LHC experiments join forces to zoom in on the Higgs boson
LHC experiments join forces to zoom in on the Higgs boson
Candidate Higgs boson event from collisions between protons in
the CMS detector on the LHC. From the collision at the centre, the
particle decays into two photons (dashed yellow lines and green towers)
(Image: CMS/CERN)
Today during the 50th session of “Rencontres de Moriond” in La Thuile Italy, the ATLAS and CMS experiments presented for the first time a combination of their results on the mass of the Higgs boson.
The combined mass of the Higgs boson is mH = 125.09 ± 0.24
(0.21 stat. ± 0.11 syst.) GeV, which corresponds to a measurement
precision of better than 0.2%. The Higgs boson is an essential
ingredient of the Standard Model of particle physics, the theory that describes all known elementary particles and their interactions. The Brout-Englert-Higgs mechanism,
through which the existence of the Higgs boson was predicted, is
believed to give mass to all elementary particles. Today’s result is the
most precise measurement of the Higgs boson mass yet and among the most
precise measurements performed at the LHC to date.
“Collaboration is really part of our organization’s DNA,” says CERN
Director General Rolf Heuer. “I’m delighted to see so many brilliant
physicists from ATLAS and CMS joining forces for the very first time to
obtain this important measurement at the LHC”.
The Higgs boson decays into various different particles. For this
measurement, results on the two decay channels that best reveal the mass
of the Higgs boson have been combined. These two decay channels are:
the Higgs boson decaying to two photons; and the Higgs boson decaying to
four leptons – where the leptons are an electron or muon. Candidate
Higgs boson event from collisions between protons in the ATLAS detector
on the LHC. From the collision at the centre, the particle decays into
four muons (red tracks)(Image:ATLAS/CERN)
Each experiment has found a few hundred events in the Higgs to
photons channel and a few tens of events in the Higgs to leptons
channel. The analysis uses the data collected from about 4000 trillion
proton-proton collisions at the Large Hadron Collider (LHC) in 2011 and 2012 at centre-of-mass energies of 7 and 8 TeV.
“The Higgs Boson was discovered at the LHC in 2012 and the study of
its properties has just begun. By sharing efforts between ATLAS and CMS,
we are going to understand this fascinating particle in more detail and
study its behaviour,” says CMS spokesperson Tiziano Camporesi.
The Standard Model does not predict the mass of the Higgs boson
itself, so it must be measured experimentally. But once supplied with a
Higgs mass, the Standard Model does make predictions for all the other
properties of the Higgs boson, which can then be tested by the
experiments. This mass combination is the first step towards a
combination of other measurements of the Higgs boson’s properties, which
will include its other decays.
"While we are just getting ready to restart the LHC, it is admirable
to notice the precision already achieved by the two experiments and the
compatibility of their results,” says CERN Director of Research Sergio
Bertolucci. “This is very promising for LHC Run 2.”
Up to now, increasingly precise measurements from the two experiments
have established that all observed properties of the Higgs boson,
including its spin, parity and interactions with other particles are
consistent with the Standard Model Higgs boson. With the upcoming
combination of other Run 1 Higgs results from the two experiments and
with higher energy
and more collisions to come during LHC Run 2, physicists expect to
increase the precision of the Higgs boson mass even more and to explore
in more detail the particle’s properties. During Run 2, they will be
able to combine their results promptly and thus increase the LHC’s
sensitivity to effects that could hint at new physics beyond the Standard Model. For a longer version of this article, see the CERN press release
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