Hi Michael,
Sure; see the minutes of my talk at the last collaboration
meeting, or my thesis p.137 (not much there). I used the path length
in calculation of Q^2 from the TOF's, and had to add my own
reconstructed variables 'ltwl,r' to the flr ntuple to use instead of
'Lwl,r', since I didn't have time to debug the reconstruction code.
See '~chris2/exp/2006-01-06_qtof/track_length.{log,root}' for
details. The friend ntuples were created with 'xsc_ntuple.cc', which
is also use to calculate 'xtwl,r', which are used to extract the TOF
efficiency.
--Chris
_______________________________________
TA-53/MPF-1/D111 P-23 MS H803
LANL, Los Alamos, NM 87545
505-665-9804(o) 665-4121(f) 662-0639(h)
_______________________________________
On Mar 17, 2006, at 09:09:52, Michael Kohl wrote:
> Hi Chris,
>
> we had a meeting with the "pion group" on campus.
> Data indicated that there may be an issue with the calculated
> pathlength Lwl of positive tracks in the left sector. Please read
> the minutes below, in particular the paragraph on pathlength double
> peaks.
>
> Can you comment on this?
>
> Thank and regards,
>
> Michael
>
>
>
>
> ---------- Forwarded message ----------
> Date: Fri, 17 Mar 2006 11:06:45 -0500 (EST)
> From: Michael Kohl <kohlm@mit.edu>
> To: Yuan Xiao <yxiao@MIT.EDU>
> Cc: William Bertozzi <bertozzi@lns.MIT.EDU>, Bill Turchinetz
> <billt@mit.edu>,
> Akihisa Shinozaki <shino@lns.MIT.EDU>, Chi Zhang
> <zhangchi@MIT.EDU>,
> Shalev Gilad <sgilad@mitlns.MIT.EDU>, Douglas Hasell
> <hasell@mit.edu>,
> Renee H Fatemi <rfatemi@mit.edu>
> Subject: My minutes from Thursday 3/16
>
> Hi,
>
> I have some minutes from yesterday because I'm forgetting so fast.
> Next meeting is on Tuesday 3/21/2006 at 14:30.
>
> Regards,
>
> Michael
>
>
> Discussing double peaks in time-of-flight, and in pathlength.
> Consideration for electron-right (negative charge and Cerenkov)
> and positive track in left pad 13 (features are also in 12,14,15).
> Assuming electron triggers event.
> Twr is the time-of-flight for the electron calculated from momentum
> pwr, velocity(=c) and pathlength Lwr.
> ttwl and ttwr are the left and right sector TDC's with TDCoffsets
> subtracted and the result converted to ns.
> The time-of-flight of the positive track in the left sector is thus
> TOF(pos)=ttwl-ttwr+Twr !note ttwl-ttwr and not ttwr-ttwl
> In fact, I believe the tracking code assigns the above TOF(pos) to
> Twl=TOF(pos) (not sure).
> We saw a double peak structure 1-2 ns apart in the histogram of ttwr
> which is not understood. We expected only a single self-timing peak
> for the electron, if the electronics processing time for the delay is
> the same for all channels. If it is channel-dependent though, the
> corresponding TDC distribution for the triggered positive track should
> nevertheless be shifted by the same amount, so a cancelation of the
> self-timing is expected by considering ttwl-ttwr, UNLESS the TDC
> offsets in the right sector were not all adjusted well (but I thought
> they were). We saw a triple peak structure in TOF(pos), of which two
> peaks were due to the double peak in ttwr (concluded from plotting
> [ttwl-ttwr+Twr]:ttwr).
>
> We also saw a double peak structure in the pathlength of the positive
> track Lwl. These two groups of short and long pathlengths (about 20cm
> apart, ~260 vs. ~280 cm for left pad 13) are not correlated with
> neither the double time peak in ttwr, nor with any coordinate
> associated with the positive track such as momentum pwl, angle twl,
> vertex zwl. Therefore, the pathlength double peak appears
> unphysical and it is questioned wether this points to a bug in the
> tracking code. A 20cm shift between the two pathlength peaks
> corresponds to ~2 ns difference
> in calculated time-of-flight. I will check with Chris Crawford
> wether he knows anything about it.
>
> Returning to the time-of-flight consideration from above:
> Assuming that all positive tracks in the above case are protons, one
> can also calculate the expected TOF(pos) from tracking,
> TOFcalc(p)=Lwl/(beta*c)=Lwl/(pc/E)=Lwl/(pwl*c/sqrt(Mp^2+pwl^2)).
> The quantity dt=TOF(pos)-TOFcalc(p) should
> therefore be a Gaussian at zero with a width of the convoluted
> uncertainties in TDC's, Lwl, and pwl. It is indeed a Gaussian at zero,
> and has a sigma of ~2ns.
> We correlated dt with all variables and found:
> The double peak structure in Lwl broadens the Gaussian dt;
> the double peak structure in ttwr also broadens the Gaussian dt
> independently from the double peak in Lwl;
> the Gaussian is also broadened by summing over all electron paddles in
> the right sector. The latter effect is due to uncertainties in the TDC
> offset calibration in the right sector.
> Before the TDCs are recalibrated though, the first two broadening
> effects should be cured/corrected in order to sharpen up the dt
> Gaussian first.
>
>
> On Fri, 10 Mar 2006, Yuan Xiao wrote:
>
>> Sorry, I almost forgot:
>> 7. Try the available kine. corrections.
>> Quoting Yuan Xiao <yxiao@MIT.EDU>:
>>> Dear all,
>>> The following are what we mentioned during yesterday's meeting:
>>> 1. Have a look at the reconstructed mom and induced mass (Mwl/Mwr)
>>> for the region where Mm2 > 1.05 GeV.
>>> 2. In the first 10 runs, stopped protons show two bands in TOF-
>>> ADC spectrum
>>> for e left case. Find out which paddle(s) deviated.
>>> 3. In the last 10 runs, punching thru protons form several
>>> islands in
>>> TOF-ADC spectrum. Is there any time (run #) dependence here?
>>> 4. Has the Blast acceptance effect been considered in the analysis?
>>> If there any contamination from the very low angle positons?
>>> 5. Have a look at thcms_pi vs phcms_pi distribution when thq(lab)
>>> > 40 deg.
>>> Should there be a peak around phcms_pi = 0 region?
>>> 6. Further TOF study; what's that horizontal needle structure in
>>> TOF-vs-ADC
>>> plot around 20 ns?
>>> If you have any suggestion, please let me know.
>>> Best,
>>> Yuan
>>
>
>
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