NNLO soft function for top quark pair production at small transverse momentum

Understand

The cross section for top quark pair production factorizes at small transverse momentum of the heavy quark pair, $q_T$.

• One of the key ingredients that appears in the factorization formula is the soft function, which mediates soft gluon exchanges between particles and gives rise to colour correlations.
• We present the complete result for the small-$q_T$ soft function at the next-to-next-to-leading order.
• This is the last missing element needed to calculate the NNLO cross section for top quark pair production by means of the $q_T$ slicing method.