[Halld-pid-upgrade] DIRC meeting tomorrow at 11 am

[John Hardin]

>Does he mean that no photons should hit the mirror that continues the top
of the old wedge?  You and/or John can check how often photons hit there (I
think it's not very many).

On this comment, you're right that not very many photons hit this mirror,
but some do (~10%, depending on kinematics).  I think his comment was that
there was no point in making it 30 deg rather than some other angle, since
the interface already introduces a discontinuity there.  This is true, but
I don't think that it's wrong to keep that angle, and another angle would
make things even more complicated.  I don't think pulling it in would save
any photons.

Cheers,
John

On Wed, Dec 21, 2016 at 5:27 PM, Michael Williams <mwill at mit.edu> wrote:

> Going from the cylindrical mirror geometry of FDIRC
> to the flat mirror (albeit segmented) geometry of GlueX
> does remove the focussing of the FDIRC design
> and re-introduces the pin-hole "focussing"
> as it was present in the BaBar DIRC.
> The mirror segmentation "only" helps to reduce the MaPMT area,
> using the vertical shift as described in lines 79-81.
>
> — this comment does not require my action, right?
>
>
> Doesn't seem like it.
>
> Figure 3: middle flat mirror (in yellow) - what is the purpose
> of this mirror? Given that there is the fused silica to water
> transition before, changing photon directions, which renders
> the continuation of the 30 degrees top wedge slope pointless.
>
>
> Does he mean that no photons should hit the mirror that continues the top
> of the old wedge?  You and/or John can check how often photons hit there (I
> think it's not very many).
>
> Fig. 3: Though it is no doubt true that a water filled camera is less
> expensive than fused silica, the magnification at the interface is a mixed
> blessing.
> Our experience with long term reflectivity of mirrors in water is less
> optimistic than the test you describe in ref 9. Have you done accelerated
> tests (at high temperature)?
>
>
> Here I'd remind him that we will use ordinary distilled water.
>
> 2. In the following pic the referee asked to add labels for the DIRC boxes
> and camera.
> <2016-12-21_12-20-01.png>
>
>
> Are you asking then for whoever made this plot to add the labeling?
>
>
> 3. Referee suggested to add PID performance plots (currently I have the
> ones below) for the forward part - I’m not sure I know where to take them
> from.
> <2016-12-21_12-20-46.png>
>
>
> Presumably there are some official ones to use that have been previously
> shown in public.
>
> 4. Comment is “slide vertically - swap” for the sentence:
>
> The support structure of the DIRC will allow the pairs of bar boxes to slide vertically out of the active area of the detector for experiments requiring minimal material budget in front of the forward calorimeter.
>
>
> I think in this sentence "slide vertically" can not be substituted by
> “swap” here. But I’m not sure.
>
>
> I think "swap" is OK.
>
> Mike
>
>
>
> Thank you and have a nice holidays!!
> Best regards,
> Maria
>
>
>
> On Dec 15, 2016, at 12:44 PM, Justin Stevens <jrsteven at jlab.org> wrote:
>
> Hi All,
>
> We'll have a DIRC meeting tomorrow at 11 am.  You can find the agenda at
> https://halldweb.jlab.org/wiki/index.php/December_16,_2016_PID_Upgrade.
>
> -Justin
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