Search for gamma-ray line emission from Dark MaGer annihila+on in the Galac+c Centre with the MAGIC telescopes

17th Interna+onal Conference On Topics in Astropar+cle and Underground Physics (TAUP 2021) 1

Search for gamma-ray line emission from

Dark MaGer annihila+on in the Galac+c Centre with the MAGIC telescopes

Tomohiro Inada (ICRR, UTokyo)

Daniel Kerszberg, Moritz HüGen, Masahiro Teshima

Javier Rico, Daniele Ninci, for the MAGIC Collabora+on

The MAGIC telescopes

MAGIC (Major Atmospheric Gamma Imaging Cherenkov telescopes)  ・Observatorio del Roque de los Muchachos (ORM)

  ・~ 2200 m a.s.l., La Palma, Canary Islands, Spain  ・2-telescope stereoscopic system

  ・17m diameter

 ・Energy : 50 GeV - 50 TeV (Low Zd ~20°)  ・FoV : 3.5°

 ・Angular resoluVon : 0.06° @ 1 TeV  ・Energy resoluVon : 15 % - 25 %

MAGIC-I MAGIC-II

Observatorio del Roque de los Muchachos, La Palma (Spain)

Gamma Proton

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Gamma-ray Signal from Dark Matter (DM)

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ρ : dark maGer (DM) density

・depends on source type,  DM profile of a source, etc.

J-factor :

・integrated DM density along the line of sight σv : annihila+on cross-sec+on

mχ : mass of DM parVcle

BRi : branching raVo of each channel

dNⁱ/dE : differenVal gamma-ray yield of each channel

dN_γ

dE = 2δ(E − m_χ)

・DM is expected to annihilate into gamma rays

・Indirect signal point back to the source

 ・can determine DM abundance and distribuVon in the universe

・characterisVc spectral features

 ・can idenVfy the characterisVcs of parVcle, mass, cross-secVon/lifeVme

Why gamma rays?

Line signal :

Expected gamma-ray flux from DM annihila+on

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Motivation for line search

J. Hisano, S. Matsumoto, M. M. Nojiri and O. Saito 2005 M. Cirelli, N. Fornengo and A. Strumia (2006) H. E.S.S. collaboraVon JCAP11(2018)

Triplet (wino-like in SUSY)

Cirelli et al. (2011)

m_χ = 10 TeV

・Clear peak at DM mass

 ・No astrophysical contaminaVon is expected

・ Test interes+ng par+cle models

 ・ channel is loop-suppressed by

 ・But some promising heavy DM models are expected   ・to increase σv by the Sommerfeld enhancement.

χχ → γγ α

© L.Bergström

DM searches with the Galactic Centre

Simulated all-sky map of gamma-rays from DM annihilaVon (GalacVc coordinates) PRD 83, 023518 (2011)

N-Body simulaVon Via Lactea II

Galac+c Centre (GC) and Halo

・the largest J-factor

・extended

・source confusion, diffuse bkg and  Cusp/core differences in DM profiles

Need to consider both scenarios 7

(α,β,γ) = (1,3,0)

The GC observation by MAGIC

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Cherenkov light

Cherenkov light pool

ZA

Vertical observations Large Zenith angle observations

Zenith

The GC observaVon by MAGIC

・zenith angle : 58 - 70 [deg]

 ・large zenith angle      observaVon, LZA

Pros

・increase the γ-ray detectable area  ・get larger staVsVcs at TeV energies Cons

・increase the energy threshold

Large Zenith angle observaVons boost the sensiVvity to line signals from TeV DM!!

l l ′ l ′ ≃ l / cos ( Zd )

A

∝ 1/ cos

θ

Data : March 2013 - August 2019

 ・zd range : 58° < Zd < 70°

 ・total observa+on +me : 204 hours   ・Aqer quality cuts

Dataset

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SgrA* (the GC)

J-factor

 ・computed with each ROI

  ・for both a cuspy and core profile

Analysis region (ROI)

 ・ regions within 1.5° distance from the camera centre   ・different ROI sizes used

   ・due to the variaVon in poinVng direcVons

Likelihood analysis for line search

Sliding window

Log10 (Energy (GeV))

dN/dE e.g.

Unbinned likelihood analysis with a sliding window

to treat systemaVc uncertainty of a bkg model

Index : data samples

: observed events in a ROI : es+mated signal events

: esVmated background events

: normalizaVon factor for bkg model : line signal pdf

 ・ -funcVon convolved with the response funcVon : background pdf

 ・interpolated from energy spectra

  ・assumpVon : background behaves as power-law    spectrum in a sliding window

N_on i gb τf_g f_b δ

Parameters of interest Nuisance parameters

Interpola+on for bkg pdf Assumed line signal

at 2.5 TeV

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Uncertainty in background model ?

τ = Gaus(τ_obs, σ_τ)

If systematic offsets or statistical fluctuation

look like line-signal

bkg interpolation can be affected

= 1

τ

Ideal Case RealisVc case

We could interpolate and know background perfectly

Data (No line present)

Nominal bkg Nominal bkg

Modelled bkg Fitted line

signal

Data (No line present)

ConvenVonal On/Off analysis

・how to obtain the background model?

Normalize off events by Ton/Toff

Sliding window

Data (OFF) Data (ON)

Data (Norm. Off)

・systemaVc uncertainty in the background pdf is included in Likelihood

given by Gaussian

Need to esVmate

May find spurious line excess

= Ton/Toff

τ σ_τ² = σ_τ²_,stat + (τσ_syst)²

Study for systematic uncertainty

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Sample counts

Sample counts Sample counts

Es+mated systema+c uncertainty in a bkg pdf determina+on

・applied the line search analysis to data without DM target sources with 120 samples  ・divided into 3 energy categories, E < 3 TeV, 3 TeV < E < 10 TeV, E > 10 TeV

・computed residual R_i and its staVsVcal error size R_i^stat with the error propagaVon

σ_R² = σ_stat² + σ_syst² σ_syst² < 1 %

R distribuVon R distribuVon R distribuVon

Preliminary Preliminary Preliminary

E < 3 TeV 3 TeV < E < 10 TeV E > 10 TeV

Entries 120 Mean -5.962e-05 Std. Dev. 0.001301

σ_R > σ_R σ_R

σ_statσ_R

σ_R >σ_stat σ_R >σ_stat

: included likelihood eq.

Std. Dev. of distribution

R_i^stat Std. Dev. of

distribution

R_i^stat Std. Dev. of

distribution R_i^stat

Entries 120 Mean 0.0001613 Std. Dev. 0.0005661

Entries 120 Mean -0.0002965 Std. Dev. 0.001239

R_i^stat = (

∂R_i

∂N_i^ex ⋅ σ_Ni^ex )

2

+(

∂R_i

∂N_i^tot ⋅σ_Ni^tot )

R_i = N_i^ex 2

N_i^tot

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Results

No significant line-like excess found

・ set upper limits at 95% C.L. on 15 masses  ・ 912 GeV - 43 TeV

・ calculated the sensiVvity with 300 simulaVons

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Results

No significant excess

・

set upper limits with 95% C.L. on 15 masses

・

912 GeV - 43 TeV

・

considered with Einasto (cuspy) and cored profile.

 ・

cuspy : E > 10 TeV : compeVVve

cored : compeVVve to dSph results

Summary

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・Search for line-like signals in VHE gamma rays can test promising    TeV DM parVcle models

・We reported observaVons with the MAGIC telescopes located on  La Palma, Spain

 ・performed large zenith angle observaVons to focus on TeV DM  ・first search for DM lines at the GC with MAGIC

・No significant excess was discovered

・Upper limits were set on the annihilaVon cross secVon  ・compeVVve for both cuspy and cored DM profiles

・For the future (CTA era)

 ・large zenith angle observaVons of the GC are well suited to search for     heavy DM candidates

 ・high potenVal of the northern site to contribute to next-generaVon DM   searches

χχ → γγ

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