Evidence for non-exponential elastic proton-proton differential cross-section at low |t| and √s=8 TeV by TOTEM

The TOTEM experiment has made a precise measurement of the elastic proton proton differential cross-section at the centre-of-mass energy root s = 8 TeV based on a high-statistics data sample obtained with the beta* = 90 m optics. Both the statistical and systematic uncertainties remain below 1%, except for the t-independent contribution from the overall normalisation. This unprecedented precision allows to exclude a purely exponential differential cross-section in the range of four-momentum transfer squared 0.027 < vertical bar t vertical bar < 0.2 GeV2 with a significance greater than 7 sigma. Two extended parametrisations, with quadratic and cubic polynomials in the exponent, are shown to be well compatible with the data. Using them for the differential cross-section extrapolation to t = 0, and further applying the optical theorem, yields total cross-section estimates of (101.5 +/- 2.1) mb and (101.9 +/- 2.1) mb, respectively, in agreement with previous TOTEM measurements.