316 research outputs found
Recent charm mixing results from BABAR, Belle, and CDF
A summary of the results of several recent studies of charm mixing is
presented. A number of different methods were used, including the measurement
of lifetime ratios for final states of different CP, time dependence of
wrong-sign hadronic decays, fits to time-dependent Dalitz plots, and searches
for wrong-sign semi-leptonic decays. Taken together, they suggest mixing is of
order 1%. The status of searches for indirect CP violation is also reported.Comment: 7 pages, 2 figures, proceedings from PHIPSI0
Collinear effective theory at subleading order and its application to heavy-light currents
We consider a collinear effective theory of highly energetic quarks with
energy E, interacting with collinear and soft gluons by integrating out
collinear degrees of freedom to subleading order. The collinear effective
theory offers a systematic expansion in power series of a small parameter
lambda ~ p_{\perp}/E, where p_{\perp} is the transverse momentum of a collinear
particle. We construct the effective Lagrangian to first order in ,
and discuss its features including additional symmetries such as collinear
gauge invariance and reparameterization invariance. Heavy-light currents can be
matched from the full theory onto the operators in the collinear effective
theory at one loop and to order lambda. We obtain heavy-light current operators
in the effective theory, calculate their Wilson coefficients at this order, and
the renormalization group equations for the Wilson coefficients are solved. As
an application, we calculate the form factors for decays of B mesons to light
energetic mesons to order lambda and at leading-logarithmic order in alpha_s.Comment: 29 pages, 5 figures, revised versio
Probing CP Violation with the Deuteron Electric Dipole Moment
We present an analysis of the electric dipole moment (EDM) of the deuteron as
induced by CP-violating operators of dimension 4, 5 and 6 including theta QCD,
the EDMs and color EDMs of quarks, four-quark interactions and the Weinberg
operator. We demonstrate that the precision goal of the EDM Collaboration's
proposal to search for the deuteron EDM, (1-3)\times 10^{-27} e cm, will
provide an improvement in sensitivity to these sources of one-two orders of
magnitude relative to the existing bounds. We consider in detail the level to
which CP-odd phases can be probed within the MSSM.Comment: 5 pages, 4 figures; precision estimates clarified, to appear in Phys.
Rev.
SU(3) Relations and the CP Asymmetries in B Decays to , and
We consider CP asymmetries in neutral meson decays to , , and . We use SU(3) relations to estimate or bound the
contributions to these amplitudes proportional to . Such
contributions induce a deviation of the terms measured in these time
dependent CP asymmetries from that measured for . For the mode, we estimate the deviation to be of order 0.1. For the
mode, we obtain an upper bound on this deviation of order 0.3. For the mode, we have to add a mild dynamical assumption to the SU(3) analysis due
to insufficient available data, yielding an upper bound of order 0.25. These
bounds may improve significantly with future data. While they are large at
present compared to the usually assumed Standard Model contribution, they are
obtained with minimal assumptions and hence provide more rigorous tests for new
physics. If measurements yield that are much larger than our
bounds, it would make a convincing case for new physics.Comment: 24 pages; corrections in Sec. III.A and V, results hardly affected,
to appear in Phys Rev
B-->pi and B-->K transitions in standard and quenched chiral perturbation theory
We study the effects of chiral logs on the heavy-->light pseudoscalar meson
transition form factors by using standard and quenched chiral perturbation
theory combined with the static heavy quark limit. The resulting expressions
are used to indicate the size of uncertainties due to the use of the quenched
approximation in the current lattice studies. They may also be used to assess
the size of systematic uncertainties induced by missing chiral log terms in
extrapolating toward the physical pion mass. We also provide the coefficient
multiplying the quenched chiral log, which may be useful if the quenched
lattice studies are performed with very light mesons.Comment: 33 pages, 8 PostScript figures, version to appear in PR
Electromagnetic Decays of Heavy Baryons
The electromagnetic decays of the ground state baryon multiplets with one
heavy quark are calculated using Heavy Hadron Chiral Perturbation Theory. The
M1 and E2 amplitudes for S^{*}--> S gamma, S^{*} --> T gamma and S --> T gamma
are separately computed. All M1 transitions are calculated up to
O(1/Lambda_chi^2). The E2 amplitudes contribute at the same order for S^{*}-->
S gamma, while for S^{*} --> T gamma they first appear at O(1/(m_Q
\Lambda_\chi^2)) and for S --> T gamma are completely negligible. The
renormalization of the chiral loops is discussed and relations among different
decay amplitudes are derived. We find that chiral loops involving
electromagnetic interactions of the light pseudoscalar mesons provide a sizable
enhancement of these decay widths. Furthermore, we obtain an absolute
prediction for the widths of Xi^{0'(*)}_c--> Xi^{0}_c gamma and Xi^{-'(*)}_b-->
Xi^{-}_b gamma. Our results are compared to other estimates existing in the
literature.Comment: 17 pages, 3 figures, submitted to Phys. Rev.
Towards a Model-Independent Analysis of Rare Decays
Motivated by the experimental accessibility of rare decays in the ongoing
and planned experiments, we propose to undertake a model-independent analysis
of the inclusive decay rates and distributions in the processes \bgamaxs~ and
\Bsell ~( or ). We show how measurements of the decay rates and
distributions in these processes would allow us to extract the magnitude and
sign of the dominant Wilson coefficients of the magnetic moment operator \mb
\bar{s}_L \sigma_{\mu \nu} b_R F^{\mu \nu } and the four-fermion operators
and . Non-standard-model
effects could thus manifest themselves at low energy in rare decays through
the Wilson coefficient having values distinctly different from their
standard-model counterparts. We illustrate this possibility using the examples
of the two-doublet Higgs models and the minimal supersymmetric models. The
dilepton invariant mass spectrum and the forward-backward asymmetry of
in the centre-of-mass system of the dilepton pair in the decay \Bsell ~are also
worked out for the standard model and some representative solutions for the
other two models.Comment: LaTeX, 36 pages, 11 figures appended after \end{document} as
uu-encoded and compressed .eps files, uses epsf, CERN-TH.7346/9
The QCD heavy-quark potential to order v^2: one loop matching conditions
The one-loop QCD heavy quark potential is computed to order v^2 in the color
singlet and octet channels. Several errors in the previous literature are
corrected. To be consistent with the velocity power counting, the full
dependence on |p' + p|/|p' - p| is kept. The matching conditions for the NRQCD
one-loop potential are computed by comparing the QCD calculation with that in
the effective theory. The graphs in the effective theory are also compared to
terms from the hard, soft, potential, and ultrasoft regimes in the threshold
expansion. The issue of off-shell versus on-shell matching and gauge dependence
is discussed in detail for the 1/(m k) term in the potential. Matching on-shell
gives a 1/(m k) potential that is gauge independent and does not vanish for
QED.Comment: 28 pages, References added and minor changes to section III, results
unchange
SU(3) Breaking and D0-D0bar Mixing
The main challenge in the Standard Model calculation of the mass and width
difference in the D0-D0bar system is to estimate the size of SU(3) breaking
effects. We prove that D meson mixing occurs in the Standard Model only at
second order in SU(3) violation. We consider the possibility that phase space
effects may be the dominant source of SU(3) breaking. We find that y=(Delta
Gamma)/(2Gamma) of the order of one percent is natural in the Standard Model,
potentially reducing the sensitivity to new physics of measurements of D meson
mixing.Comment: 18 pages; minor corrections, version to appear in Phys. Rev.
Phenomenology of non-standard Z couplings in exclusive semileptonic b -> s transitions
The rare decays , and
are analyzed in a generic scenario where New Physics effects
enter predominantly via penguin contributions. We show that this
possibility is well motivated on theoretical grounds, as the vertex
is particularly susceptible to non-standard dynamics. In addition, such a
framework is also interesting phenomenologically since the coupling
is rather poorly constrained by present data. The characteristic features of
this scenario for the relevant decay rates and distributions are investigated.
We emphasize that both sign and magnitude of the forward-backward asymmetry of
the decay leptons in , , carry sensitive information on New Physics. The observable is proposed as a useful probe of
non-standard CP violation in couplings.Comment: Minor modifications; version to appear in Phys. Rev.
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