226 research outputs found

### Improved Calculations of Quark Distributions in Hadrons: the case of pion

The earlier introduced method of calculation of quark distributions in
hadrons, based on QCD sum rules, is improved. The imaginary part of the virtual
photon forward scattering amplitude on some hadronic current is considered in
the case, when initial and final virtualities of the current $p^2_1$, and
$p^2_2$ are different, $p^2_1\not= p^2_2$. The operator product expansion (OPE)
in $p^2_1$, $p^2_2$ is performed. The sum rule for quark distribution is
obtained using double dispersion representation of the amplitude on one side in
terms of calculated in QCD OPE and on the other side in terms of physical
states contributions. Double Borel transformation in $p^2_1$, $p^2_2$ is
applied to the sum rule, killing background non-diagonal transition terms,
which deteriorated the accuracy in previous calculations. The case of valence
quark distribution in pion is considered, which was impossible to treat by the
previous method. OPE up to dimension 6 operators is performed and leading order
perturbative corrections are accounted. Valence $u$-quark distribution in
$\pi^+$ was found at intermediate $x$, $0.15 < x < 0.7$ and normalization point
$Q^2=2 GeV^2$. These results may be used as input for evolution equations.Comment: 29 pages, LaTeX 2e, 13 eps figures include

### Intrinsic transverse parton momenta in deeply inelastic reactions

Intrinsic transverse parton momenta pT play an important role in the
understanding of azimuthal/spin asymmetries in semi-inclusive deep-inelastic
scattering (SIDIS) and the Drell-Yan process (DY). We review and update what is
presently known about pT from these processes. In particular, we address the
question to which extent data support the popular Gauss model for the
pT-distributions. We find that the Gauss model works very well, and observe
that the intrinsic transverse momenta in SIDIS and DY are compatible, which is
a support for the factorization approach. As a byproduct we recover a simple
but practical way of taking into account the energy dependence of
pT-distributions.Comment: 19 pages, 11 figure

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