[Jlab-seminars] Theory Center Seminar - TODAY at 2:00 P.M.

[Mary Fox]

Theory Center Seminar
Wed., June 13, 2012
2:00 p.m. (coffee at 1:45 p.m.)
CEBAF Center, Room A210A

Hrayr Matevosyan
University of Adelaide

*Collins Fragmentation Functions Within NJL-jet Model***

The Collins Fragmentation Functions allow access to parton transversity 
distribution function
in nucleon in SIDIS experiments, and have been widely explored recently 
both in theoretical
and experimental studies. Most notably, the experimental measurements 
hint that, unlike the
unpolarized fragmentation functions, the favored and unfavored Collins 
functions have a similar
size but opposite sign. This is in distinct contrast with most 
theoretical models, which lack a
mechanism for calculating the unfavored fragmentation functions 
altogether. In this talk I will
present our recent work on extending the NJL-jet model to accommodate 
hadronization of a
transversely polarized quark and explore the Collins effect. Our model 
calculation of transverse
momentum dependent pion and kaon Collins functions will be presented. 
The remarkable feature
of this model is that, for very clear physical reasons which we explain, 
the one-half moment of the
favored Collins fragmentation functions, are positive and peak at large 
values of $z$, but decrease
and oscillate at small values of $z$. The one-half moment of the 
unfavored Collins functions have
comparable magnitude but opposite sign to the favored functions, vanish 
at large $z$ and peak
at small values of $z$. Moreover, the transverse momentum dependence of 
the model Collins
functions differs significantly from the Gaussian form widely used in 
empirical parametrizations.
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