We present a field-programmable gate array (FPGA)-based technique for the on-line identification of highly ionizing particles in a liquid xenon (LXe) detector. The method was developed and ...successfully exploited to select <inline-formula> <tex-math notation="LaTeX">\alpha </tex-math></inline-formula> particles emitted by 241 Am sources submerged in LXe in an overwhelming, mostly beam-related, <inline-formula> <tex-math notation="LaTeX">\gamma </tex-math></inline-formula>-ray background. After revising the main features of xenon and other liquid noble gases as ultra-violet (UV) scintillating media, we describe the algorithm idea and its firmware implementation. We then present the results in terms of efficiency and background suppression for the real-time <inline-formula> <tex-math notation="LaTeX">\alpha </tex-math></inline-formula>-particle tagging and the limits of the MEG trigger configuration. Finally, we show that in MEG II we are going to overcome the main issues and further improve the performances.
This final article about the CHOOZ experiment presents a complete description of the \(\bar{\nu}_e\) source and detector, the calibration methods and stability checks, the event reconstruction ...procedures and the Monte Carlo simulation. The data analysis, systematic effects and the methods used to reach our conclusions are fully discussed. Some new remarks are presented on the deduction of the confidence limits and on the correct treatment of systematic errors.
The MEG experiment has set the latest limit of 5.7×10−13(90% C.L.) on the branching ratio of the charged lepton flavor violating decay μ+→e+γ, making use of the most intense continuous surface muon ...beam in the world at the Paul Scherrer Institut (PSI), Villigen, Switzerland. High resolutions in terms of energy, timing and relative opening angle are needed in the detection of the e+ and gamma, requiring careful calibration and monitoring of the experimental apparatus. A dedicated calibration method involving Mott scattering of a monochromatic positron beam at energies close to the MEG signal energy is presented.
The MEG experiment makes use of one of the world's most intense low energy muon beams, in order to search for the lepton flavour violating process Formula omitted. We determined the residual beam ...polarization at the thin stopping target, by measuring the asymmetry of the angular distribution of Michel decay positrons as a function of energy. The initial muon beam polarization at the production is predicted to be Formula omitted by the Standard Model (SM) with massless neutrinos. We estimated our residual muon polarization to be Formula omitted at the stopping target, which is consistent with the SM predictions when the depolarizing effects occurring during the muon production, propagation and moderation in the target are taken into account. The knowledge of beam polarization is of fundamental importance in order to model the background of our Formula omitted search induced by the muon radiative decay: Formula omitted.
Initial results are presented from CHOOZ
1
The CHOOZ experiment is named after the new nuclear power station operated by Électricité de France (EdF) near the village of Chooz in the Ardennes region ...of France.
1
, a long-baseline reactor-neutrino vacuum-oscillation experiment. The data reported here were taken during the period March to October 1997, when the two reactors ran at combined power levels varying from zero to values approaching their full rated power of 8.5
GW
(thermal). Electron antineutrinos from the reactors were detected by a liquid scintillation calorimeter located at a distance of about 1
km
. The detector was constructed in a tunnel protected from cosmic rays by a 300
MWE
rock overburden. This massive shielding strongly reduced potentially troublesome backgrounds due to cosmic-ray muons, leading to a background rate of about one event per day, more than an order of magnitude smaller than the observed neutrino signal. From the statistical agreement between detected and expected neutrino event rates, we find (at 90% confidence level) no evidence for neutrino oscillations in the
ν
e
disappearance mode for the parameter region given approximately by
Δm
2>0.9
10
−3
eV
2
for maximum mixing and sin
22
θ>0.18 for large
Δm
2.
We present new results based on the entire CHOOZ (The CHOOZ experiment is named after the new nuclear power station operated by Électricité de France (EdF) near the village of Chooz in the Ardennes ...region of France) data sample. We find (at 90% confidence level) no evidence for neutrino oscillations in the
ν
̄
e
disappearance mode, for the parameter region given by approximately
δm
2>7·10
−4
eV
2
for maximum mixing, and sin
22
θ=0.10 for large
δm
2. Lower sensitivity results, based only on the comparison of the positron spectra from the two different-distance nuclear reactors, are also presented; these are independent of the absolute normalization of the
ν
̄
e
flux, the cross section, the number of target protons and the detector efficiencies.
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.
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.
Liquid scintillator calorimeters and in particular liquid cryogenic noble gas detectors can be calibrated and monitored by the use of multiple
α
-sources distributed in the detector sensitive volume. ...For the MEG experiment we developed a method based on the use of
Po
210
and
Am
241
point sources deposited on thin (
100
μ
m
diameter) gold-plated tungsten wires permanently suspended in the volume and fixed at the surfaces of the large vessel containing the LXe. The method is valuable in measuring the relative QEs of all PMTs surrounding the sensitive LXe volume, in determining the LXe optical properties for the UV scintillation light and in checking the stability of the calorimeter properties during the experiment.
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