cern.ch

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

[to restricted-access page]

Abstract

Time-dependent $CP$ asymmetries in the decay rates of the singly Cabibbo-suppressed decays $D^0\rightarrow K^-K^+$ and $D^0\rightarrow \pi^-\pi^+$ are measured in $pp$ collision data corresponding to an integrated luminosity of 3.0 fb$^{-1}$ collected by the LHCb experiment. The $D^0$ mesons are produced in semileptonic $b$-hadron decays, where the charge of the accompanying muon is used to determine the initial state as $D^0$ or $\bar{D}^0$. The asymmetries in effective lifetimes between $D^0$ and $\bar{D}^0$ decays, which are sensitive to indirect $CP$ violation, are determined to be \begin{align*} A_{\Gamma}(K^-K^+) = (-0.134 \pm 0.077 \; {}^{+0.026}_{-0.034})\% A_{\Gamma}(\pi^-\pi^+) = (-0.092\pm 0.145 \; {}^{+0.025}_{-0.033})\% \end{align*} where the first uncertainties are statistical and the second systematic. This result is in agreement with previous measurements and with the hypothesis of no indirect $CP$ violation in $D^0$ decays.

Figures and captions

Invariant mass distributions for (a) $ D ^0 \rightarrow K ^- K ^+ $ , (b) $ D ^0 \rightarrow \pi ^- \pi ^+ $ and (c) $ D ^0 \rightarrow K ^- \pi ^+ $ candidates. The results of the fits are overlaid. Underneath each plot the pull in each mass bin is shown, where the pull is defined as the difference between the data point and total fit, divided by the corresponding uncertainty.

massal[..].pdf [21 KiB]
HiDef png [238 KiB]
Thumbnail [214 KiB]
*.C file
massallfullselKK_combined.pdf
massal[..].pdf [21 KiB]
HiDef png [246 KiB]
Thumbnail [219 KiB]
*.C file
massallfullselpipi_combined.pdf
massal[..].pdf [21 KiB]
HiDef png [207 KiB]
Thumbnail [191 KiB]
*.C file
massallfullselKpi_combined.pdf

Raw $ C P$ asymmetry as function of $ D ^0$ decay time for (a) $ D ^0 \rightarrow K ^- K ^+ $ , (b) $ D ^0 \rightarrow \pi ^- \pi ^+ $ and (c) $ D ^0 \rightarrow K ^- \pi ^+ $ candidates. The results of the $\chi^2$ fits are shown as blue, solid lines with the $\pm1$ standard-deviation ($\sigma$) bands indicated by the dashed lines. The green, dashed lines indicate one $ D ^0$ lifetime ($\tau=410.1\rm fs $). Underneath each plot the pull in each time bin is shown.

Agamma[..].pdf [28 KiB]
HiDef png [216 KiB]
Thumbnail [181 KiB]
*.C file
Agamma_ACP_AllKKSimfit.pdf
Agamma[..].pdf [28 KiB]
HiDef png [226 KiB]
Thumbnail [190 KiB]
*.C file
Agamma_ACP_AllpipiSimfit.pdf
Agamma[..].pdf [27 KiB]
HiDef png [183 KiB]
Thumbnail [164 KiB]
*.C file
Agamma_ACP_AllKpiSimfit.pdf

Mistag probability, before subtracting the contribution from wrong-sign (WS) decays, determined with $ D ^0 \rightarrow K ^- \pi ^+ $ candidates. The result of the fit to the data points with an exponential function is overlaid (solid, blue line). The red, dashed line indicates the expected mistag contribution from WS decays.

momega[..].pdf [21 KiB]
HiDef png [208 KiB]
Thumbnail [160 KiB]
*.C file
momega_Kpiomega_fullrange.pdf

Measured values of $ A_{\Gamma}$ for different magnet polarities and data-taking periods for (a) $ D ^0 \rightarrow K ^- K ^+ $ , (b) $ D ^0 \rightarrow \pi ^- \pi ^+ $ and (c) $ D ^0 \rightarrow K ^- \pi ^+ $ decays. The vertical line and error band indicate the average $ A_{\Gamma}$ obtained from the combined data set. The error bars indicate the statistical uncertainty only.

polari[..].pdf [13 KiB]
HiDef png [112 KiB]
Thumbnail [101 KiB]
*.C file
polarity_KK_check.pdf
polari[..].pdf [13 KiB]
HiDef png [110 KiB]
Thumbnail [99 KiB]
*.C file
polarity_pipi_check.pdf
polari[..].pdf [13 KiB]
HiDef png [106 KiB]
Thumbnail [97 KiB]
*.C file
polarity_Kpi_check.pdf

Animated gif made out of all figures.

PAPER-2014-069.gif
Thumbnail
thumbnail_PAPER-2014-069.gif

Tables and captions

Contributions to the systematic uncertainty of $ A_{\Gamma}( K ^- K ^+ )$ and $ A_{\Gamma}(\pi ^- \pi ^+ )$ . The constant and multiplicative scale uncertainties are given separately.

Table_1.pdf [47 KiB]
HiDef png [99 KiB]
Thumbnail [46 KiB]
tex code
Table_1.pdf

Supplementary Material [file]

Supplementary material full pdf

supple[..].pdf [118 KiB]
supplementary.pdf

This ZIP file contains supplemetary material for the publication LHCb-PAPER-2014-053. The files are: Supplementary.pdf : An overview of the extra figures *.pdf, *.png, *.eps, *.C : The figures in variuous formats

Fig1-S.pdf [14 KiB]
HiDef png [208 KiB]
Thumbnail [191 KiB]
*C file
Fig1-S.pdf

Created on 17 August 2019.Citation count from INSPIRE on 23 August 2019.