Hi Michael,
If you look closely, the offsets are added to the top pmt, and
subtracted from the bottom pmt. So when the flashers are used to
determine the timing offset (top+bot)/2, as opposed the positional
offset (top-bot)/2, the end result is independent of FLASH_POS,
COPL_POS, so it really isn't circular. Also, note that the offsets have
been determined once, while the calibration can be done for any set of runs.
--chris
Michael Kohl wrote:
>Thank you Peter for your explanations.
>However, in regard of the FLASH_POS, COPL_POS offsets that are applied in
>addition to what you determine from the flasher data, this confuses me
>even more. It looks to me like a tautology.
>
>Which offsets are used for crunching (blast.sc_cal) and how have they
>been determined??
>
>
>MK
>
>
>
>
>On Mon, 15 Mar 2004, Peter Karpius wrote:
>
>
>
>>Hi guys-
>>
>> OK I have put the macro that I used in January to incorporate
>>Chris' results and get the tdc offsets fro the tofs (which seem to be
>>correct mow after the recent test of last week). This macro runs off of
>>raw data (so you know you are not crunching with any offsets!) It is:
>>
>>/home/daq/blast/pro2004/analysis/macros/Raw/tof_tdc_offsets.C
>>
>>As for your questions:
>>
>>
>>>Chris has told me that your offsets analysis for the ToFs from flasher and
>>>his offsets analysis from cosmics both yield compatible results.
>>>
>>>
>>>
>>This is correct but it is like "an identity" i.e. 1=1. This is because my
>>macro incorporates Chris' flasher position offsets and his offsets from
>>cosmics for coplanarity (which I believe give sector-sector offsets)" You
>>can see this in the initial lines of the macro where there is an array of
>>numbers:
>>int L_FLASH_POS[16] = {...}
>>int R_FLASH_POS[16] = {...}
>>int L_COPL_POS[16] = {...}
>>int R_COPL_POS[16] = {...}
>>
>>The first two arrays address the fact that the flasher is offset and align
>>remove the offset between top and bottom tube and flasher, the second two
>>arrays remove any sector-sector offsets (but again these numbers were
>>handed to me by Chris so he can explain from where they come)
>>
>>
>>
>>>Could you perhaps explain once exactly what the criterium is for the
>>>"offset" of a channel which enters the blast.sc_cal file?
>>>
>>>
>>OK, in the macro mentioned, here is how the offsets are determined:
>>//CALCULATE THE OFFSETS
>>___________________________________________________________
>> for (int i=0;i<16;i++){
>>
>> LOFF0[i] = tdc_left_top[i]->GetMean() - 1000 - L_FLASH_POS[i] + L_COPL_POS[i];
>> LOFF1[i] = tdc_left_bot[i]->GetMean() - 1000 + L_FLASH_POS[i] - L_COPL_POS[i];
>> ROFF0[i] = tdc_right_top[i]->GetMean() - 1000 - R_FLASH_POS[i] + R_COPL_POS[i];
>> ROFF1[i] = tdc_right_bot[i]->GetMean() - 1000 + R_FLASH_POS[i] - R_COPL_POS[i];
>>
>>So the target flasher channel is 1000. I take the difference with the
>>raw tdc and 1000. As for why I subtract L_FLASH_POS[i] and add
>>L_COPL_POS[i] or vice versa, why? -> you have to ask Chris. You see I
>>just put it all together in this little macro
>>Chris was the brains behind it!
>>
>>
>>
>>>Can you just use the flasher in common start mode as it is in every run or
>>>do you need coda in "flashrun" configuration (thinking of downloaded
>>>delays etc.)?
>>>
>>>
>>>
>>You definitely want to use the flasher with real physics data with beam.
>>This way you know you have the right delays already. Just select event
>>type 7 to extract flasher events (I thought it was 8
>>but I just checked my code and it has):
>>
>>if (raw.GetEventClass() == 7){ // is this a flasher event?
>>...}
>>
>>
>>
>>>I found a macro of yours (tdc_offsets.C) which determines offsets such
>>>that tdcsum becomes 2000 (or 1000 for the average) and tdcdiff=0. Does
>>>this "target channel 1000" requirement already account for the light
>>>traveling times?
>>>
>>>
>>This is an old macro - use the one listed above _ I should go through and
>>delete all of this junk.
>>
>>
>>
>>>Please let me know which macro you are presently using to determine the
>>>ToF offsets from flasher.
>>>
>>>
>>>
>>/home/daq/blast/pro2004/analysis/macros/Raw/tof_tdc_offsets.C
>>
>>but notice that it uses a class called TBLScRecon that writes the
>>blast.sc_cal file - you should make a version of this for the NC bars-
>>
>>Take a look at this class in BlastLib2
>>
>>
>>
>>>Thanks and regards,
>>>
>>> Michael
>>>
>>>
>>>
>> Sure, no problem!
>>
>> Pete
>>
>>PS Chris, if you have read this, please correct any mistakes I have made!
>>
>>
>>
>>
>>----------------------------------------------
>>Pete Karpius
>>Graduate Research Assistant
>>Nuclear Physics Group
>>University of New Hampshire
>>phone: (603)862-1220
>>FAX: (603)862-2998
>>email: karpiusp@einstein.unh.edu
>>http://pubpages.unh.edu/~pkarpius/homepage.htm
>>----------------------------------------------
>>
>>
>>
>>
>>
>>
>>
>>
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