443 research outputs found
On the forward-backward charge asymmetry in e+e- -annihilation into hadrons at high energies
The forward-backward asymmetry in e+ e- annihilation into a quark-antiquark
pair is considered in the double-logarithmic approximation at energies much
higher than the masses of the weak bosons. It is shown that after accounting to
all orders for the exchange of virtual photons and W, Z -bosons one is lead to
the following effect (asymmetry): quarks with positive electric charge (e.g. u,
\bar{d}) tend to move in the e+ - direction whereas quarks with negative
charges (e.g. d, \bar{u}) tend to move in the e- - direction. The value of the
asymmetry grows with increasing energy when the produced quarks are within a
cone with opening angle, in the cmf, \theta_0\sim 2M_Z/\sqrt{s} around the e+e-
-beam. Outside this cone, at \theta_0 << \theta << 1, the asymmetry is
inversely proportional to \theta .Comment: 17 Pages, 2 Tables, 4 Figures. Hadronization effects to the asymmetry
are considered with more detail
Light-by-light scattering in Double-Logarithmic Approximation
In the present paper we consider the elastic 2 -> 2 -scattering of virtual
photons at high energies in the forward kinematics at zero and non-zero values
of t. Accounting for both gluon and quark double-logarithmic (DL) contributions
to all orders in the QCD coupling, we obtain explicit expressions for
amplitudes of this process in Double-Logarithmic Approximation (DLA). First we
keep the QCD coupling fixed and then account for running coupling effects.
Applying the saddle-point method to the obtained expressions for the scattering
amplitude, we calculate the high-energy asymptotics of the amplitude, which
proved to be of the Regge form. The Reggeon bears the vacuum quantum numbers
and therefore it is a new, DL contribution to Pomeron. Comparison of the DL
Pomeron to the BFKL Pomeron shows that contribution of the DL Pomeron to the
high-energy asymptotics is of the same order as contribution of the BFKL
Pomeron, so the DL Pomeron should be taken into account together with the BFKL
Pomeron. We estimate the applicability region for the asymptotics of the
light-by-light scattering amplitude, where the the DL Pomeron can reliably
represent the parent amplitude.Comment: 16 pages, 4 figures. Multiple errors are corrected, 2 figs are added,
comparizon to BFKL is done in more detai
Comment on the recent COMPASS data on the spin structure function g_1
We examine the recent COMPASS data on the spin structure function g_1
singlet. We show that it is rather difficult to use the data in the present
form in order to draw conclusions on the initial parton densities. However, our
tentative estimate is that the data better agree with positive rather than
negative initial gluon densities.Comment: 8 pages, 1 figur
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