Jong Yoon Sohn | Searcharxiv

arXiv2025

Probing the 3+1 neutrino model in the SHiP experiment

In this study, as an extension of our previous work, we estimate the sensitivity of the Search for Hidden Particles (SHiP) experiment to the 3+1 model using the charged-current deep inelastic scattering event spectrum. We employ the Feldman-Cousins method with a parametric bootstrap to account for nuisance parameters and systematic uncertainties. In the previous study, we proposed a dual baseline approach by suggesting Far SND (FSND) at 120 m with Near SND (NSND) at 27 m. We employ the same approach in this study. The NSND-only configuration can probe mixing parameters of $|U_{\alpha4}|^2 \gtrsim 0.1$ near $Δm_{41}^2 \sim 10^3\,\mathrm{eV}^2$, with a reduction of normalized systematic uncertainties from 20\% to 10\% improving sensitivity by roughly a factor of two. Moreover, the inclusion of FSND significantly enhances the sensitivity by a factor of 2 to 10 depending on the flavor and the systematic uncertainty. In two-flavor mixing scenarios, a cancellation between neutrino appearance and disappearance generates kinks in the sensitivity curves, that are vanished in the dual-baseline approach.

hep-ph↗

arXiv2024

Probing the mixing between sterile and tau neutrinos in the SHiP experiment

We study the expected sensitivity to the mixing between sterile and tau neutrinos directly from the tau neutrino disappearance in the high-energy fixed target experiment. Here, the beam energy is large enough to produce tau neutrinos at the target with large luminosity. During their propagation to the detector, tau neutrinos may oscillate into sterile neutrinos. By examining the energy spectrum of the observed tau neutrino events, we can probe the mixing between sterile and tau neutrinos directly. In this paper, we consider Scattering and Neutrino Detector (SND) at SHiP experiment as a showcase, which uses 400 GeV protons from SPS at CERN, and expect to observe 7,300 tau and anti-tau neutrinos from the $2\times 10^{20}$ POT for 5 years operation. Assuming the uncertainty of 10\%, we find the sensitivity $|U_{τ4}|^2 \sim 0.08$\, (90\% CL) for $Δm_{41}^2 \sim 500\ \mathrm{eV}^2$ with 10\% background to the signal. We also consider a far SND at the end of the SHiP Hidden Sector Decay Spectrometer (HSDS), in which case the sensitivity would be enhanced to $|U_{τ4}|^2 \sim 0.02$. Away from this mass, the sensitivity becomes lower than $|U_{τ4}|^2 \sim 0.15$ for $Δm_{41}^2 \lesssim 100\ \mathrm{eV}^2$ or $Δm_{41}^2\gtrsim 10^4 \mathrm{eV}^2$.

hep-ph↗