Search for $CP$ violation in the phase space of $D^0 \to \pi^-\pi^+\pi^0$ decays with the energy test

Information

LHCb-PAPER-2023-005
CERN-EP-2023-103
arXiv:2306.12746 [PDF]

(Submitted on 22 Jun 2023)
JHEP 09 (2023) 129
Inspire 2670819

Tools

Abstract

A search for $CP$ violation in $D^0 \to \pi^-\pi^+\pi^0$ decays is reported, using $pp$ collision data collected by the LHCb experiment from 2015 to 2018 corresponding to an integrated luminosity of 6$fb^{-1}$. An unbinned model-independent approach provides sensitivity to local $CP$ violation within the two-dimensional phase space of the decay. The method is validated using the Cabibbo-favoured channel $\D^0 \to \K^-\pi^+\pi^0$ and background regions of the signal mode. The results are consistent with $CP$ symmetry in this decay.

Figures and captions

Distributions of $\Delta m$ for (left) the resolved and (right) merged $\pi^0$ samples after the application of all selection criteria except the $\Delta m$ requirement. Also shown are projections of the fit model used to evaluate signal yields and purity.	fig1a.pdf [202 KiB] HiDef png [208 KiB] Thumbnail [154 KiB] *.C file
	fig1b.pdf [200 KiB] HiDef png [225 KiB] Thumbnail [174 KiB] *.C file
Dalitz plots for the background-subtracted signal samples for (left) the resolved and (right) merged $\pi^0$ categories, with the two $m^2(\pi^{\pm}\pi^0)$ variables chosen for the projection. The three $\rho^{\pm,0}$ resonances dominate the phase space.	fig2a.pdf [113 KiB] HiDef png [850 KiB] Thumbnail [433 KiB] *.C file
	fig2b.pdf [114 KiB] HiDef png [885 KiB] Thumbnail [456 KiB] *.C file
Average $p$-value as a function of the energy test distance parameter $\delta$, for different values of the $ D ^0$ - $\overline{ D } {}^0$ phase difference for the $ D ^0 \rightarrow \rho(770)^{-}\pi^+$ amplitude. Straight guide lines are also drawn connecting successive points for each scenario.	fig3.pdf [134 KiB] HiDef png [311 KiB] Thumbnail [200 KiB] *.C file
Distribution of $T$-values obtained by running the energy test over the final signal $ D ^0 \rightarrow \pi^-\pi^+\pi^0$ sample (red dashed line) superimposed on the corresponding distribution for the $ C P$ -symmetry hypothesis, obtained from flavour-randomised permutations of the same data sample.	fig4.pdf [162 KiB] HiDef png [141 KiB] Thumbnail [132 KiB] *.C file
Animated gif made out of all figures.	PAPER-2023-005.gif Thumbnail