Searching a dark photon with HADES

• DOI: 10.1016/j.physletb.2014.02.035
• Publication Date: 2014-02-26T17:01:46Z
• Authors: G. Agakishiev; A. Balanda; D. Belver; A. Belyaev; J.C. Berger-Chen; A. Blanco; M. Böhmer; J.L. Boyard; P. Cabanelas; S. Chernenko; A. Dybczak; E. Epple; L. Fabbietti; O. Fateev; P. Finocchiaro; P. Fonte; J. Friese; I. Fröhlich; T. Galatyuk; J.A. Garzón; R. Gernhäuser; K. Göbel; M. Golubeva; D. González-Díaz; F. Guber; M. Gumberidze; T. Heinz; T. Hennino; R. Holzmann; A. Ierusalimov; I. Iori; A. Ivashkin; M. Jurkovic; B. Kämpfer; T. Karavicheva; I. Koenig; W. Koenig; B.W. Kolb; G. Kornakov; R. Kotte; A. Krása; F. Krizek; R. Krücken; H. Kuc; W. Kühn; A. Kugler; A. Kurepin; V. Ladygin; R. Lalik; S. Lang; K. Lapidus; A. Lebedev; T. Liu; L. Lopes; M. Lorenz; L. Maier; A. Mangiarotti; J. Markert; V. Metag; B. Michalska; J. Michel; C. Müntz; L. Naumann; Y.C. Pachmayer; M. Palka; Y. Parpottas; V. Pechenov; O. Pechenova; V. Petousis; J. Pietraszko; W. Przygoda; B. Ramstein; A. Reshetin; A. Rustamov; A. Sadovsky; P. Salabura; T. Scheib; H. Schuldes; A. Schmah; E. Schwab; J. Siebenson; Yu.G. Sobolev; S. Spataro; B. Spruck; H. Ströbele; J. Stroth; C. Sturm; A. Tarantola; K. Teilab; P. Tlusty; M. Traxler; R. Trebacz; H. Tsertos; T. Vasiliev; V. Wagner; M. Weber; C. Wendisch; J. Wüstenfeld; S. Yurevich; Y. Zanevsky
• Keywords: Helicity; Branching fraction; Dark photon; Anomaly (physics); Vector boson; Vector meson

We present a search for the e+e− decay of hypothetical dark photon, also named U vector boson, in inclusive dielectron spectra measured by HADES p(3.5 GeV) + p, Nb reactions, as well Ar (1.756 GeV/u) KCl reaction. An upper limit on kinetic mixing parameter squared ϵ2 at 90% CL has been obtained mass range MU=0.02–0.55 GeV/c2 and is compared with world data set. For masses 0.03–0.1 GeV/c2, lowered respect to previous results, allowing now exclude large part region favored muon g−2 anomaly. Furthermore, an improved branching ratio 2.3×10−6 set helicity-suppressed direct eta meson, η→e+e−, CL.