The new analysis, published in The European Physical Journal C by Yin Huang and Xurong Chen, tackles the problem from a fresh angle. Rather than relying on the traditional method of fitting invariant mass spectra, the researchers focus on the transverse momentum of the final-state D mesons produced in electron-positron collisions. Their central insight is deceptively simple but theoretically powerful: if G(3900) is a real resonance, it must imprint a distinctive kinematic fingerprint on the angular distribution of its decay products, a fingerprint that no amount of interference between intermediate states can mimic. This fingerprint is known as a Jacobian peak, and its predicted position can be calculated with extraordinary precision from first principles.

The mathematics behind the proposal rests on the geometry of two-body decays. When a resonance of a given mass decays into a pair of D mesons, kinematics dictate that the transverse momentum of each meson cannot exceed a maximum value determined by the Källén function of the participating masses. When the cross section is re-expressed as a function of the transverse momentum rather than the emission angle, a characteristic singularity appears at this kinematic limit, producing a sharp enhancement called a Jacobian peak. For G(3900), the peak should appear at approximately 520.995 MeV for neutral D meson pairs and 504.018 MeV for charged pairs. Crucially, the position of this peak depends only on the mass of the parent resonance, not on the details of any theoretical model used to describe the production amplitudes.

This model independence is precisely what makes the proposal so compelling. The authors demonstrate that when G(3900) is treated as a genuine resonance alongside the known charmonium states psi(3686), psi(3770), psi(4040), and psi(4160), the calculated transverse momentum distribution displays a clear Jacobian peak at the predicted location. When the G(3900) contribution is removed and the observed enhancement is instead attributed entirely to interference effects and the opening of the D D* threshold, the peak vanishes completely. Because interference between intermediate states cannot produce this kinematic singularity, the presence or absence of the peak in experimental data would constitute direct evidence for or against the existence of G(3900) as a bona fide hadronic state.

The theoretical framework underpinning the study combines an effective Lagrangian approach with loop calculations that account for the opening of the D D* threshold. The coupling constants for the charmonium states are fixed from known decay widths, while other parameters are fitted to the existing body of electron-positron collision data. The authors performed a series of fits using different model assumptions, including scenarios with and without G(3900), and found that all of them describe the measured invariant mass spectra reasonably well. This degeneracy explains why nearly twenty years of fitting mass spectra have failed to settle the debate: the two-body invariant mass distribution alone simply does not contain enough information to discriminate between a genuine resonance and cleverly arranged interference effects.

Intriguingly, the analysis also sheds new light on the internal structure of G(3900). Its measured mass of about 3872.5 MeV sits remarkably close to the D D* threshold, prompting several theoretical groups to interpret it as a P-wave molecular state composed of a D meson and a D* meson bound together. The new study explores this possibility but finds that different, equally reasonable fits lead to contradictory conclusions about the molecular interpretation. In one favored fit, the ratio of the G(3900) decay width into D meson pairs to its width into electron-positron pairs appears incompatible with a molecular assignment, while in another equally successful fit the numbers permit it. The authors emphasize that this ambiguity in classification does not undermine the Jacobian peak criterion, which remains valid regardless of the particle’s ultimate structural identity.

The experimental prospects for testing the prediction appear highly favorable. The authors estimate that the predicted Jacobian peaks have characteristic widths of roughly 14 MeV at a normalized cross section value of 3, narrowing to about 5 MeV at a value of 6, features that are easily resolvable by modern detectors. The momentum resolution of the BESIII detector is approximately 0.5 percent at momenta around 1 GeV, corresponding to uncertainties of only about 2.6 MeV at the relevant transverse momenta. Combined with the beam-energy spread of roughly 1.5 MeV, the total experimental uncertainty amounts to about 3 MeV, far smaller than the width of the predicted peak. Moreover, BESIII has already accumulated large datasets of electron-positron collisions producing D meson pairs, providing ample statistics, and the estimated signal-to-background ratio in the most favorable region reaches approximately 110.

The authors also identify an important caveat that itself constitutes a valuable experimental probe. If the production amplitude for the process carries a purely angular dependence proportional to the cosine of the emission angle, the Jacobian peak could be dynamically suppressed, because the squared amplitude would vanish exactly at the kinematic limit. Measuring the differential cross section at a scattering angle of 90 degrees would therefore provide an important consistency check: a vanishing cross section at that angle would indicate suppression of the peak without negating the underlying kinematic structure. This subtlety underscores the care required in interpreting the proposed measurement, but it does not diminish the power of the criterion when applied with full awareness of the angular dynamics.

Beyond its immediate implications for G(3900), the Jacobian peak method offers a broadly applicable tool for hadron spectroscopy. The field has been flooded in recent years with candidate exotic states whose reality is debated, from tetraquarks to hadronic molecules, and many of these controversies stem from the same fundamental limitation: interference effects can mimic resonance signals in invariant mass spectra. A model-independent observable whose position is fixed purely by the mass of the hypothesized parent state provides exactly the kind of clean discriminator the field needs. The authors suggest that the same transverse momentum analysis can be extended to other hadronic systems, potentially resolving long-standing disputes about the existence of various resonance candidates across the light, strange, charm, and bottom sectors.

The study represents a convergence of precision experiment and incisive theoretical reasoning at a moment when the particle physics community is actively re-examining the census of hadronic matter. With BESIII’s confirmation of the G(3900) structure having reignited interest in the 3.9 GeV region, and with the proposed Jacobian peak test requiring no new instrumentation beyond what existing datasets already permit, the coming analysis of transverse momentum distributions may soon deliver one of the cleanest verdicts in modern hadron physics. Whether G(3900) emerges as a genuine new state of matter or fades into the machinery of quantum interference, the criterion developed by Huang and Chen is poised to become a standard instrument in the ongoing effort to map the true spectrum of strongly interacting particles.

Subject of Research: Criterion for establishing the existence of the G(3900) hadronic resonance through transverse momentum distributions in electron-positron collisions

Article Title: Criterion for the existence of the G(3900) resonance

Article References: Huang, Y., & Chen, X. (2026). Criterion for the existence of the G(3900) resonance. The European Physical Journal C, 86(10), Article 1161. https://doi.org/10.1140/epjc/s10052-026-16432-2

Image Credits: AI Generated

DOI: 10.1140/epjc/s10052-026-16432-2

Keywords: G(3900), BESIII, charmonium, D meson, Jacobian peak, hadron spectroscopy, resonance, electron-positron annihilation, D D* threshold, molecular state, quantum interference, particle physics

The stakes are higher than they might first appear. Light non-strange mesons, built from up and down valence quarks, are the cleanest laboratory available for studying the nonperturbative dynamics of quantum chromodynamics. Because the Higgs-generated current masses of the up and down quarks are nearly negligible, at roughly two to five MeV, almost all of the observable mass of these particles is generated by spontaneous chiral symmetry breaking and dynamic gluon dressing. Unlike heavy quarkonia, where large bare masses rigidify the quantum fluctuations, the light non-strange sector exposes confinement, dynamic mass generation, and short-range relativistic interactions in their purest form. Mapping the excitation spectrum of these mesons therefore offers direct insight into the structural dynamics of nucleons and atomic nuclei, which are built from the very same valence quarks.

Fortunately, the experimental dataset is unusually rich. Decades of high-energy hadronic production experiments have established long, continuous excitation bands of non-strange mesons extending up to total angular momentum J equal to six, providing the statistical leverage needed for genuine multi-parameter optimization. Afonin assembled a compilation of 85 light meson states, of which 27 are especially well-established benchmarks with robust quantum number assignments and minimal experimental errors. The pion was deliberately excluded, since its inclusion in Regge or string frameworks remains an open problem, and states with significant hidden strangeness were also set aside because nonlinearity is already appreciable there.

The analysis compared three competing models. Model 1 is the traditional linear trajectory with independent radial and orbital slopes. Model 2 enforces a universal slope, collapsing the spectrum into the simple form in which squared mass is proportional to the sum of the radial and orbital quantum numbers, a degeneracy reminiscent of the Coulomb problem in atomic physics. Model 3 keeps the universal slope but adds a nonlinear correction proportional to one over the quantity l plus one, motivated by the leading-order relativistic correction to the principal quantum number for a Dirac particle bound in a Coulomb field. This Dirac-Coulomb term is expected to matter most for S-wave states, where the centrifugal barrier vanishes and the quark-antiquark wave function probes very short distances dominated by one-gluon exchange rather than linear confinement.

The statistical machinery was as important as the physics. Because experimental uncertainties on meson masses vary by two orders of magnitude, a naive chi-squared fit would be dominated by a handful of states. Afonin instead introduced a universal theoretical model uncertainty, combined with the experimental errors through first-order error propagation from masses to squared masses, and determined that theoretical uncertainty self-consistently by enforcing the condition that the reduced chi-squared equals exactly one. The global optimization ran on a two-tier numerical routine combining the CERN MINUIT algorithm with SciPy root-finding solvers, and parameter errors were extracted from the Hessian curvature matrix of the log-likelihood function. Model selection then relied on the Akaike and Bayesian information criteria, which penalize unnecessary parameters, supplemented by Wald tests and a systematic scan of the likelihood across the full physical range of the theoretical error scale.

The results are striking. On the 27 benchmark states, both linear models fail badly, requiring intrinsic model uncertainties of 87 and 91 MeV respectively, and splitting the slopes barely helps, indicating that independent radial and orbital slopes are a statistical over-parameterization. Adding the Dirac-Coulomb term, however, cuts the required intrinsic error by more than half, down to 42 MeV, and the extracted correction of 0.410 plus or minus 0.097 GeV squared is significant at about 4.2 standard deviations. When the analysis is scaled to the full dataset of 85 states, the universal slope remains remarkably stable, shifting only from about 1.153 to 1.189 GeV squared, and the significance of the nonlinear term climbs to roughly 6.0 standard deviations, crossing the five-sigma discovery threshold conventionally demanded in high-energy physics. Model 3 wins decisively under both information criteria, with a Bayesian information advantage of 10.8, which on Jeffreys’ scale constitutes decisive evidence.

The most physically illuminating result comes from the truncation tests. When all S-wave states are removed, the significance of the Dirac-Coulomb term collapses, falling from 6 sigma to about 3 sigma on the global sample and to an insignificant 1.7 sigma on the benchmark subset, while the Bayesian criterion reverses its preference in favor of the simpler linear model. If the nonlinear term were a mere overfitting artifact, its significance would have survived the deletion of a single row of the spectrum. Instead, the distortions are demonstrably localized in the l equals zero sector, exactly where quantum mechanics predicts that a short-range relativistic interaction should dominate. For states with orbital angular momentum of one or higher, the centrifugal barrier pushes the wave function outward and restores the classical, linear string-like behavior. In other words, the light non-strange meson spectrum exhibits not only a Coulomb-like degeneracy but also a fine splitting analogous to the first relativistic correction in the Coulomb problem.

Robustness checks reinforce the conclusion. A parametric scan treating the theoretical uncertainty as a free variable between 0.01 and 0.10 GeV reveals that the chi-squared decays monotonically as the error scale grows, but the Akaike and Bayesian criteria trace a U-shaped profile whose minimum for Model 3 sits near 0.042 GeV, well within the typical phenomenological benchmark of 0.05 GeV. Throughout the entire scanned range, the nonlinear trajectory maintains a Bayesian advantage greater than ten units over the linear alternatives. A correlation analysis of the covariance matrix further shows that the slope and the Coulomb magnitude are only moderately correlated, at 0.647, proving that the nonlinear term models distinct low-angular-momentum physics rather than mimicking a global shift of the trajectory slope.

Beyond its theoretical elegance, the framework offers a practical tool for hunting exotic particles. One of the long-standing puzzles of hadron spectroscopy is whether the lightest scalar glueball, a bound state of pure gluons predicted by lattice QCD, hides among the scalar isoscalar resonances f0(1370), f0(1500) and f0(1710). The new analysis shows that the masses of these three candidates lie on the radial trajectories of ordinary quark-antiquark states: f0(1370) and f0(1710) fit neatly into the established clusters, while f0(1500) matches the expected position of a state with a dominant hidden-strangeness component between neighboring clusters. A glueball admixture is therefore not needed to explain their masses, a conclusion consistent with recent coupled-channel classifications of scalar isoscalar mesons.

The study demonstrates how modern statistical inference, from self-consistent error propagation to information criteria and likelihood scans, can extract crisp physical statements from a phenomenological spectrum long thought to be understood. The universal slope of the light non-strange Regge trajectories is real, the deviations from linearity are real too, but they belong to a specific and identifiable mechanism: short-range relativistic gluon exchange that distorts the S-wave states. With the methodology now validated, the natural next step is to extend the same statistical treatment to heavy-light systems and heavy quarkonia, where short-range interactions play an even more dominant role in shaping the bound-state structure, and to continue using trajectory statistics as an automated sieve for separating ordinary quark-antiquark resonances from anything more exotic.

Subject of Research: Statistical analysis of linear and nonlinear Regge trajectories in the light non-strange meson spectrum

Article Title: Advanced statistical analysis of linear and nonlinear Regge trajectories for light non-strange mesons

Article References: Afonin, S. S. (2026). Advanced statistical analysis of linear and nonlinear Regge trajectories for light non-strange mesons. The European Physical Journal C, 86(9), Article 1076. https://doi.org/10.1140/epjc/s10052-026-16378-5

Image Credits: AI Generated

DOI: 10.1140/epjc/s10052-026-16378-5

Keywords: Regge trajectories, light mesons, QCD, hadron spectroscopy, chi-squared minimization, Akaike information criterion, Bayesian information criterion, Dirac-Coulomb correction, glueball, quark-antiquark states, confinement, nonperturbative dynamics

The study, published in The European Physical Journal C by Teng Ji and Ulf-G. Meißner of the University of Bonn and Forschungszentrum Jülich, tackles the near-threshold structures that experiments at BESIII in Beijing, BaBar at SLAC, and CMD-3 and SND in Novosibirsk have observed in electron-positron annihilation. These anomalies appear not only in the direct production of proton-antiproton and neutron-antineutron pairs, but also, remarkably, in final states containing no baryons whatsoever: three charged pion pairs, two charged pion pairs plus a neutral pion, an omega meson accompanied by pions, and even kaon-pion combinations. The fact that the same threshold energy shows up in so many different channels is precisely what makes the puzzle so tantalizing, and so resistant to explanations based on a single new particle.

The key insight behind the new work is that when a proton-antiproton pair is produced in the aftermath of an annihilation, the pair does not simply fly apart. The proton and antiproton interact strongly with each other before separating, a phenomenon known as final-state interaction. This interaction is not a weak correction; it is powerful enough to reshape the entire line shape of the production cross section near threshold. Crucially, quantum mechanics dictates that these threshold effects must also leak into other reaction channels, a consequence of the fundamental requirements of unitarity and analyticity that govern all scattering amplitudes. In other words, the opening of the proton-antiproton and neutron-antineutron channels leaves fingerprints everywhere, including in final states made purely of mesons.

To make this idea quantitative, the authors relied on chiral effective field theory, the modern framework that derives nuclear forces from the approximate symmetries of quantum chromodynamics. Chiral effective field theory has been spectacularly successful in describing the ordinary interaction between two nucleons, and it has been extended to the nucleon-antinucleon system, where it must additionally handle the violent annihilation of the pair into mesons. Ji and Meißner used the highest-order available description, complete to next-to-next-to-next-to-leading order, with its parameters fixed entirely by low-energy nucleon-antinucleon scattering data. That fixed interaction was never adjusted to fit the annihilation data, which makes the subsequent agreement all the more meaningful.

The calculation proceeds in three carefully separated steps. First, the strong nucleon-antinucleon interaction is taken as given from the chiral effective field theory description of the coupled spin-triplet S-wave and D-wave system, solved through the coupled-channel Lippmann-Schwinger equation. Second, with this interaction frozen, the electromagnetic production amplitudes for proton-antiproton and neutron-antineutron pairs are determined by fitting only a handful of short-distance source coefficients to the measured cross sections. These sources are assumed to vary slowly with energy, so that all the sharp structure near threshold must come from the final-state interaction itself. Third, the same nucleon-antinucleon amplitudes are used as input for five inelastic mesonic channels, each described by a slowly varying polynomial background plus the universal rescattering response.

The results are striking. For the baryonic channels, the fit achieves a chi-squared per degree of freedom of essentially one, meaning the theory reproduces the data at the level of the experimental uncertainties, using just seven real parameters across fifty-four data points spanning the region from threshold up to two gigaelectronvolts. No additional narrow resonance is needed to explain the rapid rise of the cross sections just above the proton-antiproton and neutron-antineutron thresholds. The framework also incorporates the subtle isospin-breaking effects that matter at this precision, including the small mass difference between the proton and neutron and the Coulomb attraction between the proton and antiproton, treated through the Vincent-Phatak matching method that separates short-range and long-range physics cleanly.

Underlying the line shapes are near-threshold poles of the scattering amplitude, the mathematical signatures that would correspond to physical particles if they sat close enough to the real-energy axis. The chiral interaction generates one such pole in each isospin channel: an isospin-one pole near 2122 megaelectronvolts with a small imaginary part, and an isospin-zero pole near 1840 megaelectronvolts with a larger imaginary part reflecting the strong annihilation into mesons. Because annihilation makes the interaction absorptive, these poles acquire finite widths and sit on different Riemann sheets of the complex energy plane. Their proximity to the physical thresholds is what sculpts the observed enhancements, providing a dynamical origin for structures that might otherwise be misread as evidence for new particles.

The real test comes with the non-baryonic channels, where the same nucleon-antinucleon dynamics is used without modification. The authors allowed each mesonic channel its own slowly varying polynomial background and a small set of complex transition parameters connecting the intermediate baryon-antibaryon state to the final mesons, with the allowed isospin components fixed by the quantum numbers of each final state. A simultaneous fit to all five channels yields a chi-squared per degree of freedom of 1.7, reproducing the main near-threshold features of the data. The message is that the threshold structures in these mesonic channels can be understood as echoes of the same baryon-antibaryon final-state interaction, transmitted through off-shell nucleon-antinucleon amplitudes, rather than as independent resonances requiring separate explanations in each channel.

The implications reach well beyond electron-positron physics. Similar threshold enhancements have been reported in the invariant-mass spectra of proton-antiproton pairs produced in the radiative decays of the J/psi meson and in B-meson decays at Belle and LHCb, and the timelike electromagnetic form factors of the proton and neutron show dramatic rises near the same thresholds. If the unified picture holds, many of these anomalies may share a common dynamical origin, and the widespread habit of labeling every threshold bump as a new particle, from the X(1835) onward, may need systematic re-examination. The authors caution that a naive Breit-Wigner resonance interpretation can be actively misleading in the near-threshold region when the underlying rescattering dynamics is ignored.

The analysis is not without caveats. The chiral effective field theory description is restricted to low energies, so the fits stop at two gigaelectronvolts, and explicit excited vector mesons such as a possible rho state near 2.04 gigaelectronvolts are not included in the framework. The finest experimental points from CMD-3 immediately at the proton-antiproton threshold involve experiment-specific corrections for initial-state radiation and beam-energy spread that the Born-level theory curves do not attempt to replicate point by point. Yet the authors verified that their conclusions are stable under the estimated truncation uncertainties of the chiral expansion: repeating the analysis with lower-order interactions and refitting the short-distance parameters leaves the line shapes essentially unchanged. The next step will be for experimentalists to test the framework’s predictions with precision data, and for theorists to extend the same unified logic to the threshold structures seen in heavy-quark systems. If the pattern holds, physics may have gained something rare and valuable: a case where a flock of apparent new particles dissolves into the familiar, if ferociously complicated, dance of nucleons and antinucleons.

Subject of Research: Near-threshold nucleon-antinucleon final-state interactions in electron-positron annihilation

Article Title: Understanding the near-threshold structures in (e^+e^-) annihilation from a unified (N\bar{N})-interaction perspective

Article References: Ji, T., & Meißner, U.-G. (2026). Understanding the near-threshold structures in $$e^+e^-$$ annihilation from a unified $$N\bar{N}$$-interaction perspective. The European Physical Journal C, 86(9), Article 1116. https://doi.org/10.1140/epjc/s10052-026-16364-x

Image Credits: AI Generated

DOI: 10.1140/epjc/s10052-026-16364-x

Keywords: particle physics, nuclear physics, electron-positron annihilation, nucleon-antinucleon interaction, chiral effective field theory, near-threshold structures, final-state interaction, proton-antiproton, BESIII, CMD-3, hadron spectroscopy, scattering poles

The work, carried out by Emmanuel Ortiz-Pacheco of ELTE Eötvös Loránd University in Budapest and the Universidad Nacional Autónoma de México, together with Roelof Bijker of the Universidad Nacional Autónoma de México, tackles a deceptively simple question: when a heavy baryon decays into a lighter baryon and a meson, how fast does it happen? The answer, expressed as a decay width, is a fingerprint of the particle’s internal structure. Because the strong force that binds quarks is intrinsically non-perturbative, no exact solution of quantum chromodynamics exists for these processes, and theorists must rely on models built around the symmetries of the quark content itself.

Ortiz-Pacheco and Bijker combined a non-relativistic quark model, in which baryons are described as three quarks moving in a harmonic oscillator potential, with the elementary emission model for the strong couplings. In this picture, a baryon emits a fully formed meson through one of its constituent quarks, much as an excited atom emits a photon. The total number of quarks is conserved before and after the emission, and the interaction takes the form of a three-line vertex between a quark and the elementary meson, mirroring the structure of fundamental gauge interactions. The emitted particles considered are the light pseudoscalar mesons: the pion, kaon, eta and eta-prime.

The study covers baryons containing one or two heavy quarks, either charm or bottom, in both their ground-state S-wave configurations and their first orbitally excited P-wave states. Singly heavy baryons fall into a flavor sextet, containing the Sigma, Xi-prime and Omega families, and an anti-triplet, containing the Lambda and Xi families. Doubly heavy baryons form flavor triplets, the Xi-QQ and Omega-QQ families. The relative strengths of the allowed decays are fixed by isoscalar factors of the SU(3) flavor symmetry, evaluated in the Baird-Biedenharn phase convention, while the two coupling constants governing the meson emission were determined in a global fit to 52 measured baryon decay widths, 32 in the charm sector and 20 in the bottom sector. The fit yielded values of g equal to 3.32 per GeV and h equal to minus 0.16 per GeV.

A central result of the analysis is a set of selection rules that forbid entire classes of decays. These rules emerge not from conservation laws alone but from the detailed structure of the spin-flavor wave functions of the baryons. For example, the decay of the rho-configuration of a sextet baryon into an anti-triplet baryon plus an octet meson vanishes because the flavor part of the transition involves only the two light quarks while the spin part involves only the heavy quark, and the two contributions cannot combine. Analogous cancellations forbid anti-triplet to anti-triplet transitions and the rho-mode decays of doubly heavy baryons. Such forbidden channels are marked explicitly in the calculated tables, distinguishing them from decays that are merely kinematically closed.

The comparison with experiment is encouraging for the singly heavy sector. The calculated widths of the ground-state Sigma-c baryons, which decay almost entirely through the Lambda-c pion channel, agree with the observation that these channels carry roughly one hundred percent of the branching fraction. The P-wave Sigma-c(2800) resonance, assigned to a lambda-mode excitation, is reproduced within the large experimental uncertainties reported by Belle and BaBar. In the bottom sector, the model reproduces the widths of the Sigma-b states observed by LHCb and supports the interpretation of the Sigma-b(6097) resonances as P-wave baryons. For the Lambda, Xi and Omega families, the calculated widths, generally below about 28 MeV, are in reasonable agreement with the available data, with the notable exception of the poorly established Lambda-c(2765), whose measured width of roughly 50 to 73 MeV far exceeds the calculated 5.8 MeV and whose very status remains uncertain.

The doubly heavy baryons tell a strikingly different story. Following recent discoveries by the LHCb Collaboration, including the doubly charmed Xi-cc(3621) states and the newly announced Omega-cc at a mass of 3727 MeV, interest in these particles has surged. In the elementary emission model, their strong decay widths are either forbidden outright or suppressed to less than about 1 MeV. The suppression arises from quark-mass-dependent factors in the radial integrals: because the meson is emitted by a light quark, the orbital contribution scales with ratios of light to heavy quark masses, which become very small when two heavy quarks are present. This contrasts sharply with chiral quark model and constituent quark model predictions, which often give widths of hundreds of MeV, a discrepancy that future experiments can decisively test.

The study also highlights how much work remains. In the charm sector, candidates exist for roughly half of the fourteen predicted P-wave Xi baryons, while in the bottom sector only three have been seen. Recent LHCb measurements of spin and parity for states such as Xi-c(3055) have overturned some quark model assignments, pointing instead to D-wave interpretations. The authors note that the puzzling Lambda-c(2765) might even be a Roper-like excitation, a radially excited 2S state lying some 500 MeV above the ground state, an interpretation that lies beyond the present 1S and 1P analysis but could be addressed in future work. Meanwhile, states such as Lambda-c(2880) with spin-parity 5/2-positive would require two quanta of excitation.

For the physics community, the value of this calculation lies in its completeness and its testability. By treating all singly and doubly heavy charm and bottom baryons within a single framework, with one set of fitted couplings and masses taken from the authors’ previous spectroscopic analysis, the model produces internally consistent predictions across the entire spectrum. Where the elementary emission model, the 3P0 model and the chiral quark model agree qualitatively for known decays, they diverge wildly, sometimes by an order of magnitude, for states not yet observed. That divergence is an opportunity: the next round of LHCb and Belle measurements of strong and radiative decay widths, together with spin-parity determinations, will sort the competing pictures and may reveal the missing P-wave baryons that the quark model insists must be there.

Subject of Research: Theoretical calculation of strong two-body decay widths of S- and P-wave singly and doubly heavy charm and bottom baryons using a non-relativistic quark model with the elementary emission model.

Article Title: Strong decay widths of S- and P-wave singly- and doubly-heavy charm and bottom baryons

Article References: Ortiz-Pacheco, E., & Bijker, R. (2026). Strong decay widths of S- and P-wave singly- and doubly-heavy charm and bottom baryons. The European Physical Journal C, 86(9), Article 1091. https://doi.org/10.1140/epjc/s10052-026-16344-1

Image Credits: AI Generated

DOI: 10.1140/epjc/s10052-026-16344-1

Keywords: heavy baryons, strong decay widths, quark model, charm baryons, bottom baryons, doubly heavy baryons, elementary emission model, SU(3) flavor symmetry, LHCb, hadron spectroscopy, pseudoscalar meson emission, selection rules

Glueballs are hypothetical particles made entirely of gluons, the elementary force carriers responsible for binding quarks inside protons, neutrons and other hadrons. In quantum chromodynamics, or QCD, gluons are unlike photons because they carry the strong charge associated with the force they mediate. This allows gluons to interact directly with one another and, in principle, to form bound states without any quarks. Such states would represent an entirely different form of matter: particles composed solely of force-mediating fields.

The existence of glueballs is a fundamental prediction of the non-Abelian gauge structure of QCD, the theory of the strong interaction. At high energies, the strong force becomes weaker, a behavior known as asymptotic freedom. At lower energies, however, QCD becomes highly complex, and quarks and gluons are confined inside composite particles. Calculating the properties of a pure gluon bound state in this regime requires powerful numerical techniques, particularly lattice QCD, in which space-time is represented as a discrete grid. These calculations have long predicted that the lightest pseudoscalar glueball should have a mass close to that of X(2370).

The X(2370) first appeared in BESIII data from decays of the J/ψ particle in 2011. The J/ψ is a charmonium state, consisting of a charm quark and its antiquark, and its decays can produce gluon-rich final states. This makes the enormous samples generated by the Beijing Electron Positron Collider especially valuable in the search for glueballs. Because the strong interaction can transform the energy of the J/ψ into multiple gluons, its decay products provide an unusually sensitive environment for identifying resonances with a substantial gluonic component.

For more than a decade, the identity of X(2370) remained uncertain. A particle’s mass alone is not enough to establish whether it is a glueball, because ordinary mesons made from quark-antiquark pairs can occupy the same mass range. Researchers must determine its quantum numbers, decay behavior and relationship to flavor symmetry. Using a greatly expanded data set containing approximately 10 billion J/ψ events, BESIII determined the particle’s spin and parity for the first time in 2024. The result, 0⁻⁺, matches the expected quantum numbers of a pseudoscalar glueball.

The notation 0⁻⁺ carries specific physical information. The first number indicates that the particle has zero total spin. The minus sign denotes negative parity, describing how its quantum state behaves under spatial inversion, while the plus sign refers to positive charge-conjugation parity, the transformation that exchanges particles with antiparticles. This combination is rare and highly informative. Its agreement with lattice-QCD predictions for a pseudoscalar glueball strengthened the case that X(2370) is not simply an ordinary meson.

BESIII has now added another crucial piece of evidence by observing several previously unreported decay modes of X(2370). The collaboration also identified the particle’s flavor-singlet character. In particle physics, a flavor-singlet state is not associated primarily with one particular quark flavor, such as up, down or strange. Instead, it couples symmetrically to the light-quark flavor sector, a behavior expected for a state built predominantly from gluons. Since gluons do not carry quark flavor, a strong flavor-singlet signal is one of the most important experimental clues supporting a glueball interpretation.

Together, the quantum-number measurement, the agreement with lattice-QCD mass expectations, the newly measured decay channels and the flavor-singlet behavior form what BESIII describes as a complete chain of evidence. The collaboration’s conclusion is that a pseudoscalar-glueball component must dominate X(2370). The result does not necessarily mean that the particle is a perfectly pure glueball. In the strongly interacting world, states with identical quantum numbers can mix, allowing gluonic and quark-based configurations to overlap. Even so, demonstrating dominant gluonic content would represent the clearest experimental indication yet that gluons can bind into a new type of hadronic matter.

The significance extends beyond the discovery of a single resonance. A confirmed glueball would provide a direct low-energy test of QCD’s non-Abelian structure, complementing the earlier discovery of asymptotic freedom at high energies. It would also give theorists a rare opportunity to compare detailed predictions of nonperturbative QCD with measured masses, decay rates and production patterns. The BESIII findings therefore touch one of the most persistent unanswered questions in particle physics: whether the force carriers of a fundamental interaction can assemble themselves into stable, observable particles.

The result also highlights the scientific value of sustained data collection and large international facilities. Since the major upgrade of the Beijing Electron Positron Collider was completed in 2008, BESIII has accumulated more than 10 billion J/ψ events, making it the leading experiment in the tau-charm energy region. Its collaboration includes approximately 700 scientists from about 96 research institutions in 15 countries. The latest analysis depended on years of accelerator operation, detector development, software engineering and computational work. If confirmed through further measurements and independent analyses, X(2370) could become the first compelling experimental window into matter made primarily from gluons—and a landmark validation of QCD in its most difficult domain.

Subject of Research: Experimental evidence for a pseudoscalar glueball component in the X(2370) particle.

Article Title: BESIII Reports Strongest Evidence Yet for a Pseudoscalar Glueball

Web References: BESIII Collaboration; Beijing Electron Positron Collider; Institute of High Energy Physics, Chinese Academy of Sciences.

Keywords

Glueball, X(2370), BESIII, Beijing Electron Positron Collider, quantum chromodynamics, QCD, gluons, particle physics, pseudoscalar particle, lattice QCD, J/ψ decays, hadron spectroscopy