Saturday, February 6, 16
NSW Detector construction requirements working group:
C. Amelung, C. Bini, P.-F. Giraud, G. Iakovidis, P. Iengo, M. Iodice, D. Lelouch, G.
Mikenberg, L. Pontecorvo, P. Schune and S. Vlachos.
From studies of the current muon spectrometer it turns out that in order to maintain
excellent muon momentum reconstruction a transverse momentum (pt) should be
measured with a resolution better than 15% for 1 TeV muons. This translates to a
chamber construction accuracy (σchamber) of approximately 40 μm considering the 16
measurement planes with a resolution of 100 μm per plane (for comparison the MDT
design value for σchamber was 20 μm). The σchamber includes both contributions from
readout strip position accuracy and planarity of readout and drift planes accuracy.
These requirements translate to the following list for any NSW detector.
Recommendations for the construction precision of any NSW chamber:

For every detector plane, the position along the precision coordinate should be
known with an RMS error of less than 30 μm. This requirement applies equally to
the position of the detector strips as well as that of the alignment sensor base-plates.
 The position of any chamber element on the coordinate perpendicular to the above
precision coordinate should be known with an RMS error of less than 80 μm. This
combines planarity of detector planes where the RMS is evaluated with respect to
the nominal element position, including nominal thickness as well as parallelism
between plane faces. (How the actual precision is split among these terms is of no
importance). The positioning precision should be achieved for planes of a complete
detector quadruplet. Consequently planes of any single detector element should be
positioned as well with 80 μm precision or better.
All above requirements refer to a chamber/plane lying flat on a granite table.
Deformations due to gravity, temperature, humidity, gas pressure etc. when the detector
will be installed and used in ATLAS should be described by an appropriate model.
Furthermore, in addition to the above requirements, a maximum deviation of 100 μm
and 200 μm is permitted for the above two variables respectively. All measurements
should have a high statistical significance and therefore a few points along a strip should
be measures. It is suggested that at least five points per strip (e.g. the two endpoints, the
center, and two points half-way between endpoints and center), and a reasonable
fraction of all strips (a few percent) is measured.

As far as stereo strips are concerned, the performance requirements described
above translate to a positioning precision of the stereo strips crossing points of 30
μm along the precision coordinate and 80 μm perpendicular to that one. All the
other details of the previous paragraph apply here as well.

In order for the inplane alignment system to measure well the deformation of the
read-out planes, mechanical continuity should be provided between these planes
and the alignment devices

MM specific: The deviation of the drift gap size from its nominal value (5 mm)
should be less than 100 μm (RMS) anywhere in a chamber.
It should be noted that the above is not a complete specification set for building a NSW
detector accurately. Other considerations, such as requirements of the precision needed
for the MM pcb assembly (including the mesh positioning accuracy and the alignment
between resistive and read-out strips) or alignment between detector quadruplets, the
thickness of the detector in radiation lengths etc have still to be taken into account.