The annihilation of antiprotons on deuterons at rest via the channels
p
̄
d→πΔ
and
p
̄
d→πN
is studied. The two-step mechanism is investigated by analysing these processes when either
π
0
n,
π
0
Δ
0 ...or
π
−
p,
π
−
Δ
+ are produced in the final state. Predictions for the branching ratios of the annihilations
p
̄
d→π
−p
and
p
̄
d→π
−Δ
+
are presented. From comparison of the presented results with the experimental data new information on the mechanism of the
Δ-isobar production in antiproton-deuteron annihilation can be deduced.
The OBELIX spectrometer, studying at the Low Energy Antiproton Ring (LEAR) of CERN the
N̄N annihilation, has collected annihilation data with very low momentum
p̄(≈ 50
MeV/c). The results of the ...spin-parity analysis on the
p̄p annihilation into four and five pions are briefly described.
The results of a study of the annihilation reactions
np → θπ
+
and
np → ωπ
+
are reported; the data were collected by the OBELIX apparatus, with antineutrons annihilating in flight (momenta from ∼ 50 ...MeV/
c to 405 MeV/
c). Annihilation frequencies and annihilation cross sections have been deduced, for both channels, as a function of antineutron momentum. From the cross section ratio, a substantial deviation from OZI rule expectations is observed. An
ss
quark content in the nucleon offers a fairly plausible explanation for such an effect.
The reaction
p
̄
p→K
+K
−π
0
was analysed for antiproton annihilations at rest at three hydrogen target densities. A strong dependence of the
p
̄
p→φπ
0
yield on the quantum numbers of the initial ...state is observed. The branching ratio of the
φπ
0 channel from the
3
S
1 initial state is more than 15 times larger than the one from the
1
P
1 state. A large apparent violation of the OZI rule for tensor meson production from
p
̄
p
-annihilations from the
P-waves (1
+++2
++) is observed:
R
exp(
f′
2
π
0/
f
2
π
0)=(149±20)·10
−3, significantly exceeding the OZI-rule prediction
R=16·10
−3.
The
p
̄
p
annihilation at rest into the
φη final state was measured for three different target densities: liquid hydrogen, gaseous hydrogen at NTP and at a low pressure of 5 mbar. The yield of this ...reaction in the liquid hydrogen target is smaller than in the low-pressure gas target. The branching ratios of the
φη channel were calculated on the basis of simultaneous analysis of the three data samples. The branching ratio for annihilation into
φη from the
3S
1
protonium state turns out to be about ten times smaller as compared to the one from the
1P
1
state.
The study of the
I=1,
J
PC
=0
++ states with the OBELIX detector in the channel
p
̄
p→K
±K
0
Sπ
∓
at three different target densities is reported. The data show the evidence for an extra scalar state ...with mass 1.29±0.01 GeV/
c
2 and width 0.080±0.005 GeV/
c
2.
We measured the in flight annihilation frequencies and cross sections of reactions
np → π
+π
0,π
+η
and
K
+
K
S
in the antineutron momentum range between 50 and 400 MeV/c. The annihilation ...frequencies of these channels from the different allowed initial states were calculated and some information about the
np
annihilation dynamics were obtained. The first determination of the D-wave contribution in this momentum range was also obtained.
The results of the spin-parity analysis of
pp → 2π
+2π
−
annihilations at very low momentum
p
(≈ 50 MeV/
c) are reported. To describe the data the production of the
ϱ,
f
2,
a
2 and
a
1 mesons and the ...presence of the ππ interaction in
S-wave (the σ term) in the final state are necessary. The best fit solution requires also the presence of a ϱ′ state of mass and width
M = 1.282 ± 0.037,
Γ = 0.236 ± 0.036 GeV/
c
2 and of a heavy pion π(1300) of mass and width
M = 1.275 ± 0.015,
Γ = 0.218 ± 0.100 GeV/
c
2. The measured fraction of the annihilation cross section into 2
π
+2
π
− is (7.61 ± 0.35) · 10
−2.
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![Study of [formula omitted] ...](http://api.summon.serialssolutions.com/2.0.0/image/issn/XR4PS5YY4K/0375-9474/small "Study of [formula omitted] and [formula omitted] annihilation reactions in flight")
