Gauge Invariance and the Unstable Particle

It is shown how to construct exactly gauge-invariant S-matrix elements for processes involving unstable gauge particles such as the $Z^0$ boson. The results are applied to derive a physically meaningful expression for the cross-section $\sigma(e^+e^-\to Z^0Z^0)$ and thereby provide a solution to the long-standing problem of the unstable particle.Comment: 8 pages LaTeX. Uses aipproc.sty and epsfig.sty. Talk presented at 1st Latin American Symposium on High-energy Physics, SILAFAE-I, Merida, November 1--5, 199

Complete 2-loop quantum electrodynamic contributions to the muon lifetime in the Fermi model

The complete 2-loop QED contributions to the muon lifetime have been calculated analytically in the Fermi theory. The exact result for the effects of virtual and real photons, virtual electrons, muons and hadrons as well as e+e- pair creation is Delta Gamma^(2)=Gamma_0(alpha/pi)^2[(156815/5184)-(1036/27)zeta(2) -(895/36)zeta(3)+(67/8)zeta(4) +53zeta(2)ln(2)-(0.042+/-0.002)] where Gamma_0 is the tree-level width. This eliminates the theoretical error in the extracted value of the Fermi coupling constant, G_F, which was previously the source of the dominant uncertainty. The new value is G_F=(1.16637 +/- 0.00001) x 10^-5 GeV^-2 with the error being entirely experimental. Several experiments are planned for the next generation of muon lifetime measurements and these can proceed unhindered by theoretical uncertainties.Comment: 9 pages, LaTeX, uses sprocl.sty, amsmath.sty, amssymb.sty and axodraw.sty. To appear in the Proceedings of the IVth International Symposium on Radiative Corrections (RADCOR98), Barcelona, Spain, 8-12 September, 1998, edited by J. Sol

Exploring where Designers and Non-Designers meet within the Service Organisation: Considering the value designers bring to the service design process

Service design is sometimes thought of as the interface between the customer and the service provider, a design process that exists between design thinking and business practices. Service design consultancies working with service organisations are increasingly attempting to develop design thinking alongside business processes within the organisation, but if everyone becomes a ‘designer’ what value is placed on the design-trained service designer? What qualities, knowledge and skills does a designer offer that identifies them as a valuable business asset who has an integral place within the business process, rather than as someone brought in when the organisation wants to be seen to be ‘creative’ or ‘innovative.’ The process of design for services is well documented, however there is not much debate around whether the service designer needs to be design-trained, or of what benefits they would offer if they were. It is assumed that design tools and methods can be introduced and disseminated to non-designers, but if tools and methods are all it took to design services, what is the future for the ‘designer?’ From observations of students studying service design at postgraduate level and a comparative study with design and non-design staff within a service organisation, this paper aims to uncover the value and ‘craft’ of the designer within the context of the service design process

Enhancing the Reflective Capabilities of Professional Design Practitioners

According to Schon (1987), professional education should be centred on enhancing the practitioner’s ability to reflect before taking action. This is important to the designer for two reasons. The first of these concerns real world professional situations, which are rarely clear and lack ‘right answers’, the successful professional requires the ability to learn by doing in order to handle complex and unpredictable problems with confidence. The second concerns the nature of the designer’s relationship with design problems themselves. The designer’s exploration of his/her own awareness develops in parallel with problem definition. Dorst and Cross (2001) describe this as a co-evolution of problem and solution and English (2006) argues that we cannot frame the problem without including in that design space the person who designs. Thus the process of engaging with a design problem involves a journey of self-exploration for the designer who needs to be appropriately equipped for unknown terrain. A distance learning Masters programme was validated in 1999, supporting professional designers to develop as reflective practitioners. The course has run successfully for eight years with students based in Brazil, Canada, UK and Ireland, Holland, Greece, Arab Emirates, Malaysia, Thailand, Hong Kong and China. The author draws on the experience of delivering this programme to describe two approaches that have evolved in parallel to nurture the development of the reflective practitioner. The first of these encourages students to develop an action research process by applying reflective practice models as organising tools and recording templates. The second clarifies direction and focuses action to address fully and precisely the individual student’s aims, insights and motivation. Both these approaches encourage a synergy between practice and theory and involve visual modelling and collaborative reflection through communities of practice. The application of these approaches is shown to generate fundamental insights that positively influence the future actions of students in professional practice. The paper concludes that the consciousness of the expert designer is a critical element of design space and summarises how the disciplined process and clear focus of the approaches discussed contribute to the development of personal confidence and awareness. Keywords: creativity; reflective practice; design process ; design processes</p

Eliminating the Hadronic Uncertainty

The Standard Model Lagrangian requires the values of the fermion masses, the Higgs mass and three other experimentally well-measured quantities as input in order to become predictive. These are typically taken to be $\alpha$, $G_\mu$ and $M_Z$. Using the first of these, however, introduces a hadronic contribution that leads to a significant error. If a quantity could be found that was measured at high energy with sufficient precision then it could be used to replace $\alpha$ as input. The level of precision required for this to happen is given for a number of precisely-measured observables. The $W$ boson mass must be measured with an error of $\pm13$\,MeV, $\Gamma_Z$ to $0.7$\,MeV and polarization asymmetry, $A_{LR}$, to $\pm0.002$ that would seem to be the most promising candidate. The r\^ole of renormalized parameters in perturbative calculations is reviewed and the value for the electromagnetic coupling constant in the $\overline{\rm MS}$ renormalization scheme that is consistent with all experimental data is obtained to be $\alpha^{-1}_{\overline{\rm MS}}(M^2_Z)=128.17$.Comment: 8 pages LaTeX2