What do we see from the Multiplicity Tiles?

- An informal summary of some "Data" Analysis for the Mult/Tiles
   data from the RHIC commissing runs.

10/14/99  J.H. Lee

The Scintillator Tile detector, which is one of the two BRAHMS
multiplicity detectors, was installed (36 tiles/40 tiles) for the
RHIC commissioning runs.  A summary of the  installation and
performance of the tiles can be found  here .

Some "good" runs have been selected from the data sets taken during the
commissioning runs to study spectra from the tiles.  A summary
of the data taken during that time and the criteria for selecting good  runs
can be found here .

To increase statistics, the all sequential files (21 seq. files) for run #217 
in the "good" run list were "chained" together.  The data taking time interval
between the first seq. file (seq001) and the last seq. file (seq031) used for
the analysis in the run 217 is about 13 hours.  The run 217 is from the
"blue" ring runs when the lifetime of the beam was "stable" (> 45min),
 on Aug. 5th .

The triggers used for the run 217 are BB or Mult or Synchronization triggers.
Requiring an exclusive multiplicity trigger condition  show a "peak " most
clearly.  This figure  shows the ADC distributions  of the tile #1 with
different trigger conditions.  As shown in the figure, non-multiplicity
trigger requirement (blue histogram) leaves mainly pedestals.

The ADC distributions for the tiles #0-#3 (starts from #0 as in c++;) can be
found here .  The tile #0 is at "upstream" for the blue ring runs.  For the tile
configurations, see  the figure .  The ADC distributions  shows non-pedestal
peaks at ADC values  550 - 1750.  Clear peaks are shown for channel #1 and #2,
and  rather broader peaks/bumps are shown for #0 and #3 at higher values than
#1 and #2. The rest of channels show similar features similar to #0 and #3 rather
than to #1 and #2.  A root histogram file for the ADC distributions (#0-#39)
including BB counter ADC, TDC distributions can be found in ~jhlee on pii
machines. The file name is  all_mult_trigger_only.hst.  Root histogram files
with different trigger conditions are also available. If you are interested in,
let me know .  The  ADC of #2 vs ADC of #1  distribution shows clear correlations
between ADC#1and ADC#2. The requirement of 460 < ADC#1 <600 and
550 < ADC#2 < 700 also shows  that the broad peak in ADC#3 is correlated
with the peaks in ADC#1 and ADC#2.
The values for the ADC gains for a MIP from the Lab test (Mult/Tile  Logbook
page 93) were (with same HV (1500V) as run 217) 30 - 50 where the pedestal
is at ~ 0.  The lab test was done with CAMAC 2249 ADC, which has 250 fC/count
resolution.  Considering the resolution factors, 250/50 = 5, we should expect
to see MIP peaks at 150 - 250 channels away from  the pedestals.

Based on the following observations, the peaks we are seeing in the ADC
distributions are more likely NOT from  MIP's.

  • The condition of (Mult Trigger=1 and BB Trigger=0) shows clearer

    • "peaks" than the condition of (Mult trigger=1 and BB Trigger=1).
  • The peaks in the adjacent tiles (1,2,  and 3) are correlated.
  • The "peak" for tile 1 is narrower then tile 3. The tile 1 is at "upstream"

    • for the blue ring runs.
  • The peak ADC values from the run 217 are much higher than the numbers

    • from the Lab test.
      
    Particles from upstream passing through multiple tiles were
    probably dominating the Mult trigger conditions (at least 2 tiles hit), not the
    MIP's  crossing tiles vertically because of the run condition.  That
    might be the reason that no MIP peak shows up in the ADC distributions.

    It's not so obvious how we can calibrate the tiles with the date we have. There
    are too many unknown factors.  It will be very useful to have a large data set
    with cosmic rays with trigger conditions requiring vertical particle passage
    through tiles at IR using same experimental condition as "real" data taking.