Tag Archives: #LHC #Higgs #ATLAS #CMS #diphoton

The 2016 Data Kills The Two-Photon Bump

Results for the bump seen in December have been updated, and indeed, with the new 2016 data — four times as much as was obtained in 2015 — neither ATLAS nor CMS [the two general purpose detectors at the Large Hadron Collider] sees an excess where the bump appeared in 2015. Not even a hint, as we already learned inadvertently from CMS yesterday.

All indications so far are that the bump was a garden-variety statistical fluke, probably (my personal guess! there’s no evidence!) enhanced slightly by minor imperfections in the 2015 measurements. Should we be surprised? No. If you look back at the history of the 1970s and 1980s, or at the recent past, you’ll see that it’s quite common for hints — even strong hints — of new phenomena to disappear with more data. This is especially true for hints based on small amounts of data (and there were not many two photon events in the bump — just a couple of dozen).  There’s a reason why particle physicists have very high standards for statistical significance before they believe they’ve seen something real.  (Many other fields, notably medical research, have much lower standards.  Think about that for a while.)  History has useful lessons, if you’re willing to learn them.

Back in December 2011, a lot of physicists were persuaded that the data shown by ATLAS and CMS was convincing evidence that the Higgs particle had been discovered. It turned out the data was indeed showing the first hint of the Higgs. But their confidence in what the data was telling them at the time — what was called “firm evidence” by some — was dead wrong. I took a lot of flack for viewing that evidence as a 50-50 proposition (70-30 by March 2012, after more evidence was presented). Yet the December 2015 (March 2016) evidence for the bump at 750 GeV was comparable to what we had in December 2011 for the Higgs. Where’d it go?  Clearly such a level of evidence is not so firm as people claimed. I, at least, would not have been surprised if that original Higgs hint had vanished, just as I am not surprised now… though disappointed of course.

Was this all much ado about nothing? I don’t think so. There’s a reason to have fire drills, to run live-fire exercises, to test out emergency management procedures. A lot of new ideas, both in terms of new theories of nature and new approaches to making experimental measurements, were generated by thinking about this bump in the night. The hope for a quick 2016 discovery may be gone, but what we learned will stick around, and make us better at what we do.