Of Particular Significance

A Flash in the Pan Flickers Out

POSTED BY Matt Strassler

POSTED BY Matt Strassler

ON 08/04/2016

Back in the California Gold Rush, many people panning for gold saw a yellow glint at the bottom of their pans, and thought themselves lucky.  But more often than not, it was pyrite — iron sulfide — fool’s gold…

Back in December 2015, a bunch of particle physicists saw a bump on a plot.  The plot showed the numbers of events with two photons (particles of light) as a function of the “invariant mass” of the photon pair.  (To be precise, they saw a big bump on one ATLAS plot, and a bunch of small bumps in similar plots by CMS and ATLAS [the two general purpose experiments at the Large Hadron Collider].)  What was that bump?  Was it a sign of a new particle?

A similar bump was the first sign of the Higgs boson, though that was far from clear at the time.  What about this bump?

As I wrote in December,

  “Well, to be honest, probably it’s just that: a bump on a plot. But just in case it’s not…”

and I went on to describe what it might be if the bump were more than just a statistical fluke.  A lot of us — theoretical particle physicists like me — had a lot of fun, and learned a lot of physics, by considering what that bump might mean if it were a sign of something real.  (In fact I’ll be giving a talk here at CERN next week entitled “Lessons from a Flash in the Pan,” describing what I learned, or remembered, along the way.)

But updated results from CMS, based on a large amount of new data taken in 2016, have been seen.   (Perhaps these have leaked out early; they were supposed to be presented tomorrow along with those from ATLAS.)  They apparently show that where the bump was before, they now see nothing.  In fact there’s a small dip in the data there.

So — it seems that what we saw in those December plots was a fluke.  It happens.  I’m certainly disappointed, but hardly surprised.  Funny things happen with small amounts of data.

At the ICHEP 2016 conference, which started today, official presentation of the updated ATLAS and CMS two-photon results will come on Friday, but I think we all know the score.  So instead our focus will be on  the many other results (dozens and dozens, I hear) that the experiments will be showing us for the first time.  Already we had a small blizzard of them today.  I’m excited to see what they have to show us … the Standard Model, and naturalness, remain on trial.

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47 Responses

  1. BTW, “flash in the pan” does not come from gold prospecting. It refers to an embarrassing failure to fire a flintlock musket.

  2. Matt, must we conclude you had some advance warning that the bump disappeared, from the fact you already have a talk planned whose title reflects the let-down? [Please don’t read that as accusatory or snarky, I’m really curious]

    1. Body language. Lack of smiles. Scheduling the talks in an obscure parallel session with nothing planned at CERN. It was clear there was no discovery; the only thing that wasn’t known was whether there was evidence *against*. (Of course, I could always change my title and presentation at the last minute, so there was no cost to choosing the one I did.)

  3. Matt,

    Thanks for the update, not a disappointing result but just part of the screening process, I suppose.

    On the subject of LHC data released to the public, what will the scientists be looking for and what techniques will they be using for analysis of the data.


  4. Equivalence principle is unnaturalness. Classical theory itself is unnaturalness – unite with relativity at equivalence principle.
    Photon getting massive is Naturalness. To fix massless photon is the “particular mass” of the Higgs boson. Higgs mechanism was intended to gluon’s “invariant mass”.
    So some sort of invariant mass fix the rest mass ?


  5. It is a fascinating search. But the hole in the Standard Model has been dug elsewhere: there seems to be one massive neutrino, not three massless ones. A hadron/lepton symmetry is damaged.

  6. Personally, I am waiting for new ideas. Not adjustments to the old ideas or variations that lack empirical motivation. It’s been 40 years or more, but I’m in it for the long haul. Scientific advance sometimes requires a willingness to question even the most cherished assumptions. Anybody else ready yet?

    1. Include me in! I’ve always thought there was something a little epicycle-ish about QM.

      (I’m still holding out a vanishing hope that, while matter and energy obviously are quantized, spacetime turns out not to be. That Einstein and GR nailed it. There is no quantum gravity, no graviton; something else is true.)

      1. There are existing theories that embody your hopes. They are derived from empirical evidence and make testable predictions. One I know of personally that can be explored by searching on “Discrete Scale Relativity” or “Predictions of Discrete Scale Relativity”.

        There are plenty of other efforts that embody the alternative assumptions and principles that you hope for. Keep that hope alive; it is probably where theoretical physics will eventually evolve towards.

  7. What could be more exciting than to hear news re:the Standard Model and ‘naturalness’. Waiting somewhat impatiently for your next post!

  8. 1) Your first line represents an absurdly depressive conclusion; you should take some Prozac. The LHC has collected about 2% of its data, and searches through the data are far from comprehensive.

    2) If in fact your first line turns out to be the correct conclusion, it’s frustrating, but extremely fascinating (because of the naturalness problem.) Like the Michelson-Morely experiment, it could well turn out to be one of the most important null results of all time. Imagine how wrongly depressed people were not to be able to detect the ether!

    1. >>>If in fact your first line turns out to be the correct conclusion (…) it could well turn out to be one of the most important null results of all time.

      Perhaps. I hope so.
      But how do you convince young researchers to choose particle physics with such a result? They know they’ll have to wait 20 more years to have a new collider at the energy frontier.
      And how do you convince the governments to pay for a this new gigantic collider?
      I will be hard. Very hard.

      >>>you should take some Prozac

      Thats the depression after the disapearance of the diphoton bump 🙂

      1. Young researchers will look at what the 30–40 year old scientists are doing. The really good ones are putting a lot of time into thinking about how to exploit the LHC’s data more fully and about new (often non-collider) experiments that might give us new insights; they’re inventing new techniques for doing measurements by putting modern technology to work in new ways. So it’s way too early to be getting depressed about the field.

        1. Actually a lot of the really good ones left the field, having divined that the BS to doing-real-physics ratio just wasn’t worth it. Including yourself I believe. And I doubt today’s results will make them particularly remorseful about that.

      2. >”But how do you convince young researchers to choose particle physics with such a result?”

        It’s not an unexpected result. It’s really pretty typical. The hype machine got a bit carried away, the media oversold it as always, but I doubt many of the paper-writing theorists are truly shattered by the negative result. It was always a long shot, but it was a long shot on the biggest game in town. I’ll also point out that the LHC did find a pentaquark not so long ago too!

        There are plenty of interesting areas in particle physics. Just this week I read about several related experiments suggesting an anomaly between the oscillation of neutrinos compared to that of antineutrinos.

        So don’t be down! Particle physics is still a rich vein.

      1. Ho now, that must be the first time ‘ether’ has been used in that context in the history of this site’s comments section!

  9. LHC = Higgs boson and nothing more.
    How disappointing. It was the ultimate nightmare of all particle physicists during the construction and now it happens.

    1. That and the pentaquark… and a whole family of tetraquarks. Just formerly hypothetical particles now confirmed to exist, enhancing our understanding of the strong force. And I’m sure there’s nothing else interesting in the 50 or times more data the LHC has to collect. Truly its best days are behind it.

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