Hrachya,
I agree with your criticism of the particular 16+16 scheme that I
suggested, but the principle remains. I suggest that we adopt the
following constraint for the design:
- Keep the number of counters on the right and left close to equal,
for the best granularity.
One can always obtain the same final resolution for any choice of
left/right multiplicity combination. The two issues are orthogonal,
one is the left/right multiplicity, and the other is the choice of
counter positions and widths for optimal trade-off of acceptance and
resolution. To overcome the limitation of energy resolution at high
photon energy end of the spectrum that you point out in your comments
below, for my 16+16 configuration, simply slide the FSF range up to 3.6
- 4.0 GeV instead of 3.0 - 3.4 GeV, and then move the WSF counters down
in energy by 0.75 GeV. That way, the highest WSF counter is in exactly
the same spot as it is in your solution, the FSF counters coincide with
the top end of your FSF design, and the resolutions there will be the
same. You will always be able to point out differences here and there;
the numbers are not exactly the same everywhere. My point here is not
to do all of the detailed optimization, but simply to point out that by
starting with symmetric numbers of counters, we reduce our costs for a
given specified resolution and segmentation. Of course one can obtain
roughly equivalent resolutions using any choice of left/right
multiplicities, if costs are not a concern.
Richard Jones
I didn't miss the subject proposed as you believe.I was
just trying to analyze the profit of transfer to symmetric
configuration.
- Your statement is true, the maximal granularity is reachable in
symmetric sharing of counters number at fixed acceptance. Probably you
wanted to read this sentence.
- In step after thee is the question what is the profit of
symmetrization. Most evident is to decrease the number of counters
for the same granularity. But in symmetric configuration the analyzed
momentum range in WSF arm is shifted up that is important and crucial
at Bremsstrahlung end. The FSF strips are becoming thinner and more
subjected to resolution affection.
- Resolution in symmetric config. is becoming better as photon's
energy goes down below 8 Gev, while is close or even worser than in
non-symmetric configuration above 8GeV where higher analyzed momenta
in WSF arm is used. De-convolution of overlap and restore of
un-affected CB spectrum needs to be studied with MC simulation.
3. Increase in efficiency due to higher granularity is not expected
below *GeV due to app. the same product of resolution and granularity.
Above 8GeV an increase is expected due to a bigger energy
bins/resolution as a result of beam spot size.
$. Mechanical construction of non-symmetrical configuration and
adjustment is easier for non-symmetrical case.
Summarizing the possible transfer to a symmetric configuration at fixed
number of counters in FSF+WSF arms, the transfer allows a gain in
resolution and granularity below 8 GeV, while above 8GeV resolution is
dominated by the beam spot size and increase in granularity gives no
profit.
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5.The full scale advantage of high granularity selection may be
realized through the use of active PS converter on the base of one
layer of 0.5-0.8mm thick WLS fibers.
Hrachya
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