Newly released data taken using the Belle II experiment at KEK in Japan and the LHCb experiment at CERN in Switzerland show no sign of a possible anomaly that researchers think could provide a route to overturning the standard model of particle physics [1– 3].

According to the standard model, electrons, muons, and tau leptons should all behave identically when subjected to any of the fundamental forces of nature. Over a decade ago, researchers began questioning the validity of this assumption—known as lepton universality—when they observed high-energy particle decays that deviated from standard-model predictions. Specifically, the observations concerned the decay of B mesons into various leptons, with the experiments hinting that a few more tau leptons were being produced than expected. Excitement built among particle physicists, who hoped they were on the cusp of finding the long-sought standard-model violation that would uncover new physical phenomena. Hopes rose further as other experiments found hints of lepton-universality violations in the decay of B mesons into electrons and muons, but the signals remained too small to rule out experimental artifacts.

Then at the end of last year, hopes began to fade when the LHCb Collaboration released data for B-meson decays involving electrons and muons that exactly matched standard-model predictions [2, 3]. Now data from the Belle II Collaboration for a different B-meson decay involving electrons and muons dim those hopes further [1]. The study provides the most precise lepton-universality test yet in such decays. But researchers haven’t yet given up on leptons unlocking a door to new physics, says Belle II Collaboration member Henrik Junkerkalefeld of the University of Bonn, Germany. He notes that, although the results provide new constraints on the options for undiscovered physics, they don’t completely rule them all out.

The ATLAS and CMS collaborations at CENR’s Large Hadron Collider (LHC) have been making ever more precise measurements of the Higgs boson’s mass since the particle’s discovery.

The new ATLAS measurement combines two results: a new Higgs boson mass measurement based on an analysis of the particle’s decay into two high-energy photons (diphoton channel) and an earlier mass measurement based on a study of its decay into four leptons (four-lepton channel).

The new measurement in the diphoton channel, which combines analyses of the full ATLAS data sets from Runs 1 and 2 of the LHC, resulted in a mass of 125.22 billion electronvolts (GeV) with an uncertainty of only 0.14 GeV.

Naoko Kurahashi Neilson was on a Zoom call when she saw it for the first time.

She and two PhD students—Mirco Hünnefeld of TU Dortmund University in Germany and Steve Sclafani of Drexel University in the United States—had received permission to review the results of their analysis. Using 10 years of data and 60,000 detections from the IceCube Neutrino Observatory, they were trying to map the emission of tiny, ghostly particles called neutrinos from the band of the Milky Way.

Kurahashi Neilson remembers the three of them staring at the image together. Slowly, they realized that they were, indeed, looking at the first-ever neutrino image of our galaxy.