The Time-Of-Propagation (TOP) counter is a novel ring-imaging Cherenkov detector that primarily consists of a quartz bar radiator, micro-channel plate photomultipliers and front-end readout ...electronics. These TOP counters are installed in the central region of the Belle II detector to provide the crucial information on the charged particle identification (PID). Here, we present an overview of PID studies in Belle II, with a focus on the performance of the TOP detector. The results presented are from the recently recorded data which show reasonable agreement with the expectations from the simulation studies.
Punzi-loss Abudinén, F.; Bertemes, M.; Bilokin, S. ...
The European physical journal. C, Particles and fields,
2022/2, Volume:
82, Issue:
2
Journal Article
Peer reviewed
Open access
We present the novel implementation of a non-differentiable metric approximation and a corresponding loss-scheduling aimed at the search for new particles of unknown mass in high energy physics ...experiments. We call the loss-scheduling, based on the minimisation of a figure-of-merit related function typical of particle physics, a Punzi-loss function, and the neural network that utilises this loss function a Punzi-net. We show that the Punzi-net outperforms standard multivariate analysis techniques and generalises well to mass hypotheses for which it was not trained. This is achieved by training a single classifier that provides a coherent and optimal classification of all signal hypotheses over the whole search space. Our result constitutes a complementary approach to fully differentiable analyses in particle physics. We implemented this work using PyTorch and provide users full access to a public repository containing all the codes and a training example.
Punzi-loss Abudinén, F; Bertemes, M; Bilokin, S ...
The European physical journal. C, Particles and fields,
02/2022, Volume:
82, Issue:
2
Journal Article
Peer reviewed
Open access
We present the novel implementation of a non-differentiable metric approximation and a corresponding loss-scheduling aimed at the search for new particles of unknown mass in high energy physics ...experiments. We call the loss-scheduling, based on the minimisation of a figure-of-merit related function typical of particle physics, a Punzi-loss function, and the neural network that utilises this loss function a Punzi-net. We show that the Punzi-net outperforms standard multivariate analysis techniques and generalises well to mass hypotheses for which it was not trained. This is achieved by training a single classifier that provides a coherent and optimal classification of all signal hypotheses over the whole search space. Our result constitutes a complementary approach to fully differentiable analyses in particle physics. We implemented this work using PyTorch and provide users full access to a public repository containing all the codes and a training example.
Using a sample of 771.6x106 UpsilonUpsilon(4S) decays collected by the Belle experiment at the KEKB e+e-collider, we observe, for the first time, the transition Upsilon(4S) arrow right etahb(1P) with ...the branching fraction BUpsilon(4S) arrow right etahb(1P)=(2.18+ or -0.11+ or -0.18)x10-3 and we measure the hb(1P) mass Mhb(1P)= (9899.3+ or -0.4+ or -1.0) MeV/c2, corresponding to the hyperfine (HF) splitting Delta MHF(1P)= (0.6+ or -0.4+ or -1.0) MeV/c2. Using the transition hb(1P) arrow right gamma etab(1S), we measure the nb(1S) mass Metab(1S)= (9400.7+ or -1.7+ or -1.6) MeV/c2, corresponding to Delta MHF(1S)=(59.6+ or -1.7+ or -1.6) MeV/c2, the etab(1S) width Gammaetab(1S)=(8-5+6+ or -5) MeV/c2 and the branching fraction Bhb(1P) arrow right gamma etab(1S)=(56+ or -8+ or -4)%.
With the full data sample of 772×106 BB¯ pairs recorded by the Belle detector at the KEKB electron-positron collider, the decay B¯→D*τ−ν¯τ is studied with the hadronic τ decays τ−→π−ντ and τ−→ρ−ντ. ...The τ polarization Pτ(D*) in two-body hadronic τ decays is measured, as well as the ratio of the branching fractions R(D*)=B(B¯→D*τ−ν¯τ)/B(B¯→D*ℓ−ν¯ℓ), where ℓ− denotes an electron or a muon. Our results, Pτ(D*)=−0.38±0.51(stat)−0.16+0.21(syst) and R(D*)=0.270±0.035(stat)−0.025+0.028(syst), are consistent with the theoretical predictions of the standard model. The polarization values of Pτ(D*)>+0.5 are excluded at the 90% confidence level.
Global decay chain vertex fitting at Belle II Krohn, J.-F.; Tenchini, F.; Urquijo, P. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
10/2020, Volume:
976, Issue:
C
Journal Article
Peer reviewed
Open access
In this paper we report the implementation of a global vertex fitting algorithm within the Belle II analysis software environment, which was originally developed for BaBar (Hulsbergen, 2005). We ...explore the impact of global vertex fitting algorithms for flavour physics analyses with the Belle II detector at the SuperKEKB e+e− collider, such as in the reconstruction of final states with neutral particles, and in fits with geometrical constraints from SuperKEKB’s nano-beam interaction region. The algorithm is compared to the standard vertex fitting algorithm employed by the Belle experiment. We have developed the fitting framework to utilise the EIGEN library for linear algebra operations, reducing the computation time for vertex fitting operations by an order of magnitude over previous methods. This has a significant impact on physics analysis computing efficiency, where vertex fitting over large combinations of final state particles is one of the most CPU intensive operations at Belle II.
Here, we present a measurement of angular observables and a test of lepton flavor universality in the B → K*ℓ+ℓ- decay, where ℓ is either e or μ . The analysis is performed on a data sample ...corresponding to an integrated luminosity of 711fb-1 containing 772×106 B B ¯ pairs, collected at the Υ ( 4S ) resonance with the Belle detector at the asymmetric-energy e+e- collider KEKB. The finding is consistent with standard model (SM) expectations, where the largest discrepancy from a SM prediction is observed in the muon modes with a local significance of 2.6σ .
Using the entire Belle data sample of 980 fb−1 of e+e− collisions, we present the results of a study of excited Ωc charmed baryons in the decay mode Ξc+K−. We show confirmation of four of the five ...narrow states reported by the LHCb Collaboration: the Ωc(3000), Ωc(3050), Ωc(3066), and Ωc(3090).
The Full Event Interpretation Keck, T.; Abudinén, F.; Bernlochner, Florian U. ...
Computing and software for big science,
12/2019, Volume:
3, Issue:
1
Journal Article
Open access
The full event interpretation is presented: a new exclusive tagging algorithm used by the high-energy physics experiment Belle II. The experimental setup of Belle II allows the precise measurement of ...otherwise inaccessible
B
meson decay modes. The Full Event Interpretation algorithm enables many of these measurements. The algorithm relies on machine learning to automatically identify plausible
B
meson decay chains based on the data recorded by the detector. Compared to similar algorithms employed by previous experiments, the Full Event Interpretation provides a greater efficiency, yielding a larger effective sample size usable in the measurement.
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