Measurements of the Cosmic-Ray Positron Fraction from 1 to 50 G[CLC]e[/CLC]V

Abstract

Two measurements of the cosmic-ray positron fraction as a function of energy have been made using the High Energy Antimatter Telescope (HEAT) balloon-borne instrument. The first flight took place from Ft. Sumner, New Mexico in 1994, and yielded results above the geomagnetic cutoff energy of 4.5 GeV. The second flight from Lynn Lake, Manitoba in 1995 permitted measurements over a larger energy interval, from 1 GeV to 50 GeV. In this letter we present results on the positron fraction based on data from the Lynn Lake flight, and compare these with the previously published results from the Ft. Sumner flight. The results confirm that the positron fraction does not increase with energy above ≈ 10 GeV, although a small excess above purely secondary production cannot be ruled out. At low energies the positron fraction is slightly larger than that reported from measurements made in the 1960's. This effect could possibly be a consequence of charge dependence in the level of solar modulation.

Leptonic dark matter annihilation in the evolving universe: constraints and implications

“…Especially the PAMELA data confirm the hint of excess of positron fraction previously discovered by HEAT [7,8] and AMS [9]. Many theoretical models have been proposed to explain these phenomena in past years, among which a class of leptonic dark matter (DM) annihilation models is of particular interest (e.g., [10,11] or see the review [12]).…”

Cosmic ray anomalies from the MSSM?

“…Also shown is the e + /(e + + e − ) spectrum for the benchmark model (red curve). Although we only fit to data from PAMELA [4] we include also data from HEAT [93,94], AMS01 [95], and CAPRICE94 [96], for comparison. small window of N e values yield a good fit to both data sets.…”

High-energy neutrino signatures of dark matter

“…A number of recent measurements of cosmic ray electrons and positrons have been interpreted as possible evidence for dark matter [1][2][3][4][5][6]. In particular, it has been suggested that the features of the e þ e À spectrum and positron fraction reported by PAMELA [1], ATIC [2], PPB-BETS [3], the Fermi Gamma Ray Space Telescope (FGST) [4], HEAT [5], and AMS-01 [6] may originate from either DM annihilations [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21] or decays [22][23][24][25][26][27] taking place in the Galactic Halo.…”

“…Furthermore, decays or annihilations directly into e þ e À final states are disfavored by the observed spectra, requiring instead muon or tau final states. It has been shown that dark matter with a mass $10 [2][3][4][5] GeV that annihilates/decays into À þ , À þ , or À þ À þ can reproduce the observed cosmic ray features [11]. This results in copious production of neutrinos as the heavy leptons decays.…”