Woodwork

February, 1938."Cooperative Extension Work in Agriculture and Home Economics, University of Missouri, College of Agriculture and the United States Department of Agriculture cooperating."Title from cover

Precision Electron-Beam Polarimetry using Compton Scattering at 1 GeV

We report on the highest precision yet achieved in the measurement of the polarization of a low energy, $\mathcal{O}$(1 GeV), electron beam, accomplished using a new polarimeter based on electron-photon scattering, in Hall~C at Jefferson Lab. A number of technical innovations were necessary, including a novel method for precise control of the laser polarization in a cavity and a novel diamond micro-strip detector which was able to capture most of the spectrum of scattered electrons. The data analysis technique exploited track finding, the high granularity of the detector and its large acceptance. The polarization of the $180~\mu$A, $1.16$~GeV electron beam was measured with a statistical precision of $<$~1\% per hour and a systematic uncertainty of 0.59\%. This exceeds the level of precision required by the \qweak experiment, a measurement of the vector weak charge of the proton. Proposed future low-energy experiments require polarization uncertainty $<$~0.4\%, and this result represents an important demonstration of that possibility. This measurement is also the first use of diamond detectors for particle tracking in an experiment.Comment: 9 pages, 7 figures, published in PR

Wearable computing: Will it make people prosocial?

We recently reported that people who wear an eye tracker modify their natural looking behaviour in a prosocial manner. This change in looking behaviour represents a potential concern for researchers who wish to use eye trackers to understand the functioning of human attention. On the other hand, it may offer a real boon to manufacturers and consumers of wearable computing (e.g., Google Glass), for if wearable computing causes people to behave in a prosocial manner, then the public's fear that people with wearable computing will invade their privacy is unfounded. Critically, both of these divergent implications are grounded on the assumption that the prosocial behavioural effect of wearing an eye tracker is sustained for a prolonged period of time. Our study reveals that on the very first wearing of an eye tracker, and in less than 10 min, the prosocial effect of an eye tracker is abolished, but by drawing attention back to the eye tracker, the implied presence effect is easily reactivated. This suggests that eye trackers induce a transient social presence effect, which is rendered dormant when attention is shifted away from the source of implied presence. This is good news for researchers who use eye trackers to measure attention and behaviour; and could be bad news for advocates of wearable computing in everyday life