Search for Violations of Lorentz Invariance and CPT Symmetry in B_(s)^0 Mixing

Violations of CPT symmetry and Lorentz invariance are searched for by studying interference effects in B^0 mixing and in B_s^0 mixing. Samples of B^0→J/ψK_S^0 and B_s^0→J/ψK^+K^- decays are recorded by the LHCb detector in proton-proton collisions at center-of-mass energies of 7 and 8 TeV, corresponding to an integrated luminosity of 3  fb^-1. No periodic variations of the particle-antiparticle mass differences are found, consistent with Lorentz invariance and CPT symmetry. Results are expressed in terms of the standard model extension parameter Δa_μ with precisions of O(10^-15) and O(10^-14)  GeV for the B^0 and B_s^0 systems, respectively. With no assumption on Lorentz (non)invariance, the CPT-violating parameter z in the B_s^0 system is measured for the first time and found to be Re(z)=-0.022±0.033±0.005 and Im(z)=0.004±0.011±0.002, where the first uncertainties are statistical and the second systematic.