# I Decay of the Bs0 meson latest LHC results 7.8 sigma

1. Apr 12, 2017

### kodama

In its most recent analysis the LHCb experiment team took into account not only the first but also the second phase of operation of the LHC. The larger statistics helped achieve exceptional accuracy of the measurement of the decay of the beauty meson into a muon and anti-muon, of up to 7.8 standard deviations (commonly denoted by the Greek letter sigma). In practice, this means that the probability of registering a similar result by random fluctuation is less than one to over 323 trillion.

"The spectacular measurement of the decay of the beauty meson into a muon-anti-muon pair agrees with the predictions of the Standard Model with an accuracy of up to up to nine decimal places!" emphasizes Prof. Witek.

The Standard Model has emerged victorious from another confrontation with reality.

"The latest analysis significantly narrows down the values of the parameters that should be assumed by certain currently proposed extensions of the Standard Model, for example supersymmetric theories. They assume that each existing type of elementary particle has its own more massive counterpart - its superpartner. Now, as a result of the measurements, theorists dealing with supersymmetry have less and less possibility of adapting their theory to reality. Instead of coming closer, the new physics is again receding," concludes Prof. Witek.

^

so the SM model predicts decay of B meson to muon-antimuon
and the latest data set from LHC confirms SM to 7.8 sigma and dis confirms various SUSY that predict a different decay rate of B meson.

how restrictive are B meson decays on SUSY, esp at 7.8 sigma agreement with SM

2. Apr 13, 2017

### Staff: Mentor

"7.8 sigma agreement with SM" doesn't make sense. A branching fraction 0 is 7.8 standard deviations away - but no one expected the decay to be impossible anyway. This could well be the last LHCb measurement quoting a significance as the existence has been established beyond reasonable doubt. Future measurements will just give the measured branching fraction with its uncertainty. In this case, $3.0 \pm 0.6 ^{+0.3}_{-0.2}$ ppb, in agreement with the SM prediction of $3.65\pm 0.23$ ppb, and slowly approaching its accuracy.

3. Apr 13, 2017

### kodama

i think the take home message is

"The spectacular measurement of the decay of the beauty meson into a muon-anti-muon pair agrees with the predictions of the Standard Model with an accuracy of up to up to nine decimal places!" emphasizes Prof. Witek.

and

"The latest analysis significantly narrows down the values of the parameters that should be assumed by certain currently proposed extensions of the Standard Model, for example supersymmetric theories. They assume that each existing type of elementary particle has its own more massive counterpart - its superpartner. Now, as a result of the measurements, theorists dealing with supersymmetry have less and less possibility of adapting their theory to reality. Instead of coming closer, the new physics is again receding," concludes Prof. Witek.

Prof. Mariusz Witek from the Institute of Nuclear Physics of the Polish Academy of Sciences

article
https://phys.org/news/2017-04-accurate-rare-meson-modern-physics.html

The most accurate measurement of rare meson decay confirms modern physics
April 13, 2017

"
Many scientists working on the LHCb experiment at CERN had hoped that the exceptional accuracy in the measurement of the rare decay of the Bs0 meson would at last delineate the limits of the Standard Model, the current theory of the structure of matter, and reveal phenomena unknown to modern physics. But the spectacular result of the latest analysis has only served to extend the range of applicability of the Standard Model