Dark Matter searches with H.E.S.S. towards dwarf spheroidals galaxies Aion Viana On behalf of the HESS collaboration IRFU, CEA-Saclay H.E.S.S. telescope array H.E.S.S. telescope array Indirect Dark Matter search principle Dwarf spheroidal galaxies H.E.S.S. campaign Dark Matter flux enhancement effects Summary 1 A. Viana IDM2010 Montpellier: July 2010
The H.E.S.S. telescope array Array of four Imaging Atmospheric Cherenkov Telescopes Array of four Imaging Atmospheric Cherenkov Telescopes located in Namibia (1800m a.s.l.) located in Namibia (1800m a.s.l.) • 12 m diameter telescopes : 107 m 2 each • 12 m diameter telescopes : 107 m 2 each • Stereoscopic reconstruction • Stereoscopic reconstruction • Angular resolution < 0.1 ° / • Observations on moonless nights, • • ~1000h/year ~1000h/year • • Energy threshold (zenith) ~ 100 GeV • • Field of view of 5 ° • • Energy resolution ~ 15% 5th telescope(28m) in contruction: HESS 2 2 A. Viana IDM2010 Montpellier: July 2010
Indirect dark matter searches through gamma-rays 2 DM self-annihilation rate : DM self-annihilation rate : m v 2 Gamma-ray flux Gamma ray flux from from annihilation of a WIMP: annihilation of a WIMP: where where Gamma spectrum: typically a continuum with an cut-off at the DM particle mass and and Dark matter halo modeling strong dependence; density 3 10 profile model is needed 5 sr HESS point-like obs.: A. Viana IDM2010 Montpellier: July 2010
Indirect dark matter searches through gamma-rays 2 DM self-annihilation rate : DM self-annihilation rate : m v 2 Gamma-ray flux Gamma ray flux from from annihilation of a WIMP: annihilation of a WIMP: where where Gamma spectrum: typically a continuum with an cut-off at the DM particle mass and and Dark matter halo modeling strong dependence; density 4 10 profile model is needed 5 sr HESS point-like obs.: A. Viana IDM2010 Montpellier: July 2010
Indirect dark matter searches through gamma-rays 2 DM self-annihilation rate : DM self-annihilation rate : m v 2 Gamma-ray flux Gamma ray flux from from annihilation of a WIMP: annihilation of a WIMP: where where Gamma spectrum: typically a continuum with an cut-off at the DM particle mass and and Dark matter halo modeling strong dependence; density 5 10 profile model is needed 5 sr HESS point-like obs.: A. Viana IDM2010 Montpellier: July 2010
Dark Matter halo modeling ( r ) ? • N-body numerical simulations => Cusp profile • N-body numerical simulations => Cusp profile • • Solution of the Jeans equation(hydrodynamics) => Cored profile • Two differents types of DM halo profiles are taken as examples: A ( r ) NFW - NFW profile: N-body simulations 2 r ( r r ) s 2 2 2 v 3 r r - cored profile: analytic resolution of the ( r ) a c Jeans equation core 2 2 2 4 G ( r r ) c The parameters are found after observation of the stars dynamics(luminous The parameters are found after observation of the stars dynamics(luminous density, velocity dispersion, velocity anisotropy …) inside the galaxy density 6 A. Viana IDM2010 Montpellier: July 2010
Observation campaigns of dSph galaxies, satellites of the Milky Way • Four dSph galaxies (and candidates) studies published (or in process ) by HESS d(kpc) Virial mass T obs (h) Observation Tidal (solar mass) Zenith angle disruption Sagittarius 24 3.0 x 10 8 11 (> 40 h now ) 19 ° Yes Canis Major 8 3.0 x 10 8 ?? 10 10 ° Yes Sculptor 79 1.0 x 10 9 11.8 14 ° No Carina 101 2.0 x 10 8 14.8 34 ° +/- Sgr dw 7 A. Viana IDM2010 Montpellier: July 2010
Sensitivity curves to DM annihilation Observations: signal + background Carina: No significant gamma excess at target position Estimated background Observed gamma-ray candidates « Measured » : 95 % C . L . N Upper limit on the number Upper limit on the number of « true » gamma-rays 8 ON region A. Viana IDM2010 Montpellier: July 2010
Sensitivity curves to DM annihilation Expected: d 95 % N ( σv,m ) ( v , m , J ) ( active area ) time DM DM dE • Comparing the mesured N 95 to the expected N 95 => Upper limit on σ v 95 % C . L . v ( m , J ) DM DM the velocity-weighted cross-section is then calculated as function of the DM particle mass two candidates of Dark Matter particle are usually studied: - neutralino (SUSY) - Kaluza-Klein (UED) particles 9 A. Viana IDM2010 Montpellier: July 2010
Sensitivity curves for Sagittarius dSph and Canis Major overdensity Constraints on dark matter sensitivity curve at 95% C.L.: (HESS Collaboration ( F. Aharonian et al.) Astropart.Phys 2007) (HESS Collaboration (: F. Aharonian et al.). ApJ 2008) (See also C. Farnier for HESS colab., IDM2008) Excluded Excluded Cross section Cross section DM mass DM mass Sagitarius dSph Canis Major GC GC J 0 . 07 2 . 6 J J 0 . 2 J NFW NFW Large uncertainty • Disrupted dwarf galaxy or simply • Disrupted dwarf galaxy or simply • Some pMSSM models with • Some pMSSM models with a part of the warped Galactic disk? a part of higgsino-like neutralino excluded higgsino • • On the assumption of a dSph it • BUT halo modeling of Sgr dSph • has a has a very delicated halo modeling 10 too hard due to tidal stripping too hard due to tidal stripping A. Viana IDM2010 Montpellier: July 2010
Sensitivity curves for Sculptor and Carina dSph Constraints on dark matter sensitivity curve at 95% C.L.: Excluded Excluded Cross section Cross section DM mass DM mass GC GC 2 J 0 . 2 2 . 2 10 J 3 J 0 . 7 1 . 5 10 J NFW NFW • Similar analyses were made for both galaxies • Similar analyses were made for both galaxies • • Various DM halo profile were studied in the case of Sculptor => helps to estimate the errors due to the halo modeling helps to estimate the errors due to the halo • Complementary constrains from Fermi on Sculptor • 11 • No Fermi result for Carina • A. Viana IDM2010 Montpellier: July 2010
Gamma-ray signal enhancement effects The gamma-ray flux can be enhanced by changes in the particle physics nature or the The gamma-ray flux can be enhanced by changes in the particle physics nature or the particle density distribution(astrophysics) • From particle physics: • From particle physics: Boost in the annihilation cross-section; New contribution in the annihilation spectrum; • From astrophysics: • From astrophysics: Contribution of the substructures(sub-halos) to the overall density <= < ρ 2 >/< ρ > 2 12 A. Viana IDM2010 Montpellier: July 2010
Gamma-ray signal enhancement effects • Particle physics enhancements: i) Sommerfeld effect • Particle physics enhancements: i) Sommerfeld effect Low velocity QFT(Schrodinger equation) effect due v S v the interaction of the DM particles with a Yukawa o potential(weak force) in its annihilation procces Lattanzi, Silk PRD2008 Very effective on the low-velocity regime!! DM particles velocity dispersion: DM particles velocity dispersion: ∼ 10.0 km/s for Sculptor ∼ 7.5 km/s for Carina 13 A. Viana IDM2010 Montpellier: July 2010
Gamma-ray signal enhancement effects • Particle physics enhancements: ii) Light charged particles • Particle physics enhancements: ii) Light charged particles « Whenever WIMPs annihilate into pairs of charged particles, this process will with a finite probability automatically be accompanied by internal bremsstrahlung, i.e. the emission of an additional photon in the final state » Bringmann, Bergstrom and Edsjo, JHEP 2008 Virtual internal Virtual internal Final state radiation Final state radiation bremsstrahlung bremsstrahlung Total internal bremsstrahlung Total internal bremsstrahlung • Contribution will depend on the • Contribution will depend on the HESS HESS acceptance in the energy range range • In the wino case only significant • for E γ > m Χ /2 for E 14 A. Viana IDM2010 Montpellier: July 2010
Gamma-ray signal enhancement effects • Astrophysics enhancements i.e. galactic substructures(« Clumps») : Motivations: simulations are scale invariant, Motivations: simulations are scale invariant, enhancement may be important inside dSph HESS ON region for point- Pinzke, Pfrommer and Bergstrom, PRL 2009: like searches Aquarius simulation: Flux completely dominated by the smooth halo contribution a.u. Virial radius BUT No significant effect towards dSphs center in a point-like analysis BUT No significant effect towards dSphs center in a point-like analysis 15 A. Viana IDM2010 Montpellier: July 2010
Gamma-ray signal enhancement effects Sculptor: Cross section Analytical wino cross section DM mass Typical thermally produced WIMP cross section Resonant exclusion limits with Sommerfeld effect Resonant exclusion limits with Sommerfeld effect Internal Bremstrahlung only significatif for low DM particle mass 16 A. Viana IDM2010 Montpellier: July 2010
Recommend
More recommend
