Semileptonic $$B_c$$ B c meson decays to S-wave charmonium states
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Semileptonic Bc meson decays to S-wave charmonium states Sonali Patnaik1,a
, Lopamudra Nayak1, P. C. Dash1, Susmita Kar2,b , N. Barik3
1 Department of Physics, Siksha ‘O’ Anusandhan Deemed to be University, Bhubaneswar 751030, India 2 Department of Physics, North Orissa University, Baripada 757003, India 3 Department of Physics, Utkal University, Bhubaneswar 751004, India
Received: 12 February 2020 / Accepted: 29 October 2020 © Società Italiana di Fisica and Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract We study the semileptonic decays of Bc meson to S-wave charmonium states in the framework of relativistic independent quark model based on an average flavor-independent confining potential U (r ) in the scalar–vector harmonic form U (r ) = 21 (1 + γ 0 )(ar 2 + V0 ), where (a, V0 ) are the potential parameters. The form factors for Bc+ → ηc /ψe+ νe transitions are studied in the physical kinematic range. Our predicted branching ratios (BR) for transitions to ground-state charmonia are found comparatively large ∼ 10−2 , compared to those for transitions to radially excited 2S and 3S states. Like all other model predictions, our predicted BR are obtained in the hierarchy: BR(Bc+ → ηc /ψ(3S)) < BR(Bc+ → ηc /ψ(2S)) < BR(Bc+ → ηc /ψ(1S)). The longitudinal (Γ L ) and transverse (ΓT ) polarization for Bc → ψ(ns) decay modes is predicted in the small and large q 2 -region as well as in the whole physical region. Our predicted polarization ratios: ΓΓTL < 1 for Bc+ → J/ψe+ νe and Bc+ → ψ(2S)e+ νe which means these transitions take place predominantly in transverse mode, whereas for Bc → ψ(3S)eνe , Γ L is comparable with ΓT in the whole physical region. These theoretical predictions could be tested in the LHCb and the forthcoming Super-B experiments.
1 Introduction Ever since the discovery of Bc meson in the Fermilab by the collider detector (CDF) collaborations [1] in 1998, the experimental probe to detect its family members in their ground and excited states continues over the last two decades. With the observation of Bc meson at the Tevatron [2,3], a detailed study of Bc family members is expected at the LHC, where the available energy is more and luminosity is much higher. The lifetime of Bc has been measured [4–7] using decay channels: Bc ± → J/ψe± νe and Bc ± → J/ψπ ± . A more precise measurement of Bc -lifetime: τ Bc = 0.51+0.18 −0.16 (stat.) ± 0.03(syst.) ps and its mass: M = 6.40±0.39±0.13 GeV have been obtained [8] using the decay mode Bc → J/ψμνμ X , where X denotes any possible additional particle in the final state. The branching fraction
a e-mail: [email protected] (corresponding author) b e-mail: [email protected]
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for Bc+ → J/ψπ + relative to that of Bc+ → J/ψμ+ νμ has been measured by LHCb collaborations yielding [9]: B R(Bc → J/ψπ + ) = 0.0469 ± 0.0028(stat.) ± 0.0046(syst.) B R(Bc → J/ψμ+ νμ ) Recently, ATLAS collaboration at LHC has detected excited Bc state [10] through the channel Bc±
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