Strong constraints on the b → sγ photon polarisation from B0 → K*0e+e− decays



Aaij, R, Abellán Beteta, C, Ackernley, T, Adeva, B, Adinolfi, M, Afsharnia, H, Aidala, CA, Aiola, S, Ajaltouni, Z, Akar, S
et al (show 976 more authors) (2020) Strong constraints on the b → sγ photon polarisation from B0 → K*0e+e− decays. Journal of High Energy Physics, 2020 (12).

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Abstract

<jats:title>A<jats:sc>bstract</jats:sc> </jats:title><jats:p>An angular analysis of the <jats:italic>B</jats:italic><jats:sup>0</jats:sup> → <jats:italic>K*</jats:italic><jats:sup>0</jats:sup><jats:italic>e</jats:italic><jats:sup>+</jats:sup><jats:italic>e</jats:italic><jats:sup><jats:italic>−</jats:italic></jats:sup> decay is performed using a data sample corresponding to an integrated luminosity of 9 fb<jats:sup><jats:italic>−</jats:italic>1</jats:sup> of <jats:italic>pp</jats:italic> collisions collected with the LHCb experiment. The analysis is conducted in the very low dielectron mass squared (<jats:italic>q</jats:italic><jats:sup>2</jats:sup>) interval between 0<jats:italic>.</jats:italic>0008 and 0<jats:italic>.</jats:italic>257 GeV<jats:sup>2</jats:sup>, where the rate is dominated by the <jats:italic>B</jats:italic><jats:sup>0</jats:sup> → <jats:italic>K</jats:italic><jats:sup><jats:italic>*</jats:italic>0</jats:sup><jats:italic>γ</jats:italic> transition with a virtual photon. The fraction of longitudinal polarisation of the <jats:italic>K</jats:italic><jats:sup><jats:italic>*</jats:italic>0</jats:sup> meson, <jats:italic>F</jats:italic><jats:sub>L</jats:sub>, is measured to be <jats:italic>F</jats:italic><jats:sub>L</jats:sub> = (4<jats:italic>.</jats:italic>4 ± 2<jats:italic>.</jats:italic>6 ± 1<jats:italic>.</jats:italic>4)%, where the first uncertainty is statistical and the second systematic. The <jats:inline-formula><jats:alternatives><jats:tex-math>$$ {A}_{\mathrm{T}}^{\mathrm{Re}} $$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup> <mml:mi>A</mml:mi> <mml:mi>T</mml:mi> <mml:mi>Re</mml:mi> </mml:msubsup> </mml:math></jats:alternatives></jats:inline-formula> observable, which is related to the lepton forward-backward asymmetry, is measured to be <jats:inline-formula><jats:alternatives><jats:tex-math>$$ {A}_{\mathrm{T}}^{\mathrm{Re}} $$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup> <mml:mi>A</mml:mi> <mml:mi>T</mml:mi> <mml:mi>Re</mml:mi> </mml:msubsup> </mml:math></jats:alternatives></jats:inline-formula> = <jats:italic>−</jats:italic>0<jats:italic>.</jats:italic>06 ± 0<jats:italic>.</jats:italic>08 ± 0<jats:italic>.</jats:italic>02. The <jats:inline-formula><jats:alternatives><jats:tex-math>$$ {A}_{\mathrm{T}}^{(2)} $$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup> <mml:mi>A</mml:mi> <mml:mi>T</mml:mi> <mml:mfenced> <mml:mn>2</mml:mn> </mml:mfenced> </mml:msubsup> </mml:math></jats:alternatives></jats:inline-formula> and <jats:inline-formula><jats:alternatives><jats:tex-math>$$ {A}_{\mathrm{T}}^{\mathrm{Im}} $$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup> <mml:mi>A</mml:mi> <mml:mi>T</mml:mi> <mml:mi>Im</mml:mi> </mml:msubsup> </mml:math></jats:alternatives></jats:inline-formula> transverse asymmetries, which are sensitive to the virtual photon polarisation, are found to be <jats:inline-formula><jats:alternatives><jats:tex-math>$$ {A}_{\mathrm{T}}^{(2)} $$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup> <mml:mi>A</mml:mi> <mml:mi>T</mml:mi> <mml:mfenced> <mml:mn>2</mml:mn> </mml:mfenced> </mml:msubsup> </mml:math></jats:alternatives></jats:inline-formula> = 0<jats:italic>.</jats:italic>11 ± 0<jats:italic>.</jats:italic>10 ± 0<jats:italic>.</jats:italic>02 and <jats:inline-formula><jats:alternatives><jats:tex-math>$$ {A}_{\mathrm{T}}^{\mathrm{Im}} $$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup> <mml:mi>A</mml:mi> <mml:mi>T</mml:mi> <mml:mi>Im</mml:mi> </mml:msubsup> </mml:math></jats:alternatives></jats:inline-formula> = 0<jats:italic>.</jats:italic>02 ± 0<jats:italic>.</jats:italic>10 ± 0<jats:italic>.</jats:italic>01. The results are consistent with Standard Model predictions and provide the world’s best constraint on the <jats:italic>b</jats:italic> → <jats:italic>sγ</jats:italic> photon polarisation.</jats:p>

Item Type: Article
Depositing User: Symplectic Admin
Date Deposited: 24 Feb 2021 15:24
Last Modified: 02 Dec 2021 08:16
DOI: 10.1007/jhep12(2020)081
Open Access URL: https://link.springer.com/content/pdf/10.1007/JHEP...
URI: https://livrepository.liverpool.ac.uk/id/eprint/3116041