34 research outputs found
Operational experience and commissioning of the Belle II vertex detector
The construction of the new accelerator at the Super Flavor Factory in Tsukuba, Japan, has been finalized and the commissioning of its detector (Belle II) has started. This new e+e machine (SuperKEKB) will deliver an instantaneous luminosity of 8 1035 cm2s1, which is 40 times higher than the world record set by KEKB. In order to be able to fully exploit the increased number of events and provide high precision measurements of the decay vertex of the B meson systems in such a harsh environment, the Belle II detector will include a new 6 layer silicon vertex detector. Close to the beam pipe, 2 pixel and 4 double-sided strip detector layers will be installed. During its first data taking period in 2018, the inner volume of the Belle II detector was only partially equipped with the final vertex detector technologies. The remaining volume was covered with dedicated radiation monitors, collectively called BEAST II, in order to investigate the particle and synchrotron radiation backgrounds near the interaction point. In this note, the milestones of the commissioning of the Belle II vertex detector and BEAST II are reviewed and the detector performance and selected background measurements will be presented
Phenomenological Constraints on Extended Quark Sectors
We study the flavor physics in two extensions of the quark sector of the
Standard Model (SM): a four generation model and a model with a single
vector--like down--type quark (VDQ). In our analysis we take into account the
experimental constraints from tree--level charged current processes, rare Kaon
decay processes, rare B decay processes, the decay, ,
and mass differences, and the CP violating parameters \frac
\epsilon^\prime}{\epsilon}, and . All the constraints
are taken at two sigma. We find bounds on parameters which can be used to
represent the New Physics contributions in these models (, and in the
four--generation model, and , and in the VDQ model)
due to all the above constraints. In both models the predicted ranges for
(the CP asymmetry in semi-leptonic decays), ,
, and can be significantly higher than the predictions of the
SM, while the allowed ranges for and for are
consistent with the SM prediction.Comment: 22 pages, 5 figures (v3: added a reference, updated a reference,
added missing units
First Observation of CP Violation in B0->D(*)CP h0 Decays by a Combined Time-Dependent Analysis of BaBar and Belle Data
We report a measurement of the time-dependent CP asymmetry of B0->D(*)CP h0
decays, where the light neutral hadron h0 is a pi0, eta or omega meson, and the
neutral D meson is reconstructed in the CP eigenstates K+ K-, K0S pi0 or K0S
omega. The measurement is performed combining the final data samples collected
at the Y(4S) resonance by the BaBar and Belle experiments at the
asymmetric-energy B factories PEP-II at SLAC and KEKB at KEK, respectively. The
data samples contain ( 471 +/- 3 ) x 10^6 BB pairs recorded by the BaBar
detector and ( 772 +/- 11 ) x 10^6, BB pairs recorded by the Belle detector. We
measure the CP asymmetry parameters -eta_f S = +0.66 +/- 0.10 (stat.) +/- 0.06
(syst.) and C = -0.02 +/- 0.07 (stat.) +/- 0.03 (syst.). These results
correspond to the first observation of CP violation in B0->D(*)CP h0 decays.
The hypothesis of no mixing-induced CP violation is excluded in these decays at
the level of 5.4 standard deviations.Comment: 9 pages, 2 figures, submitted to Physical Review Letter
Measurement of in with decays by a combined time-dependent Dalitz plot analysis of BaBar and Belle data
We report measurements of and from a
time-dependent Dalitz plot analysis of with decays, where the light unflavored and neutral
hadron is a , , or meson. The analysis is
performed with a combination of the final data sets of the \babar\ and Belle
experiments containing and
pairs collected at the resonance at the
asymmetric-energy B factories PEP-II at SLAC and KEKB at KEK, respectively. We
measure and . The result for the direct
measurement of the angle is . The last quoted
uncertainties are due to the composition of the decay amplitude model, which is newly established by a Dalitz plot
amplitude analysis of a high-statistics data sample
as part of this analysis. We find the first evidence for at the
level of standard deviations. The measurement excludes the trigonometric
multifold solution at the level of
standard deviations and therefore resolves an ambiguity in the
determination of the apex of the CKM Unitarity Triangle. The hypothesis of
is ruled out at the level of standard deviations, and
thus CP violation is observed in decays.Comment: To be submitted to Physical Review