higgs - page 6

The Physics Teacher
Vol. 50, S
Don Lincoln,
The Quantum Frontier: The Large Hadron Col-
(Johns Hopkins University Press, Baltimore, 2009).
Ian Sample,
Massive: The Hunt for the God Particle
Books, Ireland, 2010).
Don Lincoln,
Understanding the Universe: From Quarks to the
(Revised) (World Scientific Press, Singapore, 2012).
Bruce Schumm,
Deep Down Things: The Breathtaking Beauty
of Particle Physics
(Johns Hopkins University Press, Baltimore,
Ref. 3, pp. 306–312.
Don Lincoln
is a senior researcher at Fermilab and member of both of
the Fermilab DZero and CERN CMS collaborations, and has co-authored
over 500 papers. He is also an avid popularizer of frontier physics and has
written two books on science for the public:
The Quantum Frontier: The
Large Hadron Collider
Understanding the Universe: From Quarks to
the Cosmos.
of the two big LHC experiments (Fig. 7). The results were si-
mulcast and I watched them with about 250 people who came
to Fermilab in the middle of the night to see the announce-
ment, including an inspiring number of physics undergradu-
ate students.
So what, exactly, was announced? Both CMS and ATLAS
independently claimed that they had “5 sigma” evidence for
the existence of a new boson. “5 sigma” means that there is
only about one chance in 3.5 million of seeing what was ob-
served if the universe were governed by the Standard Model
without the Higgs boson. This level of improbability is the
standard in particle physics to declare that something new
has been observed. Both experimental teams announced
measurements in the photon and Z boson decay channels,
and the CMS group also announced the outcome of studies in
the W boson, bottom quark, and tau lepton decay channels.
These three additional channels told a story that was consis-
tent with the more powerful search modes, but will require
more data before they can contribute strongly to the study of
Higgs bosons. Both experiment groups announced a mass of
the new boson of about 125 GeV (see Fig. 8).
What was discovered?
So, was the discovery of the Higgs boson announced? No.
The reason is that the Higgs boson is a theoretically very well
described particle, with specific couplings to fermions and
bosons, a completely determined range of decay modes, as
well as a specific value for its spin and parity. The amount
of data announced on July 4th was insufficient to establish
that the newly discovered boson had the required properties.
Thus the announcement was that we found something and
that it will require some work to establish precisely what it is.
The measurements reported thus far are
consistent with
Standard Model Higgs boson, but
that it is the Stan-
dard Model Higgs boson will take some additional time and
data. The CERNmanagement has instituted an operational
plan designed to allow the two LHC experiments to accumu-
late enough data in 2012 to independently verify these impor-
tant properties. The observations of July are not the end of
the story, but merely a new beginning.
As I am writing this, just a few days after the announce-
ment, here is the status. The LHC will continue to collide
beams of protons until December of 2012. After a short
winter break, the LHC will collide beams of lead ions for the
first part of 2013 and then shut down for repairs and up-
grades. While the date at which the accelerator will resume
operations is not yet specified, it is expected to be about the
beginning of 2015. The LHC will then be able to safely collide
beams at 13 or 14 TeV, opening yet another energy frontier.
The next few years promise exciting possibilities.
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