These contributions are too small to explain the current anomaly in the electron’s anomalous magnetic moment, says NA64 spokesperson Sergei Gninenko. The result sets new bounds on the e –X interaction strength and, as a result, on the contributions of X bosons to a e: X bosons with a mass below 1 GeV could contribute at most between one part in 10 15 and one part in 10 13, depending on the X-boson type and mass. The result sets new bounds on the e –X interaction strengthĪnalysing data collected in 2016, 20, corresponding to about 3 × 10 11 electrons-on-target, the NA64 team found no evidence for such events. NA64 searches for X bosons by directing 100 GeV electrons generated by the SPS onto a target, and looking for missing energy in the detector via electron–nuclei scattering e –Z → e –ZX.
Given experimental constraints on its decay modes involving Standard Model particles, it is presumed to decay predominantly invisibly, for example into dark-sector particles. The generic X boson could be a sub- GeV scalar, pseudoscalar, vector or axial- vector particle. Motivated by this inconsistency, the NA64 collaboration at CERN set out to investigate whether new physics – in the form of a lightweight “X boson” – might be influencing the electron’s behaviour. Though with a much lower significance, a similar puzzle may also be emerging for the anomalous magnetic moment of the electron, a e.ĭepending on which of two recent independent measurements of the fine-structure constant is used in the theoretical calculation of a e – one obtained at Berkeley in 2018 or the other at Kastler–Brossel Laboratory in Paris in 2020 – the Standard Model prediction stands 2.4σ higher or 1.6σ lower than the best experimental value, respectively. Recent measurements bolstering the longstanding tension between the experimental and theoretical values of the muon’s anomalous magnetic moment generated a buzz in the community. Exploration The NA64 set up is being used to search for new particles that might account for the electron g-2 and ATOMKI anomalies.
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