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Measurement of angular and CP asymmetries in $D^0\to\pi^+\pi^-\mu^+\mu^-$ and $D^0\to K^+K^-\mu^+\mu^-$ decays

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Abstract

The first measurements of the forward-backward asymmetry of the dimuon pair ($A_{FB}$), the triple-product asymmetry ($A_{2\phi}$), and the charge-parity-conjugation asymmetry ($A_{CP}$), in $D^0\to\pi^+\pi^-\mu^+\mu^-$ and $D^0\to K^+K^-\mu^+\mu^-$ decays are reported. They are performed using data from proton-proton collisions collected with the LHCb experiment from 2011 to 2016, corresponding to a total integrated luminosity of 5 fb$^{-1}$. The asymmetries are measured to be \begin{align*} A_{FB}(D^0\to\pi^+\pi^-\mu^+\mu^-) &= (\phantom{-}3.3\pm3.7\pm0.6)\%,\\ A_{2\phi}(D^0\to\pi^+\pi^-\mu^+\mu^-)&= (-0.6\pm3.7\pm0.6)\%,\\ A_{CP}(D^0\to\pi^+\pi^-\mu^+\mu^-) &= (\phantom{-}4.9\pm3.8\pm0.7)\%,\\ A_{FB}(D^0\to K^+K^-\mu^+\mu^-) &= (0\pm11\pm2)\%,\\ A_{2\phi}(D^0\to K^+K^-\mu^+\mu^-)&= (9\pm11\pm1)\%,\\ A_{CP}(D^0\to K^+K^-\mu^+\mu^-) &= (0\pm11\pm2)\%, \end{align*} where the first uncertainty is statistical and the second systematic. The asymmetries are also measured as a function of the dimuon invariant mass. The results are consistent with the Standard Model predictions.

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Diagram showing the topology of a $ D ^0 \rightarrow h^+h^-\mu^+\mu^-$ decay, with the definition of the angles that are relevant for the measurement.

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Distribution of $ m( h^+h^-\mu^+\mu^- )$ for (a) $ D ^0 \rightarrow \pi ^+ \pi ^- \mu^+\mu^-$ and (b) $ D ^0 \rightarrow K ^+ K ^- \mu^+\mu^-$ efficiency-weighted candidates, with fit projections overlaid.

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Tables and captions

Efficiency-weighted yields and measured signal asymmetries for (top) $ D ^0 \rightarrow \pi ^+ \pi ^- \mu^+\mu^-$ and (bottom) $ D ^0 \rightarrow K ^+ K ^- \mu^+\mu^-$ decays in the dimuon-mass regions. For the asymmetries the first uncertainty is statistical and the second systematic. Measurements are reported only in regions where a significant signal was previously observed [12]. The sum of the yields in the dimuon-mass regions is not expected to match the yield of the full range, because the latter includes also the regions where no yields are reported.

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Supplementary Material [file]

This ZIP file contains supplemetary material for the publication LHCb-PAPER-2018-020. The files are: Supplementary-LHCb-PAPER-2018-020.pdf : An overview of the extra figures *.pdf, *.png, *.eps, *.C : The figures in variuous formats

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Created on 17 December 2018.Citation count from INSPIRE on 18 December 2018.