Towards exotic hidden-charm pentaquarks in QCD (1507.03717v2)

Abstract: Inspired by $P_c(4380)$ and $P_c(4450)$ recently observed by LHCb, a QCD sum rule investigation is performed, by which they can be identified as exotic hidden-charm pentaquarks composed of an anti-charmed meson and a charmed baryon. Our results suggest that $P_c(4380)$ and $P_c(4450)$ have quantum numbers $J^P=3/2^-$ and $5/2^+$, respectively. Furthermore, two extra hidden-charm pentaqurks with configurations $\bar{D}\Sigma_c^*$ and $\bar{D}^\Sigma_c^$ are predicted, which have spin-parity quantum numbers $J^P=3/2^-$ and $J^P=5/2^+$, respectively. As an important extension, the mass predictions of hidden-bottom pentaquarks are also given. Searches for these partners of $P_c(4380)$ and $P_c(4450)$ are especially accessible at future experiments like LHCb and BelleII.

• The paper predicts novel hidden-charm pentaquark states with specific quantum numbers, such as J^P=3/2^- and 5/2^+, using QCD sum rules.
• The paper employs a detailed QCD sum rule approach, considering contributions up to dimension eight to evaluate masses and structural configurations.
• The paper proposes exotic configurations for both hidden-charm and hidden-bottom states, motivating further experimental investigations at LHCb and BelleII.

Overview of Exotic Hidden-Charm Pentaquarks in QCD

The paper "Towards exotic hidden-charm pentaquarks in QCD" investigates the existence and properties of exotic pentaquark states with hidden charm, particularly focusing on the pentaquark states recently observed by the LHCb collaboration, namely $P_c(4380)$ and $P_c(4450)$. The authors utilize QCD sum rules to explore the hypothesis of these states being exotic pentaquarks constituted by an anti-charmed meson and a charmed baryon. This research is part of the broader effort to understand exotic hadronic matter, which potentially encapsulates more complex configurations beyond conventional three-quark baryons and quark-antiquark mesons.

Predicted Quantum Numbers and Structures

According to the paper, the quantum numbers of pentaquark states $P_c(4380)$ and $P_c(4450)$ are proposed to be $J^P=3/2^-$ and $J^P=5/2^+$, respectively. The authors further predict additional pentaquark states with configurations $\bar{D}\Sigma_c^*$ and $\bar{D}^*\Sigma_c^*$ characterized by the same set of spin-parity quantum numbers. These predictions are extrapolated through the construction and analysis of local pentaquark interpolating currents, which are composed of either a tightly bound pentaquark structure or a meson-baryon molecular configuration. The paper also encourages future experimental endeavors at facilities such as LHCb and BelleII to investigate these particles further.

Methodology: QCD Sum Rules

The research employs QCD sum rules to analyze the spectral densities of carefully constructed interpolating currents. This approach considers contributions up to dimension eight, including the perturbative term, quark condensates, gluon condensates, and their mixed condensates. It involves deriving expressions for the correlation functions and disentangling spin-parity contributions, allowing the evaluation of masses and insights into configurations, leading to proposing the mass and quantum characteristics of $P_c(4380)$ as a $[\bar D^*\Sigma_c]$ molecule and $P_c(4450)$ as an admixture of $[\bar D^* \Lambda_c]$ and $[\bar D \Sigma_c^*]$.

Results and Implications

The predicted mass of $P_c(4380)$ is consistent with a $[\bar D^*\Sigma_c]$ structure, while $P_c(4450)$ is postulated to harbor a composite structure, potentially facilitating complex decay channels apart from $J/\psi N$. These configurations reveal deeper insights into the interactions and binding mechanisms within heavy-flavored hadrons. Furthermore, the paper predicts hidden-bottom counterparts for these pentaquark states, suggesting $M_{[\bar B^*\Sigma_b],3/2^-}$ and $M_{[\bar B\Sigma_b^*{content}\bar B^*\Lambda_b],{5/2^+}$ with masses approximated at 11.55 GeV and 11.66 GeV, respectively.

Future Outlook

The identification of hidden-charm and hidden-bottom pentaquarks presents pivotal developments in hadronic physics. The research illustrates the potential for discovering more states within this framework and understanding their underlying quark-gluon dynamics. Awareness and attention to these states might motivate additional experimental pursuits, possibly uncovering new dynamics in non-perturbative QCD and expanding the taxonomy of multi-quark configurations. While this work effectively sets the ground for future investigations, it also highlights a broader need for comprehensive experimental assessments to validate these theoretical predictions and delineate the boundaries of exotic hadronic spectra.

In summary, the paper underscores a calculated approach to demystifying recently observed hidden-charm pentaquarks, suggesting tangible follow-up experiments and theoretical work poised to unlock further structural nuances in multi-quark systems. The integration of QCD sum rules into this domain enhances the predictive toolkit available to nuclear physicists and marks a substantive stride towards quantifying conceivable hadronic states beyond textbook baryons and mesons.