The front-end electronics system for the Belle II Time-Of-Propagation (TOP) counter was fully installed in May 2016. The detector is a novel particle identification device for the barrel region, ...where Cherenkov ring images are reconstructed with precise timing information of each photon. The readout electronics need to have excellent timing performance for single photon detection. To exploit the benefit of high luminosity, the electronics must also be able to cope with a high input trigger rate (30 kHz) and have buffer memory which is deep enough to wait for a trigger decision (>5 μs). The TOP electronics has switching capacitor arrays to sample waveforms with 2.7 GSample/s, which allows a timing resolution of 50 ps for a single photon signal. The programmable logic and the processing system are the effective implementation to meet these requirements, where flexible optimization and step-by-step development of readout logic are possible. The system has been successfully operated in the first accelerator commissioning runs with beam collisions in 2018, where the typical trigger rate was 500Hz. Operation with a 20 kHz trigger rate was also tested.
•Readout electronics for the Belle II Time-Of-Propagation counter was installed.•A single photon is detected with timing resolution better than 100 ps.•The whole system was successfully operated in the physics run.
The Belle II Physics Book Kou, E; Bishara, F; Brod, J ...
Progress of theoretical and experimental physics,
12/2019, Letnik:
2019, Številka:
12
Journal Article
Recenzirano
Odprti dostop
We present the physics program of the Belle II experiment, located on the intensity frontier SuperKEKB e+e- 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, φ1 and φ2 (time-dependent CP violation) measurements, φ3 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.
Theories beyond the standard model often predict the existence of an additional neutral boson, the Z^{'}. Using data collected by the Belle II experiment during 2018 at the SuperKEKB collider, we ...perform the first searches for the invisible decay of a Z^{'} in the process e^{+}e^{-}→μ^{+}μ^{-}Z^{'} and of a lepton-flavor-violating Z^{'} in e^{+}e^{-}→e^{±}μ^{∓}Z^{'}. We do not find any excess of events and set 90% credibility level upper limits on the cross sections of these processes. We translate the former, in the framework of an L_{μ}-L_{τ} theory, into upper limits on the Z^{'} coupling constant at the level of 5×10^{-2}-1 for M_{Z^{'}}≤6 GeV/c^{2}.
The Belle II Physics Book Kou, E; Bishara, F; Brod, J ...
Progress of theoretical and experimental physics,
02/2020, Letnik:
2020, Številka:
2
Journal Article
Recenzirano
Odprti dostop
The Belle II Theory Interface Platform (B2TiP) was created as a physics prospects working group of the Belle II collaboration in June 2014. It offered a platform where theorists and experimentalists ...could work together to elucidate the potential impacts of the Belle II program, which includes a wide scope of physics topics: B physics, charm, τ, quarkonium physics, electroweak precision measurements, and dark sector searches.
The Belle II Physics Book Kou, E; Beneke, M; Crivellin, A ...
Progress of theoretical and experimental physics,
12/2019, Letnik:
2019, Številka:
12
Journal Article
Recenzirano
Odprti dostop
We present the physics program of the Belle II experiment, located on the intensity frontier SuperKEKB e+e- 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.
We present a measurement of the $B^{0} \rightarrow D^{*-} \ell^{+}
\nu_{\ell}$ ($\ell=e,\mu$) branching ratio and of the CKM parameter $|V_{cb}|$
using signal decays accompanied by a fully ...reconstructed $B$ meson. The Belle
II data set of electron-positron collisions at the $\Upsilon(4S)$ resonance,
corresponding to 189.3$\,$fb$^{-1}$ of integrated luminosity, is analyzed. With
the Caprini-Lellouch-Neubert form factor parameterization, the parameters
$\eta_{\rm EW} F(1) |V_{cb}|$ and $\rho^{2}$ are extracted, where $\eta_{\rm
EW}$ is an electroweak correction, $F(1)$ is a normalization factor and
$\rho^{2}$ is a form factor shape parameter. We reconstruct 516 signal decays
and thereby obtain $\mathcal{B} (B^{0} \rightarrow D^{*-} \ell^{+} \nu_{\ell} )
= \left(5.27 \pm 0.22~\rm{\left(stat\right)} \pm
0.38~\rm{\left(syst\right)}\right) \%$, $\eta_{EW} F(1) |V_{cb}| \times 10^{3}
= 34.6 \pm 1.8~\rm{\left(stat\right)} \pm 1.7~\rm{\left(syst\right)}$, and
$\rho^{2} = 0.94 \pm 0.18~\rm{\left(stat\right)} \pm
0.11~\rm{\left(syst\right)}$.
We present a determination of the magnitude of the Cabibbo-Kobayashi-Maskawa
(CKM) matrix element $V_{cb}$ using $B\to D\ell\nu$ decays. The result is based
on $e^+e^-\to\Upsilon(4S)$ data recorded ...by the Belle II detector corresponding
to 189.2/fb of integrated luminosity. The semileptonic decays $B^0\to D^-(\to
K^+\pi^-\pi^-)\ell^+\nu_\ell$ and $B^+\to\bar D^0(\to K^+\pi^-)\ell^+\nu_\ell$
are reconstructed, where $\ell$ is either electron or a muon. The second $B$
meson in the $\Upsilon(4S)$ event is not explicitly reconstructed. Using the
diamond-frame method, we determine the $B$ meson four-momentum and thus the
hadronic recoil. We extract the partial decay rates as functions of $w$ and
perform a fit to the decay form-factor and the CKM parameter $|V_{cb}|$ using
the BGL parameterization of the form factor and lattice QCD input from the
FNAL/MILC and HPQCD collaborations. We obtain $\eta_{EW}|V_{cb}|=(38.53\pm
1.15)\times 10^{-3}$, where $\eta_{EW}$ is an electroweak correction, and the
error accounts for theoretical and experimental sources of uncertainty.
We measure the photon-energy spectrum in radiative bottom-meson ($B$) decays
into inclusive final states involving a strange hadron and a photon. We use
SuperKEKB electron-positron collisions ...corresponding to $189~\mathrm{fb}^{-1}$
of integrated luminosity collected at the $\Upsilon(4S)$ resonance by the Belle
II experiment. The partner $B$ candidates are fully reconstructed using a large
number of hadronic channels. The $B \rightarrow X_s \gamma$ partial branching
fractions are measured as a function of photon energy in the signal $B$ meson
rest frame in eight bins above $1.8~\mathrm{GeV}$. The background-subtracted
signal yield for this photon energy region is $343 \pm 122$ events. Integrated
branching fractions for three photon energy thresholds of $1.8~\mathrm{GeV}$,
$2.0~\mathrm{GeV}$, and $2.1~\mathrm{GeV}$ are also reported, and found to be
in agreement with world averages.
We present an analysis of the charmless semileptonic decay $B^0\to\pi^-
\ell^+ \nu_{\ell}$, where $\ell = e, \mu$, from 198.0 million pairs of
$B\bar{B}$ mesons recorded by the Belle II detector at ...the SuperKEKB
electron-positron collider. The decay is reconstructed without identifying the
partner $B$ meson. The partial branching fractions are measured independently
for $B^0\to\pi^- e^+ \nu_{e}$ and $B^0\to\pi^- \mu^+ \nu_{\mu}$ as functions of
$q^{2}$ (momentum transfer squared), using 3896 $B^0\to\pi^- e^+ \nu_{e}$ and
5466 $B^0\to\pi^- \mu^+ \nu_{\mu}$ decays. The total branching fraction is
found to be $(1.426 \pm 0.056 \pm 0.125) \times 10^{-4}$ for $B^0\to\pi^-
\ell^+ \nu_{\ell}$ decays, where the uncertainties are statistical and
systematic, respectively. By fitting the measured partial branching fractions
as functions of $q^{2}$, together with constraints on the nonperturbative
hadronic contribution from lattice QCD calculations, the magnitude of the
Cabibbo-Kobayashi-Maskawa matrix element $V_{ub}$, $(3.55 \pm 0.12 \pm 0.13 \pm
0.17) \times 10^{-3}$, is extracted. Here, the first uncertainty is
statistical, the second is systematic and the third is theoretical.
We report a measurement of decay-time dependent $CP$-violating parameters in
$B^0 \rightarrow K^0_S K^0_S K^0_S$ decays. We use $(198.0 \pm 3.0) \times
10^6\ B\overline{B}$ pairs collected at the ...$\Upsilon(4S)$ resonance with the
Belle II detector at the SuperKEKB asymmetric-energy $e^+e^-$ collider. The
observed mixing-induced and direct $CP$ violation parameters are $\mathcal{S} =
-1.86\ _{-0.46}^{+0.91}~{\rm (stat)} \pm 0.09~{\rm (syst)}$ and $\mathcal{A} =
-0.22\ _{-0.27}^{+0.30}~{\rm (stat)} \pm 0.04~{\rm (syst)}$, respectively.
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