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Fermi Large Area Telescope Results: the Sky at High Energies and the Quest for Dark Matter Signals

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Fermi Large Area Telescope Results: the Sky at High Energies and the Quest for Dark Matter Signals Fermi Large area telescope results: The sky at high energies and the Quest for Dark Matter signals Aldo Morselli INFN Roma Tor Vergata 22 May 2012 Cracow School LII Course, 2012 Astroparticle Physics in the LHC Era Aldo Morselli, INFN Roma Tor Vergata 1 11 June 2008 Aldo Morselli, INFN Roma Tor Vergata 2 • Why we should go to space to see gamma-rays? Aldo Morselli, INFN Roma Tor Vergata 3 Gamma ray attenuation (2) Transparency of the atmosphere for radiation of different wavelengths. The solid line show the height above sea-level at which the atmosphere becomes tranparent. Aldo Morselli, INFN Roma Tor Vergata 4 Interaction of electrons and photons with matter Photon total cross sections Fractional energy loss for e+ and e- in lead Pair x/X0 Prob Int. 0.5 0.40 1 0.54 2 0.79 7 0.995 Aldo Morselli, INFN Roma Tor Vergata 5 Relation between altitude, number of Radiation Length and g/cm2 traversed Aldo Morselli, INFN Roma Tor Vergata 6 The Fermi LAT gamma-ray sky 3-year all-sky map, E > 1 GeV Aldo Morselli, INFN Roma Tor Vergata 7 The Fermi LAT 2FGL Source Catalog http://fermi.gsfc.nasa.gov/ssc/data/access/lat/2yr_catalog/ August 4, 2008, to July 31, 2010 100 MeV to 100 GeV energy range 1873 sources 1095 AGN’s 589 unidentified Fermi Coll. ApJS (2012) 199, 31 arXiv:1108.1435 Aldo Morselli, INFN Roma Tor Vergata 8 • Towards the Second Fermi LAT Catalog 2FGL: 1095 589 9 Aldo Morselli, INFN Roma Tor Vergata 9 Neutralino WIMPs Assume χ present in the galactic halo • χ is its own antiparticle => can annihilate in galactic halo producing gamma-rays, antiprotons, positrons…. • Antimatter not produced in large quantities through standard processes (secondary production through p + p --> anti p + X) • So, any extra contribution from exotic sources (χ χ annihilation) is an interesting signature • ie: χ χ --> anti p + X • Produced from (e. g.) χ χ --> q / g / gauge boson / Higgs boson and subsequent decay and/ or hadronisation. Aldo Morselli, INFN Roma Tor Vergata 10 Aldo Morselli, INFN Roma Tor Vergata 11 They Play Together! Aldo Morselli, INFN Roma Tor Vergata 12 Fermi Gamma-Ray Large Area Space Telescope Tracker 1.68 m 84 cm Grid Silicon Tracker tower ACD Thermal 18 planes of X Y silicon detectors + converters Anticoincidence Blanket 12 planes with 3% R.L. of W , 4 planes with 18% R.L 2 planes without converters Shield total 1.5 R.L. DAQDAQ Electronics Electronics Calorimeter ( 8.6 Rad.Length) Aldo Morselli, INFN Roma Tor Vergata 13 How Fermi LAT detects gamma rays Incoming γ 4 x 4 array of identical towers with: • Precision Si-strip tracker (TKR) Conversion – With W converter foils (γ in e+/e-) in W foils • Hodoscopic CsI calorimeter (CAL) • DAQ and Power supply box γ Incoming direction reconstruction by tracking the charged particles e+ e- Energy measurement with e.m. calorimeter An anticoincidence detector around the telescope distinguishes gamma- rays from charged particles Aldo Morselli, INFN Roma Tor Vergata 14 Aldo Morselli, INFN Roma Tor Vergata 15 Interaction of electrons and photons with matter Photon total cross sections Fractional energy loss for e+ and e- in lead Pair x/X0 Prob Int. 0.5 0.40 1 0.54 2 0.79 7 0.995 Aldo Morselli, INFN Roma Tor Vergata 16 6 5 0.15Xo(deg) 0.07Xo(deg) Multiple 4 0.05Xo(deg) 3 Scattering 2 10 1 projected angular distribution ( degrees) 0 0.1 1 10 0.15Xo(deg) 1 0.07Xo(deg) E(GeV) 0.05Xo(deg) 0.1 projected angular distribution ( degrees) 0.01 0.1 1 E(GeV) 10 E(GeV) Aldo Morselli, INFN Roma Tor Vergata 17 Fermi Instrument Response Function http://www.slac.stanford.edu/exp/glast/groups/canda/lat_Performance.htm Aldo Morselli, INFN Roma Tor Vergata 18 Fermi Instrument Response Function http://www.slac.stanford.edu/exp/glast/groups/canda/lat_Performance.htm Aldo Morselli, INFN Roma Tor Vergata 19 Nγs= number of photons from source NγB= number of photons from background ΔΩ = solid angle around dth source depends on A Effective area ( Area* efficiency ) eff = Sensitivity x = converter plane in radiation lengh field of view Sensitivity number of σ depends on angular resolution 3/3/11 Aldo Morselli, Vincenzo Vitale, Beatriz Canadas Aldo Morselli, INFN Roma Tor Vergata 20 good detector small converter plane large effective area (large geometric area and large total conversion efficiency ) large field of view Aldo Morselli, INFN Roma Tor Vergata 21 1/E Sensitivity of γ-ray detectors from here geometric angolar resolution GLAST thin section GLAST (1 yr ) GLAST (5 yr ) ARGO MAGIC 2 (exp) MAGIC (now) HAWC CTA A.Morselli.11-10 HESS limited by statistics Aldo Morselli, INFN Roma Tor Vergata 22 How Fermi LAT detects electrons Trigger and downlink • LAT triggers on (almost) Incoming Electron every particle that crosses the LAT ACD identifies – ~ 2.2 kHz trigger rate charged particle • On board processing removes many charged particles events Main track – But keeps events with more pointing to the that 20 GeV of deposited hit ACD tile energy in the CAL – ~ 400 Hz downlink rate • Only ~1 Hz are good γ-rays Same tracking and Electron identification energy • The challenge is identifying reconstruction algorithms used the good electrons among for γ-rays the proton background – Rejection power of 103 – 104 required – Can not separate electrons from positrons Aldo Morselli, INFN Roma Tor Vergata 23 Event topology A candidate electron A candidate hadron (recon energy 844 GeV) (raw energy > 800 GeV) • TKR: clean main track with extra-clusters • TKR: small number of extra very close to the track clusters around main track • CAL: clean EM shower profile, not fully contained • CAL: large and asymmetric shower • ACD: few hits in conjunction with the track profile • ACD: large energy deposit per tile Aldo Morselli, INFN Roma Tor Vergata 24 Fermi Electron + Positron spectrum Extended Energy Range (7 GeV - 1 TeV) One year statistics (8M evts) Fermi LAT Coll. Physical Review D, Aldo 82 Morselli, 092004 INFN (2010) Roma Tor[arXiv:1008.3999] Vergata 25 Geomagnetic field + Earth shadow = directions from which only electrons or only positrons are allowed events arriving from West: e+ allowed, e- blocked events arriving from East: e- allowed, e+ blocked • For some direcons, e- or e+ forbidden • Pure e+ region looking West and pure e- region looking East • Regions vary with parcle energy and spacecra posion • To determine regions, use code by Don Smart and Peggy Shea (numerically traces trajectory in geomagnec field) • Using Internaonal Geomagnec Reference Field for the 2010 epoch Aldo Morselli, INFN Roma Tor Vergata 26 Positron Fraction The Fermi-LAT has measured the cosmic-ray positron and electron spectra separately, between 20 and 130 GeV, using the Earth's magnetic field as a charge discriminator •Two independent methods of background subtraction produce consistent results •The observed positron fraction is consistent with the one measured by PAMELA Fermi Coll., PRL, 108 (2012) 011103 arXiv:1109.0521 Aldo Morselli, INFN Roma Tor Vergata 27 Lepto- philic Models here we assume a democratic dark matter pair- annihilation branching ratio into each charged lepton species: 1/3 into e+e-, 1/3 into µ+ µ- and 1/3 into τ+ τ- Here too antiprotons are not produced in dark matter pair annihilation. [arXiv:0905.0636] Aldo Morselli, INFN Roma Tor Vergata 28 Lepto- philic Models here we assume a democratic dark matter pair- annihilation branching ratio into each charged Pamela + Fermi positrons lepton species: 1/3 into e+e-, 1/3 into µ+ µ- and 1/3 into τ+ τ- Here too antiprotons are not produced in dark matter pair annihilation. Astrp Phys.32 (2009) 140 [arXiv:0905.0636] Aldo Morselli, INFN Roma Tor Vergata 29 Search Strategies Satellites: Galactic center: Milky Way halo: Low background and Good statistics but source Large statistics but good source id, but low confusion/diffuse background diffuse background statistics And electrons! and Anisotropies Spectral lines: No astrophysical Galaxy Extra-galactic: uncertainties, good clusters: Large statistics, but source id, but low astrophysics,galactic Low background but diffuse background statistics low statistics Pre-launch sensitivities published in Baltz et al., 2008, JCAP 0807:013 [astro-ph/0806.2911] Aldo Morselli, INFN Roma Tor Vergata 30 Milky Way Dark All profiles are normalized to the local Matter Profiles density 0.3 GeV cm－3 at the Sun’s location r ≈ 8.5 kpc A.Lapi et al. arXiv:0912.1766 Aldo Morselli, INFN Roma Tor Vergata 31 Differential yield for each annihilation channel WIMP mass=200GeV A.Cesarini, F.Fucito, A.Lionetto, A.Morselli, P.Ullio, Aldo Astroparticle Morselli, INFN Physics, Roma Tor Vergata 21, 267, 2004 [astro-ph/0305075] 32 Differential yield for b bar neutralino mass A.Cesarini, F.Fucito, A.Lionetto, A.Morselli, Aldo P.Ullio, Morselli, Astroparticle INFN Roma Tor Vergata Physics, 21, 267-285, 2004 [astro-ph/0305075] 33 (r) ρ r -1 log log r -3 log (r) High DM density at the Galactic center Aldo Morselli, INFN Roma Tor Vergata 34 Different spatial behaviour for decaying or annihilating dark matter The angular profile of the gamma-ray signal is shown, as function of the angle θ to the centre of the galaxy for a Navarro-Frenk-White (NFW) halo distribution for decaying DM, solid (red) line, compared to the case of self-annihilating DM, dashed (blue) line Aldo Morselli, INFN Roma Tor Vergata 35 Constraints from the Milky Way halo testing the LAT diffuse data for a contribution from a Milky Way DM annihilation/decay signal 2 years of data 1-100 GeV energy range ROI: 5° <|b|<15° and |l|<80°, chosen to: • minimize DM profile uncertainty (highest in the Galactic Center region) • limit
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