Picosecond timing of Microwave Cherenkov Impulses from High-Energy Particle Showers Using Dielectric-loaded Waveguides

We report on the first measurements of coherent microwave impulses from high-energy particle-induced electromagnetic showers generated via the Askaryan effect in a dielectric-loaded waveguide. Bunches of 12.16 GeV electrons with total bunch energy of $\sim 10^3-10^4$ GeV were pre-showered in tungsten, and then measured with WR-51 rectangular (12.6 mm by 6.3 mm) waveguide elements loaded with solid alumina ($Al_2 O_3$) bars. In the 5-8 GHz $TE_{10}$ single-mode band determined by the presence of the dielectric in the waveguide, we observed band-limited microwave impulses with amplitude proportional to bunch energy. Signals in different waveguide elements measuring the same shower were used to estimate relative time differences with 2.3 picosecond precision. These measurements establish a basis for using arrays of alumina-loaded waveguide elements, with exceptional radiation hardness, as very high precision timing planes for high-energy physics detectors.Comment: 16 pages, 15 figure

How Youth of Color Create Communities of Hope: Connecting Advocacy, Activity, and Neighborhood Change

The primary aim of this paper was to assess the association of after-school club characteristics with changes in physical activity, nutrition, and attitudes in students of color after participating in the "YEAH!" Advocacy-based Physical Activity Program. We examine the strengths of school-based vs. non-school based programs in promoting feelings of self-efficacy and empowerment among students learning to become more physically active-and importantly, also test the strength of how programs that are more connected (to community-based partners) may contribute to students' optimism around policy and public health as it directly affects them. This study examined differences in the youth advocacy training impact across four after-school club types: school-based with community partnerships, school-based without partnerships, non-school-based with community partners, and non-school-based clubs without partnerships. We measured improvements in youth's "optimism for change", "assertiveness" and "decision-making" as related to after school activities and found that non-school-based programs with community partners showed highest positive impact