First measurement of the $CP$-violating phase $\phi_s^{d\overline{d}}$ in $B_s^0\to(K^+\pi^-)(K^-\pi^+)$ decays

TL;DR

This paper reports the first measurement of the $CP$-violating phase $\,phi_s^{d\overline{d}}$ in $B_s^0$ decays to $K\pi$ pairs, using LHCb data, providing insights into $CP$ violation in $b\to d\overline{d}s$ transitions.

Contribution

It presents the first measurement of the mixing-induced $CP$-violating phase $\,phi_s^{d\overline{d}}$ in $b\to d\overline{d}s$ transitions, expanding understanding of $CP$ violation.

Findings

Measured $f_L$ for $B_s^0\to K^*(892)^0\overline{K}^*(892)^0$ as 0.208 ± 0.032 ± 0.046.

First measurement of $\,phi_s^{d\overline{d}}$ as -0.10 ± 0.13 (stat) ± 0.14 (syst) rad.

Analysis used $pp$ collision data at 7 and 8 TeV with 3.0 fb$^{-1}$ luminosity.

Abstract

A flavour-tagged decay-time-dependent amplitude analysis of $B_s^0\to(K^+\pi^-)(K^-\pi^+)$ decays is presented in the $K^{\pm}\pi^{\mp}$ mass range from 750 to 1600 MeV$/c^2$. The analysis uses $pp$ collision data collected with the LHCb detector at centre-of-mass energies of $7$ and $8$ TeV, corresponding to an integrated luminosity of $3.0$ fb$^{-1}$. Several quasi-two-body decay modes are considered, corresponding to $K^{\pm}\pi^{\mp}$ combinations with spin 0, 1 and 2, which are dominated by the $K_0^*(800)^0$ and $K_0^*(1430)^0$, the $K^*(892)^0$ and the $K_2^*(1430)^0$ resonances, respectively. The longitudinal polarisation fraction for the $B_s^0\to K^*(892)^0\overline{K}^*(892)^0$ decay is measured as $f_L=0.208 \pm 0.032 \pm 0.046$, where the first uncertainty is statistical and the second is systematic. The first measurement of the mixing-induced $CP$-violating phase, $\phi_s^{d\overline{d}}$, in $b\to d\overline{d}s$ transitions is performed, yielding a value of $\phi_s^{d\overline{d}}=-0.10$ $\pm$ $0.13$ (stat) $\pm$ $0.14$ (syst) rad.