Small-Angle Elastic Scattering of High-Energy Protons from Hydrogen

Abstract

We present the results of an experiment performed at the Brookhaven AGS to measure highenergy p-p scattering in the range of laboratory angle 2 to 20 mrad. Elastic scattering events were separated by momentum analysis. The prime purpose of the experiment was to investigate Coulomb interference effects. The range of incident particle momentum studied was 8 to 18 BeV/c.The apparatus is shown in Fig. 1. A smallangle secondary beam from the AGS was momentum analyzed (±0.8% half-width at halfmaximum) and focused on a liquid hydrogen target 18 in. long and 4 in. in diameter. The beam was defined by the scintillation counter S2 and the scintillation counter hodoscopes #02 and #03. The incident particle was selected by the differential Cherenkov counter C, 1 and its angle was measured to ±0.3 mrad (halfwidth at half-maximum) by #02 and #03. Each hodoscope was made up of \ in. wide scintillation counters in 4-element x4-element twodimensional arrays. The hodoscopes H02, #03, and #2 determined the horizontal projection of the scattering angle to ±0.4 mrad while #02, #03, and #4 determined the vertical projection to ±0.4 mrad. The momentum of the final particle was measured to ±0.8% with #03, #2, and #4. Hodoscope #2 comprised 80 counters, each | in. wide x 6 in. high. The 120 vertical elements of #4 were each | in. wide x 13 in. high and the 24 horizontal elements were each | in. high x 61 in. long. The absolute ELECTRONICS TRAILER # 2 ^MOMENTUM ANALYZED BEAM FROM AGS DEFLECTING MAGNETS FIG. 1. The experimental arrangement.mean momentum of the incident particles was determined to within 0.2%.The trigger system included the counters L2 and the sum of the outputs of the vertical elements in #4. L2 excluded the unscattered beam and #4 limited the range of momentum of the scattered particle. On a fast (~20-nsec) coincidence between these counters and a selected beam particle, 192 fast discriminator gates (-40 nsec) were opened and signals were detected from those counters which had fired. This information was then transferred to a buffer memory and, approximately 15 /usee later, the system was ready to accept another event. A signal from a ring counter (ANTI) behind the hodoscope #02 was fed into the buffer memory at the same time so that the program could reject those events with an extra particle passing through the collimator but outside of #02. The data-handling system was similar in principle to that described in earlier publications. 2 However, a new buffer memory with about 65 times the capacity 3 of the early system was used to take advantage of the high event rates available in this experiment. At the end of an AGS burst the information stored in the memory was transferred in parallel to magnetic tape and, via coaxial cables, to the Merlin computer. During the runs the computer analyzed events and stored them in a two-dimensional array of events versus angle and momentum of the scattered particle. At the end of each run the computer subtracted the inelastic background by linear interpolation and calculated the differe...

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