Constraints on heavy decaying dark matter from 570 days of LHAASO observations

TL;DR

The study targets heavy decaying dark matter in the mass range $10^{5}$–$10^{9}$ GeV by exploiting LHAASO-KM2A data from partial instrument operation. It employs a five-region, joint likelihood analysis that leverages the DM angular distribution across ROIs and includes both prompt and secondary Galactic IC gamma components, with a detailed treatment of detector response and backgrounds. The analysis yields 95% CL lower limits on the DM lifetime $ au_ ext{DM}$ that surpass previous gamma-ray constraints by factors of several, thereby challenging DM explanations for IceCube's diffuse high-energy neutrino flux in non-neutrino channels. The results demonstrate LHAASO-KM2A's strong DM indirect-detection capability with partial data and portend substantial improvements with full KM2A, additional detectors, and refined astrophysical modeling.

Abstract

The Kilometer Square Array~(KM2A) of the Large High Altitude Air Shower Observatory (LHAASO) aims at surveying the northern gamma-ray sky at energies above 10 TeV with unprecedented sensitivity. Gamma-ray observations have long been one of the most powerful tools for dark matter searches, as e.g., high-energy gamma-rays could be produced by the decays of heavy dark matter particles. In this letter, we present the first dark matter analysis with LHAASO-KM2A, using the first 340~days of data from 1/2-KM2A and 230~days of data from 3/4-KM2A. Several regions of interest are used to search for a signal and account for the residual cosmic-ray background after gamma/hadron separation. We find no excess of dark matter signals, and thus place some of the strongest gamma-ray constraints on the lifetime of heavy dark matter particles with mass between 10^5 and 10^9~GeV. Our results with LHAASO are robust, and have important implications for dark matter interpretations of the diffuse astrophysical high-energy neutrino emission.

Figures (8)

• Figure 1: 95% one-sided lower limits on DM lifetime obtained with the profile likelihood analysis (thick black lines), for DM decaying into $b$ quarks (left) or $\tau$ leptons (right). The black dashed line shows the limit obtained if we only consider prompt DM contribution. The green and yellow bands correspond to the expected 68% and 95% limit ranges from Monte Carlo simulations with the background-only hypothesis. Previous limits Cohen:2016uygIshiwata:2019aetChianese:2021jke and those from HAWC Abeysekara:2017jxs are shown with gray and blue lines
• Figure S1: Pixelated sky map highlighting the selected ROIs, labeled with indices from 0 to 4, in Galactic (left panel) and equatorial (right panel) coordinates. The dark band shows 10 degrees around the Galactic plane.
• Figure S2: The $\gamma$-ray and cosmic-ray survival fractions after $\gamma$/hadron separation. $\gamma$-ray events are obtained via simulation, while the cosmic-ray events are the actual 1/2-KM2A and 3/4-KM2A data.
• Figure S3: Total DM $\gamma$-ray intensity (solid lines) from ROI$_0$ for the benchmark case of DM particles with $10^7$ GeV mass and $10^{28}$ s lifetime. The dashed lines show the prompt Galactic component, while the shaded regions highlight the additional contribution due to the secondary Galactic IC component. Different colors correspond to different decay channels.
• Figure S4: Total $\gamma$-ray intensity from DM decays in ROI$_0$ obtained with (solid black lines) and without (dashed red lines) the SL+IR Galactic photon background, for $b\bar{b}$ and $\tau^{+}\tau{-}$ channels and with same parameters as Fig. \ref{['fig:DMfluxes']}. The lower panels show the ratio of the flux without SL+IR over the that with SL+IR.