The NA62 experiment at CERN, designed to study the ultra-rare decay K+ -> pi(+) nu(nu) over bar, has also collected data in beam-dump mode. In this configuration, dark photons may be produced by protons dumped on an absorber and reach a decay volume beginning 80 m downstream. A search for dark photons decaying in flight to mu(+) mu(-) pairs is reported, based on a sample of 1.4 x 10(17) protons on dump collected in 2021. No evidence for a dark photon signal is observed. A region of the parameter space is excluded at 90% CL, improving on previous experimental limits for dark photon masses between 215 and 550MeV/c(2).
Stewart Cole, Xin Chen, Jean-Paul Richard Kneib, Eduardo Sanchez, Zheng Zheng, Andrei Variu, Daniel Felipe Forero Sanchez, Hua Zhang, Sun Hee Kim, Cheng Zhao, Anand Stéphane Raichoor, David Schlegel, Jiangyan Yang, Ting Tan, Zhifeng Ding, Arjun Dey
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