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Представлено дополнительное описание Longidorus diadecturus, основанное на паратипных особях и на графических рисунках, приведённых в первоначальном описании. Этот вид включён в Приложение IIA к Регламентации ЕС 2019/2072 в связи с его зарегистрированной способностью быть переносчиком вируса розеточной мозаики персика.
Roper resonances in chiral quark models Golli, B.; Širca, S.
The European physical journal. A, Hadrons and nuclei,
12/2008, Volume:
38, Issue:
3
Journal Article
Peer reviewed
We derive a method to calculate the multi-channel
K
-matrix applicable to a broad class of models in which mesons linearly couple to the quark core. The method is used to calculate pion scattering ...amplitudes in the energy region of low-lying P11 and P33 resonances. A good agreement with experimental data is achieved if in addition to the elastic channel we include the
and
N
(
channels where the
-meson models the correlated two-pion decay. We solve the integral equation for the
K
-matrix in the approximation of separable kernels; it yields a sizable increase of the widths of the
(1232) and the
N
(1440) resonances compared to the bare quark values.
We present a method to calculate pion electro-production amplitudes in a coupled-channel framework incorporating quasi-bound quark-model states. The method offers a clear prescription how to extract ...the resonant part of the amplitudes, even in the presence of different decay channels and a strong mixing of neighbouring resonances. The method is applied to the calculation of the M
1-
and the S
1-
amplitudes in the
P
11 partial wave in a simple chiral quark model. A good agreement with the observed M
1-
amplitude is found with a significant contribution from the pion cloud. The same effect is also prominent in the S
1-
amplitude but a rather uncertain data prevent us to draw a definitive conclusion.
.
We report on new measurements of the electric Generalized Polarizability (GP) of the proton
α
E
in a kinematic region where a puzzling dependence on momentum transfer has been observed, and we have ...found that
α
E
=
(
5
.
3
±
0
.
6
s
t
a
t
±
1
.
3
s
y
s
)
10
-
4
fm
3
at
Q
2
=
0
.
20
(GeV/
c
)
2
. The new measurements, when considered along with the rest of the world data, suggest that
α
E
can be described by either a local plateau or by an enhancement in the region
Q
2
=
0
.
20
(GeV/
c
)
2
to 0.33 (GeV/
c
)
2
. The experiment also provides the first measurement of the Coulomb quadrupole amplitude in the
N
→
Δ
transition through the exploration of the
p
(
e
,
e
p
)
γ
reaction. The new measurement gives
C
M
R
=
(
-
4
.
4
±
0
.
8
s
t
a
t
±
0
.
6
s
y
s
)
%
at
Q
2
=
0
.
20
(GeV/
c
)
2
and is consistent with the results from the pion electroproduction world data. It has been obtained using a completely different extraction method, and therefore represents a strong validation test of the world data model uncertainties.
The mechanism for the formation of the
Λ
(
1405
)
resonance is studied in a chiral quark model that includes quark-meson as well as contact (four point) interactions. The negative-parity
S
-wave ...scattering amplitudes for strangeness
-
1
and 1 are calculated within a unified coupled-channel framework that includes the
KN
,
K
¯
N
,
π
Σ
,
η
Λ
,
K
Ξ
,
π
Λ
, and
η
Σ
channels and possible genuine three-quark bare singlet and octet states corresponding to
1
2
-
resonances. It is found that in order to reproduce the scattering amplitudes in the
S
01
partial wave it is important to include the pertinent three-quark octet states as well as the singlet state, while the inclusion of the contact term is not mandatory. The Laurent-Pietarinen expansion is used to determine the
S
-matrix poles. Following their evolution as a function of increasing interaction strength, the mass of the singlet state is strongly reduced due to the attractive self-energy in the
π
Σ
and
K
¯
N
channels; when it drops below the
KN
threshold, the state acquires a dominant
K
¯
N
component which can be identified with a molecular state. The attraction between the kaon and the nucleon is generated through the
K
¯
N
Λ
∗
interaction rather than by meson-nucleon forces.
JLab E12-19-002 Experiment is planned to measure the Λ-binding energies of
3
Λ
H
J
π
= 1/2
+
or 3/2
+
(
T
= 0) and
4
Λ
H (1
+
) at JLab Hall C. The expected accuracy for the binding-energy ...measurement is |Δ
B
total
Λ
| ≃ 70 keV. The accurate spectroscopy for these light hypernuclei would shed light on the puzzle of the small binding energy and short lifetime of
3
Λ
H, and the chargesymmetry breaking in the ΛN interaction. We aim to perform the experiment in 2025.
The meson scattering and electroproduction amplitudes in the
D
13 ,
D
33 and
D
15 partial waves are calculated in a coupled-channel formalism incorporating quasi-bound quark-model states, extending ...our previous studies of the
P
11 ,
P
33 and
S
11 partial waves. The vertices of the baryon-meson interaction including the
s
- and
d
-wave pions and
-mesons, the
s
-wave
-meson, and the
s
- and
p
-wave
-mesons are determined in the Cloudy Bag Model, with some changes of the parameters to reproduce the widths of the resonances. The helicity amplitudes and the electroproduction amplitudes exhibit consistent behavior in all channels but tend to be too weak compared to the experiment. We discuss possible origins of this discrepancy which arises also in the constituent quark model calculations.
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