First experience and results from the HERA- B vertex detector system Bauer, C.; Baumann, I.; Bräuer, M. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
11/1998, Letnik:
418, Številka:
1
Journal Article
Recenzirano
The HERA-
B collaboration is building a detector to realize the ambitious goal of observing CP violation in decays of neutral B-mesons. A central element of the apparatus is the silicon vertex ...detector used to selectively trigger on these decays in a high charged particle multiplicity background environment and to reconstruct secondary vertices from such decays with high precision. The vertex detector, the supporting infrastructure and first results using prototype detectors are described. Results include imaging of the proton interaction region on the HERA-
B target, hit distributions in the detector planes, and alignment of the detectors with each other and the target.
Using the ARGUS detector at the
e
+
e
− storage ring DORIS II, we have measured the semileptonic branching ratios of the
D
0 meson to be
Br(
D
0 →
e
+
ν
e
X) = (6.9 ± 0.3 ± 0.5) % and
Br(
D
0 →
μ
+
ν
...μ
X) = (6.0 ± 0.7 ± 1.2) %, and the semileptonic branching ratio of the charmed hadron mixture from
e
+
e
− annihilation around 10 GeV to be
Br(
c →
e
+
ν
e
X) = (9.6 ± 0.4 ± 1.1) %.
Using the ARGUS detector at the
e
+
e
− storage ring DORIS II, we have searched for the real and imaginary part of the electric dipole formfactor
d
τ
of the
τ lepton in the production of
τ pairs at
q
...2=100
GeV
2
. This is the first direct measurement of this
CP
violating formfactor. We applied the method of optimised observables which takes into account all available information on the observed
τ decay products. No evidence for
CP
violation was found, and we derive the following results:
Re(d
τ)=(1.6±1.9)·10
−16
e
cm
and
Im(d
τ)=(−0.2±0.8)·10
−16
e
cm
, where statistical and systematic errors have been combined.
Using the ARGUS detector at the
e
+
e
− storage ring DORIS II at DESY, we have found evidence for the production of the excited charmed baryon state
Λ
c
(2593)
+ in the channel
Λ
c
+
π
+
π
−. Its ...mass was determined to be (2594.6±0.9±0.4) MeV/c
2, and the natural width measured to be Γ = (2.9
−2.1−1.4
+2.9+1.8) MeV. The production cross section times the branching ratios of
σ(
e
+
e
− →
Λ
c
(2593)
+
X) ×
Br(
Λ
c
(2593)
+ →
Λ
c
+
π
+
π
−) ×
Br(
Λ
c
+ →
pK
−
π
+) was measured to be (0.25
−0.13
+0.24 ±0.13) pb. The fractions of
Λ
c
(2593)
+ decays proceeding through the
Σ
c
0
π
+ and
Σ
c
++
π
− channels were determined to be 0.29±0.10±0.11 and 0.37±0.12±0.13, respectively.
A maximum likelihood analysis of ARGUS data on two-photon production of
π
+
π
+
π
0
π
0
π
−
π
− is presented. A small fraction of events is due to the production of omega pairs. The
γγ →
ωω cross ...section has its maximum value close to threshold.
Using the ARGUS detector at the
e
+
e
− storage ring DORIS II, we have measured the Michel parameters
ρ,
ξ, and
ξδ for
τ
±→l
±ν
ν
̄
decays in
τ-pair events produced at center of mass energies in the ...region of the
ϒ resonances. Using
τ
∓→
ρ
∓
ν as spin analyzing tags, we find
ρ
e
=0.68±0.04±0.08,
ξ
e
=1.12±0.20±0.09,
ξδ
e
=0.57±0.14±0.07,
ρ
μ
=0.69±0.06±0.08,
ξ
μ
=1.25±0.27±0.14 and
ξδ
μ
=0.72±0.18±0.10. In addition, we report the combined ARGUS results on
ρ,
ξ, and
ξδ using this work und previous measurements.
Using the ARGUS detector at the
e
+
e
− storage ring DORIS II, we have determined the Michel parameters ξ and δ of
τ
∓ → l
∓ν
ν
-
decays. With an integrated luminosity of 445 pb
−1 around
s
= 10
GeV, ...we have produced approximately 415000 τ-pairs. From this data sample, 3262 events were selected with
e
+e
− → τ
+τ
− → (l
±ν
ν
-
) (π
∓π
+π
−ν)
. The semihadronic decay was used as analyser of the τ-spin and made possible - owing to the spin correlations - the determination of the parity-violating Michel parameters ξ and δ in the decay
τ
∓ → l
∓ν
ν
-
. Simultaneously to the determination of the Michel parameters, a measurement of the τ-neutrino helicity
h
ν
τ
in the decay
τ
∓ →
π
∓
π
+
π
−
ν was obtained. We observed
h
ν
τ
= −0.85
−0.17
+0.15 ± 0.05,
ϱ = 0.721 ± 0.040 ± 0.021,
ξ = 1.26
−0.26
+0.30 ± 0.09, and
ξδ = 0.77
−0.16
+0.18 ± 0.05. In addition, the combined ARGUS result on
h
ν
τ
, ϱ, ξ, and ξδ are reported using this work and previous measurements.
Among the possible approaches to tackling the problem of data incest in distributed data fusion networks, covariance intersection is a candidate that yields consistent estimates independent of ...network structure and any possible cross-correlation between local estimates. The corresponding weighting coefficients are usually chosen with the aim for a minimum trace or determinant of the resulting error variance matrix. A fast non-iterative algorithm exists that, to a certain extent, approximately solves this nonlinear optimization problem with extremely reduced numerical implementation effort. Yet, the obtained weighting coefficients do not depend on the relative orientation of the estimation error variance matrices which may lead to a degraded performance in certain applications. Hence, an improved fast covariance intersection algorithm is developed that comes with a slightly increased implementation effort while yielding significantly better estimation results in some cases and comparable results in all other ones. Simulation results confirm the postulated performance improvement.
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