DaniŽl Boer's Physics Webpage

Topic 1: Spin effects in high energy scattering

Description & objectives:

Quarks and gluons inside protons can be in various polarization states, which can give different contributions to scattering cross sections. Due to the confinement property of QCD this is not easily sorted out, rather it requires the measurement of complicated observables, typically azimuthal asymmetries, to disentangle the different spin contributions. One objective of my research is to find the simplest observables sensitive to the spin states and to predict their dependence on the energy and momentum of the particles involved.

Spin is the intrinsic angular momentum and like in any interacting theory there can be exchange between spin and orbital angular momentum. It turns out that in Quantum Field Theory, especially in the nonperturbative regime, the spin-orbit correlations are very hard to describe. Experiments have shown however that such effects are large. Once they are well-described theoretically (which is not the case yet), one can start using them as a tool. This is what my research on this topic is about: getting a handle on the spin states of quarks and gluons inside protons (which may itself be polarized or not) and try to apply the obtained knowledge. The ultimate goal is to reach the point where people view collisions with protons as the polarized quark/gluon collisions that they in essence are. This will eventually provide additional tools to study new physics beyond the Standard Model.

The possible non-trivial quark and gluon spin effects have been categorized and go by names like the Sivers effect, the Collins effect, and one is also associated with my name: the Boer-Mulders effect.

Funding:

Over the years my research in this topic has been received financial support from the Dutch foundation FOM and from the places where I had positions: NIKHEF, the RIKEN-BNL Research Center at Brookhaven National Laboratory, the VU University Amsterdam and the University of Groningen.

Highlights:

Selected publications: