Markus Diehl, Jonathan R. Gaunt, Peter Ploessl, Andreas Schafer
SciPost Phys. 7, 017 (2019) ·
published 6 August 2019

· pdf
Double parton distributions (DPDs) receive a shortdistance contribution from
a single parton splitting to yield the two observed partons. We investigate
this mechanism at nexttoleading order (NLO) in perturbation theory.
Technically, we compute the twoloop matching of both the position and momentum
space DPDs onto ordinary PDFs. This also yields the 1 > 2 splitting functions
appearing in the evolution of momentumspace DPDs at NLO. We give results for
the unpolarised, coloursinglet DPDs in all partonic channels. These quantities
are required for calculations of double parton scattering at full NLO. We
discuss various kinematic limits of our results, and we verify that the 1 > 2
splitting functions are consistent with the number and momentum sum rules for
DPDs.
Daniël Boer, Tom van Daal, Jonathan R. Gaunt, Tomas Kasemets, Piet J. Mulders
SciPost Phys. 3, 040 (2017) ·
published 19 December 2017

· pdf
It has been suggested that a colourentanglement effect exists in the
DrellYan cross section for the 'double Todd' contributions at low transverse
momentum $Q_T$, rendering the colour structure different from that predicted by
the usual factorisation formula [1]. These Todd contributions can come from
the BoerMulders or Sivers transverse momentum dependent distribution
functions. The different colour structure should be visible already at the
lowest possible order that gives a contribution to the double BoerMulders
(dBM) or double Sivers (dS) effect, that is at the level of two gluon
exchanges. To discriminate between the different predictions, we compute the
leadingpower contribution to the low$Q_T$ dBM cross section at the twogluon
exchange order in the context of a spectator model. The computation is
performed using a method of regions analysis with Collins subtraction terms
implemented. The results conform with the predictions of the factorisation
formula. In the cancellation of the colour entanglement, diagrams containing
the threegluon vertex are essential. Furthermore, the Glauber region turns out
to play an important role  in fact, it is possible to assign the full
contribution to the dBM cross section at the given order to the region in which
the two gluons have Glauber scaling. A similar disentanglement of colour is
found for the dS effect.
Daniël Boer, Tom van Daal, Jonathan R. Gaunt, Tomas Kasemets, Piet J. Mulders
SciPost Phys. 3, 040 (2017) ·
published 19 December 2017

· pdf
It has been suggested that a colourentanglement effect exists in the
DrellYan cross section for the 'double Todd' contributions at low transverse
momentum $Q_T$, rendering the colour structure different from that predicted by
the usual factorisation formula [1]. These Todd contributions can come from
the BoerMulders or Sivers transverse momentum dependent distribution
functions. The different colour structure should be visible already at the
lowest possible order that gives a contribution to the double BoerMulders
(dBM) or double Sivers (dS) effect, that is at the level of two gluon
exchanges. To discriminate between the different predictions, we compute the
leadingpower contribution to the low$Q_T$ dBM cross section at the twogluon
exchange order in the context of a spectator model. The computation is
performed using a method of regions analysis with Collins subtraction terms
implemented. The results conform with the predictions of the factorisation
formula. In the cancellation of the colour entanglement, diagrams containing
the threegluon vertex are essential. Furthermore, the Glauber region turns out
to play an important role  in fact, it is possible to assign the full
contribution to the dBM cross section at the given order to the region in which
the two gluons have Glauber scaling. A similar disentanglement of colour is
found for the dS effect.