126 research outputs found
Pedagogic model for Deeply Virtual Compton Scattering with quark-hadron duality
We show how quark-hadron duality can emerge for valence spin averaged
structure functions, and for the non-forward distributions of Deeply Virtual
Compton Scattering. Novel factorisations of the non-forward amplitudes are
proposed. Some implications for large angle scattering and deviations from the
quark counting rules are illustrated.Comment: Version accepted by Phys. Rev.
Stabilities of nanohydrated thymine radical cations: insights from multiphoton ionization experiments and ab initio calculations
Multi-photon ionization experiments have been carried out on thymine-water clusters in the gas phase. Metastable H2O loss from T+(H2O)n was observed at n ≥ 3 only. Ab initio quantum-chemical calculations of a large range of optimized T+(H2O)n conformers have been performed up to n = 4, enabling binding energies of water to be derived. These decrease smoothly with n, consistent with the general trend of increasing metastable H2O loss in the experimental data. The lowest-energy conformers of T+(H2O)3 and T+(H2O)4 feature intermolecular bonding via charge-dipole interactions, in contrast with the purely hydrogen-bonded neutrals. We found no evidence for a closed hydration shell at n = 4, also contrasting with studies of neutral clusters
On parton distributions in a photon gas
In some cases it may be useful to know parton distributions in a photon gas.
This may be relevant, e.g., for the analysis of interactions of high energy
cosmic ray particles with the cosmic microwave background radiation. The latter
can be considered as a gas of photons with an almost perfect blackbody
spectrum. An approach to finding such parton distributions is described. The
survival probability of ultra-high energy neutrinos traveling through this
radiation is calculated.Comment: 5 pages, 4 figures, EPJ style files. Some changes in the text. Two
new sections discussing ultra-high energy neutrino damping in the cosmic
microwave background radiation are include
Measuring the Relative Strong Phase in and Decays
In a recently suggested method for measuring the weak phase in
decays, the relative strong phase in and decays (equivalently, in and \od \to K^{*+} K^-) plays a role. It is shown how a study of
the Dalitz plot in can yield information on this phase,
and the size of the data sample which would give a useful measurement is
estimated.Comment: 13 pages, latex, 5 figures, submitted to Phys. Rev. D. Appendix and
some text on additional resonant contributions adde
Nuclear shadowing at low Q^2
We re-examine the role of vector meson dominance in nuclear shadowing at low
Q^2. We find that models which incorporate both vector meson and partonic
mechanisms are consistent with both the magnitude and the Q^2 slope of the
shadowing data.Comment: 7 pages, 2 figures; to appear in Phys. Rev.
Analysis of Two-Body Decays of Charmed Baryons Using the Quark-Diagram Scheme
We give a general formulation of the quark-diagram scheme for the nonleptonic
weak decays of baryons. We apply it to all the decays of the antitriplet and
sextet charmed baryons and express their decay amplitudes in terms of the
quark-diagram amplitudes. We have also given parametrizations for the effects
of final-state interactions. For SU(3) violation effects, we only parametrize
those in the horizontal -loop quark diagrams whose contributions are solely
due to SU(3)-violation effects. In the absence of all these effects, there are
many relations among various decay modes. Some of the relations are valid even
in the presence of final-state interactions when each decay amplitude in the
relation contains only a single phase shift. All these relations provide useful
frameworks to compare with future experiments and to find out the effects of
final-state interactions and SU(3) symmetry violations.Comment: 28 pages, 20 Tables in landscape form, 4 figures. Main changes are:
(i) some errors in the Tables and in the relations between the quark-diagram
amplitudes of this paper and those of Ref.[10] are corrected, (ii)
improvements are made in the presentation so that comparisons with previous
works and what have been done to include SU(3) breaking and final-state
interactions are more clearly stated; to appear in the Physical Review
Strong Decays of Strange Quarkonia
In this paper we evaluate strong decay amplitudes and partial widths of
strange mesons (strangeonia and kaonia) in the 3P0 decay model. We give
numerical results for all energetically allowed open-flavor two-body decay
modes of all nsbar and ssbar strange mesons in the 1S, 2S, 3S, 1P, 2P, 1D and
1F multiplets, comprising strong decays of a total of 43 resonances into 525
two-body modes, with 891 numerically evaluated amplitudes. This set of
resonances includes all strange qqbar states with allowed strong decays
expected in the quark model up to ca. 2.2 GeV. We use standard nonrelativistic
quark model SHO wavefunctions to evaluate these amplitudes, and quote numerical
results for all amplitudes present in each decay mode. We also discuss the
status of the associated experimental candidates, and note which states and
decay modes would be especially interesting for future experimental study at
hadronic, e+e- and photoproduction facilities. These results should also be
useful in distinguishing conventional quark model mesons from exotica such as
glueballs and hybrids through their strong decays.Comment: 69 pages, 5 figures, 39 table
SU(4) Chiral Quark Model with Configuration Mixing
Chiral quark model with configuration mixing and broken SU(3)\times U(1)
symmetry has been extended to include the contribution from c\bar c
fluctuations by considering broken SU(4) instead of SU(3). The implications of
such a model have been studied for quark flavor and spin distribution functions
corresponding to E866 and the NMC data. The predicted parameters regarding the
charm spin distribution functions, for example, \Delta c, \frac{\Delta
c}{{\Delta \Sigma}}, \frac{\Delta c}{c} as well as the charm quark distribution
functions, for example, \bar c, \frac{2\bar c}{(\bar u+\bar d)}, \frac{2 \bar
c}{(u+d)} and \frac{(c+ \bar c)}{\sum (q+\bar q)} are in agreement with other
similar calculations. Specifically, we find \Delta c=-0.009, \frac{\Delta
c}{{\Delta \Sigma}}=-0.02, \bar c=0.03 and \frac{(c+ \bar c)}{\sum (q+\bar
q)}=0.02 for the \chiQM parameters a=0.1, \alpha=0.4, \beta=0.7,
\zeta_{E866}=-1-2 \beta, \zeta_{NMC}=-2-2 \beta and \gamma=0.3, the latter
appears due to the extension of SU(3) to SU(4).Comment: 10 RevTeX pages. Accepted for publication in Phys. Rev.
Search for CP Violation in Charged D Meson Decays
We report results of a search for CP violation in the singly
Cabibbo-suppressed decays D+ -> K- K+ pi+, phi pi+, K*(892)0 K+, and pi- pi+
pi+ based on data from the charm hadroproduction experiment E791 at Fermilab.
We search for a difference in the D+ and D- decay rates for each of the final
states. No evidence for a difference is seen. The decay rate asymmetry
parameters A(CP), defined as the difference in the D+ and D- decay rates
divided by the sum of the decay rates, are measured to be: A(CP)(K K pi) =
-0.014 +/- 0.029, A(CP)(phi pi) = -0.028 +/- 0.036, A(CP)(K*(892) K) = -0.010
+/- 0.050, and A(CP)(pi pi pi) = -0.017 +/- 0.042.Comment: 13 pages, 5 figures, 1 table; Elsevier LaTe
Leptonic and Semileptonic Decays of Charm and Bottom Hadrons
We review the experimental measurements and theoretical descriptions of
leptonic and semileptonic decays of particles containing a single heavy quark,
either charm or bottom. Measurements of bottom semileptonic decays are used to
determine the magnitudes of two fundamental parameters of the standard model,
the Cabibbo-Kobayashi-Maskawa matrix elements and . These
parameters are connected with the physics of quark flavor and mass, and they
have important implications for the breakdown of CP symmetry. To extract
precise values of and from measurements, however,
requires a good understanding of the decay dynamics. Measurements of both charm
and bottom decay distributions provide information on the interactions
governing these processes. The underlying weak transition in each case is
relatively simple, but the strong interactions that bind the quarks into
hadrons introduce complications. We also discuss new theoretical approaches,
especially heavy-quark effective theory and lattice QCD, which are providing
insights and predictions now being tested by experiment. An international
effort at many laboratories will rapidly advance knowledge of this physics
during the next decade.Comment: This review article will be published in Reviews of Modern Physics in
the fall, 1995. This file contains only the abstract and the table of
contents. The full 168-page document including 47 figures is available at
http://charm.physics.ucsb.edu/papers/slrevtex.p
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