Experts may be one step closer to understanding the universe.
In a collaborative study with University of Oxford and University College London, Duke physics professor Ashutosh Kotwal and his team have produced the world’s most precise mass measurement of the W boson, an elementary particle that mediates weak nuclear force. This finding contributes significantly to scientists’ understanding of the Higgs boson in the Standard Model, the theory that physicists use to explain the dynamics of subatomic particles.
The new mass measurement of the W boson not only suggests that the Higgs boson is lighter than previously predicted but also pinpoints the upper limit on the Higgs boson mass with 95 percent certainty.
This experiment matters because the mass of the W boson is highly related to the mass of the Higgs boson, said Yu Zeng, a physics graduate student in physics who has worked with Kotwal since 2007. The Higgs boson is related to the fundamental question of the origin of mass.
“Because we have not found the Higgs boson yet, one way to pinpoint the Higgs boson is with the W boson,” Zeng said. “A precise measurement of the W boson is important because it allows us to constrain the mass range of the Higgs boson.”
Using data collected at the Fermi National Accelerator Laboratory in Illinois, Kotwal’s team measured the W boson’s mass at 80,387 million electron volts divided by the speed of light squared, with a precision of .02 percent. Precision indicates how well a result is expected to be reproduced through repeat measurements—the higher the precision, the better the reproducibility. Based on the new W boson mass, they calculated that the Higgs boson is around 90 billion electron volts, or GeV, with a precision of 30 percent. Compared to an earlier experiment conducted at the European Organization for Nuclear Research in Switzerland, Kotwal’s prediction that the Higgs boson mass is within 90-145 GeV advances the effort to narrow down the energy region in which the Higgs particle is located.
“We were able to retrieve better results because we are using more data and better techniques,” Kotwal said. “I only had 100,000 W bosons available to analyze in my first experiment—this time I used around 1,000,000 W bosons.”
Though the results of Kotwal’s experiment represent a landmark among measurements of the W boson mass, finding the Higgs boson will still require further precision on measurement of the W boson, said postdoctoral research associate Bodhitha Jayatilaka, who also contributed to the research.
“We have started laying the groundwork for a measurement of the W boson mass with another data set,” Jayatilaka wrote in an email Thursday. “We believe this can further reduce the error.”
Jayatilaka is currently presenting their latest findings of the Higgs boson measurements at the annual conference on Electroweak Interactions and Unified Theories in Italy. This will be the first presentation of the findings to the international physics community and the second public presentation after Kotwal’s seminar at Fermilab Feb. 23. Jayatilaka said.
Further research is already underway. Since there is another set of about 4,000,000 W bosons that have yet to be analyzed, the current mass measurements of the W boson can be improved by a factor of two, Kotwal noted.
“The next stage is not only to find a more accurate upper limit of the Higgs boson but also to find the lower limit as well,” he said. “Afterward, we must check to see if the Higgs boson can be found in that range.”
Get The Chronicle straight to your inbox
Signup for our weekly newsletter. Cancel at any time.