50 research outputs found
Flash generation and borylation of 1-(trifluoromethyl)vinyllithium toward synthesis of α-(trifluoromethyl)styrenes
Thermally unstable (3,3,3-trifluoroprop-1-en-2-yl)lithium was generated by lithiation of 2-bromo-3,3,3-trifluoroprop-1-ene and successively underwent borylation in a flow microreactor system. Direct use of the 1-(trifluoromethyl)vinylborate thus formed for the Suzuki–Miyaura coupling in a batch system afforded α-(trifluoromethyl)styrenes in high yields
Search for an invisible in a final state with two muons and missing energy at Belle II
The extension of the standard model predicts the existence
of a lepton-flavor-universality-violating boson that couples only
to the heavier lepton families. We search for such a through its
invisible decay in the process . We use a
sample of electron-positron collisions at a center-of-mass energy of 10.58GeV
collected by the Belle II experiment in 2019-2020, corresponding to an
integrated luminosity of 79.7fb. We find no excess over the expected
standard-model background. We set 90-confidence-level upper limits on the
cross section for this process as well as on the coupling of the model, which
ranges from at low masses to 1 at
masses of 8
Tests of light-lepton universality in angular asymmetries of decays
We present the first comprehensive tests of light-lepton universality in the
angular distributions of semileptonic \Bz-meson decays to charged spin-1
charmed mesons. We measure five angular-asymmetry observables as functions of
the decay recoil that are sensitive to lepton-universality-violating
contributions. We use events where one neutral \B is fully reconstructed in
\PUpsilonFourS{} \to\B\overline{B} decays in data corresponding to \lumion
integrated luminosity from electron-positron collisions collected with the
\belletwo detector. We find no significant deviation from the standard model
expectations
Measurement of branching fractions and direct asymmetries for and decays at Belle II
We report measurements of the branching fractions and direct
asymmetries of the decays , , , and , and use these for testing the standard
model through an isospin-based sum rule. In addition, we measure the branching
fraction and direct asymmetry of the decay and
the branching fraction of the decay . The data are
collected with the Belle II detector from collisions at the
resonance produced by the SuperKEKB asymmetric-energy collider
and contain bottom-antibottom meson pairs. Signal yields are
determined in two-dimensional fits to background-discriminating variables, and
range from 500 to 3900 decays, depending on the channel. We obtain for the sum rule, in agreement with the standard model
expectation of zero and with a precision comparable to the best existing
determinations
Measurement of asymmetries in decays with Belle II
We present a measurement of time-dependent rate asymmetries in decays to search for non-standard-model physics in transitions. The data sample is collected with the Belle II
detector at the SuperKEKB asymmetric-energy collider in 2019-2022
and contains bottom-antibottom mesons from
resonance decays. We reconstruct signal events and
extract the charge-parity () violating parameters from a fit to the
distribution of the proper-decay-time difference of the two mesons. The
measured direct and mixing-induced asymmetries are
and , respectively, where the first
uncertainties are statistical and the second are systematic. The results are
compatible with the asymmetries observed in
transitions
Measurement of the branching fraction and asymmetry of decays using pairs in Belle II data
We report measurements of the branching fraction and asymmetry in
decays reconstructed at Belle II in an
electron-positron collision sample containing
pairs. We measure a branching fraction \mathcal{B}(\Bpipi) =
(1.38 \pm 0.27 \pm 0.22) \times 10^{-6} and a asymmetry \Acp(\Bpipi)
= 0.14 \pm 0.46 \pm 0.07, where the first uncertainty is statistical and the
second is systematic
Search for a resonance in events with the Belle II experiment
We report the first search for a non-standard-model resonance decaying into
pairs in events in
the 3.6-10 GeV/ mass range. We use a 62.8 fb sample of
collisions collected at a center-of-mass energy of 10.58 GeV by the Belle II
experiment at the SuperKEKB collider. The analysis probes three different
models predicting a spin-1 particle coupling only to the heavier lepton
families, a Higgs-like spin-0 particle that couples preferentially to charged
leptons (leptophilic scalar), and an axion-like particle, respectively. We
observe no evidence for a signal and set exclusion limits at 90% confidence
level on the product of cross section and branching fraction into pairs,
ranging from 0.7 fb to 24 fb, and on the couplings of these processes. We
obtain world-leading constraints on the couplings for the leptophilic scalar
model for masses above 6.5 GeV/ and for the axion-like particle model over
the entire mass range
Erratum: The Belle II Physics Book (Progress of Theoretical and Experimental Physics (2019) 2019 (123C01) DOI: 10.1093/ptep/ptz106)
Observation of decays using the 2019-2022 Belle II data sample
We present a measurement of the branching fractions of four decay modes. The measurement is based on data from
SuperKEKB electron-positron collisions at the resonance
collected with the Belle II detector and corresponding to an integrated
luminosity of . The event yields are extracted from fits
to the distributions of the difference between expected and observed meson
energy to separate signal and background, and are efficiency-corrected as a
function of the invariant mass of the system. We find the branching
fractions to be: where the first uncertainty is statistical and
the second systematic. These results include the first observation of
, , and decays and a significant improvement in the precision
of compared to previous measurements
The Belle II Physics Book
We present the physics program of the Belle II experiment, located on the
intensity frontier SuperKEKB collider. Belle II collected its first
collisions in 2018, and is expected to operate for the next decade. It is
anticipated to collect 50/ab of collision data over its lifetime. This book is
the outcome of a joint effort of Belle II collaborators and theorists through
the Belle II theory interface platform (B2TiP), an effort that commenced in
2014. The aim of B2TiP was to elucidate the potential impacts of the Belle II
program, which includes a wide scope of physics topics: B physics, charm, tau,
quarkonium, electroweak precision measurements and dark sector searches. It is
composed of nine working groups (WGs), which are coordinated by teams of
theorist and experimentalists conveners: Semileptonic and leptonic B decays,
Radiative and Electroweak penguins, phi_1 and phi_2 (time-dependent CP
violation) measurements, phi_3 measurements, Charmless hadronic B decay, Charm,
Quarkonium(like), tau and low-multiplicity processes, new physics and global
fit analyses. This book highlights "golden- and silver-channels", i.e. those
that would have the highest potential impact in the field. Theorists
scrutinised the role of those measurements and estimated the respective
theoretical uncertainties, achievable now as well as prospects for the future.
Experimentalists investigated the expected improvements with the large dataset
expected from Belle II, taking into account improved performance from the
upgraded detector.Comment: 689 page