Search for a feebly interacting particle X in the decay K+ → π+X
E. Cortina, A. Kleimenova, E. Minucci, S. Padolski, P. Petrov, A. Shaikhiev, R. Volpe, T. Numao, B. Velghe, D. Bryman, Jie Fu, T. Husek, J. Jerhot, Karol Kampf, M. Zamkovsky, R. Aliberti, G. Khoriauli, J. Kunze, D. Lomidze, R. Marchevski, L. Peruzzo, M. Vormstein, R. Wanke, P. Dalpiaz, M. Fiorini, I. Neri, A. Norton, F. Petrucci, H. D. Wahl, A. Cotta Ramusino, A. Gianoli, E. Iacopini, G. Latino, M. Lenti, A. Parenti, A. Bizzeti, F. Bucci, A. Antonelli, G. Georgiev, V. Kozhuharov, G. Lanfranchi, S. Martellotti, M. Moulson, T. Spadaro, F. Ambrosino, T. Capussela, M. Corvino, D. Di Filippo, P. Massarotti, M. Mirra, M. Napolitano, G. Saracino, G. Anzivino, F. Brizioli, E. Imbergamo, R. Lollini, R. Piandani, C. Santoni, M. Barbanera, P. Cenci, B. Checcucci, P. Lubrano, M. Lupi, M. Pepé, M. Piccini, F. Costantini, L. Di Lella, N. Doble, M. Giorgi, S. Giudici, G. Lamanna, E. Lari, E. Pedreschi, M. Sozzi, C. Cerri, R. Fantechi, L. Pontisso, F. Spinella, I. Mannelli, G. D’Agostini, M. Raggi, A. Biagioni, E. Leonardi, A. Lonardo, P. Valente, P. Vicini, Roberto Ammendola, Vincenzo Bonaiuto, A. Fucci, Á. Salamon, F. Sargeni, R. Arcidiacono, B. Bloch-Devaux, M. Boretto, E. Menichetti, E. Migliore, D. Soldi, C. Biino, A. Filippi, F. Marchetto
Abstract
A bstract A search for the K + → π + X decay, where X is a long-lived feebly interacting particle, is performed through an interpretation of the K + → $$ {\pi}^{+}\nu \overline{\nu} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mi>π</mml:mi> <mml:mo>+</mml:mo> </mml:msup> <mml:mi>ν</mml:mi> <mml:mover> <mml:mi>ν</mml:mi> <mml:mo>¯</mml:mo> </mml:mover> </mml:math> analysis of data collected in 2017 by the NA62 experiment at CERN. Two ranges of X masses, 0–110 MeV /c 2 and 154–260 MeV /c 2 , and lifetimes above 100 ps are considered. The limits set on the branching ratio, BR( K + → π + X ), are competitive with previously reported searches in the first mass range, and improve on current limits in the second mass range by more than an order of magnitude.