Abstract
Deep inelastic scattering of e^{±} off protons is sensitive to contributions from "dark photon" exchange. Using HERA data fit to HERA's parton distribution functions (PDFs), we obtain the model-independent bound ε≲0.02 on the kinetic mixing between hypercharge and the dark photon for dark photon masses ≲10 GeV. This slightly improves on the bound obtained from electroweak precision observables. For higher masses, the limit weakens monotonically; ε≲1 for a dark photon mass of 5TeV. Utilizing PDF sum rules, we demonstrate that the effects of the dark photon cannot be (trivially) absorbed into refit PDFs and, in fact, lead to non-Dokshitzer-Gribov-Lipatov-Altarelli-Parisi (Bjorken x_{B}-independent) scaling violations that could provide a smoking gun in data. The proposed e^{±}p collider operating at sqrt[s]=1.3 TeV (Large Hadron Electron Collider) is anticipated to accumulate 10^{3} times the luminosity of HERA, providing substantial improvements in probing the effects of a dark photon: sensitivity to ε well below that probed by electroweak precision data is possible throughout virtually the entire dark photon mass range, as well as being able to probe to much higher dark photon masses, up to 100TeV.
Highlights
Using HERA data fit to HERA’s parton distribution functions (PDFs), we obtain the model-independent bound ε ≲ 0.02 on the kinetic mixing between hypercharge and the dark photon for dark photon masses
(Large Hadron Electron Collider) is anticipated to accumulate 103 times the luminosity of HERA, providing substantial improvements in probing the effects of a dark photon: sensitivity to ε well below that probed by electroweak precision data is possible throughout virtually the entire dark photon mass range, as well as being able to probe to much higher dark photon masses, up to 100 TeV
Signals of kinetic mixing in deep inelastic scattering.—we review the basics of DIS, incorporating AD exchange
Summary
Decay-agnostic limits on kinetic mixing were obtained in Refs. [4,5] from electroweak precision observables (EWPOs), driven mainly by the 0.1% precision Z pole-mass measurements at large electron-positron collider (LEP). Decay-agnostic limits on kinetic mixing were obtained in Refs. With a net luminosity of 1 fb−1, HERA achieved 1% (systematics-limited) precision, multiple measurements at this precision give additional statistical power. Decay-agnostic constraints arise from measurements of the muonic g − 2, which receives contributions from AD-mediated loop amplitudes [6]; these limits, weaken considerably for AD masses above the muon mass, becoming negligible above 10 GeV. We show that DIS can probe dark photon masses of 104 GeV and beyond. Signals of kinetic mixing in deep inelastic scattering.—we review the basics of DIS (for reviews, see, e.g., [8,9,10]), incorporating AD exchange. First we diagonalize the mixing in Eq (1) through the field redefinition
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