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Experiment TOTEM at the LHC at CERN has performed the first measurement of the rho parameter, the real to imaginary ratio of the nuclear elastic scattering amplitude, at center-of-mass collision energy 13 TeV. The unprecedented precision, combined with other TOTEM proton-proton elastic scattering data, favors alternative elastic scattering models that require, in addition to the standard C-even colourless two-gluon compound state (Pomeron) an existence of additional colourless C-odd three-gluon compound state.
Description
Comparison of TOTEM measurements (red solid markers) with predictions of COMPETE models for several values of center-of-mass energies of proton collisions. None of the models, based only on existence of two-gluon colourless Pomeron state is able to describe simultaneously the energy dependence of total elastic cross section (left) and rho parameter (right).