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Detecting Features in the Cosmic Ray Positron Spectrum with PAMELA and AMS-02

Detecting Features in the Cosmic Ray Positron Spectrum with PAMELA and AMS-02. D.T. Cumberbatch Oxford University. Rotation Curves of spiral galaxies:. M/L ratio. Galaxy clusters:. Proper motion. X-ray emissions from hot gas. Gravitational lensing. 2dFGRS. Abell 1689, HST.

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Detecting Features in the Cosmic Ray Positron Spectrum with PAMELA and AMS-02

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  1. Detecting Features in the Cosmic Ray Positron Spectrum with PAMELA and AMS-02 D.T. Cumberbatch Oxford University

  2. Rotation Curves of spiral galaxies: • M/L ratio Galaxy clusters: • Proper motion • X-ray emissions from hot gas • Gravitational lensing 2dFGRS Abell 1689, HST Large-scale structure Anisotropies in the CMB WMAP Motivation for Dark Matter

  3. Dark Matter Candidates • Weakly Interacting Massive Particles (WIMPS) • (Lightest) Neutralino, stable in R-Parity conserving SUSY models • Superposition of Higgsinos, Winos and Binos: • Sterile Neutrinos • Predominantly generated through (non) resonant oscillations e.g. Dodelson-Widrow (DW) mechanism, during QCD epoch. • Parameter space still available for subdominant DW Sterile Neutrino Dark Matter (Palazzo, Cumberbatch, Slosar & Silk arXiv:0707.1495). • Primordial Long-lived Decaying Particles • Generated in early Universe with lifetimes >1sec (e.g. Gravitinos). • Hadronic decay products can solve Li abundance problems (Cumberbatch et al. arXiv:0708.0095). … AND MANY MORE!!! (e.g. Light DM, Kaluza-Klein bosons, …)

  4. Direct Detection • Measure phonon, charge or light signals produced from elastic scattering of WIMPS with a nuclear target • DAMA, CDMS, EDELWEISS, ZEPLIN, CRESST • Indirect Detection • Measure excess in antiparticle flux from DM annihilations • PAMELA, AMS-01/02, HEAT, BESS (antiprotons, positrons, antideuterons) • GLAST, HESS, EGRET (photons) DM Detection Methods Two Complementary Methods:

  5. Background (Moskalenko & Strong) EXCESS! Positron Excess Total Positron Flux Positron Fraction= Total Positron Flux + Total Electron Flux Astrophysical Sources? • Supernovae and Wolf-Rayet stars (Ramaty et al.) • Neutron stars, Pulsars & BH’s (Milne et al., Sturrock) • Solar Modulation effects (M&S) • Cosmic Ray interactions with ISM (Kozlovsky et al.) Astrophysical sources are insufficient!!!

  6. Positron Production from 10 annihilation • Positrons from decays involving Hi0, W, Z0 and f • via Gauge Bosons (favoured by Higgsinos and Winos) Characteristic “cliff ” • via heavy quarks (favoured by Binos) • b favoured because of tan() suppression factor • via leptons (producing a much harder spectrum)  “saw-tooth”-shaped flux

  7. Cosmic Ray Propagation • Injection spectrum modified by particle diffusion through ISM • Scattering off galactic B-field, CMB radiation and starlight result in energy losses • Diffusion can be well-approximated to a random walk Energy loss rate Assuming a constant B-field: Diffusion Constant Source Term Proportional to halo annihilation rate per unit vol. (Maurin et al.) (Webber et al.)

  8. Cosmic Ray Propagation • Solve for the local differential positron flux (z=0, r=8.5 kpc) • Diffusion zone half-thickness, L~4 kpc (Webber et al.) • Investigate sensitivity of this flux to diffusion parameters , L, K, b, 

  9. L = 2, 4, 10 kpc K0 = (0.25, 1, 4) x 3x1023 m2 s-1 E = (0.25, 1, 4) x 1016 s  = 0.2, 0.6, 0.9

  10. Cosmic Ray Propagation Variation with density profile

  11. Positron Fraction • Calculate PF using injection spectra calculated by DarkSUSY (Edsjo et al.) • NFW profile used, rs=25 kpc, 0=0.3 GeV cm-3 • Normalisation of positron components left as a free parameters, ns and ks Gaugino-dominated Higgsino-dominated

  12. Positron Fraction Mixed Gaugino/Higgsino Gaugino-dominated + finite • To discern which models are relevant we need better instrumentation…

  13. PAMELA & AMS-02 • Balloon-based experiment (like HEAT) PAMELA • Designed to study (anti)matter asymmetry • Primary objectives include measurement of cosmic positron spectrum up to 270 GeV • Large acceptance of 20.5 cm2 s • Extensive exposure time of 3-years AMS-02 • To be deployed on ISS for 3-yr mission • Large acceptance of 20.5 cm2 s (!) • Superior energy resolution and bkg rejection

  14. Sensitivity of PAMELA & AMS-02 We attempt to identify at what annihilation rate the unique features of our cosmic ray spectra are statistically significant by evaluating the following parameter Where the sum is over each data point, taken to have the estimated sensitivity for each instrument

  15. Sensitivity of PAMELA & AMS-02 • Mixed Gaugino/Higgsino Neutralino annihilations

  16. Sensitivity of PAMELA & AMS-02 • Gaugino-dominated Neutralinos, with

  17. Pure Winos Pure Higgsinos • Binos • <v>>[10-26,10-27]cm3s-1 (PAMELA, AMS-02) • Prospects improve for large tan( ) • NB: <v>can.~3x10-26cm3s-1 • Winos • AMSB for m>[0.55,1] TeV (PAMELA, AMS-02) • Higgsinos • m>[230,400] GeV (PAMELA, AMS-02) Potential of PAMELA & AMS-02 • Annihilation rates needed to be distinguished from the bkg at 95% C.L. ( Hooper & Silk , 2004 ) AMS-02, BF=1 WE NEED A BETTER UNDERSTANDING OF DM SUBSTRUCTURE IN MW!!!

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