Further evidence for low-energy protonium production in vacuum

E. Lodi Rizzini; L. Venturelli; N. Zurlo; M. Charlton; C. Amsler; G. Bonomi; C. Canali; C. Carraro; A. Fontana; P. Genova; R. Hayano; L. V. Jørgensen; A. Kellerbauer; V. Lagomarsino; R. Landua; M. Macrí; G. Manuzio; P. Montagna; C. Regenfus; A. Rotondi; G. Testera; A. Variola; D. P. van der Werf

doi:10.1140/epjp/i2012-12124-9

EPJ

Further evidence for low-energy protonium production in vacuum

E. Lodi Rizzini¹^,2, L. Venturelli¹^,2, N. Zurlo¹^,2, M. Charlton³, C. Amsler⁴^,a, G. Bonomi⁵^,6, C. Canali⁴, C. Carraro⁷^,8, A. Fontana⁶, P. Genova⁶^,9, R. Hayano¹⁰, L. V. Jørgensen³^,b, A. Kellerbauer¹¹^,c, V. Lagomarsino⁷^,8, R. Landua¹¹, M. Macrí⁷, G. Manuzio⁷^,8, P. Montagna⁶^,9, C. Regenfus⁴, A. Rotondi⁶^,9, G. Testera⁷, A. Variola⁷^,d and D. P. van der Werf³

¹ Dipartimento di Chimica e Fisica per l’Ingegneria e per i Materiali, Università di Brescia, 25133, Brescia, Italy
² Istituto Nazionale di Fisica Nucleare, Gruppo Collegato di Brescia, 25133, Brescia, Italy
³ Department of Physics, College of Science, Swansea University, Singleton Park, SA2 8PP, Swansea, UK
⁴ Physik-Institut, Zürich University, 8057, Zürich, Switzerland
⁵ Dipartimento di Ingegneria Meccanica, Università di Brescia, 25123, Brescia, Italy
⁶ Istituto Nazionale di Fisica Nucleare, Sezione di Pavia, 27100, Pavia, Italy
⁷ Istituto Nazionale di Fisica Nucleare, Sezione di Genova, 16146, Genova, Italy
⁸ Dipartimento di Fisica, Università di Genova, 16146, Genova, Italy
⁹ Dipartimento di Fisica Nucleare e Teorica, Università di Pavia, 27100, Pavia, Italy
¹⁰ Department of Physics, University of Tokyo, 113-0033, Tokyo, Japan
¹¹ Physics Department, CERN, 1211, Geneva 23, Switzerland

Received: 3 September 2012
Revised: 20 September 2012
Accepted: 20 September 2012
Published online: 10 October 2012

Abstract

We describe an experiment performed in the ATHENA apparatus in which there is evidence that the antiproton-proton bound state, protonium, has been produced at very low energies in vacuum following the interaction of cold antiprotons with a trapped cloud of molecular hydrogen ions. The latter were confined in a centrifugally separated belt outside a positron plasma used for antihydrogen formation. Studies have been performed at low positron plasma temperatures in which the protonium annihilation signal has been identified along with that from antihydrogen, and we discuss how their contributions can be disentangled. With the positron plasma heated to around 10000 K the ions become distributed in the positrons, and the majority of the annihilation signal can be explained in terms of protonium formation, as antihydrogen creation is heavily suppressed. In this case we compare the observed protonium formation rate with expectations from theory and find reasonable accord, when experimental systematics are taken into account. The effect on the annihilation signals of the passage of an electron current through a pre-loaded positron plasma has been studied in detail, and the results are presented here for the first time.

Present address: Albert Einstein Center for Fundamental Physics, University of Bern, 3012, Bern, Switzerland

Present address: BE-Department, CERN, 1211, Geneva 23, Switzerland

Present address: Max Planck Institute for Nuclear Physics, Saupfercheckweg 1, 69117, Heidelberg, Germany

Present address: L.A.L. (Laboratoire de l’Accélérateur Linéaire), Université Paris-Sud, Bâtiment 209a, F-91898, Orsay Cedex, France

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EPJ

Further evidence for low-energy protonium production in vacuum

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