A determination of the backscattering probability of low-energy antiprotons
GBAR Collaboration, K. Park, E. Perez, P. Adrich, I. Belosevic, P. Cladé, M. Chung, P. Comini, P. Crivelli, P. Debu, A. Douillet, S. Geffroy, S. Guellati-Khelifa, P. Guichard, P. -A. Hervieux, L. Hilico, P. Indelicato, S. Jonsell, J. -P. Karr, B. Kim, S. Kim, E. -S. Kim, N. Kuroda, B. Lee, L. Liszkay, D. Lunney, G. Manfredi, B. Mansoulié, V. Martimort, M. Matusiak, V. Nesvizhevsky, F. Nez, N. Paul, P. Pérez, C. Regenfus, C. Roumegou, J. -Y. Roussé, F. Schmidt-Kaler, K. Szymczyk, T. A. Tanaka, B. Tuchming, D. -P. van der Werf, D. Won, S. Wronka, P. Yzombard
Abstract
It is commonly assumed that antiprotons impinging on a material surface annihilate promptly with the nuclei of the material. However, at kinetic energies of a few keV, this assumption may not hold. As with low-energy protons, electrons or positrons that can be reflected from a target, they may undergo large-angle Coulomb scattering before annihilation occurs, thereby appearing to be "backscattered" from the material surface. This backscattering fraction, largely unknown, is a crucial ingredient to the determination of the production cross-section of antihydrogen atoms in the GBAR experiment. This paper presents a determination of the probability that 4 and 6 keV antiprotons backscatter on the surface of a Micro-Channel Plate detector used for beam imaging at GBAR. No evidence for backscattering has been found and an upper limit of 14% at 68% confidence level has been set on this probability. The impact of backscattering on the determination of the number of antiprotons that participate in antihydrogen production in GBAR is also addressed.
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