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Line emission search from DM annihilation in the Galactic Center with LST-1

Abhishek Abhishek, Shotaro Abe, Tomohiro Inada, Sofia Ventura, Michele Doro, Masahiro Teshima, Gaia Verna

TL;DR

This paper assesses line-like gamma-ray signatures from WIMP DM annihilation at the Galactic Center using the LST-1 telescope at large zenith angles. It outlines a data-analysis framework combining OFF-source low-level processing with a high-level Gammapy likelihood approach to search for monoenergetic lines, carefully modeling the local background within energy windows and testing signals based on the $\gamma\gamma$ spectrum. The study demonstrates how background curvature can bias limits and quantifies a systematic floor on the DM cross-section sensitivity, proposing an energy-dependent window to optimize performance. The results emphasize the importance of background control, energy-window strategies, and ROI choices for TeV-scale DM searches and highlight plans for CTAO-North with additional LSTs to further improve sensitivity.

Abstract

Dark Matter remains a great mystery in modern physics. Among various candidates, the weakly interacting massive particles (WIMPs) scenario stands out and is under extensive study. The detection of the hypothetical gamma-ray emission from WIMP annihilation could act as a direct probe of electroweak-scale interactions, complementing DM collider searches and other direct DM detection techniques. At very high energies (VHE), WIMP self-annihilation is expected to produce gamma rays together with other Standard Model particles. The galactic center (GC), due to its relative proximity to the Earth and its high expected DM density, is a prime target for monoenergetic line searches. IACTs have placed strong constraints on the DM properties at the GC, with the MAGIC providing the most stringent limits from 20 TeV to 100 TeV, exploiting large zenith angle (LZA) observations. However, the limited field of view (FoV) of the MAGIC telescopes (< 3.5° ) prevented a detailed study of the extended region around the GC in which an enhanced DM density is expected. The LST-1 of the CTAO, located at the Roque de Los Muchachos Observatory (La Palma, Spain), close to the MAGIC site, has been observing the GC since 2021. With its wide FoV of 4.5°, LST-1 could contribute significantly to the WIMPs search at the GC. The observations are performed at LZA (ZA > 58°), which, while required due to the source's low altitude, also optimizes the detection of gamma rays up to 100 TeV and beyond. We present a study of the systematic uncertainties in WIMP line emission searches with LST-1. Our work examines the instrument response functions for LZA observations, background rejection in monoscopic mode, and includes updated results from simulations, highlighting new methods for spectral line searches.

Line emission search from DM annihilation in the Galactic Center with LST-1

TL;DR

This paper assesses line-like gamma-ray signatures from WIMP DM annihilation at the Galactic Center using the LST-1 telescope at large zenith angles. It outlines a data-analysis framework combining OFF-source low-level processing with a high-level Gammapy likelihood approach to search for monoenergetic lines, carefully modeling the local background within energy windows and testing signals based on the spectrum. The study demonstrates how background curvature can bias limits and quantifies a systematic floor on the DM cross-section sensitivity, proposing an energy-dependent window to optimize performance. The results emphasize the importance of background control, energy-window strategies, and ROI choices for TeV-scale DM searches and highlight plans for CTAO-North with additional LSTs to further improve sensitivity.

Abstract

Dark Matter remains a great mystery in modern physics. Among various candidates, the weakly interacting massive particles (WIMPs) scenario stands out and is under extensive study. The detection of the hypothetical gamma-ray emission from WIMP annihilation could act as a direct probe of electroweak-scale interactions, complementing DM collider searches and other direct DM detection techniques. At very high energies (VHE), WIMP self-annihilation is expected to produce gamma rays together with other Standard Model particles. The galactic center (GC), due to its relative proximity to the Earth and its high expected DM density, is a prime target for monoenergetic line searches. IACTs have placed strong constraints on the DM properties at the GC, with the MAGIC providing the most stringent limits from 20 TeV to 100 TeV, exploiting large zenith angle (LZA) observations. However, the limited field of view (FoV) of the MAGIC telescopes (< 3.5° ) prevented a detailed study of the extended region around the GC in which an enhanced DM density is expected. The LST-1 of the CTAO, located at the Roque de Los Muchachos Observatory (La Palma, Spain), close to the MAGIC site, has been observing the GC since 2021. With its wide FoV of 4.5°, LST-1 could contribute significantly to the WIMPs search at the GC. The observations are performed at LZA (ZA > 58°), which, while required due to the source's low altitude, also optimizes the detection of gamma rays up to 100 TeV and beyond. We present a study of the systematic uncertainties in WIMP line emission searches with LST-1. Our work examines the instrument response functions for LZA observations, background rejection in monoscopic mode, and includes updated results from simulations, highlighting new methods for spectral line searches.

Paper Structure

This paper contains 7 sections, 1 equation, 3 figures.

Table of Contents

  1. DM Line Signatures in Gamma-Ray Observations
  2. Indirect DM Searches Toward the Galactic Center with LSTs at Large Zenith Angles
  3. Data Analysis
  4. Low-level analysis
  5. High-level analysis
  6. Results
  7. Summary

Figures (3)

  • Figure 1: Energy distribution of background counts in the studied OFF regions
  • Figure 2: The gammaness efficiency (solid lines) and background efficiency (dashed lines) are plotted for gammaness cuts, and the corresponding Q-factor values (solid line with circle markers) are shown in the y-axis on right.
  • Figure 3: left: $\beta$ is varying as the window width changes showing the non-linear small scale features on the background spectrum. right: The relative sensitivity difference of statistical and systematic values displaying changing $\beta$ hindering the computation of DM parameter