C. Biino

Channeling of high-energy particles in bent crystals - Experiments at the CERN SPS

Abstract During the latest decade, experiments have been performed at the CERN SPS to investigate the use of high-energy channeled nuclei in bent crystals for extraction, beam splitting and beam bending. An understanding of channeling in a bent crystal with extraction and deflection efficiencies for different energies, crystal types and ions has been developed. Furthermore, the long-standing question of radiation damage has been addressed with encouraging outcome. This makes extrapolations possible for the construction of, e.g., an extraction device for the LHC at CERN, RHIC at Brookhaven or new splitting elements in high-energy beams.We present the main results obtained and discuss existing and future applications of bent crystals in high-energy physics.

NEW RESULTS FROM THE CERN-SPS BEAM DEFLECTION EXPERIMENTS WITH BENT CRYSTALS

Abstract Results from five distinct bending experiments performed recently in the H8 beam at CERN are presented. Firstly, deflection of a positive pion beam at 200 GeV/c is compared to the “standard” 450-GeV/c proton beam for a bending angle of 3.1 mrad along the (111) plane in a 50 mm silicon crystal. Second, deflection of negative pions at 200 GeV/c is investigated for the same crystal, for incidence along the (111) plane as well as the 〈110〉 axis. Small deflection effects are seen, but no negative particles are bent through the full bending angle of the crystal. Third, the first results from beam deflection at high energy using a germanium crystal are shown. Slightly higher deflection efficiencies than for silicon are seen for large bending angles, but significantly smaller than expected for such a crystal with higher atomic number. Fourth, deflection efficiencies using a strongly irradiated silicon crystal have been measured for the first time, and a small reduction in efficiency is seen in the irradiated region. Finally, deflection of positive particles using axial alignment of a bent silicon crystal has been investigated at 450 GeV/c. Qualitatively similar behaviour as in previous experiments at 12 GeV/c is seen; the beam splits into several beams corresponding to the different planes, and even weak planes are observed.

K/π production ratios from 450 GeV/c protons on beryllium

Abstract This paper reports on the charged K / π production ratios and on the shape of the p T distributions of π fluxes measured by the SPY/NA56 experiment for 450 GeV/c proton interactions on beryllium targets. The present data cover a secondary momentum range from 7 GeV/c to 135 GeV/c in the forward direction and with p T values up to 600 MeV/c. An experimental accuracy of about 3% has been achieved. These results will reduce the uncertainty on the estimation of the ν e component of neutrino beams.

Pair production by 5–150 GeV photons in the strong crystalline fields of germanium, tungsten and iridium

Abstract Experimental results for pair production by 20–150 GeV photons in a Ge crystal cooled to 100 K are presented. The results include total and differential enhancements for incidence of the photons along the (1xa01xa00) plane with angles 0–4.5 mrad to the 〈1 1 0〉 axis. For the first time, a comparison can be made with theoretical results which for incidence along the plane predict pronounced structural changes of a resonance type in the pair production yield as a function of angle to the axis. These changes originate from the coherent interaction with the strong field of the atomic strings in the crystal. Furthermore, results for pair production by 5–55 GeV photons in W and Ir crystals at temperatures between 100 and 300 K are presented. These results are for total enhancements with photons incident along the strongest axes in these materials, i.e. the 〈1 1 1〉 axis in W and the 〈1 1 0〉 axis in Ir. A clear disagreement with theoretical curves calls for improved calculations.

Deflection of 200 GeV/c and 450 GeV/c positively charged particles in a bent germanium crystal

Abstract Experimental results on high-energy beam deflection by means of a bent germanium crystal are presented. Record deflection efficiencies of 60% have been found for 450 GeV/c protons at small angles. The results obtained with 200 and 450 GeV/c positively charged particles are well described by a classical model, giving confidence in predictions for other crystals and different beam momenta.

Enhanced electromagnetic showers initiated by 20–180 GeV gamma rays on aligned thick germanium crystals

Abstract The distribution of the energy released in a silicon detector placed on the downstream side of thick germanium single crystals bombarded by 20–180 GeV gamma rays along directions close to the 〈1 1 0〉 axis or along a random direction has been investigated. A large enhancement of the shower for axial incidence of the gamma rays has been found. The response of the system composed of a germanium crystal and a silicon detector to single gamma rays as a function of their energy has been deduced and compared with existing Monte Carlo simulations.

On the reduced interaction probability for fully stripped 33 TeV/c Pb ions channeled in a bent Si crystal

We compare experimental results and computer simulations on the reduction of inelastic interactions for 33 TeV Pb82+ ions channeled in a bent silicon crystal. The comparison shows that a very small fraction of the initially channeled ions suffer nuclear interactions while traversing the 60 mm long crystal under perfect alignment, even though its thickness would correspond to about 1.2 nuclear interaction lengths for an amorphous material. This result indicates that a bent crystal approach to extraction of high energy, fully stripped ions from e.g. RHIC or LHC might be feasible.

Na59 Experiment at CERN

Na59 Experiment at CERN-SPS aims for obtaining circularly polarized high energy photons (~100GeV) starting from an unpolarized electron beam. The basic principle of operation was predicted in 1962 by Cabbibo and has remained untested up to now. Among other physics goals, Na59 collaboration investigates usage of crystals for high energy photon polarimetry. This paper presents the experiment and summarizes some of the results obtained as of Autumn 2000.