Most accurate measurement of W boson mass ever made differs from Standard Model prediction

The most precise measurement ever made of the mass of the W boson shows a tension with the standard model.

After 10 years of analysis and scrutiny, scientists from the Collider Detector at Fermilab (CDF) collaboration at the US Department of Energy’s Fermi National Accelerator Laboratory announced on April 7, 2022 that they had made the measurement the most accurate to date of the mass of the W boson, one of nature’s force-carrying particles. Using data collected by the CDF, scientists have now determined the mass of the particle with an accuracy of 0.01%, twice as accurate as the previous best measurement. This corresponds to measuring the weight of a gorilla from 800 pounds to 1.5 ounces.

The new precision measurement, 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 a tension with the value that scientists obtain using experimental and theoretical data in the context of the Standard Model.

Fermilab collider detector

Fermilab’s Collider Detector recorded high-energy particle collisions produced by the Tevatron collider from 1985 to 2011. About 400 scientists from 54 institutions in 23 countries are still working on the wealth of data collected by the experiment. Credit: Fermilab

“The number of improvements and additional verifications made to our result is enormous,” said Ashutosh V. Kotwal of Duke University, who led this analysis and is one of 400 scientists in the CDF collaboration. “We took into account our better understanding of our particle detector as well as advances in theoretical and experimental understanding of the interactions of the W boson with other particles. When we finally unveiled the result, we found that it differed from the Standard Model prediction.

If confirmed, this measure suggests the potential need for improvements in the calculation of the standard model or extensions of the model.

Scientists have now determined the mass of the W boson with an accuracy of 0.01%. This is twice as accurate as the previous best measurement and shows the voltage with the standard model.

The new value agrees with many previous W boson mass measurements, but there are also some disagreements. Future measurements will be needed to further shed light on the outcome.

“Although this is an intriguing result, the measurement needs to 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 the weak nuclear force. It is responsible for the nuclear processes that cause the sun to shine and particles to decay. Using high-energy particle collisions produced by Fermilab’s Tevatron collider, the CDF collaboration collected huge amounts of data containing W bosons from 1985 to 2011.

Standard model of elementary particles

The W boson is the messenger particle of the weak nuclear force. It is responsible for the nuclear processes that cause the sun to shine and particles to decay. CDF scientists are studying the properties of the W boson using data they collected at Fermilab’s Tevatron Collider. Credit: National Fermi Accelerator Laboratory

CDF physicist Chris Hays of the University of Oxford said: “The CDF measurement was carried out over many years, with the measured value hidden from the analyzers until the procedures were fully reviewed. When we discovered the value, it was a surprise.

The mass of a W boson is about 80 times the mass of a proton, or about 80,000 MeV/c2. CDF researchers have been working for more than 20 years on increasingly precise measurements of the mass of the W boson. The central value and uncertainty of their latest mass measurement is 80,433 +/- 9 MeV/c2. This result uses all the data collected from the Tevatron collider at Fermilab. It is based on the observation of 4.2 million candidate W bosons, about four times the number used in the analysis published by the collaboration in 2012.

W boson mass comparison

The mass of a W boson is about 80 times the mass of a proton, or about 80,000 MeV/c2. Scientists from the Collider Detector of the Fermilab collaboration have made the most precise measurement in the world. The CDF value has an accuracy of 0.01% and agrees with many mass measurements of the W boson. It shows the voltage with the expected value based on the Standard Model of particle physics. The horizontal bars indicate the uncertainty of the measurements obtained by various experiments. The LHCb result was published after this paper was submitted and is 80354+- 32 MeV/c2. Credit: CDF collaboration

“Many collider experiments have produced measurements of the mass of the W boson over the past 40 years,” said CDF co-spokesman Giorgio Chiarelli of Italy’s National Institute for Nuclear Physics (INFN- Pisa). “These are difficult and complicated measurements, and they have achieved ever greater precision. It took us many years to go through all the necessary details and checks. This is our most robust measurement to date, and the discrepancy between measured and expected values ​​persists.

The collaboration also compared their result to the best expected value for the mass of the W boson using the Standard Model, which is 80,357 ± 6 MeV/c2. This value is based on complex Standard Model calculations that closely relate the mass of the W boson to measurements of the masses of two other particles: the top quark, discovered at the Tevatron collider at Fermilab in 1995, and the Higgs boson, discovered at the large hadron collider at CERN in 2012.

CDF co-spokesperson David Toback of Texas A&M University said the result is an important contribution to testing the precision of the standard model. “Now it’s up to the theoretical physics community and other experiments to follow this and shed some light on this mystery,” he added. “If the difference between the experimental value and the expected value is due to some sort of new particle or subatomic interaction, which is one of the possibilities, chances are it’s something that can be discovered. in future experiments.

Reference: “High precision measurement of the mass of the W boson with the CDF II detector” by CDF Collaboration, T. Aaltonen, S. Amerio, D. Amidei, A. Anastassov, A. Annovi, J. Antos, G. Apollinari , JA Appel, T. Arisawa, A. Artikov, J. Asaadi, W. Ashmanskas, B. Auerbach, A. Aurisano, F. Azfar, W. Badgett, T. Bae, A. Barbaro-Galtieri, VE Barnes, BA Barnett, P. Barria, P. Bartos, M. Bauce, F. Bedeschi, S. Behari, G. Bellettini, J. Bellinger, D. Benjamin, A. Beretvas, A. Bhatti, KR Bland, B. Blumenfeld, A Bocci, A. Bodek, D. Bortoletto, J. Boudreau, A. Boveia, L. Brigliadori, C. Bromberg, E. Brucken, J. Budagov, HS Budd, K. Burkett, G. Busetto, P. Bussey, P Butti, A. Buzatu, A. Calamba, S. Camarda, M. Campanelli, B. Carls, D. Carlsmith, R. Carosi, S. Carrillo, B. Casal, M. Casarsa, A. Castro, P. Catastini , D. Cauz, V. Cavaliere, A. Cerri, L. Cerrito, YC Chen, M. Chertok, G. Chiarelli, G. Chlachidze, K. Cho, D. Chokheli, A. Clark, C. Clarke, ME Convery , J. Conway, M. Corbo, M. Cordelli , CA Cox , DJ Cox, M. Cremonesi, D. Cruz, J. Cuevas, R. Culbertson, N. d’Ascenzo, M. Datta, P. de Barbaro, L. Demortier, M. Deninno, M. D’ Errico, F Devoto, A. Di Canto, B. Di Ruzza, JR Dittmann, S. Donati, M. D’Onofrio, M. Dorigo, A. Driutti, K. Ebina, R. Edgar, A. Elagin, R. Erbacher, S. Errede, B. Esham, S. Farrington, JP Fernández Ramos, R. Field, G. Flanagan, R. Forrest, M. Franklin, JC Freeman, H. Frisch, Y. Funakoshi, C. Galloni, AF Garfinkel, P. Garosi, H. Gerberich, E. Gerchtein, S. Giagu, V. Giakoumopoulou, K. Gibson, CM Ginsburg, N. Giokaris, P. Giromini, V. Glagolev, D. Glenzinski, M. Gold, D Goldin, A. Golossanov, G. Gomez, G. Gomez-Ceballos, M. Goncharov, O. González López, I. Gorelov, AT Goshaw, K. Goulianos, E. Gramellini, C. Grosso-Pilcher, J. Guimaraes da Costa, SR Hahn, JY Han, F. Happacher, K. Hara, M. Hare, RF Harr, T. Harrington-Taber, K. Hatakeyama, C. Hays, J. Heinrich, M. Herndon, A. Hocker, Z. Hong, W. Hopkins, S. Hou, RE Hughes, U. Husemann, M. Hussein, J. Huston, G. Introzzi, M. Iori, A. Ivanov, E. James, D. Jang, B. Jayatilaka, EJ Jeon, S. Jindariani, M. Jones … P. Wagner, R. Wallny, SM Wang, D. Waters, WC Wester, D. Whiteson, AB Wicklund, S. Wilbur, HH Williams, JS Wilson, P. Wilson, BL Winer, P. Wittich, S. Wolbers, H. Wolfmeister, T. Wright, X. Wu, Z Wu, K Yamamoto, D. Yamato, T. Yang, UK Yang, YC Yang, W.-M. Yao, GP Yeh, K. Yi, J. Yoh, K. Yorita, T. Yoshida, GB Yu, I. Yu, AM Zanetti, Y. Zeng, C. Zhou and S. Zucchelli, April 7, 2022, Science.
DOI: 10.1126/science.abk1781

The CDF collaboration includes 400 scientists from 54 institutions in 23 countries.

Comments are closed.