2 The CDF Experiment at Fermilab Contents - Harvard University ...

Section 2: Central Muon Extension 31
\wedgelets" which cover 5 each. These chambers will lie in a plane tilted 30 with respect
to the vertical. In all respects their performance should be the same as the rest of the
CMX system. In particular, the preampliers are the same as are the ASD's and TDC's.
By design the trigger will not distinguish between the arches and the miniskirt; they must
appear to be part of one homogeneous detector.
The miniskirt wedgelets must be supported on a stand. Unfortunately, the original plans
will not work, and so a complete redesign is in progress. The main constraints come from the
access required by other detector systems, including the CMP and the central calorimeter.
The new stand must allow access for quick repairs during the run, which makes its design
challenging. Moreover, allowance has to be made for thick cooling water pipes servicing the
silicon vertex detector.
This Summer one quadrant of the miniskirt will be assembled at Fermilab. After uncovering
the diculties of assembly, we will produce the remaining quadrants in order to be
ready for installation in 2000.
With the CMX complete, the increase in data potentially is quite large. Taking inclusive
W 's as an example, the CMUP+CMX sample is 57% larger than the CMUP sample. Plugging
the gaps in coverage amounts to an increase of 11% for central muons (jj < 1), and
leaves only 6.9% uncovered.
The CMX arches functioned well in the last run, as far as identifying muons is concerned.
There were major diculties with the CMX trigger, however. The basic problem was exposure
to soft particles scattered at large angles from the beam pipe and the forward detector
systems. Since the calorimetry did not shield the CMX from particles coming from the forward
direction (opposite to the interaction region), triggers from true muons were swamped
by fake triggers. Several measures were introduced to ght this problem. First, the beam
pipe was made thinner. Second, some activity in the hadron calorimeter indicative of a
through-going minimum-ionizing particle was required. Finally, the timing information from
the scintillators was fully exploited, to dierentiate between the time required for a muon to
reach the CMX from the interaction point and the time required for the fast particles from
the interaction point to hit the forward detectors and scatter debris back upinto the CMX.
Despite these eorts, the rate for the inclusive CMX muon trigger was till too high.
A fraction of the data, adjusted according to the instantaneous luminosity, was discarded
online, in order to not exceed the trigger bandwidth. This so-called \dynamical prescaling"
strongly reduced the collected data; we want to eliminate the need of dynamical prescaling