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Search Results: 1 - 10 of 578066 matches for " B. M. K. Nefkens "
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Meson-Nucleon Physics: Past, Present and Future
B. M. K. Nefkens
Physics , 2002,
Abstract: We will present some thoughts on the following topics: 1. Major highlights in the history of strong interactions such as isospin, the pion, SU(3), quarks, the color degree of freedom, QCD. 2. Topics of high current interest such as quark confinement, the origin of mass, the search for the gluon degrees of freedom, chiral symmetry, flavor symmetry, regularities in the properties of the light-baryon families (parity doublets, clusters) decay patterns, hadronization, chiral restoration, effective Lagrangians and their degrees of freedom. 3. The input parameters for QCD and for effective models. 4. Hadron physics as a necessary aspect of precision tests of the Standard Model and of the Search for New Physics.
Highlights of Crystal Ball Physics
B. M. K. Nefkens,for the Crystal Ball Collaboration
Physics , 2004, DOI: 10.1142/S0217751X05023013
Abstract: Differential and total cross sections are presented for pi- - and K- -induced reactions on a proton target leading to all-neutral final states. Also shown are rates for rare and upper limits for forbidden eta-meson decays to test Chiral Perturbation Theory, the pi0-pi0 interactions and C and CP invariance.
Status Report on the Light Baryonic States
B. M. K. Nefkens,J. W. Price
Physics , 2002,
Abstract: The regularities in the spectrum of the light baryon resonances are reviewed and compared with those of the light mesons. We discuss the occurrence of parity doublets and clusters, and note the trends in the values of the masses, widths, spins, and parities. The importance of SU(3) flavor is illustrated and the status of quark model calculations of the baryonic spectrum is reviewed. The absence of evidence for baryonic hybrids is particularly interesting. We propose to use better symbols for the baryon resonances which do not conflict with the simple quark structure of QCD. We shall comment also on fine tuning the Star System for the hadronic states. The importance of greater support for the construction and operation of secondary beams of $\pi$, $K$, $\bar p$, $\vec{n}$ and $\vec\gamma$ up to 5 GeV/$c$ for the future of non-perturbative QCD is emphasized.
The Neutral Decay Modes of the Eta-Meson
B. M. K. Nefkens,J. W. Price
Physics , 2002, DOI: 10.1238/Physica.Topical.099a00114
Abstract: The neutral decay modes of the eta meson are reviewed. The most recent results obtained with the Crystal Ball multiphoton detector at BNL are incorporated. This includes a new, precise result for the slope parameter alpha of the Dalitz plot in eta -> 3pi0 decay and a new, lower branching ratio for eta -> pi0 gamma gamma which is consistent with chiral perturbation theory. Recently-obtained limits are given for novel tests of CP and C invariance based on several rare eta decays.
pi N --> eta N and eta N --> eta N partial wave T-matrices in a coupled, three channel model
Mijo Batinic,Ivo Slaus,Alfred Svarc,B. M. K. Nefkens
Physics , 1995, DOI: 10.1103/PhysRevC.57.1004
Abstract: The pi N --> eta N and eta N --> eta N partial wave T-matrices for the eight lowest partial waves have been obtained in a three coupled channel model with unitarity manifestly imposed. The two physical channels are pi_N and eta_N, and the third channel, pi_pi_N is an effective, but unphysical two body channel which represents all remaining processes. The pi_N elastic phase shifts and the weighted data base of the pi- p --> eta n total and differential cross sections are chosen as the input for the fitting procedure. A model containing a single resonance in each of the three partial waves that dominates the eta production at lower energies is compared with previous analyses, based on similar assumptions. A multiresonance coupled channel model is introduced which significantly improves the agreement with all input data. Our results are compared with a complementary multiresonance coupled channel analysis that is constrained with elastic and continuum production channels. The inclusion of the fourth P11 resonance in the 1440 - 2200 MeV region further improves the agreement between the analysis and the data.
In Search of the f0 (or "sigma") Meson: New data on pi0 pi0 Production by pi- and K- on Hydrogen
B. M. K. Nefkens,S. Prakhov,A. Starostin
Physics , 2002,
Abstract: We present preliminary results on the cross sections and Dalitz-plot densities for the process pi- p -> pi0 pi0 n from threshold to p(pi)=750 MeV/c as well as for K- p -> pi0 pi0 Lambda and K- p -> pi0 pi0 Sigma0 at p(K)=520 to 750 MeV/c. We have found that sigma(tot)(pi- p -> pi0 pi0 n) ~= 2sigma(tot)(K- p -> pi0 pi0 Lambda). The pi0 pi0 n Dalitz plots are very nonuniform, expecially for the higher p(pi), with a high concentration of events on an "island" around m(pi n) ~= 1.2 GeV and Gamma ~= 0.1 GeV peaking at high pi0 pi0 invariant mass. This is indicative of the dominant role of the Delta0(1234)(3/2^+) resonance in the final state. The pi0 pi0 Lambda Dalitz plots are strikingly similar to the ones for pi0 pi0 n except that the island is concentrated at m(pi Lambda) ~= 1.38 GeV and has a narrower width, Gamma ~= 0.05 GeV. This indicates the dominant role of the Sigma0(1385)(3/2+) resonance. The similarity in the Dalitz plots and the proportionality of the total cross sections are an impressive testimony of the applicability of broken SU(3) flavor symmetry to reaction dynamics. We have measured sigma(tot)(K- p -> pi0 pi0 Lambda) ~= 6sigma(tot)(K- p -> pi0 pi0 Sigma0) and observed that the Dalitz plots for these processes are very different. The Dalitz plots for pi0 pi0 Sigma0 show some enhancement at low pi0 pi0 invariant mass, and there is good indication for the Lambda(1405) intermediate state but there is no island; at the highest p(K), there is some evidence for the Lambda(1520) intermediate state. The above features of pi0 pi0 production by pi- and K- can all be understood if f0 production is small.
Meson production on complex nuclei by pi^- with the Crystal Ball detector
A. Starostin,B. M. K. Nefkens,H. M. Staudenmaier,for the Crystal Ball Collaboration
Physics , 2002,
Abstract: We report on preliminary results for the production of neutral mesons by 750 MeV/$c$ $\pi^-$ on complex nuclear targets (C, Al, Cu) and hydrogen. Our simultaneous measurement of $\pi^0$, $2\pi^0$, and $\eta$ final states allows an investigation of the nuclear final-state-interaction effects. The data show that nuclear absorption is mainly responsible for an observed change in the shape of the $2\pi^0$ invariant mass spectra. Our preliminary result for the $\sigma \to \gamma \gamma$ branching ratio is BR$(\sigma \to \gamma \gamma) < 3.6\times 10^{-3} \times \phi$ at 90% C.L. on a carbon target, where $\phi$ is the fraction of $2\pi^0$ produced via the $\sigma$ intermediate state.
Update of the pi N --> eta N and eta N --> eta N partial-wave amplitudes
Mijo Batinic,Ivan Dadic,Ivo Slaus,Alfred Svarc,B. M. K. Nefkens,T. -S. H. Lee
Physics , 1997,
Abstract: A three-channel, multi-resonance, unitary model developed in 1995 is used to determine the $\pi N \rightarrow \eta N$ and $\eta N \rightarrow \eta N$ amplitudes using as input the latest data for the dominant $S_{11}$ $\pi N$ elastic scattering partial wave following suggestions of Prof. G. H\"{o}hler. The sign error in the numerical evaluation of the dispersion integral in the original publication is eliminated. The remaining weighted data set for the $\pi N \rightarrow \eta N$ total and differential cross sections is used as in the original publication. The correction of the numerical error influences the $\eta N$ cusp effect and improves the quality of the fit to the input data. However, our new result for the $\eta N$ scattering length, $a_{\eta N }= (0.717 \pm 0.030) + i (0.263 \pm 0.025)$ fm, is a sole consequence of the correction of the $S_{11}$ input and suggests that the $\eta d$ system is unbound or loosely bound.
Photoproduction of the doubly-strange Xi Hyperons
J. W. Price,J. Ducote,J. Goetz,B. M. K. Nefkens,for the CLAS Collaboration
Physics , 2004,
Abstract: We report on the first measurement of exclusive Xi- and Xi0 photoproduction. The Xi- states are produced in the reaction gamma p --> K+ K+ Xi-, and the Xi0 states in gamma p --> K+ K+ pi- Xi0. Identification is made by the unique mass measured as the missing mass of the K+ K+ (or K+ K+ pi-) system using the CLAS detector at the Thomas Jefferson National Accelerator Facility. A systematic study of the excited Xi spectrum improves our understanding of the N* and Delta* states, since the Xi* states are related to them by SU(3) flavor symmetry. At the highest energies available at Jefferson Lab, we begin to find evidence for known excited Xi- states in the photoproduction process, and possibly new states at 1770 and 1860 MeV, although we do not have enough statistics to draw a strong conclusion. A search for the Xi5--(1862) pentaquark state seen by NA49 is made using the process gamma p -> K+ K+ pi+ X, but the result is inconclusive for lack of statistics.
Ratios of Elastic Scattering of Pions from 3H and 3He
W. J. Briscoe,B. L. Berman,R. W. C. Carter,K. S. Dhuga,S. K. Matthews,N-J. Nicholas,S. J. Greene,B. M. K. Nefkens,J. W. Price,L. D. Isenhower,M. E. Sadler,I. Slaus,I. Supek
Physics , 2002, DOI: 10.1103/PhysRevC.66.054006
Abstract: We have measured the elastic-scattering ratios of normalized yields for charged pions from 3H and 3He in the backward hemisphere. At 180 MeV, we completed the angular distribution begun with our earlier measurements, adding six data points in the angular range of 119 deg to 169 deg in the pi-nucleus center of mass. We also measured an excitation function with data points at 142, 180, 220, and 256 MeV incident pion energy at the largest achievable angle for each energy between 160 deg and 170 deg in the pi-nucleus center of mass. This excitation function corresponds to the energies of our forward-hemisphere studies. The data, taken as a whole, show an apparent role reversal of the two charge-symmetric ratios r1 and r2 in the backward hemisphere. Also, for data > 100 deg we observe a strong dependence on the four-momentum transfer squared (-t) for all of the ratios regardless of pion energy or scattering angle, and we find that the superratio R data match very well with calculations based on the forward-hemisphere data that predicts the value of the difference between the even-nucleon radii of 3H and 3He. Comparisons are also made with recent calculations incorporating different wave functions and double scattering models.
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