Electroweak production of hybrid mesons in a flux-tube simulation of lattice QCD

We make the first calculation of the electroweak couplings of hybrid mesons to conventional mesons appropriate to photoproduction and to the decays of B or D mesons. E1 amplitudes are found to be large and may contribute in charge exchange gammap-->nH(+) allowing production of (among others) the charged 1(-+) exotic hybrid off a(2) exchange. Axial hybrid meson photoproduction is predicted to be large courtesy of pi exchange, and its strange hybrid counterpart is predicted in B-->psiK(H)(1(+)) with branching ratio B approximately 10(-4). Higher multipoles and some implications for hybrid charmonium are briefly discussed.     

On the ω dependence of exclusive hadronic final states in lepton-hadron scattering

A framework is presented for studying the ω dependence of exclusive hadronic final states in lepton-hadron scattering (ω being Bjorken's scaling variable 2Mv/Q²). This is used for the analysis of K∫, KΛ, πN and πΔ final states.     

Do electromagnetic form factors and deep elastic scattering measure the number of quarks in a hadron?

By studying field theory examples we examine the claim that dimensional arguments relate the q² dependence of electromagnetic form factors and the s-dependence of large-angle scattering to the number of constituents in the systems involved. The relationship with various models in the literature is discussed.     

Multi-meson exchange in non-Abelian gauge theories

We find a new sum rule for the residue of the J = 0 fixed pole in Compton scattering. The sum rule applies to any target and links the residue to a calculable set of contributions from the resonance region. We discuss proton, neutron, deutron and pion targets and the possibility of discriminating from previous models. The relationship with the parton model is noted and the feasibility of measuring pion photoabsorption cross sections is discussed.     

Limit to minimally destructive optical detection of atoms

All optical techniques used to probe the properties of Bose-Einstein condensates have been based on dispersion and absorption that can be described by a two-level atom. Both phenomena lead to spontaneous emission that is destructive at the low energies involved with ultracold atomic systems. Recently, both were shown to lead to the same limit to the signal to noise ratio for a given destruction. We develop a new method for calculating the phase shift of a laser beam and show that no single-pass optical technique using classical light and a three-level atom can exceed this limit. This puts significant restrictions on potential nondestructive measurement schemes.     

The UV-absorption of europium atoms embedded in helium nanodroplets

We have measured the UV-absorption spectrum (4f→5d transitions) of single europium atoms embedded in helium droplets using a beam depletion technique. The electronic levels involved in the transition lie spatially within the closed 6s₂ shell leading to significant shielding from the surrounding helium environment. We observe the narrowest absorption lines ever reported in liquid helium and compare our data and experimental method, with experiments carried out in bulk liquid helium.     

The new particles and their significance

In November 1974 a dramatic revolution occurred in high-energy physics when two teams of workers independently discovered a massive subatomic particle named the J or ψmeson (Aubert et al. 1974, Augustin et al. 1974). Within two years the leaders of these two teams (B. Richter and S. C. C. Ting) had been awarded the Nobel Prize for physics. This alone bears testimony to the significance of the discovery. In this article I hope to be able to explain why this discovery was so significant, how it opened up a new conception of the sub-atomic world and describe some of the related discoveries and developments that have been made in the subsequent four years.