Forward jet production in deep inelastic ep scattering and low-x parton dynamics at HERA

Differential inclusive jet cross sections in neutral current deep inelastic ep scattering have been measured with the ZEUS detector. Three phase-space regions have been selected in order to study parton dynamics where the effects of BFKL evolution might be present. The measurements have been compared to the predictions of leading-logarithm parton shower Monte Carlo models and fixed-order perturbative QCD calculations. In the forward region, QCD calculations at order alpha_s^1 underestimate the data up to an order of magnitude at low x. An improved description of the data in this region is obtained by including QCD corrections at order alpha_s^2, which account for the lowest-order t-channel gluon-exchange diagrams, highlighting the importance of such terms in parton dynamics at low x.Comment: 25 pages, 4 figure

Study of tau-pair production at HERA

A study of events containing two tau leptons with high transverse momentum has been performed with the ZEUS detector at HERA, using a data sample corresponding to an integrated luminosity of 0.33 fb−1. The tau candidates were identified from their decays into electrons, muons or hadronic jets. The number of tau-pair candidates has been compared with the prediction from the Standard Model, where the largest contribution is expected from Bethe-Heitler processes. The total visible cross section was extracted. Standard Model expectations agree well with the measured distributions, also at high invariant mass of the tau pair. <br/

Measurement of dijet photoproduction for events with a leading neutron at HERA

Differential cross sections for dijet photoproduction and this process in association with a leading neutron, e+ + p -> e+ + jet + jet + X (+ n), have been measured with the ZEUS detector at HERA using an integrated luminosity of 40 pb-1. The fraction of dijet events with a leading neutron was studied as a function of different jet and event variables. Single- and double-differential cross sections are presented as a function of the longitudinal fraction of the proton momentum carried by the leading neutron, xL, and of its transverse momentum squared, pT^2. The dijet data are compared to inclusive DIS and photoproduction results; they are all consistent with a simple pion-exchange model. The neutron yield as a function of xL was found to depend only on the fraction of the proton beam energy going into the forward region, independent of the hard process. No firm conclusion can be drawn on the presence of rescattering effects.Comment: 40 pages, 18 figure

Detailed study of thermal lensing in Nd:YVO4 under intense diode end-pumping

Thermal lensing in diode-end-pumped Nd:YVO4 has been measured for different cooling arrangements and different neodymium concentrations under lasing and non-lasing conditions. The significant effect of energy-transfer-upconversion on lens aberration and beam quality is examined

Study of thermal lensing in Nd:YVO₄ under intense diode-end-pumping

With its natural birefringence and high στf product, Nd:YVO4 is a popular choice as a lasing material for diode pumped solid-state lasers. The short absorption length for pump light at ~809nm relaxes the constraints on diode beam quality allowing tighter pump beam focusing and hence the use of relatively small laser mode sizes. However, in comparison to Nd:YAG it has poorer thermal properties, resulting in strong thermal-lensing, a knowledge of which is essential for optimum laser design. We present the results of a detailed study, considering the effect on thermal lensing in Nd:YVO4 of neodymium concentration, heat-sinking arrangement and laser configuration. The thermal lens powers in end-pumped Nd:YVO4 were determined by measuring the induced phase difference as a function of transverse position using a Mach-Zehnder interferometer, figure 1. The interferometer was also equipped with a set of mirrors to form a stable non-collinear resonator for the Nd:YVO4 crystal to allow thermal-lensing to be investigated under lasing and non-lasing conditions. Figure 1 The interferometer set-up and figure 2 example results. Figure 2 shows the results obtained for 1% and 0.3% Nd-doped YVO4 crystals with cooled faces perpendicular to the c-axis and probe beam polarization parallel to the c-axis. The thermal lens power is ~5 times greater under non-lasing than for the lasing conditions for the 1% doped crystal, which we attribute mainly to additional heating from ETU, further compounded by reduction of thermal conductivity at higher temperature. The much smaller corresponding value for the 0.3% doped crystal indicates the potential benefits to (~2) be achieved with lower Nd concentrations. The results for the perpendicular heat-sinking direction and the orthogonal probe beam polarization, which suggest that thermally-induced stresses play a role in thermal lensing behaviour will also be presented. The results provided by this study allow formulation of a design strategy for further power-scaling of Nd:YVO4 lasers and amplifiers whilst maintaining good output beam quality

The lightwave road show

Education and Training in Optics and Photonics 2003 (SPIE 9663) Tucson AZ 6 Oct In order to change the way that school children view physics, OSA’s University of Southampton Student Chapter has developed an optic roadshow. By taking simple optics experiments and demonstrations to primary schools we aim to dispel the negative image of classroom science and help teachers to convey the fascination of physics