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The dark photon A' and the dark Higgs boson h' are hypothetical constituents featured in a number of recently proposed dark sector models. Assuming prompt decays of both dark particles, we search for their production in the so-called Higgstrahlung channel e(+)e(-) -> A'h', with h' -> A'A'. We investigate ten exclusive final states with A' -> e(+)e(-), mu(+)mu(-), or pi(+)pi(-) in the mass ranges 0.1 GeV/c(2) < m(A') < 3.5 GeV/c(2) and 0.2 GeV/c(2) < m(h') < 10.5 GeV/c(2). We also investigate three inclusive final states 2(e(+)e(-))X, 2(mu(+)mu(-))X, and (e(+)e(-))(mu(+)mu(-))X, where X denotes a dark photon candidate detected via missing mass, in the mass ranges 1.1 GeV/c(2) < m(A') < 3.5 GeV/c(2) and 2.2 GeV/c(2) < m(h') < 10.5 GeV/c(2). Using the entire 977 fb(-1) data set collected by Belle, we observe no significant signal. We obtain individual and combined 90% credibility level upper limits on the branching fraction times the Born cross section, B x sigma(Born), on the Born cross section sigma(Born), and on the dark photon coupling to the dark Higgs boson times the kinetic mixing between the standard model photon and the dark photon, alpha(D) x epsilon(2). These limits improve upon and cover wider mass ranges than previous experiments. The limits from the final states 3(pi(+)pi(-)) and 2(e(+)e(-))X are the first placed by any experiment. For alpha(D) equal to 1/137, m(h') < 8 GeV/c(2), and m(A') < 1 GeV/c(2), we exclude values of the mixing parameter epsilon above similar to 8 x 10(-4).
Andrey Shkerin, Inar Timiryasov, Sebastian Zell
Jian Wang, Olivier Schneider, Yiming Li, Yi Zhang, Aurelio Bay, Guido Haefeli, Christoph Frei, Frédéric Blanc, Tatsuya Nakada, Michel De Cian, Luca Pescatore, François Fleuret, Elena Graverini, Renato Quagliani, Maria Vieites Diaz, Federico Betti, Andrea Merli, Aravindhan Venkateswaran, Luis Miguel Garcia Martin, Vitalii Lisovskyi, Sebastian Schulte, Veronica Sølund Kirsebom, Elisabeth Maria Niel, Alexandre Brea Rodriguez, Mingkui Wang, Zhirui Xu, Lei Zhang, Ho Ling Li, Mark Tobin, Minh Tâm Tran, Niko Neufeld, Matthew Needham, Marc-Olivier Bettler, Maurizio Martinelli, Vladislav Balagura, Donal Patrick Hill, Liang Sun, Pietro Marino, Mirco Dorigo, Xiaoxue Han, Liupan An, Federico Leo Redi, Plamen Hristov Hopchev, Thibaud Humair, Maxime Schubiger, Hang Yin, Guido Andreassi, Violaine Bellée, Olivier Göran Girard, Axel Kuonen, Preema Rennee Pais, Pavol Stefko, Tara Nanut, Maria Elena Stramaglia, Yao Zhou, Tommaso Colombo, Vladimir Macko, Guillaume Max Pietrzyk, Evgenii Shmanin, Simone Meloni, Xiaoqing Zhou, Surapat Ek-In, Carina Trippl, Dipanwita Dutta, Zheng Wang, Yi Wang, Hans Dijkstra, Gerhard Raven, Peter Clarke, Frédéric Teubert, Giovanni Carboni, Victor Coco, Adam Davis, Paolo Durante, Wenyu Zhang, Yu Zheng, Anton Petrov, Maxim Borisyak, Feng Jiang, Chen Chen, Zhipeng Tang, Xuan Li, Alexey Boldyrev, Almagul Kondybayeva, Hossein Afsharnia