Measurement of the absolute differential cross section of proton–proton elastic scattering at small angles

Abstract

The differential cross section for proton-proton elastic scattering has been measured at a beam energy of 1.0 GeV and in 200 MeV steps from 1.6 to 2.8 GeV for centre-of-mass angles in the range from 12 • -16 • to 25 • -30 • , depending on the energy. Absolute normalisations of typically 3% were achieved by studying the energy losses of the circulating beam of the COSY storage ring as it passed repeatedly through the windowless hydrogen target of the ANKE magnetic spectrometer. It is shown that the data have a significant impact upon a partial wave analysis. After extrapolating the differential cross sections to the forward direction, the results are broadly compatible with the predictions of forward dispersion relations.

The legacy of the experimental hadron physics programme at COSY

“…The energy dependence of the ANKE measurements of the pp elastic differential cross sections [78] can be seen most clearly in terms of the four-momentum transfer t and the results at the eight energies are shown in Fig. 24.…”

“…angles below about 30 • . To fill some of the void left by EDDA in this region, measurements of the unpolarized differential cross section [78] and proton analyzing power [63] have been carried out at small angles at several discrete energies at the ANKE facility.…”

“…[mb] 25. Scaled ANKE proton-proton elastic differential cross sections at 1.0, 2.0, and 2.8 GeV with statistical errors [78] compared to the SAID SP07 solution [65] and a "new" partial wave solution where the ANKE data have been taken into account. For presentational reasons the 2.0 and 2.8 GeV data and curves have been reduced by factors of 0.5 and 0.25, respectively.…”

“…Before extrapolating to t = 0 the data have to be corrected for Coulomb effects. In the Gatchina case this was done by adding a spin-independent Coulomb amplitude [80] whereas the "new" SAID fit with and without Coulomb provided a means to correct the ANKE data [78]. Both sets of extrapolated values are shown in Fig.…”

“…26 and the agreement of the ANKE results with the theoretical [81] for the values of the forward pp elastic differential cross section (solid line), the corresponding lower limit provided by the spin-independent optical theorem being indicated by the broken line. The extrapolated ANKE data are shown with their quoted errors by the (blue) circles [78], whereas the (red) squares are the published Gatchina values obtained with the IKAR recoil detector [80].…”