APS : Search for pseudoscalar bosons decaying into e+e- pairs in the NA64 experiment at the CERN SPS

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

doi:10.1103/PhysRevD.104.L111102

Article
Report number	arXiv:2104.13342
Title	Search for pseudoscalar bosons decaying into e+e- pairs in the NA64 experiment at the CERN SPS
Author(s)	Andreev, Yu.M. (Valencia U., IFIC ; Moscow, INR) ; Banerjee, D. (Valencia U., IFIC ; CERN) ; Bernhard, J. (Valencia U., IFIC ; CERN) ; Burtsev, V.E. (Valencia U., IFIC ; Dubna, JINR) ; Charitonidis, N. (Valencia U., IFIC ; CERN) ; Chumakov, A.G. (Tomsk Pedagogical Inst. ; Tomsk Polytechnic U. ; Valencia U., IFIC) ; Cooke, D. (Valencia U., IFIC ; University Coll. London) ; Crivelli, P. (Valencia U., IFIC ; Zurich, ETH) ; Depero, E. (Valencia U., IFIC ; Zurich, ETH) ; Dermenev, A.V. (Valencia U., IFIC ; Moscow, INR) ; Donskov, S.V. (Valencia U., IFIC ; Serpukhov, IHEP) ; Dusaev, R.R. (Valencia U., IFIC ; Tomsk Polytechnic U.) ; Enik, T. (Valencia U., IFIC ; Dubna, JINR) ; Feshchenko, A. (Valencia U., IFIC ; Dubna, JINR) ; Frolov, V.N. (Valencia U., IFIC ; Dubna, JINR) ; Gardikiotis, A. (Valencia U., IFIC ; Patras U.) ; Gerassimov, S.G. (TUM-IAS, Munich ; Lebedev Inst. ; Valencia U., IFIC ; Munich, Tech. U. ; LPI, Moscow (main)) ; Gninenko, S.N. (Valencia U., IFIC ; Moscow, INR) ; Hösgen, M. (Valencia U., IFIC ; Bonn U., HISKP) ; Jeckel, M. (Valencia U., IFIC ; CERN) ; Kachanov, V.A. (Valencia U., IFIC ; Serpukhov, IHEP) ; Karneyeu, A.E. (Valencia U., IFIC ; Moscow, INR) ; Kekelidze, G. (Valencia U., IFIC ; Dubna, JINR) ; Ketzer, B. (Valencia U., IFIC ; Bonn U., HISKP) ; Kirpichnikov, D.V. (Valencia U., IFIC ; Moscow, INR) ; Kirsanov, M.M. (Valencia U., IFIC ; Moscow, INR) ; Kolosov, V.N. (Valencia U., IFIC ; Serpukhov, IHEP) ; Konorov, I.V. (TUM-IAS, Munich ; Lebedev Inst. ; Valencia U., IFIC ; Munich, Tech. U. ; LPI, Moscow (main)) ; Kovalenko, S.G. (Chile U., Santiago ; Valencia U., IFIC ; Andres Bello Natl. U.) ; Kramarenko, V.A. (SINP, Moscow ; Dubna, JINR ; Valencia U., IFIC) ; Kravchuk, L.V. (Valencia U., IFIC ; Moscow, INR) ; Krasnikov, N.V. (Valencia U., IFIC ; Dubna, JINR ; Moscow, INR) ; Kuleshov, S.V. (Chile U., Santiago ; Valencia U., IFIC ; Andres Bello Natl. U.) ; Lyubovitskij, V.E. (Santa Maria U., Valparaiso ; Chile U., Santiago ; Tomsk Pedagogical Inst. ; Tomsk Polytechnic U. ; Valencia U., IFIC ; CCTVal, Valparaiso) ; Lysan, V. (Valencia U., IFIC ; Dubna, JINR) ; Matveev, V.A. (Valencia U., IFIC ; Dubna, JINR) ; Mikhailov, Yu.V. (Valencia U., IFIC ; Serpukhov, IHEP) ; Molina Bueno, L. (Zurich, ETH ; Valencia U., IFIC) ; Peshekhonov, D.V. (Valencia U., IFIC ; Dubna, JINR) ; Polyakov, V.A. (Valencia U., IFIC ; Serpukhov, IHEP) ; Radics, B. (Valencia U., IFIC ; Zurich, ETH) ; Rojas, R. (Santa Maria U., Valparaiso ; Valencia U., IFIC ; CCTVal, Valparaiso) ; Rubbia, A. (Valencia U., IFIC ; Zurich, ETH) ; Samoylenko, V.D. (Valencia U., IFIC ; Serpukhov, IHEP) ; Sieber, H. (Valencia U., IFIC ; Zurich, ETH) ; Shchukin, D. (Lebedev Inst. ; Valencia U., IFIC ; LPI, Moscow (main)) ; Tikhomirov, V.O. (Lebedev Inst. ; Valencia U., IFIC ; LPI, Moscow (main)) ; Tlisova, I. (Valencia U., IFIC ; Moscow, INR) ; Toropin, A.N. (Valencia U., IFIC ; Moscow, INR) ; Trifonov, A.Yu. (Tomsk Pedagogical Inst. ; Tomsk Polytechnic U. ; Valencia U., IFIC) ; Vasilishin, B.I. (Valencia U., IFIC ; Tomsk Polytechnic U.) ; Vasquez Arenas, G. (Santa Maria U., Valparaiso ; Valencia U., IFIC ; CCTVal, Valparaiso) ; Volkov, P.V. (SINP, Moscow ; Dubna, JINR ; Valencia U., IFIC) ; Volkov, V.Yu. (Valencia U., IFIC ; SINP, Moscow) ; Ulloa, P. (Valencia U., IFIC ; Andres Bello Natl. U.)
Publication	2021-12-01
Imprint	2021-04-27
Number of pages	5
Note	6 pages, 2 figures
In:	Phys. Rev. D 104 (2021) L111102
DOI	10.1103/PhysRevD.104.L111102 (publication)
Subject category	hep-ex ; Particle Physics - Experiment
Accelerator/Facility, Experiment	CERN SPS ; NA64
Abstract	We report the results of a search for a light pseudoscalar particle $a$ that couples to electrons and decays to $e^+e^-$ performed using the high-energy CERN SPS H4 electron beam. If such pseudoscalar with a mass $\simeq 17$ MeV exists, it could explain the ATOMKI anomaly. We used the NA64 data samples collected in the "visible mode" configuration with total statistics corresponding to $8.4\times 10^{10}$ electrons on target (EOT) in 2017 and 2018. In order to increase sensitivity to small coupling parameter $\epsilon$ we used also the data collected in 2016-2018 in the "invisible mode" configuration of NA64 with a total statistics corresponding to $2.84\times 10^{11}$ EOT. A thorough analysis of both these data samples in the sense of background and efficiency estimations was already performed and reported in our previous papers devoted to the search for light vector particles and axion-like particles (ALP). In this work we recalculate the signal yields, which are different due to different cross section and life time of a pseudoscalar particle $a$, and perform a new statistical analysis. As a result, the region of the two dimensional parameter space $m_a - \epsilon$ in the mass range from 1 to 17.1 MeV is excluded. At the mass of the ATOMKI anomaly the values of $\epsilon$ in the range $2.1 \times 10^{-4} < \epsilon < 3.2 \times 10^{-4}$ are excluded.
Copyright/License	preprint: (License: CC-BY-4.0) publication: © 2021-2025 authors (License: CC BY 4.0)

$The NA64 setup to search for $A'(a)\to \ee$ decays of the bremsstrahlung $A'(a)$ produced in the reaction $eZ \to eZA'(a) $ of the 150 GeV electrons incident on the active WCAL target. The figure is reproduced from Ref. \cite{visible-2018-analysis}.$ $The 90\% C.L. limits on the pseudoscalar particles decaying to $e^+e^-$ pairs. On the right vertical axis we use the standard notation for the pseudo-scalar coupling $\xi_e=\epsilon (V/m_e) \sqrt{4 \pi \alpha_{QED}}$, where $V=246$~GeV is a vacuum expectation value of the Higgs field \cite{Andreas:2010ms}. This corresponds to the Lagrangian term $\mathcal{L}\supset -i \xi_e \frac{m_e}{V} a \bar{\psi}_e \gamma_5 \psi_e$. The red vertical line corresponds to the ATOMKI anomaly at $m_a = 16.7$ MeV (central value of the first result on berillium). The $\epsilon$ range excluded at this mass is $2.1\times 10^{-4} < \epsilon < 3.2\times 10^{-4}$. The region excluded using only the data collected with the visible mode geometry is denoted as$