Search at the Mainz Microtron for Light Massive Gauge Bosons Relevant for the Muong−2Anomaly

Abstract

A massive, but light abelian U (1) gauge boson is a well motivated possible signature of physics beyond the Standard Model of particle physics. In this paper, the search for the signal of such a U (1) gauge boson in electron-positron pair-production at the spectrometer setup of the A1 Collaboration at the Mainz Microtron (MAMI) is described. Exclusion limits in the mass range of 40 MeV/c 2 up to 300 MeV/c 2 with a sensitivity in the mixing parameter of down to 2 = 8 × 10 −7 are presented. A large fraction of the parameter space has been excluded where the discrepancy of the measured anomalous magnetic moment of the muon with theory might be explained by an additional U (1) gauge boson.

Search for a Dark Photon ine+e−Collisions atBaBar

“…No unambiguous signal for a dark photon has been reported so far, and constraints have been set on the mixing strength between the photon and dark photon as a function of the dark photon mass [11][12][13][14][15][16][17][18][19][20][21][22]. Searches for an additional low-mass, dark gauge boson [23] or dark Higgs boson [24] have also yielded negative results.…”

New Light Shed on Dark Photons

“…The average correlation between neighboring points is around 90%. Bounds at the level of 10 −4 -10 −3 for 0.02 < m A 0 < 10.2 GeV are set, significantly improving previous constraints derived from beamdump experiments [11,12,18], the electron anomalous magnetic moment [13], KLOE [14,15], WASA-at-COSY [16], HADES [17], A1 at MAMI [19], and the test run from APEX [20]. These results also supersede and extend the constraints based on a search for a light CP-odd Higgs boson at BABAR [21,22] with a smaller data set.…”

“…Dark photons could therefore be detected as narrow resonances in radiative e þ e − → γl þ l − (l ¼ e; μ) events. No unambiguous signal for a dark photon has been reported so far, and constraints have been set on the mixing strength between the photon and dark photon as a function of the dark photon mass [11][12][13][14][15][16][17][18][19][20][21][22]. Searches for an additional low-mass, dark gauge boson [23] or dark Higgs boson [24] have also yielded negative results.…”

Muong−2anomaly and dark leptonic gauge boson

“…For m Z ′ < 2m µ , it has Br(Z ′ → e + e − ) ≃ 1. Various constraints from the meson decays [32][33][34][35][36][37], fixed target experiments [38,39], beam dump experiments [40] apply, and only the relevant ones for the g µ − 2 favored region (green band) are shown in the figure. We refer the interested readers to Ref.…”

“…(i) Fixed target experiments (APEX [38], MAMI [39] with 90% C.L. ): They look for the e + e − resonance from the bremsstrahlung (eN → eN + e + e − ).…”