Performance measurement of HARPO: a Time Projection Chamber as a gamma-ray telescope and polarimeter

Abstract

We analyse the performance of a gas time projection chamber (TPC) as a high-performance gamma-ray telescope and polarimeter in the e${}^{+}$e${}^{-}$ pair creation regime. We use data collected at a gamma-ray beam of known polarisation. The TPC provides two orthogonal projections $(x,z)$ and $(y,z)$ of the tracks induced by each conversion in the gas volume. We use a simple vertex finder in which vertices and pseudo-tracks exiting from them are identified. We study the various contributions to the single-photon angular resolution using Monte Carlo simulations and compare them with the experimental data and find that they are in excellent agreement. The distribution of the azimutal angle of pair conversions shows a bias due to the non-cylindrical-symmetric structure of the detector. This bias would average out for a long duration exposure on a space mission, but for this pencil-beam characterisation we have ensured its accurate simulation by a double systematics control scheme, data taking with the detector rotated at several angles with respect to the beam polarisation direction and systematics control with a non-polarised beam. We measure, for the first time, the polarisation asymmetry of a linearly polarised gamma-ray beam in the low energy pair creation regime. This sub-GeV energy range is critical for cosmic sources as their spectra are power laws which fall quickly as a function of increasing energy. This work could pave the way to extending polarised gamma-ray astronomy beyond the MeV energy regime.

Submitted to Astroparticle Physics

References in corpus (5)

• Theoretical and simulation studies of characteristics of a Compton light source
• Study in a beam test of the resolution of a Micromegas TPC with standard readout pads
• $\gamma$-ray polarimetry with conversions to $e^{+}{e}^{-}$ pairs: polarization asymmetry and the way to measure it
• gamma-ray telescopes using conversions to electron-positron pairs: event generators, angular resolution and polarimetry
• Charged particle tracking without magnetic field: optimal measurement of track momentum by a Bayesian analysis of the multiple measurements of deflections due to multiple scattering

Cited by in corpus (14)

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• Spatial profiles of collimated laser Compton-scattering $\gamma$-ray beams
• Observable spectral and angular distributions of $\gamma$-rays from extragalactic ultrahigh energy cosmic ray accelerators: the case of extreme TeV blazars
• Signal identification with Kalman Filter towards background-free neutrinoless double beta decay searches in gaseous detectors
• Gamma-Ray Polarimetry
• Time projection chambers for gamma-ray astronomy
• MeV-GeV Polarimetry with $\gamma \to e^{+}{e}^{-}$: Asserting the Performance of Silicon Strip Detectors-Based Telescopes
• Exploring non-thermal emission from the star-forming region NGC 3603 through a realistic modelling of its environment
• A 5D, polarised, Bethe-Heitler event generator for $\gamma \to {\mu }^{+}{\mu }^{-}$ conversion
• Calorimeter-less gamma-ray telescopes: Optimal measurement of charged particle momentum from multiple scattering by Bayesian analysis of Kalman filtering innovations
• Linear Polarimetry with $\gamma \to e^{+}{e}^{-}$ conversions
• Pair Production Detectors for Gamma-ray Astrophysics