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Electromagnetic Form Factors and Structure of the Tbb Tetraquark from Lattice QCD

Ivan Vujmilovic1,2,*, Sara Collins3,†, Luka Leskovec1,2,‡, and Sasa Prelovsek1,2,§

  • *Contact author: ivan.vujmilovic@ijs.si
  • †Contact author: sara.collins@ur.de
  • ‡Contact author: luka.leskovec@ijs.si
  • §Contact author: sasa.prelovsek@ijs.si
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Phys. Rev. Lett. 136, 161901 – Published 23 April, 2026

DOI: https://doi.org/10.1103/jnsy-5nhj

Abstract

We present the first lattice QCD determination of the electromagnetic form factors of the exotic tetraquark Tbb(bbu¯d¯) with quantum numbers I(JP)=0(1+). The extracted form factors encode information about its internal structure, including the charge distribution and the magnetic dipole moments, determined separately for the light and heavy quarks. Our results provide evidence in favor of it being a bound state consisting of a compact heavy diquark [bb] in a color-antitriplet with spin one and a light antidiquark [u¯d¯] in a color-triplet with spin zero. The charge radius of Tbb is found to be significantly smaller than the combined charge radii of B and B* mesons. These two comprise the lowest-lying threshold BB* in the channel that we are considering, and their electric charge form factors are also determined. The computations were performed on a single ensemble, generated by the Coordinated Lattice Simulations effort, with Nf=2+1 dynamical quarks and a lattice spacing of approximately a≈0.064  fm at the pion mass mπ≈290  MeV.

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Phys. Rev. Lett. 136, 161901– Published 23 April, 2026
  • Received 27 October 2025
  • Revised 5 March 2026
  • Accepted 12 March 2026
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