1,096 research outputs found
Bounds on the mass of the b' quark, revisited
Recent results from the DELPHI collaboration led us to review the present
bounds on the b' quark mass. We use all available experimental data for m_b' >
96 GeV to constrain the b' quark mass as a function of the
Cabibbo-Kobayashi-Maskawa elements in a sequential four generations model. We
find that there is still room for a b' with a mass larger than 96 GeV.Comment: 9 pages and 7 figures. REVTEX
Low-Mass Baryon-Antibaryon Enhancements in B Decays
The nature of low-mass baryon-antibaryon enhancements seen in B decays is
explored. Three possibilities include (i) states near threshold as found in a
model by Nambu and Jona-Lasinio, (ii) isoscalar states with coupled to a pair of gluons, and (iii) low-mass enhancements favored by the
fragmentation process. Ways of distinguishing these mechanisms using angular
distributions and flavor symmetry are proposed.Comment: 8 pages, LaTeX, no figures, to be submitted to Phys. Rev. D. One
reference adde
elliptic Gaudin model with open boundaries
The elliptic Gaudin model with integrable boundaries specified by
generic non-diagonal K-matrices with free boundary parameters is studied.
The commuting families of Gaudin operators are diagonalized by the algebraic
Bethe ansatz method. The eigenvalues and the corresponding Bethe ansatz
equations are obtained.Comment: 21 pages, Latex fil
A first-principles study of MgB2 (0001) surfaces
We report self-consistent {\it ab initio} calculations of structural and
electronic properties for the B- and Mg-terminated MgB (0001) surfaces.
We employ ultra-soft pseudopotentials and plane wave basis sets within the
generalized gradient approximation. The surface relaxations are found to be
small for both B- and Mg-terminated surfaces. For the B-terminated surface,
both B and surface bands appear, while only one B
surface band exists near the Fermi level for the Mg-terminated surface. The
superconductivity of the MgB surfaces is discussed. The work function is
predicted to be 5.95 and 4.25 eV for the B- and Mg-terminated surfaces
respectively. The simulated scanning tunneling microscopy images of the
surfaces are not sensitive to the sign and value of the bias voltages, but
depend strongly on the tip-sample distance. An image reversal is predicted for
the Mg-terminated surface.Comment: 3 pages, 4 figures, Revte
Final-State Phases in Charmed Meson Two-Body Nonleptonic Decays
Observed decay rates indicate large phase differences among the amplitudes
for the charge states in and but
relatively real amplitudes in the charge states for . This
feature is traced using an SU(3) flavor analysis to a sign flip in the
contribution of one of the amplitudes contributing to the latter processes in
comparison with its contribution to the other two sets. This amplitude may be
regarded as an effect of rescattering and is found to be of magnitude
comparable to others contributing to charmed particle two-body nonleptonic
decays.Comment: 19 pages, latex, 4 figures, to be submitted to Phys. Rev.
Elastic and inelastic SU(3)-breaking final-state interactions in B decays to pseudoscalar mesons
We discuss all contributions from Zweig-rule-satisfying SU(3)-breaking final
state interactions (FSIs)in the B -> PP decays (neglecting charmed intermediate
states), where PP=pi pi, pi K, KK, pi eta (eta'), and K eta (eta'). First,
effects of SU(3) breaking in rescattering through Pomeron exchange are studied.
Then, after making a plausible assumption concerning the pattern of SU(3)
breaking in non-Pomeron FSIs, we give general formulas for how the latter
modify short-distance (SD) amplitudes. In the SU(3) limit, these formulas
depend on three effective parameters characterizing the strength of all
non-Pomeron rescattering effects. We point out that the experimental bounds on
the B -> K^+K^- branching ratio may limit the value of only one of these FSI
parameters. Thus, the smallness of the B -> K^+K^- decay rate does not imply
negligible rescattering effects in other decays. Assuming a vanishing value of
this parameter, we perform various fits to the available B -> PP branching
ratios. The fits determine the quark-diagram SD amplitudes, the two remaining
FSI parameters and the weak angle gamma. While the set of all B -> PP branching
ratios is well described with gamma around its expected SM value, the fits
permit other values of gamma as well. For a couple of such good fits, we
predict asymmetries for the B -> K pi, pi^+ eta (eta'), K^+ eta (eta') decays
as well as the values of the CP-violating parameters S_{pi pi} and C_{pi pi}
for the time-dependent rate of B^0(t) -> pi^+ pi^-. Apart from a problem with
the recent B^+ -> pi^+ eta asymmetry measurement, comparison with the data
seems to favour the values of gamma in accordance with SM expectations.Comment: 27 pages, 5 figure
Evidence of the Purely Leptonic Decay B- --> tau- nu_tau-bar
We present the first evidence of the decay B- --> tau- nu_tau-bar using 414
fb^-1 of data collected at the Upsilon(4S) resonance with the Belle detector at
the KEKB asymmetric-energy e+e- collider. Events are tagged by fully
reconstructing one of the B mesons in hadronic modes. We detect the signal with
a significance of 3.5 standard deviations including systematics, and measure
the branching fraction to be Br(B- --> tau- nu_tau-bar) = (1.79
+0.56-0.49(stat) +0.46-0.51(syst))*10^-4. This implies that f_B = 0.229
+0.036-0.031(stat) +0.034-0.037(syst) GeV and is the first direct measurement
of this quantity.Comment: 6 pages, 3 figures, to appear in Physical Review Letter
Search for B+ -> D*+ pi0 decay
We report on a search for the doubly Cabibbo suppressed decay B+ -> D*+ pi0,
based on a data sample of 657 million BBbar pairs collected at the Upsilon(4S)
resonance with the Belle detector at the KEKB asymmetric energy e+ e- collider.
We find no significant signal and set an upper limit of Br(B+ -> D*+ pi0) < 3.6
x 10^-6 at the 90% confidence level. This limit can be used to constrain the
ratio between suppressed and favored B -> D* pi decay amplitudes, r < 0.051, at
the 90% confidence level.Comment: 5pages, 2figures, submitted to PRL (v1); PRL published version (v2:
minor corrections in the text
Search for Resonant Decays at Belle
We report measurements and searches for resonant decays where is a
meson or
the X(3872) particle.Comment: accepted by Physics Letters
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