[Halld-cal] new round of BCAL photo-electron simulations

[Zisis Papandreou]

Hi Elton:

thanks for the comments.  We can discuss them in today's meeting.  Just one clarification for now, on my mentioning Prototype 1 and the inner detectors.  For the former, the numbers from GlueX-doc-819 were used for last summer's simulations as best estimates (prior to the construction of the Construction Prototype).  We are simply now going to our final numbers from design and/or our experience in building the first four modules.  The inner detectors would convert some photons and this would 'smear' our results somewhat.  This effect is ignored.

Cheers and talk to you later, Zisis...

On 2010-02-25, at 7:27 AM, Elton Smith wrote:

> 
> See comments below
> 
> 
>> Hello all:
>> 
>> as discussed in last week's CAL WG meeting, Irina is preparing to launch
>> a new but definitive set of FLUKA simulations in order to extract the
>> number of photo-electron distributions from the proposed BCAL readout
>> segmentation.  These will be used by Fernando to establish our full
>> dynamic range. We had agreed to circulate our proposed plans.  Here they
>> are below and please comment on it.
>> 
>> 1. Update the BCAL geometry to its final values, as specified in our
>> global coordinates and the final engineering drawings and based on our
>> construction of four modules.  This includes the average number of build
>> layers (186), and the final matrix build height (22.184 cm) and inner
>> radius (64.24803 cm) from Tim's drawings -- our first three modules are
>> within the specified tolerance (+/-2mm) for the height.  Irina will add
>> the 8mm aluminum plate, but these stand-alone simulations will not
>> include the any inner material (CDC, Start Counter, target.)  Past
>> simulations used values from Prototype 1.
>> 
> I'm confused about the connection between the prototype 1 and CDC, start
> counter, target.
> 
>> 2.  Update the attenuation length and MeV->p.e. conversion factors from
>> the measured fibre data to include the average values over the first
>> eight shipments, including the spread from the means.
> 
> If there is a conversion to p.e. we also need to include estimates for the
> collection efficiency of the light guides, along with estimates for the
> sensor PDEs. It might be useful to have a couple of extreme options for
> evaluation. As this would be after most of the shower simulation, it
> should be relatively quick.
> 
>> 
>> 3. Run the extreme situation of 3 GeV photons aimed at 14.7 degrees
>> (back, downstream corner of BCAL where we have 67X0 radiation lengths).
>> See Alex Dzierba's plot below. [Previously we had 2 GeV at 20 degrees.]
>> See the attached Pythia plot (courtesy of Blake) justifying the 3 GeV.
>> (At 4 GeV there are very few events populating the phase space near 15
>> degrees, although there are some at 3.5 GeV).  We could also repeat the
>> low end, which was done at 60 MeV and 90 degrees if necessary.
>> 
> Following GlueX-doc-1300, secion 4.2.4. Clearly both high and low ends
> need to be covered by the simulations.
> 
> Energy range:
> 
> Max. energy: Kinematic plots of photons, similar to Blake's, can be found
> in GlueX-doc-1300. However, for deciding on actual values it is useful to
> have the histogram projections on a log scale. See Fig. 2 (top right).
> This shows that less than 1% events are above 2 GeV, and 0.1% above 3 GeV.
> The 2 GeV number comes from picking the 1%, but of course can be
> discussed.
> 
> Min energy: Section 4.2.3. The lower limit to the threshold is 40 MeV,
> dictated by sampling fluctiations. Practical limits including statistics
> will be between 50 and 60 MeV. I chose 60 MeV as a reasonable lower limit.
> 
> Angular range:
> 
> Although the showers are created at fixed angles, this may not always be
> the relevant variable to determine limits. The 90 degree limit corresponds
> to perpendicular showers in the detector and therefore I think it is a
> good reference case and probably should be run.  However, for the dynamic
> range, the extremes occur when showers develop at the edges for the module
> (far end for the low-edge and near end for the high-edge).
> 
> My suggestion last summer for picking extremes was to use the impact
> postion of 20 cm from the end as "reasonable" extremes. This corresponds
> to angles of 113.6deg (upstream) and 11.2deg (downstream). Precisely where
> one picks the upstream point does not matter very much. However, this is
> not the case for downstream. For example, note that the angle of 14.7deg
> results in shower that are about 90 cm from the downstream end (~ quarter
> point on the module) and I don't think this is sufficiently close to the
> downstream end.
> 
> In the end, we will have to give up some linearity of the system to
> accomodate the entire range of energies. We certainly want to make sure
> that saturation occurs in a controlled manner and allows systematic
> corrections.
> 
> 
>> 4. Run photons centered on a cell and also equally split in the boundary
>> between two cells (as before).
> 
> Agreed.
> 
>> 
>> 5. Sum the virtual cells into the appropriate towers as per Elton's plot
>> on page 4 of GlueX-doc-1403, and attached below.
>> 
> 
> We need to agree on the virtual cells. There is no disagreement on the
> inner part. For the outer segments, I am now leaning to have a 2x2
> segmentation (instead of 1x4). Eugene argues that a 2x2 segmentation
> eliminates the need to add in additional noise from the backward-most
> cells. But this should be discussed, and if possible the effects estimated
> in the resolution.
> 
>> At the conclusion of this exercise, we will produce two reports, one on
>> the BCAL's final dimensions (updating from doc-819) and one for the
>> results (updating from doc-1301).
>> 
>> Please send us our feedback on these values, particularly the energy and
>> angle combination.
>> 
>> Cheers, Zisis...
>> 
> 

---
Dr. Zisis Papandreou		|  email: zisis at uregina.ca
Department of Physics	|  tel. : (306) 585-5379
University of Regina		|  tel. : (306) 585-4149
Regina, SK  S4S 0A2		|  fax. : (306) 585-5659
World Wide Web:    http://www.phys.uregina.ca/sparro/zisis/