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Aidan Randle-Conde | Université Libre de Bruxelles | Belgium

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Higgs Convert

Since 4th July 2012, the physicists at CERN have had a new boson to play with. This new boson was first seen in the searches that were optimised to find the world famous Higgs boson, and the experiments went as far as to call it a “Higgs-like” boson. Since then there has been an intense program to study its spin, width, decay modes and couplings and so far it’s passed every test of Higgs-ness. Whether or not the new boson is the Standard Model Higgs boson is one of the most pressing questions facing us today, as there is still room for anomalous couplings. Whatever the answer is, a lot of physicists will be pleased. If we find that the properties match those of a Standard Model Higgs boson exactly then we will hail it as a triumph of science and a fitting end to the quest for the Standard Model which has taken the work of thousands of physicists over many decades. If we find some anomaly in the couplings this would be a hint to new physics hiding “just around the corner” and tease is with what we may see at higher energies when the LHC turns on again in 2015.

A candidate for a Higgs boson decaying to two tau leptons (ATLAS)

A candidate for a Higgs boson decaying to two tau leptons (ATLAS)

For those who have read my blog for a long time, you may remember that I wrote a post saying how I was skeptical that we would find the Standard Model Higgs boson. In fact I even bet a friend $20 that we wouldn’t find the Standard Model Higgs boson by 2020, and until today I’ve been holding on to my money. This week I found that ATLAS announced the results of their search for the Higgs boson decaying to two tau leptons, and the results agree with predictions. When we take this result alongside the decays to bosons, and the spin measurements it’s seems obvious that this is the Higgs boson that we were looking for. It’s not fermiophobic, and now we have direct evidence of this. We have see the ratio of the direct ferimonic couplings to direct bosonic couplings, and they agree very well. We’d had indirect evidence of fermionic couplings from the gluon fusion production, but it’s always reassuring to see the direct decays as well. (As a side note I’d like to point out that the study of the Higgs boson decaying to two tau leptons has been the result of a huge amount of very hard work. This is one of the most difficult channels to study, requiring a huge amount of knowledge and a wide variety of final states.)

Now the reason for my skepticism was not because I thought the Standard Model was wrong. In fact the Standard Model is annoyingly accurate in its predictions, making unexpected discoveries very difficult. What I objected to was the hyperbole that people were throwing around despite the sheer lack of evidence. If we’re going to be scientists we need to rely on the data to tell us what is real about the universe and not what some particular model says. If we consider an argument of naturalness (by which I mean how few new free terms we need to add to the existing edifice of data) then the Higgs boson is the best candidate for a new discovery. However that’s only an argument about plausibility and does not count as evidence in favour of the Higgs boson. Some people would say things like “We need a Higgs boson because we need a Brout-Englert-Higgs mechanism to break the electroweak symmetry.” It’s true that this symmetry needs to be broken, but if there’s no Higgs boson then this is not a problem with nature, it’s a problem with our models!

The fact that we’ve seen the Higgs boson actually makes me sad to a certain extent. The most natural and likely prediction has been fulfilled, and this has been a wonderful accomplishment, but it is possible that this will be the LHC’s only new discovery. As we move into LHC Run II will we see something new? Nobody knows, of course, but I would not be surprised if we just see more of the Standard Model. At least this time we’ll probably be more cautious about what we say in the absence of evidence. If someone says “Of course we’ll see strong evidence of supersymmetry in the LHC Run II dataset.” then I’ll bet them $20 we won’t, and this time I’ll probably collect some winnings!

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  • http://up211.wordpress.com/ LizR

    I take it this vindication of the SM has nothing to say about the 95% of the universe’s mass-energy about which we know nothing… So I wouldn’t feel sad or pop the corks quite yet.

  • Tienzen (Jeh-Tween) Gong

    @ Aidan Randle-Conde:

    A very interesting article. I get three points from it.

    Point one: Before November 29th, 2013, we were not sure that the newly discovered particle (with 126 Gev) is a SM Higgs, as you wrote, “Whether or not the new boson is the Standard Model Higgs boson is one of the most pressing questions facing us today [November 29th, 2013?] , as there is still room for anomalous couplings.”

    Point two: You are now a Higgs convert after the Atlas announcement, as you wrote, “This week I found that ATLAS announced the results of their search for the Higgs boson decaying to two tau leptons, and the results agree with predictions. When we take this result alongside the decays to bosons, and the spin measurements it’s seems obvious that this is the Higgs boson that we were looking for. It’s not fermiophobic, and now we have direct evidence of this.”

    I have two comments on this.
    i. CMS has a similar claim on this in March this year. That is, the Atlas claims is nothing new.
    ii. The original Higgs mechanism is only a reverse-engineering for the weak processes and does not encompass the other processes. Thus, even after the discovery of this new particle, many prominent physicists do not connect the Higgs mechanism with the other processes, such as, the article by Sean Carroll on (November 13, 2012): “Top Ten Higgs Boson Facts (at http://www.preposterousuniverse.com/blog/2012/11/13/top-ten-amazing-higgs-boson-facts/ )”. The 8th fact is (8.) Your own mass doesn’t come from the Higgs. And, the theoretical Physicist Matt Strassler wrote on October 28, 2013 at (http://profmattstrassler.com/2013/10/28/quantum-field-theory-string-theory-and-predictions-part-5/ ), ” [This is one of the reasons why the naive statement that the Higgs field is responsible for all mass in the universe is dreadfully wrong (Why the Higgs and Gravity are Unrelated, … ); even if the Higgs field were zero and the quarks were massless, the protons and neutrons that provide you with most of your mass would still have masses.]” Thus, there is another mechanism to account for the mass of ordinary matter, and it is known by many prominent physicists.
    iii. There are many other models which can account for this one data point of Altas.

    Point three: You do know that the Higgs is, at best, a supporting actor in the nature’s story, as you wrote, “The fact that we’ve seen the Higgs boson actually makes me sad to a certain extent.” In fact, you are not alone. The discovery of this new particle *alone* was viewed as a nightmare by many prominent physicists, such as,
    A. In the article “What *Should* We Be Worried About? (http://www.math.columbia.edu/~woit/wordpress/?p=5465 ), the Higgs connotes a great crisis of physics.
    B. Jester (Résonaances, http://resonaances.blogspot.com/2013/08/what-about-b-to-k-star-mu-mu.html ) showed his trademark pessimism and frustration in August 2013.
    C. In the article “the crisis in modern physics, (http://www.math.columbia.edu/~woit/wordpress/?p=6238 ), Turok (Director of Perimeter Institute) said, “Theoretical physics is at a crossroads [after the Higgs] right now…In a sense we’ve entered a very deep crisis.

    A good nature story *must* encompass (resolve) the following issues.
    a. The theoretical base for the free parameters (the Cabibbo and Weinberg angles, Alpha, mass-charges, etc.)
    b. Quantum / gravity unification
    c. String unification (the theoretical base for the Standard Model particle zoo)
    d. Planck data (dark mass and dark energy)

    Higgs can help none for the above, that is, it is useless for the advancement on these future issues. By hugging a useless, we will simply sit in this Higgs-crisis pit without any desire to get out of it.

  • http://aidanatcern.wordpress.com Aidan Randle-Conde

    Hi Tienzen, thanks for your comment!

    Point 1: At which point someone decides that the new particle is the SM Higgs boson is largely up to the individual, as we’ll never be 100% certain. For me I drew the line at seeing both fermionic and bosonic decays at the expected rates- as far as I’m concerned that removed the last area of reasonable doubt. Many people were convinced long before this month, and people will stay open minded. To be clear, we should take “today” with a pinch of salt :)

    Point 2i: I am aware of the results presented by both ATLAS and CMS at Moriond 2013, as well as some of the internal results before the announcement. However I decided to wait until the signal strength improved and wait until the results were announced publicly, using state of the art techniques. (In fact I’ve been waiting since July 4th 2012- quietly watching as the results improve and the methods of analysis become more sophisticated.)

    There are, of course, still many problems that need to be solved. If the Higgs discovery was the lowest hanging fruit that the LHC has to offer, then we have our work cut out for us in Runs II and III!

  • http://quantumostinato.blogspot.com laboussoleestmonpays

    @ Tienzen

    The “good nature story” you talk about at the end of your interesting comment looks like The Theory Of Everything and I am afraid you cannot find any serious scientific theory that claims to encompass so many issues !
    One word also about your point 3 (not addressed by Aidan) that deals with what one could call the “post-Higgs sadness” of Jester (and some other courageous physics phenomenologists looking for a needle of experimental facts in a haystack of theoretical ideas). You wrote ” the Higgs is, at best, a supporting actor in the nature’s story”. Well let me tell you that some reliable theoretical physicists would definitely not agree with such a statement. It could be that the very particular Higgs boson that has been discovered in the 1st run of LHC up to 8 TeV is the lead actor for
    i) a better understanding of the very specific spontaneous-symmetry breaking of the electroweak gauge-symmetry (thanks to the noncommutative standard model for instance)
    ii) a possible reappraisal of some non supersymmetric SO(10) grand unified theories (like Pati-Salam type models)!