Gamma-ray Search of Dark Matter Nagisa Hiroshima Univ. of Toyama, - PowerPoint PPT Presentation

Gamma-ray Search of Dark Matter Nagisa Hiroshima Univ. of Toyama, RIKEN iTHEMS 1 Progress in Particle Physics 2020 2020. 8. 31

Contents: 2 1. Introduction 2. To probe heavier WIMP 3. Future prospects 4. Conclusion advantage of the gamma-ray observations facility, target, and the problems convolution of the instrumental response and models

Introduction 3 advantage of gamma-ray observations

DM Motivation & Candidate 4 baryon DM structure * * * * * structure • • motivation candidate DM=non-baryonic matter in the Universe of Ω DM h 2 ∼ 0.12 - structure formation - rotation curves * * - bullet cluster - … - Weakly Interacting Massive Particle (WIMP) - Strongly (or self) Interacting Massive Particle (SIMP) - axion/axion-like particle (ALP) - primordial black hole (PBH) - …

WIMP abundance We do not see the annihilation signature yet. cross-section 5 0.12 achieve the relic Saikawa & Shirai, 2020 - feel the gravity (massive) m DM ∼ 𝒫 (GeV) − 𝒫 (TeV) - the mass - freeze-out scenario to Ω DM h 2 ∼ - the annihilation ⟨ σ v ⟩ ∼ 𝒫 (10 − 26 cm 3 s − 1 )

Three pillars of WIMP search 6 SM SM DM DM ? collider direct detection indirect detection

Indirect detections in the Universe production 1TeV for 7 on/around the Earth • -ray search in the SM somewhere something DM + DM γ , e ± , p , ¯ p , ν , … γ - straight path from the source to the Earth z ≲ 0.1 E γ ≲ - absorption is negligible at - all the SM particle associates photons at the

Current limits for WIMP 8 Hoof et al., 2020 canonical Fermi-LAT, 11y, 27 dwarf spheroidal galaxies (dSphs) ∼ 3 × 10 − 26 cm 3 / s

To probe heavier WIMP 9 facility, target, and the problems

Current limits for WIMP 10 Hoof et al., 2020 canonical Fermi-LAT, 11y, 27 dwarf spheroidal galaxies (dSphs) probe here! ∼ 3 × 10 − 26 cm 3 / s

Probing the heavier 11

Cherenkov Telescope Array (CTA) 12 incoming -ray + atoms Cherenkov light optical telescope array on the ground high angular resolution! Imaging Atmospheric Cherenkov Telescope (IACT) γ γ → e + + e − → γ + … → e + + e − + … γ , e + , e − →

Comparison 13 0.2-0.03deg 3.5-0.15deg resolution angular , 50h) (1TeV , 10year) (100GeV flux sensitivity ~10% <8% resolution energy 30GeV-100TeV 20MeV-300GeV coverage energy pointing survey observation IACT satellite type CTA Fermi different properties & observing strategies 10 − 12 erg cm − 2 s − 1 10 − 13 erg cm − 2 s − 1

observable: -ray flux by observing dSphs with CTA! astrophysical part particle physics (integral of the squared DM density J-factor: • Observable TeV We should be able to prove WIMP of 14 What we consider is… m DM ≳ 𝒫 (1) γ ϕ dE ⋅ ∫ ΔΩ m DM ⟨ σ v ⟩ ϕ = 1 1 DM ∫ dE dN d Ω ∫ los ds ρ 2 DM m 2 2 4 π E th ρ 2 ϕ ∝ DM ∼ J

15 • G.C dSph & inactive dSphs: high Milky Way • satellite of the Milky Way dSphs are resolved as extended sources with CTA! (100) kpc •~40 are confirmed formation activities •do not show star • dist • , ρ DM M ∼ 10 8 − 9 M ⊙ M / L ∼ 𝒫 (10 3 ) M ⊙ / L ⊙ ∼ 300kpc 𝒫 (1kpc) M ∼ 10 12 M ⊙ ∼ 50kpc 𝒫 (100pc) d ∼ 𝒫 Δ θ ≲ 𝒫 (1deg)

density profile of dSphs 1. observe proper motion of stars distribution We should consider , rather than . 16 …but dSphs are dark, i.e., limited numbers of • ? 2. derive the gravitational potential dJ / d Ω J J = ∫ ΔΩ d Ω = ∫ ΔΩ d Ω dJ d Ω ∫ l . o . s ds ρ 2 DM ( r ) ρ DM ( r ) 3. reconstruct the density profile ρ DM ( r ) stars are available for reconstructing ρ DM ( r )

Varieties of profiles -(generalized) NFW -Power Law (PL) + exp.cutoff -Burkert 17 1 + ( α − ( β − γ )/ α ρ ( r ) = ρ s ( − γ r s ) r s ) r r NFW: ( α , β , γ ) = (1,3,1) 1 + ( 2 − 1 ρ ( r ) = ρ s ( 1 + r − 1 r s ) r s ) r exp [ − r ρ ( r ) = ρ s ( − γ r s ) r s ] r

Example: NFW 4 vs 18 4 [GeV /cm ] 1 + ( ρ ( r ) = ρ s ( − 2 − 1 r s ) r s ) r r ln r ln ρ DM ( r ) 0.02 ∘ 2 ∘ 2 5 log 10 J ∘ × ∘

Example: Burkert 4 vs 19 [GeV /cm ] 4 1 + ( 2 − 1 ρ ( r ) = ρ s ( 1 + r − 1 r s ) r s ) r ln r ln ρ DM ( r ) 0.02 ∘ 2 ∘ 2 5 log 10 J ∘ × ∘

Example: PL + exp.cutoff 4 vs 20 [GeV /cm ] 4 exp [ − r ρ ( r ) = ρ s ( − 0 r s ) r s ] r ln r ln ρ DM ( r ) 0.02 ∘ 2 ∘ 2 5 log 10 J ∘ × ∘

Intermediate summary 21 - -ray observation of dSphs is a powerful tool to probe the nature of WIMP . we should see dSphs as extended sources. in target dSphs. We quantify the systematic errors in our sensitivity to DM annihilation cross-section with CTA coming from the DM distribution in dSphs γ - In near future, we can go heavier with CTA, with which - Then we have to be careful about the DM distribution - However, it is difficult to model and still under debate.

Future prospect 22 convolution of the instrumental response and models

Ingredients -ray flux (observable) observable 1 2 3 simulation hadronization 16 patterns 23 model 3. How does the density profile of the target dSph affect our sensitivity to the DM annihilation cross-section with CTA? 1. density profile s of the target: Draco dSph, 2. DM annihilation spectrum: cm GeV ⟨ σ v ⟩ ϕ = 1 1 DM ∫ dE dN dE ∫ d Ω ∫ los ds ρ 2 DM m 2 2 4 π J ∼ 𝒫 (10 19 2 / 5 ) ¯ bb , W + W − , τ + τ − γ

1. - cm GeV - - radius of the outermost member star models of Draco dSph 80 kpc - # of stars 1000 - (RA, DEC) =(260.052,57.915) varies from 18.70 to 19.56 in our collection - - 10 generalized NFW, 3 Burkert, 3 PL+cutoff profiles Draco is one of the best-studied dSphs 24 ρ DM d ∼ ∼ ∼ 1.3 ∘ J ∼ 𝒫 (10 19 ) 2 / 5 log 10 J

2.DM annihilation spectra - hadronization pythia8 for (lepton) 25 (weak boson) - (quark) - ( http://home.thep.lu.se/Pythia/ ) ¯ bb W + W − τ + τ −

3. -ray flux 4 92188344 -ray like events w/o source example: for VHE -ray observations (http://cta.irap.omp.eu/ctools/) ctools: simulation and analysis software -E=0.03-180TeV photon -500 hour (RA, DEC)=(260.052, 57.915) -position center deg around Draco dSph - IRF prod3b North, z20, average, 50h -CTA-North, full array 26 4 γ γ 4 × 4 ∘ × ∘ γ

Combine: likelihood ratio test 27 Which is more likely, … “DM signal of the model exists” or “the data is consistent with the background” ? 1. simulate 500hours of observation @Draco dSph 2. select data & bin the data 0.03-180 TeV , 5 energy bin / decade 3. likelihood analysis assuming 16 profiles * 3 annihilation channels = 48 models

Our accessibility: case 28 Hiroshima et al., 2019 95% C.L ¯ bb J = 10 18.56 J = 10 18.69 J = 10 19.15 J = 10 19.15

Our accessibility: case 29 Hiroshima et al., 2019 95% C.L W + W −

Our accessibility: case 30 Hiroshima et al., 2019 95% C.L τ + τ −

Conclusion 31

Conclusion: hence their inner DM distribution becomes important. our sensitivity could differ by a factor of sure that we can access new parameter spaces, however, -Convolved with the CTA’s instrumental response, it is of dSphs is still under debate. 32 - - With CTA, we can resolve dSphs as extended sources, - We can access heavier WIMP in the near future. since they are rich in DM but poor in astrophysical . - dSphs are good targets to search the WIMP signature TeV is already successful. - WIMP search at E γ ≲ 𝒫 (1) γ ρ DM ∼ 10

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