After an unexpected measurement by the Collider Detector at Fermilab (CDF) experiment in 2022, physicists on the Compact Muon Solenoid experiment (CMS) on the Large Hadron Collider (LHC) announced today a brand new mass measurement of the W boson, one in every of nature’s force-carrying particles. This recent measurement, which is a primary for the CMS experiment, uses a brand new technique that makes it essentially the most elaborate investigation of the W boson’s mass up to now. Following nearly a decade of research, CMS has found that the W boson’s mass is consistent with predictions, finally putting a multi-year long mystery to rest. View the paper posted.
The ultimate evaluation used 300 million events collected from the 2016 run of the LHC, and 4 billion simulated events. From this dataset, the team reconstructed after which measured the mass from greater than 100 million W bosons. They found that the W boson’s mass is 80 360.2 ± 9.9 megaelectron volts (MeV), which is consistent with the Standard Model’s predictions of 80 357 ± 6 MeV. Additionally they ran a separate evaluation that cross-checks the theoretical assumptions.
“The brand new CMS result is exclusive due to its precision and the best way we determined the uncertainties,” said Patty McBride, a distinguished scientist on the U.S. Department of Energy’s Fermi National Research Laboratory and the previous CMS spokesperson. “We have learned rather a lot from CDF and the opposite experiments who’ve worked on the W boson mass query. We’re standing on their shoulders, and that is one in every of the the explanation why we’re in a position to take this study a giant step forward.”
Because the W boson was discovered in 1983, physicists on 10 different experiments have measured its mass.
The W boson is one in every of the cornerstones of the Standard Model, the theoretical framework that describes nature at its most fundamental level. A precise understanding of the W boson’s mass allows scientists to map the interplay of particles and forces, including the strength of the Higgs field and merger of electromagnetism with the weak force, which is chargeable for radioactive decay.
“The complete universe is a fragile balancing act,” said Anadi Canepa, deputy spokesperson of the CMS experiment and a senior scientist at Fermilab. “If the W mass is different from what we expect, there may very well be recent particles or forces at play.”
The brand new CMS measurement has a precision of 0.01%. This level of precision corresponds to measuring a 4-inch-long pencil to between 3.9996 and 4.0004 inches. But unlike pencils, the W boson is a fundamental particle with no physical volume and a mass that’s lower than a single atom of silver.
“This measurement is amazingly difficult to make,” Canepa added. “We’d like multiple measurements from multiple experiments to cross-check the worth.”
The CMS experiment is exclusive from the opposite experiments which have made this measurement due to its compact design, specialized sensors for fundamental particles called muons and a particularly strong solenoid magnet that bends the trajectories of charged particles as they move through the detector.
“We were in a position to do that effectively because of a mix of a bigger data set, the experience we gained from an earlier W boson study, and the most recent theoretical developments,” Bendavid said. “This has allowed us to free ourselves from the Z boson as our reference point.”
As a part of this evaluation, in addition they examined 100 million tracks from the decays of well-known particles to recalibrate a large section of the CMS detector until it was an order of magnitude more precise.
“This recent level of precision will allow us to tackle critical measurements, corresponding to those involving the W, Z and Higgs bosons, with enhanced accuracy,” Manca said.
Essentially the most difficult a part of the evaluation was its time intensiveness, because it required making a novel evaluation technique and developing an incredibly deep understanding of the CMS detector.
“I began this research as a summer student, and now I’m in my third 12 months as a postdoc,” Manca said. “It is a marathon, not a sprint.”
The Compact Muon Solenoid (CMS) experiment is funded partly by the Department of Energy’s Office of Science and the National Science Foundation. It’s one in every of two large general-purpose experiments on the Large Hadron Collider (LHC) at CERN, the European Particle Physics Laboratory.
Further information: Measurement of the W boson mass in proton-proton collisions at √s= 13 TeV
