299 research outputs found
Radiative decays of decuplet hyperons
No full textWe calculate the radiative decay widths of decuplet hyperons in a chiral constituent quark model including electromagnetic exchange currents between quarks. Exchange currents contribute significantly to the E2 transition amplitude, while they largely cancel for the M1 transition amplitude. Strangeness suppression of the radiative hyperon decays is found to be weakened by exchange currents. Differences and similarities between our results and other recent model predictions are discussed.Wagner, Georg; Buchmann, A. J.; Faessler, Aman
Exchange currents in octet hyperon charge radii
No full textOctet hyperon charge radii are calculated in a chiral constituent quark model including electromagnetic exchange currents between quarks. In the impulse approximation one observes a decrease of the hyperon charge radii with increasing strangeness. This effect is reduced by exchange currents. Due to exchange currents, the charge radius of the negatively charged hyperons is close to the proton charge radius.Georg Wagner, A. J. Buchmann, and Amand Faessle
Egyptian-German Springschool and Conference Particle and Nuclear Physics. Volume 2: Contributed Papers: Cairo April 11-19, 1992
No full textThis second part of the proceedings of the Egyptian-German School and Conference in Particle and Nuclear Physies (EGSC-PNP) whieh was held in Cairo, April 11-19, 1922, contains the contributed papers which are accepted for publication. The first article on the symmetrie and unitary groups was requested during the meeting as a necessary background and is included here since the first part which contains the lectures was already available by the opening as planned. The ceremonial opening was under the auspices of his excellency Engineer Maher Abaza, Minister of Electricity and Energy, and the presence of many distinguished guests. The whole activity was mainly adressed to young physicists from developing countries working in this field to promote their concern and standard in scientific research. To this end, the meeting was a great success due to the efforts of everyone involved. The running of the whole-day activities in the pleasant place Hotel Sonesta, where the lecturers were also housed, played an important role in creating a friendly atmosphere vivid with communications and interactions. The participants had the opportunity to acquire knowledge most effectively, to present and discuss their own research with lecturers and with each other. The EGSC-PNP is a product of the German-Egyptian cooperation between the International Bureau (IB) in Kernforschungs Anlage in Juelich and the Atomic Energy Authority (AEA) in Cairo, in the frame work of a bilateral agreement in scientific research and technological development. The personal interests and endeavours of Prof. F. Hammad, Chairman of AEA, and of Dr. N. Nentwich, Executive Director of IB, to achieve a most successful meeting are highly appreciated. Their support to invite a number of competent lecturers and to afford the best facilities played a major role towards a successful meeting. Most incÜcative and gratifying is the recommendation of alliecturers and participants in the concluding session to repeat this event in the near future in this, or even improved form
d' dibaryon in a colored cluster model
No full textThe mass and wave function of a six-quark system with quantum numbers JP=0-, T=0, called d′, are calculated. We use a colored diquark-tetraquark cluster model for the six-quark wave function. A constituent quark model Hamiltonian with a two-body confinement potential, and residual one-gluon, one-pion, and one-σ exchange interactions is used. The complications due to the quark exchange interactions between tetraquark and diquark clusters (Pauli principle) are taken into account within the framework of the resonating group method. The calculated d′ mass is some 350 MeV above the empirical value if the same two-body confinement strength as in the nucleon and Δ is used. This paper also examines the validity of the usual assumption of a universal two-quark confinement strength. We propose that the effective two-body confinement strength in an exotic six-quark system, such as the d′, could be weaker than in a single baryon. The weaker confinement hypothesis leads to a d′ mass of Md′=2092 MeV and a d′ radius of rd′=1.53 fm.A. J. Buchmann, Georg Wagner, and Amand Faessle
Dvostruki beta raspad i veliko ujedinjenje
No full textThe grand unified theories which still have a chance to be true predict preferentially that the neutrino is identical with its antiparticle and therefore that it is a Majorana particle which violates lepton number conservation. Such a neutrino should have a finite mass and also a small right handed weak interaction. If the double neutrinoless beta-decay is observed with the full decay energy in the two electrons, it would establish that the electron neutrino is a Majorana particle. The upper limit of the right handedness of the weak interaction derived from the lower limit of the life-times against the neutrinoless beta decay is IIOpažanje dvostrukog bezneutrinskog beta raspada nepobitno bi dokazalo da je elektronski neutrino čestica Majorana tipa. Pomoću toga je postavljena gornja granica za masu takvog neutrina
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