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Marco Ricci INFN, Laboratori Nazionali di Frascati, Frascati (Roma) , Italy

On behalf of the PAMELA Collaboration

TAUP 2011 Munich, September 5-9, 2011

Moscow St. Petersburg

Russia:

Sweden: KTH, Stockholm

Germany: Siegen

Italy: Bari Florence Frascati Trieste Naples Rome CNR, Florence

The PAMELA Instrument

Main antenna in NTsOMZ

Launch from Baikonur → June 15th 2006, 0800 UTC.

‘First light’ → June 21st 2006, 0300 UTC.

• Detectors operated nominally as expected after launch • Different trigger and hardware configurations evaluated

→  PAMELA in continuous data-taking mode since commissioning phase ended on July 11th 2006

Till ~now: ~1910 days of data taking ~25 TByte of raw data downlinked >2x109 triggers recorded and analyzed

PAMELA milestones

70ο

610 km

350 km

SAA

•  Low-earth elliptical orbit

•  350 – 610 km

•  Quasi-polar (70o inclination)

•  SAA crossed

ApJ 457, L 103 1996 ApJ 532, 653, 2000

arXiv:0810.4994, PRL, NJP11,105023

arXiv:0810.4995, Nature, Astrop. Phys

Science 2011 arXiv:1103.4055

arXiv:0708.2587 2008AdSpR..41..168C 2008AdSpR..41.2037D 2008AdSpR..41.2043C

Pamela data

High precision charged

cosmic ray measurement in Low Earth

Orbit

Prl in press

Scientific achievements

Cosmic Ray Spectra

Cosmic-Ray Acceleration and Propagation in the Galaxy

p & 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 (φ = 450÷550 GV)

• High-energy a complex structure of the spectra emerges…

Adriani et al. , Science 332 (2011) 6025

Proton

Helium

p & He absolute fluxes @ high energy

Deviations from single power law (SPL):

 Spectra gradually soften in the range 30÷230GV

 Abrupt spectral hardening @ ~235GV

Sola

r m

odul

atio

n

Sola

r m

odul

atio

n

2.85 2.67

232 GV

Spectral index

2.77 2.48

243 GV

Standard scenario of SN blast waves expanding in the ISM needs additional features

p/He ratio vs R

Instrumental p.o.v.

 Systematic uncertainties partly cancel out (livetime, spectrometer reconstruction, …)

Theoretical p.o.v.

 Solar modulation negligible information about IS spectra down to GV region

 Propagation effects (diffusion and fragmentation) negligible above ~100GV information about source spectra

(Putze et al. 2010)

p/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)

αHe-αp = 0.078 ±0.008 χ2~1.3

Various hypoteses •  Additional Source Wolfendale 2011

•  Spallation Blasi & Amato 2011 •  Weak local component (+ others) Vladimirov,

Johanesson, Moskalenko 2011

Electrons

Phys. Rev. Lett. 106, 201101 (2011)

PAMELA Electron flux measured up to 625 GeV

Spectrometric measurement

Adriani et al. , PRL 106, 201101 (2011) e+ +e-

Calorimetric measurements

e- Electron absolute flux

 Largest energy range covered in any experiment hitherto with no atmospheric overburden

 Low energy

•  minimum solar activity (φ = 450÷550 GV)

 High energy

 No significant disagreement with recent ATIC and Fermi data

 Softer spectrum consistent with both systematics and growing positron component

All electrons

ANTIPARTICLES

Positron fraction

 Low energy charge-dependent solar modulation (see later)

 High energy (quite robust) evidence of positron excess above 10GeV

Adriani et al. , Nature 458 (2009) 607 Adriani et al., AP 34 (2010) 1 (new results)

(Moskalenko & Strong 1998) GALPROP code •  Plain diffusion model •  Interstellar spectra

FERMI positron/electron ratio The Fermi-LAT has measured the cosmic-ray positron and electron spectra separately, between 20 – 130 GeV, using the Earth's magnetic field as a charge discriminator

The two independent methods of background subtraction,Fit-Based and MC-Based, produce consistent results

The observed positron fraction is consistent with the one measured by PAMELA

W. Mitthumsiri et al. @ Fermi Symposium (May 2011) and J.Vandenbroucke ICRC 2011

Antiproton flux

• Largest energy range covered hiterto (0.6 -180 GeV)

• Overall agreement with pure secondary calculation

• Experimental uncertainty (stat⊕sys) smaller than spread in theoretical curves constraints on propagation parameters

(Ptuskin et al. 2006) GALPROP code •  Plain diffusion model •  Solar modulation: spherical model ( φ=550MV )

(Donato et al. 2001) • Diffusion model with convection and reacceleration • Uncertainties on propagation param . and cross sec. • Solar modulation: spherical model ( φ=500MV ) A

drian

i et al. - PR

L 10

5 (2010

) 121101

Antiproton-to-proton ratio

Adriani et al. - PRL 105 (2010) 121101

•  Overall agreement with pure secondary calculation

Antiprotons Consistent with pure secondary production

Positrons Evidence for an excess

A challenging puzzle for CR physicists

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.

(Cholis et al. 2009) Contribution from DM annihilation.

26

A  NEUTRON  STAR  WITH  A  STRONG  MAGNETIC  FIELD:  

FAST  ROTATING    PULSAR                                  (P  =  33  msec)          

L(spindown)  =  5  1038  erg/s  

O. Adriani et al., Ap.J.Lett. 737 L29 (2011); arXiv:1107.4882

29

•  Antiprotons trapped in Earth’s inner radiation belt have been observed for the first time by the PAMELA experiment, confirming the existence of a significant antiproton flux in the SAA below ~1 GeV in kinetic energy.

•  The flux exceeds the galactic CR antiproton flux by three orders of magnitude at the current solar minimum, thereby constituting the most abundant antiproton source near the Earth.

•  A measurement of the sub-cutoff antiproton spectrum outside the SAA region is also under study.

•  PAMELA results allow CR transport models to be tested in the terrestrial atmosphere and significantly constrain predictions from trapped antiproton models, reducing uncertainties concerning the antiproton production spectrum in Earth’s magnetosphere.

Solar Modulation of galactic cosmic rays

BESS

Caprice / Mass /TS93 AMS-01

Pamela •  Study of charge sign

dependent effects Asaoka Y. et al. 2002, Phys. Rev.

Lett. 88, 051101), Bieber, J.W., et al. Physi-cal

Review Letters, 84, 674, 1999. J. Clem et al. 30th ICRC 2007 U.W. Langner, M.S. Potgieter,

Advances in Space Research 34 (2004)

Decreasing solar activity

Increasing GCR flux

Comparison of the proton flux measured between 1.5 and 1.57GV by PAMELA and ULYSSES as a function of time

Dec 13th largest CME since 2003, anomalous at sol min

An example is the search for “strangelets”.

There are six types of Quarks found in accelerators. All matter on Earth is made out of only two types of quarks. “Strangelets” are new types of matter composed of three types of quarks which should exist in the cosmos.

i.  A stable, single “super nucleon” with three types of quarks

ii. “Neutron” stars may be one big strangelet

Carbon Nucleus Strangelet

p! n!

AMS courtesy

•  PAMELA has been in orbit and studying cosmic rays for 5 years.

•  >109 triggers registered and > 25 TB of data have been down-linked.

•  The proton and helium nuclei spectra have been measured up to 1.2 TV. The observations challenge the current paradigm of cosmic ray acceleration and propagation.

• The e- spectrum up to 600 GeV shows no evident deviations from standard scenario, but is not inconsistent with an additional electron component.

• Antiproton-to-proton flux ratio and antiproton energy spectrum (~100 MeV - ~200 GeV) show no significant deviations from secondary production expectations.

• High energy positron fraction (>10 GeV) increases significantly (and unexpectedly!) with energy. Primary source?

• Discovery of geomagnetically trapped cosmic-ray antiprotons.

•  Analysis ongoing to finalize the antiparticle measurements (positron flux, positron fraction), continuous study of solar modulation effects at low energy; primary and secondary nuclei abundance (up to Oxygen); isotopes; upper limit to anti-He.

• Extension of the mission to 2012? Agreements INFN-RSA in progress.

ApJ 457, L 103 1996 ApJ 532, 653, 2000

arXiv:0810.4994, PRL, NJP11,105023

arXiv:0810.4995, Nature, Astrop. Phys

Science 2011 arXiv:1103.4055

arXiv:0708.2587 2008AdSpR..41..168C 2008AdSpR..41.2037D 2008AdSpR..41.2043C

Pamela data

High precision charged

cosmic ray measurement in Low Earth

Orbit

Prl in press