Detection of low energy antimatter with emulsions

Abstract

Emulsion detectors feature a very high position resolution and consequently represent an ideal device when particle detection is required at the micrometric scale. This is the case of quantum interferometry studies with antimatter, where micrometric fringes have to be measured. In this framework, we designed and realized a new emulsion based detector characterized by a gel enriched in terms of silver bromide crystal contents poured on a glass plate. We tested the sensitivity of such a detector to low energy positrons in the range 10-20 keV. The obtained results prove that nuclear emulsions are highly efficient at detecting positrons at these energies. This achievement paves the way to perform matter-wave interferometry with positrons using this technology.

First demonstration of antimatter wave interferometry

“…This result is the first step in the QUPLAS (QUantum interferometry with Positrons and LASers) program ( 21 , 23 , 24 , 35 ) and paves the way not only to interferometric studies on neutral antimatter systems such as positronium, muonium, or antihydrogen but also to the measurement of their gravitational acceleration in the field of Earth. The technique we demonstrated is able to cope with the poor coherence and low intensity of realistic antimatter beams.…”

“…A monochromatic and continuous beam is thus formed with an energy spread less than 0.1%, limited by the stability of the power supplies. The positron rate is (5 ± 1) × 10 3 e + /s, and beam focusing can be tuned to reach a spot size of the order of several millimeters of full width at half maximum (FWHM), an approximately Gaussian intensity profile ( 23 ) and an angular divergence at the level of a few milliradians ( 24 ). A suitable model ( 25 ) of grating-based interferometry with a partially coherent beam exploits the analogy with Gaussian Schell-model beams of classical optics (Materials and Methods).…”

“…To ensure uniform working conditions throughout the explored energy range, we used nuclear emulsions prepared without the standard surface protective gelatin layer. The presence of even a micrometric layer would have introduced detection efficiency ( 23 ) and positron trajectory smearing ( 24 ) that are both energy dependent. Thermally induced grains are the dominant source of background noise in emulsion detectors.…”

“…Exposure times between 120 and 200 hours were required to accumulate sufficient statistics (about 2 × 10 7 grains in the analysis region). These time intervals were selected to match the total counts under the 511 keV annihilation peak on the calibrated HpGe detector ( 23 ) measured at 14 keV. Beam focusing was tuned to ensure that beam spot size, and hence the geometrical features of the beam such as angular divergence, did not appreciably vary with the energy.…”

First Demonstration of Antimatter Quantum Interferometry

“…suitable for anti-electrons (positrons) in the 5-18 keV energy range. This development is part of the QUPLAS (QUantum interferometry and gravitation with Positrons and LASers) research program[17][18][19][20] . Sketch of the setup: the beam, prepared by two 2-mm-wide collimators, reaches the gratings and the emulsion detector.…”