Search for Pcs(4459) and Pcs(4338) in Upsilon(1S,2S) inclusive decays at Belle (2502.09951v2)

Abstract: Using data samples of 102 million Upsilon(1S) events and 158 million Upsilon(2S) events collected by the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider, we search for [udsccbar] pentaquark states decaying to Jpsi Lambda. Using the first observations of Upsilon(1S, 2S) inclusive decays to Jpsi Lambda, we find evidence of the P_ccbars(4459)0 state with a local significance of 3.3 standard deviations, including statistical and systematic uncertainties. We measure the mass and width of the Pccbars(4459)0 to be (4471.7 +- 4.8 +- 0.6) MeV/c2 and (21.9 +- 13.1 +- 2.7) MeV, respectively. The branching fractions for P_ccbars(4459)0 production are measured to be B[Upsilon(1S) -> P_ccbars(4459)0/ Pbar_ccbars(4459)0 + anything] = (3.5 +- 2.0 +- 0.2)*10-6 and B[Upsilin(2S) -> P_ccbars(4459)0/ Pbar_ccbars(4459)0 +anything] = (2.9 +- 1.7 +- 0.4)*10-6. The inclusive branching fractions of Upsilon(1S, 2S) -> Jpsi Lambda/Lambdabar are measured to be B[Upsilin(1S) -> Jpsi Lambda/Lambdabar + anything] = (36.9 +- 5.3 +- 2.4)*10-6 and B[Upsilon(2S) -> Jpsi Lambda/Lambdabar + anything] = (22.3 +- 5.7 +- 3.1)*10-6. We measure the visible cross section $\sigma(e^+e^- \to J/psi \Lambda/\bar\Lambda$ + anything) = (90 +- 14 +- 6) fb for the continuum production at $\sqrt{s} = 10.52$ GeV. In all cases, the first uncertainties are statistical and the second are systematic.

• The paper presents evidence for an exotic Pcs state with a 3.3σ significance in Upsilon decays.
• It analyzes over 260 million Upsilon events using advanced tools like PYTHIA and EvtGen to isolate the signal.
• The findings support theoretical pentaquark models and suggest future research directions at Belle II.

Evidence of Pentaquark States in $\Upsilon(nS)$ Decays at Belle

The pursuit of understanding exotic states such as pentaquarks has made notable progress through this paper at the Belle detector. This paper details the search for states in the $\Upsilon(1S, 2S)$ inclusive decays leading to $J/\psi$ final states, with specific attention to the $P_c$ candidate evidences. Such inquiries are rooted in the context of the earlier LHCb results that suggested the existence of the $P_c$ states in the $\Lambda_b \rightarrow J/\psi p K^-$ decay subchannels, with these states being hypothesized as potential pentaquark candidates.

The Research Context

Historically, the existence of pentaquark states was indirectly proposed through the quark model by Gell-Mann and Zweig. Subsequent experiments, notably by the LHCb collaboration, have reported resonances consistent with pentaquark interpretations, thereby reinvigorating interest in searches for these exotic forms of hadronic matter. The $P_c(4458)$ state, among others observed by the LHCb with significant precision, serves as a paradigmatic example of potentially bound quark configurations extending beyond conventional baryons and mesons.

Methodology and Dataset

The paper conducted by the Belle collaboration utilized data from the KEKB asymmetric-energy $e^+e^-$ collider, encompassing 102 million $\Upsilon(1S)$ and 158 million $\Upsilon(2S)$ events. These large datasets allowed for a robust search for $P_c$ states through $J/\psi$ channels, employing finely tuned particle identification and selection criteria, as well as sophisticated background estimation methods. Simulation frameworks such as PYTHIA for hadronization processes, alongside EvtGen for event generation, were pivotal in establishing signal characteristics against physical and instrumental background processes.

Key Findings

This analysis presented compelling evidence for the existence of the $P_c$ state with a statistical significance of 3.3 standard deviations. The measured mass and width for the state were found to be $4471.7 \pm 4.8 \pm 0.6$ MeV and $21.9 \pm 13.1 \pm 2.7$ MeV, respectively. This substantiates prior hypotheses about the nature of these states as exotic baryonic matter configurations. Moreover, the obtained branching fractions for $\Upsilon \rightarrow P_c$ decays were in the order of $10^{-6}$, supporting the rarity yet feasibility of such exotic decays in $\Upsilon(1S, 2S)$ transitions within the experimental reach.

Implications and Future Directions

The confirmation of $P_c$ signals in $\Upsilon$ decays contributes significantly to our understanding of exotic hadronic states. Such studies enhance our comprehension of QCD in the non-perturbative regime and the dynamics governing multi-quark states. Given the corroborating evidence from Belle, future explorations should focus on a more granular understanding of these structures—potentially expanding into continuum analyses or leveraging higher luminosity facilities like the upcoming Belle II experiment. Moreover, as theoretical models diverge between tightly-bound pentaquark states versus molecular configurations, further research is warranted to decisively categorize these observations.

Conclusion

In summary, the work by the Belle team enriches the phenomenological discourse on multiquark states and provides tangible leads for subsequent investigative efforts in high-energy physics. As measurements continue to align more closely with theoretical predictions, collaborations like Belle and LHCb are indispensable to push the empirical boundaries of modern particle physics.