For nearly eight months, physicists have been waiting for confirmation of a potential new particle that could change our entire view of physics. Now it seems the hinted particle was nothing more than a statistical blip.
In December 2015, the ATLAS and CMS collaborations at CERN announced that they had each found a bump in their data
at an energy of 750 gigaelectronvolts (GeV): an excess in the number of
photon pairs produced inside the Large Hadron Collider, compared with
predictions from the standard model of particle physics.
A week after the announcement, theorists had written over 100
possible explanations; today, there are over 500. Nearly all of these
papers posit the existence of a particle with a mass of 750 GeV or
higher whose decay created the extra photons. Because this particle
would have been outside the standard model of particle physics, it could
have forced a reconsideration of how particles and forces interact.
Sadly, it seems that the 750 GeV particle wasn’t meant to be. Physicists at the International Conference on High Energy Physics (ICHEP) in Chicago were due to reveal the latest data on the excess of photon pairs at 750 GeV later today, but a paper accidentally posted online last night
by the CMS collaboration states that their new round of data found no
extra photons. This suggests the earlier hints were just a statistical
fluke.
Statistical fluke
“As data comes in, excesses tend to come and go,” says CMS researcher
Nadja Strobbe at Fermilab, near Batavia, Illinois. Researchers from
ATLAS are due to present their results later today, but rumours suggest
they will announce that the 750 GeV bump is gone.
The loss of the supposed particle means theorists now have nothing to
guide them in the search for physics beyond the standard model, and
must wait for the next bump from the LHC. We know the standard model is
incomplete as it has nothing to say about dark energy or dark matter, which make up 95 per cent of the known universe, so something else must be out there.
“We have just started the hunt,” says CMS spokesperson Tiziano
Camporesi. “We could achieve it by the end of this year, by the next two
or three years, but there is still the possibility that it could take
longer.”
The discovery of the Higgs boson in 2012
was celebrated, but hasn’t helped push particle physics on, as its
properties were exactly as predicted. “It is the standard model exactly
like it was ordered, this feels like something my parents or my
grandparents wrote down, and so far nature is delivering exactly that,
which is sort of fantastic, and sort of very frustrating,” says former
ATLAS researcher Adam Gibson
at Valparaiso University, Indiana. “Apart from the Higgs, this is the
most exciting bump that we’ve had at the LHC, but I think a lot of us
thought there was a fair chance it was just a statistical fluctuation.”
Excitement over the 750 GeV bump may be just about over, but particle
physicists soldier on, scouring the data for bumps that might
illuminate surprises. “What’s next is to continue to do the work which
we are doing as best as we can,” says Camporesi. “[Non-standard model
physics] will be discovered, if it is there.” This result may have been
negative, but the prevailing attitude at ICHEP seems to be that it’s
just a matter of time.
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