Monophotons from Scalar Portal Dark Matter at Neutrino Experiments

Abstract

In this work, we investigate monophoton signatures arising from dark matter via a $2\to 3$ scattering process $χ+ N \to χ+ N + γ$ that is mediated by a virtual scalar and a Standard Model photon. Since the final-state photon carries a large fraction of the initial dark matter's energy, this process offers a compelling handle for probing scalar portal dark matter scenarios. Their distinctive energy, angular, and timing distributions allow for effective separation of signal from neutrino-induced backgrounds. We analyze several models featuring different couplings to the scalar mediator, with the scalar photon coupling serving as the common detection channel. To distinguish between the models, we further examined their distinct spatial distributions. We considered the flux of dark matter produced both at the target and absorber of neutrino facilities such as the BNB, NuMI, and LBNF, and investigated the sensitivities at the ongoing SBND, ICARUS-NuMI, and future DUNE ND detectors. We further investigated the differences in the DM fluxes arising from various production mechanisms, as well as the distinctions between the target and absorber contributions. Our results demonstrate that the sensitivities at the considered experiments, especially DUNE ND, can place significantly improved constraints on viable parameter space in various scenarios.

Figures (17)

• Figure 1: Feynman diagrams illustrate the production of (a) photophilic scalars via photon, (b) neutrinophilic and (c) electro/muon-philic scalars, both via three-body decays of charged mesons, (d) up-philic scalars via kaon two-body decays, and (e) via proton bremsstrahlung, and (f) top-philic scalars via one-loop kaon two-body decays.
• Figure 2: Feynman diagrams depicting (a) the two-body decay of scalar mediator into dark matter, that occurs with 100% probability, and (b) the $2 \rightarrow 3$ process for detecting DM. Here, the incoming DM particle scatters with the target nuclei in the detector via scalar and photon propagators to produce a photon in the final state.
• Figure 3: Schematic diagram (Ref. PRISM) of the SBN experimental program (not to scale), showing the layout of the Booster Neutrino Beam (BNB) line and the Neutrinos at the Main Injector (NuMI) line. The positions of the four detectors-SBND, MicroBooNE, MiniBooNE, and ICARUS are shown. SBND is located 110 meters downstream from the BNB target, while ICARUS is positioned 803 meters from the NuMI target. Red dotted lines show the directions of the BNB and NuMI beams. Both SBND BNB, and ICARUS-NuMI are situated off-axis with respect to their respective beam sources.
• Figure 4: Schematic diagram of the DUNE near detector experimental setup (not to scale), showing the Long-Baseline Neutrino Facility (LBNF) beamline infrastructure. The decay pipe is 221 meters long. Downstream of this, the muon shielding and the absorber hall are also shown. The DUNE near detector is located 574 meters from the target. (Source: Fermilab)
• Figure 5: Schematic layout of the ICARUS detector in the NuMI beamline. The diagram illustrates the geometric configuration relative to the NuMI target and absorber. The ICARUS detector is positioned 803 meters from the target and 115 meters from the absorber, with off-axis angles of $5.56^\circ$ from the target and $42.71^\circ$ from the absorber, respectively. These off-axis placements significantly influence the detector's angular acceptance and sensitivity to various particle production mechanisms. The beam direction is shown as a red dashed line.