There’s one thing amiss with a mass.
A brand new measurement of the mass of an elementary particle, the W boson, has defied expectations. The consequence hints at a attainable flaw in physicists’ in any other case stalwart concept of the basic ins and outs of our world, generally known as the usual mannequin.
That concept predicts a W boson with a mass of about 80,357 million electron volts, or MeV. But the brand new measured mass is bigger, at 80,433.5 MeV, physicists with the Collider Detector at Fermilab, or CDF, collaboration report within the April 8 Science.
The discovering may trace at new particles or different mysteries of physics but to be found. “If confirmed, this would clearly mean very interesting new physics that we can explore,” says theoretical physicist Sven Heinemeyer of the Institute for Theoretical Physics in Madrid.
Still, a number of earlier, much less exact measurements discovered W boson plenty extra carefully aligned with the usual mannequin, together with one from the ATLAS experiment on the Large Hadron Collider at CERN close to Geneva. So physicists are awaiting additional affirmation earlier than declaring their prized concept incorrect.
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“CDF’s new result seems barely compatible with the previous ones, including its own previous result, which prompts questions,” says ATLAS physicist Maarten Boonekamp of the Institute of Research into the Fundamental Laws of the Universe at Université Paris-Saclay.
Discovered in 1983, the W boson performs an essential function in the usual mannequin (SN: 2/5/83). The particle is available in two varieties, with both constructive or destructive electrical cost. Together with their uncharged accomplice, the Z boson, the particles carry the weak nuclear drive, which is accountable for sure forms of radioactive decay and performs an essential function within the nuclear reactions that energy the solar.
Using knowledge that CDF collected from 2002 to 2011, the group regarded for W bosons produced in collisions of protons and their antimatter counterparts, antiprotons, within the now-shuttered Tevatron particle collider at Fermilab in Batavia, Ill. (SN: 9/9/11). The evaluation was designed in order that researchers couldn’t inform what the top consequence was till they have been executed.
The second of the disclosing was hanging, says experimental particle physicist Ashutosh Kotwal of Duke University. “When the answer popped up … we were awestruck about what we might have just learned.”
With a precision of 0.01 %, the brand new W boson mass measurement is about twice as exact because the earlier report. “This is a very special measurement; this is a true legacy,” says experimental particle physicist Rafael Coelho Lopes de Sá of the University of Massachusetts Amherst, who labored on measuring the W boson mass for an additional Tevatron experiment. “The level of dedication and care and detail … is amazing.”
The new measurement disagrees with the usual mannequin expectation by 7 sigma, a measure of the statistical significance of a consequence. That’s properly above the 5 sigma that physicists often require to assert a discovery.
Still, “before getting too excited,” says ATLAS physicist Guillaume Unal of CERN, “I would like to see an independent measurement that confirms the CDF measurement.” In addition to the ATLAS measurement, described in 2018 within the European Physical Journal C, one other measurement of the W boson’s mass from the CERN experiment LHCb was additionally in keeping with the usual mannequin prediction, researchers reported within the January Journal of High Energy Physics.
“The W boson mass is notoriously difficult to measure,” says LHCb physicist Mika Vesterinen of the University of Warwick in Coventry, England. That explains why it took CDF so lengthy to wrap up this evaluation, revealed greater than 10 years after the experiment ended.
Hopefully, scientists received’t have to attend that lengthy for an additional measurement. The ATLAS and LHCb collaborations are already engaged on improved W boson mass analyses. CMS, one other experiment at CERN, may additionally measurement up the particle.
If the brand new measurement holds up, it’s not but clear what secrets and techniques of physics is likely to be at play. New particles — reminiscent of these predicted by the speculation of supersymmetry, which posits that every identified particle has a heavier accomplice — may assist shift the W boson mass upward (SN: 9/6/16). Intriguingly, Heinemeyer factors out, those self same particles may also assist clarify one other current physics thriller — the magnetic gyrations of muons reported by the Muon g−2 experiment (SN: 4/7/21).
Whatever physicists uncover, they’ll acquire a brand new grasp on the particulars of this significant particle, says theoretical physicist Nathaniel Craig of the University of California, Santa Barbara. “At the end of the day, the added energy and attention devoted to the W mass measurement … will be an immensely positive thing.”