Measurement of the energy dependence of the e+e− → $$ B\overline{B} $$, $$ B{\overline{B}}^{\ast } $$ and $$ {B}^{\ast }{\overline{B}}^{\ast } $$ exclusive cross sections

We report the first measurement of the exclusive cross sections e+e− → $$ B\overline{B} $$ B B ¯ , e+e− → $$ B{\overline{B}}^{\ast } $$ B B ¯ ∗ , and e+e− → $$ {B}^{\ast }{\overline{B}}^{\ast } $$ B ∗ B ¯ ∗ in the energy range from 10.63 GeV to 11.02 GeV. The B mesons are fully reconstructed in a large number of hadronic final states and the three channels are identified using a beam-constrained-mass variable. The shapes of the exclusive cross sections show oscillatory behavior with several maxima and minima. The results are obtained using data collected by the Belle experiment at the KEKB asymmetric-energy e+e− collider.

Monte Carlo matching in the Belle II software

The Belle II experiment is an upgrade to the Belle experiment, and is located at the SuperKEKB facility in KEK, Tsukuba, Japan. The Belle II software is completely new and is used for everything from triggering data, generation of Monte Carlo events, tracking, clustering, to high-level analysis. One important feature is the matching between the combinations of reconstructed objects which form particle candidates and the underlying simulated particles from the event generators. This is used to study detector effects, analysis backgrounds, and efficiencies. This document describes the algorithm that is used by Belle II.

Analysis of the $$ \varvec{e^+ e^- \rightarrow J/\psi D{\bar{D}}}$$ reaction close to the threshold concerning claims of a $$\chi _{c0}(2P)$$ state

We analyze the $$D{\bar{D}}$$ D D ¯ mass distribution from a recent Belle experiment on the $$e^+e^- \rightarrow J/\psi D{\bar{D}}$$ e + e - → J / ψ D D ¯ reaction, and show that the mass distribution divided by phase space does not have a clear peak above the $$D{\bar{D}}$$ D D ¯ threshold that justifies the experimental claim of a $$\chi _{c0}(2P)$$ χ c 0 ( 2 P ) state from those data. Then we use a unitary formalism with coupled channels $$D^+D^-$$ D + D - , $$D^0{\bar{D}}^0$$ D 0 D ¯ 0 , $$D_s{\bar{D}}_s$$ D s D ¯ s , and $$\eta \eta $$ η η , with some of the interactions taken from a theoretical model, and use the data to fix other parameters. We then show that, given the poor quality of the data, we can get different fits leading to very different $$D{\bar{D}}$$ D D ¯ amplitudes, some of them supporting a $$D{\bar{D}}$$ D D ¯ bound state and others not. The main conclusion is that the claim for the $$\chi _{c0}(2P)$$ χ c 0 ( 2 P ) state, already included in the PDG, is premature, but refined data can provide very valuable information on the $$D{\bar{D}}$$ D D ¯ scattering amplitude. As side effects, we warn about the use of a Breit-Wigner amplitude parameterization close to threshold, and show that the $$D_s{\bar{D}}_s$$ D s D ¯ s channel plays an important role in this reaction.

The Belle II Experiment at the SuperKEKB

Belle II experiment at the SuperKEKB collider is a major upgrade of the Belle experiment at the KEKB asymmetric e+e− collider at the KEK. The experiment will focus on the search for new physics beyond the standard model via high precision measurement of heavy flavor decays and search for rare signals. In this talk, we present the status of the SuperKEKB collider and the Belle II detector.

The data management of heterogeneous resources in Belle II

The Belle II experiment at the SuperKEKB collider in Tsukuba, Japan, has started taking physics data in early 2018 and plans to accumulate 50 ab-1, which is approximately 50 times more data than the Belle experiment. The collaboration expects it will require managing and processing approximately 200 PB of data. Computing at this scale requires efficient and coordinated use of the geographically distributed compute resources in North America, Asia and Europe and will take advantage of high-speed global networks. We present the general Belle II the distributed data management system and computing results from the first phase of data taking.

New results on charmonium like states at Belle

New results on charmonium-like states measured by the Belle experiment at the KEKB asymmetric e+e- collider are presented, in particular (a) Search for the Zc pair production in $\Upsilon (1{\rm{S}}),\,\Upsilon (2S)$ decays and in e+e- $\sqrt s $ of 10.52, 10.58, and 10.867 GeV. (b) Measurement of the absolute branching fractions of ${B^ + } \to {X_{c\overline c }}{K^ + }$ decays. (c) Observation of Ξc(2930)0 in the updated measurement of ${B^ - } \to {K^ - }{\Lambda _c}{\overline \Lambda _{\overline c }}.$ (d) Angular analysis of ${e^ + }{e^ - } \to {D^{(*) \pm }}{D^{* \mp }}$ process near the open charm threshold using initial state radiation.

Belle II Track Reconstruction and Results from first Collisions

In April 2018, e+e- collisions of the SuperKEKB B-Factory have been recorded by the Belle II detector in Tsukuba (Japan) for the first time. The new accelerator and detector represent a major upgrade from the previous Belle experiment and will achieve a 40 times higher instantaneous luminosity. Special considerations and challenges arise for track reconstruction at Belle II due to multiple factors. This high luminosity configuration of the collider increases the beam-induced background by many factors compared to Belle and a new track reconstruction software has been developed from scratch to achieve an excellent physics performance in this busy environment. Even though on average only eleven signal tracks are present in one event, all of them need to be reconstructed down to a transverse momentum of 50 MeV and no fake tracks should be present in the event. Many analyses at Belle II rely on the advantage that the initial state in B-factories is well known and a clean event reconstruction is possible if no tracks are left after assigning all tracks to particle hypotheses. This contribution will introduce the concepts and algorithms of the Belle II tracking software. Special emphasis will be put on the mitigation techniques developed to perform track reconstruction in high-occupancy events. First results from the data-taking with the Belle II detector will be presented.

The Belle II Experiment: Status and Prospects

The Belle II experiment is a substantial upgrade of the Belle detector and will operate at the SuperKEKBenergy-asymmetric e + e − collider. The accelerator has already successfully completed the first phase of commissioning in 2016. The first electron versus positron collisions in Belle II were delivered in April 2018. The design luminosity of SuperKEKB is 8 × 10 35 cm−2s−1, and the Belle II experiment aims to record 50 ab−1 of data, a factor of 50 more than the Belle experiment. This large dataset will be accumulated with low backgrounds and high trigger efficiencies in a clean e + e − environment. This contribution will review the detector upgrade, the achieved detector performance and the plans for the commissioning of Belle II.