decays into and and and heavy quark spin symmetry

J. Nieves; R. Pavao; S. Sakai

doi:10.1140/epjc/s10052-019-6929-7

EPJ

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2023 Impact factor 4.2

Particles and Fields

Open Access

Eur. Phys. J. C (2019) 79: 417
https://doi.org/10.1140/epjc/s10052-019-6929-7

Regular Article - Theoretical Physics

$\Lambda _b$ decays into $\Lambda _c^\ell \bar{\nu }_\ell$ and $\Lambda _c^\pi ^-$ $[\Lambda _c^*=\Lambda _c(2595)$ and $\Lambda _c(2625)]$ and heavy quark spin symmetry

J. Nieves¹, R. Pavao¹ and S. Sakai²^*

¹ Instituto de Física Corpuscular (Centro Mixto CSIC-UV), Institutos de Investigación de Paterna, Aptdo. 22085, 46071, Valencia, Spain
² Institute of Theoretical Physics, CAS, Zhong Guan Cun East Street 55, Beijing, 100190, China

^* e-mail: shsakai@itp.ac.cn

Received: 28 March 2019
Accepted: 3 May 2019
Published online: 17 May 2019

Abstract

We study the implications for $\Lambda _b \rightarrow \Lambda _c^*\ell \bar{\nu }_\ell$ and $\Lambda _b \rightarrow \Lambda _c^*\pi ^-$ $[\Lambda _c^*=\Lambda _c(2595)$ and $\Lambda _c(2625)]$ decays that can be deduced from heavy quark spin symmetry (HQSS). Identifying the odd parity $\Lambda _c(2595)$ and $\Lambda _c(2625)$ resonances as HQSS partners, with total angular momentum–parity $$j_q^P=1^-$$ for the light degrees of freedom, we find that the ratios $\Gamma (\Lambda _b\rightarrow \Lambda _c(2595)\pi ^-)/\Gamma (\Lambda _b\rightarrow \Lambda _c(2625)\pi ^-)$ and $\Gamma (\Lambda _b\rightarrow \Lambda _c(2595) \ell \bar{\nu }_\ell )/ \Gamma (\Lambda _b\rightarrow \Lambda _c(2625) \ell \bar{\nu }_\ell )$ agree, within errors, with the experimental values given in the Review of Particle Physics. We discuss how future, and more precise, measurements of the above branching fractions could be used to shed light into the inner HQSS structure of the narrow $\Lambda _c(2595)$ odd-parity resonance. Namely, we show that such studies would constrain the existence of a sizable $$j^P_q=0^-$$ component in its wave-function, and/or of a two-pole pattern, in analogy to the case of the similar $\Lambda (1405)$ resonance in the strange sector, as suggested by most of the approaches that describe the $\Lambda _c(2595)$ as a hadron molecule. We also investigate the lepton flavor universality ratios $R[\Lambda _c^*] = \mathcal{B}(\Lambda _b \rightarrow \Lambda _c^* \tau \,\bar{\nu }_\tau )/\mathcal{B}(\Lambda _b \rightarrow \Lambda _c^* \mu \,\bar{\nu }_\mu )$ , and discuss how $R[\Lambda _c(2595)]$ may be affected by a new source of potentially large systematic errors if there are two $\Lambda _c(2595)$ poles.