Sterile Neutrinos at MAPP in the B-L Model

Abstract

The possibility of searching for right-handed neutrinos at the MoEDAL's Apparatus for Penetrating Particles (MAPP) detector is investigated in this work. In particular, pair-production of right-handed (RH) neutrinos $N$ from either a $B-L$ gauge boson $Z'$, as well as Standard Model (SM) $Z$ boson are considered. Under a no-background assumption, we show that the MAPP detector can be sensitive to active-sterile neutrino mixing strengths as low as $V_{μN}^2 \approx 10^{-12}$ for multiple choices of $m_N / m_{Z'}$ values, when taking the $B-L$ gauge coupling $g_{B-L} = 10^{-3}$ near its current limit. The SM $Z$ boson portal can reach a similar sensitivity, when the effective mixing between the $B-L$ and SM gauge boson is $α\approx 0.002$.

Figures (5)

• Figure 1: Constraints on the $U(1)_{B-L}$ gauge coupling $g_1' = g_{B-L}$ as a function of the $Z'$ mass $m_{Z'}$, taken from Deppisch:2019kvs using DarkCast. The constraints are from decays to SM final states in the $B-L$ model with three generations of heavy neutrinos.
• Figure 2: As Fig. \ref{['fig:userzp']}, but showing constraints from decays to stable heavy neutrinos with $m_N = 0.3\times m_{Z'}$ in the $B-L$ model with three generations of heavy neutrinos.
• Figure 3: Projected sensitivity at 95% confidence level of the MAPP-2 detector on the active-sterile mixing strength $V^2_{\mu N}$ as a function of the RH neutrino mass $m_N$ in the process $pp\to Z' \to NN$ for a luminosity of 300 fb$^{-1}$. Also shown are the corresponding sensitivities of the CODEX-b (300 fb$^{-1}$), FASER-2 and MATHUSLA (3000 fb$^{-1}$) detectors. The $U(1)_{B-L}$ gauge coupling and the $Z'$ mass are chosen as $g_{B-L} = 10^{-3}$ and $m_N/m_{Z'} = 0.1$ (top left), 0.2 (top right), 0.3 (bottom left) and 0.4 (bottom right). The grey curves are contours of constant proper RH neutrino decay lengths $L_N = 1$ m and 100 m. The grey shaded band indicates the preferred parameter region where the light neutrinos acquire a mass between $10^{-2}$ eV and $0.3$ eV in a canonical seesaw mechanism.
• Figure 4: As Fig. \ref{['fig:big']} but showing the projected sensitivity of MAPP-2 in the process $pp\to Z \to NN$. The gauge mixing parameter is $\alpha = g_{B-L}\sin\theta_{ZZ'} = 0.001$ (left) and $\alpha = 0.002$ (right).
• Figure 5: Current constraints (shaded regions) and future sensitivity on the active-sterile neutrino mixing strength $V^2_{\mu N}$ as a function of the sterile neutrino mass $m_N$. Here, the sterile neutrinos only couple through the mixing and they are produced via SM neutral or charged current, i.e., effectively, $g_{B-L} = \alpha = 0$. The corresponding data is taken from sterile-neutrino.org. In comparison, the future sensitivity of MAPP-2 and MATHUSLA in the $B-L$ model for fixed $g_{B-L} = 10^{-3}$ and $m_{N} = 0.4 m_{Z^\prime}$ is shown. The grey shaded region labelled BBN is disfavoured by Big Bang Nucleosynthesis whereas the grey shaded band indicates the preferred parameter region where the light neutrinos acquire a mass between $10^{-2}$ eV and $0.3$ eV in a canonical seesaw mechanism.