LHCb

Abstract:

A search for $CP$ violation with an entangled system of ${\mathrm{\Xi }}^{-}{\overline{\mathrm{\Xi }}}^{+}$ pairs is performed, using $(10,087\pm 44)\times {10}^{6}J/\psi$ events collected with the BESIII experiment. A nine-dimensional helicity amplitude is used to fit $e^{+}{e}^{-}\to J/\psi \to {\mathrm{\Xi }}^{-}{\overline{\mathrm{\Xi }}}^{+}$ and its subsequent decays. The ${\mathrm{\Xi }}^{-}$ and ${\overline{\mathrm{\Xi }}}^{+}$ decay parameters are determined with higher precision compared to the best results reported so far. Furthermore, the strong phase difference, $({\delta }_P-{\delta }_S)=(0.3\pm 1.2\pm 0.2)\times {10}^{-2}\mathrm{rad}$ , and the weak phase difference, $({\xi }_P-{\xi }_S)=(-0.2\pm 1.2\pm 0.1)\times {10}^{-2}\mathrm{rad}$ , are directly determined. These are the most precise measurements to date. The $CP$ asymmetry observables $A_{CP}^{\mathrm{\Xi }}=(-7.8\pm 4.8\pm 0.8)\times {10}^{-3}$ and $\mathrm{\Delta }{\varphi }_{CP}^{\mathrm{\Xi }}=(0.6\pm 5.1\pm 0.2)\times {10}^{-3}\mathrm{rad}$ are determined, which are consistent with $CP$ conservation. In addition, independent measurements of the $\mathrm{\Lambda }$ decay parameter and $CP$ asymmetry $A_{CP}^{\mathrm{\Lambda }}=(-2.9\pm 4.3\pm 0.7)\times {10}^{-3}$ are also obtained, which are in agreement with the previous measurements, but with much improved precision.

Abstract:

An amplitude analysis of the B0→ηc(1S)K+π-$${{{B} ^0} \!\rightarrow {\eta _{c}} (1S) {{K} ^+} {{\pi } ^-}} $$ decays with ηc(1S)→pp¯$${\eta _{c}} (1S) \rightarrow {p} {\overline{{p}}} $$ is performed using a sample corresponding to an integrated luminosity of 9fb-1$$\,\text {fb} ^{-1}$$ of p$$p $$p$$p $$ collision data collected by the LHCb detector at centre-of-mass energies of s$$\sqrt{s}$$ = 7, 8 and 13TeV$$\,\text {Te\hspace{-1.00006pt}V}$$. The data are described with a model including only intermediate contributions from known K∗0$${K} ^{*0}$$ resonances. Evidence for an exotic resonance in the ηc(1S)π-$${\eta _{c}} (1S) {{\pi } ^-} $$ system, reported in a previous analysis of this decay channel, is not confirmed. The inclusive branching fraction of the B0→ηc(1S)K+π-$${{B} ^0} \rightarrow {\eta _{c}} (1S) {{K} ^+} {{\pi } ^-} $$ decays is measured to be B(B0→ηc(1S)K+π-)=(5.82±0.20±0.23±0.55)×10-4,$$\begin{aligned}&\mathcal {B}({{B} ^0} \rightarrow {\eta _{c}} (1S) {{K} ^+} {{\pi } ^-}) \\&\quad = (5.82 \pm 0.20 \pm 0.23 \pm 0.55) \times 10^{-4}, \end{aligned}$$where the first uncertainty is statistical, the second systematic, and the third arises from the limited knowledge of external branching fractions.

Abstract:

The first searches for $B^0\to K^{+}{\pi }^{-}{\tau }^{+}{\tau }^{-}$ and $B_s^0\to K^{+}{K}^{-}{\tau }^{+}{\tau }^{-}$ decays at the LHCb experiment are conducted with $pp$ collision data corresponding to an integrated luminosity of $5.4{\mathrm{fb}}^{-1}$ . The tau leptons are reconstructed using the ${\tau }^{+}\to {\mu }^{+}{\overline{\nu }}_{\tau }{\nu }_{\mu }$ decay and the results are presented in bins of $K^{+}{\pi }^{-}$ or $K^{+}{K}^{-}$ mass. No signal is observed and upper limits are set on the branching fractions. The searches result in the first upper limits for $B^0\to K^{+}{\pi }^{-}{\tau }^{+}{\tau }^{-}$ decays outside the $K^{*}(892{)}^0$ region in $K^{+}{\pi }^{-}$ mass and the first limits for $B_s^0\to K^{+}{K}^{-}{\tau }^{+}{\tau }^{-}$ decays. The searches are recast into limits on the decays $B^0\to K^{*}(892{)}^0{\tau }^{+}{\tau }^{-}$ and $B_s^0\to \varphi (1020){\tau }^{+}{\tau }^{-}$ , yielding $2.8\times {10}^{-4}$ ( $2.5\times {10}^{-4}$ ) and $4.7\times {10}^{-4}$ ( $4.1\times {10}^{-4}$ ) at the 95% (90%) confidence level, respectively. For the decay $B^0\to K^{*}(892{)}^0{\tau }^{+}{\tau }^{-}$ , this result improves on the current best upper limit by an order of magnitude.

Abstract:

The first search for the $B_s^0\to K^{-}{\pi }^{+}\gamma$ decay in the range $796<m(K^{-}{\pi }^{+})<1800\mathrm{MeV}/c^2$ is performed using data from proton-proton collisions collected by the LHCb experiment at center-of-mass energies of 7, 8, and 13 TeV, corresponding to an integrated luminosity of $9{\mathrm{fb}}^{-1}$ . The photons are reconstructed through their conversion into an electron-positron pair, which significantly improves the mass resolution of the reconstructed decays with respect to decays with an unconverted photon. A signal excess with a significance of 3.5 standard deviations is measured, constituting the first experimental evidence for this decay. In the range $796<m(K^{-}{\pi }^{+})<996\mathrm{MeV}/c^2$ , the ratio $\mathcal{R}$ between the branching fractions of the signal decay and the favored ${\overline{B}}^0\to K^{-}{\pi }^{+}\gamma$ decay is measured to be $\mathcal{R}=(3.7\pm 1.2\pm 0.4)\times {10}^{-2}$ where the first uncertainty is statistical and the second is systematic. This measurement is consistent with the value predicted in the Standard Model. In the range $996<m(K^{-}{\pi }^{+})<1800\mathrm{MeV}/c^2$ , the ratio $\mathcal{R}=(0.2\pm 2.7\pm 1.3)\times {10}^{-2}$ is measured.