Cosmic-Ray Electron Flux Measured by the PAMELA Experiment between 1 and 625 GeV O. Adriani, 1,2 G. C. Barbarino, 3,4 G. A. Bazilevskaya, 5 R. Bellotti, 6,7 M. Boezio, 8 E. A. Bogomolov, 9 M. Bongi, 2 V. Bonvicini, 8 S. Borisov, 10,11,12 S. Bottai, 2 A. Bruno, 6,7 F. Cafagna, 7 D. Campana, 4 R. Carbone, 4,11 P. Carlson, 13 M. Casolino, 10 G. Castellini, 14 L. Consiglio, 4 M. P. De Pascale, 10,11 C. De Santis, 10 N. De Simone, 10,11 V. Di Felice, 10 A. M. Galper, 12 W. Gillard, 13 L. Grishantseva, 12 G. Jerse, 8,15 A. V. Karelin, 12 S. V. Koldashov, 12 S.Y. Krutkov, 9 A. N. Kvashnin, 5 A. Leonov, 12 V. Malakhov, 12 V. Malvezzi, 10 L. Marcelli, 10 A. G. Mayorov, 12 W. Menn, 16 V. V. Mikhailov, 12 E. Mocchiutti, 8 A. Monaco, 6,7 N. Mori, 1,2 N. Nikonov, 9,10,11 G. Osteria, 4 F. Palma, 10,11 P. Papini, 2 M. Pearce, 13 P. Picozza, 10,11 C. Pizzolotto, 8 M. Ricci, 17 S. B. Ricciarini, 2 L. Rossetto, 13 R. Sarkar, 8 M. Simon, 16 R. Sparvoli, 10,11 P. Spillantini, 1,2 S. J. Stochaj, 18 J. C. Stockton, 18 Y. I. Stozhkov, 5 A. Vacchi, 8 E. Vannuccini, 2 G. Vasilyev, 9 S. A. Voronov, 12 J. Wu, 13, * Y. T. Yurkin, 12 G. Zampa, 8 N. Zampa, 8 and V.G. Zverev 12 1 University of Florence, Department of Physics, I-50019 Sesto Fiorentino, Florence, Italy 2 INFN, Sezione di Florence, I-50019 Sesto Fiorentino, Florence, Italy 3 University of Naples ‘‘Federico II,’’ Department of Physics, I-80126 Naples, Italy 4 INFN, Sezione di Naples, I-80126 Naples, Italy 5 Lebedev Physical Institute, RU-119991 Moscow, Russia 6 University of Bari, Department of Physics, I-70126 Bari, Italy 7 INFN, Sezione di Bari, I-70126 Bari, Italy 8 INFN, Sezione di Trieste, I-34149 Trieste, Italy 9 Ioffe Physical Technical Institute, RU-194021 St. Petersburg, Russia 10 INFN, Sezione di Rome ‘‘Tor Vergata,’’ I-00133 Rome, Italy 11 University of Rome ‘‘Tor Vergata,’’ Department of Physics, I-00133 Rome, Italy 12 National Research Nuclear University ‘‘MEPHI,’’ RU-115409 Moscow, Russia 13 KTH, Department of Physics, and the Oskar Klein Centre for Cosmoparticle Physics, AlbaNova University Centre, SE-10691 Stockholm, Sweden 14 IFAC, I-50019 Sesto Fiorentino, Florence, Italy 15 University of Trieste, Department of Physics, I-34147 Trieste, Italy 16 Universita ¨t Siegen, Department of Physics, D-57068 Siegen, Germany 17 INFN, Laboratori Nazionali di Frascati, Via Enrico Fermi 40, I-00044 Frascati, Italy 18 New Mexico State University, Las Cruces, New Mexico 88003, USA (Received 23 December 2010; published 19 May 2011) Precision measurements of the electron component in the cosmic radiation provide important infor- mation about the origin and propagation of cosmic rays in the Galaxy. Here we present new results regarding negatively charged electrons between 1 and 625 GeV performed by the satellite-borne experiment PAMELA. This is the first time that cosmic-ray e  have been identified above 50 GeV. The electron spectrum can be described with a single power-law energy dependence with spectral index 3:18  0:05 above the energy region influenced by the solar wind ( > 30 GeV). No significant spectral features are observed and the data can be interpreted in terms of conventional diffusive propagation models. However, the data are also consistent with models including new cosmic-ray sources that could explain the rise in the positron fraction. DOI: 10.1103/PhysRevLett.106.201101 PACS numbers: 98.70.Sa, 95.35.+d, 95.85.Ry, 96.50.sb Cosmic-ray electrons are a small but important compo- nent of the cosmic radiation. They provide information regarding the origin and propagation of cosmic rays in the Galaxy that is not accessible from the study of the cosmic-ray nuclear components due to their differing energy-loss processes. Cosmic-ray electrons and positrons are produced as secondaries by the interactions between cosmic-ray nuclei and the interstellar matter. However, since the observed positron fraction (ðe þ Þ=½ðe þ Þþ ðe  Þ, where  is the flux, is of the order of 10% and less above a few GeV [1–3], a majority of electrons must be of primary origin. Because of their low mass and the intergalactic magnetic field, cosmic-ray electrons undergo severe energy losses during their propagation in the Galaxy. Therefore, it can be expected that a significant fraction of high energy (> 10 GeV) electrons and positrons are produced in the solar neighborhood ( 1 kpc)[4] with the majority of the primary electron component probably originating from a small number of sources, which may induce features in the spectral shape of the electron energy spectrum [5,6]. Spectral features may also arise from the contribution of more exotic sources such as dark matter particles, e.g. [7], or other astrophysical objects such as pulsars, e.g., [8]. PRL 106, 201101 (2011) PHYSICAL REVIEW LETTERS week ending 20 MAY 2011 0031-9007= 11=106(20)=201101(5) 201101-1 Ó 2011 American Physical Society