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Re: UPV region - photon detection (fwd)





FYI


Hi Matt and Elton:

We have been discussing similar ideas in the last couple calorimeter
meetings.   The only non-nightmarish read-out of a wedge or a step
inside the BCAL and downstream of the FDC in on the downstream only.
One side read-out is not so bad for this region because the wedge will
only have a limited length and the long attenuation length of the fibers
minimize energy variations.  Timing will suffer somewhat but it looks
that timing from the BCAL does not offer much anyway.

Technically speaking, the easiest way to build such a wedge is to build
a block as for the BCAL and then machine it at an angle on the upstream
and as a flat on the downstream where the read-out will be.  Or am I
missing some issues here?  As for the photons converting in the FDC and
wanting to capture the e+,e-, wouldn't they curve so much in the field
that the wedge will miss many?

Cheers,

George


Matthew Shepherd wrote:

>
> Hi Elton,
>
> I'm not quite sure I see your geometry.  Do your wedges sit entirely
> inside the BCAL, both in z and r?
>
> This sounds similar to something Beni and I were talking about over
> the summer.  I was thinking of a ring of wedges that would sit just
> inside of the BCAL and downstream from the last FDC package.  The
> inner surface of these wedges is cut at the angle from the target and
> the thickness in z would be equivalent to ~15 radiation lengths or so
> -- enough to contain a shower.
>
> The ring has two advantages:
>
> - It minimizes showers that clip the corner of the BCAL and spray
> into the FCAL.
> - It also collects conversions in the last FDC ring.
>
> The big disadvantage would be that it might require a change to the
> cabling scheme of the FDC.  Ideally one wants this ring to be pressed
> right up against BCAL so the two work in unison as a single
> calorimeter.  The FDC cables would complicate this.
>
> Readout would need some work.  Downstream end readout is tricky
> because of the taper.  Upstream end readout creates a gap between the
> FDC and the wedge that is not so desirable.
>
> Maybe we should spend some time at the collaboration meeting next
> week to toss around some of these design ideas. If we come up with
> something we like we should probably make the plunge and try to build
> a GEANT model of it.  I think our neutral particle reconstruction
> framework might be in good enough shape to be able to examine how
> some of these gap sealing detectors might work.  (We're also at a
> stage where we are starting to be able to understand the physics
> implications of leaving the gap just as it is currently.)
>
> -Matt
>
>
> On Oct 16, 2007, at 9:12 AM, Elton Smith wrote:
>
>>
>> Hi all,
>>
>> One possibility for covering the gap between the bcal and the fcal
>> would
>> be to build wedge-shaped calorimeters about 25 cm long with the 5.3 cm
>> base upstream and perpendicular to incident photons.  These wedges
>> would
>> be located at the downstream end of the barrel creating an inside ring
>> that would collect photons that would otherwise clip the corner of the
>> bcal.  The way to read this out would have to be upstream (i.e.  photons
>> would be incident through the readout, likely SiPMs).  In order to
>> contain
>> the showers as much as possible, the calorimeter should have a small
>> Moller radius. A practical solution might be be to machine them out
>> of the
>> same scint-fiber-lead matrix used for the barrel.
>>
>> Comments/suggestions?
>>
>> Cheers, Elton.
>>
>>
>>
>>
>>
>>
>>
>> Elton Smith
>> Jefferson Lab MS 12H5
>> 12000 Jefferson Ave
>> Suite # 16
>> Newport News, VA 23606
>> elton@jlab.org
>> (757) 269-7625
>>
>> On Mon, 15 Oct 2007, Alex Dzierba wrote:
>>
>>> Dear Paul, George, et al
>>>
>>> Please see the attached note - your comments/suggestion most welcome.
>>> I believe, based on these simulations and given the dearth of
>>> manpower,
>>> that we might want to review the cost/benefit of  instrumenting both
>>> the current gap between UPV and BCAL and the the UPV region.
>>>
>>> Perhaps we can discuss at a future phone conference?
>>>
>>> Alex
>>> --
>>> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>>> Alex R. Dzierba
>>> Chancellor's Professor of Physics (Emeritus)
>>> Department of Physics / Indiana U / Bloomington IN 47405 /
>>> 812-855-9421
>>> JLab Visiting Fellow
>>> Jefferson Lab / 12000 Jefferson Ave / Newport News, VA 23606 /
>>> 757-269-7577
>>> Home Phone: 812-825-4063  Cell:  812-327-1881  Fax: 866-541-1263
>>> http://dustbunny.physics.indiana.edu/~dzierba/
>>> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>>
>>
>