Missing Resonances Research Articles

Nucleon resonances with spin and isospin

Investigation of the nucleon’s excited states has always become an important research topic because of the rich information they provide. Since their first observation, dating back about 70 years, the investigation of their various parameters contributed both to the development of the quark model and a better understanding of the QCD as the theory of strong interaction. Their investigation still has importance. The research conducted on the nucleon excited states is helpful to probe the missing resonances predicted by the quark model but not observed yet. With this motivation, we study the low lying nucleon resonance with and its corresponding orbital and radial excitations with and , respectively. Using the QCD sum rule method, we calculate the masses and pole residues of these states. The obtained mass results are consistent with the mass ranges presented in PDG for the resonances N(1520)(3/2−), N(1700)(3/2−), and N(1720)(3/2+). The results of masses and residues of these states may be used as input parameters to calculate various quantities related to their electromagnetic, weak and strong interactions with other particles with the aim of getting more information on their natures and structures.

Decay patterns of low-lying Nss¯ states via strangeness channels

Here we investigate the decay patterns of the low-lying hidden strangeness nucleon resonances ($\equiv N_{s\bar{s}}$) to the strangeness channels by employing the chiral Lagrangian approach, where the $N_{s\bar{s}}$ states are treated as compact pentaquark states. The $S$-wave decays of these states to the $PB$ (pseudoscalar meson and baryon) and $VB$ (vector meson and baryon) channels are studied. According to the obtained masses and decay properties, we find four states, namely, $N_{s\bar{s}}(1874)$ with quantum numbers $I(J^{P})=1/2(1/2^{-})$, $N_{s\bar{s}}(1885)$ with $I(J^{P})=1/2(3/2^{-})$, $N_{s\bar{s}}(2327)$ with $I(J^{P})=1/2(1/2^{-})$, and $N_{s\bar{s}}(2252)$ with $I(J^{P})=1/2(3/2^{-})$, may be associated to the well established nucleon resonances $N^*(1895)$, $N^{*}(1875)$, and the newly predicted $N^{*}(2355)$ and $N^{*}(2250)$ by CLAS collaboration, respectively. In addition, several other obtained hidden strangeness nucleon resonances may be expected to be dominant components of the predicted missing resonances in the literatures.

Effective Degrees of Freedom in Baryon Spectroscopy

Three quark and quark–diquark models are characterized by several missing resonances, even if in the latter case the state space is a reduced one. Moreover, even quark–diquark models show some differences in their predictions for missing states. After several years of discussion, we still do not know whether baryons can be completely described in terms of three quark models or if diquark correlations have to be taken into account; another possibility, suggested in Santopinto (Phys Rev C 72:022201, 2005), Ferretti et al. (Phys Rev C 83:065204, 2011) and Galata and Santopinto (Phys Rev C 86:045202, 2012), is that the previous pictures (three-quark and quark–diquark) represent the dominant descriptions of baryons at different energy scales. New experiments may be planned at Jlab (JLab12), Bes, Belle and LHCb in order to answer this fundamental open question.

Spectral statistics of molecular resonances in erbium isotopes: How chaotic are they?

We perform a comprehensive analysis of the spectral statistics of the molecular resonances in (166)Er and (168)Er observed in recent ultracold collision experiments [Frisch et al., Nature (London) 507, 475 (2014)] with the aim of determining the chaoticity of this system. We calculate different independent statistical properties to check their degree of agreement with random matrix theory (RMT), and analyze if they are consistent with the possibility of having missing resonances. The analysis of the short-range fluctuations as a function of the magnetic field points to a steady increase of chaoticity until B∼30 G. The repulsion parameter decreases for higher magnetic fields, an effect that can be interpreted as due to missing resonances. The analysis of long-range fluctuations allows us to be more quantitative and estimate a 20%-25% fraction of missing levels. Finally, a study of the distribution of resonance widths provides additional evidence supporting missing resonances of small width compared with the experimental magnetic field resolution. We conclude that further measurements with increased resolution will be necessary to give a final answer to the problem of missing resonances and the agreement with RMT.

Research with real photons at the MAMI 1.6 GeV electron accelerator

The A2-CB Collaboration at Mainz is studying the structure of hadrons by meson photoproduction using unpolarised, linearly polarised and circularly polarised photons with energies up to 1.6 GeV. Photons are energy-tagged using the Glasgow-Mainz tagged photon spectrometer and a new high-energy end-point tagger which allows η’ reactions to be studied. Reaction products are detected in a ~4π detector consisting of the Crystal Ball detector and TAPS forward wall. Transverse or longitudinally polarised proton targets are available and new techniques have been developed to measure the polarisation of recoiling protons. These facilities have allowed an extensive programme of double-polarisation meson-photoproduction experiments to be carried out to search for so-called “missing baryon resonances” on proton and deuteron targets. Searches have also been carried out to investigate narrow resonances in the η-photoproduction channel at invariant masses around 1680 MeV. Coherent π 0 production measurements have been used to estimate the neutron skin thickness in 208 Pb. This paper presents selected highlights from the A2-CB collaboration research programme at MAMI.

Trace formula for chaotic dielectric resonators tested with microwave experiments

We measured the resonance spectra of two stadium-shaped dielectric microwave resonators and tested a semiclassical trace formula for chaotic dielectric resonators proposed by Bogomolny et al. [Phys. Rev. E 78, 056202 (2008)]. We found good qualitative agreement between the experimental data and the predictions of the trace formula. Deviations could be attributed to missing resonances in the measured spectra in accordance with previous experiments [Phys. Rev. E 81, 066215 (2010)]. The investigation of the numerical length spectrum showed good qualitative and reasonable quantitative agreement with the trace formula. It demonstrated, however, the need for higher-order corrections of the trace formula. The application of a curvature correction to the Fresnel reflection coefficients entering the trace formula yielded better agreement, but deviations remained, indicating the necessity of further investigations.

Study of nucleon resonances in a chiral quark model via η productions

In this report we investigate η-meson productions on the proton via electromagnetic and hadron probes in a chiral quark model approach. The observables, such as, differential cross section and beam asymmetry for the two productions are calculated and compared with the experiment. The five known resonances S11(1535), S11(1650), P13(1720), D13(1520), and F15(1680) are found to be dominant in the reaction mechanisms in both channels. Significant contribution from a new S11 resonances are deduced. For the so-called “missing resonances”, no evidence is found within the investigated reactions. The partial wave amplitudes for π−p → ηn are also presented.

Extinction of impurity resonances in large-gap regions of inhomogeneousd-wave superconductors

Impurity resonances observed by scanning tunneling spectroscopy in the superconducting state have been used to deduce properties of the underlying pure state. Here we study a longstanding puzzle associated with these measurements, the apparent extinction of these resonances for Ni and Zn impurities in large-gap regions of the inhomogeneous BSCCO superconductor. We calculate the effect of order parameter and hopping suppression near the impurity site, and find that these two effects are sufficient to explain the missing resonances in the case of Ni. There are several possible scenarios for the extinction of the Zn resonances, which we discuss in turn; in addition, we propose measurements which could distinguish among them.

The CMU Baryon Amplitude Analysis Program

The PWA group at Carnegie Mellon University has developed a comprehensive approach and analysis package for the purpose of extracting the amplitudes for photoproduced baryon resonances. The end goal is to identify any missing resonances that are predicted by the constituent quark model, but not definitively observed in experiments. The data comes from the CEBAF Large Acceptance Spectrometer (CLAS) at Jefferson Lab.

PHOTOPRODUCTION OF η AND η′ MESONS ON THE NUCLEON

The isobar models η-MAID and η′-MAID have been used to analyze new data on quasi-free η photoproduction on the deuteron from Bonn and recent η′ data on the proton from Jlab. In η photoproduction on the neutron a bump around W = 1700 MeV was observed which could possibly arise from a narrow P11 state that is discussed as a non-strange member of the Θ+ antidecuplett. In η′ photoproduction on the proton resonance contributions are found that can be attributed to missing resonances in the energy region around W = 1900 MeV .

Kaon photoproduction in a multipole approach

The recently published experimental data on K{sup +}{lambda} photoproduction by the SAPHIR, CLAS, and LEPS Collaborations are analyzed by means of a multipole approach. For this purpose the background amplitudes are constructed from appropriate Feynman diagrams in a gauge-invariant and crossing-symmetric fashion. The results of our calculation emphasize the lack of mutual consistency between the SAPHIR and CLAS data previously found by several independent research groups, whereas the LEPS data are found to be more consistent with those of CLAS. The use of SAPHIR and CLAS data, individually or simultaneously, leads to quite different resonance parameters that, therefore, could lead to different conclusions on 'missing resonances'. Fitting to the SAPHIR and LEPS data simultaneously indicates that the S{sub 11}(1650),P{sub 13}(1720),D{sub 13}(1700),D{sub 13}(2080),F{sub 15}(1680), and F{sub 15}(2000) resonances are required, whereas fitting to the combination of CLAS and LEPS data leads alternatively to the P{sub 13}(1900),D{sub 13}(2080),D{sub 15}(1675),F{sub 15}(1680), and F{sub 17}(1990) resonances. Although yielding different results in most cases, both SAPHIR and CLAS data indicate that the second peak in the cross sections at W{approx}1900 MeV originates from the D{sub 13}(2080) resonance with a mass between 1911 and 1936 MeV. Furthermore, in contrast to the results of currently available modelsmore » and the Table of Particle Properties, both data sets do not exhibit the need for a P{sub 11}(1710) resonance. The few data points available for target asymmetry cannot be described by the models proposed in the present work.« less

New aspects of experimental study of the pion-nucleon interaction in the resonance region

New experimental data that were obtained by the PNPI-ITEP Collaboration have resolved some discrete ambiguities in the partial-wave analysis (PWA). These results were used in the new FA02 PWA performed at George Washington University. At the same time, the FA02 PWA has revealed considerable fewer N* and Δ resonances than those listed in the RPP tables. This circumstance aggravated the known problem of so-called missing resonances. The program for further measurements of the spin rotation parameters in elastic πN scattering that are required to eliminate the remaining discrete PWA ambiguities is discussed.

Structure and Dynamics of Micelle-bound Human α-Synuclein

Misfolding of the protein alpha-synuclein (aS), which associates with presynaptic vesicles, has been implicated in the molecular chain of events leading to Parkinson's disease. Here, the structure and dynamics of micelle-bound aS are reported. Val3-Val37 and Lys45-Thr92 form curved alpha-helices, connected by a well ordered, extended linker in an unexpected anti-parallel arrangement, followed by another short extended region (Gly93-Lys97), overlapping the recently identified chaperone-mediated autophagy recognition motif and a highly mobile tail (Asp98-Ala140). Helix curvature is significantly less than predicted based on the native micelle shape, indicating a deformation of the micelle by aS. Structural and dynamic parameters show a reduced helical content for Ala30-Val37. A dynamic variation in interhelical distance on the microsecond timescale is complemented by enhanced sub-nanosecond timescale dynamics, particularly in the remarkably glycine-rich segments of the helices. These unusually rich dynamics may serve to mitigate the effect of aS binding on membrane fluidity. The well ordered conformation of the helix-helix connector indicates a defined interaction with lipidic surfaces, suggesting that, when bound to larger diameter synaptic vesicles, it can act as a switch between this structure and a previously proposed uninterrupted helix.

When Monomers Are Preferred: A Strategy for the Identification and Disruption of Weakly Oligomerized Proteins

Oligomerization is important for the structure and function of many proteins, but frequently complicates their characterization. It is often desirable to obtain the protein in monomeric form. Here, we report a strategy that allows the generation of monomers from weakly associated oligomers but does not require knowledge of the three-dimensional structure of the protein. The dynamics of protein association are used in solution NMR spectroscopy to identify regions of the polypeptide chain that are likely to be responsible for the interaction. Protein sequence analysis further refines the selection, as conserved sites with moderate hydrophobicity are targeted for modification. Gel filtration and activity assays straightforwardly reveal the consequences of the change and are used to screen for the desired mutants. The strategy is demonstrated for the Rac1 binding domain of plexin-B1. A monomeric variant is generated which preserves the Rac1 binding activity and the wild-type protein structure.

Relativistic photoionization cross sections for C II

The first measurement of highly resolved photoionization cross sections of the ground state of C II was reported recently by Kjeldsen et al. [Astrophys. J. 524, L143 (1999)]. The observed resonance features showed good agreement with the theoretical calculations in the close-coupling approximation [S. Nahar, Astrophys. J. Suppl. Ser. 101, 423 (1995)]. However, there were several observed resonances that were missing in the theoretical predictions. The earlier theoretical calculation was carried out in $\mathrm{LS}$ coupling where the relativistic effects were not included. Present paper reports photoionization cross sections including relativistic effects in the Breit-Pauli R-matrix (BPRM) approximation. The configuration interaction eigenfunction expansion for the core ion C III consists of 20 fine-structure levels dominated by the configurations from ${1s}^{2}{2s}^{2}$ to ${1s}^{2}2s3d.$ Detailed features in the calculated cross sections exhibit the missing resonances due to fine structure. The results provide a benchmark for the accuracy of BPRM photoionization cross sections, as needed for the recent and ongoing experiments for high-resolution photoionization cross sections at synchrotron-radiation sources.

Nucleonic resonance excitations and “missing resonances” in the ω meson photoproduction

In this work, an improved quark model approach to the ω meson photoproduction with an effective Lagrangian is reported. The t-channel natural parity exchange is consistently taken into account through the Pomeron exchange, while the unnatural parity exchange is described by the π 0 exchange. With very limited number of parameters, the available data in the low energy regime can be consistently reproduced in this framework. Effects from the intermediate nucleonic resonances are investigated in several polarization observables. The sensitivities of these observables to the resonance effects are probably the best way for identifying those so-called “missing resonances” in the baryon spectrum.

Exploring the reaction mechanism of eta prime photoproduction

Abstract We examine theoretical implications of studying the differential cross-section and some key polarization observables in the η′ photoproduction reaction off protons, from its threshold to about 2 GeV of cm energy, the region of the so-called “missing baryon resonances”. We compare implications of different models all of which generate the observed peak in the total η′ photproduction cross section, but have very different differential cross section and polarization profields. Their measurements are thus crucial in distinguishing these reaction mechanisms, of interest to understanding QCD in its nonperturbative domain.

Negative-parity hyperons in the constituent quark model with meson-quark couplings

Negative-parity hyperons are systematically studied by means of the constituent quark model which incorporates the effect of the meson-quark coupling. Some unresolved puzzles of these resonances are investigated; the mass splitting between Λ(1405) and Λ(1520) can be realized by the difference of their self-energies due to the mesonic effect, without losing the general success of the constituent quark model; the coupling of the so-called “missing resonances” to the meson-baryon states are shown to be suppressed owing to the spin-flavor symmetry of the quark wave functions of the resonances. Although only the resonance contribution is considered for the meson-baryon scattering, the calculated amplitudes have the energy dependence consistent with the phase-shift analyses of the data. To obtain more quantitative agreement, however, the improvement of the model will be necessary; for example, non-resonant contribution is required to explain the isovector K N amplitude at low energies.