Lifetime of Higgs boson measured to within septillionths of a second
Physicists at CERN have measured the life of the Higgs boson with greater accuracy than ever before. Since the legendary particle only lives for a tiny fraction a second, the scientists came up with a creative workaround to calculate the new figure.
First hypothesized in the 1960s, the Higgs boson was the final elementary particle predicted by the Standard Model, and other particles gain mass through interactions with it. Its detection in 2012 was one of the most important scientific breakthroughs in a century, earning the scientists who formulated the idea the 2013 Nobel Prize in Physics.
The Higgs boson has since been regularly produced in the Large Hadron Collider (LHC), allowing physicists to study its properties, but some of these are tricky to pin down precisely because it only lives for a few septillionths of a second before decaying into other particles. In fact, its lifespan is itself one of the hardest properties to directly measure, because it doesn’t allow enough time to travel through the instrument to reach detectors.
So for the new study, scientists with the CMS Collaboration used an indirect method to measure the lifespan of the Higgs boson more precisely than ever before. Instead, they turned to a different property called its mass width – the range of possible masses that the particle can have. Essentially, the wider the particle’s mass width, the shorter its lifespan, allowing the physicists to calculate the latter by measuring the former.
The Higgs boson’s nominal mass – its usual, most common value – is 125 Gigaelectronvolts (GeV). But thanks to the quantum weirdness of the Heisenberg uncertainty principle, sometimes versions with larger masses are produced as well. The team analyzed data from the LHC’s second observing run, to calculate the ratio of “on-shell” Higgs bosons (those close to the nominal mass) to “off-shell” Higgs bosons (those with a much larger mass than usual).
Using this technique, the researchers calculated that the lifetime of the Higgs boson is 210 yoctoseconds – that’s in the realm of septillionths of a second, or a decimal point followed by 22 zeroes. The uncertainty of this value is (+2.3/-0.9) x 10-22 seconds, making it the most precise measurement of the Higgs boson’s lifetime yet.
“Our result demonstrates that off-shell Higgs-boson production offers an excellent way to measure the Higgs boson’s lifetime,” says Pascal Vanlaer, a physicist at CMS. “And it sets a milestone in the study of the properties of this unique particle. The precision of the measurement is expected to improve in the coming years with data from the next LHC runs and new analysis ideas.”
The next observing run of the LHC is due to kick off in 2022.
The research is available on CERN’s document server.