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<tt>Theory Center Seminar<br>
Wed., June 13, 2012<br>
2:00 p.m. (coffee at 1:45 p.m.)<br>
CEBAF Center, Room A210A<br>
<br>
Hrayr Matevosyan <br>
University of Adelaide<br>
<br>
<big><b>Collins Fragmentation Functions Within NJL-jet Model</b></big></tt><big><b>
</b></big><tt><br>
<br>
The Collins Fragmentation Functions allow access to parton
transversity distribution function</tt> <tt><br>
in nucleon in SIDIS experiments, and have been widely explored
recently both in theoretical<br>
and experimental studies. Most notably, the experimental
measurements hint that, unlike the<br>
unpolarized fragmentation functions, the favored and unfavored
Collins functions have a similar<br>
size but opposite sign. This is in distinct contrast with most
theoretical models, which lack a <br>
mechanism for calculating the unfavored fragmentation functions
altogether. In this talk I will <br>
present our recent work on extending the NJL-jet model to
accommodate hadronization of a<br>
transversely polarized quark and explore the Collins effect. Our
model calculation of transverse<br>
momentum dependent pion and kaon Collins functions will be
presented. The remarkable feature<br>
of this model is that, for very clear physical reasons which we
explain, the one-half moment of the<br>
favored Collins fragmentation functions, are positive and peak at
large values of $z$, but decrease<br>
and oscillate at small values of $z$. The one-half moment of the
unfavored Collins functions have<br>
comparable magnitude but opposite sign to the favored functions,
vanish at large $z$ and peak<br>
at small values of $z$. Moreover, the transverse momentum
dependence of the model Collins<br>
functions differs significantly from the Gaussian form widely used
in empirical parametrizations. </tt>
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