Drell-Yan angular lepton distributions at small x from TMD factorization.

Abstract

The Drell-Yan process is studied in the framework of TMD factorization in the Sudakov region s » Q2 » $$ {q}_{\perp}^2 $$ q ⊥ 2 corresponding to recent LHC experiments with Q2 of order of mass of Z-boson and transverse momentum of DY pair ∼ few tens GeV. The DY hadronic tensors are expressed in terms of quark and quark-gluon TMDs with $$ \frac{1}{Q^2} $$ 1 Q 2 and $$ \frac{1}{N_c^2} $$ 1 N c 2 accuracy. It is demonstrated that in the leading order in Nc the higher-twist quark-quark-gluon TMDs reduce to leading-twist TMDs due to QCD equation of motion. The resulting hadronic tensors depend on two leading-twist TMDs: f1 responsible for total DY cross section, and Boer-Mulders function $$ {h}_1^{\perp } $$ h 1 ⊥ . The corresponding qualitative and semi-quantitative predictions seem to agree with LHC data on five angular coefficients A0− A4 of DY pair production. The remaining three coefficients A5− A7 are determined by quark-quark-gluon TMDs multiplied by extra $$ \frac{1}{N_c} $$ 1 N c so they appear to be relatively small in accordance with LHC results.

Transverse momentum dependent operator expansion at next-to-leading power

“…In the past years, computations of power correction for TMD factorized cross-sections have been made by several groups, see [13][14][15][16][17][18][19]. These computations required an update of existing methods.…”

Factorization for azimuthal asymmetries in SIDIS at next-to-leading power

“…SCET has already been used to study subleading-power factorization in other processes, allowing us to leverage various results in the literature [42,43,, see also [82][83][84][85][86][87][88][89][90][91][92]. Recently, there have been first attempts to study TMD factorization at subleading power, including analysis at small-x [93,94] and investigations of the factorization structure with SCET and similar techniques [95,96].…”

Several Topics on Transverse Momentum-Dependent Fragmentation Functions

“…Contributions from higher twist TMD PDFs and FFs were studied some time ago [42], but few advances have been made in the systematic derivations of the TMD factorization formula at the higher twist gain. Various theoretical methods have been applied to derive the TMD factorization scheme at the twist-3 level, such as the TMD operator expansion technique [67][68][69], the soft-colinear effective theory approach [70], factorization from functional integral [71][72][73][74], and a very recent work from [75], etc. The TMD factorization at the higher twist level is far from being completed, which requires further theoretical efforts.…”

“…In addition to the leading-twist FFs, which usually have probability interpretations, the high-twist FFs have been found o be much more important than expected in recent years for understanding precise experimental data . Although the colinear factorization at subleading power was demonstrated some time ago, the TMD factorization beyond the leading power is still under exploration, and some approaches have been proposed [67][68][69][70][71][72][73][74][75]. Although high-twist contributions are formally power suppressed, their contributions to the cross section might not be negligible and may have significant effects in certain kinematics or observables.…”