https://doi.org/10.1140/epjc/s10052-019-7112-x
Regular Article - Experimental Physics
Search for the rare decay 
1
Centro Brasileiro de Pesquisas Físicas (CBPF), Rio de Janeiro, Brazil
2
Universidade Federal do Rio de Janeiro (UFRJ), Rio de Janeiro, Brazil
3
Center for High Energy Physics, Tsinghua University, Beijing, China
4
University of Chinese Academy of Sciences, Beijing, China
5
Institute Of High Energy Physics (ihep), Beijing, China
6
Univ. Grenoble Alpes, Univ. Savoie Mont Blanc, CNRS, IN2P3-LAPP, Annecy, France
7
Université Clermont Auvergne, CNRS/IN2P3, LPC, Clermont-Ferrand, France
8
Aix Marseille Univ, CNRS/IN2P3, CPPM, Marseille, France
9
LAL, Univ. Paris-Sud, CNRS/IN2P3, Université Paris-Saclay, Orsay, France
10
LPNHE, Sorbonne Université Paris Diderot, Sorbonne Paris Cité, CNRS/IN2P3, Paris, France
11
I. Physikalisches Institut, RWTH Aachen University, Aachen, Germany
12
Fakultät Physik, Technische Universität Dortmund, Dortmund, Germany
13
Max-Planck-Institut für Kernphysik (MPIK), Heidelberg, Germany
14
Physikalisches Institut, Ruprecht-Karls-Universität Heidelberg, Heidelberg, Germany
15
School of Physics, University College Dublin, Dublin, Ireland
16
INFN Sezione di Bari, Bari, Italy
17
INFN Sezione di Bologna, Bologna, Italy
18
INFN Sezione di Ferrara, Ferrara, Italy
19
INFN Sezione di Firenze, Florence, Italy
20
INFN Laboratori Nazionali di Frascati, Frascati, Italy
21
INFN Sezione di Genova, Genoa, Italy
22
INFN, Sezione di Milano-Bicocca, Milan, Italy
23
INFN Sezione di Milano, Milan, Italy
24
INFN Sezione di Cagliari, Monserrato, Italy
25
INFN Sezione di Padova, Padua, Italy
26
INFN Sezione di Pisa, Pisa, Italy
27
INFN Sezione di Roma Tor Vergata, Rome, Italy
28
INFN Sezione di Roma La Sapienza, Rome, Italy
29
Nikhef National Institute for Subatomic Physics, Amsterdam, The Netherlands
30
Nikhef National Institute for Subatomic Physics and VU University Amsterdam, Amsterdam, The Netherlands
31
Henryk Niewodniczanski Institute of Nuclear Physics Polish Academy of Sciences, Kraków, Poland
32
Faculty of Physics and Applied Computer Science, AGH-University of Science and Technology, Kraków, Poland
33
National Center for Nuclear Research (NCBJ), Warsaw, Poland
34
Horia Hulubei National Institute of Physics and Nuclear Engineering, Bucharest-Magurele, Romania
35
Petersburg Nuclear Physics Institute NRC Kurchatov Institute (PNPI NRC KI), Gatchina, Russia
36
Institute of Theoretical and Experimental Physics NRC Kurchatov Institute (ITEP NRC KI), Moscow, Russia, Moscow, Russia
37
Institute of Nuclear Physics, Moscow State University (SINP MSU), Moscow, Russia
38
Institute for Nuclear Research of the Russian Academy of Sciences (INR RAS), Moscow, Russia
39
Yandex School of Data Analysis, Moscow, Russia
40
Budker Institute of Nuclear Physics (SB RAS), Novosibirsk, Russia
41
Institute for High Energy Physics NRC Kurchatov Institute (IHEP NRC KI), Protvino, Russia, Protvino, Russia
42
ICCUB, Universitat de Barcelona, Barcelona, Spain
43
Instituto Galego de Física de Altas Enerxías (IGFAE), Universidade de Santiago de Compostela, Santiago de Compostela, Spain
44
European Organization for Nuclear Research (CERN), Geneva, Switzerland
45
Institute of Physics, Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland
46
Physik-Institut, Universität Zürich, Zurich, Switzerland
47
NSC Kharkiv Institute of Physics and Technology (NSC KIPT), Kharkiv, Ukraine
48
Institute for Nuclear Research of the National Academy of Sciences (KINR), Kyiv, Ukraine
49
University of Birmingham, Birmingham, UK
50
H.H. Wills Physics Laboratory, University of Bristol, Bristol, UK
51
Cavendish Laboratory, University of Cambridge, Cambridge, UK
52
Department of Physics, University of Warwick, Coventry, UK
53
STFC Rutherford Appleton Laboratory, Didcot, UK
54
School of Physics and Astronomy, University of Edinburgh, Edinburgh, UK
55
School of Physics and Astronomy, University of Glasgow, Glasgow, UK
56
Oliver Lodge Laboratory, University of Liverpool, Liverpool, UK
57
Imperial College London, London, UK
58
School of Physics and Astronomy, University of Manchester, Manchester, UK
59
Department of Physics, University of Oxford, Oxford, UK
60
Massachusetts Institute of Technology, Cambridge, MA, USA
61
University of Cincinnati, Cincinnati, OH, USA
62
University of Maryland, College Park, MD, USA
63
Syracuse University, Syracuse, NY, USA
64
Laboratory of Mathematical and Subatomic Physics, Constantine, Algeria
65
Pontifícia Universidade Católica do Rio de Janeiro (PUC-Rio), Rio de Janeiro, Brazil
66
South China Normal University, Guangzhou, China
67
School of Physics and Technology, Wuhan University, Wuhan, China
68
Institute of Particle Physics, Central China Normal University, Wuhan, Hubei, China
69
Departamento de Fisica, Universidad Nacional de Colombia, Bogotá, Colombia
70
Institut für Physik, Universität Rostock, Rostock, Germany
71
Van Swinderen Institute, University of Groningen, Groningen, The Netherlands
72
National Research Centre Kurchatov Institute, Moscow, Russia
73
National University of Science and Technology “MISIS”, Moscow, Russia
74
National Research University Higher School of Economics, Moscow, Russia
75
National Research Tomsk Polytechnic University, Tomsk, Russia
76
Instituto de Fisica Corpuscular, Centro Mixto Universidad de Valencia-CSIC, Valencia, Spain
77
University of Michigan, Ann Arbor, USA
78
Los Alamos National Laboratory (LANL), Los Alamos, USA
79
CERN, 1211, Geneva 23, Switzerland
* e-mail: slavomira.stefkova@desy.de
Received:
20
December
2018
Accepted:
5
July
2019
Published online:
13
August
2019
A search for the rare leptonic decay is performed using proton-proton collision data corresponding to an integrated luminosity of 
collected by the LHCb experiment. The search is carried out in the region where the lowest of the two 
mass combinations is below 
. The data are consistent with the background-only hypothesis and an upper limit of 
at 95% confidence level is set on the branching fraction in the stated kinematic region.
© The Author(s), 2019
