1. Design and First Results of a Cosmic Ray Telescope For Use In Testing a Focusing DIRC M. P. Belhorn University of Cincinnati The BELLE group at the University of Cincinnati has been studying various designs of a Focusing Detector of Internally Reflected Cherenkov radiation (DIRC) for use in particle identification systems at e + e - "B factory" experiments. In particular the UC BELLE group is concerned with the development of a focusing DIRC to replace the Aerogel Cherenkov Counter already in use in the BELLE experiment in either an intermediate upgrade to the detector or for a Super-KEKB major upgrade. The proposed detector would be used for pion-kaon separation of tracks having momenta p < 5 GeV/c. The design of a focusing DIRC is based off of work started by J. Va'vra and B. Ratcliff at SLAC. The process of developing a working prototype focusing DIRC at UC requires a means of testing its functionality in order to compare the working model to the currently implemented PID system. Since there is no accelerator facility at our disposal here, the chosen solution is to use cosmic rays as the source of charged particles for studying the resolution and other characteristics of the prototype focusing DIRC. The Cherenkov cone produced by a charged particle traveling at a rate greater than the phase velocity of light through a dielectric has a central angle dependent on the speed of the particle while the image of that cone produced on the device's detector surface will depend on the total velocity. It is therefore critical to know the trajectory of the charged particle track that produces a particular Cherenkov ring image in the DIRC to correlate the image with a specific speed (not the total velocity). Since we are using cosmic rays to test our DIRC prototype and not a beam of particles with known velocity it is necessary to build a device that measures the trajectory of cosmic rays through the DIRC. This device is known within the UC BELLE group as a cosmic ray telescope (CRT). In the final prototype focusing DIRC, the CRT will operate in multiple roles providing cosmic ray trajectory information, cosmic ray counting, and it will function as a fine trigger for DIRC readout. WHY BUILD A CR TELESCOPE? DESIGN & COMPONENTSFIRST RESULTS The CRT is uses two groups (one is pictured below) of scintillating optical fibers to track particle positions. The fibers ultimately form two 32x32 mm 2 planes formed by orthogonal fibers. As a charged particle passes through both planes, four fibers illuminate. Using 2 64 anode PMT arrays, we can determine which fibers illuminate giving us the trajectory of the particle. The timing of signals with respect to a trigger differentiate particles from noise. The basic components of the CRT are: 1.) Scintillating Optical Fibers (Bicron BCF-10) 2.) A Chassis (Designed and built within UC Dept. of Physics) 3.) Multi-Anode PMT Arrays (Hamamatsu H8500) 4.) Preampliers/Signal Discriminators (Phillips Scientic 6816) 5.) A NIM Triggering Device (several components) 6.) A Time-To-Digitial Converter (Caen V1190A TDC) 7.) Data buffer and USB Controller (Wiener P&B VM-USB) 8.) A PC The first data runs of the CRT are used to discover the operating parameters of the device. This includes fine-tuning the trigger and signal thresholds, optimizing the matching window, checking for faulty wiring or dead channels, and comparing results to accepted values for the cosmic ray flux rate. Below is are plots (upper left & upper right) that identifies the signal peak of all hits (left) and cosmic rays (right) with respect to the trigger time (red line at 500 ns). With this information, we can reduce the matching window to a region localized at the signal peak to simplify the reconstruction of track trajectories in events with a large number of hits. The plots at the bottom of this poster identify hit rates and can be used to adjust threshold levels. They also indicate 2 malfunctioning channels. The signal feed from the H8500 PMTs is conditioned by eight PS6816 preamps, which check for noise threshold crossing and convert PMT pulses to ECL logic pulses. These ECL signals are fed into the Caen V1190A TDC, which continuously records them within a 800 ns wide matching window until a trigger is received. The CRT is triggered by two scintillating paddles that intersect the acceptance cone above and below the device. Signals from these paddles are checked for threshold crossing above background noise and then checked for coincidence (within 5ns). If coincident, a TTL high signal is sent to the Caen V1190 TDC. When triggered, the CRT dumps all data signals stored in the matching window buffer to an output buffer that can be read via USB. The data is analyzed on the PC to reconstruct the track trajectory. A group of scintillating fibers outside the chassis. The trigger logic block. It consists of two Ortec 473A discriminators, a LeCroy 622 coincidence comparator and a logic converter (NIM->TTL) The software used to communicate with the TDC over the VMEbus was written as part of this project. It was one of the most challenging parts of the construction of the CRT. Its success has prompted the manufacturer of the VMEbus (Wiener P&B) to direct regional questions about the operation of the TDC on their equipment to the BELLE group at UC. The TDC and VMEbus crate. Also visible (at the top) are the PS6816s This information organizes the number of events by the independent Hits variable. This allows us to fine tune data analysis to remove noise or cosmic ray showers. The particle transit times through the CRT. Note that the peak has a width of ~5 ns. This is due to the fluorescent decay time of the Bicron fibers (2.7 ns decay constant)