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 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.
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 Liquid Argon calorimeters play a central role in the ATLAS (A Toroidal LHC Apparatus) experiment. The environment at the Large Hadron Collider (LHC) imposes strong constraints on the detectors ...readout systems. In order to achieve very high precision measurements, the detector signals are processed at various stages before reaching the Data Acquisition system (DAQ). Signals from the calorimeter cells are received by on-detector Front End Boards (FEB), which sample the incoming pulse every 25ns and digitize it at a trigger rate of up to 75~kHz. Off-detector Read Out Driver (ROD) boards further process the data and send reconstructed quantities to the DAQ while also monitoring the data quality. In this paper, the ATLAS Liquid Argon electronics chain is described first, followed by a detailed description of the off-detector readout system. Finally, the tests performed on the system are summarized.
We report a measurement of the CP violation parameter
η
+− from the time-dependent asymmetry between the decay rates of initially tagged K
0 and
K
0
. The results are based on the complete data ...sample collected by the CPLEAR collaboration. With
Δm=(530.1±1.4)×10
7ℏs
−1 and
τ
S=(89.34±0.08) ps, the values obtained are |
η
+−|=(2.264±0.023
stat±0.026
syst±0.007
τ
S
)×10
−3 and
φ
+−=43.19°±0.53°
stat±0.28°
syst±0.42°
Δm
.
Performance of the ATLAS electromagnetic calorimeter barrel module 0 Aubert, B.; Ballansat, J.; Beaugiraud, B. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
2003, Letnik:
500, Številka:
1
Journal Article
Recenzirano
Odprti dostop
The construction and performance of the barrel pre-series module 0 of the future ATLAS electromagnetic calorimeter at the LHC is described. The signal reconstruction and performance of ATLAS-like ...electronics has been studied. The signal to noise ratio for muons has been found to be 7.11±0.07. An energy resolution of better than
9.5%
GeV
1/2/
E
(sampling term) has been obtained with electron beams of up to
245
GeV
. The uniformity of the response to electrons in an area of Δ
η×Δ
φ=1.2×0.075 has been measured to be better than 0.8%.
The construction and the assembly of the two end-caps of the ATLAS liquid argon electromagnetic calorimeter as well as their test and qualification programs are described. The work described here ...started at the beginning of 2001 and lasted for approximately three years. The results of the qualification tests performed before installation in the LHC ATLAS pit are given. The detectors are now installed in the ATLAS cavern, full of liquid argon and being commissioned. The complete detectors coverage is powered with high voltage and readout.
We report on a new measurement of the K
L–K
S mass difference
Δm using the CPLEAR full data sample of neutral-kaon decays to e
πν. The result is
Δm=(0.5295±0.0020
stat±0.0003
syst)×10
10 ℏ/s. It ...includes earlier data reported in R. Adler et al., CPLEAR Collaboration, Phys. Lett. B 363 (1995) 237. A measurement of the
ΔS=
ΔQ violating parameter Re(
x) is also obtained.
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