The GlueX experiment at Je↵erson Lab has been designed to study photoproduction reactions with a 9-GeV linearly polarized photon beam. The energy and arrival time of beam photons are tagged using a scintillator hodoscope and a scintillating fiber array. The photon flux is determined using a pair spectrometer, while the linear polarization of the photon beam is determined using a polarimeter based on triplet photoproduction. Charged-particle tracks from interactions in the central target are analyzed in a solenoidal field using a central straw-tube drift chamber and six packages of planar chambers with cathode strips and drift wires. Electromagnetic showers are reconstructed in a cylindrical scintillating fiber calorimeter inside the magnet and a lead-glass array downstream. Charged particle identification is achieved by measuring energy loss in the wire chambers and using the flight time of particles between the target and detectors outside the magnet. The signals from all detectors are recorded with flash ADCs and/or pipeline TDCs into memories allowing trigger decisions with a latency of 3.3 µs. The detector operates routinely at trigger rates of 40 kHz and data rates of 600 megabytes per second. We describe the photon beam, the GlueX detector components, electronics, data-acquisition and monitoring systems, and the performance of the experiment during the first three years of operation.

We present the design of the pair spectrometer hodoscope fabricated at Jefferson Lab and installed in the experimental Hall D. The hodoscope consists of thin scintillator tiles; the light from each tile is collected using wave-length shifting fibers and detected using a Hamamatsu silicon photomultiplier. Light collection was measured using relativistic electrons produced in the tagger area of the experimental Hall B.

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The design, simulation, fabrication, calibration, and performance of the GlueX Start Counter detector is described. The Start Counter was designed to operate at integrated rates of up to 9 MHz with a timing resolution in the range of 500 to 825 ps (FWHM). The Start Counter provides excellent solid angle coverage, a high degree of segmentation for background rejection, and can be utilized in the level 1 trigger for the experiment. It consists of a cylindrical array of 30 thin scintillators with pointed ends that bend towards the beam line at the downstream end. Magnetic field insensitive silicon photomultiplier detectors were used as the light sensors.

A Bekesy Ascending Descending Gap Evaluation (BADGE) procedure is described for distinguishing between organic and nonorganic hearing loss. This BADGE procedure involves a comparison of the differences between the following 1 000 cps discrete frequency Bekesy tracing types: (1) continuous tone with tracing begun well below threshold, (2) pulsed tone with tracing begun well below threshold, and (3) pulsed tone with tracing begun well above threshold. These gaps were examined for two groups of 27 each, one containing those individuals judged to display only organic hearing loss and the other containing those individuals judged to display nonorganic hearing loss. Relationships between Bekesy thresholds, differences between Bekesy thresholds, and estimates of “best hearing loss” were examined. The continuous ascending thresholds early in the one minute tracing were found to correlate most closely with the best hearing loss estimates. Correlations between the size of the gaps between tracings and the discrepancy between a Bekesy threshold and the best estimates were low. The nonorganic group more commonly displayed greater, readily visible, gaps between the ascending and descending tracings than did the organic group. The BADGE test is offered as a clinically useful device for differentiating between non-organic and organic hearing losses.