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TOPIC: PAMELA experiment
Blobrana


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RE: PAMELA experiment
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Title: What Does The PAMELA Antiproton Spectrum Tell Us About Dark Matter?
Author: Dan Hooper, Tim Linden, Philipp Mertsch

Measurements of the cosmic ray antiproton spectrum can be used to search for contributions from annihilating dark matter and to constrain the dark matter annihilation cross section. Depending on the assumptions made regarding cosmic ray propagation in the Galaxy, such constraints can be quite stringent. We revisit this topic, utilizing a set of propagation models fit to the cosmic ray boron, carbon, oxygen and beryllium data. We derive upper limits on the dark matter annihilation cross section and find that when the cosmic ray propagation parameters are treated as nuisance parameters (as we argue is appropriate), the resulting limits are significantly less stringent than have been previously reported. We also note (as have several previous groups) that simple GALPROP-like diffusion-reacceleration models predict a spectrum of cosmic ray antiprotons that is in good agreement with PAMELA's observations above ~5 GeV, but that significantly underpredict the flux at lower energies. Although the complexity of modeling cosmic ray propagation at GeV-scale energies makes it difficult to determine the origin of this discrepancy, we consider the possibility that the excess antiprotons are the result of annihilating dark matter. Suggestively, we find that this excess is best fit for a dark matter mass of approximately 35 GeV and annihilation cross section of approximately 1e-26 cm³/s (to b-bbar), in good agreement with the mass and cross section previously shown to be required to generate the gamma-ray excess observed from the Galactic Center.

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Blobrana


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Title: B/C ratio and the PAMELA positron excess
Authors: M.Kachelriess, S.Ostapchenko

We calculate the diffuse intensity of cosmic ray (CR) nuclei and their secondaries in the Boron-Carbon group produced by supernova remnants (SNR). The trajectories of charged particles in the SNR are modelled as a random walk in the test particle approximation. Secondary production by CRs colliding with gas in the SNR is included as a Monte Carlo process, while we use Galprop to account for the propagation and interactions of CRs in the Galaxy. In the vicinity of a source, we find an approximately constant B/C ratio as a function of energy. As a result, the B/C ratio at Earth does not rise with energy, but flattens instead in the high energy limit. This prediction can be soon tested by the AMS-2 collaboration.

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Blobrana


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Title: On the Special Significance of the Latest PAMELA Results in Astroparticle Physics
Authors: Goutam Sau, S. Bhattacharyya

In continuation of their earlier measurements, the PAMELA group reported data on antiproton flux and \bar{P}/P ratios in 2010 at much higher energies. In past we had dealt with these specific aspects of PAMELA data in great detail and each time we captured the contemporary data-trends quite successfully with the help of a multiple production model of secondary antiprotons with some non-standard ilk and with some other absolutely standard assumptions and approximations. In this work we aim at presenting a comprehensive and valid description of all the available data on antiproton flux and the nature of \bar{P}/P ratios at the highest energies reported so far by the PAMELA experiment in 2010. The main physical implication of all this would, in the end, be highlighted.

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Blobrana


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Antimatter surplus is not dark matter's smoking gun

Antimatter enthusiasts will love it; dark matter hunters not so much. NASA's FERMI satellite has confirmed a previous hint that there is more antimatter than expected coming from space. The bad news is that the result almost certainly rules out dark matter as the source.
The results were reported online by the FERMI Large Area Telescope Collaboration. They hit the web just in time for the Topics in Astroparticle and Underground Physics conference taking place in Munich, Germany, this week, where they were immediately incorporated into the first talks.
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Blobrana


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PAMELA anomaly
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Title: The 'PAMELA anomaly' indicates a nearby cosmic ray accelerator
Authors: Philipp Mertsch, Subir Sarkar (Oxford)

We discuss the recently observed 'excesses' in cosmic ray electron and positron fluxes which have been widely interpreted as signals of dark matter. By considering the production and acceleration of secondary electrons and positrons in nearby supernova remnants, we predict an additional, harder component that becomes dominant at high energies. The unknown spatial distribution of the supernova remnants introduces a stochastic uncertainty which we estimate analytically. Fitting the prediction for different source distributions to the total electron + positron flux measured by Fermi--LAT fixes all free parameters and allows us to 'postdict' the rise in the positron fraction seen by PAMELA. A similar rise in the B/C ratio is predicted at high energies.

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Blobrana


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Title: The cosmic-ray electron flux measured by the PAMELA experiment between 1 and 625 GeV
Authors: PAMELA Collaboration: O. Adriani, G. C. Barbarino, G. A. Bazilevskaya, R. Bellotti, M. Boezio, E. A. Bogomolov, M. Bongi, V. Bonvicini, S. Borisov, S. Bottai, A. Bruno, F. Cafagna, D. Campana, R. Carbone, P. Carlson, M. Casolino, G. Castellini, L. Consiglio, M. P. De Pascale, C. De Santis, N. De Simone, V. Di Felice, A. M. Galper, W. Gillard, L. Grishantseva, G. Jerse, A. V. Karelin, S. V. Koldashov, S. Y. Krutkov, A. N. Kvashnin, A. Leonov, V. Malakhov, V. Malvezzi, L. Marcelli, A. G. Mayorov, W. Menn, V. V. Mikhailov, E. Mocchiutti, A. Monaco, N. Mori, N. Nikonov, G. Osteria, F. Palma, P. Papini, M. Pearce, P. Picozza, C. Pizzolotto, M. Ricci, S. B. Ricciarini, L. Rossetto, R. Sarkar, M. Simon, R. Sparvoli, P. Spillantini, S. J. Stochaj, J. C. Stockton, Y. I. Stozhkov, A. Vacchi, E. Vannuccini,
G. Vasilyev, S. A. Voronov, J. Wu, Y. T. Yurkin, G. Zampa, N. Zampa, V. G. Zverev
et al. (7 additional authors not shown)

Precision measurements of the electron component in the cosmic radiation provide important information 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 electrons 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.

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Blobrana


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Title: PAMELA Measurements of Cosmic-Ray Proton and Helium Spectra
Authors: 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, N. De Simone, V. Di Felice, 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, E. Mocchiutti, S. Orsi, G. Osteria, P. Papini, M. Pearce, P. Picozza, M. Ricci, S. B. Ricciarini, M. Simon, R. Sparvoli, P. Spillantini, Y. I. Stozhkov, A. Vacchi, E. Vannuccini, G. Vasilyev, S. A. Voronov, Y. T. Yurkin, G. Zampa, N. Zampa, V. G. Zverev

Protons and helium nuclei are the most abundant components of the cosmic radiation. Precise measurements of their fluxes are needed to understand the acceleration and subsequent propagation of cosmic rays in the Galaxy. We report precision measurements of the proton and helium spectra in the rigidity range 1 GV-1.2 TV performed by the satellite-borne experiment PAMELA. We find that the spectral shapes of these two species are different and cannot be well described by a single power law. These data challenge the current paradigm of cosmic-ray acceleration in supernova remnants followed by diffusive propagation in the Galaxy. More complex processes of acceleration and propagation of cosmic rays are required to explain the spectral structures observed in our data.

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Blobrana


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Title: PAMELA through a Magnetic Lense
Authors: J. P. Roberts

The PAMELA satellite has observed an excess of positrons over electrons in the energy range 1-100 GeV that increases with energy. We propose that the excess is not due to a change in the local interstellar spectrum, but is due to heliospheric modulation. We motivate this from the known form of the heliospheric magnetic field and predict that the excess will disappear when we enter a period of solar maximum activity.

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Blobrana


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Title: Results from PAMELA, ATIC and FERMI : Pulsars or Dark Matter ?
Authors: Debtosh Chowdhury, Chanda J. Jog, Sudhir K Vempati
(Version v3)

It is well known that the dark matter dominates the dynamics of galaxies and clusters of galaxies. Its constituents remain a mystery despite an assiduous search for them over the past three decades. Recent results from the satellite-based PAMELA experiment detect an excess in the positron fraction at energies between 10-100 GeV in the secondary cosmic ray spectrum. Other experiments namely ATIC, HESS and FERMI show an excess in the total electron (\ps + \el) spectrum for energies greater 100 GeV. These excesses in the positron fraction as well as the electron spectrum could arise in local astrophysical processes like pulsars, or can be attributed to the annihilation of the dark matter particles. The second possibility gives clues to the possible candidates for the dark matter in galaxies and other astrophysical systems. In this article, we give a report of these exciting developments.

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Blobrana


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Title: Slightly Non-Minimal Dark Matter in PAMELA and ATIC
Authors: Ann E. Nelson, Christopher Spitzer
(Version v3)

We present a simple model in which dark matter couples to the standard model through a light scalar intermediary that is itself unstable. We find this model has several notable features, and allows a natural explanation for a surplus of positrons, but no surplus of anti-protons, as has been suggested by early data from PAMELA and ATIC. Moreover, this model yields a very small nucleon coupling, well below the direct detection limits. In this paper we explore the effect of this model in both the early universe and in the galaxy.

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