Curtain closing on Higgs boson photon soap opera

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It was the daytime soap opera of particle physics.
But the final episode of the first season ends in
an anticlimax. The Higgs boson's decay into pairs
of photons – the strongest yet most confusing
clue to the particle's existence – is looking utterly
normal after all.
Experiments don't detect the Higgs boson directly
– instead, its existence is inferred by looking at
the particles left behind when it decays. One way
it made itself known at CERN's Large Hadron
Collider near Geneva, Switzerland, two years ago
was by decaying into pairs of photons. Right at
the start, there were so many photons that
physicists considered it a "deviant decay" – and a
possible window into new laws of physics, which
could help explain the mysteries of dark energy
and the like.
Even as other kinks in the data got ironed out,
the excess of photons remained . At the time,
physicists speculated that it could be due to a
mysterious second Higgs boson being created, or
maybe the supersymmetric partner of the top
quark.
Identity crisis
If unheard of particles and physical laws weren't
dramatic enough, six months later, the decay into
photons was giving the Higgs an identity crisis .
When physicists measured the Higgs mass by
observing it decaying into another type of particle,
called a Z boson, it appeared lighter than when
doing a similar calculation using the decay into
photons. "The results are barely consistent,"
Albert de Roeck, one of the key Higgs hunters at
CERN's CMS experiment, said at the time.
But over the past year, physicists at CERN have
found that the Higgs boson is acting exactly as
the incomplete standard model of particle physics
predicts , leaving us with no clues about how to
extend it.
Now, in an anticlimactic summary on the two
photon decay, both big experiments at the LHC
have posted results showing the photons are,
after all the fuss, also doing exactly what the
standard model predicts.
Powering up
"This is probably the final word," wrote CERN
physicist Adam Falkowski on his blog .
Ever the optimist, de Roeck thinks there's still
room in the data for the two photon decay
channel to be caught misbehaving. Our present
outlook is due to our relatively fuzzy view of the
behaviour so far, he says. When the LHC is
switched back on next year after an upgrade, it
will be smashing protons together with double the
previous energy.
With that kind of power, the measurements will be
more exact, and any small deviations from
standard model predictions could emerge. "It is
most likely the last word for run one of the LHC,
but definitely not the last word," de Roeck says.
"I still believe ultimately we will find significant
deviations or something unexpected in the Higgs
sector. Then all hell will break loose."
Journal refs: ATLAS, arxiv.org/abs/1408.7084 ;
CMS, arxiv.org/abs/1407.0558
Posted by: Dr. Deepak Kumar and Associate Professor Dr. Tarun Kumar