abdus Salam tried to combine quantum electrodynamics with what’s called the ‘weak interactions’ (interactions with W’s) into one quantum theory, and they did it. But if you just look at the results they get you can see the glue, so to speak. It’s very clear that the photon and the three W’s are interconnected somehow, but … you can still see the ‘seams’ in the theories; they have not yet been smoothed out so that the connection becomes … more correct.”

    - Richard P. Feynman, QED, 1985, p. 142.

  3. Pauline Gagnon says:

    Sorry, the phrasing misled you. Of course, these two hypotheses have to be tested separately. what I meant to say is that we expect enough data in 2012 to be able to test these two hypotheses, in turns, not together.

    Pauline Gagnon

    • Md Santo says:

      “Top Down Mechanism” vs “Bottom Up Mechanism” on the issues of “God Particle”

      Dear Pauline,

      I have to admit you, part of your sentences I have cited to my article justfor the sake of public information. I’d like to thanking you regarding this and would you please to follow my article as follow :

      Our Human System Biology-based Knowledge Management (HSBKM) model framework , relying on Top Down Mechanism : “Inverted Paradigm Method” by doing a kind of “reverse enginnering” based on “of proof” to a Knowledge-intensive body of Knowledge Management (KM) as applied science (Knowledgeable Science) for the benefit of basic science (Physics) development regarding the issues of “God Particle”.

      On the contrary, Large Hadron Collider (LHC) used by CERN, relying on Bottom Up Mechanism : “Deducto – Hypothetico – Verificative” scientific mind set principles (Scientific Knowledge) regarding the issues of “God Particle”

      What we’ve done, our “Top Down Mechanism” on the issues of Higgs Boson, in reality is to complement the “Bottom UP Mechanism” of what CERN have done on the issues of Higgs Boson

      To get comprehended, would you like to take a visit to our URL http://bit.ly/uUfNPx – “HSBKM vs LHC Higgs Boson”

      Your feedback will be greatly appreciated. Thank you

      Regards,

      Md Santo – moesdar@gmail.comhttp://gravatar.com/mdsanto

  4. Alec says:

    Thanks for help clearing this up! :)

  5. Zephir says:

    In dense aether model the space-time is modelled with water surface: the time dimension is perpendicular to the water surface. The light waves correspond the transverse waves in this analogy. The dimensional scale for their spreading is limited with dispersion at both ends: the tiny ripples are dispersing with Brownian noise, whereas these large ones are dispersing into longitudinal waves at distance. The point is, the geometry of these fluctuations is self-similar: they can be modelled with system of dense packed hyperspheres, which leads into dodecahedral geometry of density fluctuations. At the case of CMBR this geometry can be observed like the peaks at the power spectrum of CMBR field.

    My assumption is, the same feature should be observable at the power spectrum of particle collisions, attributed to Higgs field. IMO Higgs field is simply extremely miniaturized version of dark matter foam, which reflects the symmetry of Universe.

  6. I have a naive question: if the Higgs is only a potential (like Prof.Higgs predicted in the first version of is paper before it was published in Phys Rev) and you do not find the Higgs particle,does it mean that the standard model is dead?
    of course one could say that a potential ‘is’ a particle because it leads to the same effects…

    • Paul Hoiland says:

      That actually is a bit incorrect. Certain Higgsless models have existed for sometime now. There is a mechanism or mechanisms in all these that takes the place of the Higgs. As such it has the potential of the Higgs, but no real Higgs particle exists in these models If the Higgs particle is found to not exist then in essence at least part(that part) of the SM would be proven inccorect and as such false. We would then have to look for a mechanism that takes it’s place like perhaps one of the Highgsless models.

  7. Mario E de Souza says:

    The Higgs boson does not exist simply because quarks are composite. You may say now ‘come on, we haven’t seen it’, and the truth is that we have seen several indications of it. The first one was found in 1956 by Hofstadter when he determined the charge distributions of both nucleons. (one can see them around p. 450 (depending on edition) of the Berkeley Physics Course, vol. 1 (Mechanics)). We clearly see that both nucleons have two layers of internal constituents. Unfortunately these results were put aside from 1964 on due to the success of the quark model and of QCD later on. From 1985 on we began to see more indications of compositeness, but we were so enthusiastic with the SM that we didn’t pay much attention to them. A partial list of them: 1) in 1983 the European Muon Collaboration (EMC) at CERN found that the quarks of nucleons are slower when the nucleons are inside nuclei; 2) in 1988 the SLAC E143 Collaboration and the Spin Muon Collaboration found that the three quarks of the proton account for only half of its total spin (other subsequent collaborations (EMC in 1989 and Hermes in 2007) have confirmed this result which is called the proton spin puzzle); 3) in 1995 CDF at Fermilab found hard collisions among quarks indicating that they have constituents (this was not published because CDF didn’t reach a final consensus); 4) Gerald Miller at Argonne (Phys. Rev. Lett. 99, 112001 (2007)) found that close to its center the neutron has a negative charge equal to -1/3e (inside the positive region with +1/2e); 5) new measurements of the EMC effect have been carried out by J. Arrington et al. at Jefferson Lab and they have shown that the effect is much stronger than was previously observed; 6) the ad hoc terms of the matrix of Kobayashi-Maskawa; etc.
    Gerald Miller wrongly attributed to d quarks the -1/3 charge at the neutron center, but as the neutron ia a udd system we know (from QCD) that none of the 3 quarks spends much time at the center.
    The relevant paper on this subject is Weak decays of hadrons reveal compositeness of quarks which can be accessed from Google (it is at the top of the list on the subjects Weak decays of hadrons, Decays of Hadrons and Weak decays).

    Therefore, we should go back and probe further the nucleons in the low energy scale, and carry on Miller’s experiment with the proton.

  8. Mike says:

    Question A:
    What would have happened if LEP wouldn´t have shut down in 2001 – but pushed to the highest possible energies by repair and installation of all accellerator stations then, and run then for 2-3 years?

    Question B:
    What would have happened if even a smaller version of TESLA would have been built in 2003?

    Question C:
    Would the LHC allow to accelerate also electrons and positrons to
    100-150GeV energies (COG)?

    • Mike himself says:

      Answer A:
      If existing in the energy region left by the LHC now it would have been found twelve years earlier, but then with cleaner signal to noise as can be expected by the LHC experiments.

      Answer B:
      It would have found the Higgs about five years earlier and with better S/N as can be expected by the LHC experiments (ATLAS and CMS).

      Answer C:
      Maybe yes, but not from design, maybe with much extra effort. If nothing really new can be found the next ten years (no Higgs, no SUSY, etc.) an upgrade to SLHC may bring less news than a switch back to a 200 GeV lepton collider.

  9. Gordon says:

    I am not in physics anymore. Some day I noticed that all the particles follow the formula 10^n GeV +/- 2^i 5^j MeV. I am surprised that the
    125 GeV fits that formula also.

  10. anonymous says:

    I think the LHC people should look at all values i,j of 10^n+/- 2^i 5^j MeV to find any weird data. It’s a lot easier then all the continuous data. The formula fits all of the known particles. Could be symmetry.

  11. [...] It might look like a Higgs but does it really sing like one? | CERN | Quantum Diaries [...]

  12. Ignacio Fernandez says:

    Definitive correct , sing Higgs , sing the song , excellent , excellent, that one day we can hear it. thanks team.

  13. Excellent! See my prediction of Higgs at 124.443 (or postdiction, since it wasn’t made public until last Dec.) …
    http://theoryofeverything.org/wordpress/?p=563

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