Search for Cosmic-Ray Produced Dark Meson via the $U(1)_\text{D}$ Portal at JUNO

Abstract

We investigate the atmospheric production and subsequent detection of sub-GeV dark mesons within the framework of a confining dark sector coupled to the Standard Model (SM) via a $U(1)_{\text{D}}$ vector portal. High-energy cosmic ray interactions in the atmosphere produce dark quarks through proton bremsstrahlung, rare decay of Standard Model mesons, and Drell-Yan processes, which subsequently hadronize into dark mesons. We adopt a modified Quark Combination Model to describe the non-perturbative dark hadronization process, allowing for a detailed event-level characterization of the dark meson flux. We simulate the flux and the interaction of these relativistic dark mesons in the Jiangmen Underground Neutrino Observatory (JUNO) using the GENIE generator, considering both elastic scattering off nuclei and deep inelastic scattering channels. Based on the projected 20 kton$\cdot$year exposure, we derive sensitivity limits on the coupling strength between the dark gauge boson and the SM sector. Our results demonstrate that JUNO can probe substantial unexplored parameter space, particularly for light mediators ($m_{Z^\prime} \lesssim 10$ MeV), where it achieves sensitivities to the portal interaction as low as $2.4 \times 10^{-4}$.

Figures (8)

• Figure 1: Average meson multiplicity $\langle N \rangle$ as a function of the dimensionless scaled center-of-mass energy $\sqrt{s}/m_{q_k}$. The separation of curves indicates a violation of simple scaling, revealing the dependence of multiplicity on the absolute energy scale $\sqrt{s}$ in addition to the kinematic ratio.
• Figure 2: Kinematic distributions of the produced dark mesons in the $q_k \bar{q}_k$ rest frame for a center-of-mass energy $\sqrt{s}=100~\text{GeV}$. The distributions are shown for three benchmark dark meson masses: $m_{\pi_D}=1.0~\text{GeV}$ (red), $0.1~\text{GeV}$ (blue), and $0.01~\text{GeV}$ (green). Left: dark meson energy spectrum. Right: transverse momentum distribution of dark mesons.
• Figure 3: Left: The bremsstrahlung production cross-section $\sigma(pp \to p p Z')$ as a function of the incident proton energy $E_p$ for $m_{Z'} = 0.01,\,0.1,\,0.5,\,1.0,\,5.0$ GeV, computed with the benchmark coupling $g_{SM}=1$ (to be rescaled when deriving limits). Right: The corresponding differential flux of $Z'$ at the production point as a function of $E_{Z'}$, obtained from the multiplicity convolution in Eq. \ref{['eq:Phi_Zp']}.
• Figure 4: $Z^\prime$ Flux from $\pi^0$ and $\eta$ decay
• Figure 5: The differential production cross section of the Drell-Yan process for different incident proton energies ($E_p$). From left to right, $E_p = 40, 100,$ and $1000$ GeV.