First determination of the 蟻 parameter at鈭� s= 13 TeV鈥損robing the existence of a colourless three-gluon bound state

Abstract

The TOTEM experiment at the LHC has performed the first measurement at 鈭�

s = 13TeV of the 蟻 parameter, the real to imaginary ratio of the nuclear elastic scattering amplitude at t = 0, obtaining the following results: 蟻 = 0.09卤0.01 and 蟻 = 0.10卤0.01, depending on different physics assumptions and mathematical modelling. The unprecedented precision of the 蟻 measurement, combined with the TOTEM total cross-section measurements in an energy range larger than 10TeV (from 2.76 to 13TeV), has implied the exclusion of all the models classified and published by COMPETE. The 蟻 results obtained by TOTEM are compatible with the predictions, from alternative theoretical models both in the Regge-like framework and in the modern QCD framework, of a colourless 3-gluon bound state exchange in the t-channel of the proton-proton elastic scattering. On the contrary, if shown that the 3-gluon bound state t-channel exchange is not of importance for the description of elastic scattering, the 蟻 value determined by TOTEM would represent a first evidence of a slowing down of the total cross-section growth at higher energies.