Hunting dark matterin TeV region
by VHE gamma-ray
ICRR, University of Tokyo
Tomohiro Inada
The workshop"The extreme Universe viewed in very-high-energy gamma rays 2018”
La Palma, 12/10/2018

Hunting TeV dark matter in theGalactic Center with VHE gamma-raysin the northern hemisphere
ICRR, University of Tokyo
Tomohiro Inada
The workshop"The extreme Universe viewed in very-high-energy gamma rays 2018”
La Palma, 12/10/2018

Motivation

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Dark Matter Search★ Dark matter dominates ~23% of mass-energy of the universe.
★ Good candidate : Weakly Interactive Massive Particle, WIMP
★ “WIMP Miracle” : expects DM mass, O(GeV - TeV) range

Direct Search©XENON collaboration

DMSMDMSM

Production at Collider

Many experiments aretrying, but no evidence
for detection yet…
©ATLAS collaboration

Indirect Search©Fermi collaboration

Where is a “next frontier”?
pMSSM model parameter space

M. Cahill-Rowley et al, (2013)

Scattering cross-section
Between DM and nucleus (pb)(phenomenological minimum supersymmetric model)

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Dark matter mass(TeV)

1035

Where is a “next frontier”?
pMSSM model parameter space

M. Cahill-Rowley et al, (2013)

Scattering cross-section
Between DM and nucleus (pb)(phenomenological minimum supersymmetric model)

Direct search
can exclude

Collider search
can exclude
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Dark matter mass(TeV)103

A. DM in the TeV range by indirect search6DM searchby Cherenkov telescope

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Imaging Cherenkov Technique★Image intensity➔ Energy of primary★Image orientation➔ Direction of primary★Image shape➔ Kind of primary

Reconstructed direction ofprimary particle

Extensive
Air Shower
Camera with
PMT pixel
Air Shower Image with
Cherenkov telescopes8

Current Cherenkov Telescopes
・Effective area : 104 ~105 m2

・Energy range : O(100) GeV - O(100)TeV
・Energy resolution : between ~10% and ~20%
・Angular resolution : ~0.06 deg @ 1TeV
・FoV : 3 ~ 5 deg

・Stereoscopic system : 2 - 5 telescopes

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Why VHE gamma-ray ?
★DM annihilating into gamma-rays★ Point back to the source★

Can determine DM abundance and distribution in the universe★ Characteristics spectral features★

Can identify the characteristics of particle, mass, cross-section/lifetime★Focus on line search !
★Line emission easily distinguishable fromastrophysical and cosmic-rays backgrounds

10Benchmark for DM line search◆Test of DM production via thermal freeze-out
・DM is in thermal equilibrium
・DM is diluted by the cosmic expansion
・DM cannot find each other and stop annihilating
・DM number in comoving volume is frozen
・The expected relic abundance is:・Correct dark matter abundance, ΩDMh2〜0.1(Time->)◆DMDM -> γγ is suppressed by factor α2.

h v i  10

32cm

3s1

increaseh vi = h v⌧ ⌧ i + h vbb i + h v i ・・・Several models suggest σv increases byquantum effects (Sommerfeld enhancement)

h v i  10 28 cm 3 s 1
In detail, J. Hisano, et al, L. Bergstrom et al, etc… 11

Gamma ray Flux from DM
Gamma ray flux

Particle physics termin case of annihilation

Astrophysical termMχ : Mass of DM particle<σann v> : cross-section times velocity
dN/dE : differential gamma-ray yield per annihilation

In case of line search, spectral
shape is delta function at Mχ
dN= 2 (E m )dEρ : dark matter densityΔΩ : solid angle
l : line of sight

Depends on the given source, on DM
distribution and on the instrument
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Observational targets★Condition to choose targets for DM search◆ Maximize the quantity of DM signal (close distance and large DM density)★Dwarf-Sph galaxies◆Galaxy satellites of the Milky Way■ Close (approximately 100 kpc from GC)◆High J-Factor : 1018 - 1019 GeV2/cm5◆Much less astrophysical background◆"Point-like” source★Galactic Center◆Proximity (~8 kpc)
◆Highest J-Factor : ~ 1020-1021 GeV2/cm5◆High astrophysical background andsource confusion.
◆Extended source

Simulated all-sky map of gamma-rays
from DM annihilation
PRD 83, 023518 (2011)13

Observed targets★Most popular targets

arXiv:1810.00995v1◆dwarf-Sph galaxies◆Galactic Centre region
Deep observation by IACT (recently published)

Ref : PRD 95, 082001 (2017), arXiv:1810.00995v1,
JCAP 02 (2014) 008, JCAP03(2018)009, PRL120, 201101 (2018)
PRL 120, 201101 (2018)

Many telescopes are observing dwarf-sph galaxies.
But from a point of view about DM search in G.C.,
results are published only by H.E.S.S.

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Galactic Centre★Current Status◆ Galactic Centre in GeV - TeV range is occupied by H.E.S.S…
◆ because of good observability◆ Zenith angle ~ 20 [deg] (average)

E. Moulin@ICRC2017◆ Observation time : 254 h (10 years)

GeV range is excellent!
But what about the TeV range…?
The limit is getting worse rapidly.

PRL 120, 201101 (2018)15

Galactic Centre★Current Status◆ Galactic Centre in GeV - TeV range is occupied by H.E.S.S…
◆ because of good observability◆ Zenith angle ~ 20 [deg] (average)

E. Moulin@ICRC2017◆ Observation time : 254 h (10 years)

GeV range is excellent!
But what about the TeV range…?
The limit is getting worse rapidly.

`16What is the situation for MAGIC?
・G.C observation in La Palma.

・Zenith Angle : ~60 [deg] (High Zenith, HZ)

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What is the situation for MAGIC?
・G.C observation in La Palma.

・Zenith Angle : ~60 [deg] (High Zenith, HZ)
Zd range 5 - 35
(Low Zd Crab sample)
HZ range 58 - 70(GC sample)

・Merit and demerit HZ observation
・Effective area : increasing

・by factor ~10 in TeV range・Threshold : increasing© C. Fruck@TeVPa2017

・~ 500GeV (MAGIC case)

OK, I have to dismiss GeV range…, but what is the situation in TeV range???

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Observability of G.C. from La Palma
Let’s estimate observation time to be competitive with H.E.S.S !!
Gamma-rays rate from DM
Z
1 < v>
dN00NDM =R(E,E)TA(E)dE⇥ J( )
obs ef f
204⇡ 2mDM
dE
Realistic values・R(E, E’) : Energy Resolution
・HESS : ~ 10 %・MAGIC : ~ 15 % in HZ observation・Recently ΔE/E of MAGIC is improved
very well by K. Ishio(MPP) ref. DPG 2018
・Tobs : observation time・HESS : 254 h・MAGIC : ??? h・Aeff : effective area
・MAGIC / HESS ~ 10Significance calculation
MAGIC case・R(E, E’) : factor 1.5 worse
・Aeff : factor 10 is better.

rNs ⇥1010⇥S = p1.5
Nb ⇥1.5 ⇥10THESS
2.58 ⇥ S =TM AGICTM AGIC ⇠ 100 hours

Looks not so bad ???

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Future Prospect
・Problems to be solved

・Systematics from atmosphere by High Zenith observation.

・Ld : 16 - 20%, Hz : 20 - 30% for absolute energy scale in MAGIC
・cf : J. Aleksic et al. (2012), C.Fruck Ph.D thesis(2015)

・LIDAR of MAGIC can correct the energy bias in event by event
・ref. C.Fruck Ph.D theis(2015)

・It can reduce the effect by atmosphere, estimation in detail is needed.

・Astrophysical background in G.C. region.

・Assume the simple background model or just comparison between ON andOFF while observing far points from galactic plane like H.E.S.S.

・But once we establish the method in MAGIC, we can do with CTA-LSTs !
・We will have “the fast pass” to reach TeV DM.

・Science in G.C. region is fruitful, in any case, it is worth observing!!

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Summary
・Many experiments are trying to search DM, but not detected yet.
・TeV region is next frontier for DM search.
・Cherenkov telescope are very strong tools to search DM in TeV range.
・It has a chance to detect DM or finally “kill” the WIMP paradigm.
・Most popular targets
・dwarf spheroidal galaxies :・low background & high DM density. many telescopes are observing.
・Galactic Center :・High background & Very high DM density.
・So far, results about DM search are published only by H.E.S.S.
・Strong tool for northern site : High zenith observation.
・MAGIC is possibly competitive with H.E.S.S. in TeV range
・We can get “fast pass” to reach TeV DM.
・Stay tuned!!

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