2,811 research outputs found
Coulomb scattering of quantum dipoles in QED
We calculate the total scattering cross-section of a dynamical quantum
electrically neutral dipole in QED of the infinitely heavy charge and of the
infinitely heavy dipole in the leading order in electromagnetic coupling
constant.Comment: 7 pages, no figure
The Bose-Einstein Correlations and the strong coupling constant at low energies
It is shown that , the strong coupling constant, can be
determined in the non-perturbative regime from Bose-Einstein correlations
(BEC). The obtained is in agreement with the prescriptions dealt
with in the Analytic Perturbative Theory approach. It also extrapolates
smoothly to the standard perturbative at higher energies. Our
results indicate that BEC dimension can be considered as an alternative
approach to the short range measure between hadrons.Comment: 7 pages, 4 figure
Two-body hadronic charmed meson decays
We study in this work the two-body hadronic charmed meson decays, including
both the PP and VP modes. The latest experimental data are first analyzed in
the diagrammatic approach. The magnitudes and strong phases of the flavor
amplitudes are extracted from the Cabibbo-favored (CF) decay modes using
minimization. The best-fitted values are then used to predict the
branching fractions of the singly-Cabibbo-suppressed (SCS) and
doubly-Cabibbo-suppressed decay modes in the flavor SU(3) symmetry limit. We
observe significant SU(3) breaking effects in some of SCS channels. In the case
of VP modes, we point out that the and amplitudes cannot be
completely determined based on currently available data. We conjecture that the
quoted experimental results for both and are overestimated. We compare the sizes of color-allowed and
color-suppressed tree amplitudes extracted from the diagrammatical approach
with the effective parameters and defined in the factorization
approach. The ratio is more or less universal among the , and modes. This feature allows
us to discriminate between different solutions of topological amplitudes. For
the long-standing puzzle about the ratio , we argue that, in addition to the SU(3)
breaking effect in the spectator amplitudes, the long-distance resonant
contribution through the nearby resonance can naturally explain why
decays more copiously to than through the
-exchange topology.Comment: 32 pages, 5 figures. An alternative method for error bar extraction
is used; last columns of Tables~I to VI, and all entries in Tables~VII, VIII
and X are modified. To appear in PRD
Dynamical approach to MPI four-jet production in Pythia
We improve the treatment of Multiple Parton Interactions (MPI) in
\textsc{Pythia} by including the \12 mechanism and treating the \22 mechanism
in a model-independent way. The \22 mechanism is calculated within the mean
field approximation, and its parameters are expressed through Generalized
Parton Distributions extracted from HERA data.
The parameters related to the transverse parton distribution inside the
proton are thus independent of the performed fit.
The \12 mechanism is included along the lines of the recently developed
perturbative QCD formalism. A unified description of MPI at moderate and hard
transverse momenta is obtained within a consistent framework, in good agreement
with experimental data measured at 7 TeV. Predictions are shown for the
considered observables at 14 TeV. The corresponding code implementing the new
MPI approach is available.Comment: 24 pages, 12 figures, An additional chapter"Comparison with recent
HERWIG Tunes" is added,1 figure adde
Dynamical approach to MPI in W+dijet and Z+dijet production within the PYTHIA event generator
The new numerical approach that includes 1 to 2 mechanism is applied to
double parton scattering (DPS) in W+dijet and Z+dijet final state production in
proton-proton collisions at LHC. By using the underlying event (UE) simulation
from a pythia 8 tune extracted in hadronic events, we show that, like in the
case of a four-jet final state, the inclusion of 1 to 2 mechanism improves the
description of experimental data measured at 7 TeV. In addition, predictions
for proton-proton collisions at a center-of-mass energy of 14 TeV are shown for
DPS- and UE-sensitive observables.Comment: 24 pages 10 figures. arXiv admin note: text overlap with
arXiv:1503.0824
Rapidity distribution of particle multiplicity in DIS at small x
Analytical study of the rapidity distribution of the final state particles in
deep inelastic scattering at small x is presented. We separate and analyse
three sources of particle production: fragmentation of the quark-antiquark
pair, accompanying coherent soft gluon radiation due to octet color exchange in
the t-channel, and fragmentation of gluons that form parton distribution
functions. Connection to Catani-Ciafaloni-Fiorani-Marchesini (CCFM) equations
and the role of gluon reggezation are also discussed.Comment: 14 pages, 6 Figures. Abstract extended, minor misprints corrected,
derivations improved and explanations are streamlined. Published in Physics
Letters, B
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