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Search for $C\!P$ violation in $\Lambda^0_b \to p K^-$ and $\Lambda^0_b \to p \pi^-$ decays

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Abstract

A search for $C\!P$ violation in $\Lambda^0_b \to p K^-$ and $\Lambda^0_b \to p \pi^-$ decays is presented using a sample of $pp$ collisions collected with the LHCb detector and corresponding to an integrated luminosity of 3.0 fb$^{-1}$. The $C\!P$-violating asymmetries are measured to be $A_{\mathrm{CP}}^{pK^-} = -0.020 \pm 0.013\pm 0.019$ and $A_{\mathrm{CP}}^{p\pi^-} = -0.035 \pm 0.017 \pm 0.020 $, and their difference $A_{\mathrm{CP}}^{pK^-}-A_{\mathrm{CP}}^{p\pi^-} = 0.014 \pm 0.022 \pm 0.010$, where the first uncertainties are statistical and the second systematic. These are the most precise measurements of such asymmetries to date.

Figures and captions

Invariant-mass distributions: (top left) $m_{ p K ^- }$, (top right) $m_{\overline p K ^+ }$, (bottom left) $m_{ p \pi ^- }$ and (bottom right) $m_{\overline p \pi ^+ }$ for candidates passing the (top) $ S_{ p K ^- }$ and (bottom) $ S_{ p \pi ^- }$ selections. The results of the fits are superimposed.

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Distributions of (top) momentum, (middle) transverse momentum and (bottom) pseudorapidity for (left) protons from $\Lambda ^0_ b $ decays and (right) $\Lambda ^0_ b $ baryons. The distributions are background-subtracted and normalised to unit area. Below each plot the ratio between the two distributions corresponding to $\Lambda ^0_ b \!\rightarrow p K ^- $ and $\Lambda ^0_ b \!\rightarrow p \pi ^- $ decays is also shown.

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Tables and captions

Systematic uncertainties on $ A_ C\!P ^{ p K ^- }$ and $ A_\mathcal{C}_{P} ^{ p \pi ^- }$ .

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Supplementary Material [file]

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Created on 11 December 2018.Citation count from INSPIRE on 11 December 2018.