Performance measured with test beam and status

The efficiency and resolution of the drift chamber filled with Ar-Ethane 50/50 gas were studied with converted $e^+ e^-$ from $\gamma$-rays at LNS. Converted $e^+ e^-$ pairs were separated by the dipole magnetic field, and the particles could be momentum analyzed. Figure 57 shows efficiency curves for typical layers. It can be seen that the plane efficiency is almost 100% with HV of $< -2100$V. Figure 58 shows momentum sliced spatial resolution for straight wires (xx'). There exists no significant dependence on the momentum and $\sim250 \mu$m (rms) layer resolution was achieved. The information was converted to the position and angle resolutions in horizontal (X) and vertical (Y) directions (table 18). It should be emphasized that the basic analysis routine of this drift chamber was already developed (figure 59) and it can be incorporated into the E01-011 analysis program.

表 18: Position and angular resolution in horizontal (X) and vertical (Y) directions

Position (X)	86 $\mu$m (rms)
Position (Y)	210 $\mu$m (rms)
Angle (X)	0.7 mrad (rms)
Angle (Y)	2.8 mrad (rms)