120 research outputs found
Production of massless charm jets in pp collisions at next-to-leading order of QCD
We present predictions for the inclusive production of charm jets in
proton-proton collisions at 7 TeV. Several CTEQ parton distribution functions
(PDFs) of the CTEQ6.6M type are employed, where two of the CTEQ6.6 PDFs have
intrinsic charm. At large enough jet transverse momentum and large jet
rapidity, the intrinsic charm content can be tested.Comment: 11 pages, 4 figure
TEVATRON-HERA Colour-Octet Charmonium Anomaly Versus Higher-Order QCD Effects
Approximately taking into account the higher-order effects due to
multiple-gluon initial-state radiation, we extract from the latest Tevatron
data of prompt J/psi hadroproduction the leading colour-octet matrix elements
within the nonrelativistic-QCD (NRQCD) factorization formalism proposed by
Bodwin, Braaten, and Lepage. We find that the matrix elements which describe
the formation of J/psi mesons from colour-octet cc-bar pairs in the
angular-momentum states ^{2S+1}L_J = ^1S_0 and ^3P_J, with J = 0,1,2, which are
responsible for the excess of the predicted cross section of inelastic J/psi
photoproduction over the existing HERA data at high values of the inelasticity
variable z, are significantly reduced. We conclude that it is premature to
proclaim a discrepancy between the Tevatron and HERA measurements of inclusive
J/psi production in the NRQCD framework. We also consider J/psi mesons
originating from the radiative feed down of promptly produced chi_{cJ} mesons.Comment: 28 pages (Latex), 12 figures (Postscript
Anatomy of the pQCD Approach to the Baryonic Decays
We calculate the CP-averaged branching ratios and CP-violating asymmetries
for the two-body charmless hadronic decays in the
perturbative QCD (pQCD) approach to lowest order in . The baryon
distribution amplitudes involved in the factorization formulae are considered
to the leading twist accuracy and the distribution amplitudes of the proton are
expanded to the next-to-leading conformal spin (i.e., "P" -waves), the moments
of which are determined from QCD sum rules. Our work shows that the
contributions from the factorizable diagrams in
decays are much smaller compared to the non-factorizable diagrams in the
conventional pQCD approach. We argue that this reflects the estimates of the
transition form factors in the factorization approach,
which are found typically an order of magnitude smaller than those estimated in
the light-cone sum rules and in the non-relativistic quark model. As an
alternative, we adopt a hybrid pQCD approach, in which we compute the
factorizable contributions with the form factors taken from
the light cone QCD sum rules. The non-factorizable diagrams are evaluated
utilizing the conventional pQCD formalism which is free from the endpoint
singularities. The predictions worked out here are confronted with the recently
available data from the CDF collaboration on the branching ratios and the
direct CP asymmetries for the decays , and . The asymmetry parameter relevant for the anisotropic angular
distribution of the emitted proton in the polarized baryon decays
is also calculated for the two decay modes.Comment: 47 pages, 9 figures, 8 tables; typos and references corrected;
version corresponds to the one accepted for publication in Phys. Rev.
Evidence for Factorization Breaking in Diffractive Low-Q^2 Dijet Production
We calculate diffractive dijet production in deep-inelastic scattering at
next-to-leading order of perturbative QCD, including contributions from direct
and resolved photons, and compare our predictions to preliminary data from the
H1 collaboration at HERA. In contrast to recent experimental claims, evidence
for factorization breaking is found only for resolved, and not direct, photon
contributions. No evidence is found for large normalization uncertainties in
diffractive parton densities. The results confirm theoretical expectations for
the (non-)cancellation of soft singularities in diffractive scattering as well
as previous results for (almost) real photoproduction.Comment: 4 pages, 3 figure
Open charm hadroproduction and the charm content of the proton
We advocate charmed-hadron inclusive hadroproduction as a laboratory to probe
intrinsic charm (IC) inside the colliding hadrons. Working at next-to-leading
order in the general-mass variable-flavor-number scheme endowed with
non-perturbative fragmentation functions recently extracted from a global fit
to e^+e^- annihilation data from KEKB, CESR, and LEP1, we first assess the
sensitivity of Tevatron data of D^0, D^+, and D^{*+} inclusive production to
the IC parameterizations provided by Pumplin et al. We then argue that similar
data from pp collisions at RHIC would have the potential to discriminate
between different IC models provided they reach out to sufficiently large
values of transverse momentum.Comment: 22 pages, 7 figures; discussion of large-p_T range at the Tevatron
and high-energy mode of RHIC included, 2 figures added; accepted for
publication in Phys. Rev.
Factorization scheme and scale dependence in diffractive dijet production at low Q^2
We calculate diffractive dijet production in deep-inelastic scattering at
next-to-leading order of perturbative QCD, including contributions from direct
and resolved photons, and compare our predictions to preliminary data from the
H1 collaboration at HERA. We study how the cross section depends on the
factorization scheme and scale M_\gamma at the virtual photon vertex for the
occurrence of factorization breaking. The strong M_\gamma-dependence, which is
present when only the resolved cross section is suppressed, is tamed by
introducing the suppression also into the initial-state NLO correction of the
direct part.Comment: 14 pages, 6 figure
Non-Leptonic Decays of B Mesons and Strong Coupling Constants
Non-leptonic decays of B mesons into two mesons or meson resonances are
studied on the basis of two versions of simple pole-dominance models involving
scalar, vector, pseudoscalar and axial-vector poles. The results are compared
with those obtained from the usual factorization model and used to obtain
information on strong coupling constants between B meson and one light or one
charmed meson, respectively. These coupling constants are compared to results
from various QCD sum rule calculations.Comment: Latex file 35 pages, including 3 figure
Review of factorization breaking in diffractive photoproduction of dijets
After the final analyses of the H1 and ZEUS collaborations for the
diffractive photoproduction of dijets have appeared, we have recalculated these
cross sections in next-to-leading order (NLO) of perturbative QCD to see
whether they can be interpreted consistently. The results of these calculations
are compared to the data of both collaborations. We find that at NLO the cross
sections disagree with the data, showing that factorization breaking occurs at
this order. If direct and resolved contributions are both suppressed by the
same amount, the global suppression factor depends on the transverse-energy cut
and is 0.42 for the H1 and 0.71 for the ZEUS analysis. However, by suppressing
only the resolved contribution by a factor of approximately three, also
reasonably good agreement with all the data is found. The size of the
factorization breaking effects for resolved photons agrees with
absorptive-model predictions.Comment: 22 pages, 2 tables, 8 figures. Invited brief review for Modern
Physics Letters
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