Of Particular Significance

Day 2 of Higgs Symposium

POSTED BY Matt Strassler

POSTED BY Matt Strassler

ON 01/10/2013

Day 2 of the Higgs Symposium is flying by, with very interesting presentations… and with little time for me to finish the last details of my own talk for tomorrow.  (Tomorrow’s program includes a talk by Professor Peter Higgs himself!)  But here’s a quick summary.

In my last post I mentioned a couple of the early talks; here’s a bit more about the later talks from yesterday, and then a bit about the first part of today.  Caveat: all descriptions below are brief and necessarily incomplete!

Joe Incandela, spokesman for the CMS experiment at the Large Hadron Collider [LHC], presented the Higgs results for CMS.  The data shown has been seen before; but Incandela provided some public insight into why the CMS experiment has not updated their results searching for Higgs particles decaying to two photons.  If I understand correctly what he said, the situation is roughly the following.  In the run-up to the November conference in Kyoto, after re-blinding their data and attempting to improve their techniques (including recalibration of their measurements of photon energies), they looked at their data after unblinding and found some changes from their results in July that were somewhat larger than they naively expected. Concerned they might have made an error, or at least underestimated the size of the uncertainties on their results, they have been going through their methods with a fine-tooth comb, doing many studies.  These efforts have convinced them that no mistake was made, and that their new results are indeed consistent with the older ones, given the size of the uncertainties that they quoted in July.  They’re now applying what they’ve learned to the full 2011-2012 data set, and they aim to present an updated result, and the above-mentioned studies checking their results, for the spring — perhaps as soon as March, perhaps a bit later.

Eilam Gross, co-convener of the Higgs search group at ATLAS, similarly presented results for the ATLAS experiment.  ATLAS, you may recall, also had a little surprise in their recent data, which is why they did not update their results in Kyoto for Higgs decaying either to photons or to two lepton/anti-lepton pairs (often called “four leptons” for short).  We learned about this surprise in December; the two measurements give values for the Higgs mass that differ by a somewhat surprising amount.  ATLAS, like CMS, chose to do many studies to make sure they had made no errors before they released their data; and similarly they’ve concluded there are no errors in their results.  At this point it is widely believed that their mass discrepancy involves an unlikely (but possible) statistical fluke, probably combined with some uncertainties in energy measurements.

An aside: every time in my career that a new particle has been studied for the first time, there was some funny business in the data early on.   This is just something that happens when you have small amounts of data; there are so many weird things that could happen that the probability that one of them will happen is higher than you think.  There’s no evidence that there’s anything truly odd going on.

Riccardo Rattazzi (professor at EPFL in Lausanne, who has shown up on this blog a couple of times before, here and here) then gave a beautiful talk about the possibility that the Higgs particle is a composite object, the way the proton is a composite object made from smaller things.  This possibility is now highly constrained, but not ruled out yet; for it to work presumably requires that the matter particles of the world (the quarks and leptons) are partly composite (meaning they are mixtures of elementary particles and composite particles.)  A generic feature of these theories is that there is at least one “top partner”, a particle resembling the top quark but heavier, with a mass below about 1 TeV.  Searches for such particles at the LHC are now pushing the mass of such particles into the 600-700 GeV; they will get a bit higher using the 2012 data, but ruling out the full reasonable range of possibilities will require waiting for the next proton-proton collision run of the LHC, beginning in 2015.

Sir Michael Atiyah, one of the world’s great mathematicians, whose work has had enormous influence in physics, gave a talk about the relationships between Higgs phenomena and solitons — in particular, magnetic monopoles, instantons and Skyrmions. I won’t go into these interesting objects here, as it would require a long set of articles, but the talk highlighted the role of fields like the Higgs field in both physics and mathematics of the past forty years.

That was yesterday.  As for today…

Howie Haber (professor at the University of California Santa Cruz) gave a fantastic talk about the possibilities, which he has studied actively over his career, that there is more than one Higgs field in nature.  His talk has so many interesting features that I think I’ll devote an entire post to it next week.  But the most important element of his talk has to do with what is known as the “decoupling limit”, whereby there can easily and naturally be a Higgs particle that resembles, but is not, a Higgs of the simplest type — a so-called “Standard Model Higgs”.  The existence of this limit, which he and Yossi Nir described in 1989, explains why, as everyone needs to keep in mind, the fact that the new Higgs-like particle resembles a Standard Model Higgs is not, by itself, strong evidence that the Standard Model is the correct and complete description of all physical phenomena at the LHC.

Next, Misha Shaposhnikov, one of Rattazzi’s colleagues at EPFL, who with Christof Wetterich suggested a scenario that predicts a Standard Model Higgs with a mass in roughly the 123-135 GeV/c² range, gave arguments in favor of his prediction, discussed its implications, and talked about whether it would allow the Higgs to serve as the driver of cosmological inflation (which is the rapid expansion of the early universe thought to explain why the universe is so uniform and geometrically flat).  This also deserves a longer discussion, which I’ll try to provide soon; suffice it to say that the theoretical arguments underlying the prediction are open to question, though the calculations which give the prediction are solid.  Unfortunately, testing whether this prediction does give the right answer, and whether it does so for a deep reason or just by coincidence, is going to be very difficult for the foreseeable future.  I’ll go into this later.

All of these talks are being or will be posted on-line so you’ll be able to read them on your own if you’re sufficiently expert.  I’ll try to boil them some of them down for wider readership next week.

We’re heading into the afternoon talks, so I’ll stop here.

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26 Responses

  1. Living in the UK I grabbed the opportunity of attending, although felt a bit of an impostor since it is 30 years since I was a student of particle physics. It was nice to see some of the old faces still around, albeit somewhat older.

    Every talk was of such a high standard. Shame Professor Higgs was not able to present.

    It would have been if the talks had been recorded. I would have loved to watch them again to see if I could understand a bit more. There seemed to be some controversy over an explicit scale parameter in the gravitational beta function but it went over my head ( like so much else 🙂 ).

    I wonder if there is a consensus amongst today’s physicists is that the hierarchy problem is the current number one most important outstanding problem in HEP.

    1. Hierarchy problem: Close to consensus among high-energy theorists that it is number 2. Number 1 is the problem of dark energy/cosmological constant. If you consider dark energy / cosmological constant to not be a high-energy physics problem, then yes, it is number 1, and widely seen as such — almost every talk at the workshop discussed it in one way or another.

      Sorry you did not say hello! Do so next time.

  2. I just took a look at the participants at the Symposium (or whatever) that Howie Haber chaired (?) at UCSC. It reads like a who’s who, so I am definitely looking forward to the post about his talk, as well as the one about the Higgs driving cosmological inflation. (Can I say TIA?)

  3. The difference in physical effect(quantum action) between theoritical model and its application in expriments, lies in Correspondence principle ?
    This difference was first elucidated by Heisenberg through a thought experiment and Schrödinger equation(non relative), thru quantum state or state vector. Can we say it was the base to describe non local, pseudo scalar Higgs(h) ?

    But in General relativity, Geometric intuition clearly played a strong role, theories of relativity were formulated entirely in terms of geometric concepts. Can we say this is the base to create mass in scalar field of yukawa interaction with vector Higgs(h) ?
    Thus the positive pressure created influence space expansion ?

    1. Geometric intuition has not played as strong a role in particle physics generally as it did in the development of general relativity. However, more generalized and less intuitive notions of geometry do underlie quantum field theory more generally, which is the language of particle physics. This more general approach to geometry is important in supersymmetry, and often plays a role in applications of string theory to particle physics. (Professor Atiyah played a significant role in some of these developments.) I haven’t discussed these issues here because the jury is still out as to whether these geometric viewpoints are really that useful for understanding the Standard Model and other particle physics issues.

      I don’t understand your question about “non local, pseudo scalar Higgs”; I am not sure it makes sense.

      1. Thank you Professor, I must ask ony one question at a time. Iam not sensible to coin “non local, pseudo scalar Higgs”. I confuse….
        Like in thought experiment, the cat is dead and alive simultaneously, Higgs field is in local realism(Principle of locality) and out of local realism – so pseudo scalar- actually it is non local and make Quantum entanglement(Superluminal communication), which supplement gravity(quantum?) without relativity ?
        Iam unsure about its logics.

        1. There is nothing non-local about the Higgs field; nor does it have anything to do with superluminal communication or gravity. The equations that govern the Higgs field and its behavior are local equations, those of an ordinary special-relativistic, local, causal quantum field theory… of the sort taught to first-year or second-year graduate students in their first quantum field theory class.

          1. Yes Professor, it enter cul-de-sac at quantum field theory where polarization and electron positron parity from electrodynamics and special relativity gave masless known particles – and the entry of relativity(special) gave intuition to give mass through Higgs field – where general relativity has been confined to less intuitive notions of geometry in QFT – avoiding curved spacetime. Thus making the intuition of relativity(c^2), a simple mathematical logic without physical effect(quantum action) ?

  4. If time runs slower in stronger gravity, mightn’t that provide sufficient occasion for primordial matter to disperse, without having to undergo unfathomable rates of change of position, or is it more likely that my ability at fathoming is inadequate?

    1. The dilation of time in stronger gravity is already accounted for in calculations of how the universe evolves, using Einstein’s equations. When you calculate, you find it doesn’t “provide sufficient occasion for primordial matter to disperse” — but that was never the problem anyway. The problem is this. The big bang is not an explosion from a point; it is an overall expansion of a space that was perhaps infinite to start with, of matter that was extremely dense and hot. In such a circumstance one would expect the temperature and density at extremely distant locations to be different, because there hasn’t been time for communication between those locations — accounting already for time dilation in stronger gravity. But we measure the temperature and density are nearly constant across the visible part of the universe. Cosmic “inflation” — the unfathomably fast expansion of space — solves this problem in a way that time dilation isn’t nearly strong enough to do.

  5. Thanks for the great article. If you allow, I would like to summarize what you have said or implied.
    a. The mass discrepancy of the new particle, reported by Altas in December last year, is not retracted.
    b. For CMS, the new data has some agreement issues with the last July data. But, any system error as the cause is ruled out. And, the final answer for this issue might not be available for the up-coming March conference.
    c. Someone is now eagerly proposing a composited-higgs model. Seemingly, there is a hint in the “data” that the new particle could be a composite.
    d. If the new particle is composited, then quark must be somewhat composited. But, a composited-quark model is highly constrained.

    Is my summary above accurately reflecting your article? The following is my personal opinion.

    i. The quark-composite idea was killed by the Preon and Rishon Models, as both of them are simply wrong.
    ii. The Higgs field is only a shadow of the Prequark field. Thus, the new particle will be extremely Higgs-like.

    Your article is very much strengthening my opinion.

    1. Here is my commentary on your summary
      a. correct
      b. correct
      c. no. composite Higgs particles have been around for dozens of years; the current versions were proposed about a decade ago; and no, the speaker was not particularly eager; in fact I would say he was moderately skeptical, and merely laid out the options and implications.
      d. more or less right; but the constraints are weaker for heavier quarks, such as the top quark, and the effects of partial compositeness are small for lighter quarks, so they wouldn’t yet have been observed.

      i. wrong; quark compositeness ideas of a non-preon and non-rishon type are alive and well. See the references in Rattazzi’s talk.
      ii. that’s up to you.

      1. Standard model is correct within local realism(Dirac’s logic of mathematics as a means to physical reasoning). It enter cul-de-sac at quantum field theory where polarization and electron positron parity from electrodynamics and special relativity ?
        Supersymmetry try to break the cul-de-sac with the same logic but, out of local realism ?

  6. Dear Prof. Strassler, thanks for this nice overview so far 🙂

    I’d really like to read more about what Sir Michael Atiyah talked about here …

    Looking forward to posts about if the higgs could take the role of an inflaton and to a new multiple higgs post 😀


    1. No, this upper bound isn’t correct. First, the top quark turned out to be heavier than they expected; second, the argument isn’t foolproof; and third, the true upper bound on the Higgs particle’s mass was computed many years earlier.

  7. Eagerly looking forward to your post on whether the 125 Gev Higgs could serve as the driver of cosmological inflation! (I reserve the right not to be overly interested with whether it would do so for a deep reason or just by coincidence 🙂

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