B_c^+

B_c^+
Name	B_c^+
Type	Meson
Composition	b̄c
Charge	+1 e
Mass	6274.9 MeV/c^2
Lifetime	0.510 ps
Discovered	1998
Discoverer	CDF Collaboration

B_c^+ The B_c^+ meson is a heavy, charged meson formed from a bottom antiquark and a charm quark, notable for carrying two different heavy flavors and for its unique weak-decay properties. It occupies an important place in studies connecting the CERN experimental program to theoretical frameworks developed by Quantum Chromodynamics, Andrei Sakharov-era heavy-flavor phenomenology, and lattice methods exemplified by groups at Fermilab, DESY, and IHEP. Measurements by collaborations at Fermilab Tevatron, Large Hadron Collider, and detectors such as CDF II, D0, ATLAS, CMS, and LHCb have mapped its spectrum, lifetimes, and branching fractions.

Introduction

The B_c^+ is the ground-state charged heavy meson composed of a bottom antiquark and a charm quark; it contrasts with flavor-neutral states like the J/ψ and the Υ (1S) as it carries net charge and two distinct heavy flavors. Its existence was anticipated in quark-model treatments by proponents of the Quark model such as Murray Gell-Mann and George Zweig and in potential-model calculations from groups influenced by Nathan Isgur and Mark Wise. The B_c^+ provides a laboratory for testing predictions of Heavy Quark Effective Theory, perturbative calculations from Gerard 't Hooft-inspired techniques, and nonperturbative tools like Lattice QCD pursued at institutions including Brookhaven National Laboratory, University of Oxford, and Institute for High Energy Physics (Russia).

Composition and quantum numbers

The valence structure is a bottom antiquark (b̄) bound to a charm quark (c), giving the meson charge +1 and containing both second- and third-generation flavor. In the quark-model classification it is a pseudoscalar ground state with total spin-parity J^P = 0^−, analogous in spin structure to the D^+ and B^+ but with unique interplays between charm and bottom mass scales. Spectroscopic excitations—radial and orbital—were predicted by potential models developed by Eichten-style groups and by relativistic quark models advocated by Godfrey and Isgur, with excited states compared against results from Lattice QCD collaborations at CERN and Fermilab.

Production and decay modes

Production mechanisms in high-energy collisions involve heavy-quark pair creation via gluon fusion and flavor excitation in processes modeled by perturbative Quantum Chromodynamics and implemented in event generators such as PYTHIA, HERWIG, and SHERPA. B_c^+ production rates were studied in ppbar collisions at the Tevatron and pp collisions at the Large Hadron Collider, with analyses carried out by CDF Collaboration, D0 Collaboration, ATLAS Collaboration, CMS Collaboration, and LHCb Collaboration. Decay modes proceed through three classes: b̄-quark decay with spectator c, c-quark decay with spectator b̄, and weak annihilation of b̄ and c; dominant channels include semileptonic decays to J/ψℓ^+ν and hadronic modes such as J/ψπ^+, along with rare modes sensitive to flavor-changing currents scrutinized by Flavor Physics programs at Belle II and BaBar. Branching fractions and differential distributions test predictions from Nonrelativistic QCD factorization and potential-model form factors computed by groups at MIT, Caltech, and University of California, San Diego.

Experimental discovery and measurements

The first observation of the B_c^+ was reported by the CDF II Collaboration at the Fermilab Tevatron in 1998 using the J/ψπ^+ channel, with supporting measurements by D0 (detector). Follow-up measurements of mass, lifetime, and production cross sections were performed by LHCb Collaboration, CMS Collaboration, and ATLAS Collaboration during Run 1 and Run 2 of the LHC, with precision inputs informing the Particle Data Group averages. Techniques employed included vertexing with silicon microstrip detectors developed by groups at SLAC National Accelerator Laboratory and timing systems influenced by detector R&D at KEK. Measurements of excited B_c states, such as B_c(2S), were reported by ATLAS and CMS and compared with predictions from potential models by theorists like E. Eichten and lattice determinations by collaborations at HPQCD and JLQCD.

Theoretical significance and models

The B_c^+ occupies a unique theoretical niche because both constituent quarks can decay weakly, offering complementary tests of heavy-quark symmetry frameworks like Heavy Quark Effective Theory and calculations in Nonrelativistic QCD. Phenomenological descriptions draw on potential models by Godfrey and Isgur, QCD sum rules developed by Shifman, Vainshtein, and Zakharov, and lattice simulations by consortia including HPQCD, Fermilab Lattice and MILC Collaborations, and ETM Collaboration. Precision predictions for decay constants, form factors, and lifetimes are used to constrain CKM-matrix elements in the Cabibbo–Kobayashi–Maskawa matrix program championed by Kobayashi and Maskawa, and to probe nonperturbative dynamics relevant to flavor anomalies studied by groups at CERN and KEK.

Applications and future research

Studies of the B_c^+ contribute to broader efforts in flavor physics at facilities like the High-Luminosity LHC and proposed colliders such as the Future Circular Collider and CEPC. Future measurements aim to refine branching ratios, search for rare or lepton-flavor-violating decays linked to models from groups at DESY and Perimeter Institute, and to resolve discrepancies between potential-model and lattice determinations of spectroscopic splittings. Experimental programs at LHCb Upgrade and detector upgrades from collaborations including ATLAS Collaboration and CMS Collaboration will increase sensitivity to excited-state spectroscopy, CP-violation searches inspired by CP violation studies from Cronin and Fitch-era experiments, and precision tests of heavy-flavor dynamics relevant to beyond-Standard-Model scenarios investigated by theorists at CERN Theory Department and SLAC.

Category:Mesons