Of Particular Significance

The Summer View at CERN

POSTED BY Matt Strassler

POSTED BY Matt Strassler

ON 07/27/2016

For the first time in some years, I’m spending two and a half weeks at CERN (the lab that hosts the Large Hadron Collider [LHC]). Most of my recent visits have been short or virtual, but this time* there’s a theory workshop that has collected together a number of theoretical particle physicists, and it’s a good opportunity for all of us to catch up with the latest creative ideas in the subject.   It’s also an opportunity to catch a glimpse of the furtive immensity of Mont Blanc, a hulking bump on the southern horizon, although only if (as is rarely the case) nature offers clear and beautiful weather.

More importantly, new results on the data collected so far in 2016 at the LHC are coming very soon!  They will be presented at the ICHEP conference that will be held in Chicago starting August 3rd. And there’s something we’ll be watching closely.

You may remember that in a post last December I wrote:

  “Everybody wants to know. That bump seen on the ATLAS and CMS two-photon plots!  What… IS… it…?

Why the excitement? A bump of this type can be a signal of a new particle (as was the case for the Higgs particle itself.) And since a new particle that would produce a bump of this size was both completely unexpected and completely plausible, there was hope that we were seeing a hint of something new and important.

However, as I wrote in the same post,

  “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 discuss briefly what it might mean if it wasn’t just a statistical fluke. But speculation may be about to end: finally, we’re about to find out if it was indeed just a fluke — or a sign of something real.

Since December the amount of 13 TeV collision data available at ATLAS and CMS (the two general purpose experiments at the LHC) has roughly quadrupled, which means that typical bumps and wiggles on their 2015-2016 plots have decreased in relative size by about a factor of two (= square root of four). If the December bump is just randomness, it should also decrease in relative size. If it’s real, it should remain roughly the same relative size, but appear more prominent relative to the random bumps and wiggles around it.

Now, there’s a caution to be added here. The December ATLAS bump was so large and fat compared to what was seen at CMS that (since reality has to appear the same at both experiments, once enough data has been collected) it was pretty obvious that even if it there were a real bump there, at ATLAS it was probably in combination with a statistical fluke that made it look larger and fatter than its true nature. [Something similar happened with the Higgs; the initial bump that ATLAS saw was twice as big as expected, which is why it showed up so early, but it gradually has shrunk as more data has been collected and it is now close to its expected size.  In retrospect, that tells us that ATLAS’s original signal was indeed combined with a statistical fluke that made it appear larger than it really is.] What that means is that even if the December bumps were real, we would expect the ATLAS bump to shrink in size (but not statistical significance) and we would expect the CMS bump to remain of similar size (but grow in statistical significance). Remember, though, that “expectation” is not certainty, because at every stage statistical flukes (up or down) are possible.

In about a week we’ll find out where things currently stand. But the mood, as I read it here in the hallways and cafeteria, is not one of excitement. Moreover, the fact that the update to the results is (at the moment) unobtrusively scheduled for a parallel session of the ICHEP conference next Friday, afternoon time at CERN, suggests we’re not going  to see convincing evidence of anything exciting. If so, then the remaining question will be whether the reverse is true: whether the data will show convincing evidence that the December bump was definitely a fluke.

Flukes are guaranteed; with limited amounts of data, they can’t be avoided.  Discoveries, on the other hand, require skill, insight, and luck: you must ask a good question, address it with the best available methods, and be fortunate enough that (as is rarely the case) nature offers a clear and interesting answer.


*I am grateful for the CERN theory group’s financial support during this visit.

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19 Responses

  1. Pr Strassler,
    you did not comment on the book you were writing?
    It is always a pleasure to read you, thank you.


  2. /And since a new particle that would produce a bump of this size was both completely unexpected and completely plausible./ – Humble words from the Professor ?

    /Do you call that “accomplishing nothing” even though it provided the basic knowledge that eventually led to the theory of relativity?/

    We feel the Mass, if the photon has zero mass (equivalence principle). If it is “almost c” – then the equivalence principle is violated ?

    Higgs mass only fix the zero rest-mass of photons – thus preserving the equivalence principle. At higher energies, equivalence principle is violated – exposing the Isomorphic fluorescence – showing heavy Higgs (source of fluorescence) ?

  3. “it sounds like you guys aren’t accomplishing anything, at all.”

    “The ever-worsening climate for science in the US isn’t helpful.”

    This, quite literally, makes me want to cry. The effects of our failure to invest in research at the (already low) levels we have in the past will be paid for, dearly, many times over for a generation in lost knowledge and lost productivity. Worse yet, both are fundamental to keeping the quality of life we have come to expect through higher wages, reduced unemployment, and general improvements to our daily lives. People don’t seem to understand that if we do not have a percentage of research that truly “finds nothing” then we are not pushing the envelope of our knowledge to the extent that we could and should be.

  4. Ah well… on a positive note, the LHC will be running for the next 20 years mercilessly probing the properties of the Higgs for deviations from the standard model. And there’s, of course, the continued slaying of SUSY models to look forward to.

    I feel the “ever-worsening climate for science in the US” is very pessimistic given the astonishing engineering/scientific feat of LIGO and more recent incredible skill of The Large Underground Xenon experiment at Stanford. But there’s no denying the difficulty of being a cutting edge theoretical physicist in a world where one’s skills tend to become obsolete over the years, unless one also specializes in teaching.

    1. The funding climate in the US for science is pretty terrible.

      Today, there’s no chance that a LIGO-like experiment would be funded; it’s success today is due to vision and funding from 30 years ago.

      As for LUX, it’s the exception that proves the rule. Why not count all the cancelled experiments before you mention the one that wasn’t cancelled? Of course LUX is terrific, they funded the best scientists to do a great experiment; but that doesn’t mean that the climate for young people trying to get off the ground with new experiments is good.

      Have you seen what’s happened to NIH? http://www.faseb.org/Portals/2/images/opa/Factsheet_Restore-NIH-Funding-Graph1.gif

      Here’s another useful graph that makes things look ok — in 2016 dollars, non-defense expenditures (blue curve) have been constant for a while
      *but* there have been increases in costs for non-research items under the research budget (e.g. healthcare and insurance costs) which means the actual money spent on doing research has significantly declined.

      As for the remark: “But there’s no denying the difficulty of being a cutting edge theoretical physicist in a world where one’s skills tend to become obsolete over the years, unless one also specializes in teaching”, would you care to elaborate? This remark makes you appear a bit uninformed, but perhaps I’ve misunderstood you.

      As for your initial remark about the LHC: again, this makes you appear a bit uninformed, on many levels.

  5. “… The December ATLAS bump was so large and fat compared to what was seen at CMS …”

    This could be the best news since the Higgs boson! Here’s my point, the resonance is the same but at different times. Yes, I understand that the beams are ALMOST at c, but at that scale “almost” makes a difference. Could we, for the first time, be witnessing the “buildup” of a particular resonance, i.e. maybe nature is analog after all?

    PS; I am very pleased to see get off that sofa and do some work for change, :-).

    “So many questions, so little time.”

  6. Matt i’m sure a lot of your readers would like to know where you are working these days. We know you went through some major disruptions in your career

    1. I work outside science and academe, though I gratefully remain an Associate of the Harvard physics department, which is not really a “position” but allows me to keep a computer account and library privileges. The ever-worsening climate for science in the US isn’t helpful.

      1. To get money you have to predict doom and gloom 🙂
        Thank you for keeping us informed.

    2. Hi matt,
      Thanks for the update. Are you hearing any rumours in the hallways, cafeteria that this indeed is firming up to be something real. I’m getting all excited.

    1. That’s like saying that a bomb squad that clears a building without finding a bomb has done nothing at all.

      Our job is to find out the truth. If nature offers something accessible for us to discover, our job is to discover it. If nature offers nothing for us to discover, then our job is to turn over every stone and be sure there’s nothing that we missed. We would accomplish nothing only if we failed to do a thorough search [and most of my research involves making sure that we are thorough.] A thorough search that finds nothing, by contrast, is extremely useful scientific information.

      For instance, the Michelson-Moreley experiment sought evidence of the ether for light waves. It found nothing. Do you call that “accomplishing nothing” even though it provided the basic knowledge that eventually led to the theory of relativity?

    2. What about the new particle consisting of 4 quarks?
      That is certainly Not Nothing!
      Matt, we are still looking forward to any book you will publish!

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