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Author Archives: Dr Anselm Vossen, Ph.D.

New review on transverse spin physics

Happy to announce our comprehensive review on transverse spin physics in semi-inclusive processes:


New publication in PRD: Azimuthal asymmetries of back-to-back π±−(π0, η, π±) pairs in e+e− annihilation

journal reference:

Phys. Rev. D 100, 092008

Welcome Frank Meier

Frank Meier started as a postdoctoral research associate in our group in October. His research focuses on flavor physics at the Belle II experiment.

He brings rich experience from his previous experience at the University of Sydney and he also serves as the analysis tools convener for the Belle II experiment.

Frank Meier

First observation of the the Collins effect for neutral pions and eta mesons submitted for publication

This paper is based on the thesis of  Hairong Li

From the abstract:

This work reports the first observation of azimuthal asymmetries around the thrust axis in

Workshop picture FF2019

Thanks for a successful workshop!

Fragmentation Function Workshop at Duke

Our group is organizing an international workshop on hadronization phenomena at Duke, March 14-16, 2019.

All interested are welcome to attend:


New Postdoc Christopher Dilks

Chris explored the spin structure of the proton in p+p collisions at RHIC and is now using novel probes to study quark-gluon correlations with the CLAS12 detector

First observation of Lambda polarization in e+e- published in PRL




First data on beam-spin asymmetries of di-hadron pairs at CLAS12 shown at DNP

I just came back from the Division of Nuclear Physics meeting of the APS where I could show our first data on beam spin asymmetries from hadron pairs:

This plot shows the asymmetry vs. x Bjorken (roughly the momentum that the struck quark carries of the parent nucleon). There is a very suggestive rise of the measurement that can be interpreted as the force that the gluons exert on a transversely polarized quark as it moves through the proton after being struck.

This is quite interesting since it open up a window to quark-gluon interactions inside the proton and because our understanding is that quarks can only have transverse polarization in an unpolarized nucleon if they also carry transverse momentum (Boer-Mulders effect).

More background can be found in my recent write-up here:


Belle II might revamp the standard model

…well we already knew that, but it made the list of the three experiments which might revamp the standard model in this article here: