Updated determination of $D^0$-$\overline{D}{}^0$ mixing and CP violation parameters with $D^0\to K^+\pi^-$ decays

Information

LHCb-PAPER-2017-046
CERN-EP-2017-304
arXiv:1712.03220 [PDF]

(Submitted on 08 Dec 2017)
Phys. Rev. D97 (2018) 031101
Inspire 1642234

Tools

Abstract

We report measurements of charm-mixing parameters based on the decay-time-dependent ratio of $D^0\to K^+\pi^-$ to $D^0\to K^-\pi^+$ rates. The analysis uses a data sample of proton-proton collisions corresponding to an integrated luminosity of $5.0$ fb$^{-1}$ recorded by the LHCb experiment from 2011 through 2016. Assuming charge-parity (CP) symmetry, the mixing parameters are determined to be $x'^2=(3.9 \pm 2.7) \times10^{-5}$, $y'=(5.28 \pm 0.52) \times 10^{-3}$, and $R_D=(3.454 \pm 0.031)\times10^{-3}$. Without this assumption, the measurement is performed separately for $D^0$ and $\overline{D}{}^0$ mesons, yielding a direct CP-violating asymmetry $A_D =(-0.1\pm9.1)\times10^{-3}$, and magnitude of the ratio of mixing parameters $1.00< |q/p| <1.35$ at the $68.3\%$ confidence level. All results include statistical and systematic uncertainties and improve significantly upon previous single-measurement determinations. No evidence for CP violation in charm mixing is observed.

Figures and captions

Distribution of $ M( D ^0 \pi_{\rm s} ^+)$ for selected (a) right-sign $ D ^0 \rightarrow K^-\pi^+$ and (b) wrong-sign $ D ^0 \rightarrow K^+\pi^-$ candidates.	Fig1a.pdf [31 KiB] HiDef png [201 KiB] Thumbnail [165 KiB] *.C file
	Fig1b.pdf [32 KiB] HiDef png [222 KiB] Thumbnail [213 KiB] *.C file
Efficiency-corrected ratios of WS-to-RS yields for (a) $ D ^{+}$ decays, (b) $ D ^{-}$ decays, and (c) their differences as functions of decay time in units of $ D ^0$ lifetime. Projections of fits allowing for (dashed line) no $ C P$ violation, (dotted line) no direct $ C P$ violation, and (solid line) direct and indirect $ C P$ violation are overlaid. The last two curves overlap. The abscissa of each data point corresponds to the average decay time over the bin. The error bars indicate the statistical uncertainties.	Fig2.pdf [14 KiB] HiDef png [245 KiB] Thumbnail [225 KiB] *.C file
Two-dimensional confidence regions in the $(x'^2,y')$ plane obtained (a) without any restriction on $ C P$ violation, (b) assuming no direct $ C P$ violation, and (c) assuming $ C P$ conservation. The dashed (solid) curves in (a) and (b) indicate the contours of the mixing parameters associated with $\overline{ D }{} {}^0$ ( $ D ^0$ ) decays. The best-fit value for $\overline{ D }{} {}^0$ ( $ D ^0$ ) decays is shown with an open (filled) point. The solid, dashed, and dotted curves in (c) indicate the contours of $ C P$ -averaged mixing parameters at 68.3%, 95.5%, and 99.7% confidence levels (CL), respectively, and the point indicates the best-fit value.	Fig3.pdf [18 KiB] HiDef png [159 KiB] Thumbnail [134 KiB] *.C file
Animated gif made out of all figures.	PAPER-2017-046.gif Thumbnail

Tables and captions

Results of fits for different $ C P$ -violation hypotheses. The first contribution to the uncertainties is statistical and the second systematic. Correlations include both statistical and systematic contributions.

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Supplementary Material [file]

This ZIP file contains supplemetary material for the publication LHCb-PAPER-2017-046. The files are: Supplementary-LHCb-PAPER-2017-046.pdf : An overview of the extra figures .pdf, .png, .eps, .C : The figures in various formats	Fig10.pdf [15 KiB] HiDef png [233 KiB] Thumbnail [160 KiB] *C file
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