On Thu, 18 Aug 2005, Hal Evans wrote:
This is great! We should now start thinking about how to best
quantify the precision readout - Run IIb TT comparison. Our
reviewers will, no doubt, want to know how they RMS of precision-TT
compares to that for Run IIa. Presumably the new system will not yet
be as good as what we have now (but maybe we'll be lucky!). So we
should also have in mind a clear procedure to better calibrate the
new IIb TTs. Dan - do you have any thoughts here?
Hello,
The RMS (i.e. the Width of the hopefully 45 deg line that compares
the Cal Precision readout with the Cal Trig readout) should currently
be the same for the new trig system as it is for the old trig system.
The filter in the ADF card of the new system is currently using
just a single ADC sample to "calculate" the Et of a given beam crossing.
This is very similar to how the old trig system works. The main
difference is that the new system has only 2 poles of 30 MHz low
pass anti-aliasing analog filter in front of its ADCs were as the
old trig has a 3 pole 15 MHz low pass analog filter in front of
its ADCs.
I can turn on fancier digital filtering in the ADF cards but I do not
want to do that until things are fully understood with this simple
fool proof single ADC sample "filter". The other advantage of using
the simple single ADC sample "filter" is that it is the easiest (most
fool proof) way to study/verify the correct timing of the ADF wrt the
BLS analog signals.
Once we run a fancier digital filter in the ADF then we have a *chance*
that the RMS, i.e. the energy resolution, of the new Cal Trig will be
better than that of the old Cal Trig.
Calibration Cal Precision vs Cal Trig
Remember all of the calibration is done in the ADF card before the Et
data is sent to the TAB. From the TAB on through everything down
steam of it, 1 LSBit count = 0.25 GeV of Et. As a reminder at the
end of this note I have included the full definition of the data that
comes out of the ADFs and is sent to the TABs.
An issue with this is that right now the ADF is not doing this job.
All of the "machinery" is in the ADF to do the BLS Energy signal to
calibrated Et output conversion but right now just default values are
being loaded into this conversion lookup memory. We can start loading
the correct values into this conversion lookup memory soon after
Philippe gets back. If useful, I could tell you what values I have
calculated should come out of the ADF per GeV of Et as it is running now.
I know what values to put into the conversion lookup memories to make
the Et output from the ADF calibrated at 0.25 GeV per count based on
the understanding of the calibration of the old Cal Trig system.
Simply put, knowing the calibrated of the old Cal Trig system means
that I can work backwards through it and know how many Volts per GeV a
given BLS signal is really giving to the trig system. I can then work
forward through the new trig system and know what data must be put
into the lookup memory for a given channel in the new system so that
it will put out 1 count per 0.25 GeV.
Take home points:
- From TAB through everything down stream it is 0.25 GeV per LSBit.
This is fixed.
- If the ADF is not delivering Et data with this calibration - then it
is the ADF that is adjusted to bring the trigger system into
calibration.
- The trigger system is not like, for example the Cal Precision
readout, where offline (in RECO or someplace) tables of calibration
constants are used to convert ADC counts into GeV. A trigger
system can not work that way because the logic in the trig system
(e.g. in the TABs) must work with the data in real time.
- My ability to turn on the new trigger's ADFs fully calibrated is
limited only by how well the old trig system is calibrated. That
has not been studied since summer 2003.
- As soon as the new trig is turned ON and sees beam, the D-Zero
community will be asking, "Is it calibrated ?". That's why I've been
pushing for people to make the software machinery *now* to check
the calibration. Use it to check the old trig system and give me
those numbers. Then you will have this calibration checking software
tested and ready to use as soon as the new system sees beam.
- "Calibrating" the new system consists of some one telling me
that they have studied a bunch of real beam data and by comparing
Cal Precision readout to Cal Trig readout they find that TT eta,phi
bla is actually giving foo GeV per LSB. I then adjust the
data in the ADF lookup memory for that channel to make it 0.25 GeV
per LSB. Initially this is probably done in rings of TTs all at
the same TT eta - but eventually it can be done on a per TT basis
if that gains us anything.
- Broken BLS signals, i.e. things wrong on the BLS cards or in the
long blue BLS cables cause additional problems for all of this.
If there are questions/comments about this please speak up. The
intent is that it is a simple clear system that can work with real
time hardware.
Dan
clip from the web document about the ADF filter:
Filter Output Values - Technical Details
----------------------------------------
- Note that this is a definition of the Et data that is sent to
the TAB cards by the ADF-2 cards.
- The Et value delivered by the Filter goes through an Et Lookup
memory to set the final scale of the 8 bit Et data that is sent
to the TAB. This scale is:
Zero GeV of Et is represented by 0x08
The most negative value is represented by 0x00 - 2.0 GeV
The most positive value is represented by 0xff + 61.75 GeV
The scale is 0.25 GeV per LSBit.
All Trigger Towers, both the EM and HD sections, will
provide Et data to the TAB at the same scale.
- The limiting Et values will be saturating. That is:
If the Et value calculated from the BLS signal is
more negative than -2.0 GeV the signal sent to
the TAB will be 0x00.
If the Et value calculated from the BLS signal is
more positive than +61.75 GeV the signal sent to
the TAB will be 0xff.
Logic in the ADF-2 Filter and Et Lookup Memory will
prevent the Et values sent to the TAB from "rolling over".
- Et Data for Live and for Not Live Beam Crossings:
There are 159 "Ticks" i.e. periods of 132 nsec or 7 RF Buckets,
in an Accelerator Turn. These tick are numbered 1:159 and
are often referred to as "beam crossings"
With the current Tevatron beam structure only 36 of these
159 ticks are "Live Beam Crossings", i.e. actually have
proton anti-proton bunches crossing in the center of D-Zero.
For details and tick numbering see:
www.pa.msu.edu/hep/d0/ftp/l1/framework/timing/
scl_frame_description.txt
The ADF-2 Cards send Et data to the TAB cards for all 159
ticks in a turn of the accelerator.
For the 123 ticks in a turn that are not Live Crossings
the Et values sent to the TAB will be all 0x08 i.e.
zero Et energy.
For the 36 ticks in a turn that are Live Crossings the
Et values sent to the TAB will be the filtered Et data
based on the BLS signals.
The BX_Number that is sent to the TAB, as part of a frame
of ADF to TAB Et data, is the number of the accelerator
beam crossing that caused the energy deposits in the Calorimeter
that are represented by the Et values in this frame of data.