Workshop summary: Kaons@CERN 2023 Anzivino, G.; Cuendis, Sergio Arguedas; Bernard, V. ...
The European physical journal. C, Particles and fields,
04/2024, Volume:
84, Issue:
4
Journal Article
Peer reviewed
Open access
Kaon physics is at a turning point – while the rare-kaon experiments NA62 and KOTO are in full swing, the end of their lifetime is approaching and the future experimental landscape needs to be ...defined. With HIKE, KOTO-II and LHCb-Phase-II on the table and under scrutiny, it is a very good moment in time to take stock and contemplate about the opportunities these experiments and theoretical developments provide for particle physics in the coming decade and beyond. This paper provides a compact summary of talks and discussions from the Kaons@CERN 2023 workshop, held in September 2023 at CERN.
Performance of the NA62 trigger system Cortina Gil, E.; Kleimenova, A.; Minucci, E. ...
The journal of high energy physics,
03/2023, Volume:
2023, Issue:
3
Journal Article
Peer reviewed
Open access
A
bstract
The NA62 experiment at CERN targets the measurement of the ultra-rare
K
+
→
π
+
ν
ν
¯
decay, and carries out a broad physics programme that includes probes for symmetry violations and ...searches for exotic particles. Data were collected in 2016–2018 using a multi-level trigger system, which is described highlighting performance studies based on 2018 data.
A
bstract
Measurement of the ultra-rare
K
+
→
π
+
ν
ν
¯
decay at the NA62 experiment at CERN requires high-performance particle identification to distinguish muons from pions. Calorimetric ...identification currently in use, based on a boosted decision tree algorithm, achieves a muon misidentification probability of 1
.
2 × 10
−
5
for a pion identification efficiency of 75% in the momentum range of 15–40 GeV/
c
. In this work, calorimetric identification performance is improved by developing an algorithm based on a convolutional neural network classifier augmented by a filter. Muon misidentification probability is reduced by a factor of six with respect to the current value for a fixed pion-identification efficiency of 75%. Alternatively, pion identification efficiency is improved from 72% to 91% for a fixed muon misidentification probability of 10
−
5
.
The beam and detector, used for the NA48 experiment, devoted to the measurement of
Re
(
ε
′
/
ε
)
, and for the NA48/1 experiment on rare
K
S
and neutral hyperon decays, are described.
A
bstract
A measurement of the form factors of charged kaon semileptonic decays is presented, based on 4.4 × 10
6
K
±
→
π
0
e
±
ν
e
(
K
e
3
±
) and 2.3 × 10
6
K
±
→
π
0
μ
±
ν
μ
(
K
μ
3
±
) decays ...collected in 2004 by the NA48/2 experiment. The results are obtained with improved precision as compared to earlier measurements. The combination of measurements in the
K
e
3
±
and
K
μ
3
±
modes is also presented.
A measurement of the ratio RK to check lepton universality has been performed by NA48 at CERN in 2003 and 2004, with an uncertainty of about 2%. Following recent theoretical studies, whereby the ...ratio could differ from the SM value in supersymmetric models by few percent, a dedicated run has been approved and performed at CERN in summer 2007 to reach an error of a measurement of ≈ 0.3% with the collection of ≈ 120000 events.
A
bstract
The NA62 experiment reports the branching ratio measurement
BR
K
+
→
π
+
ν
ν
¯
=
10.6
−
3.4
+
4.0
stat
±
0.9
syst
×
10
−
11
at 68% CL, based on the observation of 20 signal candidates with ...an expected background of 7.0 events from the total data sample collected at the CERN SPS during 2016–2018. This provides evidence for the very rare
K
+
→
π
+
ν
ν
¯
decay, observed with a significance of 3.4
σ
. The experiment achieves a single event sensitivity of (0
.
839
±
0
.
054)
×
10
−
11
, corresponding to 10.0 events assuming the Standard Model branching ratio of (8
.
4
±
1
.
0)
×
10
−
11
. This measurement is also used to set limits on BR(
K
+
→ π
+
X
), where
X
is a scalar or pseudo-scalar particle. Details are given of the analysis of the 2018 data sample, which corresponds to about 80% of the total data sample.
A sample of 7253 K±→π±e+e−(γ) decay candidates with 1.0% background contamination has been collected by the NA48/2 experiment at the CERN SPS, which allowed a precise measurement of the decay ...properties. The branching ratio in the full kinematic range was measured to be BR=(3.11±0.12)×10−7, where the uncertainty includes also the model dependence. The shape of the form factor W(z), where z=(Mee/MK)2, was parameterized according to several models, and, in particular, the slope δ of the linear form factor W(z)=W0(1+δz) was determined to be δ=2.32±0.18. A possible CP violating asymmetry of K+ and K− decay widths was investigated, and a conservative upper limit of 2.1×10−2 at 90% CL was established.
The parallel computing power of commercial Graphics Processing Units (GPUs) is exploited to perform real-time ring fitting at the lowest trigger level using information coming from the Ring Imaging ...Cherenkov (RICH) detector of the NA62 experiment at CERN. To this purpose, direct GPU communication with a custom FPGA-based board has been used to reduce the data transmission latency. The GPU-based trigger system is currently integrated in the experimental setup of the RICH detector of the NA62 experiment, in order to reconstruct ring-shaped hit patterns. The ring-fitting algorithm running on GPU is fed with raw RICH data only, with no information coming from other detectors, and is able to provide more complex trigger primitives with respect to the simple photodetector hit multiplicity, resulting in a higher selection efficiency. The performance of the system for multi-ring Cherenkov online reconstruction obtained during the NA62 physics run is presented.
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