Relativistic quark spin coupling effects in the correlations between nucleon electroweak properties
Abstract We investigate the effect of different relativistic spin couplings of constituent quarks on nucleon electroweak properties. Within each quark spin coupling scheme the correlations between static electroweak observables are found to be independent of the particular shape of the momentum part of the nucleon light-front wave function. The neutron charge form factor is very sensitive to different choices of spin coupling schemes once the magnetic moment is fitted to the experimental value. However, it is found rather insensitive to the details of the momentum part of the three-quark wave function model.
Electromagnetic N-->N*(1535) transition in the relativistic constituent-quark model.
We study a light-cone model of the nucleon and the {ital S}{sub 11}(1535) resonance which provides a relativistic generalization of the constituent-quark model in the nonperturbative low-{ital Q}{sup 2} regime. The two parameters of the model, namely, the size parameter {alpha} and the constituent-quark mass {ital m}{sub {ital q}}{approx}300 MeV, are fixed by the axial form factor. We find good agreement for the electromagnetic form factors of the nucleon up to {ital Q}{sup 2}{approx}1--2 GeV{sup 2}. All static properties of the nucleon, except for the neutron charge radius, are reproduced within 10%. In addition, we show that the electromagnetic current of the nucleon is conserved. The {ital S}{sub 11}(1535) transition amplitudes, where gauge invariance is achieved by including a three-body current, are calculated from a constraint-free form-factor set. They are in reasonable agreement with the available photo- and electroproduction data.
Reduction of Surface Flashover of the Beam Screen of the LHC Injection Kickers
The LHC injection kicker magnets include beam screens to shield the ferrite yokes against wake fields resulting from the high intensity beam. The screening is provided by conductors lodged in the inner wall of a ceramic support tube. Operation with increasingly higher bunch intensity, and narrow bunches, now requires improved ferrite screening. This will be implemented by additional conductors; however the good high-voltage behaviour of the kicker magnets must not be compromised by the supplementary screening. Extensive studies and optimisations have been carried out, to better satisfy the often conflicting requirements for low beam coupling impedance, fast magnetic field rise-time, high vacuum and good high voltage behaviour. A new configuration is proposed which reduces significantly the electric field associated with the screen conductors and the secondary electron yield of the surface of the ceramic tube. Results of high voltage test results are also presented.