162 research outputs found
Remarks on Form Factor Bounds
Improved model independent upper bounds on the weak transition form factors
are derived using inclusive sum rules. Comparison of the new bounds with the
old ones is made for the form factors h_{A_1} and h_V in B -> D* decays.Comment: 8 pages, 2 figures, title changed and typos corrected for journal
publicatio
Inclusive Quasi-Elastic Charged-Current Neutrino-Nucleus Reactions
The Quasi-Elastic (QE) contribution of the nuclear inclusive electron
scattering model developed in Nucl. Phys. A627 (1997) 543 is extended to the
study of electroweak Charged Current (CC) induced nuclear reactions, at
intermediate energies of interest for future neutrino oscillation experiments.
The model accounts for, among other nuclear effects, long range nuclear (RPA)
correlations, Final State Interaction (FSI) and Coulomb corrections.
Predictions for the inclusive muon capture in C and the reaction
C near threshold are also given. RPA correlations are
shown to play a crucial role and their inclusion leads to one of the best
existing simultaneous description of both processes, with accuracies of the
order of 10-15% per cent for the muon capture rate and even better for the LSND
measurement.Comment: 31 pages and 14 figures, accepted for publication as a regular
article in Physical Review
Power corrections in e+ e- --> pi+ pi-, K+ K- and B --> K pi, pi pi
CLEO-c measurements of the timelike form factors F_pi, F_K at \sqrt{s}=3.671
GeV provide a direct probe of power corrections (PC's) at energies near m_B.
PC's in F_pi, F_K and B \to K pi, pi pi are separated into perturbative and
soft parts. In F_pi, F_K the latter are \ge O(10) larger. A PC fit to the B \to
K pi, pi pi data also yields a \ge O(10) soft-to-perturbative hierarchy for the
QCD penguin PC's. Hence, both can be attributed to dominance of the soft-ovelap
between energetic (approximately) back-to-back collinear partons, and
consistency of the B\to K pi, pi pi fit with the Standard Model appears to be
naturally realized. The CP asymmetries S_{K_s pi^0}, C_{K_s pi^0} are well
determined, providing a clean test for new physics.Comment: 4 pages, 4 figures, version published in Eur. Phys. J. C; elaborated
on the connection between power corrections in e+e- ->M1 M2 and the B-> M1 M2
QCD penguin amplitudes; removed speculation that soft-overlaps are much
larger for PP than for VP and VV final states, this is not supported by a new
analysis in preparatio
and the tree amplitude in
The recently-observed decay is expected to proceed
mainly by means of a tree amplitude in the factorization limit: , . Under this assumption, we predict the
corresponding contribution of the tree amplitude to . We
indicate the needed improvements in data that will allow a useful estimate of
this amplitude with errors comparable to those accompanying other methods.
Since the factorization hypothesis for this process goes beyond that proved in
most approaches, we also discuss independent tests of this hypothesis.Comment: 7 pages, LaTeX, 1 figure, to be submitted to Phys. Rev. D (Brief
Reports
Strong Phases and Factorization for Color Suppressed Decays
We prove a factorization theorem in QCD for the color suppressed decays B0->
D0 M0 and B0-> D*0 M0 where M is a light meson. Both the color-suppressed and
W-exchange/annihilation amplitudes contribute at lowest order in LambdaQCD/Q
where Q={mb, mc, Epi}, so no power suppression of annihilation contributions is
found. A new mechanism is given for generating non-perturbative strong phases
in the factorization framework. Model independent predictions that follow from
our results include the equality of the B0 -> D0 M0 and B0 -> D*0 M0 rates, and
equality of non-perturbative strong phases between isospin amplitudes,
delta(DM) = delta(D*M). Relations between amplitudes and phases for M=pi,rho
are also derived. These results do not follow from large Nc factorization with
heavy quark symmetry.Comment: 38 pages, 6 figs, typos correcte
Two-Body Cabibbo-Suppressed Charmed Meson Decays
Singly-Cabibbo-suppressed decays of charmed particles governed by the quark
subprocesses and are analyzed using a
flavor-topology approach, based on a previous analysis of the Cabibbo-favored
decays governed by . Decays to and , where is a
pseudoscalar meson and is a vector meson, are considered. We include
processes in which and are produced.Comment: 18 pages, latex, 2 figures, to be submitted to Phys. Rev.
Charmless decays using flavor SU(3) symmetry
The decays of mesons to a pair of charmless pseudoscalar () mesons are
analyzed within a framework of flavor SU(3). Symmetry breaking is taken into
account in tree () amplitudes through ratios of decay constants; exact SU(3)
is assumed elsewhere. Acceptable fits to and
branching ratios and CP asymmetries are obtained with tree, color-suppressed
(), penguin (), and electroweak penguin () amplitudes. Crucial
additional terms for describing processes involving and include
a large flavor-singlet penguin amplitude () as proposed earlier and a
penguin amplitude associated with intermediate and quarks. For
the mode a term associated with intermediate
and quarks also may be needed. Values of the weak phase are
obtained consistent with an earlier analysis of decays, where
denotes a vector meson, and with other analyses of CKM parameters.Comment: 26 pages, 1 figure. To be submitted to Phys. Rev. D. Reference
update
Z decays into light gluinos: a calculation based on unitarity
The Z boson can decay to a pair of light gluinos through loop-mediated
processes. Based on unitarity of the S-matrix, the imaginary part of the decay
amplitude is computed in the presence of a light bottom squark. This imaginary
part can provide useful information on the full amplitude. Implications are
discussed for a recently proposed light gluino and light bottom squark
scenario.Comment: 19 pages, LaTeX, 3 figures, submitted to Phys. Rev.
Hadronic Charmed Meson Decays Involving Tensor Mesons
Charmed meson decays into a pseudoscalar meson P and a tensor meson T are
studied. The charm to tensor meson transition form factors are evaluated in the
Isgur-Scora-Grinstein-Wise (ISGW) quark model. It is shown that the
Cabibbo-allowed decay is dominated by the
W-annihilation contribution and has the largest branching ratio in
decays. We argue that the Cabibbo-suppressed mode
should be suppressed by one order of magnitude relative to . When the finite width effect of the tensor resonances is taken
into account, the decay rate of is generally enhanced by a factor of
. Except for , the predicted branching ratios
of decays are in general too small by one to two orders of magnitude
compared to experiment. However, it is very unlikely that the
transition form factors can be enhanced by a factor of within the
ISGW quark model to account for the discrepancy between theory and experiment.
As many of the current data are still preliminary and lack sufficient statistic
significance, more accurate measurements are needed to pin down the issue.Comment: 11 page
Search for Top Quark FCNC Couplings in Z' Models at the LHC and CLIC
The top quark is the heaviest particle to date discovered, with a mass close
to the electroweak symmetry breaking scale. It is expected that the top quark
would be sensitive to the new physics at the TeV scale. One of the most
important aspects of the top quark physics can be the investigation of the
possible anomalous couplings. Here, we study the top quark flavor changing
neutral current (FCNC) couplings via the extra gauge boson Z' at the Large
Hadron Collider (LHC) and the Compact Linear Collider (CLIC) energies. We
calculate the total cross sections for the signal and the corresponding
Standard Model (SM) background processes. For an FCNC mixing parameter x=0.2
and the sequential Z' mass of 1 TeV, we find the single top quark FCNC
production cross sections 0.38(1.76) fb at the LHC with sqrt{s_{pp}}=7(14) TeV,
respectively. For the resonance production of sequential Z' boson and decays to
single top quark at the Compact Linear Collider (CLIC) energies, including the
initial state radiation and beamstrahlung effects, we find the cross section
27.96(0.91) fb at sqrt{s_{e^{+}e^{-}}}=1(3) TeV, respectively. We make the
analysis to investigate the parameter space (mixing-mass) through various Z'
models. It is shown that the results benefit from the flavor tagging.Comment: 20 pages, 17 figures, 6 table
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