98 research outputs found
Rare K and B Decays in a Warped Extra Dimension with Custodial Protection
We present a complete study of rare K and B meson decays in a warped extra
dimensional model with a custodial protection of (both diagonal and
non-diagonal) Z d_L^i \bar d_L^j couplings, including K^+ -> pi^+ nu anti-nu,
K_L -> pi^0 nu anti-nu, K_L -> pi^0 l^+ l^-, K_L -> mu^+ mu^-, B_{s,d} -> mu^+
mu^-, B -> K nu anti-nu, B -> K^* nu anti-nu and B -> X_{s,d} nu anti-nu. In
this model in addition to Standard Model one loop contributions these processes
receive tree level contributions from the Z boson and the new heavy electroweak
gauge bosons. We analyse all these contributions that turn out to be dominated
by tree level Z boson exchanges governed by right-handed couplings to down-type
quarks. Imposing all existing constraints from Delta F=2 transitions analysed
by us recently and fitting all quark masses and CKM mixing parameters we find
that a number of branching ratios for rare K decays can differ significantly
from the SM predictions, while the corresponding effects in rare B decays are
modest, dominantly due to the custodial protection being more effective in B
decays than in K decays. In order to reduce the parameter dependence we study
correlations between various observables within the K system, within the B
system and in particular between K and B systems, and also between Delta F=2
and Delta F=1 observables. These correlations allow for a clear distinction
between this new physics scenario and models with minimal flavour violation or
the Littlest Higgs Model with T-parity, and could give an opportunity to future
experiments to confirm or rule out the model. We show how our results would
change if the custodial protection of Z d_L^i bar d^j_L couplings was absent.
In the case of rare B decays the modifications are spectacular.Comment: 50 pages, 17 figures. v2: minor clarifying comments and references
added. v3: few clarifying comments added, matches published versio
Electroweak and Flavour Structure of a Warped Extra Dimension with Custodial Protection
We present the electroweak and flavour structure of a model with a warped
extra dimension and the bulk gauge group SU(3) x SU(2)_L x SU(2)_R x P_LR x
U(1)_X. The presence of SU(2)_R implies an unbroken custodial symmetry in the
Higgs system allowing to eliminate large contributions to the T parameter,
whereas the P_LR symmetry and the enlarged fermion representations provide a
custodial symmetry for flavour diagonal and flavour changing couplings of the
SM Z boson to left-handed down-type quarks. We diagonalise analytically the
mass matrices of charged and neutral gauge bosons including the first KK modes.
We present the mass matrices for quarks including heavy KK modes and discuss
the neutral and charged currents involving light and heavy fields. We give the
corresponding complete set of Feynman rules in the unitary gauge.Comment: 74 pages, 2 figures. clarifying comments and references added,
version to be published in JHE
B-flavor tagging at Belle II
We report on new flavor tagging algorithms developed to determine the quark-flavor content of bottom ( ) mesons at Belle II. The algorithms provide essential inputs for measurements of quark-flavor mixing and charge-parity violation. We validate and evaluate the performance of the algorithms using hadronic decays with flavor-specific final states reconstructed in a data set corresponding to an integrated luminosity of 62.8 fb−1
, collected at the resonance with the Belle II detector at the SuperKEKB collider. We measure the total effective tagging efficiency to be
εeff=(30.0±1.2(stat)±0.4(syst))%
for a category-based algorithm and
εeff=(28.8±1.2(stat)±0.4(syst))%
for a deep-learning-based algorithm
Measurements of the branching fractions for decays at Belle II
This paper reports a study of decays using
fb of data collected during 2019--2020 by the Belle II experiment at the
SuperKEKB asymmetric-energy collider, corresponding to events. We find , ,
, and signal events in the decay modes , ,
, and , respectively. The uncertainties quoted for the
signal yield are statistical only. We report the branching fractions of these
decays: where the first
uncertainty is statistical, and the second is systematic. The results are
consistent with world-average values
Angular analysis of decays reconstructed in 2019, 2020, and 2021 Belle II data
We report on a Belle II measurement of the branching fraction
(), longitudinal polarization fraction (), and CP asymmetry
() of decays. We reconstruct decays in a
sample of SuperKEKB electron-positron collisions collected by the Belle II
experiment in 2019, 2020, and 2021 at the (4S) resonance and
corresponding to 190 fb of integrated luminosity. We fit the
distributions of the difference between expected and observed candidate
energy, continuum-suppression discriminant, dipion masses, and decay angles of
the selected samples, to determine a signal yield of events. The
signal yields are corrected for efficiencies determined from simulation and
control data samples to obtain $\mathcal{B}(B^+ \to \rho^+\rho^0) = [23.2^{+\
2.2}_{-\ 2.1} (\rm stat) \pm 2.7 (\rm syst)]\times 10^{-6}f_L = 0.943 ^{+\
0.035}_{-\ 0.033} (\rm stat)\pm 0.027(\rm syst)\mathcal{A}_{CP}=-0.069
\pm 0.068(\rm stat) \pm 0.060 (\rm syst)\mathcal{A}_{CP}B^+\to
\rho^+\rho^0$ decays reported by Belle II
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