The MEG experiment at the Paul Scherrer Institut, searching for the charged lepton flavour violating decay μ+→e+γ, took physics data from 2009 until 2013. The drift chamber system was part of the ...dedicated positron spectrometer that was designed to ensure a precision measurement of 52.8 MeV positrons and consisted of 16 individual drift chamber modules. The individual detector modules were operated with a He/C2H6 (50:50) gas mixture to combine a long radiation length with good high voltage stability properties ensured by the high hydrocarbon fraction.
During long-term operation several aging phenomena were observed. A continuous decrease of the electron multiplication factor was caused by a continuously growing layer on the node wires, most likely caused by polymerisation of the hydrocarbon in high gain and high rate operation. The aluminum coating of the cathodes showed damages most probably due to ion impact, in some cases the layer even peeled off. In addition, some drift chamber modules suffered from Malter effect, showing remaining and fluctuating currents during beam of periods, most likely caused by remaining photo resist on the cathode foils.
The drift chamber system of the MEG experiment Hildebrandt, Malte
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
11/2010, Letnik:
623, Številka:
1
Journal Article
Recenzirano
The MEG experiment searches for the lepton flavour violating decay μ→eγ and is aiming for a sensitivity of 10−13 in the branching ratio in order to probe new physics beyond the standard model. The ...experiment is located at the Paul Scherrer Institut (PSI) in Switzerland, where one of the world's most intensive surface muon beams is located. Physics data taking started in September 2008.
The drift chamber system is part of the innovative positron spectrometer of the MEG experiment and consists of 16 drift chamber modules. The system is designed to ensure precision measurement of 52.8MeV/c positrons. Design, construction, geometrical alignment and performance of the drift chamber system are presented.
The singlet muon capture rate
\Lambda_S
Λ
S
on the proton
\mu^-\ p \to \nu_\mu~n
μ
−
p
→
ν
μ
n
is determined in a high precision lifetime measurement. The main
apparatus consists of a new hydrogen ...time projection chamber as muon
detector, developed by PSI, surrounded by cylindrical wire chambers and
a plastic scintillator hodoscope as electron detectors. The parameter
\Lambda_S
Λ
S
is evaluated as the difference between the inverse
\mu\,p
μ
p
lifetime and that of the free
\mu^+
μ
+
.
The result
\Lambda_S^\text{MuCap} = (715.6 \pm 5.4^\text{stat} \pm 5.1^\text{sys})\,\text{s}^{-1}
Λ
S
MuCap
=
(
715.6
±
5.4
stat
±
5.1
sys
)
s
−
1
is in excellent agreement with the prediction of chiral perturbation
theory
\Lambda_S^{\chi\text{PT}} = (715.4 \pm 6.9)\,\text{s}^{-1}
Λ
S
χ
PT
=
(
715.4
±
6.9
)
s
−
1
.
From
\Lambda_S^\text{MuCap}
Λ
S
MuCap
a recent analysis derives for the induced pseudoscalar coupling
g^\text{MuCap}_p = 8.23 \pm 0.83
g
p
MuCap
=
8.23
±
0.83
whereas
\bar{g}^{\chi\text{PT}}_p = 8.25 \pm 0.25
g
‾
p
χ
PT
=
8.25
±
0.25
.
The energy levels of hydrogen-like atomic systems can be calculated with great precision. Starting from their quantum mechanical solution, they have been refined over the years to include the ...electron spin, the relativistic and quantum field effects, and tiny energy shifts related to the complex structure of the nucleus. These energy shifts caused by the nuclear structure are vastly magnified in hydrogen-like systems formed by a negative muon and a nucleus, so spectroscopy of these muonic ions can be used to investigate the nuclear structure with high precision. Here we present the measurement of two 2S-2P transitions in the muonic helium-4 ion that yields a precise determination of the root-mean-square charge radius of the α particle of 1.67824(83) femtometres. This determination from atomic spectroscopy is in excellent agreement with the value from electron scattering
, but a factor of 4.8 more precise, providing a benchmark for few-nucleon theories, lattice quantum chromodynamics and electron scattering. This agreement also constrains several beyond-standard-model theories proposed to explain the proton-radius puzzle
, in line with recent determinations of the proton charge radius
, and establishes spectroscopy of light muonic atoms and ions as a precise tool for studies of nuclear properties.
It is generally accepted that the count rate capability of ZnS: 6 LiF neutron detectors is strongly limited due to the long afterglow of the scintillator. However, realized as an array of individual ...sensitive elements (pixels) with independent signal readout and processing, such detectors can be operated with blocking times down to 1 <inline-formula> <tex-math notation="LaTeX">\mu \text{s} </tex-math></inline-formula> and promising counting rates up to 100 kHz/pixel. In this paper, we investigate how the long emission of the ZnS scintillator influences the detector performance apart from requiring a finite blocking time to suppress the probability of multiple counts. We also study the potential of the ZnO: 6 LiF scintillator with lower afterglow as a possible replacement of ZnS: 6 LiF.
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