Indirect searches for new physics beyond the standard model employ precision measurements of low energy observables like for example the weak mixing angle expressed as $\sin^2 \theta_W$. There are several possibilities to measure this quantity, one is the measurement of a parity-violating asymmetry in elastic electron-proton scattering.
The P2 experiment at the upcoming Mainz energy recovering electron accelerator MESA aims for a 2% measurement of such an asymmetry at very low four-momentum transfer of q^2= 0.005 (GeV/c)^2. This measurement allows the extraction of a precise determination of the weak mixing angle with an accuracy of 0.15%.
In combination with the high energy physics measurement of $\sin^2 \theta_W$ at the Z-pole it comprises a test of the Standard Model. Any significant deviation is a sign for new physics beyond the Standard Model with a sensitivity to a mass scale up to about 50 TeV. Further measurements employing a Carbon target will increase this reach.