Recent results from the space experiment PAMELA

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Recent results from the space experiment PAMELA . Roberta sparvoli University of rome Tor Vergata & INFN ( italian National institute of nuclear physics). PAMELA Payload for Matter/antimatter Exploration and Light-nuclei Astrophysics. Direct detection of CRs in space
Recent results from the space experimentPAMELA Roberta sparvoli University of rome Tor Vergata & INFN (italian National institute of nuclear physics) PAMELAPayload for Matter/antimatter Exploration and Light-nuclei Astrophysics
  • Direct detection of CRs in space
  • Main focus on antiparticles(antiprotons and positrons)
  • PAMELA on board of Russian satellite Resurs DK1
  • Orbital parameters:
  • inclination ~70o ( low energy)
  • altitude ~ 360-600 km (elliptical)
  •  Launched on 15th June 2006  PAMELA in continuous data-taking mode since then! Launch from Baykonur + - PAMELA detectors
  • 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
  • Main requirements: - high-sensitivity antiparticle identification - precise momentum measurement
  • Spectrometer
  • microstrip silicon tracking system+ permanent magnet
  • It provides:
  • - Magnetic rigidity R = pc/Ze
  • Charge sign
  • Charge value from dE/dx
  • GF: 21.5 cm2 sr Mass: 470 kg Size: 130x70x70 cm3 Power Budget: 360W Antiparticles Adriani et al. - PRL 105 (2010) 121101 Antiproton-to-proton ratio 100 MeV- 200 GeV Largest energy range covered so far ! Adriani et al. - PRL 105 (2010) 121101 Antiproton flux 100 MeV- 200 GeV Largest energy range covered so far ! New antiproton flux –> 300 GeV Using all data till 2010 and multivariate classification algorithms 40% increase in antiprespect to published analysis New antiproton/proton ratio 300 GeV Overall agreement with models of pure secondary calculations for solar minimum (constraints at low and high energy for DM models!) Adriani et al. , Nature 458 (2009) 607 Adriani et al., AP 34 (2010) 1 Positron fraction Low energy  charge-dependent solar modulation (see later) High energy  (quite robust) evidence of positron excess above 10 GeV
  • (Moskalenko & Strong 1998)
  • GALPROP code
  • Plain diffusion model
  • Interstellar spectra
  • New positron fraction data 300 GeV Using all data till 2010 and multivariate classification algorithms about factor 2increase in positronstatisticsrespect to published analysis Good agreement with FERMI and AMS data Adriani et al. , PRL 111 (2013) 081102 Published August 19, 2013 New positron flux The paper has been highlighted with a Synopsis on the Physics website In the highest bin a lower limit has been estimated with 90% confidence level, due to a possible overestimation of the proton contamination. (Cholis et al. 2009) Contribution from DM annihilation. Positron-excess interpretations Dark matter boost factor required lepton vs hadron yield must be consistent with p-bar observation Astrophysical processes known processes large uncertainties on environmental parameters (Blasi 2009) e+ (and e-) produced as secondaries in the CR acceleration sites (e.g. SNR) (Hooper, Blasi and Serpico, 2009) contribution from diffuse mature & nearby young pulsars. Anisotropy studies (p up to 1 TeV) Search for an excess in the Sun direction No significant departure from isotropy is observed Cumulative number of events with E> 40 GeV as a function of the angular distance from the direction of the Sun. The grey boxes are the background. AntiHe/He No antiHe detected in a sample of 6.330.000 events with |Z|>=2, from 0.6 to 600 GV. Widest energy range ever reached Absolute fluxes of primary GCRs Adriani et al. , Science 332 (2011) 6025 H & He absolute fluxes First high-statistics and high-precision measurement over three decades in energy Dominated by systematics (~4% below 300 GV) Low energy  minimum solar activity (f = 450÷550 GV) High-energy  a complex structure of the spectra emerges… H& He absolute [email protected] high energy Spectral index Deviations from single power law (SPL): Spectra gradually soften in the range 30÷230GV Abrupt spectral hardening @ ~235GV Eg: statistical analysis for protons SPL hp in the range 30÷230 GV rejected @ >95% CL SPL hpabove 80 GV rejected @ >95% CL 2.85 2.77 2.48 2.67 232 GV 243 GV Solar modulation Solar modulation At low R selection-efficiency uncertainties dominate Above 500 GV tracking-system (coherent) misalignment dominates Overall systematic uncertainties spectrometer systematic error selection-efficiency uncertainties Fluxes evaluated by varying the selection conditions: Flux vs time Flux vs polar/equatorial Flux vs reduced acceptance Flux vs different tracking conditions ( different response matrix) … Check of systematics Integral proton flux (>50GV) 3% Time interval (2 months) Comparison with high-energy experiments H/He ratio vs R First clear evidence of different H and He slopes above ~10GV Ratio described by a single power law (in spite of the evident structures in the individual spectra)
  • aP-aHe = - 0.101 ±0.0014
  • c2~1.3
  • Isotopes H isotope fluxes 2H/1H ratio Adriani et al. , ApJ770 (2013) 2 PAMELA’s are the most complete measurements so far Isotopes He isotope fluxes 3He/4He ratio Adriani et al. , ApJ 770 (2013) 2 PAMELA’s are the most complete measurements so far Adriani et al. , PRL 106 (2011) 201101 Electron energy measurements spectrometer Two independent ways to determine electron energy: Spectrometer Most precise Non-negligible energy losses (bremsstrahlung) above the spectrometer  unfolding Calorimeter Gaussian resolution No energy-loss correction required Strong containment requirements  smaller statistical sample calorimeter
  • Electron identification:
  • Negative curvature in the spectrometer
  • EM-like interaction pattern in the calorimeter
  • Electron absolute flux e+ +e- e- Adriani et al. , PRL 106 (2011) 201101 Largest energy range covered in any experiment hitherto with no atmospheric overburden Low energy minimum solar activity (f = 450÷550 GV) High energy Significant disagreement with GALPROP calculations (that assumes a continuous distribution of the sources). Spectrometric measurement Calorimetric measurements Solar and terrestrial physics Solar modulation: proton spectra Adriani et al, ApJ765 (2013) 91 The evolution of the proton energy spectrum as particle intensities approached the period of minimum solar activity, from July 2006 (violet), to December 2009 (red). The region between the blue and red curves indicates the spread in proton fluxes during this time. Proton spectra & LIS calculations LIS based on that by Langner and Potgieter, modified at high energies to match PAMELA data Solar events (SEP from Dec. 13, 2006) Adrianiet al. - ApJ 742 102, 2011 SAA morphology Latitude Altitude Altitude Neutron rate Longitude South-Atlantic Anomaly (SAA) SAA Discovery of geomagnetically Trapped antiprotons First measurement of p-bar trapped in the inner belt 29 p-bars discovered in SAA and traced back to mirror points p-bar flux exceeds GRC flux by 3 orders of magnitude, as expected by models Adrianiet al. ApJ 737 (2011) L29 All particlesPAMELA results Results span 4 decades in energy and 13 in fluxes Summary and conclusions (1) PAMELA has been in orbit and studying cosmic rays for more 7 years. Its operation time will continue in 2014.
  • Antiproton energy spectrum and ratio Measured up to ~300 GeV. No significant deviations from secondary production expectations.
  • High energy positron fraction (>10 GeV)  Measured up to ~300 GeV. Increases significantly (and unexpectedly!) with energy. Primary source?
  • Positron flux -> Consistent with a new primary source.
  • Anisotropy studies: no evidence of anisotropy.
  • AntiHe/He ratio: broader energy range ever achieved.
  • Summary and conclusions (2)
  • H and He absolute fluxes  Measured up to ~1.2 TV. Complex spectral structures observed (spectral hardening at ~200 GV).
  • H and He isotope fluxes and ratio -> most complete measurements so far.
  • Electron absolute flux Measured up to ~600 GeV. Possible deviations from standard scenario, not inconsistent with an additional electron component.
  • Solar physics: measurement of modulated fluxes and solar-flare particle spectra
  • Physics of the magnetosphere: first measurement of trapped antiproton flux. Other studies and forthcoming results:
  • Primary and secondary-nuclei abundance (up to Oxygen)
  • Solar modulation (long-term flux variation and charge-dependent effects)
  • Solar events: several new events under study
  • PAMELA on Physics Reports “The PAMELA Space Mission: Heralding a New Era in Precision Cosmic Ray Physics” Ready to be submitted to Physics Reports (78 pages). Summarizes published and unpublished (but final) PAMELA results.
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