Abstract
The repeated passage of a coasting ion beam of a storage ring through a thin target induces a shift in the revolution frequency due to the energy loss in the target. Since the frequency shift is proportional to the beam-target overlap, its measurement offers the possibility of determining the target thickness and hence the corresponding luminosity in an experiment. This effect has been investigated with an internal proton beam of energy 2.65 GeV at the COSY-J\ulich accelerator using the ANKE spectrometer and a hydrogen cluster-jet target. Possible sources of error, especially those arising from the influence of residual gas in the ring, were carefully studied, resulting in an accuracy of better than 5%. The luminosity determined in this way was used, in conjunction with measurements in the ANKE forward detector, to determine the cross section for elastic proton-proton scattering. The result is compared to published data as well as to the predictions of a phase shift solution. The practicability and the limitations of the energy-loss method are discussed.
Highlights
In an ideal scattering experiment with an external beam, the particles pass through a wide homogeneous target of known thickness
The repeated passage of a coasting ion beam of a storage ring through a thin target induces a shift in the revolution frequency due to the energy loss in the target
Since the frequency shift is proportional to the beam-target overlap, its measurement offers the possibility of determining the target thickness and the corresponding luminosity in an experiment
Summary
In an ideal scattering experiment with an external beam, the particles pass through a wide homogeneous target of known thickness. Knowing the characteristics of the machine and, assuming that other contributions to the energy loss outside the target are negligible or can be corrected for, this allows the effective target thickness to be deduced. It is the purpose of this article to show how this procedure could be implemented at the COSY storage ring of the Forschungszentrum Julich. D where d=d is the cross section, the solid angle of the detector, and L the beam-target luminosity This is related to the effective target thickness nT, expressed as an areal density, through.
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