Non-universality of transverse momentum dependent parton distribution functions

In the field theoretical description of hadronic scattering processes, single transverse-spin asymmetries arise due to gluon initial and final state interactions. These interactions lead to process dependent Wilson lines in the operator definitions of transverse momentum dependent parton distribution functions. In particular for hadron-hadron scattering processes with hadronic final states this has important ramifications for possible factorization formulas in terms of (non)universal TMD parton distribution functions. In this paper we will systematically separate the universality-breaking parts of the TMD parton correlators from the universal T-even and T-odd parts. This might play an important role in future factorization studies for these processes. We also show that such factorization theorems will (amongst others) involve the gluonic pole cross sections, which have previously been shown to describe the hard partonic scattering in weighted spin asymmetries.Comment: v2: some textual changes in the paper and corrections in references, to appear in Nucl. Phys.

Gluonic Pole Cross Sections and Single Spin Asymmetries in Hadron-Hadron Scattering

The gauge-links connecting the parton field operators in the hadronic matrix elements appearing in the transverse momentum dependent distribution functions give rise to T-odd effects. Due to the process-dependence of the gauge-links the T-odd distribution functions appear with different pre-factors. A consequence is that in the description of single spin asymmetries the parton distribution and fragmentation functions are convoluted with gluonic pole cross sections rather than the basic partonic cross sections. In this paper we calculate the gluonic pole cross sections encountered in single spin asymmetries in hadron-hadron scattering. The case of back-to-back pion production in polarized proton-proton scattering is worked out explicitly. It is shown how T-odd gluon distribution functions originating from gluonic pole matrix elements appear in twofold.Comment: v2: includes explicit definitions of polarized cross sections + minor corrections; to appear in JHE

Sivers Effect Asymmetries in Hadronic Collisions

We argue that weighted azimuthal single spin asymmetries in back-to-back jet or pion production in polarized proton-proton scattering can be written as convolutions of universal distribution and fragmentation functions with gluonic pole cross sections as hard functions. Gluonic pole cross sections are gauge-invariant weighted sums of Feynman diagrams. The weight factors are a direct consequence of the (diagram-dependence of) gauge links. The best known consequence of the gauge links is the generation of the Sivers effect that is a source for single-spin asymmetries. Moreover, due to the dependence of the gauge links on the color-flow of the hard diagram the Sivers effect in SIDIS enters with opposite sign as it does in Drell-Yan scattering. The weight factors in the gluonic pole cross sections are the appropriate generalizations to more complicated processes of this relative sign difference. Furthermore, it is argued that the gluon-Sivers effect appears in twofold.Comment: Contribution to the 17th International Spin Physics Symposium (SPIN2006), Kyoto, Japan, Oct. 2-7, 200

Azimuthal Spin Asymmetries in Hadronic Processes

Mulders, P.J.G. [Promotor

Universality of Single Spin Asymmetries in Hard Processes

We discuss the use of time reversal symmetry in the classification of parton correlators. Specifically, we consider the role of (small) intrinsic transverse momenta in these correlators and the determination of the proper color gauge link. The transverse momentum weighted correlators in hard processes can be expressed as a product of universal gluonic pole matrix elements and gluonic pole cross sections.Comment: Contributed paper at DIS2006, 4 page

Generalized Universality for TMD Distribution Functions

Azimuthal asymmetries in high-energy processes, most pronounced showing up in combination with single or double (transverse) spin asymmetries, can be understood with the help of transverse momentum dependent (TMD) parton distribution and fragmentation functions. These appear in correlators containing expectation values of quark and gluon operators. TMDs allow access to new operators as compared to collinear (transverse momentum integrated) correlators. These operators include nontrivial process dependent Wilson lines breaking universality for TMDs. Making an angular decomposition in the azimuthal angle, we define a set of universal TMDs of definite rank, which appear with process dependent gluonic pole factors in a way similar to the sign of T-odd parton distribution functions in deep inelastic scattering or the Drell-Yan process. In particular, we show that for a spin 1/2 quark target there are three pretzelocity functions.Comment: 9 pages, updated references and minor corrections, to appear in the proceedings of the QCD Evolution Workshop 2012 (May 14-17, JLAB

Systematic Analysis of Rebound Effects for "Greening by ICT" Initiatives

The application of ICT can lead to considerable reductions in the energy consumption of society. Although ICT itself consumes energy, there are many good reasons to explore the possibilities of 'green ICT'. After decades of experiments and research, ICTs designed to be 'green' still holds the promise of leading to substantial ecological benefits by means of dematerialisation, more efficient production processes and changed (more sustainable) human behaviour. Up till now, the effects of ICT on energy consumption are much less straightforward due to rebound effects: effects that have a negative influence on the intended positive effect. In parallel, rebound effects themselves have in turn other side effects as well, so there are many interacting effects to account for, greatly adding to complexity of the discussion. Despite evidence that suggests otherwise, initiatives that focus on 'greening by ICT' do notaccount for a consistent analysis of these rebound effects. This paper proposes an approach that enables to map and analyze these rebound effects systematically. This approach is applied in two related cases, teleworking and the use of Smart Working Centres. The Rapid Assessment Program (RAP) is used as a simulation model to identify which chains of effects are most interesting to consider for intervention. The application in the two cases demonstrates that rebound effects can by structured and that the RAP is a very suitable way to do so and provides a good assessment of net sustainability effects.rebound effects, Rapid Assesment Program, greening by ICT, teleworking.

Spin asymmetries in jet-hyperon production at LHC

We consider polarized Lambda hyperon production in proton-proton scattering, p p -> (\Lambda^\uparrow jet) jet X, in the kinematical region of the LHC experiments, in particular the ALICE experiment. We present a new Lambda polarization observable that arises from the Sivers effect in the fragmentation process. It can be large even at midrapidity and therefore, is of interest for high energy hadron collider experiments. Apart from its potential to shed light on the mechanisms behind the phenomenon of Lambda polarization arising in unpolarized hadronic collisions, the new observable in principle also allows to test the possible color flow dependence of single spin asymmetries and the (non)universality of transverse momentum dependent fragmentation functions.Comment: 11 pages, 10 eps figures; minor modifications, conclusions unchanged, version to be publishe

Single spin asymmetries in hadron-hadron collisions

We study weighted azimuthal single spin asymmetries in hadron-hadron scattering using the diagrammatic approach at leading order and assuming factorization. The effects of the intrinsic transverse momenta of the partons are taken into account. We show that the way in which $T$-odd functions, such as the Sivers function, appear in these processes does not merely involve a sign flip when compared with semi-inclusive deep inelastic scattering, such as in the case of the Drell-Yan process. Expressions for the weighted scattering cross sections in terms of distribution and fragmentation functions folded with hard cross sections are obtained by introducing modified hard cross sections, referred to as gluonic pole cross sections.Comment: 22 pages, 4 figures; minor text modifications and some additional reference