Examinando por Autor "Kovalenko S.G."

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    Hunting down the X17 boson at the CERN SPS
    (Springer Science and Business Media Deutschland GmbH, 2020-12) Depero E.; Andreev Y.M.; Banerjee D.; Bernhard J.; Burtsev V.E.; Charitonidis N.; Chumakov A.G.; Cooke D.; Crivelli P.; Dermenev A.V.; Donskov S.V.; Dusaev R.R.; Enik T.; Feshchenko A.; Frolov V.N.; Gardikiotis A.; Gerassimov S.G.; Girod S.; Gninenko S.N.; Hösgen M.; Kachanov V.A.; Karneyeu A.E.; Kekelidze G.; Ketzer B.; Kirpichnikov D.V.; Kirsanov M.M.; Kolosov V.N.; Konorov I.V.; Kovalenko S.G.; Kramarenko V.A.; Kravchuk L.V.; Krasnikov N.V.; Kuleshov S.V.; Lyubovitskij V.E.; Lysan V.; Matveev V.A.; Mikhailov Y.V.; Bueno L.M.; Peshekhonov D.V.; Polyakov V.A.; Radics B.; Rojas R.; Rubbia A.; Samoylenko V.D.; Shchukin D.; Sieber H.; Tikhomirov V.O.; Tlisova I.; Tlisov D.A.; Toropin A.N.; Trifonov A.Y.; Vasilishin B.I.; Arenas G.V.; Volkov P.V.; Volkov V.Y.; Ulloa P.; NA64 Collaboration
    Recently, the ATOMKI experiment has reported new evidence for the excess of e+e- events with a mass ∼ 17 MeV in the nuclear transitions of 4He, that they previously observed in measurements with 8Be. These observations could be explained by the existence of a new vector X17 boson. So far, the search for the decay X17 → 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 X17 parameter space. If a signal-like event is detected, an unambiguous observation is achieved by reconstructing the invariant mass of the X17 decay with the proposed method. To reach this goal an optimization of the X17 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. © 2020, The Author(s).
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    Improved exclusion limit for light dark matter from e+e- annihilation in NA64
    (American Physical Society, 2021-11-01) Andreev, Yu. M.; Banerjee D.; Bernhard J.; Bondì M.; Burtsev V.E.; Celentano A.; Charitonidis N.; Chumakov A.G.; Cooke D.; Crivelli P.; Depero E.; Dermenev A.V.; Donskov S.V.; Dusaev R.R.; Enik T.; Feshchenko A.; Frolov V.N.; Gardikiotis A.; Gerassimov S.G.; Gninenko S.N.; Hösgen M.; Jeckel M.; Kachanov V.A.; Karneyeu A.E.; Kekelidze G.; Ketzer B.; Kirpichnikov D.V.; Kirsanov M.M.; Kolosov V.N.; Konorov I.V.; Kovalenko S.G.; Kramarenko V.A.; Kravchuk L.V.; Krasnikov N.V.; Kuleshov S.V.; Lyubovitskij V.E.; Lysan V.; Marsicano L.; Matveev V.A.; Mikhailov, Yu. V.; Molina Bueno L.; Peshekhonov D.V.; Polyakov V.A.; Radics B.; Rojas R.; Rubbia A.; Samoylenko V.D.; Sieber H.; Shchukin D.; Tikhomirov V.O.; Tlisova I.; Toropin A.N.; Trifonov, A. Yu.; Ulloa P.; Vasilishin B.I.; Vasquez Arenas G.; Volkov P.V.; Volkov, V. Yu.
    The current most stringent constraints for the existence of sub-GeV dark matter coupling to Standard Model via a massive vector boson A′ were set by the NA64 experiment for the mass region mA′≲250 MeV, by analyzing data from the interaction of 2.84×1011 100-GeV electrons with an active thick target and searching for missing-energy events. In this work, by including A′ production via secondary positron annihilation with atomic electrons, we extend these limits in the 200-300 MeV region by almost an order of magnitude, touching for the first time the dark matter relic density constrained parameter combinations. Our new results demonstrate the power of the resonant annihilation process in missing energy dark-matter searches, paving the road to future dedicated e+ beam efforts.