  The TOTEM 2.76, 7, 8, and 13 TeV pp elastic differential cross sections are
extrapolated using a data-driven approach to obtain the 1.96 TeV pp elastic
cross section. A difference with a 3.4$\sigma$ significance is observed between
the extrapolated pp elastic cross section and the D0 p$\bar{\rm p}$ elastic
cross section at 1.96 TeV in the region of the diffractive minimum and the
second maximum of the pp cross section, providing evidence for colourless C-odd
gluonic exchanges, also denoted as odderon. These results are combined with a
TOTEM analysis of the same $t$-channel C-odd exchanges based on forward pp
elastic scattering at TeV scale. The combined significance is larger than
5$\sigma$ and is interpreted as the first observation of odderon exchange.
