659 research outputs found

    Quasi-Two-Body Decays of Nonstrange Baryons

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    We examine the decays of nonstrange baryons to the final states Δπ\Delta\pi, NρN\rho, NηN\eta, NηN\eta^\prime, NωN\omega, N1/2+(1440)πN1/2^+(1440)\pi, and Δ3/2+(1600)π\Delta3/2^+(1600)\pi, in a relativized pair-creation(3P0^3P_0) model which has been developed in a previous study of the NπN\pi decays of the same baryon states. As it is our goal to provide a guide for the possible discovery of new baryon states at CEBAF and elsewhere, we examine the decays of resonances which have already been seen in the partial-wave analyses, along with those of states which are predicted by the quark model but which remain undiscovered. The level of agreement between our calculation and the available widths from the partial-wave analyses is encouraging.Comment: 41 pages, CEBAF-TH-93-1

    Evidence for the fourth P11 resonance predicted by the constituent quark model

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    It is pointed out that the third of five low-lying P11 states predicted by a constituent quark model can be identified with the third of four states in a solution from a three-channel analysis by the Zagreb group. This is one of the so-called ``missing'' resonances, predicted at 1880 MeV. The fit of the Zagreb group to the pi N -> eta N data is the crucial element in finding this fourth resonance in the P11 partial wave.Comment: 8 pages, revtex; expanded acknowledgement

    K*{\Lambda}(1116) photoproduction and nucleon resonances

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    In this presentation, we report our recent studies on the KΛ(1116)K^*\Lambda(1116) photoproduction off the proton target, using the tree-level Born approximation, via the effective Lagrangian approach. In addition, we include the nine (three- or four-star confirmed) nucleon resonances below the threshold sth2008\sqrt{s}_\mathrm{th}\approx2008 MeV, to interpret the discrepancy between the experiment and previous theoretical studies, in the vicinity of the threshold region. From the numerical studies, we observe that the S11(1535)S_{11}(1535) and S11(1650)S_{11}(1650) play an important role for the cross-section enhancement near the sth\sqrt{s}_\mathrm{th}. It also turns out that, in order to reproduce the data, we have the vector coupling constants gKS11(1535)Λ=(7.09.0)g_{K^*S_{11}(1535)\Lambda}=(7.0\sim9.0) and gKS11(1650)Λ=(5.06.0)g_{K^*S_{11}(1650)\Lambda}=(5.0\sim6.0).Comment: 2 pages, 2 figures, talk given at International Conference on the structure of baryons, BARYONS'10, Dec. 7-11, 2010, Osaka, Japa

    New Baryons in the Delta eta and Delta omega Channels

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    The decays of excited nonstrange baryons into the final states Delta eta and Delta omega are examined in a relativized quark pair creation model. The wavefunctions and parameters of the model are fixed by previous calculations of N pi and N pi pi, etc., decays through various quasi-two body channels including N eta and N omega. Our results show that the combination of thresholds just below the region of interest and the isospin selectivity of these channels should allow the discovery of several new baryons in such experiments.Comment: 10 pages, RevTe

    Model-independent resonance parameter extraction using the trace of K and T matrices

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    A model-independent method for the determination of Breit-Wigner resonance parameters is presented. The method is based on eliminating the dependence on the choice of channel basis by analyzing the trace of the K and T matrices in the coupled-channel formalism, rather than individual matrix elements of the multichannel scattering matrix.Comment: 6 pages, 16 figure

    Strong decays of N(1535)N^{*}(1535) in an extended chiral quark model

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    The strong decays of the N(1535)N^{*}(1535) resonance are investigated in an extended chiral quark model by including the low-lying qqqqqˉqqqq\bar{q} components in addition to the qqqqqq component. The results show that these five-quark components in N(1535)N^{*}(1535) contribute significantly to the N(1535)NπN^{*}(1535)\to N\pi and N(1535)NηN^{*}(1535)\to N\eta decays. The contributions to the NηN\eta decay come from both the lowest energy and the next-to-lowest energy five-quarks components, while the contributions to the NπN\pi decay come from only the latter one. Taking these contributions into account, the description for the strong decays of N(1535)N^{*}(1535) is improved, especially, for the puzzling large ratio of the decays to NηN\eta and NπN\pi.Comment: 6 pages, 1 figur

    Strange Decays of Nonstrange Baryons

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    The strong decays of excited nonstrange baryons into the final states Lambda K, Sigma K, and for the first time into Lambda(1405) K, Lambda(1520) K, Sigma(1385) K, Lambda K*, and Sigma K*, are examined in a relativized quark pair creation model. The wave functions and parameters of the model are fixed by previous calculations of N pi and N pi pi, etc., decays. Our results show that it should be possible to discover several new negative parity excited baryons and confirm the discovery of several others by analyzing these final states in kaon production experiments. We also establish clear predictions for the relative strengths of certain states to decay to Lambda(1405) K and Lambda(1520) K, which can be tested to determine if a three-quark model of the Lambda(1405) K is valid. Our results compare favorably with the results of partial wave analyses of the limited existing data for the Lambda K and Sigma K channels. We do not find large Sigma K decay amplitudes for a substantial group of predicted and weakly established negative-parity states, in contrast to the only previous work to consider decays of these states into the strange final states Lambda K and Sigma K.Comment: 25 pages, 8 figures, RevTe

    Delta isobar masses, large N_c relations, and the quark model

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    Motivated by recent remarks on the Delta+ mass and comparisons between the quark model and relations based on large-N_c with perturbative flavor breaking, two sets of Delta masses consistent with these constraints are constructed. These two sets, based either on an experimentally determined mass splitting or a quark model of isospin symmetry breaking, are shown to be inconsistent. The model dependence of this inconsistency is examined, and suggestions for improved experiments are made. An explicit quark model calculation and mass relations based on the large-N_c limit with perturbative flavor breaking are compared. The expected level of accuracy of such relations is realized in the quark model, except for mass relations spanning more than one SU(6) representation. It is shown that the Delta0 and Delta++ pole masses and Delta0 - Delta+ = (Delta- - Delta++)/3 about 1.5 MeV are more consistent with model expectations than the analogous Breit-Wigner masses and their splittings.Comment: 10 pages, including 1 eps figure, revte

    Comment on ZZ''s and the H1 and ZEUS High Q2Q^2 Anomalies

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    We investigate the effects of extra neutral gauge bosons on the high Q2Q^2 region of the e+pe+Xe^+p \to e^+ X cross section at s=300\sqrt{s}=300 GeV. We found that the only models with electroweak strength coupling, typical of extended gauge theories, that give a better fit to the H1 and ZEUS high Q2Q^2 data than the standard model, are ruled out by existing data from the Tevatron. From general scaling arguments, using the allowed contact interactions, the only allowed models with ZZ''s would be those with strong couplings although even in this case the statistical evidence is not compelling.Comment: Latex file uses revtex version 3, epsfig, 1 postscript figure is attache

    η\eta production off the proton in a Regge-plus-chiral quark approach

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    A chiral constituent quark model approach, embodying s- and u-channel exchanges,complemented with a Reggeized treatment for t-channel is presented. A model is obtained allowing data for πpηn\pi^- p \to \eta n and γpηp\gamma p \to \eta p to be describe satisfactorily. For the latter reaction, recently released data by CLAS and CBELSA/TAPS Collaborations in the system total energy range 1.6W2.81.6 \lesssim W \lesssim 2.8 GeV are well reproduced due to the inclusion of Reggeized trajectories instead of simple ρ\rho and ω\omega poles. Contribution from "missing" resonances is found to be negligible in the considered processes.Comment: 23 pages.4 figures,4 tables, to appear in Phys.Rev.
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