## Abstract

Transverse momentum dependent (TMD) parton distribution functions (PDFs), TMDs for short, are defined as the Fourier transform of matrix elements of non-local combinations of quark and gluon fields. The nonlocality is bridged by gauge links, which for TMDs have characteristic paths (future or past pointing), giving rise to a process dependence that breaks universality. It is possible, however, to construct sets of universal TMDs of which in a given process particular combinations are needed with calculable, process-dependent, coefficients. This occurs for both T-odd and T-even TMDs, including also the unpolarized quark and gluon TMDs. This extends the by now well-known example of T-odd TMDs that appear with opposite sign in single-spin azimuthal asymmetries in semi-inclusive deep inelastic scattering or in the Drell-Yan process. In this paper we analyze the cases where TMDs enter multiplied by products of two transverse momenta, which includes besides the p(T)-broadening observable, also instances with rank-2 structures. To experimentally demonstrate the process dependence of the latter cases requires measurements of second harmonic azimuthal asymmetries, while the p(T)-broadening will require measurements of processes beyond semi-inclusive deep inelastic scattering or the Drell-Yan process. Furthermore, we propose specific quantities that will allow for theoretical studies of the process dependence of TMDs using lattice QCD calculations.

Original language | English |
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Article number | 053 |

Number of pages | 16 |

Journal | Journal of High Energy Physics |

Issue number | 8 |

DOIs | |

Publication status | Published - 13-Aug-2015 |

## Keywords

- QCD Phenomenology
- TRANSVERSE-SPIN ASYMMETRIES
- PARTON DISTRIBUTION-FUNCTIONS
- STATE INTERACTIONS
- HARD PROCESSES
- SINGLE-SPIN
- DRELL-YAN
- TWIST-4
- QCD
- LEPTOPRODUCTION
- DISTRIBUTIONS