Abstract
We study the three-body decay of the newly observed bottom baryon $\Lambda_b^*(6072)$ by LHCb; $\Lambda_b^*(6072) \to \Lambda_b \pi \pi$. Its mass about 500 MeV above the ground state $\Lambda_b$ and a broad width imply that the state could be an analogue of the Roper resonance of the nucleon $N(1440)$. In terms of sequential processes going through $\Sigma_b$ and $\Sigma_b^*$, we find that the observed invariant mass distribution is reproduced assuming its spin and parity $J^P = 1/2^+$. We discuss that the ratio of the two sequential processes and angular correlation of two pions are useful for the determination of spin and parity. We suggest further studies for the Roper resonance analogue in various flavor contents, raising an interesting and important question in baryon spectroscopy.
Highlights
We study the three-body decay of the newly observed bottom baryon ΛÃbð6072Þ by LHCb; ΛÃbð6072Þ → Λbππ
In this work, motivated by the recent observation of ΛÃbð6072Þ by CMS and LHCb collaborations [1,2], with the mass and width M 1⁄4 6072.3 MeV and Γ 1⁄4 72 MeV measured by LHCb [2], we discuss it as a state analogous to the Roper resonance Nð1440Þ with spin and parity JP 1⁄4 1=2þ in heavy flavor sectors
The Roper resonance is the first excited state of the nucleon of JP 1⁄4 1=2þ [3]. It has been a mysterious state because its properties such as the mass and level ordering with negative parity nucleons have not been explained by the conventional quark model
Summary
Roper-like resonances with various flavor contents and their two-pion emission decays. They are similar in masses and in decays through two pion emission which is dominated by the sequential processes going through intermediate baryon resonances as shown, while a nonresonant contribution is insignificant. These rather universal features in various flavor sectors may suggest important dynamics of low energy QCD
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