S5-73/206
CYLINDRICAL PROPORTIONAL WIRE CHAMBERS FOR VERTEX DETECTION
R. M. Edelstein
Carnegie -Mellon University
A suggested layout of vertex detectors for the proposed NAL spectrometer system is shown
in Fig. t.
This s.rray is motivated by the need for
t . essentially 4n geometrical detection eftlciency
2.
adequate momentum resolution
3.
ultimate event rate capability.
The detectors shown are all proportional wire chambers in a dipole magnetic field.
In order to
achieve "41T" detection efficiency the planar chambers downstream from the target are supplemented by a cylindrical proportional wire chamber system coaxial with the beam and surrounding
the target.
The cylindrical system is intended to yield both transverse and longitudinal track
coordinate information through the stereo provided by nonaxial wires, that is, wires at finite
angles to the beam direction.
Although cylindrical proportional wire chambers with axial wires
have been constructed, there is no information yet in the literature on chambers with nonzero
pitch angles. t
There are two important problems to solve in these chambers:
1. Nonaxial wires.
Straight nanaxial wires form a hyperboloid of one sheet.
from the axis is not constant ae illustrated in Fig. 2.
The distance
One solution to this problem is for the pitch
angle for each surface of revolution to vary in such a way as to maintain these surfaces approximately parallel locally.
Since the sense of the pitch angle is immaterial in generating a surface,
by alternating the sense one can obtain stereo information.
angles alternates, the net torque on the end rings is zero.
small so that for
ends.
Ii
Also, since the sense of the pitch
The pitch angle would necessarily be
given surface the diameter at the waist is not too different from that at the
The pitch angles can be increased in order to improve the stereo angle by adding support
rings at intervals along the axial direction.
These can be small in crOElS section and light weight
so the dead Bpac e and multiple scattering are small.
2.
Supporting the modules.
The support structure for the modules would have to be
worked out in detail. One imagines each module to be self contained with six wire-generated
surfaces, hence two surfaces pf sense wires.
Each module could be supported by an inner and
outer cylinder of aluminum, foam, or paper honeycomb. or by a set of hollow Al posts.
By such
means, a mean radiation length for the system of -8 -1 0 inches should be achievable.
With these considerations in m.ind
Ii
cylindrical system is drawn in Fig. 3.
There are nine
modules, each with six wire generated surfaces of which two are sense wire surfaces.
thickness of each module is 8 em.
maximum diameter.
The
The overall system has a 10 -em minimum diameter and 80 -crn
The pitch angle is 0.36 rad for the smallest chamber and t .16 rad for the
largest, so that the geometrical resolution in z (parallel to the axis) varies from
smallest chamber to ±1.0 mm for the largest, for 2. mm wire spacing throughout.
-51 -
~2.5
mm at the
Then for each
surface the variaticn in radius is l em.
over multiple scattering. being
For momenta >0.6 Gev/c the setting error dominates
=4% at (J s c
= 90·. dJ
= O.
and p = i GeV I c.
This setting error
4
tt at fixed p. The total number of sense wires is l X to • representing
sca
a small but nonnegligible contribution to the readout system for the vertex detector.
decreases like v II sin Z(J
It is a rand hope that despite the exotic geometry event reconstruction will not be prohibitively complicated.
Reference
i G. Buschborn informs me that a cylindrical chamber with nonaxial wires has been constructed at
DESY by L. Criegie and collaborators and is now being tested.
PLANAR MODULES
3.4m
\
1
I
I
TARG
~~l
U5m
~ II
~
I
I
~
I
CYLlNDR1CAL MODULES IN
~Im
CROSS SECTION 1.2mLONG
VERTEX DETECTION WITH CYLINDRICAL CHAMBER
SYSTEM SURROUNDING TARGET.
FIG.I
ILLUSTRATION OF FORMATION OF HYPERBOLOID BY
NON-AXIAL WIRES.
FIG.2
~----I20cm
----~
. . . . . . - - - - - 9Ocm----..
~30cm__t
BEAM
ITARGET
I
I
RINGS t-ERE
•
MAX. RADIUS .em
(CONTINUE 120cm LONG MODULES)
CROSS SECTIONS OF SURFACES OF REVOLUTION
FORMED BY NON-AXIAL WIRES IN'-CYLINDRICAL''
PROPORTIONAL CHAMBER MODULES. EACH
SURFACE HAS A 2cm VARIATION IN RADIUS.
FIG.3
-53-