The fight about the heft of a really hard-to-detect particle is heating up. What’s at stake? Only the primary concept describing all identified subject in the universe.
A recalculation of the mass of an elementary particle, the W boson, has elevated the pressure involving measurements from competing particle collider experiments. The supreme end result could bolster the common model of particle physics, which describes the basic forces and quantum bits that make up anything we see in the cosmos. Or it could expose symptoms of the typical model’s breakdown, relying on which lab’s respond to prevails.
A reanalysis of previous information from the Large Hadron Collider’s ATLAS experiment yields a W boson mass of about 80,360 million electron volts, or MeV. Scientists with the experiment, at CERN in Geneva, claimed the measurement March 23 at the Rencontres de Moriond convention in La Thuile, Italy. The revised value is closely aligned with predictions from the common model.
It also boasts minimized uncertainty from the researchers’ prior examination of the information, which they noted in 2018, rising their self confidence that they got the mass appropriate.
But the up to date mass is at odds with that of yet another team. In 2022, researchers from the Collider Detector at Fermilab, or CDF, experiment shocked the physics local community with a measurement of 80,434 MeV — about 100 MeV heavier than envisioned (SN: 4/7/22). If the CDF report is right, it implies that some thing is off with the conventional product that has persevered in the face of every experimental problem thrown at it about the previous 50 decades.
The W boson is dependable for the weak pressure, just one of 3 elementary forces in the typical model (SN: 2/5/83). And “it’s the only mass of a particle in the normal product that can be calculated,” claims theoretical physicist Sven Heinemeyer of the Karlsruhe Institute of Technologies in Germany. That is, the common product theory yields a distinct mass for the W boson, whilst the masses of other particles these kinds of as electrons and quarks are inputs and can be — as far as the principle is anxious — any value. Getting a W boson mass that’s diverse from regular model predictions would present the latest theory is incorrect.
The ATLAS reanalysis presents a more robust counterpoint to the CDF assert than the previously ATLAS investigation of the exact knowledge. “The new analysis is an essential affirmation of our previous outcome,” says Andreas Hoecker, a physicist at CERN.
The most current ATLAS worth widens the chasm that separates CDF’s mass measurement from the herd of other scientific tests. But it should not be witnessed as erasing CDF’s typical model problem, claims Duke College physicist Ashutosh Kotwal, a member of the CDF collaboration.
“The perspective on the CDF [announcement of a heavy W boson in 2022] does not change due to the fact of the ATLAS reanalysis,” Kotwal claims. Simply because the reanalysis is based mostly on data that ATLAS currently unveiled in 2017, he says, “the reality that ATLAS obtains a comparable value as just before is to be predicted.”
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Heinemeyer, who is not affiliated with ATLAS or CDF, sees a change in the W boson mass landscape, but no indicator of a resolution of the discrepancy.
“Having 1 new measurement is not ample,” Heinemeyer claims. “If a lot more and far more measurements ended up to occur out now from ATLAS and [other experiments], and they would all be in the very same ballpark, at some stage the local community would determine CDF did one thing wrong.”
The up coming word on the W boson mass will likely arrive with pending studies from ATLAS and other experiments at CERN. The CDF experiment shut down in 2011, so it will not add further more to the debate.
In the meantime, scientists hope to scrutinize each other’s analyses to look for for clues that may well enable describe discrepancies in W boson mass measurements. “The CDF April 2022 paper supplies a quantity of cross-checks of the CDF methodology and is clear,” Kotwal claims. “I seem ahead to thorough conversations of the ATLAS methodology.”
In the conclude, the conflict could reveal a new crack in the standard design. Or it could flip out to be yet another example of one of the most successful theories in record standing potent.