Higgs Boson Gets New Mass Limit
Ashutosh Kotwal and his Fermilab team offer more
precise prediction for Higgs boson mass
February 23, 2012
The W boson is squeezing in on what the mass of
the Higgs can be. Image courtesy of symmetry magazine/plush toys
by artist Julie Peasley/photo by Robert Tilden.
DURHAM, NC -
New, more precise measurements of a particle called the W boson
are again suggesting that physicists' prized Higgs boson is
lighter than previously predicted.
Using detectors at the Fermi National Accelerator
Laboratory in Illinois, Duke physicist Ashutosh Kotwal and his
collaborators have made the world's most precise mass
measurement of the W boson, a key quantity in the Standard Model
-- the theory physicists use to explain the dynamics of
According to the results of the experiment, the W
boson's new mass was measured at 80387 million electron volts
divided by the speed of light squared, give or take 19 MeV
(80387 +- 19 MeV/c^2), with a precision of 0.02 percent.
"This result significantly improves the world
knowledge of the Higgs boson," Kotwal said, explaining that the
precise measurement of the mass of the W boson makes a precise
prediction for the mass of the Higgs.
Based on the new W boson mass, Kotwal's team has
calculated that the Higgs boson mass is roughly 90 GeV, or
billion electron volts, with a precision of 30 percent.
"The best way to think of this is to present the
upper limit on the Higgs boson mass with 95 percent probability,
which means that there is only one 1 in 20 chance of the Higgs
being heavier than this upper limit," Kotwal said. The new upper
limit is 145 GeV.
When Kotwal presented his last measurement of the
W boson's mass in 2007, it put the upper limit of the Higgs
boson mass at 161 GeV. With the new measurement of the W boson
mass, the new upper limit of the Higgs has dropped to 145 GeV,
"so it is now more likely that the Higgs boson is light," Kotwal
He announced the finding in a talk at Fermilab on
Feb. 23 and will submit the results of the experiment for
publication in the near future.
Last December, physicists from two experiments at
CERN's Large Hadron Collider announced data that hinted the
Higgs boson mass was between 115-130 GeV. Kotwal's new W boson
mass measurement and predicted Higgs mass within 90-145 GeV
suggests that the physicists are narrowing in on the energy
region where the Higgs particle may be hiding.
CERN and Fermilab physicists are expected to
present their latest direct-search Higgs measurements at the
annual conference on Electroweak Interactions and Unified
Theories known as Rencontres de Moriond in Italy next month.
"If the Higgs boson is soon discovered and its
mass agrees with the precise prediction given by the W boson
mass measurement, then the Standard Model will be proven correct
once again," Kotwal said "But, if the Higgs boson is not found
where it is predicted, then this model will be proven wrong
He explained that physicists ultimately want to
know whether or not their model of the behavior of fundamental
particles is correct. If the model is proven wrong, "we would
have learned that there is something really new and more
fundamental going on in nature, and this will be a major
scientific advance of the last 50 years," Kotwal said.
His team includes Duke graduate student Yu Zeng
and post-doctoral researcher Bodhitha Jayatilaka.
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