The existence of a heavy neutrino, ν H , in the K + → μ + ν H decays was tested using the E949 experimental data with an exposure of 1.70 × 1012 stopped kaons. The allowed heavy neutrino mass region ...for the analysis is from 175 MeV/c 2 to 300 MeV/c 2. With major background from the radiative K + → μ + ν μ γ decay understood and suppressed, the preliminary new upper limits (90% C.L.) on the neutrino mixing matrix element between muon and heavy neutrino, |U μ H|2, were set at the level of 10−8 to 10−9. New limit on the K + → μ + ν ν ¯ ν branching ratio assuming Standard Model muon spectrum is set to be 2.4 × 10−6.
A
bstract
The NA62 experiment at CERN, designed to study the ultra-rare decay
K
+
→
π
+
ν
ν
¯
, has also collected data in beam-dump mode. In this configuration, dark photons may be produced by ...protons dumped on an absorber and reach a decay volume beginning 80 m downstream. A search for dark photons decaying in flight to
μ
+
μ
−
pairs is reported, based on a sample of 1
.
4 × 10
17
protons on dump collected in 2021. No evidence for a dark photon signal is observed. A region of the parameter space is excluded at 90% CL, improving on previous experimental limits for dark photon masses between 215 and 550 MeV
/c
2
.
The first search for ultra-rare K+ decays into the π+e+e−e+e− final state is reported, using a dataset collected by the NA62 experiment at CERN in 2017–2018. An upper limit of 1.4×10−8 at 90% CL is ...obtained for the branching ratio of the K+→π+e+e−e+e− decay, predicted in the Standard Model to be (7.2±0.7)×10−11. Upper limits at 90% CL are obtained at the level of 10−9 for the branching ratios of two prompt decay chains involving pair-production of hidden-sector mediators: K+→π+aa, a→e+e− and K+→π+S, S→A′A′, A′→e+e−.
Measurement of the K+ → π+γγ decay Kleimenova, A.; Padolski, S.; Petrov, Y. ...
Physics letters. B,
March 2024, 2024-03-00, 2024-03-01, Letnik:
850
Journal Article
Recenzirano
Odprti dostop
A sample of 3984 candidates of the K+→π+γγ decay, with an estimated background of 291±14 events, was collected by the NA62 experiment at CERN during 2017–2018. In order to describe the observed ...di-photon mass spectrum, the next-to-leading order contribution in chiral perturbation theory was found to be necessary. The decay branching ratio in the full kinematic range is measured to be (9.61±0.17)×10−7. The first search for production and prompt decay of an axion-like particle with gluon coupling in the process K+→π+a, a→γγ is also reported.
The T2K experiment presents new measurements of neutrino oscillation parameters using
protons on target (POT) in (anti-)neutrino mode at the far detector (FD). Compared to the previous analysis, an ...additional
POT neutrino data was collected at the FD. Significant improvements were made to the analysis methodology, with the near-detector analysis introducing new selections and using more than double the data. Additionally, this is the first T2K oscillation analysis to use NA61/SHINE data on a replica of the T2K target to tune the neutrino flux model, and the neutrino interaction model was improved to include new nuclear effects and calculations. Frequentist and Bayesian analyses are presented, including results on
and the impact of priors on the
measurement. Both analyses prefer the normal mass ordering and upper octant of
with a nearly maximally CP-violating phase. Assuming the normal ordering and using the constraint on
from reactors,
using Feldman-Cousins corrected intervals, and
using constant
intervals. The CP-violating phase is constrained to
using Feldman-Cousins corrected intervals, and
is excluded at more than 90% confidence level. A Jarlskog invariant of zero is excluded at more than
credible level using a flat prior in
and just below
using a flat prior in
When the external constraint on
is removed,
in agreement with measurements from reactor experiments. These results are consistent with previous T2K analyses.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
7.
A study of the K + → π 0 e + νγ decay The NA62 collaboration; A. Kleimenova; S. Padolski ...
The journal of high energy physics,
09/2023, Letnik:
2023, Številka:
9
Journal Article
Recenzirano
Odprti dostop
Abstract A sample of 1.3 × 105 K + → π 0 e + νγ candidates with less than 1% background was collected by the NA62 experiment at the CERN SPS in 2017–2018. Branching fraction measurements are obtained ...at percent relative precision in three restricted kinematic regions, improving on existing results by a factor larger than two. An asymmetry, possibly related to T-violation, is investigated with no evidence observed within the achieved precision.
Abstract The T2K experiment presents new measurements of neutrino oscillation parameters using $$19.7(16.3)\times 10^{20}$$ 19.7 ( 16.3 ) × 10 20 protons on target (POT) in (anti-)neutrino mode at ...the far detector (FD). Compared to the previous analysis, an additional $$4.7\times 10^{20}$$ 4.7 × 10 20 POT neutrino data was collected at the FD. Significant improvements were made to the analysis methodology, with the near-detector analysis introducing new selections and using more than double the data. Additionally, this is the first T2K oscillation analysis to use NA61/SHINE data on a replica of the T2K target to tune the neutrino flux model, and the neutrino interaction model was improved to include new nuclear effects and calculations. Frequentist and Bayesian analyses are presented, including results on $$\sin ^2\theta _{13}$$ sin 2 θ 13 and the impact of priors on the $$\delta _{\textrm{CP}}$$ δ CP measurement. Both analyses prefer the normal mass ordering and upper octant of $$\sin ^2\theta _{23}$$ sin 2 θ 23 with a nearly maximally CP-violating phase. Assuming the normal ordering and using the constraint on $$\sin ^2\theta _{13}$$ sin 2 θ 13 from reactors, $$\sin ^2\theta _{23}=0.561^{+0.021}_{-0.032}$$ sin 2 θ 23 = 0 . 561 - 0.032 + 0.021 using Feldman–Cousins corrected intervals, and $$\varDelta {}m^2_{32}=2.494_{-0.058}^{+0.041}\times 10^{-3}~\text {eV}^2$$ Δ m 32 2 = 2 . 494 - 0.058 + 0.041 × 10 - 3 eV 2 using constant $$\varDelta \chi ^{2}$$ Δ χ 2 intervals. The CP-violating phase is constrained to $$\delta _{\textrm{CP}}=-1.97_{-0.70}^{+0.97}$$ δ CP = - 1 . 97 - 0.70 + 0.97 using Feldman–Cousins corrected intervals, and $$\delta _{\textrm{CP}}=0,\pi $$ δ CP = 0 , π is excluded at more than 90% confidence level. A Jarlskog invariant of zero is excluded at more than $$2\sigma $$ 2 σ credible level using a flat prior in $$\delta _{\textrm{CP}},$$ δ CP , and just below $$2\sigma $$ 2 σ using a flat prior in $$\sin \delta _{\textrm{CP}}.$$ sin δ CP . When the external constraint on $$\sin ^2\theta _{13}$$ sin 2 θ 13 is removed, $$\sin ^2\theta _{13}=28.0^{+2.8}_{-6.5}\times 10^{-3},$$ sin 2 θ 13 = 28 . 0 - 6.5 + 2.8 × 10 - 3 , in agreement with measurements from reactor experiments. These results are consistent with previous T2K analyses.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Search for heavy neutrinos in K + → μ + ν H decays Artamonov, A. V.; Bassalleck, B.; Bhuyan, B. ...
Physical review. D, Particles, fields, gravitation, and cosmology,
03/2015, Letnik:
91, Številka:
5
Journal Article
Odprti dostop
Here, evidence of a heavy neutrino, νH, in the K+→μ+νH decays was sought using the E949 experimental data with an exposure of 1.70 × 1012 stopped kaons. With the major background from the radiative ...K+→μ+νμγ decay understood and suppressed, upper limits (90% C.L.) on the neutrino mixing matrix element between the muon and heavy neutrinos, |UμH|2, were set at the level of 10–7 to 10–9 for the heavy neutrino mass region 175 to 300 MeV/c2.
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