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A new measurement of the antiproton-to-proton flux ratio up to 100 GeV in the cosmic radiation

O. Adriani, G. C. Barbarino, G. A. Bazilevskaya, R. Bellotti, M. Boezio, E. A. Bogomolov, L. Bonechi, M. Bongi, V. Bonvicini, S. Bottai, A. Bruno, F. Cafagna, D. Campana, P. Carlson, M. Casolino, G. Castellini, M. P. De Pascale, G. De Rosa, D. Fedele, A. M. Galper, L. Grishantseva, P. Hofverberg, S. V. Koldashov, S. Y. Krutkov, A. N. Kvashnin, A. Leonov, V. Malvezzi, L. Marcelli, W. Menn, V. V. Mikhailov, M. Minori, E. Mocchiutti, M. Nagni, S. Orsi, G. Osteria, P. Papini, M. Pearce, P. Picozza, M. Ricci, S. B. Ricciarini, M. Simon, R. Sparvoli, P. Spillantini, Y. I. Stozhkov, E. Taddei, A. Vacchi, E. Vannuccini, G. Vasilyev, S. A. Voronov, Y. T. Yurkin, G. Zampa, N. Zampa, V. G. Zverev

TL;DR

A new measurement of the cosmic-ray antiproton-to-proton flux ratio between 1 and 100 GeV is presented, which is a tenfold improvement in statistics with respect to all previously published data.

Abstract

A new measurement of the cosmic ray antiproton-to-proton flux ratio between 1 and 100 GeV is presented. The results were obtained with the PAMELA experiment, which was launched into low-earth orbit on-board the Resurs-DK1 satellite on June 15th 2006. During 500 days of data collection a total of about 1000 antiprotons have been identified, including 100 above an energy of 20 GeV. The high-energy results are a ten-fold improvement in statistics with respect to all previously published data. The data follow the trend expected from secondary production calculations and significantly constrain contributions from exotic sources, e.g. dark matter particle annihilations.

A new measurement of the antiproton-to-proton flux ratio up to 100 GeV in the cosmic radiation

TL;DR

A new measurement of the cosmic-ray antiproton-to-proton flux ratio between 1 and 100 GeV is presented, which is a tenfold improvement in statistics with respect to all previously published data.

Abstract

A new measurement of the cosmic ray antiproton-to-proton flux ratio between 1 and 100 GeV is presented. The results were obtained with the PAMELA experiment, which was launched into low-earth orbit on-board the Resurs-DK1 satellite on June 15th 2006. During 500 days of data collection a total of about 1000 antiprotons have been identified, including 100 above an energy of 20 GeV. The high-energy results are a ten-fold improvement in statistics with respect to all previously published data. The data follow the trend expected from secondary production calculations and significantly constrain contributions from exotic sources, e.g. dark matter particle annihilations.

Paper Structure

This paper contains 4 figures, 1 table.

Figures (4)

  • Figure 1: The deflection reconstructed by the track fitting procedure for negatively- and positively-charged down-going particles with a reconstructed MDR $\geq$ 850 GeV and that did not produce an electromagnetic shower in the calorimeter. The shaded histogram corresponds to the selected antiprotons.
  • Figure 2: An example of a topological calorimeter variable used for antiproton identification (see text for explanation). Positively-charged events are shown in the lower plot. The upper plot shows negatively-charged events. The vertical scale for the open histogram has been multiplied by a factor of 30 (compared to the filled histogram) for clarity.
  • Figure 3: The antiproton-to-proton flux ratio obtained in this work compared with theoretical calculations for a pure secondary production of antiprotons during the propagation of cosmic rays in the galaxy. The dashed lines show the upper and lower limits calculated by sim98 for the standard Leaky Box Model, while the dotted lines show the limits from don01 for a Diffusion model with reacceleration. The solid line shows the calculation by ptu06 for the case of a Plain Diffusion model. The curves were obtained using appropriate solar modulation parameters (indicated as $\phi$) for the PAMELA data taking period.
  • Figure 4: The antiproton-to-proton flux ratio obtained in this work compared with contemporary measurements hof96mit96boe97boe01bea01asa02ham06.