HARPO, prototype of a gamma-ray polarimeter: Results of a polarised photon beam test between 1.7 and 74 MeV

David Attié, S. Amano, P. Baron, D. Bauduin, D. Bernard, P. Bruel, D. Calvet, P. Colas, S. Daté, A. Delbart, M. Frotin, Y. Geerebaert, B. Giebels, D. Götz, P. Gros, S. Hashimoto, D. Horan, T. Kotaka, M. Louzir, F. MagnietteY. Minamiyama, S. Miyamoto, H. Ohkuma, P. Poilleux, I. Semeniouk, P. Sizun, A. Takemoto, M. Yamaguchi, R. Yonamine, S. Wang

Research output: Contribution to journalConference articlepeer-review


Access to the photon polarisation in the 1-100 MeV energy range is a challenge for the next generation of space telescopes. The current telescopes in space are almost blind in this energy range, mainly due to the degradation of the angular resolution of e+e-pair and due to elastic scattering in the matter. Pair-conversion detector technologies as gaseous detectors are a promising alternative to the technologies based on tungsten-converter/thin-sensitive-layer stacks such as COS-B/EGRET/Fermi-LAT, firstly to improve the single-photon angular resolution and secondly for the polarisation information. The use of a time projection chamber (TPC) as a target and a tracking detector will improve by up to one order of magnitude the single-photon angular resolution (0.5°@100 MeV) with respect to the Fermi-LAT (5°@100 MeV), and by up to a factor of three with respect to what can be expected for silicon detectors (1.0-1.5°@100 MeV). With such a good angular resolution, a TPC can close the sensitivity gap at the level of 10-6 MeV/cm2.s) between 3 and 300 MeV despite having e lower sensitive mass. Furthermore, this good single-track angular resolution allows us to measure the linear polarisation fraction. The HARPO (Hermetic ARgon POlarimeter) detector prototype that we built is a high pressure (0.5-4 bar) low pile-up and low-diffusion gas detector. We will present the results of its high-statistics characterisation in the 1.7-74 MeV fully-polarised and non-polarised gamma-ray beam provided by the BL01 line at NewSUBARU. The excellent value of the polarisation asymmetry dilution factor that we measured opens the possibility of having a polarimeter in space working in the MeV-GeV energy range. In conclusion, we will present the design of a balloon-flight prototype ST3G (Self-Triggered Time projection chamber as a Gamma-ray Telescope) which is being developed. We will discuss its expected performance.

Original languageEnglish
JournalProceedings of Science
Publication statusPublished - 2017
Externally publishedYes
Event35th International Cosmic Ray Conference, ICRC 2017 - Bexco, Busan, Korea, Republic of
Duration: 2017 Jul 102017 Jul 20

ASJC Scopus subject areas

  • General


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