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Indirect searches of Dark Matter in space: results from the PAMELA space experiment

Indirect searches of Dark Matter in space: results from the PAMELA space experiment. Roberta Sparvoli University of Rome ”Tor Vergata” and INFN. Everything starts with …. Evaporation of primordial black holes. Anti-nucleosyntesis. WIMP dark-matter annihilation in the galactic halo.

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Indirect searches of Dark Matter in space: results from the PAMELA space experiment

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  1. Indirect searches of Dark Matter in space:results from the PAMELA space experiment Roberta Sparvoli University of Rome ”Tor Vergata” and INFN

  2. Everything starts with …  Roberta Sparvoli  July 17th, 2009  Paris

  3. Evaporation of primordial black holes Anti-nucleosyntesis WIMP dark-matter annihilation in the galactic halo Background: CR interaction with ISM CR + ISM  p-bar + … and various ideas of theoretical interpretations  Roberta Sparvoli  July 17th, 2009  Paris

  4.  Roberta Sparvoli  July 17th, 2009  Paris

  5.  Roberta Sparvoli  July 17th, 2009  Paris

  6. Charge-dependent solar modulation Solar polarity reversal 1999/2000 Asaoka Y. Et al. 2002 Positron excess? ? ? ¯ + • CR + ISM  p-bar + … • Propagation dominated by nuclear interactions • Kinematical threshold: Eth~5.6 for the reaction CR antimatter Experimental scenario before PAMELA WHAT DO WE NEED TO BETTER UNDERSTAND ? Measurements at higher energies Better knowledge of background High statistics Continuous monitoring of solar modulation Long Duration Flights Positrons Antiprotons ___ Moskalenko & Strong 1998 • CR + ISM  p± + x m± + x  e± + x • CR + ISM  p0 + x gg e± • Propagation dominated by energy losses • (inverse Compton & synchrotron radiation) • Local origin (@100GeV 90% from <2kpc)  Roberta Sparvoli  July 17th, 2009  Paris

  7. PAMELA pre-history  Roberta Sparvoli  July 17th, 2009  Paris

  8. Italy CNR, Florence Bari Florence Frascati Naples Rome Trieste Russia Moscow St. Petersburg Germany Sweden Siegen KTH, Stockholm The PAMELA collaboration  Roberta Sparvoli  July 17th, 2009  Paris

  9. PAMELA Scientific goals Halo p-bar, e+  Roberta Sparvoli  July 17th, 2009  Paris

  10. PAMELA design performance Maximum detectable rigidity (MDR) energy rangeparticles in 3 years Antiprotons80 MeV ÷190 GeV O(104) Positrons50 MeV ÷ 270 GeV O(105) Electrons up to 400 GeV O(106) Protonsup to 700 GeV O(108) Electrons+positronsup to 2 TeV (from calorimeter) LightNuclei up to 200 GeV/n He/Be/C: O(107/4/5) Anti-Nuclei searchsensitivity of 3x10-8 in anti-He/He Magnetic curvature & trigger spillover shower containment  Roberta Sparvoli  July 17th, 2009  Paris

  11. PAMELA detectors Main requirements  high-sensitivity antiparticle identification and precise momentum measure + - • Time-Of-Flight • plastic scintillators + PMT: • Trigger • Albedo rejection; • Mass identification up to 1 GeV; • - Charge identification from dE/dX. • Electromagnetic calorimeter • W/Si sampling (16.3 X0, 0.6 λI) • Discrimination e+ / p, anti-p / e- • (shower topology) • Direct E measurement for e- • Neutron detector • 36 He3 counters • High-energy e/h discrimination GF: 21.5 cm2 sr Mass: 470 kg Size: 130x70x70 cm3 Power Budget: 360W • Spectrometer • microstrip silicon tracking system+ permanent magnet • It provides: • - Magnetic rigidity R = pc/Ze • Charge sign • Charge value from dE/dx  Roberta Sparvoli  July 17th, 2009  Paris

  12. The Resurs DK-1 spacecraft  Roberta Sparvoli  July 17th, 2009  Paris

  13.  Roberta Sparvoli  July 17th, 2009  Paris

  14.  Roberta Sparvoli  July 17th, 2009  Paris

  15. Launch from Baikonur June 15th 2006, 0800 UTC. ‘First light’ June 21st 2006, 0300 UTC. • Detectors operated as expected after launch • Different trigger and hardware configurations evaluated  PAMELA in continuous data-taking mode since commissioning phase ended on July 11th 2006 PAMELA milestones Main antenna in NTsOMZ Trigger rate* ~ 25 Hz Fraction of live time* ~ 75% Event size (compressed mode) ~ 5kB 25 Hz x 5 kB/ev ~ 10 GB/day (*outside radiation belts) • Today 1129 days in flight • >13 TBytes of raw data downlinked • >109 triggers recorded and under analysis  Roberta Sparvoli  July 17th, 2009  Paris

  16. Antiproton/positron discrimination energy measurement  Roberta Sparvoli  July 17th, 2009  Paris

  17. e- e+ ‘Electron’ ‘Hadron’ p, d p Antiparticle selection  Roberta Sparvoli  July 17th, 2009  Paris

  18. Antiprotons  Roberta Sparvoli  July 17th, 2009  Paris

  19. High-energy antiproton analysis • Analyzed data July 2006 – February 2008 (~500 days) • Collected triggers ~108 • Identified ~ 10 106 protons and ~ 1 103 antiprotons between 1.5 and 100 GeV ( 100 p-bar above 20 GeV ) • Antiproton/proton identification: • rigidity (R)  SPE • |Z|=1 (dE/dx vs R)  SPE&ToF • b vs R consistent with MpToF • p-bar/p separation (charge sign)  SPE • p-bar/e- (and p/e+ ) separation CALO • Dominant background spillover protons: • finite deflection resolution of the SPE  wrong assignment of charge-sign @ high energy • proton spectrum harder than positron  p/p-bar increase for increasing energy (103 @1GV 104 @100GV) •  Required strong SPE selection  Roberta Sparvoli  July 17th, 2009  Paris

  20. Proton-spillover background • Electrons: efficiently removed by CALO • Pions (from interactions in dome) : about 3% in the pbar sample  Roberta Sparvoli  July 17th, 2009  Paris

  21. PAMELA: Antiproton-to-proton ratio PRL 102, 051101 (2009)  Roberta Sparvoli  July 17th, 2009  Paris

  22. PAMELA: Antiproton-to-proton ratio PRL 102, 051101 (2009)  Roberta Sparvoli  July 17th, 2009  Paris

  23. PAMELA: Antiproton-to-proton ratioNew (preliminary) data ! Full statistics  Roberta Sparvoli  July 17th, 2009  Paris

  24. PAMELA: Antiproton flux preliminary • PAMELA  Roberta Sparvoli  July 17th, 2009  Paris

  25. Positrons  Roberta Sparvoli  July 17th, 2009  Paris

  26. S1 CARD CAT S2 TOF SPE CAS S3 CALO S4 ND High-energy positron analysis • Analyzed data July 2006 – February 2008 (~500 days) • Collected triggers ~108 • Identified ~ 150 103 electrons and ~ 9 103 positrons between 1.5 and 100 GeV (180 positrons above 20 GeV) • Electron/positron identification: • rigidity (R)  SPE • |Z|=1 (dE/dx=MIP)  SPE&ToF • b=1 ToF • e-/e+ separation (charge sign)  SPE • e+/p (and e-/p-bar) separation CALO • Dominant background interacting protons: • fluctuations in hadronic shower development  p0 ggmight mimic pure em showers • proton spectrum harder than positron  p/e+ increase for increasing energy (103 @1GV 104 @100GV) •  Required strong CALO selection  Roberta Sparvoli  July 17th, 2009  Paris

  27. Positron identification with CALO 51 GV positron • Identification based on: • Shower topology (lateral and longitudinal profile, shower starting point) • Total detected energy (energy-rigidity match) • Analysis key points: • Tuning/check of selection criteria with: • test-beam data • simulation • flight data  dE/dx from SPE & neutron yield from ND • Selection of pure proton sample from flight data (“pre-sampler” method): • Background-suppression method • Background-estimation method 80 GV proton Final results make NO USE of test-beam and/or simulation calibrations. The measurement is based only on flight data with the background-estimation method  Roberta Sparvoli  July 17th, 2009  Paris

  28. Particle selection after total energy cut and starting point of the shower e+ e - (anti p) p + -  Roberta Sparvoli  July 17th, 2009  Paris

  29. PAMELA: Positron fraction NATURE 458, 697, 2009 • (Moskalenko & Strong 1998) • GALPROP code • Plain diffusion model • Interstellar spectra Solar modulation effects Anomalous increasing ?  Roberta Sparvoli  July 17th, 2009  Paris

  30. PAMELA: Positron fraction NATURE 458, 697, 2009  Roberta Sparvoli  July 17th, 2009  Paris

  31. Low energy e+: solar modulation effects  Roberta Sparvoli  July 17th, 2009  Paris

  32. PAMELA antimatter data: Do we have any antimatter excess in CRs?  Roberta Sparvoli  July 17th, 2009  Paris

  33. ~20% • NB! • Solar modulation • Nuclear cross-section • … Antiproton-to-proton ratioSecondary Production Models CR + ISM  p-bar + …  Uncertainty band related to propagation parameters (~10% @10 GeV)  Additional uncertainty of ~25% due to production cs should be considered !! No evidence for any antiproton excess  Roberta Sparvoli  July 17th, 2009  Paris

  34. Positron fractionSecondary Production Models CR + ISM  p± + … m± + …  e± + … CR + ISM  p0 + … gg e± • Increasing positron fraction only if • ge- gp > 0.6 • unlikely (Serpico 2008) Quite robust evidence for a positron excess  Roberta Sparvoli  July 17th, 2009  Paris

  35. Primary positron sources Dark Matter • e+ yield depend on the dominant decay channel • LSPs (SUSY) seem disfavored due to suppression of e+e- final states • low yield (relative to p-bar) • soft spectrum from cascade decays • LKPs seem favored because can annihilate directly in e+e- • high yield (relative to p-bar) • hard spectrum with pronounced cutoff @ MLKP (>300 GeV) • Boost factor required to have a sizable e+ signal • NB: constraints from p-bar data!! • Other hypothesys possible and under study (i.e. Minimal DM Model, decaying DM, new gauge bosons, …) LKP -- M= 300 GeV (Hooper & Profumo 2007) More than 150 articles claim DM is discovered !  Roberta Sparvoli  July 17th, 2009  Paris

  36. Example: dark matter  Roberta Sparvoli  July 17th, 2009  Paris

  37. Primary positron sources Astrophysical processes • Local pulsars are well-known sites of e+e- pair production (the spinning B of the pulsars strips e- that emit gammas then converting to pairs trapped in the cloud, accelerated and then escaping at the Poles) :  they can individually and/or coherently contribute to the e+e- galactic flux and explain the PAMELA e+ excess (both spectral feature and intensity) • No fine tuning required • if one or few nearby pulsars dominate, anisotropy could be detected in the angular distribution • possibility to discriminate between pulsar and DM origin of e+ excess All pulsars (rate = 3.3 / 100 years) (Hooper, Blasi, Seprico 2008)  Roberta Sparvoli  July 17th, 2009  Paris

  38. Example: pulsars  Roberta Sparvoli  July 17th, 2009  Paris

  39. Explanation with supernovae remnantsShaviz and al. astro-ph.HE0902.0376  Roberta Sparvoli  July 17th, 2009  Paris

  40. Positrons from old SNR’sP. Blasi 0903.2794  Roberta Sparvoli  July 17th, 2009  Paris

  41. Standard Positron Fraction Theoretical Uncertainties γ = 3.54 γ = 3.34 Need for high statistics CR measurements T. Delahaye et al., arXiv: 0809.5268v3  Roberta Sparvoli  July 17th, 2009  Paris

  42. Protons, electrons, nuclei, …  Roberta Sparvoli  July 17th, 2009  Paris

  43. PAMELA electron flux preliminary  Roberta Sparvoli  July 17th, 2009  Paris

  44. PAMELA electron flux  Roberta Sparvoli  July 17th, 2009  Paris

  45. PAMELA proton and helium fluxes preliminary See next talk by M. Casolino  Roberta Sparvoli  July 17th, 2009  Paris

  46. PAMELA secondary/primary nuclei ratios preliminary  Roberta Sparvoli  July 17th, 2009  Paris

  47. Summary ~37 13 Additional info in talk by M. Casolino  Roberta Sparvoli  July 17th, 2009  Paris

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