Wednesday, May 10, 2017

Some B Meson Decay Anomalies Disappear In Run-2 Data

The LHCb had detected a four sigma anomaly from the expected decays of B mesons into decays including two leptons of opposite charge in Run-1. But, the anomaly appears to have vanished once Run-2 data is included (original formatting of preprint abstract retained).

This is a big deal, because real anomalies, unlike experimental errors or flukes, should be significantly stronger when the size and robustness of the data set increases, not less significant. Anomalies the decline in significance as more data is collected are almost always flukes or experimental errors even if the results are sufficiently significant that they might otherwise constitute a notable anomaly.

The branching fraction and effective lifetime of B0(s)μ+μ at LHCb with Run 1 and Run 2 data

After Run 1 of the LHC, global fits to bs observables show a deviation from the Standard Model (SM) with a significance of  4 standard devations. An example of a bs process is the decay of a B0s meson into two muons (B0sμ+μ). The latest analysis of B0(s)μ+μ decays by LHCb with Run 1 and Run 2 data is presented. The B0sμ+μ decay is observed for the first time by a single experiment. In addition, the first measurement of the B0sμ+μeffective lifetime is performed. No significant excess of B0μ+μ decays is observed. All results are consistent with the SM and constrain New Physics in bs processes.
Not every single pathway that is the subject of the anomalies tending to show lepton non-universality in B meson decays is ruled out by this result, but is does disfavor these hints of beyond the Standard Model physics.

Another result disfavoring the anomaly in B meson decays is here. So do these experiments. And these experiments. And these experiments. And these experiments. It is also disfavored by the frequency of Higgs boson decays to tau leptons.

Thus, while there is some experimental data that seems to show anomalies, finding a theory that can accommodate these data points while simultaneously being consistent with the substantial experimental evidence tending to show that there are not violations of lepton flavor universality, is quite challenging. As a result, even though the anomaly is putatively a four sigma effect, it is probably really just a statistical fluke, or a consequence of underestimating systemic error or look elsewhere effects, or is a consequence of a mistake in conducting the experiment or analyzing it.

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