Hopes for brand spanking new physics dashed by ordinary-looking W bosons at CERN

A attainable crack within the customary mannequin of particle physics appears to be shrinking, as new knowledge from CERN’s Massive Hadron Collider (LHC) contradicts a earlier puzzling end result that had physicists enthusiastic about the potential for new, unique physics – however some mysteries stay.

“The standard model survives for the moment,” Josh Bendavid on the Massachusetts Institute of Know-how instructed a packed seminar room at CERN, the particle physics laboratory close to Geneva, Switzerland, on 17 September. He was presenting new knowledge on the mass of the W boson, a basic particle that’s essential for processes like nuclear decay and setting the mass of the Higgs boson.

Questions concerning the W boson mass started in 2022, when physicists working with knowledge from the Tevatron collider at Fermilab in Illinois despatched shockwaves by means of the particle physics neighborhood. Their worth for the W boson mass was starkly completely different from that predicted by the usual mannequin, our greatest image of how the universe’s particles and forces work together, suggesting physicists might have missed one thing.

However in 2023, researchers at CERN solid doubt on this discrepancy, after they reanalysed outdated knowledge taken by the ATLAS detector on the LHC. They discovered a price for the W boson mass that when once more agreed with the usual mannequin prediction, dampening hopes for a deviation from recognized physics.

Now, Bendavid and his colleagues have produced a brand new worth for the W boson mass, utilizing new knowledge from one other of the LHC’s detectors, the Compact Muon Solenoid (CMS), and located a price of 80,353 million electronvolts (MeV) which, with an uncertainty of 6 MeV, agrees with the usual mannequin. The tiny uncertainty additionally makes this essentially the most exact measurement produced on the LHC, stated Bendavid.

Ashutosh Kotwal at Duke College in North Carolina, who led the scientific collaboration that produced the Tevatron end result, says that it’s nice to have one other measurement of the W boson mass, however because the LHC and Tevatron colliders use completely different strategies to supply the particle, it’s tougher to check the outcomes. Nevertheless, Martijn Mulders at CERN, who’s a part of the CMS collaboration, says this distinction can have been taken under consideration within the general uncertainty.

“In this fundamental respect of the beams, ATLAS and CMS are identical,” says Kotwal. “What would have been ideal is additional or independent data at the Tevatron.” Sadly, the Tevatron shut down in 2011, so there shall be no extra new knowledge.

All of this implies it’s too early to inform which W boson mass measurement is appropriate and that the variations should nonetheless be defined. “It doesn’t end with two numbers on the table, it’s the beginning,” says Kotwal. “It’s when we start discussing scientific and technical details about procedures. The truth is out there, there is a W boson mass in the universe. We’re all trying to find it.”

The mannequin behind the CMS calculation differs from that used to acquire different outcomes, says Matthias Schott at CERN, who works on the ATLAS collaboration. This makes its alignment with outcomes that use different fashions an indication that it’s extra prone to be appropriate, he says. “This gives us extremely high confidence now,” says Schott. “All the measurements align so well within each other, except for the one which is just off, so I would tend to say that this solves the case.”

Mulders agrees that the onus is now on the Fermilab, or CDF, group to clarify its end result. “Most of my colleagues will now believe that these W boson mass result measurements agree with each other and with the standard model prediction, and that that is probably the real answer and the CDF result is an outlier,” says Mulders. Schott and his colleagues on ATLAS are at present getting ready a totally new measurement of the W boson, additionally from new knowledge, which ought to assist settle the matter, he says.