Muon A-phi Scintillation Trigger Counters

New scintillation counterslocated between the magnet and calorimeter in the centralregion have been constructed for the Run II D0detector. These "a-phi" counters will be used to give a fasttime stamp (a few nanoseconds) on particles passing throughthem, and will aid in triggering on muons. They are 33 incheslong, and come in three widths: 9.25, 11.00 and 14.63 inches.The different widths are so that each counter spans about thesame 4.5 degrees in phi. The 270 narrow counters were builtat NIU by Hedin and students while the 144 medium width, and 216 wide a-phi counters were constructed at the Institute forTheoretical and Experimental Physics in Moscow. All counters werethen tested at D0 with their final tubes and basesbefore installation on the detector in April 1999.

The construction of the a-phi counters (see photos ) starts with 1/2 inch Bicron scintillating plastic, with grooves forreadout fibers cut into each half of the counter. The fibers are used to collect scintillation light and carry it to a photomultiplier tube (PMT). The attenuation length was typically 3 m, and each fiber roll was tested to ensure it had good light collecting properties. Placing the phototube in the middleof the counter minimizes thge time variation of the light carriedby the fibers. Six individual fibers are epoxied intoeach groove, and then all the fibers from the 10-16 grooves/counter arecombined into one bundle which directs light to the PMT.The ends of the counters are polished and covered with a mirrorlikemetal plate, and the entire counter itself is covered with whitereflective paper to maximize the amount of light transmitted by the fibers.Finally, the entire assembly is wrapped with an opaque plastic film,and placed inside a light-tight aluminum case.

We completed the construction of the a-phi counters in October 1998. NIU students Dale Beutel, James Raskowski, Kristy Sipe, Kristina Lehmann, and Cullen Nicholson participated in counter assembly. Counters were tested for light tightness and efficiency as the last step in the assemblyprocess. Counters were retested using their assigned photomultiplierbefore installation on the D0 detector.