# High Energy Physics Seminar

Wednesday, November 7, 2018
4:00pm to 5:00pm
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Lauritsen 469
Precision microwave spectroscopy of positronium fine structure
Alberto M. Alonso, University College London,

Positronium is the bound state of an electron and a positron [1]. In the ground state, positronium has a self-annihilation lifetime of 142~ns [2], however, it is possible to excite it to high-$n$ Rydberg states using nanosecond pulsed lasers before it decays [3]. These states have low annihilation rates and lifetimes in excess of 1$\mu$s [4,5]. In these longer-lived states precision spectroscopy and antimatter-gravity free-fall measurements are feasible [6].

In this seminar, I will show how pulses of positronium atoms can be produced and excited using lasers [3], and I will present results of precision microwave spectroscopy measurements of the $2\,^3\mathrm{S}_1\rightarrow2\,^3\mathrm{P}_2$ fine structure interval, which is sensitive to QED effects [6]. The excited $2\,^3\mathrm{S}_1$ states used in these experiments were initially populated by laser excitation to a mixed-$\ell$ state in the presence of an electric field, which was rapidly switched off [8,9].

References
[1] J. A. Wheeler. Ann. N. Y. Acad. Sci., 48, 219 (1946).
[2] A. Ore and J. L. Powell. Phys. Rev., 75, 1696 (1949).
[3] D. B. Cassidy, T. H. Hisakado, H. W. K. Tom, and A. P. Mills, Jr. Phys. Rev. Lett., 108, 043401 (2012).
[4] A. M. Alonso, B. S. Cooper, A. Deller, L. Gurung, S. D. Hogan, and D. B. Cassidy. Phys. Rev. A, 95, 053409 (2017).
[5] A. Deller, A. M. Alonso, B. S. Cooper, S. D. Hogan, and D. B. Cassidy. Phys. Rev. A, 93, 062513 (2016).
[6] A. P. Mills, Jr. and M. Leventhal. Nucl. Instrum. Meth. B, 192, 102 (2002).
[7] D. Hagena, R. Ley, D. Weil, G. Werth, W. Arnold, and H. Schneider. Phys. Rev. Lett., 71, 2887 (1993).
[8] A. M. Alonso, B. S. Cooper, A. Deller, S. D. Hogan, and D. B. Cassidy. Phys. Rev. Lett., 115, 183401 (2015).
[9] A. M. Alonso, S. D. Hogan, and D. B. Cassidy. Phys. Rev. A, 95, 033408 (2017).

For more information, please visit http://theory.caltech.edu/people/carol/seminar.html.

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