Precision $YN$ and $\bar{n}N$ measurements with an LH$_2$/LD$_2$ target in the BESIII detector

Abstract

Located at the BEPCII $e^{+}e^{-}$ collider, the BESIII experiment provides a robust platform for investigating (anti)hyperon-nucleon ($YN$) and antineutron-nucleon ($\bar{n}N$) interactions. This is made possible by the high production cross-sections of $J/ψ$ and $ψ(3686)$ resonances and their substantial decay branches into these baryons. Although previous studies using the beam pipe as a target demonstrated feasibility, statistical precision remains constrained by the limited material budget. To address this, we propose installing a dedicated liquid hydrogen or liquid deuterium target between the beam pipe and the Cylindrical Gas Electron Multiplier Inner Tracker. Monte Carlo simulations confirm that the added material has a negligible effect on charged particle tracking. This upgrade is expected to enhance the effective luminosity for scattering on free protons by a factor of 10--30 for $Λ$, $Σ^{+}$, $Ξ$, and $\bar{n}$ beams, enabling high-precision measurements of $YN$ and $\bar{n}N$ interactions that will significantly advance our knowledge of non-perturbative strong interactions.

Figures (2)

• Figure 1: Survival ratio $N/N_0$ of hyperons ($\Lambda$, $\Sigma^{+}$, $\Xi^{0}$, $\Omega^{-}$) and antineutrons ($\bar{n}$) from the interaction point to the target region as a function of radial distance $r$, with different particles indicated by different colored lines. The beam pipe and target regions are indicated by grey and yellow shaded areas, respectively. Considering the detector acceptance, particles with $|\cos\theta|>0.8$ are rejected.
• Figure 2: Relative changes in (left) detection efficiency $\Delta\epsilon/\epsilon_0$, (middle) momentum resolution $\Delta\sigma_p/\sigma_{p0}$, and (right) polar angle resolution $\Delta\sigma_\theta/\sigma_{\theta0}$. Red circles and green squares represent LD$_2$ and LH$_2$, respectively; open and filled symbols denote target thicknesses of 20 mm and 40 mm.