Eur. Phys. J. A (2014) 50: 91
https://doi.org/10.1140/epja/i2014-14091-0

Letter

L-series X-ray yields of kaonic ³He and ⁴He atoms in gaseous targets

¹ INFN, Laboratori Nazionali di Frascati, Via E. Fermi 40, C.P. 13, I-00044, Frascati, Italy
² Department of Physics and Astronomy, University of Victoria, STN CNC, P.O. Box 1700, BC V8W 2Y2, Victoria, Canada
³ Stefan-Meyer-Institut für subatomare Physik, Boltzmanngasse 3, 1090, Wien, Austria
⁴ IFIN-HH, Institutul National pentru Fizica si Inginerie Nucleara Horia Hulubei, Reactorului 30, Magurele, Romania
⁵ Dipartimento di Elettronica, Informazione e Bioingegneria, Politecnico di Milano, Milano, Italy
⁶ INFN, Sezione di Milano, Milano, Italy
⁷ INFN, Sezione di Roma I and Instituto Superiore di Sanità, I-00161, Roma, Italy
⁸ University of Tokyo, 7-3-1, Hongo, Bunkyo-ku, Tokyo, Japan
⁹ Institute of Physical and Chemical Research, RIKEN, 2-1 Hirosawa, Wako, 351-0198, Saitama, Japan
¹⁰ Excellence Cluster Universe, Technische Universität München, Boltzmannstraße 2, D-85748, Garching, Germany
¹¹ Universidade de Santiago de Compostela, Casas Reais 8, 15782, Santiago de Compostela, Spain

^* e-mail: tomoichi.ishiwatari@assoc.oeaw.ac.at

Received: 20 February 2014
Revised: 25 April 2014
Accepted: 15 May 2014
Published online: 28 May 2014

Abstract

The SIDDHARTA experiment measured X-rays from kaonic helium atoms using, for the first time, gaseous ³He and ⁴He targets. Clear patterns of the L-series X-rays of kaonic ³He and ⁴He atoms were observed. By using accurate Monte Carlo simulations, the absolute yields of these X-ray transitions were determined to be Y(3d → 2p) = 25.0 _−5.8 ^+6.7 % for ³He (0.96 g/l), Y(3d → 2p) = 23.1 _−4.2 ^+6.0 % for ⁴He (1.65 g/l), and Y(3d → 2p) = 17.2 _−9.5 ^+2.6 % for ⁴He (2.15g/l). In addition, the yields Y (nd → 2p), with n > 3 were also determined. The measured yields provide valuable information for understanding the cascade processes of kaonic helium atoms as a function of the target density.