πM1 Beam Line

πM1 is a high resolution pion beam line with a momentum range between 100 and 500 MeV/c. It is attached to the target station TM at an extraction angle of 22°, which corresponds to the orientation of the target wheel. Because of this, the spot where the pions are produced is horizontally as small as the target width of 2 mm. Together with the high dispersion of 7 cm/% and a magnification of 1 at the intermediate focus (IF) about half way between the production target and the end of the beam line, a momentum resolution of better than 0.1 % is achieved. The pion momentum can be determined from the hits in a hodoscope made of 64 scintillators strips, located at the intermediate focus. The characteristics of the beam line are listed in the following table.

A layout of experimental area and of the magnetic components are shown in Fig 1 and Fig 2

Table 1 : Characteristics of the piM1 beam line

Fig 3 gives the measured particle fluxes for the standard beam-line tune as a function of momentum with an uncertainty of 10% at the peak of the yield curves. The flux of muons is 100 times smaller than the corresponding pion flux at momenta around 300 MeV/c, and falls more slowly than for the pions toward low momenta. Since πM1 is the only beam line with a vacuum system separated from the proton-channel vacuum by a thin window, there are no "surface" muons available.