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Re: Low energy thresholds
Geoge -
this sounds like a very good idea. Is it something that you in Regina
can do, or do we need additional resources to proceed with this and
acheive an answer on the time scale to CD3?
Curtis
On Thu November 1 2007, George Lolos wrote:
> Hi all:
>
> I believe that by now we all have been convinced that detection of low
> energy photons is very important due to the physics interest in that
> region of phase space for reactions of interest. The main problem here
> is the number of photons reaching the sensors, the number of pe's we
> collect, and the noise we allow to leak in that imposes higher
> thresholds. From Elton's plots, the main culprit is the limitations due
> to sampling fraction so whatever attempts we make to improve the sensor
> side of the problem is guided by the sampling fraction contribution to
> the energy resolution. So, the way I see it, we have two avenues to
> push the limits:
>
> 1. Push SensL for as high a PDE and as low a DR as possible. We will
> do this, however, I believe that we will reach a stage where we will hit
> the ceiling of technology and will need substantial cooling of the
> sensors to keep high PDE and low DR. This has budgetary and technical
> challenges we may not wish to face. In addition, after pulsing becomes
> more severe with lower temperatures and this imposes an additional R&D
> to reduce this. What I am saying is that we can only push DR down so
> far without cooling and we should have other options.
>
> 2. Increase the number of photons reaching the SiPM's by increasing the
> number of SciFi's read out by them. This, in practical terms means
> increasing the SciFi to Pb ratio, so increasing the sampling fraction.
> This has two benefits by improving both the pe statistics and improving
> the contributions due to the sampling fraction fluctuations. However,
> the down side may be more leakage out the back and many more SciFi's
> than we can afford or want, for that matter, if we go for, say, 3 mm
> instead of the present 5 mm of Pb thickness.
>
> One now has to ask, what region of the BCAL is really the one that needs
> the increased photo-statistics and higher sampling fraction? This is
> clear, the critical region of the BCAL is that of the inner layers.
> Using 3 mm Pb for the inner layers will increase the sampling fraction
> by almost a factor of 5/3 over the present one. This will also increase
> the number of photons by almost the same amount while keeping the DR
> constant. The outer layers of ~ 12 cm, on the other hand, have no need
> for such improvements and we are better off to keep the Pb thickness to
> 5 mm to contain as much of the shower energy as possible.
>
> I am proposing then that we pursue a MC study of the "hybrid" 3 mm and 5
> mm Pb thickness and investigate how many layers do we need for the
> former and how many for the latter to reach an optimum figure of merit.
>
> Any comments/shoot-downs/new ideas?
>
> George
>
--
Professor Curtis A. Meyer Department of Physics
Phone: (412) 268-2745 Carnegie Mellon University
Fax: (412) 681-0648 Pittsburgh PA 15213-3890
cmeyer@ernest.phys.cmu.edu http://www.curtismeyer.com/