The design of the MEG II experiment Baldini, A. M; Baracchini, E; Bemporad, C ...
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 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.
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.
The cylindrical drift chamber is the most innovative part of the MEG II detector, the upgraded version of the MEG experiment. The MEG II chamber differs from the MEG one because it is a single volume ...cylindrical structure, instead of a segmented one, chosen to improve its resolutions and efficiency in detecting low energy positrons from muon decays at rest. In this paper, we show the characteristics and performances of this fundamental part of the MEG II apparatus and we discuss the impact of its higher resolution and efficiency on the sensitivity of the MEG II experiment. Because of its innovative structure and high quality resolution and efficiency the MEG II cylindrical drift chamber will be a cornerstone in the development of an ideal tracking detector for future positron-electron collider machines.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
We describe and show results of a photographic technique for continuously monitoring the position, orientation, and shape of a thin-film muon stopping target for the MEG II experiment Baldini et al. ...(2018). The measurement is complicated by the target being located in a region with 1.3 T magnetic field, significant positron flux, and limited access. The technique achieves a measurement precision of 10 μm normal to and 30 μm parallel to the film surface, significantly better than required for the MEG II experiment.
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.
This paper describes applications of two neural networks to improve drift chamber position measurements. One network calculates a data-driven estimate of the drift cell time-to-distance relationship ...that is conventionally estimated by a numerical calculation based on the anode and cathode wire geometry, wire potentials, and gas properties. The second network additionally uses the full digital waveform of the signal in the drift chamber, hence accessing information on the full ensemble of ionization clusters. This network uses more information than the conventional position estimate that relies exclusively on the arrival time of the first drift electron. In principle, this technique improves resolution even when multiple ionization clusters cannot be separated, in contrast with a cluster-counting technique. The performance of both networks when applied to MEG II drift chamber data is reported and compared to that of a conventional approach.
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 studied the radiative muon decay
μ
+
→
e
+
ν
ν
¯
γ
by using for the first time an almost fully polarized muon source. We identified a large sample (
∼
13,000) of these decays in a total sample of
...1.8
×
10
14
positive muon decays collected in the MEG experiment in the years 2009–2010 and measured the branching ratio
B
(
μ
→
e
ν
ν
¯
γ
)
=
(
6.03
±
0.14
(
stat
.
)
±
0.53
(
sys
.
)
)
×
10
-
8
for
E
e
>
45
MeV
and
E
γ
>
40
MeV
, consistent with the Standard Model prediction. The precise measurement of this decay mode provides a basic tool for the timing calibration, a normalization channel, and a strong quality check of the complete MEG experiment in the search for
μ
+
→
e
+
γ
process.
Operation and performance of the MEG II detector Afanaciev, K.; Baldini, A. M.; Ban, S. ...
The European physical journal. C, Particles and fields,
02/2024, Letnik:
84, Številka:
2
Journal Article
Recenzirano
Odprti dostop
The MEG II experiment, located at the Paul Scherrer Institut (PSI) in Switzerland, is the successor to the MEG experiment, which completed data taking in 2013. MEG II started fully operational data ...taking in 2021, with the goal of improving the sensitivity of the
μ
+
→
e
+
γ
decay down to
∼
6
×
10
-
14
almost an order of magnitude better than the current limit. In this paper, we describe the operation and performance of the experiment and give a new estimate of its sensitivity versus data acquisition time.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
10.
The Cylindrical Drift Chamber of the MEG II experiment Chiappini, M.; Baldini, A.M.; Benmansour, H. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
02/2023, Letnik:
1047
Journal Article
Recenzirano
The MEG experiment at the Paul Scherrer Institut (PSI) represents the state of the art in the search for the charged Lepton Flavor Violating μ+→e+γ decay, setting the most stringent upper limit on ...the BR (μ+→e+γ)≤4.2×10−13 (90% C.L.). An upgrade of MEG, MEG II, was designed, commissioned and recently started the physics data taking. Its goal is to reach a sensitivity level of 6×10−14. In order to reconstruct the positron momentum vector a Cylindrical Drift CHamber (CDCH) with unprecedented peculiarities was built, featuring angular and momentum resolutions at the 6.5 mrad and 100 keV/c level. The CDCH is a 2-meter long, 60 cm in diameter, low-mass, single volume detector with high granularity: 9 layers of 192 drift cells, few mm wide, defined by ∼12000 wires in a stereo configuration for longitudinal hit localization. The filling gas mixture is Helium:Isobutane 90:10. The total radiation length is 1.5×10−3 X0, thus minimizing the Multiple Coulomb Scattering and allowing for a single-hit resolution <120μm. After the assembly at INFN Pisa, the CDCH was transported to PSI and integrated into the MEG II experimental apparatus since 2018. The commissioning phase lasted for the past three years until the operational stability was reached in 2020. The analysis software is continuously developing and the tuning of the reconstruction algorithms is one of the main activities. The latest updates on the positron momentum vector resolutions and tracking efficiency are presented.
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