A set of theoretical calculations suggests that measuring the magnetic moment of the exotic Tcc(3875)+ state could help test how its constituent particles are arranged. The predicted value is 0.45 µN if Tcc is treated as a compact tetraquark, but about −0.07 µN if it is modeled as a DD∗ molecule.
A calculated comparison, not a measurement
The document is an arXiv preprint that studies magnetic moments and radiative decay widths for S-wave doubly heavy tetraquarks. It uses a chromomagnetic-interaction framework: diagonalizing its matrices supplies eigenvalues and eigenvectors, and the resulting states are then used for magnetic-moment and radiative-decay calculations.
The modeled systems include heavy-flavor labels b and c and light-flavor labels n and s, across isospin-triplet and isospin-singlet sectors. The model adopts effective couplings extracted from mass splittings in conventional hadrons, along with quark magnetic moments, constituent masses and calculated tetraquark masses.
The signal is selective
The Tcc contrast is a comparison between two structural assumptions. The compact-tetraquark calculation and the DD∗ molecular calculation produce different magnetic moments, but the result does not by itself identify which configuration describes the physical state.
The study also finds that a magnetic moment is not a universal structural fingerprint. For modeled J^P=2+ doubly heavy tetraquarks, magnetic moment alone cannot separate compact from molecular configurations. The same limitation appears in the specified isospin-one, one-plus ccn̄n̄′ case, where the two descriptions give identical predictions.
For modeled J^P=0+ states, the magnetic moment is zero. Other observables, including radiative transitions, are therefore needed to probe their internal structures within the study’s framework.
Radiative decays add another route
Radiative transition amplitudes provide a complementary structural probe in the calculation because they contain weights tied to the states’ spin and color configurations. The paper describes those amplitudes as encoding information about internal structure.
For channels associated with Tcc, the calculation identifies five radiative transitions with predicted widths ranging from 6.07 keV to 306.37 keV. The figures are model outputs that mark specific channels for future tests of the competing structural descriptions.
The predicted widths also vary sharply in other systems. In the bcn̄s̄ case, the largest reported width is 79.52 keV, while the weakest is 1.20 × 10−6 keV. Across QQn̄s̄ states, widths are generally larger for the negative third-isospin component, although some bbn̄s̄ and bcn̄s̄ channels reverse that ordering.
What the calculations leave open
The study identifies diquark-spin mixing as relevant to magnetic moments in the one-plus bcq̄q̄′ and QQn̄s̄ systems. It also defines magnetic coupling matrices for one-plus tetraquarks and reports that they constrain the allowed range of magnetic moments.
Taken together, the results present magnetic moments and radiative transitions as complementary probes, with clear limits on what either can show for particular quantum-number assignments. The calculations do not establish a compact, molecular or mixed structure for Tcc, and future measurements would be needed to test the predicted values and widths.
The document remains an arXiv preprint, and no journal or DOI is reported in the supplied record.
Paper data and sources
Original title: Magnetic Moments and Radiative Transitions of the $T_{cc}(3875)^+$ and its partner states
Authors: Jing Wu, Yi-Kun Wang, Kai-Bao Chen et al.
Journal/Repository: arXiv
Status: Preprint, not yet peer-reviewed
First online: 2026-08-28
DOI: Not available
Original paper · Full text