1. Trigger Background Experience & Predictions
Su Dong
Sep/23/2003 Su Dong
BaBar Background Workshop

2. Trigger Background Perspective
The most significant issue is simply the impact of L1 rate growth on the DAQ dead time. The only systematic data for extrapolation is still the Feb/02 background runs.
The Drift Chamber Trigger upgrade to reject tracking trigger background using Z information will be a major improvement. Its design robustness at high background conditions was evaluated.
L3 now has considerable head room after moving to Linux and have straightforward path for upgrade with faster CPU and more nodes still.
Sep/23/2003 Su Dong
BaBar Background Workshop

3. BaBar Background Workshop
L1 Rate Projection
Feb/02 background
run result suggest
Possible model
at good conditions:
L1 Rate (Hz)
= (cosmic)
*ILER(A)
*IHER(A)
*I2HER(A)
*L/1033
*ILER*IHER
How well does this work ?
How should we use such
a model ?
Sep/23/2003 Su Dong
BaBar Background Workshop

4. BaBar Background Workshop
The need for head room
Assumed ground rules:
Need to find strategy to keep dead time at <~3% even at bad conditions.
Cannot operate on the DAQ rate limit. Always need head room.
Sep/23/2003 Su Dong
BaBar Background Workshop

5. Checking L1 Rate Projection
All colliding beam runs longer than 10min and dead time <40%.
Examine ratio of average L1 rate vs prediction.
Now we know the background runs were really at best conditions !
There are significant tails in the L1 rate.
Sep/23/2003 Su Dong
BaBar Background Workshop

6. Checking L1 Rate Projection
Derived background
L1 rate compared to
prediction:
>2*backgr 24%
>3*backgr %
>4*backgr %
Use prediction with
caution !
Sep/23/2003 Su Dong
BaBar Background Workshop

7. BaBar Background Workshop
L1 Trigger Rate Growth vs Trigger Types
Sep/23/2003 Su Dong
BaBar Background Workshop

8. Improvements from DCT Upgrade (FDR Apr/03)
Very simple usage:
DCT triggers 1Z track (|z0|<10cm)
Can reject ~53% of DCT background
(A crude test with more elaborate usage:
1Z Pt>0.6GeV OR 2Z Pt>0.25GeV
can reject ~67% of DCT background )
Sep/23/2003 Su Dong
BaBar Background Workshop

9. DCT Upgrade Effect on L1 Rate
CDR study
Sep/01.
Simple 1Z cut,
assuming EMT
unchanged.
Can assume
New DCZ allow
Reduction of all
Background
triggers by 40%.
Sep/23/2003 Su Dong
BaBar Background Workshop

10. DCT Upgrade Robustness at High Background
Open background
D2 track triggers
with multiple
background overlays.
Background rejection
Capabilities largely
Preserved up to ~5-6
times of Sep/01
Background.
Physics efficiency at
higher background
behaves even better.
Sep/23/2003 Su Dong
BaBar Background Workshop

11. Real boards running at IR2 for 1/8 of f !
Status of DCT Upgrade
Real boards running at IR2 for 1/8 of f !
Sep/23/2003 Su Dong
BaBar Background Workshop

12. BaBar Background Workshop
L1 Rate Projection
Feb/02 background studies concluded:
L1 (Hz) = 125 (cosmic) + 50*ILER + 180*IHER + 190*I2HER
+ 100* ILER* IHER *L/1033
Prediction based on Seeman model (Feb/03):
Lumi LER HER No-DCZ DCZ `2*bck’ `3*bck’
Given the discrepancy even extrapolating into 2003, this
projection clearly has to be read with caution !
Sep/23/2003 Su Dong
BaBar Background Workshop

13. Trigger Background Perspective
L1 Rate is worse than Feb/02 projection. We clearly need to be cautious in extrapolating rates based on a particular machine configuration and condition. We need to continue to preserve head room.
L1 DCT upgrade is on its way. We still have some work to do to make the best use of this upgrade through optimized trigger configuration.
There is on more possibility of L1 upgrade to veto Bhabhas in GLT, which only needs GLT firmware updates. However, benefit is only significant for luminosity well beyond 1034.
Sep/23/2003 Su Dong
BaBar Background Workshop