Examinando por Autor "Bernhard J."

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    First constraints on the Lμ− Lτ explanation of the muon g-2 anomaly from NA64-e at CERN
    (Springer Science and Business Media Deutschland GmbH, 2024-07) Andreev, Yu. M.; Antonov A.; Banerjee D.; Banto Oberhauser B.; Bernhard J.; Bisio P.; Celentano A.; Charitonidis N.; Cooke D.; Crivelli P.; Depero E.; Dermenev A.V.; Donskov S.V.; Dusaev R.R.; Enik T.; Frolov V.N.; Gardikiotis A.; Gertsenberger S.V.; Girod S.; Gninenko S.N.; Hösgen M.; Kachanov V.A.; Kambar Y.; Karneyeu A.E.; Kasianova E.A.; Kekelidze G.; Ketzer B.; Kirpichnikov D.V.; Kirsanov M.M.; Kolosov V.N.; Kramarenko V.A.; Kravchuk L.V.; Krasnikov N.V.; Kuleshov S.V.; Lyubovitskij V.E.; Lysan V.; Marini A.; Marsicano L.; Matveev V.A.; Mena Fredes R.; Mena Yanssen R.; Molina Bueno L.; Mongillo M.; Peshekhonov D.V.; Polyakov V.A.; Radics B.; Salamatin K.; Samoylenko V.D.; Sieber H.; Shchukin D.; Soto O.; Tikhomirov V.O.; Tlisova I.; Toropin A.N.; Tuzi M.; Ulloa P.; Volkov P.V.; Volkov, V. Yu.; Voronchikhin I.V.; Zamora-Saá J.
    The inclusion of an additional U(1) gauge Lμ − Lτ symmetry would release the tension between the measured and the predicted value of the anomalous muon magnetic moment: this paradigm assumes the existence of a new, light Z′ vector boson, with dominant coupling to μ and τ leptons and interacting with electrons via a loop mechanism. The Lμ − Lτ model can also explain the Dark Matter relic abundance, by assuming that the Z′ boson acts as a “portal” to a new Dark Sector of particles in Nature, not charged under known interactions. In this work we present the results of the Z′ search performed by the NA64-e experiment at CERN SPS, that collected ~ 9 × 1011 100 GeV electrons impinging on an active thick target. Despite the suppressed Z′ production yield with an electron beam, NA64-e provides the first accelerator-based results excluding the g − 2 preferred band of the Z′ parameter space in the 1 keV
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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.
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    Probing light dark matter with positron beams at NA64
    (American Physical Society, 2024-02-01) Andreev, Yu. M.; Antonov A.; Banerjee D.; Banto Oberhauser B.; Bernhard J.; Bisio P.; Bondí M.; Celentano A.; Charitonidis N.; Cooke D.; Crivelli P.; Depero E.; Dermenev A.V.; Donskov S.V.; Dusaev R.R.; Enik T.; Frolov V.N.; Gardikiotis A.; Gninenko S.N.; Hösgen M.; Kachanov V.A.; Kambar Y.; Karneyeu A.E.; Kekelidze G.; Ketzer B.; Kirpichnikov D.V.; Kirsanov M.M.; Gertsenberger S.V.; Girod S.; Kasianova E.A.; Kramarenko V.A.; Kravchuk L.V.; Krasnikov N.V.; Kuleshov S.V.; Lyubovitskij V.E.; Lysan V.; Marini A.; Marsicano L.; Matveev V.A.; Mena Fredes R.; Mena Yanssen R.; Molina Bueno L.; Mongillo M.; Peshekhonov D.V.; Polyakov V.A.; Radics B.; Salamatin K.; Samoylenko V.D.; Sieber H.; Shchukin D.; Soto O.; Tikhomirov V.O.; Tlisova I.; Toropin A.N.; Tuzi M.; Ulloa P.; Volkov P.V.; Volkov, V. Yu.; Voronchikhin I.V.
    We present the results of a missing-energy search for light dark matter which has a new interaction with ordinary matter transmitted by a vector boson, called dark photon A′. For the first time, this search is performed with a positron beam by using the significantly enhanced production of A′ in the resonant annihilation of positrons with atomic electrons of the target nuclei, followed by the invisible decay of A′ into dark matter. No events were found in the signal region with (10.1±0.1)×109 positrons on target with 100 GeV energy. This allowed us to set new exclusion limits that, relative to the collected statistics, prove the power of this experimental technique. This measurement is a crucial first step toward a future exploration program with positron beams, whose estimated sensitivity is here presented.
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    Search for Light Dark Matter with NA64 at CERN
    (American Physical Society, 2023-10-20) Andreev, Yu. M.; Banerjee D.; Banto Oberhauser B.; Bernhard J.; Bisio P.; Celentano A.; Charitonidis N.; Chumakov A.G.; Cooke D.; Crivelli P.; Depero E.; Dermenev A.V.; Donskov S.V.; Dusaev R.R. .; Enik T.; Frolov V.N.; Galleguillos Silva R.B.; Gardikiotis A.; Gertsenberger S.V.; Girod S.; Gninenko S.N.; Hösgen M.; Kachanov V.A.; Kambar Y.; Karneyeu A.E.; Kasianova E.A.; Kekelidze G.D.; Ketzer B.; Kirpichnikov D.V.; Kirsanov M.M.; Kolosov V.N.; Kramarenko V.A.; Kravchuk L.V.; Krasnikov N.V.; Kuleshov S.V.; Lyubovitskij V.E.; Lysan V.; Marini A.; Marsicano L.; Matveev V.A.; Mena Fredes R.; Mena Yanssen R.G.; Molina Bueno L.; Mongillo M.; Peshekhonov D.V.; Polyakov V.A.; Radics B.; Salamatin K.M.; Samoylenko V.D.; Sieber H.; Shchukin D.A.; Soto O.; Tikhomirov V.O.; Tlisova I.V.; Toropin A.N.; Tuzi M.; Vasilishin B.I.; Volkov P.V.; Volkov, V. Yu.; Voronchikhin I.V.; Zamora-Saá J.; Zhevlakov A.S.
    Thermal dark matter models with particle χ masses below the electroweak scale can provide an explanation for the observed relic dark matter density. This would imply the existence of a new feeble interaction between the dark and ordinary matter. We report on a new search for the sub-GeV χ production through the interaction mediated by a new vector boson, called the dark photon A′, in collisions of 100 GeV electrons with the active target of the NA64 experiment at the CERN SPS. With 9.37×1011 electrons on target collected during 2016-2022 runs NA64 probes for the first time the well-motivated region of parameter space of benchmark thermal scalar and fermionic dark matter models. No evidence for dark matter production has been found. This allows us to set the most sensitive limits on the A′ couplings to photons for masses mA′≲0.35 GeV, and to exclude scalar and Majorana dark matter with the χ-A′ coupling αD≤0.1 for masses 0.001≲mχ≲0.1 GeV and 3mχ≤mA′.