The BESIII collaboration recently reported the first study of antihyperon-nucleon scattering Λbar p→Λbar p with “Λbar beam” from the decay J/ψ→ΛΛbar based on 10 billion J/ψ data. The results have been published recently in Physics Review Letters on June 4, 2024 [Phys. Rev. Lett. 132, 231902 (2024)].
Measurements of hyperon-nucleon scattering are important to constrain theoretical models of hyperon-nucleon interaction and to understand the so-called “hyperon puzzle” concerning the masses of neutron stars. However, it is limited by the availability and short-lifetime of hyperon beams, leading to a scarcity of hyperon-nucleon scattering data. Compared to the hyperon-nucleon scattering, the situation is even worse for antihyperon-nucleon scattering. Until now, no antihyperon-nucleon scattering data have been obtained due to the absence effective antihyperon sources, which results in the very limited related theoretical research. Therefore, the realization of antihyperon-nucleon scattering measurements can fill this gap, and new measurements will motivate more effort for the understanding of the antihyperon-nucleon interaction. More importantly, antihyperon-nucleon scattering data can further constrain the hyperon-nucleon interaction theory from another angle.
In this work, using 10 billion J/ψ events collected with the BESIII detector at the BEPCII storage ring, the reactions Λp→Λp and Λbar p→Λbar p are studied, where Λ/Λbar baryons are produced in the process J/ψ→ΛΛbar and protons are the hydrogen nuclei in the cooling oil of beam pipe. Clear signals are observed for the two reactions. The cross sections in -0.9≤cosθΛ/Λbar≤0.9 are measured to be σ(Λp→Λp)=(12.2
±1.6
stat±1.1
syst) and σ(Λbar p→Λbar p)=(17.5
±2.1
stat±1.6
syst) mb at the Λ/Λbar momentum of 1.074 GeV/c within a range of
±0.017 GeV/c, where θ
Λ/Λbar are the scattering angles of the Λ/Λbar in Λ p/Λbar p rest frames. Furthermore, the differential cross sections of the two reactions are also measured. There is a slight tendency of forward scattering for Λp→Λp, while a strong forward peak for Λbar p→Λbar p is observed. We present an approach to extract the total elastic cross sections integrated over the full angular region by extrapolation, which are determined to be σ
t(Λp→Λp)=(14.2
±1.8stat
±1.3syst) and σ
t(Λbar p→Λbar p)=(27.4
±3.2
stat±2.5
syst) mb. This work is the first study of antihyperon-nucleon scattering, and these new measurements will serve as important inputs for the theoretical understanding of the (anti)hyperon-nucleon interaction.
FIG. 1. Differential cross sections of the reactions Λp→Λp (left) and Λbar p→Λbar p (right).
Further reading:
PRL publication link:
https://link.aps.org/doi/10.1103/PhysRevLett.132.231902arXiv link:
https://arxiv.org/abs/2401.09012
