slac-pub-2605 - SLAC - Stanford University

form factor. It is also clear then that the Drell-Yan-West
between deep inelastic scattering and hadronic form factors
-ll-
connection
is invalid in QCD.
It should be emphasized that, given that the Sudakov form factor S(Q) is a
decreasing function of Q2, the short distance domain where (l-x) >> m/Q gives
the correct asymptotic QCD behavior for the baryon form factor up to correc-
tions of relative order az(Q)S(Q) from the Drell-Yan-West region. In the case
of meson form factors, F,,(Q2), yy+M& etc., the endpoint region (l-x) 5 m/Q
is suppressed by a kinematic factor of m/Q allowing a direct proof of short
distance dominance using operator product and renormalization group methods
i-1,2,61. Further discussion of the exclusive-inclusive connection will be
given in Sect. 4.
Following the above prescription, we can reduce the pion's electro-
magnetic form factor to the form:
F,$Q2) =
(1.12)
where T contains all two-particle irreducible amplitudes for y*+q{ + q - The leading contribution comes from one-gluon
exchange
TH(Xi’Yi,Q) = 1's cl>(Q2) [& + ~][l+b(as~Ql),m/Q)] (1.13)
where e 1 and e2 are the charges carried by particles 1 and 2 (in units of e).
The properties of 4 insure there is no singularity in (1.12) at yi or xi w 0.
Consequently, in leading order, we can replace 6, and cy by Q in (1.12) to
obtain the QCD prediction for the pion form factor [1,8,91
47~ CF as(Q2)
F,(Q2) =.
Q2