Transcript BABAR Risks and Mitigations David B. MacFarlane B Factory Operations Review April 26, 2006

BABAR Risks and Mitigations
David B. MacFarlane
B Factory Operations Review
April 26, 2006
Sources of risk
 Installation and schedule risk associated with
replacing barrel RPCs with LST modules
o
Extensive discussion of planning and issues in Bill Wisniewski’s
talk
 Radiation damage and occupancy in detector
hardware systems
o
Extensive discussion for SVT in Bill Wisniewski’s talk;
background studies in Matt Weaver’s talk
 Ability to maintain an open trigger for full physics
potential
o
Discussed here
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Risks to the Detector
 Radiation Damage
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o
o
o
SVT sensors, readout electronics (S/N degradation, shorts)
• Replacements available for horizontal modules, but will not
be installed based on risk/benefit analysis
• Remainder of detector will remain operational through at
least 2008
DCH damage to wires (Malter effect): lifetime well beyond
2008
EMC damage to crystals (color centers): lifetime well beyond
2008
Continuing to monitor damage
• Have performed extensive irradiation studies, understand
limits of SVT very well
• Maintain tight control of beam abort and injection inhibits
(relaxed to improve data collection efficiency and machine
performance once understood)
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Risks to the Detector
 Data-taking inefficiency & dead-time
o
o
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Services: system backups (chillers) (continuing)
DAQ: upgrade to online farm (replacement funded and in planning)
Trigger: upgrade for z info (successfully deployed and operational
since the end of Run 4)
DCH: data transmission bottleneck (successfully deployed and
operational since February)
• Understanding other possible bottlenecks, e.g., SVT, EMC
• Additional tools: shielding & restrictive trigger & understanding
 Machine Detector Interface Group
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Existed during BABAR construction & commissioning
Re-established with added scope in 2003
• New mandate includes working with accelerator team on machine
background simulations, beam parameters at the collision point,
instrumentation & analysis
Addresses issues of extrapolation and modeling of backgrounds that
contribute to radiation damage and data-taking inefficiencies
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Trigger Rate Projections
 From the Trigger Group: need <140us
Extrapolation prior to
DCZ deployment: will
revisit this spring
Actual experience
in 2005 and 2006
has proven better
than extrapolation
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Processing Time
Fiber Transfer Bottleneck
Eliminated by DCH
readout upgrade
ROM (only 2 for EMC:
endcap/barrel)
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Present DAQ limit seen in October
Deadtime (%)
Deadtime problem was foreseen in DAQ projections
DCH
Feature
Extraction
Bottleneck
Phase
I DCH
Installed
forupgrade
Run5a
Factor 2 improvement
Phase II DCH upgrade
Installed for Run5b but
not activated in October
FEX code now installed and
operational on DCH endplate
Front-end
Readout
(4 buffers)
Actual soft rise in deadtime
somewhat faster than model
predicts: under investigation
Trigger Rate (Hz)
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Behavior of Fiber Bottleneck
Current performance
equivalent to ~3 FE
buffers: under
investigation
Deadtime behavior on this plot is worse if L1 more “bursty” than Poisson
(current evidence suggests not Poisson).
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Possible Plan of Attack for Fiber
SVT:

o
o
o
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Readout specific bad modules from both left and right.
Factor of 2 gain? Might not work everywhere (especially for
damaged modules?)
Mask out small regions with high occupancy
Try running system at 60MHz (requires substantial new
effort, may not work)
Reduce occupancy with thresholds
Plan: Investigate 60MHz clock rate for data
acquisition, thresholds, and masking techniques
Impact: Should allow L1 rates up to 5Khz
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FEX Bottleneck
Can be improved
Challenging
Eliminated by DCH
readout upgrade
140us
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Plan of Attack for FEX
 EMC FEX hard! Already a lot of work on this, not likely to be
substantially improved.
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New CPUs won't work easily: mechanical, electrical, software issues.
significant work and money ($300K).
May be possible to pass EMC data to a small secondary farm, but
substantial work would be required to investigate and deploy
 DRC and SVT FEX relatively easy (don’t “do” anything) but still
have to be validated carefully.
 EMT FEX: Event “prescaling” deployed, with expected
improvement
 Currently SVT, EMT, GLT deadtime behavior not as predicted
and under investigation
Plan: Removing EMC FEX limit may be prohibitive at this
point, although some ideas are under consideration
Impact: L1 rates could be limited to 5Khz
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VME Bottleneck
Will re-split this crate
Overestimated
140us
Plan: May be possible to speed up EMC
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L1 Trigger System
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L1 Trigger Primitives (I)
 DCT primitives:
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BLT coarse rf tracks with no Z/tanl/Pt info
• A16: long track reaching SL10 (Pt>180MeV)
• B16: short track reaching SL5 (Pt>120MeV)
ZPD 3D tracks with Z/tanl/Pt info reaching SL7
• Z16: standard Z track (|Z|<12cm, |Pt|>200 MeV)
• Zt8: tight Z cut track (|Z|<10cm, |Pt|>200 MeV)
• Z’8: high Pt track
(|Z|<15cm, |Pt|>800 MeV)
• Zk4: moderate Pt cut (|Z|<10cm, |Pt|>350 MeV)
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L1 Trigger Primitives (II)
 EMT primitives:
o
o
o
o
M20: f strip energy sum MIP
(>120MeV)
G20: f strip energy sum medium E (>300MeV)
E20: f strip energy sum high E (>800MeV)
Y10: Backward barrel high E
(>1 GeV)
 IFT primitive:
o
U3: coded pattern number for various 2 muon and 1 muon
barrel/endcap hit topologies
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This configuration
is used throughout
2001-2004 runs.
Feb/02
The ‘Beam/beam’
contribution can
also be due to low
angle Bhabha
debris.
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Possible L1 configuration improvements
Present DCZ trigger
Additional 1Zn
track for some lines
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Possible L1 configuration improvements
Example of tighter DCZ configuration: Add a requirement for a loose
ZPD track = 1Zn, with either Pt>+0.8GeV/c or Pt<-0.25GeV/c
BB generic
B->p0p0 + B->X
B->tn + B->X
cc
uds
Bhabha
mm
tt
Current DCZ Test case
100.0%
100.0%
99.85%
99.85%
100.0%
100.0%
99.98%
99.96%
98.92%
98.78%
99.94%
99.94%
99.74%
99.68%
98.58%
98.35%
Reduces L1 trigger
rate by 13% with
no impact on
physics acceptance
(Hadronic final states: all events
Leptonic final states: fiducial events)
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Conclusions
 Radiation damage to hardware systems carefully
monitored and controlled
o
o
Except for a small angular range in horizontal plane of the SVT,
all systems will continue to perform through and beyond 2008
Occupancies also result in modest impact on efficiency, under
investigation and study
 Approaching a number limits for daq system
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Removing fiber limit for SVT next goal, as well as resolving
small discrepancies in model performance vs data
EMC FEX would be a substantial challenge, possibly
representing a limit for L1 trigger rate at ~5kHz
L1 trigger investigations ongoing; should be sufficient handles
with new DCZ trigger elements to keep rate below 5kHz with
little or no physics impact
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