Using data collected from the Collider probe at Fermilab, or CDF, scientists have now determined the particle mass to the nearest 0.01% – twice that of the previous best measurement. Corresponds to measuring the weight of an 800 pound gorilla at 1.5 ounces. The new measurement of accuracy, published in the journal Science, allows scientists to test the Standard Model of Particle Physics, the theoretical framework that describes nature at its most fundamental level. The result: The new mass value shows intensity with the value obtained by scientists using experimental and theoretical inputs under the Standard Model. “The number of improvements and additional tests performed on our result is enormous,” said Ashutosh V. Kotwal of Duke University, who led the analysis and is one of 400 scientists working with the CDF. “We took into account the improved understanding of our particle detector as well as the progress in the theoretical and experimental understanding of the interactions of the W boson with other particles. When we finally discovered the result, we found that it differed from the prediction of the Standard Model.” If confirmed, this measure indicates the potential need for improvements to the standard model calculation or extensions to the model. The new value agrees with many previous W boson mass measurements, but there are some disagreements. Future measurements will be needed to shed more light on the result. “While this is an interesting result, the measurement must be confirmed by another experiment before it can be fully interpreted,” said Fermilab deputy director Joe Lykken. The W boson is a messenger particle of weak nuclear power. It is responsible for the nuclear processes that make the sun shine and the particles decompose. Using high-energy particle collisions produced by the Tevatron accelerator at Fermilab, the CDF collaboration collected vast amounts of data containing W bosons from 1985 to 2011. CDF physicist Chris Hays of the University of Oxford said: “The CDF measurement was done over many years, with the measured value hidden from analysts until the procedures were fully examined. When we found out the value, it was a surprise.” The mass of a boson W is about 80 times the mass of a proton or about 80,000 MeV / c2. CDF researchers have been working for more and more accurate measurements of W boson mass for more than 20 years. The central value and uncertainty of their last mass measurement is 80.433 +/- 9 MeV / c2. This result uses the entire data set collected by the Tevatron accelerator in Fermilab. It is based on the observation of 4.2 million W boson candidates, about four times the number used in the analysis published by the collaboration in 2012. “Many accelerator experiments have provided measurements of the W boson mass over the past 40 years,” said CDF co-spokesman Giorgio Chiarelli of the Italian National Institute of Nuclear Physics (INFN-Pisa). “These are challenging, complex measurements and have achieved even greater accuracy. It took us many years to go through all the details and necessary checks. It is our strongest measurement to date and the discrepancy between measured and expected values persists.” . The collaboration also compared their result with the best expected value for the mass of boson W using the Standard Model, which is 80,357 ± 6 MeV / c2. This value is based on complex Standard Model calculations that intricately link the mass of the W boson to the mass measurements of two other particles: the top quark, discovered at the Tevatron accelerator in Fermilab in 1995, and the Higgs boson, discovered at the Large Accelerator. Hadronias at CERN in 2012. CDF co-spokesman David Toback of Texas A&M University said the result is a significant contribution to testing the accuracy of the Standard Model. “It is now up to the community of theoretical physics and other experiments to follow it and shed light on this mystery,” he added. “If the difference between the experimental and the expected value is due to some kind of new particle or subatomic interaction, which is one of the possibilities, there is a high probability that it could be something that could be discovered in future experiments.” Source:
