Global QCD analysis and dark photons

We perform a global QCD analysis of high energy scattering data within the JAM Monte Carlo framework, including a coupling to a dark photon that augments the Standard Model (SM) electroweak coupling via kinetic mixing with the hypercharge B boson. We first set limits on the dark photon mass and mixing parameter assuming that the SM is the true theory of Nature, taking into account also the effect on g - 2 of the muon. If instead we entertain the possibility that the dark photon may play a role in deep-inelastic scattering (DIS), we find that the best fit is preferred over the SM at 6.5 & sigma;, even after accounting for missing higher order uncertainties. The improvement in & chi;2 with the dark photon is stable against all the tests we have applied, with the improvements in the theoretical predictions spread across a wide range of x and Q2. The largest improvement corresponds to the fixed target and HERA DIS data, while the best fit yields a value of g - 2 which significantly reduces the disagreement with the latest experimental determination.

Automated summary

In this study, we performed a global QCD analysis of high energy scattering data using the JAM Monte Carlo framework. We introduced a coupling to a dark photon and investigated its potential role in deep-inelastic scattering. The results show that the dark photon significantly improves the fit compared to the Standard Model, even after considering higher order uncertainties. The improvement is observed across a wide range of parameters and is particularly significant for fixed target and HERA DIS data. Additionally, the best fit value of g - 2 is reduced, reducing the disagreement with the latest experimental determination.