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Title: Origin of the tentative AMS antihelium events

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Journal Article: Publisher's Accepted Manuscript
Journal Name:
Physical Review D
Additional Journal Information:
Journal Volume: 96; Journal Issue: 8; Related Information: CHORUS Timestamp: 2017-10-31 11:12:56; Journal ID: ISSN 2470-0010
American Physical Society
Country of Publication:
United States

Citation Formats

Coogan, Adam, and Profumo, Stefano. Origin of the tentative AMS antihelium events. United States: N. p., 2017. Web. doi:10.1103/PhysRevD.96.083020.
Coogan, Adam, & Profumo, Stefano. Origin of the tentative AMS antihelium events. United States. doi:10.1103/PhysRevD.96.083020.
Coogan, Adam, and Profumo, Stefano. 2017. "Origin of the tentative AMS antihelium events". United States. doi:10.1103/PhysRevD.96.083020.
title = {Origin of the tentative AMS antihelium events},
author = {Coogan, Adam and Profumo, Stefano},
abstractNote = {},
doi = {10.1103/PhysRevD.96.083020},
journal = {Physical Review D},
number = 8,
volume = 96,
place = {United States},
year = 2017,
month =

Journal Article:
Free Publicly Available Full Text
This content will become publicly available on October 31, 2018
Publisher's Accepted Manuscript

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  • A balloon-borne instrument has measured the cosmic-ray antiproton flux between 130 and 320 MeV and searched for antihelium between 130 and 370 MeV per nuclear. These particles were selected from the background of normal-matter cosmic rays by combining a selective trigger with a detailed spark chamber visualization of each recorded event. Antiprotons are identified by their characteristic annihilatin radiation. Residue from background processes meeting the selection criteria is small. The observed 14 antiprotons yield a measured differential flux of 1.7 +- 0.5 x 10/sup -4/ antiprotons m/sup -2/ sr/sup -1/ s/sup -1/ MeV/sup -1/ at the top of the atmosphere.more » The corresponding antiproton/proton ratio is 2.2 +- 0.6 x 10/sup -4/,, only slightly smaller than the ratio observed by other experiments at higher energies. Thus the antiprotons have a spectral shape similar to the protons, at least down to about 100 MeV. The expected flux of these particles can be calculated under the assumption that they were created by collisions of high-energy cosmic rays with the interstellar gas. Calculations using the standard leaky box model for propagation in the Galaxy predict a flux two orders of magnitude smaller than observed. A small low-energy flux is predicted due to a kinematic suppression of the production of low-energy antiprotons. The discrepancy between calculatons and experiment may be evidence that cosmic-ray protons have passed through substantially more than 5 g cm/sup -2/ of material during their lifetime. In addition, the combined results from this experiment and previous ones may be evidence for stochastic, energy-changing processes in interstellar space which act upon the secondary antiprotons after their creation. The search for cosmic-ray antihelium sets a 95% confidence level upper limit on the He/H ratio of 2.2 x 10/sup -5/.« less
  • The Transantarctic Mountains extend over 4,000 kilometers between the Weddell and Ross seas and form the western boundary of the east antarctic craton. Within the mountain chain and in the Ellsworth Mountains in West Antarctica, Upper Proterozoic and Lower Paleozoic rocks crop out in isolated areas. From regional mapping and some detailed studies geologists have shown that generally these areas have similar geologic histories, but these studies also have indicated that differences in stratigraphy and structure exist. The study focuses on two sequences of conglomerate and sandstone, one in the central Transantarctic Mountains and the other in northern Victoria Land.more » The similarity in stratigraphy of the clastic sequences in these areas suggests that a genetic relationship may exist between the two geographically widespread areas. To improve the understanding of the tectonic and geologic history of rocks in these areas, the authors will analyze facies to establish the depositional settings, evaluate the sediment composition to ascertain the lithologies and ages of the source areas, determine ages of interbedded volcanic rocks, collect fossils from fine-grained sedimentary units to establish the age of deposition, and examine the relationship between the coarse-clastic sequences and underlying formations. From these data, he will try to determine if the tectonic setting that controlled the origin and distribution of the sequences later deformed them. If he can determine that there is a genetic relationship between the coarse-clastic rocks of the Bowers terrane and those in the central Transantarctic Mountains, these data will greatly modify scientific understanding of the lower Paleozoic development of the western continental margin of Antarctica and perhaps of Gondwana.« less