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

Search for an Axion-Like Particle in B decays at the BaBar experiment and projections to the Belle II data sample

The goal of this thesis is the search for an Axion-Like Particle (ALP) A in the decay B±→K±A, A→γγ in the data collected by the BABAR experiment, and the projections to the Belle II experiment. I reconstructed the decay of a charged B meson into a charged K and two photons, and searched resonances in the diphoton invariant mass spectrum. Various multivariate analysis have been tested to discriminate the signal from the two main backgrounds, i.e. the one related to B decays and the one related to light quarks production (uds) and quark c. The signal yield is extracted from a fit to the diphoton invariant mass distribution. The efficiency of the selection is between 17% and 19% for the signal, while the efficiency for the background events of type B and uds is, respectively, 5.0 × 10−6 and 3.9 × 10−6. I also contributed to the Belle II Silicon Vertex Detector reconstruction software, developing and implementing the algorithm to extract the hit time of the particles crossing the detector. Using this time information it is possible to reduce the off-time background and therefore significantly improve the tracking performances

Search for Axion-Like Particles produced in e+e−e^+e^- collisions at the Belle II experiment.

Search for Axion-like Particles produced in e+e- collisions at the Belle II experiment. PRL-published results obtained with early calibration & tuning 2018 data

Search for Axion-Like Particles produced in e+^+e−^− collisions and photon energy resolution studies at Belle II

Despite the great successes achieved by the Standard Model (SM) in explaining and predicting the behavior and existence of particles, multiple phenomena are yet to be given a satisfying explanation. Amongst these is Dark Matter (DM), a kind of matter that would permeate the whole Universe and that so far has been observed only via its gravitational interactions.One possible extension of the SM, which may contribute to solve the mystery of DM and/or explain some astrophysical anomalies, are Axion-Like Particles (ALPs). The model taken into consideration in this thesis is of an ALP interacting with SM photons with a coupling strength g$_{aγγ}$ and having mass m$_a$. This thesis describes a search for the direct production of such ALP via the process e+e− → γa(a → γγ), in the mass range 0.2 < m$_a$ < 9.7 GeV/c$^2$. This search is performed using 0.445 fb$^{−1}$ of data collected in 2018 by the Belle II detector.No evidence for ALPs is found, and a 95%-confidence-level upper limit is set on the coupling constant g$_{aγγ}$ at the level of 10$^{−3}$ GeV$^{−1}$. These limits are the strongest to date for 0.2 < m$_a$ < 1 GeV/c$^2$.Given that the final state of the e+e− → γa(a → γγ) process is fully neutral, being made up by three photons, a proper kinematic fit with neutral particles may be a powerful tool to improve signal resolution. To achieve such a kinematic fit, a precise knowledge of the photon covariance matrix is needed. Such matrix is obtained from the results of photon resolution studies, whose status and results are presented in this thesis

Track finding at Belle II

This paper describes the track-finding algorithm that is used for event reconstruction in the Belle II experiment operating at the SuperKEKB B-factory in Tsukuba, Japan. The algorithm is designed to balance the requirements of a high efficiency to find charged particles with a good track parameter resolution, a low rate of spurious tracks, and a reasonable demand on CPU resources. The software is implemented in a flexible, modular manner and employs a diverse selection of global and local track-finding algorithms to achieve an optimal performance

Track finding at Belle II

International audienceThis paper describes the track-finding algorithm that is used for event reconstruction in the Belle II experiment operating at the SuperKEKB B-factory in Tsukuba, Japan. The algorithm is designed to balance the requirements of a high efficiency to find charged particles with a good track parameter resolution, a low rate of spurious tracks, and a reasonable demand on CPU resources. The software is implemented in a flexible, modular manner and employs a diverse selection of global and local track-finding algorithms to achieve an optimal performance