3 research outputs found
Inclusive production of meson in proton-proton collisions at BNL RHIC
Inclusive cross sections for production in proton-proton collisions
were calculated in the -factorization approach for the RHIC energy.
Several mechanisms were considered, including direct color-singlet mechanism,
radiative decays of mesons, decays of , open-charm associated
production of as well as weak decays of B mesons. Different
unintegrated gluon distributions from the literature were used. We find that
radiative decays and direct color-singlet contributions constitute the
dominant mechanism of production. These process cannot be consistently
treated within collinear-factorization approach. The results are compared with
recent RHIC data. The new precise data at small transverse momenta impose
stringent constraints on UGDFs. Some UGDFs are inconsistent with the new data.
The Kwieci\'nski UGDFs give the best description of the data. In order to
verify the mechanism suggested here we propose -- jet correlation
measurement and an independent measurement of meson production in
and/or decay channels. Finally, we address the issue of
\J spin alignment.Comment: 26 pages, 20 figures, the text was slightly modified, the title was
modified, more discussion was added, one figure was removed, one was adde
Central exclusive production of scalar \chi_c meson at the Tevatron, RHIC and LHC energies
We calculate several differential distributions for exclusive double
diffractive production in proton-antiproton collisions at the
Tevatron and in proton-proton collisions at RHIC and LHC in terms of
unintegrated gluon distributions (UGDFs) within the -factorisation
approach. The uncertainties of the Khoze-Martin-Ryskin approach are discussed
in detail. The transition vertex is calculated as
a function of gluon virtualities applying the standard pNRQCD technique. The
off-shell effects are discussed and quantified. They lead to a reduction of the
cross section by a factor 2--5, depending on the position in the phase space
and UGDFs. Different models of UGDFs are used and the results are shown and
discussed. The cross section for diffractive component depends strongly on
UGDFs. We calculate also the differential distributions for the fusion mechanism. The integrated cross section for
photon-photon fusion is much smaller than that of diffractive origin. The two
components have very different dependence on momentum transfers in
the nucleon lines as well as azimuthal-angle correlations between both outgoing
nucleons.Comment: 34 pages, 23 figures, 2 table
THE GLUON DISTRIBUTION AT SMALL x OBTAINED FROM A UNIFIED EVOLUTION EQUATION.
We solve a unified integral equation to obtain the and
dependence of the gluon distribution of a proton in the small regime; where
and are the longitudinal momentum fraction and the transverse
momentum of the gluon probed at a scale . The equation generates a gluon
with a steep behaviour, with , and a
distribution which broadens as decreases. We compare our solutions with, on
the one hand, those that we obtain using the double-leading-logarithm
approximation to Altarelli-Parisi evolution and, on the other hand, to those
that we determine from the BFKL equation.Comment: LaTeX file with 10 postscript figures (uuencoded