Electromagnetic form factors and structure of the $T_{bb}$ tetraquark from lattice QCD

Vujmilović, Ivan (author), Collins, Sara (author), Leskovec, Luka (author), Prelovšek, Saša (author)

We present the first lattice QCD determination of the electromagnetic form factors of the exotic tetraquark ▫$T_{bb}(bb\overline{u}\overline{d})$▫ with quantum numbers ▫$I(J^P) = 0(1^+)$▫. 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 [▫$\overline{u}\overline{d}$▫] in a color-triplet with spin zero. The charge radius of ▫$T_{bb}$▫ 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 ▫$N_f = 2 + 1$▫ dynamical quarks and a lattice spacing of approximately ▫$a \approx 0.064$▫ fm at the pion mass ▫$m_\Pi \approx 290$▫ MeV.

• Language: English
• Keywords: lattice QCD, tetraquarks, form factors, magnetic moment
• Work type: Article
• Typology: 1.01 - Original Scientific Article
• Organization: FMF - Faculty of Mathematics and Physics
• Publication status: Published
• Publication version: Version of Record
• Year: 2026
• Number of pages: Str. 161901-1-161901-9
• Numbering: Vol. 136, iss. 16
• PID: 20.500.12556/RUL-182132
• UDC: 539.120
• ISSN on article: 0031-9007
• DOI: 10.1103/jnsy-5nhj
• COBISS.SI-ID: 276531715
• Publication date in RUL: 24.04.2026

Record is a part of a journal

• Title: Physical review letters
• Shortened title: Phys. rev. lett.
• Publisher: American Physical Society
• ISSN: 0031-9007
• COBISS.SI-ID: 1282575

Licences

• License: CC BY 4.0, Creative Commons Attribution 4.0 International
• Link: http://creativecommons.org/licenses/by/4.0/
• Description: This is the standard Creative Commons license that gives others maximum freedom to do what they want with the work as long as they credit the author.

Secondary language

• Language: Slovenian
• Keywords: kvantna kromodinamika na mreži, tetrakvarki, oblikovni faktorji, magnetni moment