Searching for new physics from SMEFT and leptoquarks at the P2 experiment

The P2 experiment aims at high-precision measurements of the parity-violating asymmetry in elastic electron-proton and electron-${}^{12}\mathrm{C}$ scatterings with longitudinally polarized electrons. We discuss here the sensitivity of P2 to leptoquarks, which within the P2 energy range can be described in the language of Standard Model effective field theory (SMEFT). We give the expected P2 limits on the SMEFT operators and on the leptoquark parameters, which will test energy scales up to 15 TeV. In many cases those limits exceed current constraints from LHC and atomic parity violation (APV) experiments. We also demonstrate that degeneracies of different SMEFT operators can partially be resolved by use of APV experiments and different targets (protons and ${}^{12}\mathrm{C}$) at P2. Moreover, we show that P2 could confirm or resolve potential tensions between the theoretical and experimental determinations of the weak charge of ${}^{133}\mathrm{Cs}$.

Figure 1

Expected 95% CL exclusion limits from P2 for scalar leptoquarks assuming one coupling to dominate, compared to existing bounds from APV [72] and the LHC limits from pair production (PP) [73, 74], dilepton [75] and single resonant production (SRP) [76] channels. The constant ratios $m_{\mathrm{LQ}}/g_{\mathrm{LQ}}$ from P2, APV and ATLAS-Dilepton correspond to the entries of Table 5.

Figure 2

Expected 95% CL exclusion limits from P2 for vector leptoquarks assuming one coupling to dominate, compared to existing bounds from APV [72] and the LHC limits from pair production (PP) [73, 74], dilepton [75] and single resonant production (SRP) [76] channels. The constant ratios $m_{\mathrm{LQ}}/g_{\mathrm{LQ}}$ from P2, APV and ATLAS-Dilepton correspond to the entries of Table 5.

Figure 3

Expected exclusion limits from P2 considering two SMEFT coefficients at a time, compared with existing measurement from APV [72]. The SM expectation is marked by an asterisk and the best fit to APV is shown as a dark green line. The EFT scale $\mathrm{\Lambda }$ is set to 1 TeV.