69 research outputs found
Exploring CP Violation through B Decays
The B-meson system provides many strategies to perform stringent tests of the
Standard-Model description of CP violation. In this brief review, we discuss
implications of the currently available B-factory data on the angles alpha,
beta and gamma of the unitarity triangle, emphasize the importance of Bs
studies at hadronic B experiments, and discuss new, theoretically clean
strategies to determine gamma.Comment: 22 pages, 4 figures, invited brief review for Modern Physics Letters
B -> pi pi, New Physics in B -> pi K and Implications for Rare K and B Decays
The measured B -> pi pi, pi K branching ratios exhibit puzzling patterns. We
point out that the B -> pi pi hierarchy can be nicely accommodated in the
Standard Model (SM) through non-factorizable hadronic interference effects,
whereas the B -> pi K system may indicate new physics (NP) in the electroweak
(EW) penguin sector. Using the B -> pi pi data and the SU(3) flavour symmetry,
we may fix the hadronic B -> pi K parameters, which allows us to show that any
currently observed feature of the B -> pi K system can be easily explained
through enhanced EW penguins with a large CP-violating NP phase. Restricting
ourselves to a specific scenario, where NP enters only through Z^0 penguins, we
derive links to rare K and B decays, where an enhancement of the K_L-> pi^0 nu
nu_bar rate by one order of magnitude, with BR(K_L -> pi^0 nu nu_bar) > BR(K^+
-> pi^+ nu nu_bar), BR(K_L -> pi^0 e^+ e^-)=O(10^{-10}), (\sin2\beta)_{pi nu
nu_bar} K* mu^+ mu^-,
are the most spectacular effects. We address also other rare K and B decays,
epsilon'/epsilon and B_d -> phi K_S.Comment: 6 pages, LaTeX, reference added and a few typos correced, to appear
in Physical Review Letter
CP violation and CKM phases from angular distributions for decays into admixtures of CP eigenstates
We investigate the time-evolutions of angular distributions for decays
into final states that are admixtures of CP-even and CP-odd configurations. A
sizable lifetime difference between the mass eigenstates allows a probe
of CP violation in time-dependent untagged angular distributions. Interference
effects between different final state configurations of , determine the Wolfenstein parameter from
untagged data samples, or -- if one uses as an additional
input -- the notoriously difficult to measure CKM angle . Another
determination of is possible by using isospin symmetry of strong
interactions to relate untagged data samples of
and . We note that the untagged angular
distribution for provides interesting information about
electroweak penguins.Comment: 19 pages, LaTeX, no figure
Electron Neutrino Pair Annihilation: A New Source for Muon and Tau Neutrinos in Supernovae
We show that in a supernova core the annihilation process nu_e nu_e-bar ->
nu_{mu,tau} nu_{mu,tau}-bar is always more important than the traditional
reaction e^+ e^- -> nu_{mu,tau} nu_{mu,tau}-bar as a source for muon and tau
neutrino pairs. We study the impact of the new process by means of a Monte
Carlo transport code with a static stellar background model and by means of a
self-consistent hydrodynamical simulation with Boltzmann neutrino transport.
Nucleon bremsstrahlung NN -> NN nu_{mu,tau} nu_{mu,tau}-bar is also included as
another important source term. Taking into account nu_e nu_e-bar -> nu_{mu,tau}
nu_{mu,tau}-bar increases the nu_mu and nu_tau luminosities by as much as 20%
while the spectra remain almost unaffected. In our hydrodynamical simulation
the shock was somewhat weakened. Elastic nu_{mu,tau} nu_e and nu_{mu,tau} nu_e
scattering is not negligible but less important than nu_{mu,tau} e^+ or e^-
scattering. Its influence on the nu_{mu,tau} fluxes and spectra is small after
all other processes have been included.Comment: 11 pages, 9 eps-figs, submitted to Ap
Constraining the CKM Parameters using CP Violation in semi-leptonic B Decays
We discuss the usefulness of the CP violating semi-leptonic asymmetry a_{SL}
not only as a signal of new physics, but also as a tool in constraining the CKM
parameters. We show that this technique could yield useful results in the first
years of running at the B factories. We present the analysis graphically in
terms of M_{12}, the dispersive part of the B-Bbar mixing amplitude. This is
complementary to the usual unitarity triangle representation and often allows a
cleaner interpretation of the data.Comment: 15 pages REVTEX, 7 figure
Bounds on the Unitarity Triangle, and Decays in Models with Minimal Flavour Violation
We present a general discussion of the unitarity triangle from ,
and in models with minimal
flavour violation (MFV), allowing for arbitrary signs of the generalized
Inami--Lim functions and relevant for and , respectively. In the models in
which has a sign opposite to the one in the Standard Model, i.e.
, the data for imply an absolute lower
bound on the CP asymmetry of 0.69, which is
substantially stronger than 0.42 arising in the case of . An
important finding of this paper is the observation that for given
and only two values for
, corresponding to the two signs of ,
are possible in the full class of MFV models, independently of any new
parameters arising in these models. This provides a powerful test for this
class of models. Moreover, we derive absolute lower and upper bounds on
as functions of
. Using the present experimental upper bounds
on and , we obtain the
absolute upper bound
(90% C.L.).Comment: 25 pages, LaTeX, 4 figures. Few comments and one figure in view of
new B-factory results added, conclusions unchange
Universal Constraints on Low-Energy Flavour Models
It is pointed out that in a general class of flavour models one can identify
certain universally present FCNC operators, induced by the exchange of heavy
flavour messengers. Their coefficients depend on the rotation angles that
connect flavour and fermion mass basis. The lower bounds on the messenger scale
are derived using updated experimental constraints on the FCNC operators. The
obtained bounds are different for different operators and in addition they
depend on the chosen set of rotations. Given the sensitivity expected in the
forthcoming experiments, the present analysis suggests interesting room for
discovering new physics. As the highlights emerge the leptonic processes,
, and
conversion in nuclei.Comment: 18 pages, 3 figures; v2 matches published versio
Exploring CP Violation through Correlations in B --> pi K, B_d --> pi^+pi^-, B_s --> K^+K^- Observable Space
We investigate allowed regions in observable space of B --> pi K, B_d -->
pi^+pi^- and B_s --> K^+K^- decays, characterizing these modes in the Standard
Model. After a discussion of a new kind of contour plots for the
system, we focus on the mixing- induced and direct CP asymmetries of the decays
B_d --> pi^+pi^- and B_s--> K^+K^-. Using experimental information on the
CP-averaged B_d --> pi^{+/-}K^{+/-} and B_d --> pi^+pi^- branching ratios, the
relevant hadronic penguin parameters can be constrained,implying certain
allowed regions in observable space. In the case of B_d --> pi^+pi^-, an
interesting situation arises now in view of the recent B-factory measurements
of CP violation in this channel, allowing us to obtain new constraints on the
CKM angle gamma as a function of the B^0_d--\bar{B^0_d} mixing phase
phi_d=2beta, which is fixed through A_{CP}^{mix}(B_d --> J/psi K_S) up to a
twofold ambiguity. If we assume that A_{CP}^{mix}(B_d --> pi^+pi^-) is
positive, as indicated by recent Belle data, and that phi_d is in agreement
with the ``indirect'' fits of the unitarity triangle, also the corresponding
values for gamma around 60 degrees can be accommodated. On the other hand, for
the second solution of phi_d, we obtain a gap around gamma ~ 60 degrees. The
allowed region in the space of A_{CP}^{mix}(B_s --> K^+K^-) and
A_{CP}^{dir}(B_s --> K^+K^-) is very constrained in the Standard Model, thereby
providing a narrow target range for run II of the Tevatron and the experiments
of the LHC era.Comment: 34 pages, LaTeX, 12 figures. More detailed introduction and a few
Comments added, conclusions unchanged. To appear in Phys. Rev.
Extracting gamma and Penguin Topologies through CP Violation in B_s^0 -> J/psi K_S
The B_s^0 -> J/psi K_S decay has recently been observed by the CDF
collaboration and will be of interest for the LHCb experiment. This channel
will offer a new tool to extract the angle gamma of the unitarity triangle and
to control doubly Cabibbo-suppressed penguin corrections to the determination
of sin(2beta) from the well-known B_d^0 -> J/psi K_S mode with the help of the
U-spin symmetry of strong interactions. While any competitive determination of
gamma is interesting, the latter aspect is particularly relevant as LHCb will
enter a territory of precision which makes the control of doubly
Cabibbo-suppressed Standard-Model corrections mandatory. Using the data from
CDF and the e^+e^- B factories as a guideline, we explore the sensitivity for
gamma and the penguin parameters and point out that the B_s^0-\bar B_s^0 mixing
phase phi_s, which is only about -2 deg in the Standard Model but may be
enhanced through new physics, is a key parameter for these analyses. We find
that the mixing-induced CP violation S(B_s^0 -> J/psi K_S) shows an interesting
correlation with sin(phi_s), which serves as a target region for the first
measurement of this observable at LHCb.Comment: 20 pages, 8 figure
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