Kaon Tagging at 0° Scattering Angle for High-Resolution Decay-Pion Spectroscopy

¹ Institut für Kernphysik, Johannes Gutenberg-Universität, 55099 Mainz, Germany
² Department of Physics, Tohoku University, Sendai 980-8578, Japan
³ GSI Helmholtz Centre for Heavy Ion Research, 64291 Darmstadt, Germany
⁴ Department of Physics, University of Zagreb, Croatia
⁵ University of Ljubljana and “Josef Stefan” Institut, 1000 Ljubljana, Slovenia
⁶ Yerevan Physics Institute, 375036 Yerevan, Armenia
⁷ PRISMA Cluster of Excellence, Johannes Gutenberg-Universität, 55099 Mainz, Germany
⁸ Helmholtz Institut Mainz, 55099 Mainz, Germany
⁹ Department of Physics, Florida International University, Miami, FL 33174, USA
¹⁰ Department of Physics, Hampton University, VA 23668, USA

^a e-mail: aesser@kph.uni-mainz.de

Published online: 20 March 2014

Abstract

At the Mainz Microtron hypernuclei can be studied by (e,e’K) reactions. By detecting the kaon which is emitted in forward direction, with the KAOS spectrometer placed at 0° scattering angle, reactions involving open strangeness production are tagged. High-resolution magnetic spectrometers are then used to coincidentally detect the monoenergetic decay-pions from mesonic two-body weak decays of light hypernuclei at rest.

As a pioneering experiment has confirmed, the KAOS spectrometer is exposed to a large flux of background particles, mostly positrons from bremsstrahlung pair production. In order to increase the effciency of kaon identification the KAOS spectrometer was modified to suppress background particles at the cost of a high momentum resolution, which is less important for this experiment. This was achieved by placing up to 14 cm of lead absorbers in front of the detectors, in which positrons are blocked by forming electromagnetic showers while the effect on kaons is limited. An additional time-of-flight wall and a new threshold Čerenkov detector help to increase the detection effciency of kaons.