[Halld-tagger] [EXTERNAL] Re: microscope pictures with green / blue laser

Fri Oct 17 09:12:48 EDT 2025

Beni and all,

Granted 400ps is not great, but I think we can do a lot better using the
design we talked about yesterday because:

   1. we will have both a tdc and adc for timing
   2. we will have 2 channels of wavelength-shifting readout per column
   instead of 1
   3. we will also have direct blue light with much faster rise time on
   readout rows 2-4, albeit with lower photon statistics

In summing mode all 5 channels will be summed in analog to form the pulse,
but the blue light should increase the rise time of the leading edge
assuming any of this light reaches the SiPMs.

-Richard

On Fri, Oct 17, 2025 at 8:30 AM zihlmann <zihlmann at jlab.org> wrote:

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>
> Hi Richard,
> you can make your own conclusions  by looking at the two attached root
> files.
> TAGGER1_ps_test.root for the tagger microscope histogram 2d tagmTmRF
> and project any x-channel to the vertical axis and fit the prompt peak.
> even
> for the good columns the resolution is not better than 400ps.
> hdroot_PS_run133180 take 2d histogram psDTpsc and project any x-channel
> to the vertical axis you get better than 400ps. And remember, the ps tiles
> do not have TDCs, the time comes only from the fADCs.
>
> cheers,
> Beni
>
> On 10/17/25 07:31, Richard T. Jones wrote:
>
> Beni,
>
> Yes we are around 400ps rms in the TAGM now, but as Hovanes says it was
> closer to 200ps when the device was first installed. This shows the degree
> to which its light output has now degraded. But I think the PS coarse
> counters were always at this same level of 400-500ps.
>
> -Richard J.
>
>
> On Fri, Oct 17, 2025 at 6:48 AM zihlmann via Halld-tagger <
> halld-tagger at jlab.org> wrote:
>
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>> attachments, or requests.*
>>
>> Hi Hovanes,
>> with my naive plugin looking at tagger time minus RF time I see a sigma
>> of about 400ps.
>> nothing sophisticated to optimize the result.
>> I see similar sigmas for the PS tiles times where I use the PS coarse
>> counters as time reference.
>> Also, the PS tiles do not have TDCs only fADCs.
>>
>> cheers,
>> Beni
>>
>> On 10/16/25 19:02, Hovanes Egiyan wrote:
>>
>> Hi Beni,
>>
>> Thanks for the nice pictures.
>>
>> GlueX NIM paper quotes 230ps for the timing resolution for TAGM.
>>
>> Best,
>>     Hovanes.
>>
>> On Thu, Oct 16, 2025 at 4:06 PM zihlmann via Halld-tagger <
>> halld-tagger at jlab.org> wrote:
>>
>>>
>>> Hi All,
>>>
>>> I added several more pictures and "movies" to the photo album of the
>>> tagger microscope:
>>> https://urldefense.proofpoint.com/v2/url?u=https-3A__photos.app.goo.gl_Q9To4SutT7854mmV6&d=DwIFaQ&c=CJqEzB1piLOyyvZjb8YUQw&r=-MwMW0sKroUIjy-Lh9rb3KzmWIgdcbbr9_jez8RLmto&m=TcIvojmxs4CshyHEa8JSkCFYf8deaC455OspNOoo-F5KBB3ORgYyR_M20bQEvRIo&s=BHw0yC4CMsmJqBPShHBoS3wZr_Y4Q-UZPdx8fEQrkDE&e= 
>>> I highlighted a few points with three picked out pictures (see attached
>>> pdf file)
>>> With the green laser shining into the front face of the scintillator one
>>> can nicely see
>>> where the "losses" are in the fiber front face, in the fused section and
>>> along the light guide.
>>>
>>> In addition, I looked at the timing resolution of the pair spectrometer
>>> tiles and I find in
>>> my quick and dirty approach very similar timing resolutions as for
>>> tagger microscope
>>> of order 300ps.
>>>
>>> cheers,
>>> Beni
>>>
>>>
>>>
>>>
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>>>
>>
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