Abstract
This Letter presents a study of the flavor-changing neutral current radiative B±→K±π∓π±γ decays performed using data collected in proton-proton collisions with the LHCb detector at 7 and 8TeV center-of-mass energies. In this sample, corresponding to an integrated luminosity of 3 fb-1, nearly 14 000 signal events are reconstructed and selected, containing all possible intermediate resonances with a K±π∓π± final state in the [1.1,1.9] GeV/c2 mass range. The distribution of the angle of the photon direction with respect to the plane defined by the final-state hadrons in their rest frame is studied in intervals of K±π∓π± mass and the asymmetry between the number of signal events found on each side of the plane is obtained. The first direct observation of the photon polarization in the b→sγ transition is reported with a significance of 5.2σ.
Highlights
The standard model (SM) predicts that the photon emitted from the electroweak penguin loop in b → sγ transitions is predominantly left-handed, since the recoiling s quark that couples to a W boson is left-handed
While the measured inclusive b → sγ rate [1] agrees with the SM calculations, no direct evidence exists for a nonzero photon polarization in this type of decay
Information about the photon polarization is obtained from the angular distribution of the photon direction with respect to the normal to the plane defined by the momenta of the three final-state hadrons in their center-of-mass frame
Summary
The standard model (SM) predicts that the photon emitted from the electroweak penguin loop in b → sγ transitions is predominantly left-handed, since the recoiling s quark that couples to a W boson is left-handed. Information about the photon polarization is obtained from the angular distribution of the photon direction with respect to the normal to the plane defined by the momenta of the three final-state hadrons in their center-of-mass frame.
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