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A Compact Focusing DIRC detector for Super-Belle

A Compact Focusing DIRC detector for Super-Belle M. Belhorn, A. Drutskoy, P. Goldenzweig, A. J. Schwartz University of Cincinnati, USA. CHOICES/SOLUTIONS:

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A Compact Focusing DIRC detector for Super-Belle

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  1. A Compact Focusing DIRC detector for Super-Belle M. Belhorn, A. Drutskoy, P. Goldenzweig, A. J. Schwartz University of Cincinnati, USA CHOICES/SOLUTIONS: Babar used narrow (35 mm width) bars; performance of narrow bars for our focusing scheme is hindered by folded hit pattern, must use very good timing to resolve: Babar’s DIRC detector is a proven success – can this detector be adopted for Super-Belle? Not really, absence of gap in magnet yoke to bring quartz+light out prescribes that imaging be done inside magnet ⇒ image must be small. MC simulation track: q(dip) = 20o, f = 0o, p = 4 GeV/c Quartz bar: 17.3 x 35 mm2 x 122.5 cm Focusing mirror: R =265 cm Photon detectors: 10 cm from bar, 6x6 mm2 segmentation (e.g., Burle MCP 85010) STRATEGY: Use focusing to reduce image; this has the advantage of ~eliminating smearing due to bar thickness (as parallel photons are imaged to a point). To reduce space needed, use quartz radiator itself as the “stand-off” medium, i.e., focus at one end of bar, image at the other: Courtesy of U. Hawaii group: Super-Belle • Wide bar unfolds the hit pattern, reducing ambiguities: • (kaon track, p=4 GeV/c, q(dip) = 5o) Hamamatsu H8500 Belle bar width = 3.5 cm (Babar) bar width = 40 cm • ISSUES: • small image needs fine phototube segmentation e.g., Burle/Photonis MCP, Hamamatsu multi-anode • photons displaced from optical axis of spherical focusing mirror • ⇒ spherical aberration, focal point not sharp • photons not paraxial with respect to mirror • ⇒ astigmatism, focal points in x and y separate • long bar length relative to bar width causes photon hit pattern to “fold back” on itself • ⇒ “smile/frown” hit pattern has ambiguities • wide bars are also more economical, as price/bar is driven by edges more than by surface area (cf. discussions with Zygo) ⇒total cost (wide bars) less. • Increased stand-off distance (bar end to image plane) helps unfolds image, reducing demands on timing: (pion track, p=4 GeV/c, q(dip) = 5o) } CT < CX + XT CT < 2CX 2CF < 2CX CF < CX bar width = 10 cm Standoff = 0 (image at bar end) bar width = 10 cm Standoff = 20 cm (from bar end) } Superimpose equivalent kaon hits, clear difference is seen: Now doing more detailed simu-lations, building small prototype

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