Roles of scalar mesons in charmless ${\mathrm{\Lambda }}_b$ decays

We first study the charmless two-body ${\mathrm{\Lambda }}_b$ decays with the scalar mesons as the final states and predict that ${\cal B}(\Lambda_b\to \Lambda f_0(980,1500))=(2.9\pm 0.7,12.4\pm 3.8)\times 10^{-6}$and${\cal B}(\Lambda_b\to p K^{-}_0(800,1430))=(1.9\pm 0.5,14.1\pm 4.5)\times 10^{-6}$. With the resonant $f_0(980,1500)\to ({\pi }^{+}{\pi }^{-},K^{+}{K}^{-})$ and $K^{-}_0\to \bar K^0 \pi^-$decays,wethenobtain${\cal B}(\Lambda_b\to \Lambda (\pi^+\pi^-,K^+K^-))=(4.2\pm 1.0,3.5\pm0.7)\times 10^{-6}$and${\cal B}(\Lambda_b\to p\bar K^0 \pi^-)=(10.4\pm2.9)\times 10^{-6}$, in comparison with the data of $(4.6\pm 1.9,15.9\pm 2.6)\times {10}^{-6}$ and $(12.6\pm 4.0)\times 10^{-6}$fromLHCb,respectively\mathrm{.}Ourresultsfor$\Lambda_b\to \Lambda\pi^+\pi^-$and$\Lambda_b\to p\bar K^0 \pi^-$ would be regarded as the first evidences of the scalar meson productions in the anti-triplet $b$-baryon decays. The smaller predicted value of $\mathcal{B}({\mathrm{\Lambda }}_b\to \mathrm{\Lambda }{K}^{+}{K}^{-})$ indicates the existences of other resonant contributions to the decay, such as ${\mathrm{\Lambda }}_b\to K^{-}(N^{\ast +}\to )\mathrm{\Lambda }{K}^{+}$.