International Conference on Exotic Atoms and Related Topics - EXA2017

The ASACUSA collaboration at CERNs Antiproton Decelerator aims to measure the ground-state hyperfine splitting of antihydrogen using a spec- troscopy method as a means to test CPT symmetry. The Rabi-type setup consists of an antiproton accumulator, a positron source, and a mixing trap functioning as antihydrogen source and a spectroscopy apparatus made out of a microwave cavity and a superconduction sextupole magnet, terminating in a tracking detector [1]. In previous beamtimes, this detector was made up out of a central BGO crystal and two layers of scintillating bars parallel to the beam direction [2][3]. This setup allowed measurements of the point of annihilation and the energy deposited as well as the angle of escaping π-mesons. Moreover, as the bars are read out on both sides a coarse position resolution in beam direction was also achieveable using timing information. For 2017s beamtime the detector was modified to allow a more precise spatial resolution in the beam direction by incorporating two additional layers of scintillating fibers perpendicular to the existing scintillating bars. The additional layers provide a spatial resolution in the order of millimeter which allows for an efficient discrimination of cosmic background as well as advanced tracking of the products of annihilation reactions. This contri- bution covers the design and construction of this upgrade to ASACUSAs detector as well as the results of preliminary performance studies. [1] E. Widmann et al. “Measurement of the hyperfine structure of antihy- drogen in a beam”. In: (Jan. 2013). arXiv: 1301.4670v1. url: http: //arxiv.org/abs/1301.4670v1 (cit. on p. 1). [2] Y. Nagata et al. “The development of the antihydrogen beam detec- tor and the detection of the antihydrogen atoms for in-flight hyperfine spectroscopy”. In: Journal of Physics: Conference Series 635.2 (2015), p. 022061. url: http://stacks.iop.org/1742-6596/635/i=2/a= 022061 (cit. on p. 1). [3] C. Sauerzopf et al. “Annihilation detector for an in-beam spectroscopy apparatus to measure the ground state hyperfine splitting of antihy- drogen”. In: (June 2016). url: http://www.sciencedirect.com/ science/article/pii/S0168900216305630 (cit. on p. 1).