135 research outputs found
Recent Belle II results on BSM physics
We report on recent results obtained by the Belle II experiment related to
searches for beyond-the-standard-model physics. The meson decay data sample
used corresponds to an integrated luminosity of fb. In recent
years, discrepancies from standard-model predictions, which suggest violation
of lepton-flavor universality, have emerged in multiple measurements of
-meson decays. In this document two analyses aimed to search for violation
of the light-lepton universality are reported: the inclusive
measurement and an angular analysis of the , with
, decays. In addition, beyond-the-standard-model physics can manifests
itself with the production of new particles. The search for a long-lived spin-0
particle in transitions, and its interpretation in two dark sector
models, is reported.Comment: Presented at DIS2023: XXX International Workshop on Deep-Inelastic
Scattering and Related Subjects, Michigan State University, USA, 27-31 March
2023. Updated version includes a reference to a preprint which is just
release
Flavor Changing Effects in Family Nonuniversal Z' Models
Flavor-changing and CP-violating interactions of Z' to fermions are generally
present in models with extra U(1) gauge symmetry that are string-inspired or
related to broken gauged family symmetry. We study the consequences of such
couplings in fermion electric dipole moments, muon g-2, and K and B meson
mixings. From experimental limits or measured values, we constrain the
off-diagonal Z' couplings to fermions. Some of these constraints are comparable
or stronger than the existing constraints obtained from other observables.Comment: 17 pages, 2 figure
Charged-Lepton Flavour Physics
This writeup of a talk at the 2011 Lepton-Photon symposium in Mumbai, India,
summarises recent results in the charged-lepton flavour sector. I review
searches for charged-lepton flavour violation, lepton electric dipole moments
and flavour-conserving CP violation. I also discuss recent progress in
tau-lepton physics and in the Standard Model prediction of the muon anomalous
magnetic moment.Comment: Presented at Lepton-Photon 2011, Mumbai, India; 23 pages, 14 figure
Global Decay Chain Vertex Fitting at B-Factories
We present a particle vertex fitting method designed for B factories. The
presented method uses a Kalman Filter to solve a least squares estimate to
globally fit decay chains, as opposed to traditional methods that fit each
vertex at a time. It allows for the extraction of particle momenta, energies,
vertex positions and flight lengths, as well as the uncertainty estimates of
these quantities. Furthermore, it allows for the precise extraction of vertex
parameters in complex decay chains containing neutral final state particles,
such as or , which cannot properly be tracked due to limited
spatial resolution of longitudinally segmented single-layer crystal
calorimeters like the Belle II ECL. The presented technique can be used to
suppress combinatorial background and improve resolutions on measured
parameters. We present studies using Monte Carlo simulations of collisions in
the Belle II experiment, where modes with neutrals are crucial to the physics
analysis program
Status of the BELLE II Pixel Detector
The Belle II experiment at the super KEK B-factory (SuperKEKB) in Tsukuba, Japan, has been collecting collision data since March 2019. Operating at a record-breaking luminosity of up to , data corresponding to has since been recorded. The Belle II VerteX Detector (VXD) is central to the Belle II detector and its physics program and plays a crucial role in reconstructing precise primary and decay vertices. It consists of the outer 4-layer Silicon Vertex Detector (SVD) using double sided silicon strips and the inner two-layer PiXel Detector (PXD) based on the Depleted P-channel Field Effect Transistor (DePFET) technology. The PXD DePFET structure combines signal generation and amplification within pixels with a minimum pitch of . A high gain and a high signal-to-noise ratio allow thinning the pixels to while retaining a high pixel hit efficiency of about . As a consequence, also the material budget of the full detector is kept low at per layer in the acceptance region. This also includes contributions from the control, Analog-to-Digital
Converter (ADC), and data processing Application Specific Integrated Circuits (ASICs) as well as from cooling and support structures. This article will present the experience gained from four years of operating PXD; the first full scale detector employing the DePFET technology in High Energy Physics. Overall, the PXD has met the expectations. Operating in the intense SuperKEKB environment poses many challenges that will also be discussed. The current PXD system remains incomplete with only 20 out of 40 modules having been installed. A full replacement has been constructed and is currently in its final testing stage before it will be installed into Belle II during the ongoing long shutdown that will last throughout 2023
Search for Axionlike Particles Produced in e⁺ e⁻ Collisions at Belle II
International audienceWe present a search for the direct production of a light pseudoscalar a decaying into two photons with the Belle II detector at the SuperKEKB collider. We search for the process e+e-→γa, a→γγ in the mass range 0.2
Precise measurement of the lifetime at Belle II
We measure the lifetime of the meson using a data sample of 207
fb collected by the Belle II experiment running at the SuperKEKB
asymmetric-energy collider. The lifetime is determined by fitting the
decay-time distribution of a sample of
decays. Our result is \tau^{}_{D^+_s} = (498.7\pm
1.7\,^{+1.1}_{-0.8}) fs, where the first uncertainty is statistical and the
second is systematic. This result is significantly more precise than previous
measurements.Comment: 7 pages, 4 figures, to be submitted to Physical Review Letter
Measurement of the lifetime
An absolute measurement of the lifetime is reported using
decays in events reconstructed from data
collected by the Belle II experiment at the SuperKEKB asymmetric-energy
electron-positron collider. The total integrated luminosity of the data sample,
which was collected at center-of-mass energies at or near the
resonance, is 207.2~\mbox{fb}^{-1}. The result, fs, is the most precise
measurement to date and is consistent with previous determinations.Comment: Accepted for publication in PR
Precise Measurement of the D and D Lifetimes at Belle II
We report a measurement of the D and D lifetimes using D→Kπ and D→Kππ decays reconstructed in ee→ data recorded by the Belle II experiment at the SuperKEKB asymmetric-energy ee collider. The data, collected at center-of-mass energies at or near the Υ(4S) resonance, correspond to an integrated luminosity of 72 fb. The results, τ(D)=410.5±1.1(stat)±0.8(syst) fs and τ(D)=1030.4±4.7(stat)±3.1(syst) fs, are the most precise to date and are consistent with previous determinations
First measurement of as an inclusive test of the anomaly
We measure the tau-to-light-lepton ratio of inclusive -meson branching
fractions , where indicates an electron or muon, and thereby test
the universality of charged-current weak interactions. We select events that
have one fully reconstructed meson and a charged lepton candidate from
of electron-positron collision data collected with the
Belle II detector. We find , in agreement with standard-model expectations. This
is the first direct measurement of
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