Leading hadronic contribution to the muon magnetic moment from lattice QCD

The standard model of particle physics describes the vast majority of experiments and observations involving elementary particles. Any deviation from its predictions would be a sign of new, fundamental physics. One long-standing discrepancy concerns the anomalous magnetic moment of the muon, a measure of the magnetic field surrounding that particle. Standard-model predictions¹ exhibit disagreement with measurements² that is tightly scattered around 3.7 standard deviations. Today, theoretical and measurement errors are comparable; however, ongoing and planned experiments aim to reduce the measurement error by a factor of four. Theoretically, the dominant source of error is the leading-order hadronic vacuum polarization (LO-HVP) contribution. For the upcoming measurements, it is essential to evaluate the prediction for this contribution with independent methods and to reduce its uncertainties. The most precise, model-independent determinations so far rely on dispersive techniques, combined with measurements of the cross-section of electron-positron annihilation into hadrons^3-6. To eliminate our reliance on these experiments, here we use ab initio quantum chromodynamics (QCD) and quantum electrodynamics simulations to compute the LO-HVP contribution. We reach sufficient precision to discriminate between the measurement of the anomalous magnetic moment of the muon and the predictions of dispersive methods. Our result favours the experimentally measured value over those obtained using the dispersion relation. Moreover, the methods used and developed in this work will enable further increased precision as more powerful computers become available.

Cognitive impairment, emotional disorder and length of stay of elderly patients in a district general hospital

All patients over 65 in a district general teaching hospital (n = 204) were screened for cognitive impairment and emotional disorder using the Clifton Assessment Procedures for the Elderly, the Mini-Mental State and the General Health Questionnaire. Patients scoring in the disordered range were psychiatrically assessed. These procedures gave an estimated prevalence of cognitive impairment of 22 per cent in the 164 patients satisfactorily assessed. Forty-three per cent of patients scored beyond the GHQ cut-off, but there was a high false positive rate. Cognitively impaired patients had a significantly longer hospital stay than the unimpaired. The majority (60 per cent) of these patients could not be discharged because of lack of an appropriate place elsewhere. Amongst all elderly patients whose discharge was prevented in this way, the cognitively impaired were markedly over-represented. The data have implications for the efficient use of hospital beds and for the welfare of elderly patients in acute hospitals.