The dark photon A^{'} and the dark Higgs boson h^{'} are hypothetical particles predicted in many dark sector models. We search for the simultaneous production of A^{'} and h^{'} in the dark ...Higgsstrahlung process e^{+}e^{-}→A^{'}h^{'} with A^{'}→μ^{+}μ^{-} and h^{'} invisible in electron-positron collisions at a center-of-mass energy of 10.58 GeV in data collected by the Belle II experiment in 2019. With an integrated luminosity of 8.34 fb^{-1}, we observe no evidence for signal. We obtain exclusion limits at 90% Bayesian credibility in the range of 1.7-5.0 fb on the cross section and in the range of 1.7×10^{-8}-200×10^{-8} on the effective coupling ϵ^{2}×α_{D} for the A^{'} mass in the range of 4.0 GeV/c^{2}<M_{A^{'}}<9.7 GeV/c^{2} and for the h^{'} mass M_{h^{'}}<M_{A^{'}}, where ϵ is the mixing strength between the standard model and the dark photon and α_{D} is the coupling of the dark photon to the dark Higgs boson. Our limits are the first in this mass range.
A
bstract
We report results from a study of
B
±
→ DK
±
decays followed by
D
decaying to the
CP
-even final state
K
+
K
−
and CP-odd final state
K
S
0
π
0
, where
D
is an admixture of
D
0
and
D
¯
0
...states. These decays are sensitive to the Cabibbo-Kobayashi-Maskawa unitarity-triangle angle
ϕ
3
. The results are based on a combined analysis of the final data set of 772
×
10
6
B
B
¯
pairs collected by the Belle experiment and a data set of 198
×
10
6
B
B
¯
pairs collected by the Belle II experiment, both in electron-positron collisions at the Υ(4
S
) resonance. We measure the CP asymmetries to be
A
CP
+
= (+12.5
±
5.8
±
1.4)% and
A
CP−
= (
−
16.7
±
5.7
±
0.6)%, and the ratios of branching fractions to be
R
CP
+
= 1.164
±
0.081
±
0.036 and
R
CP−
= 1.151
±
0.074
±
0.019. The first contribution to the uncertainties is statistical, and the second is systematic. The asymmetries
A
CP
+
and
A
CP−
have similar magnitudes and opposite signs; their difference corresponds to 3.5 standard deviations. From these values we calculate 68.3% confidence intervals of (8.5
°
<
ϕ
3
< 16.5
°
) or (84.5
°
<
ϕ
3
< 95.5
°
) or (163.3
°
<
ϕ
3
< 171.5
°
) and 0.321 <
r
B
< 0.465.
A
bstract
We measure
CP
asymmetries and branching-fraction ratios for
B
±
→ DK
±
and
Dπ
±
decays with
D →
K
S
0
K
±
π
∓
, where
D
is a superposition of
D
0
and
D
¯
0
. We use the full data set of the ...Belle experiment, containing 772
×
10
6
B
B
¯
pairs, and data from the Belle II experiment, containing 387 × 10
6
B
B
¯
pairs, both collected in electron-positron collisions at the Υ(4
S
) resonance. Our results provide model-independent information on the unitarity triangle angle
ϕ
3
.
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.
The Belle II Physics Book Kou, E; Bishara, F; Brod, J ...
Progress of theoretical and experimental physics,
12/2019, Letnik:
2019, Številka:
12
Journal Article
Recenzirano
Odprti dostop
We present the physics program of the Belle II experiment, located on the intensity frontier SuperKEKB e+e- collider. Belle II collected its first collisions in 2018, and is expected to operate for ...the next decade. It is anticipated to collect 50/ab of collision data over its lifetime. This book is the outcome of a joint effort of Belle II collaborators and theorists through the Belle II theory interface platform (B2TiP), an effort that commenced in 2014. The aim of B2TiP was to elucidate the potential impacts of the Belle II program, which includes a wide scope of physics topics: B physics, charm, tau, quarkonium, electroweak precision measurements and dark sector searches. It is composed of nine working groups (WGs), which are coordinated by teams of theorist and experimentalists conveners: Semileptonic and leptonic B decays, Radiative and Electroweak penguins, φ1 and φ2 (time-dependent CP violation) measurements, φ3 measurements, Charmless hadronic B decay, Charm, Quarkonium(like), tau and low-multiplicity processes, new physics and global fit analyses. This book highlights "golden- and silver-channels", i.e. those that would have the highest potential impact in the field. Theorists scrutinised the role of those measurements and estimated the respective theoretical uncertainties, achievable now as well as prospects for the future. Experimentalists investigated the expected improvements with the large dataset expected from Belle II, taking into account improved performance from the upgraded detector.
We present the first measurement of the ratio of branching fractions of inclusive semileptonic $B$-meson decays, $R(X_{e/\mu}) = \mathcal{B}(B\to X \, e \, \nu) / \mathcal{B}(B\to X \, \mu \, \nu)$, ...a precision test of electron-muon universality, using data corresponding to $189\,\mathrm{fb}^{-1}$ from electron-positron collisions collected with the Belle II detector. In events where the partner $B$ meson is fully reconstructed, we use fits to the lepton momentum spectra above $1.3\,\mathrm{GeV}/c$ to obtain $R(X_{e/\mu}) = 1.007 \pm 0.009~(\mathrm{stat}) \pm 0.019~(\mathrm{syst})$, which is the most precise lepton-universality test of its kind and agrees with the standard-model expectation.
The L_{μ}-L_{τ} extension of the standard model predicts the existence of a lepton-flavor-universality-violating Z^{'} boson that couples only to the heavier lepton families. We search for such a ...Z^{'} through its invisible decay in the process e^{+}e^{-}→μ^{+}μ^{-}Z^{'}. We use a sample of electron-positron collisions at a center-of-mass energy of 10.58 GeV collected by the Belle II experiment in 2019-2020, corresponding to an integrated luminosity of 79.7 fb^{-1}. We find no excess over the expected standard-model background. We set 90%-confidence-level upper limits on the cross section for this process as well as on the coupling of the model, which ranges from 3×10^{-3} at low Z^{'} masses to 1 at Z^{'} masses of 8 GeV/c^{2}.
We report the first search for a non-standard-model resonance decaying into $\tau$ pairs in $e^{+}e^{-}\rightarrow \mu^{+}\mu^{-} \tau^+\tau^-$ events in the 3.6-10 GeV/$c^{2}$ mass range. We use a ...62.8 fb$^{-1}$ sample of $e^+e^-$ collisions collected at a center-of-mass energy of 10.58 GeV by the Belle II experiment at the SuperKEKB collider. The analysis probes three different models predicting a spin-1 particle coupling only to the heavier lepton families, a Higgs-like spin-0 particle that couples preferentially to charged leptons (leptophilic scalar), and an axion-like particle, respectively. We observe no evidence for a signal and set exclusion limits at 90% confidence level on the product of cross section and branching fraction into $\tau$ pairs, ranging from 0.7 fb to 24 fb, and on the couplings of these processes. We obtain world-leading constraints on the couplings for the leptophilic scalar model for masses above 6.5 GeV/$c^2$ and for the axion-like particle model over the entire mass range.
We measure the tau-to-light-lepton ratio of inclusive B -meson branching fractions R ( X τ / ℓ ) ≡ B ( B → X τ ν ) / B ( B → X ℓ ν ) , where ℓ indicates an electron or muon, and thereby test the ...universality of charged-current weak interactions. We select events that have one fully reconstructed B meson and a charged lepton candidate from 189 fb − 1 of electron-positron collision data collected with the Belle II detector. We find R ( X τ / ℓ ) = 0.228 ± 0.016 ( stat ) ± 0.036 ( syst ) , in agreement with standard-model expectations. This is the first direct measurement of R ( X τ / ℓ ) . Published by the American Physical Society 2024
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