[Solid_ec] SoLID SIDIS TOF pid

[J. P. Chen]

Hi, Xiaochao,

First, if using RF, we do not need SPD timing for hadron PID. We will 
use MRPC in
the forward region. The approved SIDIS experiments only detector hadrons 
in forward region.
  However, experience from 6 GeV transversity experiment tells us it is 
much better to
use coincidence TOF for hadron PID.

The plots Zhiwen show are only part of the information. The requirement 
for TOF resolution
depends on how well you need to do hadron PID at which momentum range. 
For coincidence
time, the relevant plot is the Delta_t(K-pi) at forward angle. The time 
difference range we care
up to 2.5 GeV is 400 ps. But this is not the requirement for solution. 
You typically like to have
the combined timing resolution to be a few sigmas to not have the two 
peaks mixed too much.
Exact amount of sigma separation can be determined from the pi/K ratio 
and the requirement
for contamination (or rejection).  Roughly speaking, to actually detect 
Kaon (suppress pi), we
will need 4 sigma or better. To detect pi (reject Kaon), probably 2 
sigma is enough. So I will aim for
200 ps combined resolution.
The spec for MRPC is sigma <100 ps. If SPD can reach similar level (~100 
ps), we should be
in good shape for Kaon rejection (combined resolution  ~ 140 s).
If SPD ~150 ps, it might still be ok (combined 180 ps), but SPD alone to 
be 400 ps, I don't think
is good enough.

Thanks.

Jian-ping

On 9/30/2014 4:48 PM, Xiaochao Zheng wrote:
> 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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