The design of the MEG II experiment Baldini, A. M; Baracchini, E; Bemporad, C ...
European physical journal. C, Particles and fields,
05/2018, Volume:
78, Issue:
5
Journal Article
Peer reviewed
Open access
The MEG experiment, designed to search for the Formula omitted decay, completed data-taking in 2013 reaching a sensitivity level of Formula omitted for the branching ratio. In order to increase the ...sensitivity reach of the experiment by an order of magnitude to the level of Formula omitted, 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.
In the COMET experiment, it is essential to establish the online monitor that enables to detect few residual protons between consecutive main proton bunches to search for the muon-to-electron(μ-e) ...conversion with a sensitivity below 10−16. A thin diamond based detector is proposed because of its ideal characteristics. To realise the diamond based residual proton monitor, a noise suppression is essential since the number of electron–hole pairs generated by a single proton is relatively small in a thin diamond (∼5000 e-h/100μm). The prototype detector based on a 0.5 mm thick diamond was developed to evaluate the proton counting capability. The beam test using a 30 GeV proton beam was performed with this prototype and the result is reported in this paper.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
3.
COMET Phase-I technical design report Abramishvili, R; Adamov, G; Allin, A ...
Progress of theoretical and experimental physics,
03/2020, Volume:
2020, Issue:
3
Journal Article
Peer reviewed
Open access
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 COMET experiment at J-PARC aims to search for a lepton-flavour violating process of muon to electron conversion in a muonic atom, μ-e conversion, with a branching-ratio sensitivity better than ...10−16, 4 orders of magnitude better than the present limit, in order to explore the parameter region predicted by most well-motivated theoretical models beyond the Standard Model. The need for such an excellent sensitivity places several stringent requirements on the detector; (i) good momentum resolution, <2%, for 100 MeV/c electron, which is primarily limited by multiple scattering effect for this momentum region; and (ii) high rate capability, up to 5×109μ−/s muon beam enabled by J-PARC. In order to fulfil such requirements a vacuum-compatible, ultra-thin-wall straw tracker has been designed, and a 20μm-thick Mylar straw with 70 nm Al cathode has been developed employing an ultrasonic-welding technique. The detector performances such as detection efficiency and intrinsic spatial resolutions were investigated with test-beam experiments and confirmed to be acceptable for the COMET experiment. The construction of the straw tracker for COMET Phase-I has been completed.
In parallel to the construction of present tracker a thinner 12μm-thick straw has been developed with joint collaboration among KEK, JINR and CERN. During this R&D, it was noticed that the current technology cannot achieve tubes much smaller than 5 mm in diameter or walls much thinner than 12μm. We also launched a brand-new project to realize the graphite-textile straw which has a potential to realize an extremely low material tracker.
In this article, a brief report on detector construction with a present 20μm-thick straw, R&D on a new 12μm-thick straw, and a brand-new graphite straw, is provided.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
COMET (Coherent Muon to Electron Transition, J-PARC, Japan) is one of the experiments that studies extensions of the Standard Model (SM) of elementary particle physics. The main purpose of the COMET ...experiment is to search for charged lepton flavor violating neutrinoless conversion of muons into electrons in the field of a nucleus (μ–e conversion, μ–N → e–N). The goal is to achieve a sensitivity to the branching ratio superior to 10−17, that four orders of magnitude smaller than the present limit. In the experiment a straw detector will be used to measure the momentum of the signal electrons from the μ–e conversion. In order to satisfy the requirements of the momentum measurements, we plan to develop a planar tracking device consisting of thin-wall straws made with an extremely light material to reduce multiple scattering and that is capable of operation in vacuum. Research the mechanical properties of straws will allow us to choose their optimal tension, to estimate the influence of the temperature and humidity, to assess the straws service life in the experiment, which we define as the tension relaxation time to the minimum working value.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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.
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CMK, CTK, FMFMET, IJS, NUK, PNG, UM
The porous structure of anodes in SOFCs is the key factor to improve its performance and the manufacturing method to control its design needs to be established. Additive manufacturing, so-called 3D ...printing technology can be a prospective method for the fabrication of electrodes of SOFCs. In this experiment, stereolithography, which is a form of 3D printing technology using UV-light with approximately 365nm wavelength and photo-curable resin, is applied. The UV-light that goes through pinholes enables the production of multiple cylindrical objects at once. As a result, the objects and the empty spaces between them make the porous structure. Moreover, by changing the size and the number of holes and distance between them, the fabrication of an anode with the desired microstructure can be expected.
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.
We present the first direct search for lepton flavour violating muon decay mediated by a new light particle X,
μ
+
→
e
+
X
,
X
→
γ
γ
. This search uses a dataset resulting from
7.5
×
10
14
stopped ...muons collected by the MEG experiment at the Paul Scherrer Institut in the period 2009–2013. No significant excess is found in the mass region 20–45 MeV/c
2
for lifetimes below 40 ps, and we set the most stringent branching ratio upper limits in the mass region of 20–40 MeV/c
2
, down to
O
(
10
-
11
)
at 90% confidence level.
Construction on vacuum-compatible straw tracker for COMET Phase-I Nishiguchi, H.; Evtoukhovitch, P.; Fujii, Y. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
04/2020, Volume:
958
Journal Article
Peer reviewed
The COMET experiment at J-PARC aims to search for a lepton-flavour violating process of muon to electron conversion in a muonic atom, μ-e conversion, with a branching-ratio sensitivity of better than ...10−16, 4 orders of magnitude better than the present limit, in order to explore the parameter region predicted by most of well-motivated theoretical models beyond the Standard Model. The need for such an excellent sensitivity places several stringent requirements on the detector; (i) good momentum resolution, <2%, for 100 MeV/c electron, which is primarily limited by multiple scattering effect for this momentum region, and (ii) high rate capability, up to 5×109μ−/s muon beam by J-PARC. In order fulfil such requirements, we decided to develop the straw-base planar tracker which is operational in vacuum and made of an extremely light material. The COMET straw tracker consists of 10 mm diameter straw tube, longer than 1 m length, with 20μm-thick Mylar foil and 70 nm-thick aluminium cathode.
Recently, two big milestones, detector-performance verification by the full-scale prototype with 100 MeV/c electron beam, and start the assembly of final straw tracker for COMET Phase-I, were achieved. In this article, details of these two big milestones are provided. In addition, some prospects on the straw tracker development towards the COMET Phase-II are also given.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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