In a sample of 1.5 million hadronic decays of the Z collected by the ALEPH detector, a search is carried out for the decays
B → D
1
0(2420)l
−
ν
X
and
B → D
2
∗0(2460)l
−
ν
X
. The product branching ...ratio for D
1
0 production is measured to be
Br(b →
B) × Br(
B → D
1
0l
−
ν
X) × Br(D
1
0 → D
∗+π
−) = (2.04 ± 0.58
stat
± 0.34
syst
) × 10
−3
, and a 95% confidence level limit of
Br(b →
B) × Br(
B → D
2
∗0l
−
ν
X) × Br(D
2
∗0 → D
∗+π
−) ≤ 0.81 × 10
−3
is obtained for D
2
∗0 production.
A topological search sensitive to the processes above, but also to wide resonances that decay to
D
∗+π
−
and to non-resonant
D
∗+π
−
production is also carried out, yielding
Br(b→
B) ×Br(
B →D
∗+π
−l
−
ν
X)= (3.7 ± 1.0
stat
± 0.7
syst
) × 10
−3
. Direct evidence of D
∗π production inconsistent with D
1
0 and D
2
∗0 in semileptonic B decay is presented.
The lifetime of the B
s
0 meson is measured in approximately 3 million hadronic Z decays accumulated using the ALEPH detector at LEP from 1991 to 1994. Seven different D
s
− decay modes were ...reconstructed and combined with an opposite sign lepton as evidence of semileptonic B
s
0 decays. Two hundred and eight D
s
−ℓ
+ candidates satisfy selection criteria designed to ensure precise proper time reconstruction and yield a measured B
s
0 lifetime of
τ(B
s
0) = 1.59
−0.15
+0.17 (stat) ±0.03 (syst) ps. Using a larger, less constrained sample of events, the product branching ratio is measured to be
Br(
b →
B
s
0) ·
Br(B
s
0 →
D
s
−ℓ
+νX) = 0.82 ± 0.09
(stat)
−0.14
+0.13 (syst) %.
A study of scaling violations in fragmentation functions performed by the ALEPH collaboration at LEP is presented. Data samples enriched in
uds, c, b and gluon jets, respectively, together with ...measurements of the longitudinal and transverse inclusive cross sections are used to extract the fragmentation function for the gluon and for each flavour. The measurements are compared to data from experiments at energies between 22 GeV and 91 GeV and scaling violations consistent with QCD predictions are observed. From this, a measurement of the strong coupling constant
α
s
(
Mz) = 0.126 ±0.009 is obtained.
From a sample of 152,000 τ decays collected by the ALEPH detector at LEP an upper limit of 24 MeV at 95% CL on the τ neutrino mass has been determined. The limit is obtained using a two dimensional ...likelihood fit of the visible energy and the invariant mass distribution of 25
τ → 5
π(
π
0)
ν
τ
events.
Since carbon molecules with geodesic structures have been detected, the question for potential silicon-based analogues of these species has been raised. The existence of these hypothetical `silicon ...balls', however, has not been ascertained so far in spite of several theoretical as well as experimental attempts to do so. Several theoretical approaches have been put forward in the past to explain the experimentally observed features of Si
N
clusters and thus to account for the obvious dissimilarity between finite systems based on the isovalent elements silicon and carbon, but no comprehensive growth sequence model has been generally accepted for Si
N
so far.
The present work is aimed at an exploration of closed-shell Si
N
systems, derived from highly symmetric cage-like geometries, in the size range
N≤26 by means of Hartree–Fock and post-Hartree–Fock procedures. Particular emphasis is placed on the question of the stabilities of these isomers as compared to the corresponding ground states, wherever available. Cohesive energy calculations suggest a tendency towards an increase of cluster stability with the number of constituents for cage-like Si
N
isomers up to
N=10, while a trend towards destabilization with growing size is found for larger clusters.
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