Abstract
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.
Highlights
Future colliders with center-of-mass energies in the tens to even a hundred TeV are under detailed study [1,2]
Cherenkov emission from the Askaryan effect well above any subdominant transition radiation effects, we focused our efforts on using higher energy bunches, in this case 12.16 GeV which was available during our run
It is worth noting that energy resolution is normally quoted for an entire detector system, whicphffiiffiffinffi our case would most likely improve the resolution by N for N detector elements. We fit these data to a standard parametric curve vs shower energy E, and find that the fit is dominated by the 1=E term; for these data we find ΔE=E 1⁄4 0.35E−Te1V for the quadrature response, or ΔE=E 1⁄4 0.23E−Te1V for a single calibrated element
Summary
Future colliders with center-of-mass energies in the tens to even a hundred TeV are under detailed study [1,2]. The coherent microwave and millimeter emission from the latter process was studied in detail in the 1990s in accelerator experiments [14]. In these efforts the difference between Cherenkov and transition radiation becomes indistinct when the track length becomes comparable to the wavelength scale of the frequencies involved, as is the case for our experiment. Tamm assumed open boundary conditions for the radiation; a bounded waveguide structure will modify the results These modifications lessen the direct applicability of Tamm’s theory to our experiment, we will use it as a basis for comparison, because it encompasses both Cherenkov and closely related transition radiation which are the appropriate emission processes in our case
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