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ELENA VANNUCCINI ON BEHALF OF PAMELA COLLABORATION Measurement of the Hydrogen and Helium absolute fluxes with the PAMELA experiment.

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Presentation on theme: "ELENA VANNUCCINI ON BEHALF OF PAMELA COLLABORATION Measurement of the Hydrogen and Helium absolute fluxes with the PAMELA experiment."— Presentation transcript:

1 ELENA VANNUCCINI ON BEHALF OF PAMELA COLLABORATION Measurement of the Hydrogen and Helium absolute fluxes with the PAMELA experiment

2 Direct detection of CRs in space Main focus on antiparticles (antiprotons and positrons) Launch from Baykonur PAMELA on board of Russian satellite Resurs DK1 Orbital parameters: - inclination ~70 o (  low energy) - altitude ~ km (elliptical) - active life >3 years (  high statistics)  Launched on 15th June 2006  PAMELA in continuous data-taking mode since then!

3 Main requirements: - high-sensitivity antiparticle identification - precise momentum measure GF: cm 2 sr Mass: 470 kg Size: 130x70x70 cm 3 Power Budget: 360W Spectrometer microstrip silicon tracking system + permanent magnet It provides: - Magnetic rigidity  R = pc/Ze = 1/|  - Charge sign  sign of  - Charge value from dE/dx MDR* up to 1400GV *MDR = Maximum Detectable Rigidity   R/R=100% 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 plastic scintillators + PMT: - High-energy e/h discrimination + -

4 Single good-quality track in the spectrometer  Particle rigidity (R = pc/Ze ) Downward-going (  >0) & positive-curvature (R>0) trajectory  Positive-charge particle from above Clean pattern through the apparatus  Not an interaction product Energy deposits in the tracking system consistent with H and He nuclei He H  High-statistic (~10 8 ) sample of H and He (no isotope separation)  Negligible bk of -interaction products -misidentified particles

5 Galactic particles selected by requiring: R >1.3  C C = vert. Störmer cutoff H flux Polar regions Equator

6 Selection cuts R

7 Protons 10% Bayesian unfolding Spectrometer response matrix from MC

8  Possibility of residual coherent misalignment (distortion) of the tracking system  Evaluated from in-flight electron/positron data by comparing the spectrometer momentum with the calorimeter energy  Upper limit set by positron statistics:  sys ~10 -4 GV -1   ~ GV -1 A systematic deflection shift causes an offset between e - and e + distribution e+e+ e-e-   sys

9  At low R selection- efficiency uncertainties dominate  Above 500GV tracking- system (coherent) misalignment dominates selection-efficiency uncertainties spectrometer systematic error

10 Fluxes evaluated by varying the selection conditions: Total vs time Total vs polar/equatorial Total vs reduced acceptance Total vs different tracking conditions (  different response matrix) … Time interval (2 months) Integral proton flux (>50GV) 3%

11 First high-statistics and high-precision measurement over three decades in energy Low energy  minimum solar activity (  450÷550 GV) High-energy (>30GV)  a complex structure of the spectra emerges… Adriani et al. - Science (2011) 6025 PAMELA data  Jul 2006 ÷ Mar 2008

12 Deviations from single power law (SPL):  Spectra gradually soften in the range 30÷230GV  Spectral R~235GV  ~0.2÷0.3 SPL hp rejected at 98% CL Origin of the structures? - At the sources: multi- populations, non-linear DSA - Propagation effects Solar modulation GV Spectral index GV H He

13 Power-law fit (  2 ~1.3)  He -  p = ±0.008

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15 Very large statistics collected Precise spectral measurement down to 400MV  Detailed study of solar modulation effect Protons

16 Summary and conclusions PAMELA has been in orbit and studying cosmic rays for ~4.5 years. >10 9 triggers registered H and He absolute fluxes up to 1.2TV  Most precise measurement so far.  Complex spectral structures observed (spectral hardening at ~200GV!)  Step forward in understanding galactic CR origin and propagation! Forthcoming results on long-term flux variations down to few hundred MV  Step forward in understanding propagation in the Solar System!

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18 Putze et al. A&A 526 (2011) A101


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