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Positrons bind with many molecules through Feshbach-resonant excitation of fundamental
vibrational modes which leads to greatly enhanced annihilation rates. However, recently new
resonances beyond the fundamental modes have been observed [1, 2]. In this talk, I will discuss
about these new resonances and the possible physical interpretations about them. Annihilation
resonances were identified by using a state-of-the-art cold positron beam, where the positron
temperature is about 6 times colder than the room temperature. The process of generating this
high-resolution (FWHM ∼ 22 meV) slow positron beam will also be discussed as the shape of
the energy resolved annihilation spectra are determined by the positron beam energy
distribution.
[1] S. Ghosh, J. R. Danielson, and C. M. Surko, Phys. Rev. Lett., 125, 173401 (2020).
[2] S. Ghosh, J. R. Danielson, and C. M. Surko, Phys. Rev. Lett., 129, 123401 (2022). |