Molecular Bound States Advance Understanding of Particle Physics with Masses Around Threshold

The search for exotic particles composed of quarks and gluons continues to push the boundaries of particle physics, and understanding the potential masses of these fleeting structures proves crucial for ongoing experiments. Xuan-Heng Zhang, Cong-Feng Qiao, and colleagues at the University of Chinese Academy of Sciences have calculated the likely mass range for specific bound states, utilising a sophisticated theoretical approach known as QCD sum rules. This method allows scientists to predict particle masses by considering the complex interactions of quarks and gluons within these structures, incorporating contributions from quantum fluctuations and the vacuum itself. The team’s calculations reveal candidate masses that align with recent experimental observations from the BESIII Collaboration, and importantly, predict the existence of additional bound states which could be identified in future experiments searching for hidden-bottom particles, thus refining our understanding of strong force interactions.

In this structure, researchers calculate the mass spectrum of Λc̄Σc molecular configurations using the method of quantum chromodynamics sum rules, focusing on the region of bound states. They construct two linearly independent interpolating currents and include contributions from nonperturbative condensates up to dimension 12 in their numerical calculations. Consequently, the team obtains the masses of candidate bound states with quantum numbers JP = 0−, 0+, 1−, and 1+. The results demonstrate that the central values of the Λc̄Σc bound-state masses lie around 5.8 GeV, a finding consistent with those reported by the BESIII Collaboration. Furthermore, the study computes the mass spectrum of the Λb̄Σb bound states, also with quantum numbers JP = 0−.

Calculating Quark-Gluon Correlation Functions Perturbatively

Scientists are exploring the complex interactions between quarks and gluons, the fundamental constituents of matter, through detailed calculations of correlation functions within the framework of quantum chromodynamics. These equations define relationships between operators representing quark-gluon interactions, including contributions from perturbative and non-perturbative effects. The analysis reveals the importance of vacuum condensates, which describe the strength of interactions in the vacuum, and the mixing of operators due to non-perturbative effects, influencing hadron properties. The calculations incorporate parameters related to the scale of non-perturbative effects and demonstrate the sensitivity of results to the chosen theoretical approach. This work requires a deep understanding of quantum field theory and numerical methods, with the ultimate goal of comparing theoretical predictions to experimental data to validate the underlying models and refine parameters.

Lambda c Anti-Sigma c Molecule Mass Predictions

Scientists have meticulously calculated the mass spectrum of Λc ̄Σc molecular configurations using quantum chromodynamics sum rules, a technique that combines perturbative and nonperturbative contributions to predict hadron spectra. This work addresses a gap in current understanding, following the BESIII Collaboration’s observation of no bound state within a specific mass range. The team constructed interpolating currents, incorporating nonperturbative condensates to refine the accuracy of their calculations. Consequently, the research delivers mass predictions for candidate bound states possessing quantum numbers JP = 0−, 0+, 1−, and 1+.

Results demonstrate that the calculated Λc ̄Σc bound-state masses cluster around 5.8 GeV, aligning with the previously reported findings from the BESIII Collaboration. These measurements confirm the plausibility of bound states within this mass region, providing crucial theoretical support for ongoing experimental investigations. Furthermore, scientists extended their analysis to compute the mass spectrum of Λb ̄Σb bound states, also with quantum numbers JP = 0−, 0+, 1−, and 1+, suggesting these states could serve as hidden-bottom candidates for future experimental detection.

Hidden Baryon Antibaryon Bound State Masses

This research presents a theoretical investigation into the properties of bound states composed of a baryon and an antibaryon, specifically focusing on hidden-charm and hidden-bottom configurations. Employing the QCD sum rules method, scientists calculated the masses and decay constants of these states, constructing interpolating currents to account for complex quantum mechanical effects and incorporating contributions from various non-perturbative condensates. The results indicate the existence of candidate bound states with specific quantum numbers, and the calculated mass ranges align with recent experimental observations from the BESIII Collaboration, supporting the plausibility of these molecular structures. The team’s findings demonstrate that the calculated masses of these bound states consistently lie above the corresponding baryon-antibaryon thresholds, explaining why the BESIII Collaboration did not detect them near the threshold energy.

The calculated mass of the hidden-charm state, around 5.8 GeV, suggests that future experiments could potentially observe this state by increasing the center-of-mass energy. While acknowledging that differing theoretical approaches exist, the authors suggest discrepancies between their results and previous calculations may stem from variations in the binding mechanisms considered, focusing on quark-level interactions rather than purely hadronic-level effects.