First constraint on Born-rule violations at high-energy colliders

Abstract

We obtain an experimental constraint on possible Born-rule violations at high-energy colliders. We model Born-rule violations with differential scattering cross sections $d\ddot{I}ƒ/d\hat{I}\text{c◯}$ subject to an angular smearing by a narrow Gaussian of width $\epsilon$ (with respect to $x=\cos \hat{I}¸$ for scattering angle $\hat{I}¸$). For large-angle Bhabha ($e^{+}{e}^{-}\to e^{+}{e}^{-}$) scattering, at a centre-of-mass energy $\sqrt{s}=29\mathrm{GeV}$, data from the PEP collider at SLAC allow us to set an upper bound of $\epsilon <0.042$ at $95\%$ confidence. This corresponds to a Gaussian smearing over an angular range of twice the experimental bin width, and hence provides a physically meaningful limit on deviations from the Born rule. Future prospects for improving this limit are discussed.

6 pages, RevTex, 3 figures