Hunting down the X17 boson at the CERN SPS

NA64 Collaboration; E Depero; Yu M Andreev; D Banerjee; J Bernhard; V E Burtsev; N Charitonidis; A G Chumakov; D Cooke; P Crivelli; A V Dermenev; S V Donskov; R R Dusaev; T Enik; A Feshchenko; V N Frolov; A Gardikiotis; S G Gerassimov; S Girod; S N Gninenko; M Hösgen; V A Kachanov; A E Karneyeu; G Kekelidze; B Ketzer; D V Kirpichnikov; M M Kirsanov; V N Kolosov; I V Konorov; S G Kovalenko; V A Kramarenko; L V Kravchuk; N V Krasnikov; S V Kuleshov; V E Lyubovitskij; V Lysan; V A Matveev; Yu V Mikhailov; L Molina Bueno; D V Peshekhonov; V A Polyakov; B Radics; R Rojas; A Rubbia; V D Samoylenko; D Shchukin; H Sieber; V O Tikhomirov; vI Tlisova; D A Tlisov; A N Toropin; A Yu Trifonov; B I Vasilishin; G Vasquez Arenas; P V Volkov; V Yu Volkov; P Ulloa

doi:10.1140/epjc/s10052-020-08725-x

Hunting down the X17 boson at the CERN SPS

Eur Phys J C Part Fields. 2020;80(12):1159. doi: 10.1140/epjc/s10052-020-08725-x. Epub 2020 Dec 15.

Authors

NA64 Collaboration; E Depero¹, Yu M Andreev², D Banerjee^{3

4}, J Bernhard³, V E Burtsev⁵, N Charitonidis³, A G Chumakov⁶, D Cooke⁷, P Crivelli¹, A V Dermenev², S V Donskov⁸, R R Dusaev⁹, T Enik⁵, A Feshchenko⁵, V N Frolov⁵, A Gardikiotis¹⁰, S G Gerassimov^{11

12}, S Girod³, S N Gninenko², M Hösgen¹³, V A Kachanov⁸, A E Karneyeu², G Kekelidze⁵, B Ketzer¹³, D V Kirpichnikov², M M Kirsanov², V N Kolosov⁸, I V Konorov^{11

12}, S G Kovalenko¹⁴, V A Kramarenko^{5

15}, L V Kravchuk², N V Krasnikov^{2

5}, S V Kuleshov¹⁴, V E Lyubovitskij^{6

16}, V Lysan⁵, V A Matveev⁵, Yu V Mikhailov⁸, L Molina Bueno¹, D V Peshekhonov⁵, V A Polyakov⁸, B Radics¹, R Rojas¹⁶, A Rubbia¹, V D Samoylenko⁸, D Shchukin¹², H Sieber¹, V O Tikhomirov¹², vI Tlisova², D A Tlisov², A N Toropin², A Yu Trifonov⁶, B I Vasilishin⁹, G Vasquez Arenas¹⁶, P V Volkov^{5

15}, V Yu Volkov¹⁵, P Ulloa¹⁴

Affiliations

¹ ETH Zürich Institute for Particle Physics and Astrophysics, 8093 Zurich, Switzerland.
² Institute for Nuclear Research, 117312 Moscow, Russia.
³ CERN, EN-EA, 1211 Geneva 23, Switzerland.
⁴ University of Illinois at Urbana Champaign, Urbana, IL 61801-3080 USA.
⁵ Joint Institute for Nuclear Research, 141980 Dubna, Russia.
⁶ Tomsk State Pedagogical University, 634061 Tomsk, Russia.
⁷ UCL Department of Physics and Astronomy, University College London, Gower St., London, WC1E 6BT UK.
⁸ State Scientific Center of the Russian Federation Institute for High Energy Physics of National Research Center 'Kurchatov Institute' (IHEP), 142281 Protvino, Russia.
⁹ Tomsk Polytechnic University, 634050 Tomsk, Russia.
¹⁰ Physics Department, University of Patras, 265 04 Patras, Greece.
¹¹ Physik Department, Technische Universität München, 85748 Garching, Germany.
¹² P.N. Lebedev Physical Institute, 119 991 Moscow, Russia.
¹³ Universität Bonn, Helmholtz-Institut für Strahlen-und Kernphysik, 53115 Bonn, Germany.
¹⁴ Departamento de Ciencias Físicas, Universidad Andres Bello, Sazié 2212, Piso 7, Santiago, Chile.
¹⁵ Skobeltsyn Institute of Nuclear Physics, Lomonosov Moscow State University, 119991 Moscow, Russia.
¹⁶ Universidad Técnica Federico Santa María, 2390123 Valparaiso, Chile.

Abstract

Recently, the ATOMKI experiment has reported new evidence for the excess of $e^{+} e^{-}$ events with a mass $\sim$ 17 MeV in the nuclear transitions of $^{4}$ He, that they previously observed in measurements with $^{8}$ Be. These observations could be explained by the existence of a new vector $X 17$ boson. So far, the search for the decay $X 17 \to e^{+} e^{-}$ with the NA64 experiment at the CERN SPS gave negative results. Here, we present a new technique that could be implemented in NA64 aiming to improve the sensitivity and to cover the remaining $X 17$ parameter space. If a signal-like event is detected, an unambiguous observation is achieved by reconstructing the invariant mass of the $X 17$ decay with the proposed method. To reach this goal an optimization of the $X 17$ production target, as well as an efficient and accurate reconstruction of two close decay tracks, is required. A dedicated analysis of the available experimental data making use of the trackers information is presented. This method provides independent confirmation of the NA64 published results [1], validating the tracking procedure. The detailed Monte Carlo study of the proposed setup and the background estimate show that the goal of the proposed search is feasible.