March 27,1998




                            ESTIMATIONS
                 OF CROSS TALK VALUES FOR CHAMBERS

                          (Technical note)

            Y.I.Davydov, Y.Y.Lachin, V.I.Selivanov, V.D.Torokhov

        Goal of this note is an estimation of a cross talk value for
different chambers with a different lamel design. Conclusion: lowest
cross talk level is for a lamel design with grounded strips between
sense strips.
____________________________


        1. Proportional chamber PC4.
Sense wire - 12um x 12um, length - 400mm.
Distance between sense wires - 4mm.
Distance between sense wire plane and H.V. plane - 2mm.
Thickness of copper strips - 70um.
Permeability of DME gas - 1.
Permeability of system {G10(250um)+glass(3.2mm)+ DME gas(0.45mm)} - 2.3.
C11 - capacity of a wire (pF).
C12 - capacity between 1st and 2nd wire (pF).
C13 - capacity between 1st and 3rd wire (pF).
C14 - capacity between 1st and 4th wire (pF).

Results of the calculation by FASTCAP package are below.

1.1. Sense wires:
                                  C11        C12        C13       C14
                                  2.90       0.57       0.26      0.16

1.2. Lamel strips with
     length 100mm, width:
                          1.6mm:  3.64       1.34       0.35      0.19
                          0.8mm:  3.03       0.96       0.31      0.17
                          0.3mm:  2.50       0.68       0.26      0.15
                           12um:  1.67       0.33       0.15      0.09

1.3. Lamel with grounded
     strips between sense
     strips, length of
     strips 100mm:
ground strip - 1.6mm,
sense strip - 12um:               2.20       0.03       0.01      0.005

ground strip - 2mm,
sense strip - 0.5mm:              4.38       0.05       0.03      0.01

1.4. Full PC4 chamber with
strip width 1.6mm, with
length 100+100mm (tested
on Aug.97 run):                  10.18       3.25       1.05      0.54

1.5. Full PC4 chamber with
ground strip 2mm, sense
strip 0.5mm, length of
strips 100mm:                    7.28       0.62        0.29      0.17


        We had the cross talk value 2.8% between next wires for #1.4
during Aug. 97 run. Suggesting that the cross talk value is proportional
to the capacity between the wires, we can hope to have 2.8 x 0.6/3.25=
= 0.52% of the value for the lamel design #1.5.
        Average number of ionising electrons from a relativistic
positron
is <120e ( theta angle is 45 degree, path length is 6.9mm). It means
that
we will have zero cross talk value for positrons if we use a threshold
1e
and a cross talk value is <0.8%.
        Besides that we will have an induced opposite sign charge from
a hitted wire to next wire. This value is ~-1%. We can compensate it by
a resistor between the wires.
        The above estimations are not an exact calculation. We can
suggest
an another method of the estimation of the cross talk. The above
measured
cross talk value 2.8% is  2.8% = + 3.8%(capacity cross talk) -
1%(induced
charge). It means that we will have for #1.5 the capacity cross talk
3.8 x 0.6/3.25 = 0.7%. Total value of the cross talk is +0.7 - 1 =
-0.3%.
We are believed we must have a small negative value of the total cross
talk in order to supress a cross talk produced by a big signal from
muon.
        We had the cross talk value ~2.9% between next X planes for #1.4
lamel design during Aug.98 run. This cross talk is not so important
because we will use (X+Y) pairs in E614 detector. The cross talk between
X and Y planes of (X+Y) pair was small. We need to measure it in future.
__________________________

        2. Proportional chamber PC2.
Sense wires - 12um x 12um, distance between wires - 2mm.
Rest values equal to #1.

2.1. Sense wires:
                              C11         C12         C13         C14

                              3.1         0.76        0.36        0.22

2.2. Lamel with sense
strips 0.5mm, ground
strips 0.5mm, length
100mm:                        4.7         0.34        0.09        0.05

2.3. Full PC2 chamber
with 2.1+2.2:                 7.8         1.1         0.45        0.27
______________________

        3. Drift chamber PDC4.
Sense wires - 12um x 12um, field wires - 25um x 25um, distance between
sense and field wires - 2mm, field wires are grounded.
Rest values equal to #1.

3.1. Sense wires:

                              C11         C12         C13         C14

                              3.3         0.27        0.1         0.05

3.2. Full PDC4 chamber
with sense strips 0.5mm,
ground strips 2mm, length
100mm:                        7.68       0.32        0.13       0.06
_______________________

        4. Summary:
Below we can try to estimate a cross talk value for different chambers
suggesting:
* The measured cross talk value for # 1.4 is 2.8%.
* Cross talk value is proportional to capacity between wires.
* Induced charge signal for PC4 is -1%.
* Induced charge signal for PC2 is -1.5%.
* Induced charge signal for PDC4 is 0%.


                   C11    C12    capacity   induced    total
                                 cross      cross      cross
                                  (%)        (%)        (%)
Tested PC4
chamber #1.4:     10.18   3.25    +3.8       -1        +2.8

PC4 #1.5:          7.28   0.62    +0.72      -1        -0.28

PC2 #2.3:          7.8    1.1     +1.29      -1.5      -0.21

PDC4 #3.2:         7.68   0.32    +0.37       0        +0.37
_________________________________________


        5.Several words about ADC analysis of muon signal. We need to
have
the analysis of incoming muon in a central part of a PC2 {4 planes of
input PC2 + PC(-2) + PC(-1) + PC(+1) + PC(+2)}. We believe that 32
channels
will be enough for the analysis. Total amount is 32 x 8 = 256.
        Muon will produce in 10-20 times more electrons than positron.
It will saturate the VTX. We are suggesting to split the wire output
signal before VTX input. For example we can use 90-95% of the signal for
positron registration and 5-10% for the muon ADC analysis. We need to
calculate a deposit energy of a surface muon and a relativistic positron
in order to select a correct value of the split.
_____________________________________________

-- 
*****************************************************
David R. Gill (drgill@triumf.ca)   (604) 221-3219
TRIUMF                              Fax  222-1074
Vancouver, BC
V6T 2A3

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