SPIN@U‐70: An Experiment to Measure the Analyzing Power An in Very‐high‐P⊥2 p‐p Elastic Scattering at 70 GeV

The SPIN@U‐70 experiment plans to measure the one‐spin analyzing power An for 70 GeV proton‐proton elastic scattering at large P⊥2 values of 1 to 12 (GeV/c)2. The Michigan frozen NH3 polarized proton target (Solid PPT) should later be installed in the Channel 8 extracted beam‐line of the 70 GeV U‐70 accelerator in IHEP, Protvino. The forward‐scattered protons are detected by small scintillation counters placed at about 9 m from the PPT, while the recoil‐scattered protons are detected by a 35‐m‐long focusing magnetic spectrometer, with a 12 degree vertical bend, placed at 30 degrees to the beam. A tune‐up run for testing the beam and the spectrometer, using a polyethylene target, was carried out in April 2002 at IHEP. The layout and the results of the test run are presented.