COMET Phase-I technical design report Abramishvili, R; Adamov, G; Allin, A ...
Progress of theoretical and experimental physics,
03/2020, Letnik:
2020, Številka:
3
Journal Article
Recenzirano
Odprti dostop
Abstract
The Technical Design for the COMET Phase-I experiment is presented in this paper. COMET is an experiment at J-PARC, Japan, which will search for neutrinoless conversion of muons into ...electrons in the field of an aluminum nucleus ($\mu$–$e$ conversion, $\mu^{-}N \rightarrow e^{-}N$); a lepton flavor-violating process. The experimental sensitivity goal for this process in the Phase-I experiment is $3.1\times10^{-15}$, or 90% upper limit of a branching ratio of $7\times 10^{-15}$, which is a factor of 100 improvement over the existing limit. The expected number of background events is 0.032. To achieve the target sensitivity and background level, the 3.2 kW 8 GeV proton beam from J-PARC will be used. Two types of detectors, CyDet and StrECAL, will be used for detecting the $\mu$–$e$ conversion events, and for measuring the beam-related background events in view of the Phase-II experiment, respectively. Results from simulation on signal and background estimations are also described.
The design of the MEG II experiment Baldini, A. M.; Baracchini, E.; Bemporad, C. ...
The European physical journal. C, Particles and fields,
05/2018, Letnik:
78, Številka:
5
Journal Article
Recenzirano
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The MEG experiment, designed to search for the
μ
+
→
e
+
γ
decay, completed data-taking in 2013 reaching a sensitivity level of
5.3
×
10
-
13
for the branching ratio. In order to increase the ...sensitivity reach of the experiment by an order of magnitude to the level of
6
×
10
-
14
, a total upgrade, involving substantial changes to the experiment, has been undertaken, known as MEG II. We present both the motivation for the upgrade and a detailed overview of the design of the experiment and of the expected detector performance.
An experimental high-strength steel 20Kh2G2SNMA with high resistance of supercooled austenite to formation of diffusion transformation products is studied. Dilatometric analysis of the phase and ...structural transformations under continuous cooling and isothermal holding is performed. The time-temperature ranges of the transformations are found. The thermokinetic diagram is plotted. The mechanical properties of the steel are determined after different treatments, i.e., annealing, normalizing, quenching, tempering, isothermal and step quenching. It is shown that the presence of bainite in the structure lowers the impact toughness of the steel independently of its morphology and of the temperature range of its formation.
Interaction between water and composite films based on chitosan and chitin nanofibrils was studied. Isotherms of water vapor sorption by composite films were used to calculate partial values of ...entropy and enthalpy of sorbate; dependences of entropy and enthalpy on water sorption value were obtained. It was demonstrated that introducing chitin nanofibrils into chitosan matrix leads to decrease in sorption capacity of composite films. Apparently, this phenomenon is caused by formation of ordered structures consisting of chitosan macromolecules on the surface of chitin nanofibrils. The hypothesis was confirmed by calculations of thermodynamic parameters of the chitosan/chitin/water system. The calculations led to the conclusion that thermodynamically stable chitosan/chitin system is formed in composite films; in addition, it was revealed that the strongest chitosan-chitin interaction arises in the composite containing 1−5 wt.% of chitin nanofibrils. In this concentration range, Gibbs energy, entropy and enthalpy of mixing pass through a minimum; this result indicates that the highest affinity between chitosan and chitin exists when concentration of chitin nanofibrils varies from 1 to 5 wt.%.
The final results of the search for the lepton flavour violating decay
μ
+
→
e
+
γ
based on the full dataset collected by the MEG experiment at the Paul Scherrer Institut in the period 2009–2013 and ...totalling
7.5
×
10
14
stopped muons on target are presented. No significant excess of events is observed in the dataset with respect to the expected background and a new upper limit on the branching ratio of this decay of
B
(
μ
+
→
e
+
γ
)
<
4.2
×
10
-
13
(90 % confidence level) is established, which represents the most stringent limit on the existence of this decay to date.
Features of the microstructure formation in steel 30Cr2MnSiNi2WMo (VL-1) are studied with various heat treatment regimes: stepwise quenching at temperature below M
s
(quenching and partitioning), and ...isothermal quenching for bainite. It is shown that the calculated optimum temperature of stepwise quenching does not provide the predicted amount of stable retained austenite in the test steel microstructure. Mechanical properties of steel 30Cr2MnSiNi2WMo after implementation of stepwise and isothermal quenching are determined. It is established that after isothermal heat treatment the steel studied exhibits reduced viscoplastic properties compared with a condition after bulk hardening and tempering.
The analysis of a combined data set, totaling 3.6 × 10(14) stopped muons on target, in the search for the lepton flavor violating decay μ(+) → e(+)γ is presented. The data collected by the MEG ...experiment at the Paul Scherrer Institut show no excess of events compared to background expectations and yield a new upper limit on the branching ratio of this decay of 5.7 × 10(-13) (90% confidence level). This represents a four times more stringent limit than the previous world best limit set by MEG.
The influence of ultrasonic treatment parameters of chitin nanofibrils aqueous suspension on structure, strength and deformation properties of chitosan-based composite films and fibers was ...investigated. Model calculations of ultrasound-induced cavitation parameters in the aqueous suspension of the chitin nanofibrils showed that an increase in the field power up to 630 W led to destruction of the cavity, to an increase in the temperature in the vicinity of cavitation area (up to 507 °C) and, as a consequence, to destruction of chitin glycoside ring (which is confirmed by the IR data). The results of light scattering, IR spectroscopy, and electron microscopy investigations indicated that the optimal duration of ultrasonic treatment of the chitin nanofibrils aqueous solution was 4–10 min (depending on oriented state of the scaffold). Tensile strength of the composites was 130 ± 11 MPa (films), 226 ± 4.8 MPa (fibers); deformation at break was 43 ± 7.5% (films), 10 ± 0.6% (fibers).
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Ametallographic study of advanced low-carbon martensitic steel with high resistance of the supercooled austenite to the transformations by pearlitic and bainitic mechanisms under continuous cooling ...is performed. The critical temperatures of the transformations occurring under heating and cooling are determined. The kinetics of the isothermal transformation of the austenite in the temperature range of 300 – 400°C is analyzed. The possibility of successful implementation of isothermal quenching of the steel after carburizing is demonstrated.
The MEG II experiment, based at the Paul Scherrer Institut in Switzerland, reports the result of a search for the decay
μ
+
→
e
+
γ
from data taken in the first physics run in 2021. No excess of ...events over the expected background is observed, yielding an upper limit on the branching ratio of
B
(
μ
+
→
e
+
γ
)
<
7.5
×
10
-
13
(90% CL). The combination of this result and the limit obtained by MEG gives
B
(
μ
+
→
e
+
γ
)
<
3.1
×
10
-
13
(90% CL), which is the most stringent limit to date. A ten-fold larger sample of data is being collected during the years 2022–2023, and data-taking will continue in the coming years.
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