Precision measurement of the B c + $$ {B}_c^{+} $$ meson mass
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Springer
Received: April 20, 2020 Accepted: June 16, 2020 Published: July 20, 2020
The LHCb collaboration E-mail: [email protected] Abstract: A precision measurement of the Bc+ meson mass is performed using protonproton collision data collected with the LHCb experiment at centre-of-mass energies of 7, 8 and 13 TeV, corresponding to a total integrated luminosity of 9.0 fb−1 . The Bc+ mesons are reconstructed via the decays Bc+ → J/ψ π + , Bc+ → J/ψ π + π − π + , Bc+ → J/ψ p¯ pπ + , Bc+ → J/ψ Ds+ , Bc+ → J/ψ D0 K + and Bc+ → Bs0 π + . Combining the results of the individual decay channels, the Bc+ mass is measured to be 6274.47 ± 0.27 (stat) ± 0.17 (syst) MeV/c2 . This is the most precise measurement of the Bc+ mass to date. The difference between the Bc+ and Bs0 meson masses is measured to be 907.75 ± 0.37 (stat) ± 0.27 (syst) MeV/c2 . Keywords: B physics, Hadron-Hadron scattering (experiments), QCD, Spectroscopy ArXiv ePrint: 2004.08163
Open Access, Copyright CERN, for the benefit of the LHCb Collaboration. Article funded by SCOAP3 .
https://doi.org/10.1007/JHEP07(2020)123
JHEP07(2020)123
Precision measurement of the Bc+ meson mass
Contents 1
2 Detector and simulation
2
3 Event selection
3
4 Mass measurement
3
5 Systematic uncertainties
6
6 Combination of the measurements
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7 Summary
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The LHCb collaboration
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15
Introduction
The Bc meson family is unique in the Standard Model as its states contain two different heavy-flavour quarks, a ¯b and a c quark. Quantum Chromodynamics (QCD) predicts that the ¯b and c quarks are tightly bound in a compact system, with a rich spectroscopy of excited states. Studies of the Bc mass spectrum can reveal information on heavy-quark dynamics and improve our understanding of the strong interaction. Due to the presence of two heavy-flavour quarks the mass spectrum of the Bc states can be predicted with much better precision than many other hadronic systems. The mass spectrum of the Bc family has been calculated with nonrelativistic quark potential models [1–8], nonperturbative phenomenological models [9, 10], perturbative QCD [11, 12], relativistic quark models [13–17], and lattice QCD [18–23]. The ground state of the Bc meson family, denoted hereafter as Bc+ , decays only through the weak interaction, with a relatively long lifetime. The most accurate prediction of the Bc+ mass, M (Bc+ ) = 6278 ± 6 ± 4 MeV/c2 [22], is obtained with unquenched lattice QCD. In 1998 the CDF collaboration discovered the Bc+ meson via its semileptonic decay modes and measured its mass to be 6400 ± 390 ± 130 MeV/c2 [24]. At the LHCb experiment, considerable progress has been made on measurements of the Bc+ production [26–30], spectroscopy [26, 31–34], lifetime [35, 36], and new decay modes [30, 33, 37–45]. The world average of the Bc+ mass has an uncertainty of 0.8 MeV/c2 [46]. This is the dominant systematic uncertainty in the recent Bc (2S)(∗)+ mass measurements [34, 47]. This paper presents a precision measurement of the Bc+ mass using the decay modes Bc+ → J/ψ π + , Bc+ → J/ψ
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