Title: Geminga周围介质性质及对宇宙线正电子超出的影响

　　Speaker: 毕效军 (Institute of High Energy Physics)

　　Time: 3:00 pm, April 11 (Thursday)

　　Location: Lecture Hall, 3rd floor

　　Abstract: In the last 10 years the most important achievement in cosmic ray physics is the discovery of positron excess above ~10GeV, which has simulated a lot of interests as it may be related with signals from dark matter. Later study shows the positron excess favors its origin as nearby pulsars rather than dark matter. However, recent HAWC observation of ~100TeV γ-ray halo around pulsars Geminga and Monogem indicates a very slow diffusion of cosmic rays around these sources that results in a tiny contribution of positrons from these two pulsars to the local ?ux. This makes the cosmic positron excess anomaly observed by PAMELA and AMS-02 even more puzzling. We have proposed a two-zone diffusion model in which positron excess can be naturally explained with parameters even more reasonable than those in the conventional scenario. We further discuss the possible origin of such slow diffusion region, which may be universal phenomena around cosmic ray sources.