First experimental study of photon polarization in radiative $B^{0}_{s}$ decays

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Abstract

The polarization of photons produced in radiative $B^{0}_{s}$ decays is studied for the first time. The data are recorded by the LHCb experiment in $pp$ collisions corresponding to an integrated luminosity of 3fb$^{-1}$ at center-of-mass energies of $7$ and $8$TeV. A time-dependent analysis of the $B^{0}_{s} \to \phi \gamma$ decay rate is conducted to determine the parameter ${\mathcal{A}}^\Delta$, which is related to the ratio of right- over left-handed photon polarization amplitudes in $b \to s \gamma$ transitions. A value of ${\mathcal{A}}^\Delta=-0.98^{ +0.46 +0.23}_{ -0.52 -0.20}$ is measured. This result is consistent with the Standard Model prediction within two standard deviations.

Figures and captions

 Fits to the invariant mass distributions of the $B ^0$ (top) and $B ^0_ s$ (bottom) candidates. Fig1a.pdf [32 KiB] HiDef png [526 KiB] Thumbnail [324 KiB] *.C file Fig1b.pdf [30 KiB] HiDef png [617 KiB] Thumbnail [346 KiB] *.C file Background-subtracted decay-time distributions for $B ^0 \rightarrow K ^{*0} \gamma$ (top) and $B ^0_ s \rightarrow \phi \gamma$ (bottom) decays with the fit projections overlaid and normalized residuals shown below. The projections of a fit with ${\mathcal{A}}^\Delta$ fixed to the central value of the SM prediction [2] are also shown. For display purposes, the PDF is shown as a histogram, integrated across each decay-time interval. Fig2a.pdf [18 KiB] HiDef png [161 KiB] Thumbnail [150 KiB] *.C file Fig2b.pdf [18 KiB] HiDef png [168 KiB] Thumbnail [156 KiB] *.C file Decay-time dependence of the ratio of the yields of $B ^0_ s \rightarrow \phi \gamma$ and $B ^0 \rightarrow K ^{*0} \gamma$ , with the fit overlaid. The expected distribution for the central value of the SM prediction [2] is also shown. Fig3.pdf [15 KiB] HiDef png [134 KiB] Thumbnail [132 KiB] *.C file Animated gif made out of all figures. PAPER-2016-034.gif Thumbnail

Supplementary Material [file]

 Supplementary material full pdf supple[..].pdf [141 KiB] This ZIP file contains supplemetary material for the publication LHCb-PAPER-2016-034. The files are: Supplementary.pdf : An overview of the extra figures *.pdf, *.png, *.eps, *.C : The figures in variuous formats Fig4a.pdf [31 KiB] HiDef png [218 KiB] Thumbnail [191 KiB] *C file Fig4b.pdf [31 KiB] HiDef png [218 KiB] Thumbnail [193 KiB] *C file

Created on 20 February 2021.