Measurement of Spin-Correlation Parameters $A_{NN}$, $A_{SS}$, and $A_{SL}$ at 2.1 GeV in Proton-Proton Elastic Scattering

At the Cooler Synchrotron COSY/Jülich spin-correlation parameters in elastic proton-proton ($pp$) scattering have been measured with a 2.11 GeV polarized proton beam and a polarized hydrogen atomic beam target. We report results for $A_{NN}$, $A_{SS}$, and $A_{SL}$ for c.m. scattering angles between $30°$ and $90°$. Our data on $A_{SS}$—the first measurement of this observable above 800 MeV—clearly disagrees with predictions of available $pp$ scattering phase-shift solutions while $A_{NN}$ and $A_{SL}$ are reproduced reasonably well. We show that in the direct reconstruction of the scattering amplitudes from the body of available $pp$ elastic scattering data at 2.1 GeV the number of possible solutions is considerably reduced.

Figure 1

Schematic overview of the atomic beam target (top) and the EDDA-detector (bottom).

Figure 2

Distribution of the kinematic deficit $\alpha$ for two ranges of c.m. scattering angles. Events with $\alpha >6.25°$, mainly due to inelastic processes or secondary reactions of the final-state protons in the detector, are discarded.

Figure 3

Results for $A_{NN}$, $A_{SS}$, and $A_{SL}$ in comparison to PSA predictions from the Virginia [7] (solution FA00, solid) and Saclay-Geneva [8] (dashed lines) groups as well as data from SATURNE ($A_{NN}$: [21, 22, 23], $A_{SL}$: [24, 25, 26]).

Figure 4

DRSA solutions for some helicity amplitudes without (open) and with (solid) inclusion of the new data on $A_{NN}$, $A_{SS}$, and $A_{SL}$ in comparison to PSA solutions (as in Fig. 3). All amplitudes have been divided by $\sqrt{2{\sigma }_0}=(\sum _{i=1}^5|{\varphi }_i{|}^2+3|{\varphi }_5{|}^2{)}^{1/2}$. The symbols (●, ■, ▲, ▼, and ○, □, △, ◇, respectively) distinguish DRSA solutions, corresponding to different minima of the ${\chi }^2$-function.