References - Bogoliubov Laboratory of Theoretical Physics - JINR

C1 C2
π
CH1,2 CH3,4 CH5,6
111 000
111 000
AGCC
π C9
C10
C3 C4
C8
CH11−14
000 111
000 111
PT CH7−10 C7
Figure 1: Schematic top view of the SPIN-P02 setup.
PT
(a) (b)
Figure 2: Deviations from elastic kinematics at various background conditions: (a) - Bg/S ≈0.15, (b)
- Bg/S ≈0.8.
– the difference in c.m. scattering angle for the pion and the proton and Δφ –sumof
their azimuthal deviations from the scattering plane, and two-dimensional distributions
in these variables were filled. For the best background estimate the distributions were fit
with a 2-dim 12-parameter polynomial excluding the area of the elastic peak and the error
matrix was calculated for the obtained fit parameters. The number of the elastic events
was determined as the distribution excess over the background, interpolated to the area
under the peak. To account for the different statistics with opposite target polarization
signs the intensity normalization was done based on the quasi-elastic event counts which
are believed to be unpolarized and represent the main content of the background. Comparison
of the results with various cuts around the elastic peak allowed to make additional
systematic error tests. The selected events were divided into several angular intervals in
θcm and average angle was calculated for each interval according to the individual values
from each event.
The asymmetry P wasmeasuredintheπp elastic scattering in the very backward
angular region of θcm ≈ (150 − 170) o at several beam momenta. The values of the
momentum were intentionally chosen so that the disagreement in the PWA predictions is
most pronouncing in the backward hemisphere. The differential cross section significantly
varies in the measurement regions but always stays very small (� 0.1 mb/sr). Dependent
366
C6
p
C5