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The PHENIX Muon Tracker
Abstract
The PHENIX south muon spectrometer is nearing completion. We expect to commence data collection at the beginning of the next RHIC run in May 2001. This detector system will provide general muon
tracking measurements. Processes to be studied include Drell/Yan, J/Psi and other heavy vector mesons, and open heavy flavor. This includes measurements with ion beams, p-A collisions, and polarized p-p
collisions.
The south muon tracking system contains approximately 20,000 channels of tracking chamber cathode strips and associated front-end electronics. Using cosmic ray data we have achieved 100 micron
spatial resolution in the tracking chambers with an RMS noise level of less than 2mV in the front-end electronics.
Simulated
signals in the
muon arms of
single muons
from various
channels.
PISA Geometry for the Muon Arms.
Momentum resolution for the north(top) and south(bottom) muon arms.
Acceptance for Drell-Yan
events in the central (red
line) and muon arms
(blue and black lines).
A reconstructed PISA track in the north muon arm.
Simulated di-muon signals for the muon arms (1 RHIC
year at design luminosity).
Physics Capabilities
These plots describe the physics
capabilitites and kinematic coverage
of the muon arms. Substantial modeling
has been done to predict signals from
single and di-muons in the muon tracking
system. Out resolution goals are
- resolve phi from rho+omega
-resolve J/psi from psi’
-resolve Upsilon(1S) from Upsilon(2S+3S)
Muon Tracker Overview
The PHENIX Muon Arms detect vector mesons decaying into muon pairs, allow the study of the Drell-Yan process, and provide
muon detection in semileptonicdecay of open charm, in the relativistic heavy ion and spin physics programs of PHENIX.
Each muon arm must track and identify muons, as well as provide good rejection of pions and kaons; therefore, both a Muon
Tracker (µTr) and a Muon Identifier (µID) are needed. Each arm of the Muon Tracker is comprised of three stations of tracking
chambers, mounted inside the end-cap muon magnets. Stations 1 and 2 have three chamber gaps with two cathode planes read
out in each gap and station 3 has two chamber gaps. Various stereo and non-stereo angles are used at each station to allow for
maximal rejection of ghost intersections of cathode hits. Two different construction techniques are being used for the µTr
chambers: the first and last stations are constructed as honeycomb panels with cathode strips on the inside surfaces and the central
stations are constructed as stacks of wires and etched metallized foils attached to aluminum frames. The muon identification system
follows the muon tracker and is comprised of 6 steel plates interspersed with Iarocci tubes. The first absorber plate also functions as
the backplate of the muon tracker magnet. A cutaway view of the North muon arm is shown below. In this picture you can see the
conical shaped magnet with three tracking stations, followed by the muon identification system.
Instrumentation
These plots demonstrate the performance
of the south muon tracker chambers and
electronics. In constructing the muon
tracking system, we were challenged to
provide 100 micron resolution with less
than 0.6fC of noise (less than 1.5 ADC
counts after pulse amplification and
digitization) in the front end electronics.
Efficiency of
a station 2
chamber for
different gas
mixtures.
Plot of input calibration DAC
vs. digitized ADC value of the
induced pulse on the cathode
strip for several channels.
Pulse sharing between adjacent cathode strips for a single
cosmic ray event. The injected charge is converted to the
pulse shapes above by a 3-stage preamplifier chip.
100 micron resolution obtained
with production electronics and
station 2 chamber. X axis shows
CSC residuals.
Cosmic ray
spectrum
obtained from
production
electronics
and chambers.
RMS noise for all
station 1 electronics. Design
spec is about 1.5 ADC counts.
RMS of pedestal
values for several
channels of
electronics. The
design spec of
about 1.5 ADC
counts has been met.
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