[Solid_daq] [Solid_ec] SoLID SIDIS TOF pid

[Xiaochao Zheng]

Thanks for the plot, Zhiwen, that saves me time to do the TOF calculations myself.

Still, I have some questions:

1) Given that we can live with 400ps of TOF from SPD if the RF is used. I presume the RF gives the event time and SPD-RF is the TOF.

Then, without RF, we need the MRPC to back-calculate the event time, in which case the event time has an uncertainty that equals to the MRPC timing resolution (assuming the uncertainty from flight distance and speed is negligible, which should be the case with GEM), let's say 100ps.  In this case, shouldn't the timing resolution requirement on the SPD to be (400ps)-(100ps) (subtraction by quadrature), which means 300ps should be more than good enough?

2) The other question is how do we calibrate the TOF?  Using DIS electrons and RF? (Then wouldn't the "unreliablity" of RF come into the calibration?).  Or do we use some coincidence events? If so then what kind of events?

3) I ran my simulation and found I can reproduce some of the test results (CLAS12 TOF-USC/S2), but not some others (S2m, CLAS6 TOF). For S2m I suspect we don't really understand the TDC resolution and/or PMT TTS in the real situation.  In principle, once nphe is larger than ~100, the TOF resolution is completed dominated by the TDC and the PMT TTS. 

I also found that the PMT TTS could differ from what the manufacturer specify (CLAS6 PMT test showed factor of 3 larger TTS than manufacturer's datasheet for XP2262, 30% larger for Hamamatsu R329). For HRS S2 I used the Burle PMT TTS measured by CLAS6 in the same test and the agreement with HRS data is good. Hence the reason I suspect the problem with S2m data might be due to PMT TTS data not reliable.

Bottom line, the simulation so far shows good timing resolution for the SPD, but it depends greatly on the PMT and the TDC.  Therefore, I think it might be a good idea to go ahead and order some SPD prototypes, six fast PMTs from Hamamatsu, and do our own tests.

Please comment, thanks.

Xiaochao

----- Original Message -----
From: "Zhiwen Zhao" <zwzhao at jlab.org>
To: "solid ec" <solid_ec at jlab.org>, "Solid daq" <solid_daq at jlab.org>
Sent: Tuesday, September 30, 2014 4:20:21 PM
Subject: Re: [Solid_ec] SoLID SIDIS TOF pid

correct second link
http://hallaweb.jlab.org/12GeV/SoLID/download/pid/tofpid_TCS_LA.png
It's for TCS setup, so target a bit downstream, but the result is 
similar to SIDIS

Zhiwen

On 9/30/2014 3:44 PM, Zhiwen Zhao wrote:
> hi, All
>
> Here are plots for SoLID SIDIS setup TOF pid
> http://hallaweb.jlab.org/12GeV/SoLID/download/pid/tofpid_SIDIS_FA.png
> http://hallaweb.jlab.org/12GeV/SoLID/download/pid/tofpid_SIDIS_LA.png
> The flight distance is about 2.9m for LA and 7.7m for FA
>
> Zhiwen
>
>
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> Solid_ec at jlab.org
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