A telescope of three silicon detectors has been installed close to the internal target position of the ANKE spectrometer, which is situated inside the ultra-high vacuum of the COSY-Juelich light-ion storage ring. The detection and identification of slow protons and deuterons emerging from a deuterium cluster-jet target thus becomes feasible. A good measurement of the energy and angle of such a spectator proton (p_sp) allows one to identify a reaction as having taken place on the neutron in the target and then to determine the kinematical variables of the ion-neutron system on an event-by-event basis over a range of c.m. energies. The system has been successfully tested under laboratory conditions. By measuring the spectator proton in the p d to p_sp d pi^0 reaction in coincidence with a fast deuteron in the ANKE Forward Detector, values of the p n to d pi^0 total cross-section have been deduced. Further applications of the telescope include the determination of the luminosity and beam polarisation which are required for several experiments.
@article{arxiv.nucl-ex/0701008,
title = {Spectator detection for the measurement of proton neutron interactions at ANKE},
author = {I. Lehmann and S. Barsov and R. Schleichert and C. Wilkin and M. Drochner and M. Hartmann and V. Hejny and S. Merzlyakov and S. Mikirtychyants and A. Mussgiller and D. Protic and H. Stroher and S. Trusov and P. Wustner},
journal= {arXiv preprint arXiv:nucl-ex/0701008},
year = {2008}
}