Weak decays of the vector
D
∗
0
and
B
(
s
)
∗
0
mesons to the
μ
+
μ
-
final state provide novel potential to test the Standard Model of particle physics. Such processes have extremely small branching ...fractions as the vector mesons are able to decay through electromagnetic and (for the
D
∗
0
meson) strong interactions. Nonetheless, the production of copious quantities of these particles in LHC collisions, and the ability to exploit experimental techniques that can suppress background to low levels, provides good potential to reach interesting sensitivity. The possibility to reconstruct these processes as part of the decay chain of
B
-
or
B
c
+
mesons appears particularly attractive due to the clean experimental signature of the displaced vertex. Indeed, published LHCb data on
B
-
→
π
-
μ
+
μ
-
decays already implies a stringent limit on the branching fraction of
D
∗
0
→
μ
+
μ
-
. Estimates are made on the achievable sensitivity to
D
∗
0
→
μ
+
μ
-
and
B
(
s
)
∗
0
→
μ
+
μ
-
decays with the LHCb experiment.
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.
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, Letnik:
976, Številka:
C
Journal Article
Recenzirano
Odprti dostop
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.
Weak decays of the vector Formula omitted and Formula omitted mesons to the Formula omitted final state provide novel potential to test the Standard Model of particle physics. Such processes have ...extremely small branching fractions as the vector mesons are able to decay through electromagnetic and (for the Formula omitted meson) strong interactions. Nonetheless, the production of copious quantities of these particles in LHC collisions, and the ability to exploit experimental techniques that can suppress background to low levels, provides good potential to reach interesting sensitivity. The possibility to reconstruct these processes as part of the decay chain of Formula omitted or Formula omitted mesons appears particularly attractive due to the clean experimental signature of the displaced vertex. Indeed, published LHCb data on Formula omitted decays already implies a stringent limit on the branching fraction of Formula omitted. Estimates are made on the achievable sensitivity to Formula omitted and Formula omitted decays with the LHCb experiment.
Abstract
Weak decays of the vector
$${{D} ^*} ^0$$
D
∗
0
and
$${{B} ^{*0}_{({s})}} $$
B
(
s
)
∗
0
mesons to the
$${\mu ^+\mu ^-} $$
μ
+
μ
-
final state provide novel potential to test the Standard ...Model of particle physics. Such processes have extremely small branching fractions as the vector mesons are able to decay through electromagnetic and (for the
$${{D} ^*} ^0$$
D
∗
0
meson) strong interactions. Nonetheless, the production of copious quantities of these particles in LHC collisions, and the ability to exploit experimental techniques that can suppress background to low levels, provides good potential to reach interesting sensitivity. The possibility to reconstruct these processes as part of the decay chain of
$${{{B} ^-}} $$
B
-
or
$${{B} _{c} ^+} $$
B
c
+
mesons appears particularly attractive due to the clean experimental signature of the displaced vertex. Indeed, published LHCb data on
$${{{B} ^-}} \rightarrow {{\pi } ^-} {\mu ^+\mu ^-} $$
B
-
→
π
-
μ
+
μ
-
decays already implies a stringent limit on the branching fraction of
$${{D} ^{*0}} \rightarrow {\mu ^+\mu ^-} $$
D
∗
0
→
μ
+
μ
-
. Estimates are made on the achievable sensitivity to
$${{D} ^{*0}} \rightarrow {\mu ^+\mu ^-} $$
D
∗
0
→
μ
+
μ
-
and
$${{B} ^{*0}_{({s})}} \rightarrow {\mu ^+\mu ^-} $$
B
(
s
)
∗
0
→
μ
+
μ
-
decays with the LHCb experiment.
Using a proton-proton collision data sample collected by the LHCb detector and corresponding to an integrated luminosity of Formula omitted, the lifetime of the light Formula omitted mass eigenstate, ...Formula omitted, is measured using the Formula omitted decay mode to be tauL=1.445±0.016(stat)±0.008(syst)ps.A combination of this result with a previous LHCb analysis using an independent dataset corresponding to 3 fb Formula omitted of integrated luminosity gives tauL=1.452±0.014±0.007±0.002ps,where the first uncertainty is statistical, the second due to the uncorrelated part of the systematic uncertainty and the third due to the correlated part of the systematic uncertainty.
The measurement of charmonium states produced in proton-neon ( Formula omitted) collisions by the LHCb experiment in its fixed-target configuration is presented. The production of Formula omitted and ...Formula omitted mesons is studied with a beam of 2.5 Formula omitted protons colliding on gaseous neon targets at rest, corresponding to a nucleon-nucleon centre-of-mass energy Formula omitted. The data sample corresponds to an integrated luminosity of Formula omitted nb Formula omitted. The Formula omitted and Formula omitted hadrons are reconstructed in Formula omitted Formula omitted final states. The Formula omitted production cross-section per target nucleon in the centre-of-mass rapidity range Formula omitted is found to be Formula omitted. The ratio of Formula omitted and Formula omitted cross-sections is evaluated to Formula omitted. The Formula omitted to Formula omitted relative production rate is found to be Formula omitted in good agreement with other measurements involving beam and target nuclei of similar sizes.
The very rare Formula omitted decay is searched for by analysing Formula omitted decays. The analysis uses a sample of beauty mesons produced in proton-proton collisions collected with the LHCb ...detector between 2011 and 2018, corresponding to an integrated luminosity of 9 Formula omitted. The signal signature corresponds to simultaneous peaks in the Formula omitted and Formula omitted invariant masses. No evidence for an excess of events over background is observed and an upper limit is set on the branching fraction of the decay at Formula omitted at Formula omitted confidence level. This is the first limit on the branching fraction of Formula omitted decays and the most stringent limit on Formula omitted decays to leptonic final states. The analysis is the first search for a rare charm-meson decay exploiting production via beauty decays.
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