Measurement of the ratio of branching fractions ${\cal B}(B^0 \to K^{\ast 0} \gamma)/{\cal B}(B^0_s \to \phi \gamma)$

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The ratio of branching fractions of the radiative B decays B0 -> K*0 gamma and Bs0 -> phi gamma has been measured using 0.37 fb-1 of pp collisions at a centre of mass energy of sqrt(s) = 7 TeV, collected by the LHCb experiment. The value obtained is BR(B0 -> K*0 gamma)/BR(Bs0 -> phi gamma) = 1.12 +/- 0.08 ^{+0.06}_{-0.04} ^{+0.09}_{-0.08}, where the first uncertainty is statistical, the second systematic and the third is associated to the ratio of fragmentation fractions fs/fd. Using the world average for BR(B0 -> K*0 gamma) = (4.33 +/- 0.15) x 10^{-5}, the branching fraction BR(Bs0 -> phi gamma) is measured to be (3.9 +/- 0.5) x 10^{-5}, which is the most precise measurement to date.

Figures and captions

Result of the fit for the $ B ^0 \rightarrow K ^{*0} \gamma $ (left) and $ B ^0_ s \rightarrow \phi \gamma $ (right). The black points represent the data and the fit result is represented as a solid line. The signal is fitted with a Crystal Ball function (light dashed line) and the background is described as an exponential (dark dashed line). Below each invariant mass plot, the Poisson $\chi^2$ residuals [21] are shown.

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Animated gif made out of all figures.


Tables and captions

Correction factors and corresponding uncertainties affecting the signal yields, in percent, induced by peaking backgrounds, partially reconstructed backgrounds, signal cross-feed and multiple candidates. The total uncertainty is obtained by summing the individual contributions in quadrature.

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Summary of contributions to the relative systematic uncertainty on the ratio of branching fractions. Note that $f_s/f_d$ is quoted as a separate systematic uncertainty.

Table_2.pdf [58 KiB]
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Created on 20 February 2021.