BBC ADC Signatures of SpaceCharge azimuthal anisotropy
In my azimuthal sDCA studies, I observed static and dynamic azimuthal asymmetries in the CuCu200 data. One suggested possible way to avoid this in upcoming heavy ion runs is to see if there are any online scalers which could be used to give feedback to C-AD as to whether backgrounds at STAR are acceptable in terms of TPC ionization distortions. Towards this end, I have begun a study of whether the BBC scalers might be useful in this regard.
It is important to understand some things about the BBC geometry (see this postscript file). Ideally, the large outer tiles are closer to the TPC and more likely represent information relevant to what is happening in the TPC. We would most likely want to implement scalers for these in an upcoming heavy ion run. Unfortunately, in the past we have only taken ADC data with these large tiles. I have already done a study using scaler information from the small BBC tiles which demonstrates some fluctuations at similar azimuth to where the TPC shows problems.
For this study, I use only the outer ring of large BBC tiles on the east and west ends separately. These twelve tiles (numbered 25-36) are covered by 4 PMTs (numbered 21-24), which integrate over 3 tiles each, spanning nearly equivalent ranges of azimuth. Also, to avoid biasing the ADC contributions towards those from triggered nuclear collisions, only zerobias events are useful for such analysis.
I have arranged the following plots similarly to my azimuthal sDCA studies. I define NADC (normalized ADC values) to be the rate of a given PMT's ADC divided by the sum of all 8 large tile PMT ADCs. This is done simply to normalize against overall changes in gains.
In the plots below, the first row shows the <NADC> (mean normalized rate) value for each phi bin. In the subsequent rows, I plot NADC-<NADC> versus day (with each phi bin offset) to see what's happening on sub-day time scales, and versus day in a colored 2D graph to see what's happening on larger time scales. There are three sets of plots: the first is all the CuCu200 BBC FF ADC data I have for zerobias triggers; the second is the CuCu200 BBC RFF ADC data I have between days 20 and 46 for all triggers (zerobias trigger data only seems to be available after day 32); the third is RFF zerobias data only for days 37-44 (runs 6037039-6044001) to provide more direct comparison with the CuCu200 data in the sDCA studies.
Additional comments below the plots.
CuCu200 FF
Zerobias triggers.
| 2005 CuCu 200 FF | Large outer tiles east | Large outer tiles west |
|---|---|---|
| <NADC> |
 |
 |
| NADC - <NADC> vs. day |
 |
 |
| NADC - <NADC> vs. day |
 |
 |
CuCu200 RFF
Zerobias triggers only started in this data on day 32, so this is ALL TRIGGERS starting on day 20.
| 2005 CuCu 200 RFF | Large outer tiles east | Large outer tiles west |
|---|---|---|
| <NADC> |
 |
 |
| NADC - <NADC> vs. day |
 |
 |
| NADC - <NADC> vs. day |
 |
 |
Just a small note as to why I started with day 20 (even though there is earlier data): there seemed to be some notable changes in running conditions and/or gains during the period prior to day 20, as can be seen in these variance charts:
| 2005 CuCu 200 RFF | Large outer tiles east |
|---|---|
| NADC - <NADC> vs. day |
 |
CuCu200 (days37-44)
Zerobias data, RFF.
| days 37-44 | Large outer tiles east | Large outer tiles west |
|---|---|---|
| <NADC> |
 |
 |
| NADC - <NADC> vs. day |
 |
 |
| NADC - <NADC> vs. day |
 |
 |
While there are some faint signs of fluctuations in the azimuthal BBC large tile ADC data, these fluctuations seem to be rather small. My conclusion at this point is that the BBC ADC data is not as sensitive to the problematic backgrounds as the BBC scaler data, despite being at larger radius.