Search for $CP$ violation in ${\mathrm{\Xi }}_b^{-}\to p{K}^{-}{K}^{-}$ decays

A search for $CP$ violation in charmless three-body ${\mathrm{\Xi }}_b^{-}\to p{K}^{-}{K}^{-}$ decays is performed using $pp$ collision data recorded with the LHCb detector, corresponding to integrated luminosities of $1{\mathrm{fb}}^{-1}$ at a center-of-mass energy $\sqrt{s}=7\mathrm{TeV}$, $2{\mathrm{fb}}^{-1}$ at $\sqrt{s}=8\mathrm{TeV}$ and $2{\mathrm{fb}}^{-1}$ at $\sqrt{s}=13\mathrm{TeV}$. A good description of the phase-space distribution is obtained with an amplitude model containing contributions from $\mathrm{\Sigma }(1385)$, $\mathrm{\Lambda }(1405)$, $\mathrm{\Lambda }(1520)$, $\mathrm{\Lambda }(1670)$, $\mathrm{\Sigma }(1775)$ and $\mathrm{\Sigma }(1915)$ resonances. The model allows for $CP$ -violation effects, which are found to be consistent with zero. The branching fractions of ${\mathrm{\Xi }}_b^{-}\to \mathrm{\Sigma }(1385)K^{-}$, ${\mathrm{\Xi }}_b^{-}\to \mathrm{\Lambda }(1405)K^{-}$, ${\mathrm{\Xi }}_b^{-}\to \mathrm{\Lambda }(1520)K^{-}$, ${\mathrm{\Xi }}_b^{-}\to \mathrm{\Lambda }(1670)K^{-}$, ${\mathrm{\Xi }}_b^{-}\to \mathrm{\Sigma }(1775)K^{-}$ and ${\mathrm{\Xi }}_b^{-}\to \mathrm{\Sigma }(1915)K^{-}$ decays are also reported. In addition, an upper limit is placed on the product of ratios of ${\mathrm{\Omega }}_b^{-}$ and ${\mathrm{\Xi }}_b^{-}$ fragmentation fractions and the ${\mathrm{\Omega }}_b^{-}\to p{K}^{-}{K}^{-}$ and ${\mathrm{\Xi }}_b^{-}\to p{K}^{-}{K}^{-}$ branching fractions.

Figure 1

Distributions of $p{K}^{-}{K}^{-}$ invariant mass for $X_b^{-}$ candidates in (left) Run 1 and (right) Run 2 data with results of the unbinned extended maximum-likelihood fits superimposed. The total fit result is shown as the blue solid curve, with individual components shown as indicated in the legend.

Figure 2

Distributions of selected candidates from (left) Run 1 and (right) Run 2 data in the (top) Dalitz-plot and (bottom) square Dalitz-plot representations of the phase space.

Figure 3

Efficiency as a function of square Dalitz-plot position for (left) ${\mathrm{\Xi }}_b^{-}$ and (right) ${\overline{\mathrm{\Xi }}}_b^{+}$ decays, for (top) Run 1 and (bottom) Run 2.

Figure 4

SDP distributions of (top) combinatorial and (bottom) cross feed background components for (left) Run 1 and (right) Run 2.

Figure 5

Dalitz-plot distributions from (left) data and (right) the fit model for (top) ${\mathrm{\Xi }}_b^{-}$ and (bottom) ${\overline{\mathrm{\Xi }}}_b^{+}$ candidates.

Figure 6

Distributions of (top) $m_{\mathrm{low}}$ and (bottom) $m_{\mathrm{high}}$ for (left) ${\mathrm{\Xi }}_b^{-}$ and (right) ${\overline{\mathrm{\Xi }}}_b^{+}$ candidates, with results of the fits superimposed. The total fit result is shown as the blue solid curve, with contributions from individual signal components and from combinatorial (Comb) and cross feed (Crsfd) background shown as indicated in the legend.

Figure 7

Distributions of (top) $m_{\mathrm{low}}$ and (bottom) $m_{\mathrm{high}}$, with $1.43<m_{\mathrm{low}}<1.60\mathrm{GeV}$, for (left) ${\mathrm{\Xi }}_b^{-}$ and (right) ${\overline{\mathrm{\Xi }}}_b^{+}$ candidates, with results of the fits superimposed. The total fit result is shown as the blue solid curve, with contributions from individual signal components and from combinatorial (Comb) and cross feed (Crsfd) background shown as indicated in the legend.

Figure 8

Distributions of (top) $m_{\mathrm{low}}$ and (bottom) $m_{\mathrm{high}}$, with $1.6<m_{\mathrm{low}}<1.8\mathrm{GeV}$, for (left) ${\mathrm{\Xi }}_b^{-}$ and (right) ${\overline{\mathrm{\Xi }}}_b^{+}$ candidates, with results of the fits superimposed. The total fit result is shown as the blue solid curve, with contributions from individual signal components and from combinatorial (Comb) and cross feed (Crsfd) background shown as indicated in the legend.

Figure 9

Distributions of (top) $m_{\mathrm{low}}$ and (bottom) $m_{\mathrm{high}}$, with $1.8<m_{\mathrm{low}}<2.2\mathrm{GeV}$, for (left) ${\mathrm{\Xi }}_b^{-}$ and (right) ${\overline{\mathrm{\Xi }}}_b^{+}$ candidates, with results of the fits superimposed. The total fit result is shown as the blue solid curve, with contributions from individual signal components and from combinatorial (Comb) and cross feed (Crsfd) background shown as indicated in the legend.

Figure 10

Distributions of (top) $m_{\mathrm{low}}$ and (bottom) $m_{\mathrm{high}}$, with $2.2<m_{\mathrm{low}}<2.8\mathrm{GeV}$, for (left) ${\mathrm{\Xi }}_b^{-}$ and (right) ${\overline{\mathrm{\Xi }}}_b^{+}$ candidates, with results of the fits superimposed. The total fit result is shown as the blue solid curve, with contributions from individual signal components and from combinatorial (Comb) and cross feed (Crsfd) background shown as indicated in the legend.

Figure 11

Distributions of (top) $m_{\mathrm{low}}$ and (bottom) $m_{\mathrm{high}}$, with $m_{\mathrm{low}}>2.8\mathrm{GeV}$, for (left) ${\mathrm{\Xi }}_b^{-}$ and (right) ${\overline{\mathrm{\Xi }}}_b^{+}$ candidates, with results of the fits superimposed. The total fit result is shown as the blue solid curve, with contributions from individual signal components and from combinatorial (Comb) and cross feed (Crsfd) background shown as indicated in the legend.

Figure 12

Distributions of (top) $m_{\mathrm{low}}$ and (bottom) $m_{\mathrm{high}}$, with $m_{\mathrm{high}}<3.15\mathrm{GeV}$, for (left) ${\mathrm{\Xi }}_b^{-}$ and (right) ${\overline{\mathrm{\Xi }}}_b^{+}$ candidates, with results of the fits superimposed. The total fit result is shown as the blue solid curve, with contributions from individual signal components and from combinatorial (Comb) and cross feed (Crsfd) background shown as indicated in the legend.

Figure 13

Distributions of (top) $m_{\mathrm{low}}$ and (bottom) $m_{\mathrm{high}}$, with $3.15<m_{\mathrm{high}}<3.95\mathrm{GeV}$, for (left) ${\mathrm{\Xi }}_b^{-}$ and (right) ${\overline{\mathrm{\Xi }}}_b^{+}$ candidates, with results of the fits superimposed. The total fit result is shown as the blue solid curve, with contributions from individual signal components and from combinatorial (Comb) and cross feed (Crsfd) background shown as indicated in the legend.

Figure 14

Distributions of (top) $m_{\mathrm{low}}$ and (bottom) $m_{\mathrm{high}}$, with $m_{\mathrm{high}}>3.95\mathrm{GeV}$, for (left) ${\mathrm{\Xi }}_b^{-}$ and (right) ${\overline{\mathrm{\Xi }}}_b^{+}$ candidates, with results of the fits superimposed. The total fit result is shown as the blue solid curve, with contributions from individual signal components and from combinatorial (Comb) and cross feed (Crsfd) background shown as indicated in the legend.