Baryons with two heavy quarks: Masses, production, decays, and detection

Abstract: The large number of $B_c$ mesons observed by LHCb suggests a sizable cross section for producing doubly-heavy baryons in the same experiment. Motivated by this, we estimate masses of the doubly-heavy $J=1/2$ baryons $\Xi_{cc}$, $\Xi_{bb}$, and $\Xi_{bc}$, and their $J=3/2$ hyperfine partners, using a method which accurately predicts the masses of ground-state baryons with a single heavy quark. We obtain $M(\Xi_{cc}) = 3627 \pm 12$ MeV, $M(\Xi_{cc}^*)= 3690 \pm 12$ MeV, $M(\Xi_{bb}) = 10162 \pm 12$ MeV, $M(\Xi_{bb}^*)= 10184 \pm 12$ MeV, $M(\Xi_{bc}) = 6914 \pm 13$ MeV, $M(\Xi'{bc}) = 6933 \pm 12$ MeV, and $M(\Xi{bc}^*) = 6969 \pm 14$ MeV. As a byproduct, we estimate the hyperfine splitting between $B_c^*$ and $B_c$ mesons to be $68 \pm 8$ MeV. We discuss P-wave excitations, production mechanisms, decay modes, lifetimes, and prospects for detection of the doubly heavy baryons.

Analysis of Doubly Heavy Quark Baryons: Masses, Production, and Detection

The paper by Karliner and Rosner provides a comprehensive theoretical evaluation of baryons comprising two heavy quarks, specifically focusing on the Ξcc, Ξbb, and Ξbc states. Employing a quark model similar to those used for predicting masses of baryons with a single heavy quark, the study presents estimates for the masses of several doubly heavy baryons and discusses their production mechanisms, decay modes, detection prospects, and implications for experimental observations.

Mass Predictions

The authors leverage the quark model framework to calculate the masses of baryons containing two charm quarks (cc), two bottom quarks (bb), and one charm and one bottom quark (bc). By maintaining consistency with established quark interaction principles, the model predicts:

• For the Ξcc baryon, a mass of 3627 ± 12 MeV for the J = 1/2 state and 3690 ± 12 MeV for its J = 3/2 hyperfine partner.
• For the Ξbb baryon, masses are estimated at 10162 ± 12 MeV (J = 1/2) and 10184 ± 12 MeV (J = 3/2).
• For the Ξbc baryon, which can exist in a variety of spin configurations, a mass of 6914 ± 13 MeV is suggested for the [bq] configuration, with a slight increase to 6933 ± 12 MeV for the (bq) configuration indicating a different internal spin alignment. Its J = 3/2 state is predicted at 6969 ± 14 MeV.

These estimates align with several theoretical predictions but deviate significantly from the experimental results reported by the SELEX collaboration, suggesting discrepancies in either the experimental detection or need for refined theoretical models.

Implications for Production and Detection

The production of such baryons requires the simultaneous creation of two heavy quark-antiquark pairs and the eventual coalescence of two heavy quarks into a diquark that can attract a light quark to complete baryon formation. The authors estimate that the probability of producing these states could be comparable to the known production rates of similar baryons containing single heavy quarks. Detection at facilities like the LHCb would rely on certain decay signatures such as Ξcc decaying to charmed baryons with pions in association.

Decay Mechanisms and Lifetimes

The paper outlines potential decay pathways for these baryons, noting the important role of Cabibbo-favored decay processes such as b → c and c → s transitions. The authors anticipate that doubly heavy baryons would exhibit significant branching ratios into modes involving J/ψ production, leveraging these pathways both for search strategies and for signature identification in high-energy experiments. The lifetime predictions for these states, ranging from about 50 fs for Ξcc to 370 fs for Ξbb, imply that experimental setups must be capable of identifying very short-lived particle decays.

Challenges and Future Directions

The detection and analysis of doubly heavy baryons remain experimental challenges due to the complexities of their production and decay signatures amid high-energy collisions. Karliner and Rosner suggest that forthcoming experimental campaigns, bolstered by increased luminosity and refined trigger mechanisms, could improve the likelihood of observing these elusive states. Moreover, the paper highlights the Bridging New Landmarks Dilemma, emphasizing the dynamic nature of future theoretical and experimental advancements in heavy baryon physics.

Overall, this paper sets a foundational theoretical framework for understanding doubly heavy baryons, providing key insights into their mass spectra, production likelihood, decay channels, and experimental observability while also challenging current models in light of emerging data. The findings bring anticipation that the discovery of such baryons can offer profound insights into quantum chromodynamics, particularly concerning the interplay of heavy quarks.