Precise determination of decay rates for ηc → γγ, J/ψ → γηc and J/ψ → ηce+e− from lattice QCD

Colquhoun, B. , Cooper, L. J., Davies, C. T.H. and Lepage, G. P. (2023) Precise determination of decay rates for ηc → γγ, J/ψ → γηc and J/ψ → ηce+e− from lattice QCD. Physical Review D, 108(1), 014513. (doi: 10.1103/PhysRevD.108.014513)

Abstract

We calculate the decay rates for η c → γ γ , J / ψ → γ η c and J / ψ → η c e + e − in lattice QCD with u , d , s and c quarks in the sea for the first time. We improve significantly on previous theory calculations to achieve accuracies of 1–2%, giving lattice QCD results that are now more accurate than the experimental values. In particular our results transform the theoretical picture for η c → γ γ decays. We use gluon field configurations generated by the MILC collaboration that include n f = 2 + 1 + 1 flavors of highly improved staggered sea quarks at four lattice spacing values from 0.15 fm to 0.06 fm and with sea u/d masses down to their physical value. We also implement the valence c quarks using the highly improved staggered quark action. We find Γ ( η c → γ γ ) = 6.788 ( 45 ) fit ( 41 ) syst     keV , in good agreement with experimental results using γ γ → η c → K ¯ K π but in 4 σ tension with the Particle Data Group global fit result [R. L. Workman (Particle Data Group), Prog. Theor. Exp. Phys. 2022, 083C01 (2022)]; we suggest this fit is revisited. We also calculate Γ ( J / ψ → γ η c ) = 2.219 ( 17 ) fit ( 18 ) syst ( 24 ) expt ( 4 ) QED     keV , in good agreement with results from CLEO, and predict the Dalitz decay rate Γ ( J / ψ → η c e + e − ) = 0.01349 ( 15 ) latt ( 15 ) expt ( 13 ) QED     keV . We use our results to calibrate other theoretical approaches and to test simple relationships between the form factors and J / ψ decay constant expected in the nonrelativistic limit.

• Item Type: Articles
• Additional Information: The DiRAC component of CSD3 was funded by BEIS capital funding via STFC capital Grants No. ST/ P002307/1 and No. ST/R002452/1 and STFC operations Grant No. ST/R00689X/1. DiRAC is part of the National e-Infrastructure. We are grateful to the CSD3 support staff for assistance. Funding for this work came from STFC Grant No. ST/T000945/1.
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Colquhoun, Dr Brian and Davies, Professor Christine
• Authors: Colquhoun, B., Cooper, L. J., Davies, C. T.H., and Lepage, G. P.
• College/School: College of Science and Engineering > School of Physics and Astronomy
• Journal Name: Physical Review D
• Publisher: American Physical Society
• ISSN: 2470-0010
• ISSN (Online): 2470-0029
• Published Online: 24 July 2023
• Copyright Holders: Copyright © 2023 The Authors
• First Published: First published in Physical Review D 108(1): 014513
• Publisher Policy: Reproduced under a Creative Commons License

Project Code	Award No	Project Name	Principal Investigator	Funder's Name	Funder Ref	Lead Dept
306883		Research in Particle Physics Theory - Phenomenology from lattice QCD and collider physics	Christine Davies	Science and Technology Facilities Council (STFC)	ST/T000945/1	P&S - Physics & Astronomy