Aug 21 – 25, 2017
University of Washington, Seattle
US/Pacific timezone

Machine Learning for Antihydrogen Detection at ALPHA

Aug 24, 2017, 5:30 PM
107 (Alder Hall)


Alder Hall

Oral Track 2: Data Analysis - Algorithms and Tools Track 2: Data Analysis - Algorithms and Tools


Andrea Capra (TRIUMF (CA))


The ALPHA experiment at CERN is designed to produce, trap and study antihydrogen, which is the antimatter counterpart of the hydrogen atom. Since hydrogen is one of the best studied physical system, both theoretically and experimentally, experiments on antihydrogen permit a precise direct comparison between matter and antimatter. Our basic technique consists of driving an antihydrogen resonance which will cause the antiatom to leave our trap and annihilate. This resonant frequency can be compared with its corresponding value in hydrogen. The antihydrogen annihilation location, called the vertex, is determined by reconstructing the trajectories of the annihilation products and by finding the point where they pass closest to each other. The main background to antihydrogen detection is due to cosmic rays. When an experimental cycle extends for several minutes, while the number of trapped antihydrogen remains fixed, background rejection can become challenging. The use of ``cuts-based'' analysis is often not sufficient to reach the target statistical significance. Machine learning methods have been employed in ALPHA for several years, leading to a dramatic reduction of the background contamination. Thanks to these techniques, the ALPHA collaboration observed for the first time a transition between Zeeman levels of the antihydrogen ground state [1], placed the most stringent upper limit to the antihydrogen electric charge [2], and performed the first laser spectroscopy experiment [3]. These results will be presented along with the optimization of the analysis methods employed in these measurements.

[1] C. Amole et al., Nature 483, 439-443 (2012)

[2] M. Ahmadi et al., Nature 529, 373-376 (2016)

[3] M. Ahmadi et al., Nature 541, 506-510 (2017)

Primary authors

Andrea Capra (TRIUMF (CA)) Mostafa Ahmadi (University of Liverpool (GB)) Bruno Ximenez Rodrigues Alves (Aarhus University (DK)) Marcelo Baquero Ruiz (University of California Berkeley (US)) William Alan Bertsche (University of Manchester (GB)) Eoin Butler (Imperial College (GB)) Celeste Carruth (University of California Berkeley (US)) Claudio Lenz Cesar (Federal University of of Rio de Janeiro (BR)) Michael Charlton (Swansea University) Snir Cohen (At.En. Comm., Nucl. Res. Cen. Negev (IL)) Robert Andrew Collister (TRIUMF (CA)) Stefan Eriksson (Swansea University (GB)) Andrew Evans (University of Calgary Dep. of Phys. and Astronomy (CA)) Nathan Andrew Evetts (TRIUMF (CA)) Joel Fajans (University of California Berkeley (US)) Tim Friesen (Aarhus University (DK)) Makoto C. Fujiwara (TRIUMF (CA)) David Russell Gill (TRIUMF (CA)) Andrea Gutierrez (TRIUMF (CA)) Jeffrey Scott Hangst (Aarhus University (DK)) Walter Hardy (TRIUMF (CA)) Mike Hayden (Simon Fraser University (CA)) Aled Isaac (Swansea University (GB)) Akira Ishida (University of Tokyo (JP)) Mark Andrew Johnson (University of Manchester (GB)) Steven Armstrong Jones (Swansea University (GB)) Svante Jonsell (Stockholm University (SE)) Leonid Kurchaninov (TRIUMF (CA)) Niels Madsen (Swansea University (GB)) Melissa Rae Mathers (York University (CA)) Daniel Thomas Maxwell (Swansea University (GB)) Joseph Mc Kenna (TRIUMF (CA)) Scott Menary (TRIUMF (CA)) Juan Mario Michan (TRIUMF (CA)) Takamasa Momose (University of British Columbia) Justine Joyce Munich (Simon Fraser University (CA)) Paul Nolan (University of Liverpool) Konstantin Olchanski (TRIUMF (CA)) Art Olin (TRIUMF (CA)) Petteri Pusa (University of Liverpool (GB)) Chris Rasmussen (Aarhus University (DK)) Francis Robicheaux (Purdue University (US)) Rodrigo Lage Sacramento (Federal University of of Rio de Janeiro (BR)) Muhammed Sameed (Swansea University (GB)) Elazar Sarid (At.En. Comm., Nucl. Res. Cen. Negev (IL)) Daniel De Miranda Silveira (Federal University of of Rio de Janeiro (BR)) Simone Stracka (Universita & INFN, Pisa (IT)) Chukman So (University of Calgary (CA)) Graham Stutter (Aarhus University (DK)) Tim Tharp (Aarhus University (DK)) James Edward Thompson (York University (CA)) Robert Thompson (University of Calgary Dep. of Phys. and Astronomy (CA)) Prof. Dirk Peter Van Der Werf (Swansea University (GB)) Jonathan Syrkin Wurtele (University of California Berkeley (US))

Presentation materials

Peer reviewing