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Search for direct $CP$ violation in $D^0 \rightarrow h^- h^+$ modes using semileptonic $B$ decays

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Abstract

A search for direct CP violation in D0 -> h- h+ (where h=K or pi) is presented using data corresponding to an integrated luminosity of 1.0 fb^-1 collected in 2011 by LHCb in pp collisions at a centre-of-mass energy of 7 TeV. The analysis uses D0 mesons produced in inclusive semileptonic b-hadron decays to the D0 mu X final state, where the charge of the accompanying muon is used to tag the flavour of the D0 meson. The difference in the CP-violating asymmetries between the two decay channels is measured to be Delta A_CP = A_CP(K-K+) - A_CP(pi-pi+) = (0.49 +- 0.30 (stat) +- 0.14 (syst)) . This result does not confirm the evidence for direct CP violation in the charm sector reported in other analyses.

Figures and captions

Invariant mass distributions for (a, c) $ D ^0 \rightarrow K ^- K ^+ $ and (b, d) $ D ^0 \rightarrow \pi ^- \pi ^+ $ muon-tagged candidates for the two magnet polarities. The result of the fit is overlaid, showing the contribution from signal, combinatorial background and $ D ^0 \rightarrow K ^- \pi ^+ $ reflection. Underneath each plot the pull in each mass bin is shown.

 plot_a[..].pdf [36 KiB]
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plot_asym_KK_up.pdf
plot_a[..].pdf [36 KiB]
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plot_asym_pipi_up.pdf
plot_a[..].pdf [35 KiB]
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plot_asym_KK_down.pdf
plot_a[..].pdf [36 KiB]
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plot_asym_pipi_down.pdf

Kinematic distributions of the (a, c) $ D ^0$ meson and (b, d) muon for $ D ^0 \rightarrow \pi ^- \pi ^+ $ (black circles) and $ D ^0 \rightarrow K ^- K ^+ $ (red squares) candidates normalised to unit area. The histograms show the distributions of signal candidates, after background subtraction. Underneath each plot the ratio of the two distributions is shown.

 plot_u[..].pdf [22 KiB]
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plot_up_unweighted_d0Pt.pdf
plot_u[..].pdf [21 KiB]
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plot_up_unweighted_muonPt.pdf
plot_u[..].pdf [20 KiB]
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plot_up_unweighted_d0Eta.pdf
plot_u[..].pdf [21 KiB]
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plot_up_unweighted_muonEta.pdf

Kinematic distributions of the (a, c) $ D ^0$ meson and (b, d) muon for $ D ^0 \rightarrow \pi ^- \pi ^+ $ (black circles) and $ D ^0 \rightarrow K ^- K ^+ $ (red squares) candidates normalised to unit area after the weighting procedure. The histograms show the distributions of signal candidates, after background subtraction. Underneath each plot the ratio of the two distributions is shown.

 plot_u[..].pdf [22 KiB]
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*.C file
plot_up_weighted_d0Pt.pdf
plot_u[..].pdf [21 KiB]
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*.C file
plot_up_weighted_muonPt.pdf
plot_u[..].pdf [21 KiB]
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plot_up_weighted_d0Eta.pdf
plot_u[..].pdf [21 KiB]
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plot_up_weighted_muonEta.pdf

Decay time distribution for signal candidates (solid points) with the result from the fit overlaid for (a) $ D ^0 \rightarrow K ^- K ^+ $ and (b) $ D ^0 \rightarrow \pi ^- \pi ^+ $ decays. The distribution for background candidates scaled to a $\pm34 {\mathrm{ Me V /}c^2} $ window around the nominal $ D ^0$ mass is shown in the shaded (green) region. The distributions for signal and background candidates are obtained using the sPlot method.

 lifeti[..].pdf [10 KiB]
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lifetime_d2kk.pdf
lifeti[..].pdf [10 KiB]
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lifetime_d2pipi.pdf

Raw asymmetries and $\Delta A_{ C P }$ as a function of (a) $p_{\rm T}$ and (b) $\eta$ of the $ D ^0$ meson. No weighting is applied.

 plot_c[..].pdf [15 KiB]
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plot_crosscheck_d0Pt.pdf
plot_c[..].pdf [14 KiB]
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plot_crosscheck_d0Eta.pdf

Animated gif made out of all figures.

 PAPER-2013-003.gif
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thumbnail_PAPER-2013-003.gif

Tables and captions

Unweighted raw asymmetries (in %) for the $ D ^0 \rightarrow \pi ^- \pi ^+ $ , $ D ^0 \rightarrow K ^- K ^+ $ and $ D ^0 \rightarrow K ^- \pi ^+ $ decays for the two magnet polarities. The mean value is the arithmetic average over the two polarities. The uncertainties are statistical only.

 Table_1.pdf [53 KiB]
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Weighted raw asymmetries (in %) for the $ D ^0 \rightarrow \pi ^- \pi ^+ $ and $ D ^0 \rightarrow K ^- K ^+ $ decays for the two magnet polarities. The mean value is the arithmetic average over the two polarities. The uncertainties are statistical only.

 Table_2.pdf [52 KiB]
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Contributions to the systematic uncertainty of $\Delta A_{ C P }$ .

 Table_3.pdf [81 KiB]
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Created on 27 April 2024.