* Astronomy

Blobrana · L

RE: AMS 02 experiment

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Title: AMS-02 Antiprotons Reloaded
Author: Rolf Kappl, Annika Reinert, Martin Wolfgang Winkler

The AMS-02 collaboration has released preliminary data on the antiproton fraction in cosmic rays. The surprisingly hard antiproton spectrum at high rigidity has triggered speculations about a possible primary antiproton component originating from dark matter annihilations. In this note, we employ newly available AMS-02 boron to carbon data to update the secondary antiproton flux within the standard two-zone diffusion model. The new background permits a considerably better fit to the measured antiproton fraction compared to previous estimates. This is mainly a consequence of the smaller slope of the diffusion coefficient favoured by the new AMS-02 boron to carbon data.

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Title: Pulsar interpretation for the AMS-02 result
Authors: Peng-Fei Yin, Zhao-Huan Yu, Qiang Yuan, Xiao-Jun Bi

The AMS-02 collaboration has just published a high precision measurement of the cosmic positron fraction e^+/(e^- + e^+), which rises with energy from ~ 5 GeV to ~ 350 GeV. The result indicates the existence of primary electron/positron sources to account for the positron excess. In this work, we investigate the possibility that the nearby mature pulsars are the primary positron sources. By fitting the data we find that the positrons from a single nearby pulsar, such as Geminga or Monogem, with the spectral index \alpha ~ 2 can interpret the AMS-02 result. We also investigate the possibility that high energy positrons are generated by multiple known pulsars in the ATNF catalogue. Such a scenario can also fit the AMS-02 data well. Future precise measurements of fine structures in the positron spectrum would be a support to the pulsar scenario.

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Title: Hints of a Charge Asymmetry in the Electron and Positron Cosmic-Ray Excesses
Authors: Isabella Masina, Francesco Sannino

By combining the recent data from AMS-02 with those from Fermi-LAT, we show the emergence of a charge asymmetry in the electron and positron cosmic-ray excesses, slightly favouring the electron component. Astrophysical and dark matter inspired models introduced to explain the observed excesses can be classified according to their prediction for the charge asymmetry and its energy dependence. Future data confirming the presence of a charge asymmetry, would imply that an asymmetric production mechanism is at play.

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Title: Dark Matter and Pulsar Origins of the Rising Cosmic Ray Positron Fraction in Light of New Data From AMS
Authors: Ilias Cholis, Dan Hooper

The rise of the cosmic ray positron fraction with energy, as first observed with high confidence by PAMELA, implies that a large flux of high energy positrons has been recently (or is being currently) injected into the local volume of the Milky Way. With the new and much more precise measurement of the positron fraction recently provided by AMS, we revisit the question of the origin of these high energy positrons. We find that while some dark matter models (annihilating directly to electrons or muons) no longer appear to be capable of accommodating these data, other models in which ~1-3 TeV dark matter particles annihilate to unstable intermediate states could still be responsible for the observed signal. Nearby pulsars also remain capable of explaining the observed positron fraction. Future measurements of the positron fraction by AMS (using a larger data set), combined with their anticipated measurements of various cosmic ray secondary-to-primary ratios, may enable us to further discriminate between these remaining scenarios.

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Title: Implications of the AMS-02 positron fraction in cosmic rays
Authors: Qiang Yuan, Xiao-Jun Bi, Guo-Ming Chen, Yi-Qing Guo, Su-Jie Lin, Xinmin Zhang

The AMS-02 collaboration has just released its first result of the cosmic positron fraction e^+/(e^-+e^+) with high precision up to ~ 350 GeV. The AMS-02 result shows the same trend with the previous PAMELA result, which requires extra electron/positron sources on top of the conventional cosmic ray background, either from astrophysical sources or from dark matter annihilation/decay. In this paper we try to figure out the nature of the extra sources by fitting to the AMS-02 e^+/(e^-+e^+) data, as well as the electron and proton spectra by PAMELA and the (e^-+e^+) spectrum by Fermi and HESS. We adopt the GALPROP package to calculate the propagation of the Galactic cosmic rays and the Markov Chain Monte Carlo sampler to do the fit. We find that the AMS-02 data have implied essential difference from the PAMELA data. There is tension between the AMS-02 e^+/(e^-+e^+) data and the Fermi/HESS (e^-+e^+) spectrum, that the AMS-02 data requires less contribution from the extra sources than Fermi/HESS. Then we redo the fit without including the Fermi/HESS data. In this case both the pulsars and dark matter annihilation/decay can explain the AMS-02 data. The pulsar scenario has a soft inject spectrum with the power-law index ~ 2, while the dark matter scenario needs \tau^+\tau^- final state with mass ~ 600 GeV and a boost factor ~ 200.

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Alpha Magnetic Spectrometer zeroes in on dark matter

A $2bn experiment on the space station has made observations that could prove to be the first signs of dark matter, a mysterious component of the Universe.
It has seen evidence of what may prove to be dark matter colliding with itself in what is known as "annihilation".
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Have scientists found dark matter?

Today will hear the first results from the Alpha Magnetic Spectrometer, which was bolted on to the International Space Station and which has been scanning the heavens for evidence that it exists.
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Guardians of the antimatter hunter

A year ago, the largest and most complex scientific instrument on the International Space Station was delivered to the orbital outpost. Searching for antimatter and the origins of our Universe, it is working flawlessly thanks to the continuous support from its own 'mission control'.
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Cosmic ray haul for space 'LHC'

The largest-ever experiment in space has reported the collection of some 18 billion "cosmic ray" events that may help unravel the Universe's mysteries.
The data haul is far greater than the total number of cosmic rays recorded in a full century of looking to date.
Run from a centre at Cern, the Alpha Magnetic Spectrometer (AMS) aims to spot dark matter and exotic antimatter.
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