Speaker
Description
We discuss recent extraction of parton distribution function of pion in the valence region
which observed an unexpectedly soft $(1-x)^\beta$, $\beta\sim 1$ behavior, contradicting several theoretical predictions including the ones based on the hard
gluon exchange, according to which $\beta =2$. In this work we calculated the pion PDF within the theoretical approach based on spectral
function representation of valence structure in hadrons.
The approach was first applied for nucleon valence PDF’s which demonstrated the existence of pion-cloud structure in the nucleon already at the starting $Q_0$ for which initial PDF’s are defined. Our calculation also shows substantial high momentum component in nucleon for large x. One of the non-trivial predictions of spectral function approach is that the position of the peak for x weighted nucleon valence PDF (xPDF) has an upper bound of 1/4 (instead of 1/3 as expected in simple parton models) and confirmed experimentally.
Applying the same approach for calculation of pion valence PDF’s, we first observe that no additional residual structure exists in the pion as it was the case for nucleons. Our calculation largely describes the recently obtained phenomenological PDF’s by JAM collaboration.
We observe that the Feynman mechanism is responsible for pion PDF at
relatively large x leaving little room for the hard q\bar q interaction at large x region.One non-trivial observation is that the peak position of xPDF defines the analytic behavior of valence PDF at $x\to 1$ limit.
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