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.
Data on the reaction γp→K^{+}Λ from the CLAS experiments are used to derive the leading multipoles, E_{0+}, M_{1-}, E_{1+}, and M_{1+}, from the production threshold to 2180 MeV in 24 slices of the ...invariant mass. The four multipoles are determined without any constraints. The multipoles are fitted using a multichannel L+P model that allows us to search for singularities and to extract the positions of poles on the complex energy plane in an almost model-independent method. The multipoles are also used as additional constraints in an energy-dependent analysis of a large body of pion and photoinduced reactions within the Bonn-Gatchina partial wave analysis. The study confirms the existence of poles due to nucleon resonances with spin parity J^{P}=1/2^{-}, 1/2^{+}, and 3/2^{+} in the region at about 1.9 GeV.
.
The isobar model EtaMAID has been updated with new and high precision data for
η
and
η
photoproduction on protons and neutrons from MAMI, ELSA, GRAAL and CLAS. The background is described in a ...recently developed Regge cut model, and for the resonance part the whole list of nucleon resonances has been investigated with 21
N
*
states contributing to
η
photoproduction and 12
N
*
states contributing to
η
photoproduction. A new approach is discussed to avoid double counting in the overlap region of Regge and resonances. A comparison is done among four newly updated partial waves analyses for observables and partial waves. Finally, the possibility of a narrow resonance near
W
=
1900
MeV is discussed, that would be able to explain unexpected energy and angular dependence of observables in
p
(
γ
,
η
)
p
near
η
threshold.
Fundamental properties of resonances Ceci, S; Hadžimehmedović, M; Osmanović, H ...
Scientific reports,
03/2017, Letnik:
7, Številka:
1
Journal Article
Recenzirano
Odprti dostop
All resonances, from hydrogen nuclei excited by the high-energy gamma rays in deep space to newly discovered particles produced in Large Hadron Collider, should be described by the same fundamental ...physical quantities. However, two distinct sets of properties are used to describe resonances: the pole parameters (complex pole position and residue) and the Breit-Wigner parameters (mass, width, and branching fractions). There is an ongoing decades-old debate on which one of them should be abandoned. In this study of nucleon resonances appearing in the elastic pion-nucleon scattering we discover an intricate interplay of the parameters from both sets, and realize that neither set is completely independent or fundamental on its own.
Electromagnetic resonance properties are uniquely defined at the pole and do not depend on the separation of the resonance from background or the decay channel. Photon-nucleon branching ratios are ...nowadays often quoted at the pole, and we generalize the considerations to the case of virtual photons. In this paper, we derive and compare relations for nucleon to baryon transition form factors both for the Breit-Wigner and the pole positions. Using the MAID2007 and SAID SM08 partial wave analyses of pion electroproduction data, we compare the $G_M$, $G_E$, and $G_C$ form factors for the $\Delta(1232)$ resonance excitation at the Breit-Wigner resonance and pole positions up to $Q^2=5$ GeV$^2$. We also explore the $E/M$ and $S/M$ ratios as functions of $Q^2$. Finally, for pole and residue extraction, we apply the Laurent + Pietarinen method.
The isobar model EtaMAID has been updated with new and high precision data for
η
and
η′
photoproduction on protons and neutrons from MAMI, ELSA, GRAAL and CLAS. The background is described in a ...recently developed Regge-cut model, and for the resonance part the whole list of nucleon resonances has been investigated with 21
N
* states contributing to
η
photoproduction and 12
N
* states contributing to
η′
photoproduction. Finally, the possibility of a narrow resonance near
W
= 1900 MeV is discussed, that would be able to explain unexpected energy and angular dependence of observables in
p
(
γ
,
η′
)
p
near
η
threshold.
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