The spin analyzing power A in 28-GeVIc proton-proton elastic scattering was measured at pL2=6.5 (~e~l c )~ using a polarized proton target and a htgh-intensity unpolarized proton beam at the Brookhaven National Laboratory Alternating Gradient Synchrotron. The result of (24 f 8)% confirms that the analyzing power is large and rising in the large-p12 region.
We measured the analyzing power A and the spin-spin correlation parameter A nn , in large-Pi proton-proton elastic scattering, using a polarized-proton target and the polarized-proton beam at the Brookhaven Alternating-Gradient Synchrotron. We also used our polarimeter to measure A at small P] at 13 GeV with good precision and found some deviation from the expected 1/P| ab behavior. At 18.5 GQV/C we found A m = ( -2 ± 16)% at P\ =4.7 (GeV/c) 2 . Comparison with lower-energy data from the Argonne Zero-Gradient Synchrotron shows a sharp and surprising energy dependence for A m at large P\.
We measured the analyzing power A out to Pi =7.1 iGQV/c)^ with high precision by scattering a 24-GeV/c unpolarized proton beam from the new University of Michigan polarized proton target; the target's 1-W cooling power allowed a beam intensity of more than 2x10" protons per pulse. This high beam intensity together with the unexpectedly high average target polarization of about 85% allowed unusually accurate measurements of A at large Pi. These precise data confirmed that the one-spin parameter A is nonzero and indeed quite large at high P±; most theoretical models predict that A should go to zero.PACS numbers: 13.88.+e, 13.85.Dz Polarized beams and polarized targets allow the study of spin effects in high-energy collisions. Using the 12-GeV/c Argonne Zero Gradient Synchrotron polarized proton beam, a large and unexpected spin-spin correlation parameter Ann was found in high-Pi proton-proton elastic scattering.'"^ Our group"* later found evidence for an equally unexpected nonzero analyzing power A in P'^P]^^P'^p at 28 GeV/c at high P\. There has been a strong theoretical belief^"^^ that all spin effects should be small at high energy and large P]_ and that in particular A should then be zero. Because of their small cross section, high-Pi experiments are quite difficult; the fairly large errors in our 28-GeV/c experiment caused concern about the reliability of the nonzero-/! result."^ Our new polarized proton target has a 1-W cooling power, which allows about 4 times more beam intensity than was previously possible; moreover, the target has an unexpectedly high polarization.^"* These two factors along with an improved spectrometer increased the precision of our new measurements by a factor of about 3. The resulting precise data on A in 24-GeV/c p-p elastic scattering confirm the existence of a large one-spin effect at high P]_.The experiment was performed at the Brookhaven Alternating Gradient Synchrotron (AGS) using an extracted 24-GeV/c unpolarized proton beam of about 2x10'' protons per pulse every 2.4 sec. We scattered these protons from the new University of Michigan polarized proton target (PPT), as shown in Fig. 1. The beam position and the 13-mm-diam FWHM beam size at our PPT were monitored continuously by four segmented wire ion chambers S\, 5*2, ^'4, and 3$. Upstream steering magnets were servo-coupled to split segmented wire ion chambers to reduce the horizontal beam motion; the average beam position was kept centered to within about ±0.1 mm. The relative beam intensity was measured using an ion chamber (Ion), a secondary-emission chamber (SEC), and three scintillation-counter telescopes TV, K, and B, which counted the secondary particles produced by the beam.The new polarized proton target used the dynamic nuclear polarization technique in a magnetic field iS) of 5.0 T while operating at a temperature iT) of 1.0 K produced by a ^He evaporation refrigerator. For the target material we used ammonia (NH3) with radiationinduced^"* unpaired electrons. The 2-mm-diam ammonia beads had a hydrogen proton density...
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