Sudakov suppression in azimuthal spin asymmetries

It is shown that transverse momentum dependent azimuthal spin asymmetries suffer from suppression due to Sudakov factors, in the region where the transverse momentum is much smaller than the large energy scale Q^2. The size and Q^2 dependence of this suppression are studied numerically for two such asymmetries, both arising due to the Collins effect. General features are discussed of how the fall-off with Q^2 is affected by the nonperturbative Sudakov factor and by the transverse momentum weights and angular dependences that appear in different asymmetries. For a subset of asymmetries the asymptotic Q^2 behavior is calculated analytically, providing an upper bound for the decrease with energy of other asymmetries. The effect of Sudakov factors on the transverse momentum distributions is found to be very significant already at present-day collider energies. Therefore, it is essential to take into account Sudakov factors in transverse momentum dependent azimuthal spin asymmetries.Comment: 17 pages, Revtex, 6 Postscript figures, uses aps.sty, epsf.sty; Section II partly rewritten, Figure 4 replaced, some minor other change

Handedness inside the proton

The transversity of quarks inside unpolarized hadrons and its phenomenology are discussed. Several experimental suggestions are proposed that would allow further study of this intrinsic handedness.Comment: 5 pages, Latex, 1 Postscript figure, uses aipproc.cls; Talk presented at the 15th International Spin Physics Symposium (SPIN2002), Brookhaven National Laboratory, September 9-14, 200

Transversely polarized Lambda production

Transversely polarized Lambda production in hard scattering processes is discussed in terms of a leading twist T-odd fragmentation function which describes the fragmentation of an unpolarized quark into a transversely polarized Lambda. We focus on the properties of this function and its relevance for the RHIC and HERMES experiments.Comment: 4 pages, Latex, 3 Postscript figures; Talk presented at the 7th Conference on Intersections of Particle and Nuclear Physics (CIPANP 2000), Quebec City, Canada, May 200

Aspects of TMD evolution of azimuthal asymmetries

In this contribution TMD evolution of azimuthal asymmetries, in particular of the Sivers and double Collins asymmetries, is addressed. A comparison of the scale dependence is made between asymmetries described with TMD factorization at low transverse momentum and those described with collinear factorization at high transverse momentum. Finally, the advantages of Bessel weighting are discussed: convergence of transverse momentum integrals, suppression of large transverse momentum contributions, and well-defined lattice QCD evaluations of Bessel-weighted TMDs including proper gauge links.Comment: 9 pages, 2 figures, to appear in the proceedings of the QCD Evolution Workshop (QCD2013), Thomas Jefferson National Accelerator Facility, Newport News, VA, May 6-10, 201

Overview of TMD evolution

Transverse momentum dependent parton distributions (TMDs) appear in many scattering processes at high energy, from the semi-inclusive DIS experiments at a few GeV to the Higgs transverse momentum distribution at the LHC. Predictions for TMD observables crucially depend on TMD factorization, which in turn determines the TMD evolution of the observables with energy. In this contribution to SPIN2014 TMD factorization is outlined, including a discussion of the treatment of the nonperturbative region, followed by a summary of results on TMD evolution, mostly applied to azimuthal asymmetries.Comment: 6 pages, no figures, contribution to the proceedings of the 21st International Symposium on Spin Physics (Spin2014), Beijing, China, October 20-24, 201

Gluon TMDs in quarkonium production

Quarkonium production offers good possibilities to study gluon TMDs. In this proceedings contribution this topic is explored for the linearly polarized gluons inside unpolarized hadrons and unpolarized gluons inside transversely polarized hadrons. It is argued that $\chi_{b0/2}$ and $\eta_b$ production at LHC are best to study the effects of linearly polarized gluons in hadronic collisions, by means of angular independent ratios of ratios of cross sections. This can be directly compared to $\cos 2\phi$ asymmetries in heavy quark pair and dijet production in DIS at a future high-energy Electron-Ion Collider (EIC), which probe the same TMDs. In the small-$x$ limit this corresponds to the Weizs\"acker-Williams (WW) gluon distributions, which should show a change in behavior for transverse momenta around the saturation scale. Together with investigations of the dipole (DP) gluon distributions, this can provide valuable information about the polarization of the Color Glass Condensate if sufficiently small $x$ are reached. Quarkonia can also be useful in the study of single transverse spin asymmetries. For transversely polarized hadrons the gluon distribution can be asymmetric, which is referred to as the Sivers effect. It leads to single spin asymmetries in for instance $J/\psi$ (pair) production at AFTER@LHC, which probe the WW or $f$-type gluon Sivers TMD. It allows for a test of a sign-change relation w.r.t. the gluon Sivers TMD probed at an EIC in open heavy quark pair production. Single spin asymmetries in backward inclusive $C$-odd quarkonium production, such as $J/\psi$ production, may offer probes of the DP or $d$-type gluon Sivers TMD at small $x$-values in the polarized proton, which in that limit corresponds to a correlator of a single Wilson loop, describing the spin-dependent odderon.Comment: 9 pages, no figures, contribution to the proceedings of the ECT* Workshop: New Observables in Quarkonium Production (Quarkonium2016), Trento, Italy, 28 February - 4 March 201

Mapping the Transverse Nucleon Spin

The transverse nucleon spin can be transferred to the quarks and gluons in several ways. In the factorizing, hard scattering processes to be considered, these are parameterized at leading twist by the transversity distribution function and at next-to-leading twist by quark-gluon correlation functions. The latter enter the description of the structure function $g_2$ and possibly of single spin asymmetries. It is discussed what is known about these functions and what are the remaining open issues.Comment: 9 pages, uses espcrc1.sty, Invited talk at the European Workshop on the QCD Structure of the Nucleon (QCD-N'02), Ferrara, Italy, April 3-6, 2002, Some minor changes on page