We report on the first observation of time-reversal symmetry violation through a comparison of the probabilities of
K
0
transforming into K
0 and K
0 into
K
0
as a function of the neutral-kaon ...eigentime
t. The comparison is based on the analysis of the neutral-kaon semileptonic decays recorded in the CPLEAR experiment. There, the strangeness of the neutral kaon at time
t=0 was tagged by the kaon charge in the reaction
p
p
→
K
±π
∓
K
0
(
K
0
)
at rest, whereas the strangeness of the kaon at the decay time
t=
τ was tagged by the lepton charge in the final state. An average decay-rate asymmetry
〈
R(
K
0
t=0→
e
+
π
−
ν
t=τ)−R(
K
0
t=0→
e
−
π
+
ν
t=τ)
R(
K
0
t=0→
e
+
π
−
ν
t=τ)+R(
K
0
t=0→
e
−
π
+
ν
t=τ)
〉=(6.6±1.3
stat
±1.0
syst
)×10
−3
was measured over the interval
1
τ
S
<τ<20
τ
S
, thus leading to evidence for time-reversal non-invariance.
We present a new measurement of the K
L-K
S mass difference (
Δm) using semileptonic decays of neutral kaons. The measurement yields
Δm = (0.5274 ± 0.0029
stat. ± 0.0005
syst.) × 10
10ħ/s.
The development of methods to produce nanoparticles with unique properties via the aerosol route is progressing rapidly. Typical characterization techniques extract particles from the synthesis ...process for subsequent offiine analysis, which may alter the particle characteristics. In this work, we use laser-vaporization aerosol mass spectrometry （LV-AMS） with 70-eV electron ionization for real-time, in-situ nanoparticle characterization. The particle characteristics are examined for various aerosol synthesis methods, degrees of sintering, and for controlled condensation of organic material to simulate surface coating/functionalization. The LV-AMS is used to characterize several types of metal nanoparticles （Ag, Au, Pd, PdAg, Fe, Ni, and Cu）. The degree of oxidation of the Fe and Ni nanoparticles is found to increase with increased sintering temperature, while the surface organic-impurity content of the metal particles decreases with increased sintering temperature. For aggregate metal particles, the organic-impurity content is found to be similar to that of a monolayer. By comparing different equivalent-diameter measurements, we demonstrate that the LV-AMS can be used in tandem with a differential mobility analyzer to determine the compactness of synthesized metal particles, both during sintering and during material addition for surface functionalization. Further, materials supplied to the particle production line downstream of the particle generators are found to reach the generators as contaminants. The capacity for such in-situ observations is important, as it facilitates rapid response to undesired behavior within the particle production process. This study demonstrates the utility of real-time, in-situ aerosol mass spectrometric measurements to characterize metal nanoparticles obtained directly from the synthesis process line, including their chemical composition, shape, and contamination, providing the potential for effective optimization of process operating parameters.
Physics at CPLEAR Angelopoulos, A.; Apostolakis, A.; Aslanides, E. ...
Physics reports,
2003, 2003-1-00, Letnik:
374, Številka:
3
Journal Article
Recenzirano
LEAR offered unique opportunities to study the symmetries which exist between matter and antimatter. At variance with other approaches at this facility, CPLEAR was an experiment devoted to the study ...of
CP
,
T
and
CPT
symmetries in the neutral-kaon system. A variety of measurements allowed us to determine with high precision the parameters which describe the time evolution of the neutral kaons and their antiparticles, including decay amplitudes, and the related symmetry properties. Limits concerning quantum-mechanical predictions (EPR, coherence of the wave function) or the equivalence principle of general relativity have been obtained. An account of the main features of the experiment and its performances is given here, together with the results achieved.
The CPLEAR electromagnetic calorimeter Adler, R.; Backenstoss, G.; Bal, F. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
05/1997, Letnik:
390, Številka:
3
Journal Article
Recenzirano
Odprti dostop
A large-acceptance lead/gas sampling electromagnetic calorimeter (ECAL) was constructed for the CPLEAR experiment to detect photons from decays of π
0s with momentum
p
π
0 ≤ 800 MeV/
c. The main ...purpose of the ECAL is to determine the decay vertex of neutral-kaon decays K
0 → π
0π
0 → 4γ and K
0 → π
0π
0π
0 → 6γ. This requires a position-sensitive photon detector with high spatial granularity in
r−,
ϕ−, and
z−coordinates. The ECAL - a barrel without end-caps located inside a magnetic field of 0.44 T - consists of 18 identical concentric layers. Each layer of
1
3
radiation length (
X
0) contains a converter plate followed by small cross-section high-gain tubes of 2640 mm active length which are sandwiched by passive pick-up strip plates. The ECAL, with a total of 6
X
0 has an energy resolution of
α(E)
E
≈
13%
(E(
GeV)
and a position resolution of 4.5 mm for the shower foot. The shower topology allows separation of electrons from pions. The design, construction, read-out electronics, and performance of the detector are described.
We have improved by two orders of magnitude the limit currently available for the CPT violation parameter Re(
δ). To this purpose we have analyzed the full sample of neutral-kaon decays to e
πν ...recorded in the CPLEAR experiment, where the strangeness of the neutral kaons was tagged at production and decay time. An appropriate function of the measured decay rates, including information from the analysis of π
+π
− decay channel, gives directly Re(
δ). The result Re(
δ)=(3.0±3.3
stat±0.6
syst)×10
−4 is compatible with zero. Values for the parameters Im(
δ), Re(
x
−) and Im(
x
+) were also obtained.
We use fits to recent published CPLEAR data on neutral kaon decays to
π
+
π
− and πeν to constrain the CPT-violation parameters appearing in a formulation of the neutral kaon system as an open ...quantum-mechanical system. The obtained upper limits of the CPT-violation parameters are approaching the range suggested by certain ideas concerning quantum gravity.
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