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.
The calorimeter, range detector and active target elements of the T2K near detectors rely on the Hamamatsu Photonics Multi-Pixel Photon Counters (MPPCs) to detect scintillation light produced by ...charged particles. Detailed measurements of the MPPC gain, afterpulsing, crosstalk, dark noise, and photon detection efficiency for low light levels are reported. In order to account for the impact of the MPPC behavior on T2K physics observables, a simulation program has been developed based on these measurements. The simulation is used to predict the energy resolution of the detector.
It is proposed to use a simple switched-reluctance electric machine that does not have windings or permanent magnets on a movable part to develop a linear reciprocating electric machine intended for ...use as an electric generator together with a free-piston internal-combustion engine. It is noted that one of the most difficult problems in the development of such a linear electric machine is the development of a control system. A sensorless control algorithm is considered. Information on the stator-phase inductance of the electric machine and its variation is used to determine the position of the movable part. For its estimation, probing voltage pulses of known duration are applied to the phase. The amplitude of the current pulses caused by them will be proportional to the phase inductance. A mathematical model of electromagnetic processes is used to test the efficiency of the proposed control algorithm and determine appropriate control parameters. Since stator phases have separate magnetic circuits and are not magnetically connected, the electromagnetic processes in each phase are considered independently. Model parameters are determined experimentally using an experimental prototype of the considered electric machine, for which the dependences of the phase flux linkage and the generated force on the phase current for different positions of the movable part are obtained. The results of the investigation of processes in the considered electric machine at different frequencies of the movable part are given. It is found that, at frequencies of the movable part close to the nominal frequency, the phase should be connected to the power supply even before the movable part reaches the extreme position. Control using probing pulses applied to the operating phase is impossible, because the level of these pulses does not reach the maximum value until the phase is switched on. In this case, it is necessary to use the probing pulses of another, nonoperating phase to determine the position of the movable part. Such an algorithm makes it possible to control a linear reciprocating switched-reluctance electric machine at both low and high frequencies of the movable part. The obtained results confirmed the correctness of the adopted approaches to the development of a sensorless control algorithm.
A linear switched-reluctance electrical machine (LEM) intended to be used as an electric-power generator together with a free-piston internal-combustion engine (ICE) has been analyzed. Taking into ...account the hard service conditions of an electrical machine (EM) in close proximity to a cylinder ICE, hottemperature zones and heavy mechanical loads of the EM of the vent-inductor type have been recommended to be used. Development of a control system for this type of machine is one of the most complicated problems when developing it. It has been suggested to determine the reasonable principles and regulating algorithms of the machine that is being considered, as well as its regulation system and energy-data evaluation, on the basis of a model of the electromagnetic process. Taking into account the characteristic properties of the linear switched-reluctance machine as a modeling object, a mathematical model has been developed to solve the problems mentioned above. As stator phases have separate coil-flux guides and are not connected magnetically, the electromagnetic processes in each phase are analyzed independently. For experimental corroboration of ideas for design calculation, an experimental model of the machine has been constructed. Parameters required for modeling the characteristics’ correspondences of flux linkage and phase current’s generating force at various positions of a moving element have been determined for this machine experimentally. Performance of the linear switched reluctance electrical reciprocating machine has been analyzed with the mathematical model with moving-element movement frequencies unfeasible for study on a proving stand. Reasonable parameters of the current pulses’ phases of the machine have been determined, and its energy data have been evaluated. The obtained results have confirmed the correctness of the design approaches, choice of regulation principles, and adjustment of a linear vent-inductor electrical machine of forward and backward action and the feasibility of using it as an electric-power generator together with a free-piston ICE.
A search for heavy neutral lepton (N) production in K+→e+N decays using the data sample collected by the NA62 experiment at CERN in 2017–2018 is reported. Upper limits of the extended neutrino mixing ...matrix element |Ue4|2 are established at the level of 10−9 over most of the accessible heavy neutral lepton mass range 144–462 MeV/c2, with the assumption that the lifetime exceeds 50 ns. These limits improve significantly upon those of previous production and decay searches. The |Ue4|2 range favoured by Big Bang Nucleosynthesis is excluded up to a mass of about 340 MeV/c2.
The NA62 experiment at CERN reports searches for K+→μ+N and K+→μ+νX decays, where N and X are massive invisible particles, using the 2016–2018 data set. The N particle is assumed to be a heavy ...neutral lepton, and the results are expressed as upper limits of O(10−8) of the neutrino mixing parameter |Uμ4|2 for N masses in the range 200–384 MeV/c2 and lifetime exceeding 50 ns. The X particle is considered a scalar or vector hidden sector mediator decaying to an invisible final state, and upper limits of the decay branching fraction for X masses in the range 10–370 MeV/c2 are reported for the first time, ranging from O(10−5) to O(10−7). An improved upper limit of 1.0×10−6 is established at 90% CL on the K+→μ+ννν¯ branching fraction.
A search for heavy neutral lepton production in K+ decays using a data sample collected with a minimum bias trigger by the NA62 experiment at CERN in 2015 is reported. Upper limits at the 10−7 to ...10−6 level are established on the elements of the extended neutrino mixing matrix |Ue4|2 and |Uμ4|2 for heavy neutral lepton mass in the ranges 170–448 MeV/c2 and 250–373 MeV/c2, respectively. This improves on the previous limits from HNL production searches over the whole mass range considered for |Ue4|2, and above 300 MeV/c2 for |Uμ4|2.
The NA62 experiment at CERN reports a search for the lepton number violating decays K+→π−e+e+ and K+→π−μ+μ+ using a data sample collected in 2017. No signals are observed, and upper limits on the ...branching fractions of these decays of 2.2×10−10 and 4.2×10−11 are obtained, respectively, at 90% confidence level. These upper limits improve on previously reported measurements by factors of 3 and 2, respectively.
Hyper-Kamiokande will be a next-generation underground water Cherenkov detector with a total (fiducial) mass of 0.99 (0.56) million metric tons, approximately 20 (25) times larger than that of ...Super-Kamiokande. One of the main goals of Hyper-Kamiokande is the study of
$CP$
asymmetry in the lepton sector using accelerator neutrino and anti-neutrino beams. In this paper, the physics potential of a long-baseline neutrino experiment using the Hyper-Kamiokande detector and a neutrino beam from the J-PARC proton synchrotron is presented. The analysis uses the framework and systematic uncertainties derived from the ongoing T2K experiment. With a total exposure of 7.5 MW
$\times 10^7$
s integrated proton beam power (corresponding to
$1.56 \times 10^{22}$
protons on target with a 30 GeV proton beam) to a
$2.5^\circ$
off-axis neutrino beam, it is expected that the leptonic
$CP$
phase
$\delta _{CP}$
can be determined to better than 19 degrees for all possible values of
$\delta _{CP}$
, and
$CP$
violation can be established with a statistical significance of more than
$3\,\sigma$
(
$5\,\sigma$
) for
$76{\%}$
(
$58{\%}$
) of the
${\delta _{CP}}$
parameter space. Using both
$\nu _e$
appearance and
$\nu _\mu$
disappearance data, the expected 1
$\sigma$
uncertainty of
$\sin ^2\theta _{23}$
is 0.015(0.006) for
$\sin ^2\theta _{23}=0.5(0.45)$
.
A measurement of the K+→ π+μ+μ− decay Cortina Gil, E.; Kleimenova, A.; Minucci, E. ...
The journal of high energy physics,
11/2022, Letnik:
2022, Številka:
11
Journal Article
Recenzirano
Odprti dostop
A
bstract
A sample of 2
.
8 × 10
4
K
+
→
π
+
μ
+
μ
−
candidates with negligible background was collected by the NA62 experiment at the CERN SPS in 2017–2018. The model-independent branching fraction ...is measured to be (9
.
15 ± 0
.
08) × 10
−
8
, a factor three more precise than previous measurements. The decay form factor is presented as a function of the squared dimuon mass. A measurement of the form factor parameters and their uncertainties is performed using a description based on Chiral Perturbation Theory at
O
(
p
6
).
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