Challenges in semileptonic B decays Gambino, P.; Kronfeld, A. S.; Rotondo, M. ...
The European physical journal. C, Particles and fields,
10/2020, Letnik:
80, Številka:
10
Journal Article
Recenzirano
Odprti dostop
Two of the elements of the Cabibbo–Kobayashi–Maskawa quark mixing matrix,
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V
ub
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and
|
V
cb
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, are extracted from semileptonic
B
decays. The results of the
B
factories, analysed in the light of ...the most recent theoretical calculations, remain puzzling, because for both
|
V
ub
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and
|
V
cb
|
the exclusive and inclusive determinations are in clear tension. Further, measurements in the
τ
channels at Belle, Babar, and LHCb show discrepancies with the Standard Model predictions, pointing to a possible violation of lepton flavor universality. LHCb and Belle II have the potential to resolve these issues in the next few years. This article summarizes the discussions and results obtained at the MITP workshop held on April 9–13, 2018, in Mainz, Germany, with the goal to develop a medium-term strategy of analyses and calculations aimed at solving the puzzles. Lattice and continuum theorists working together with experimentalists have discussed how to reshape the semileptonic analyses in view of the much higher luminosity expected at Belle II, searching for ways to systematically validate the theoretical predictions in both exclusive and inclusive
B
decays, and to exploit the rich possibilities at LHCb.
This article reports world averages of measurements of
b
-hadron,
c
-hadron, and
τ
-lepton properties obtained by the Heavy Flavor Averaging Group using results available through summer 2016. For the ...averaging, common input parameters used in the various analyses are adjusted (rescaled) to common values, and known correlations are taken into account. The averages include branching fractions, lifetimes, neutral meson mixing parameters,
C
P
violation parameters, parameters of semileptonic decays, and Cabbibo–Kobayashi–Maskawa matrix elements.
Punzi-loss Abudinén, F.; Bertemes, M.; Bilokin, S. ...
The European physical journal. C, Particles and fields,
2022/2, Letnik:
82, Številka:
2
Journal Article
Recenzirano
Odprti dostop
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, Letnik:
82, Številka:
2
Journal Article
Recenzirano
Odprti dostop
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.
Performance of the Belle II Silicon Vertex Detector Tanigawa, H.; Adamczyk, K.; Aihara, H. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
08/2020, Letnik:
972
Journal Article
Recenzirano
The Belle II experiment at the SuperKEKB collider of KEK (Japan) started recording physics data in spring 2019 with all its subdetectors installed and with the goal of accumulating 50ab−1 of e+e− ...collision events at the unprecedented instantaneous luminosity of 8×1035cm−2s−1, about 40 times larger than its predecessor. The Belle II vertex detector plays a crucial role in the broad Belle II physics program, especially for time-dependent CP measurements. It consists of two layers of DEPFET-based pixels and four layers of double-sided silicon strip detectors (SVD).
The experience gained from the first period of SVD operation can be summarized as smooth and reliable running of the detector, with high stability of noise levels and calibration parameters obtained from local calibration runs. No major problem has been experienced. The detector even survived a few serious radiation accidents in which the beam was lost due to failure in the machine focusing quadrupoles without any notable damage. The SVD performance were carefully studied with these first physics data. The SVD showed excellent hit and tracking efficiency. Moreover, cluster energy and signal to noise ratio as well as the hit time and spatial resolutions measured on data showed a fair agreement with the expected performance.
•Belle II silicon vertex detector operated during the first year of the experiment.•All sensors worked with stable and excellent hit efficiencies above 99 %.•Signal-to-noise ratios between 15 and 30, cluster time resolution better than 3 ns.•First effects of irradiation visible in leakage currents.
Abstract This article reports world averages of measurements of b-hadron, c-hadron, and $$\tau $$ τ -lepton properties obtained by the Heavy Flavor Averaging Group using results available through ...summer 2016. For the averaging, common input parameters used in the various analyses are adjusted (rescaled) to common values, and known correlations are taken into account. The averages include branching fractions, lifetimes, neutral meson mixing parameters, $$C\!P$$ C P violation parameters, parameters of semileptonic decays, and Cabbibo–Kobayashi–Maskawa matrix elements.
This paper reports world averages of measurements of
b
-hadron,
c
-hadron, and
τ
-lepton properties obtained by the Heavy Flavour Averaging Group using results available through September 2018. In ...rare cases, significant results obtained several months later are also used. For the averaging, common input parameters used in the various analyses are adjusted (rescaled) to common values, and known correlations are taken into account. The averages include branching fractions, lifetimes, neutral meson mixing parameters,
C
P
violation parameters, parameters of semileptonic decays, and Cabibbo–Kobayashi–Maskawa matrix elements.
We 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<ma<9.7 GeV/c2 using data corresponding to an integrated luminosity of (445±3) pb−1. Light pseudoscalars interacting predominantly with standard model gauge bosons (so-called axionlike particles or ALPs) are frequently postulated in extensions of the standard model. We find no evidence for ALPs and set 95% confidence level upper limits on the coupling strength gaγγ of ALPs to photons at the level of 10−3 GeV−1. The limits are the most restrictive to date for 0.2<ma<1 GeV/c2.
Theories beyond the standard model often predict the existence of an additional neutral boson, the Z^{'}. Using data collected by the Belle II experiment during 2018 at the SuperKEKB collider, we ...perform the first searches for the invisible decay of a Z^{'} in the process e^{+}e^{-}→μ^{+}μ^{-}Z^{'} and of a lepton-flavor-violating Z^{'} in e^{+}e^{-}→e^{±}μ^{∓}Z^{'}. We do not find any excess of events and set 90% credibility level upper limits on the cross sections of these processes. We translate the former, in the framework of an L_{μ}-L_{τ} theory, into upper limits on the Z^{'} coupling constant at the level of 5×10^{-2}-1 for M_{Z^{'}}≤6 GeV/c^{2}.
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