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 Isotope and Muon Production using Advanced-Cyclotron and Target Technology Project (IMPACT) foresees the introduction of two new target stations and three new beamlines: one for radionuclide ...production and two for surface muon production. The latter forms the project, High-Intensity Muon Beams (HIMB), which plans to increase the muon rate from the current world record of 10 8 µ + /s up to 10 10 µ + /s. This work presents an overview of the future HIMB beamlines focusing on the magnet designs that have been developed to ensure increased muon rate production and transmission. Specific radiation-hard resistive coils, based on mineral insulation, are required in this case due to the proximity to the target station. A high muon capture and transmission efficiency requires solenoid-like magnets, as well as dipole magnets and crossed-field separators to select the desired particles, while suppressing unwanted background particles. The radiation-hard capture solenoid plays the most important role in the whole beamline since it must provide a high capture efficiency. Beam optics studies provided the on-axis field profile necessary for optimizing the size and shape of the capture solenoid. Therefore, the article will also elucidate on these solenoid design strategies for achieving the desired capture efficiency.
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
Odprti dostop
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.
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.
We present a new result based on an analysis of the data collected by the MEG detector at the Paul Scherrer Institut in 2009 and 2010, in search of the lepton-flavor-violating decay μ(+)e(+)γ. The ...likelihood analysis of the combined data sample, which corresponds to a total of 1.8×10(14) muon decays, gives a 90% C.L. upper limit of 2.4×10(-12) on the branching ratio of the μ(+)→e(+)γ decay, constituting the most stringent limit on the existence of this decay to date.
Beam monitoring detectors for High Intensity Muon Beams Dal Maso, G.; Barchetti, F.; Francesconi, M. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
February 2023, 2023-02-00, Letnik:
1047
Journal Article
Recenzirano
Odprti dostop
We present two novel beam monitors designed for use in current PSI muon beams and upgradable for the High Intensity Muon Beam (HIMB) project beamlines: the scintillating fibre (SciFi) detector, a ...grid of scintillating fibres coupled to SiPMs, and the MatriX detector, a matrix of plastic scintillators coupled to silicon photomultipliers (SiPMs), both detectors having particle ID capability. The advantage of these highly segmented detectors is the capability to withstand the high beam rate and to perform total beam rate measurements. Furthermore, the use of the SiPM as a photosensor enables operation of these detectors in high magnetic field environments (up to 1.25T). Both detectors have been tested in the beam at PSI and with continuous beam rates up to 108μ+/s. The performance of these detectors as measured on the beamlines are presented.
A new and high-performance generation of detectors based on scintillating fibres coupled to silicon photomultiplier (SiPM, MPPC) is under development. We focus here on the use of this technology as a ...beam monitoring detector with the following characteristics: high granularity, high detection efficiency, fast timing response, accurate position resolutions, minimal material budget and insensitivity to magnetic fields. We present a scintillating fibre and silicon photomultiplier-based beam monitoring detector used in one of the most intense muon beam in the world (few ×108μ+∕s). A full detector prototype was built and successfully tested at the πE5 beam line of the Paul Scherrer Institute (PSI). Beam profile and rate measurements were made with a precision of better than 1% and together with particle identification capability, are consistent with standard techniques confirming the viability of this technology for high-rate applications.
The MEG detector for μ+→e+γ decay search Adam, J.; Bai, X.; Baldini, A. M. ...
The European physical journal. C, Particles and fields,
04/2013, Letnik:
73, Številka:
4
Journal Article
Recenzirano
Odprti dostop
The MEG (Mu to Electron Gamma) experiment has been running at the Paul Scherrer Institut (PSI), Switzerland since 2008 to search for the decay
μ
+
→e
+
γ
by using one of the most intense continuous
μ
...+
beams in the world. This paper presents the MEG components: the positron spectrometer, including a thin target, a superconducting magnet, a set of drift chambers for measuring the muon decay vertex and the positron momentum, a timing counter for measuring the positron time, and a liquid xenon detector for measuring the photon energy, position and time. The trigger system, the read-out electronics and the data acquisition system are also presented in detail. The paper is completed with a description of the equipment and techniques developed for the calibration in time and energy and the simulation of the whole apparatus.
Documenting the scale and intensity of fine-scale spatial genetic structure (FSGS), and the processes that shape it, is relevant to the sustainable management of genetic resources in timber tree ...species, particularly where logging or fragmentation might disrupt gene flow. In this study we assessed patterns of FSGS in three species of Dipterocarpaceae (Parashorea tomentella, Shorea leprosula and Shorea parvifolia) across four different tropical rain forests in Malaysia using nuclear microsatellite markers. Topographic heterogeneity varied across the sites. We hypothesised that forests with high topographic heterogeneity would display increased FSGS among the adult populations driven by habitat associations. This hypothesis was not supported for S. leprosula and S. parvifolia which displayed little variation in the intensity and scale of FSGS between sites despite substantial variation in topographic heterogeneity. Conversely, the intensity of FSGS for P. tomentella was greater at a more topographically heterogeneous than a homogeneous site, and a significant difference in the overall pattern of FSGS was detected between sites for this species. These results suggest that local patterns of FSGS may in some species be shaped by habitat heterogeneity in addition to limited gene flow by pollen and seed dispersal. Site factors can therefore contribute to the development of FSGS. Confirming consistency in species' FSGS amongst sites is an important step in managing timber tree genetic diversity as it provides confidence that species specific management recommendations based on species reproductive traits can be applied across a species' range. Forest managers should take into account the interaction between reproductive traits and site characteristics, its consequences for maintaining forest genetic resources and how this might influence natural regeneration across species if management is to be sustainable.
A positron timing counter (TC) with 30–40 ps time resolution for 50 MeV/c positrons required by the MEG II experiment has been developed. We employed a highly segmented design with 512 scintillator ...plates (120 × 40 × 5 mm3 and 120 × 50 × 5 mm3) read out by 6-SiPM-arrays at the both ends. Pile up is reduced by the segmented design and multi-counter measurement improves the overall timing resolution. All the single counters were assembled and their resolutions were measured to be below 100 ps in a pre-test with a 90Sr source. The construction and installation were completed in 2017. An engineering run was performed at the end of 2017 at the πE5 muon beam line in PSI, which supplies the most intense muon beam (7 × 107 stops/s on a target) in the world. We successfully operated the full system of TC in the MEG II environment and achieved a time resolution below 40 ps with more than 6 counter hits. The overall resolution for the signal positrons is estimated to be 38.5 ps by weighting the obtained resolutions with the number of hits distribution of the signal positrons obtained by a Monte Carlo simulation. The time resolution of the TC is improved by a factor of 2 with respect to the MEG experiment.
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