There exists a possibility to improve the momentum resolution by inserting special emulsion plates in the tracking section of each module. At the same time, the tracking section can then be made shorter, allowing for more target mass.
In the TENOR approach [34], each module is about 60 cm long. In this design, a module (Fig. 13) consists of:
- one target emulsion stack; - a triplet of emulsion plates; one emulsion plate, similar to those previously described, is placed just behind the target emulsion stack, a second one is located immediately in front of the following target emulsion stack, and a third is placed halfway between the first two outer plates. The middle plate determines a high precision space segment; this information, combined with that from the other two plates, allows momentum analysis by means of a sagitta measurement in the gap between consecutive stacks. The first plate also has the additional task of precisely locating the track in the target emulsion. - a pair of silicon detector planes placed behind the first plate, to improve the track location in this emulsion sheet; - electronic trackers consisting of honeycomb chambers each about 4 cm thick and measuring one of the x,y or inclined (u,v) coordinates.
Figure:
The layout of a target module in TENOR.
With the angular measurement in the two outer plates alone one can estimate a momentum resolution:
in addition to a 2% contribution from the multiple scattering in the emulsion plates and in the electronic trackers.
The use of all information (angle and position) in all three plates
improves the resolution.
The relative alignment of the plates is performed using high-energy
halo muons, and the alignment methods (and their requirements) have to
be studied carefully. Assuming a precision (5 
m) about a factor
five worse than the intrinsic resolution of the emulsion, and
given the 51 cm total distance, we obtain a momentum resolution:
The total contribution of the Coulomb scattering to the momentum resolution amounts to about:
by combining quadratically the
position measurement and the multiple scattering contributions.
In the momentum range of interest, the Coulomb scattering is such that
the resolution does not depend
critically on the assumed measurement errors.
Even in the conservative case of a 20 m precision,
the total momentum resolution stays below 10% up to 30 GeV/c.
The requirements
on the relative plate alignment and on the spatial resolution thus appear
to be within the experimental capabilities.