The Antihydrogen Detector

The main task of the antihydrogen detector is to discriminate antihydrogen (i.e. antiproton) annihilations from cosmic rays. The detector is composed of a central BGO (bismuth germanate) crystal which measures the energy deposited by the antiproton annihilation products. The latter (mainly pions) are tracked by a surrounding detector made of two layers of each 8 x 4 plastic scintillator bars along the beam direction, arranged octagonally. The light guides glued on both ends of the bars are connected to pairs of silicon photomultipliers (for details see [1]). The detector was recently equipped with scintillating fibers wound perpendicularly around the bars to also provide the longitudinal track coordinates.

The BGO detector is a 5mm thin disk put vertically in the UHV, pushed against a CF Viewport and read out outside the vacuum with quadruple 8x8 channel Multianode (MA) PMTs. The energy deposit in the BGO is one of the most important features.


                      



The hodoscope (left [1]) and BGO crystal detector setup [4].

The BGO is covered on the upstream side with a thin carbon layer to avoid light loss. The position resolution originates from the very large refractive index of the BGO that makes light escape only in a narrow cone. The readout is made with  2 inch 8x8 multianode PMT (Hamamatsu 9500) with pixel sizes of 2.8 x 2.8 mm:

Left: drawing showing the position sensitivity of the scintillation light. The light emitted from A passes through the scintillator surface  when the incident angle is less than θc.
Right: setup to study the position sensitivity of the BGO scintillator  [4].

With a thickness of 5 mm and a critical angle of 27o, the maximum diameter of the light spot on the surface is 5 mm. The light is then traversing several boundaries (BGO-vacuum, vacuum-viewport, viewport - air, air - PMT) hence the spot on the PMT is larger, about 12 mm FWHM [4].

Full details can be found in various theses (see below) and in refs. [1]-[5]. Using a machine learning approach, ref. [6] describes the best performances achieved. 

Bibliography



Hodoscope:

 [1] C. Sauerzopf, A. A. Capon, M. Diermaier, M. Fleck, B. Kolbinger, C. Malbrunot, O. Massiczek,
M. C. Simon, S. Vamosi, J. Zmeskal and E. Widmann, 

Annihilation detector for an in-beam spectroscopy apparatus to measure the ground state hyperfine splitting of antihydrogen,

Nuclear Instruments and Methods in Physics Research Section A845 (2016) 579.

doi: 10.1016/j.nima.2016.06.023


[2] C. Sauerzopf, L. Gruber, K. Suzuki, J. Zmeskal and E. Widmann, 

Intelligent Front-end Electronics for Silicon photodetectors (IFES),

Nuclear Instruments and Methods in Physics Research Section A 819 (2016) 163.

doi: 10.1016/j.nima.2016.02.098

BGO:

 [3] Y. Nagata, N. Kuroda, B. Kolbinger, M. Fleck, C. Malbrunot, V. Mäckel, C. Sauerzopf, M.C. Simon, M. Tajima, J. Zmeskal, H. Breuker, H. Higaki, Y. Kanai, Y. Matsuda, S. Ulmer, L. Venturelli, E. Widmann, Y. Yamazaki,

Monte-Carlo based performance assessment of ASACUSA’s antihydrogen detector,

Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 910 (2018) 90.

https://doi.org/10.1016/j.nima.2018.09.013

[4] Nagata, Y.; Kuroda, N.; Sauerzopf, C.; Kolbinger, B.; Malbrunot, C.; Capon, A. A.; Dupre, P.; Radics, B.; Tajima, M.; Kaga, C.; Leali, M.; Lodi Rizzini, E.; Mascagna, V.; Massiczek, O.; Matsudate, T.;
Simon, M. C.; Breuker, H.; Higaki, H.; Kanai, Y.; Matsuda, Y.; Venturelli, L.; Widmann, E. &
Yamazaki, Y.

The Development of the Antihydrogen Beam Detector: Toward the Three Dimensional Tracking with a BGO Crystal and a Hodoscope,

JPS Conference Proceedings, Journal of the Physical Society of Japan 18 (2017) 011038.
doi 10.7566/JPSCP.18.011038

[5] Y. Nagata, C. Sauerzopf, A. Capon, N. Kuroda, Y. Abo, M. Diermaier, P. Dupre, Y. Higashi, S. Ishikawa, C. Kaga, M. Leali, C. Malbrunot, V. Mascagna, D. Murtagh, B. Radics, M. C .Simon, M. Tajima, H. A. Torii, S. Van Gorp, J. Zmeskal, H. Breuker, H. Higaki, Y. Kanai, Y. Matsuda, S. Ulmer, L. Venturelli, E. Widmann, Y. Yamazaki

The development of the antihydrogen beam detector, the detection of the antihydrogen atoms for in-flight hyperfine spectroscopy.

Journal of Physics: Conference Series 635 (2015)
 022061.
doi: 10.1088/1742-6596/635/2/022061


[6] B. Kolbinger, C. Amsler, S. Arguedas Cuendis, H. Breuker, A. Capon, G. Costantini, P. Dupré, M. Fleck, A. Gligorova, H. Higaki, Y. Kanai, V. Kletzl, N. Kuroda, A. Lanz, M. Leali, V. Mäckel, C. Malbrunot, V. Mascagna, O. Massiczek, Y. Matsuda, D.J. Murtagh, Y. Nagata, A. Nanda, L. Nowak, B. Radics, C. Sauerzopf, M.C. Simon, M. Tajima, H.A. Torii, U. Uggerhøj, S. Ulmer, L. Venturelli, A. Weiser, M. Wiesinger, E. Widmann, T. Wolz, Y. Yamazaki, J. Zmeskal,
Measurement of the Principal Quantum Number Distribution in a Beam of Antihydrogen Atoms,
Eur. Phys. J. D75 (2021) 91