31,674 research outputs found
The space-time structure of hard scattering processes
Recent studies of exclusive electroproduction of vector mesons at JLab make
it possible for the first time to play with two independent hard scales: the
virtuality Q^2 of the photon, which sets the observation scale, and the
momentum transfer t to the hadronic system, which sets the interaction scale.
They reinforce the description of hard scattering processes in terms of few
effective degrees of freedom relevant to the Jlab-Hermes energy range.Comment: 4 pages; 5 figure
The X(3872) boson: Molecule or charmonium
It has been argued that the mystery boson X(3872) is a molecule state
consisting of primarily D0-D0*bar + D0bar-D*0. In contrast, apparent puzzles
and potential difficulties have been pointed out for the charmonium assignment
of X(3872). We examine several aspects of these alternatives by
semiquantitative methods since quantitatively accurate results are often hard
to reach on them. We find that some of the observed properties of X(3872), in
particualr, the binding and the production rates are incompatible with the
molecule interpretation. Despite puzzles and obstacles, X(3872) may fit more
likely to the excited triplet P_1 charmonium than to the molecule after mixing
of cc-bar with DD*-bar +Dbar-D* is taken into account. One simple experimental
test is pointed out for distinguishing between a charmonium and an
isospin-mixed molecule in the neutral B decay.Comment: A few sentences of comment are added. One minor rewording in the
Introduction. Two trivial typos are correcte
Inelastic final-state interaction
The final-state interaction in multichannel decay processes is sytematically
studied with application to B decay in mind. Since the final-state inteaction
is intrinsically interwoven with the decay interaction in this case, no simple
phase theorem like "Watson's theorem" holds for experimentally observed final
states. We first examine in detail the two-channel problem as a toy-model to
clarify the issues and to remedy common mistakes made in earlier literature.
Realistic multichannel problems are too challenging for quantitative analysis.
To cope with mathematical complexity, we introduce a method of approximation
that is applicable to the case where one prominant inelastic channel dominates
over all others. We illustrate this approximation method in the amplitude of
the decay B to pi K fed by the intermediate states of a charmed meson pair.
Even with our approximation we need more accurate information of strong
interactions than we have now. Nonethless we are able to obtain some insight in
the issue and draw useful conclusions on general fearyres on the strong phases.Comment: The published version. One figure correcte
Measurements in the Turbulent Boundary Layer at Constant Pressure in Subsonic and Supersonic Flow. Part 2: Laser-Doppler Velocity Measurements
A description of both the mean and the fluctuating components of the flow, and of the Reynolds stress as observed using a dual forward scattering laser-Doppler velocimeter is presented. A detailed description of the instrument and of the data analysis techniques were included in order to fully document the data. A detailed comparison was made between the laser-Doppler results and those presented in Part 1, and an assessment was made of the ability of the laser-Doppler velocimeter to measure the details of the flows involved
Moments of a single entry of circular orthogonal ensembles and Weingarten calculus
Consider a symmetric unitary random matrix
from a circular orthogonal ensemble. In this paper, we study moments of a
single entry . For a diagonal entry we give the explicit
values of the moments, and for an off-diagonal entry we give leading
and subleading terms in the asymptotic expansion with respect to a large matrix
size . Our technique is to apply the Weingarten calculus for a
Haar-distributed unitary matrix.Comment: 17 page
Mean eigenvalues for simple, simply connected, compact Lie groups
We determine for each of the simple, simply connected, compact and complex
Lie groups SU(n), Spin and that particular region inside the unit
disk in the complex plane which is filled by their mean eigenvalues. We give
analytical parameterizations for the boundary curves of these so-called trace
figures. The area enclosed by a trace figure turns out to be a rational
multiple of in each case. We calculate also the length of the boundary
curve and determine the radius of the largest circle that is contained in a
trace figure. The discrete center of the corresponding compact complex Lie
group shows up prominently in the form of cusp points of the trace figure
placed symmetrically on the unit circle. For the exceptional Lie groups ,
and with trivial center we determine the (negative) lower bound on
their mean eigenvalues lying within the real interval . We find the
rational boundary values -2/7, -3/13 and -1/31 for , and ,
respectively.Comment: 12 pages, 8 figure
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The S-Wave π-π Scattering Amplitudes in the Form of the Strip Approximation
Nonlinearity of vacuum reggeons and exclusive diffractive production of vector mesons at HERA
The processes of exclusive photo- and electroproduction of vector mesons
(770), (1020) and (3096) at collision energies and transferred momenta squared are considered in
the framework of a phenomenological Regge-eikonal scheme with nonlinear Regge
trajectories in which their QCD asymptotic behavior is taken into account
explicitly. By comparison of available experimental data from ZEUS and H1
Collaborations with the model predictions it is demonstrated that corresponding
angular distributions and integrated cross-sections in the above-mentioned
kinematical range can be quantitatively described with use of two -even
vacuum Regge trajectories. These are the "soft" pomeron dominating the high
energy reactions without a hard scale and the "hard" pomeron giving an
essential contribution to photo- and electroproduction of heavy vector mesons
and deeply virtual electroproduction of light vector mesons.Comment: 25 pages, 12 figure
General moments of the inverse real Wishart distribution and orthogonal Weingarten functions
Let be a random positive definite symmetric matrix distributed according
to a real Wishart distribution and let be its inverse
matrix. We compute general moments explicitly. To do so, we employ the orthogonal Weingarten
function, which was recently introduced in the study for Haar-distributed
orthogonal matrices. As applications, we give formulas for moments of traces of
a Wishart matrix and its inverse.Comment: 29 pages. The last version differs from the published version, but it
includes Appendi
production off the proton in a Regge-plus-chiral quark approach
A chiral constituent quark model approach, embodying s- and u-channel
exchanges,complemented with a Reggeized treatment for t-channel is presented. A
model is obtained allowing data for and to be describe satisfactorily. For the latter reaction, recently released
data by CLAS and CBELSA/TAPS Collaborations in the system total energy range
GeV are well reproduced due to the inclusion of
Reggeized trajectories instead of simple and poles.
Contribution from "missing" resonances is found to be negligible in the
considered processes.Comment: 23 pages.4 figures,4 tables, to appear in Phys.Rev.
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