Top quark production in the process
e
+
e
-
→
t
t
¯
at a future linear electron positron collider with polarised beams is a powerful tool to determine indirectly the scale of new physics. The ...presented study, based on a detailed simulation of the ILD detector concept, assumes a centre-of-mass energy of
s
=
500
GeV and a luminosity of
L
=
500
fb
-
1
equally shared between the incoming beam polarisations of
P
e
-
,
P
e
+
=
±
0.8
,
∓
0.3
. Events are selected in which the top pair decays semi-leptonically and the cross sections and the forward–backward asymmetries are determined. Based on these results, the vector, axial vector and tensorial
CP
conserving couplings are extracted separately for the photon and the
Z
0
component. With the expected precision, a large number of models in which the top quark acts as a messenger to new physics can be distinguished with many standard deviations. This will dramatically improve expectations from e.g. the LHC for electro-weak couplings of the top quark.
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 ...
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 peculiarities of obtaining thin ceramic coatings (TiO2 + Al2O3, Al2O3, ZrO2) on the surfaces of dielectrics (on the example of Kr1 silicon) during their formation by thermal evaporation in vacuum ...have been established. The mechanism of increase of microhardness of such coatings by their surface modification by a ribbon-shaped electron steam is investigated. It is shown that the combined thermal vacuum deposition of thin ceramic coatings from powder materials on the surface of Kr1 silicon, followed by their modification by low energy electron flow in one technological cycle, allows to significantly reduce the micro relief and to stabilize the homogeneity of the coating surfaces, as well as to increase the chemical and biological resistance of these coatings to the influence of the environment. The conditions of qualitative determination of microhardness of the studied material with the use of atomic force microscopy are determined. Microhardness studies, both of modified coatings and of dielectric surfaces on which they were applied, were carried out. The fact of nonlinear increase of microhardness (by 13-17 %) of thin coatings deposited on the surface of dielectric material by the combined electron beam method as the thickness of these coatings is established. The possibility of determining the microhardness of multilayer multifunctional ceramic coatings obtained by combined electron beam technology under different conditions and different modes of technological experiment is shown.
B-flavor tagging at Belle II Akopov, N.; Banerjee, Sw; Bauer, M. ...
European physical journal. C, Particles and fields,
04/2022, Letnik:
82, Številka:
4
Journal Article
Recenzirano
Odprti dostop
We report on new flavor tagging algorithms developed to determine the quark-flavor content of bottom (
) mesons at Belle II. The algorithms provide essential inputs for measurements of quark-flavor ...mixing and charge-parity violation. We validate and evaluate the performance of the algorithms using hadronic
decays with flavor-specific final states reconstructed in a data set corresponding to an integrated luminosity of 62.8 fb
-
1
, collected at the
resonance with the Belle II detector at the SuperKEKB collider. We measure the total effective tagging efficiency to be
ε
eff
=
(
30.0
±
1.2
(
stat
)
±
0.4
(
syst
)
)
%
for a category-based algorithm and
ε
eff
=
(
28.8
±
1.2
(
stat
)
±
0.4
(
syst
)
)
%
for a deep-learning-based algorithm.
We report measurements of the branching fraction and $\it CP$ asymmetry in $B^{0} \to \pi^{0} \pi^{0}$ decays reconstructed at Belle II in an electron-positron collision sample containing $198 \times ...10^{6}$ $B\overline{B}$ pairs. We measure a branching fraction $\mathcal{B}(\Bpipi) = (1.38 \pm 0.27 \pm 0.22) \times 10^{-6}$ and a $\it CP$ asymmetry $\Acp(\Bpipi) = 0.14 \pm 0.46 \pm 0.07$, where the first uncertainty is statistical and the second is systematic.
We present GFlaT, a new algorithm that uses a graph-neural-network to determine the flavor of neutral B mesons produced in ϒ ( 4 S ) decays. It improves previous algorithms by using the information ...from all charged final-state particles and the relations between them. We evaluate its performance using B decays to flavor-specific hadronic final states reconstructed in a 362 fb − 1 sample of electron-positron collisions collected at the ϒ ( 4 S ) resonance with the Belle II detector at the SuperKEKB collider. We achieve an effective tagging efficiency of ( 37.40 ± 0.43 ± 0.36 % ) , where the first uncertainty is statistical and the second systematic, which is 18% better than the previous Belle II algorithm. Demonstrating the algorithm, we use B 0 → J / ψ K S 0 decays to measure the mixing-induced and direct C P violation parameters, S = ( 0.724 ± 0.035 ± 0.009 ) and C = ( − 0.035 ± 0.026 ± 0.029 ) . Published by the American Physical Society 2024
We report on a search for a resonance
X
decaying to a pair of muons in
e
+
e
−
→
μ
+
μ
−
X
events in the
0.212
–
9.000
GeV
/
c
2
mass range, using
178
fb
−
1
of data collected by the Belle II ...experiment at the SuperKEKB collider at a center of mass energy of 10.58 GeV. The analysis probes two different models of
X
beyond the standard model: a
Z
′
vector boson in the
L
μ
−
L
τ
model and a muonphilic scalar. We observe no evidence for a signal and set exclusion limits at the 90% confidence level on the products of cross section and branching fraction for these processes, ranging from 0.046 fb to 0.97 fb for the
L
μ
−
L
τ
model and from 0.055 fb to 1.3 fb for the muonphilic scalar model. For masses below
6
GeV
/
c
2
, the corresponding constraints on the couplings of these processes to the standard model range from 0.0008 to 0.039 for the
L
μ
−
L
τ
model and from 0.0018 to 0.040 for the muonphilic scalar model. These are the first constraints on the muonphilic scalar from a dedicated search.
<supplementary-material>
<copyright-statement>Published by the American Physical Society</copyright-statement>
2024
</supplementary-material>
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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