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Trigger

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processors, networking, memory, storage, fiberoptics ... applications were crucial to current generation of expts. A vital R&D program will be crucial to SLHC ... – PowerPoint PPT presentation

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Title: Trigger


1
Trigger Data Acquisitionfor LHC
UpgradesInternational Workshop on Future Hadron
CollidersFermilabOctober 16-18, 2003
  • Andrew J. Lankford
  • University of California, Irvine

2
Acknowledgements
  • My presentation draws heavily upon
  • Work performed by contributors to the preliminary
    studies reported in
  • Physics Potential and Experimental Challenges of
    the LHC Luminosity Upgrade (hep-ph/020487).
  • A recent presentation by Nick Ellis at Erice.

3
SLHC Implications of Higher Luminosity
  • Higher Luminosity gt
  • Increased detector occupancy
  • Increased trigger rates
  • Increased radiation effects
  • Assumed SLHC luminosity 1035 cm-2s-1

4
SLHC Implications of Higher Luminosity - 2
  • Higher Luminosity gt Increased detector occupancy
  • Assuming 12.5 ns bunch spacing,
  • 125 interactions/crossing
  • Occupancy of tracks increases 5-fold (10-fold for
    some sub-detectors)
  • Radiation-induced hits increase 10-fold.
  • Pile-up noise increases 2.2-fold (3-fold for some
    sub-detectors)
  • Pile-up degrades performance of trigger
    algorithms
  • Reduction in efficiency of e/gamma isolation cuts
  • Increased muon candidate rates due to
    radiation-induced accidentals
  • Larger event size to read out
  • Increased by factor between 5 and 10
  • Demands reduced trigger rate or increased data
    bandwidth

5
SLHC Implications of Higher Luminosity - 3
  • Higher Luminosity gt Increased trigger rates
  • Arising from
  • Increased interaction rates
  • Occupancy/pile-up induced trigger degradation
  • Less rejection at fixed efficiency
  • Need more selective triggers for same trigger
    rate
  • Increased thresholds
  • More exclusive selection (less inclusive trigger)
  • Fortunately, more selective triggers are okay
  • (see later)
  • Need even more data acquisition bandwidth if
    higher trigger rate.

6
SLHC Implications of Higher Luminosity - 4
  • Higher Luminosity gt Increased radiation effects
  • Directly affects on-detector trigger logic
  • Mechanisms
  • Permanent damage
  • Single-event-upset effects
  • (Note that radiation effects upon detectors and
    their electronics must be handled by trigger and
    by data acquisition.)

7
Enabling Technologies
  • Enabling technologies for readout and trigger
  • Integrated circuits
  • Custom ICs, FPGAs, memories, etc.
  • Commodity computing
  • processors, networking, memory, storage,
    fiberoptics
  • These technologies enabled current generation of
    expts.
  • Including the nearly-deadtimeless, integrated
    trigger and data acquisition systems that are now
    standard.
  • These technologies will also be the technologies
    that enable successful upgrades future
    experiments.
  • RD programs to develop these technologies for
    HEP applications were crucial to current
    generation of expts.
  • A vital RD program will be crucial to SLHC
    upgrades.

8
Data Transfer Data Processing
  • Trigger Data Acquisition systems provide
  • Data transfer
  • Data processing
  • Limitations or costs of these functions define
    limitations and costs of Trigger/DAQ systems.
  • e.g. First Level Triggers (FLT)
  • Data input to FLT limits density of FLT
    electronics.
  • Causes extensive interconnections betw. modules
    and complex backplanes.
  • Needed to connect steps in FLT selection.
  • Needed to seamlessly find tracks and clusters in
    different sections of detector (to avoid loss of
    efficiency

9
SLHC Trigger Menu
  • Need for 3 types of triggers foreseen
  • Discovery physics
  • Very high-pT (thresholds as high as hundreds of
    GeV)
  • Completion of LHC physics program
  • e.g. precise measurements of Higgs sector
  • Lepton/photon/jet thresholds as low as for LHC
  • Final states known gt exclusive selection
    possible
  • Control / Calibration triggers
  • e.g. Ws, Zs, top
  • Low thresholds needed, but can be pre-scaled
  • None of the above pose rate problems.

10
Inclusive Triggers samples rates
LHC LHC SLHC SLHC
Selection Threshold Rate Threshold Rate
  (GeV) (kHz) (GeV) (kHz)
inclusive single muon 20 4 30 25
inclusive, isolated e/gamma 30 22 55 20
muon pair 6 1 20 few
isolated e/gamma pair 20 5 30 5
         
inclusive jet 290 0.2 35 1
jet missing ET 100100 0.5 15080 1-2
inclusive ET     150 lt1
multi-jet triggers various 0.4 various low
Note that inclusive e/? trigger dominates rate.
(Added degradation from pile-up not included
above)
11
FLT Importance of FLT upgrades
  • Upgrades to First Level Trigger (FLT) are of
    central importance.
  • They can reduce new demands on
  • Front-end electronics (FEE)
  • Retaining 100 kHz FLT rate avoids changes to FEE
    systems that do not require upgrade for other
    reasons.
  • Data Acquisition (DAQ)
  • By reducing new demands for data bandwidth.
  • High Level Triggers (HLT)
  • By reducing new demands for algorithms and
    processing
  • FLT upgrades deserve early consideration.

12
FLT New Demands on Processing
  • New demands on FLT processing posed by
  • Increased event pile-up occupancy
  • New sub-detectors or readout
  • 12.5 ns crossing period
  • Some (at least) new processing will be needed.

13
FLT Impact of 12.5 ns crossings
  • LHC FLTs
  • pipelined processors
  • driven at 40 MHz LHC crossing rate
  • identify crossing of interest
  • Should SLHC FLTs run at 80 MHz Xing rate?
  • Can FLTs remain at 40 MHz ?
  • Can FLTs work at both 40 80 MHz ?

14
FLT Can SHLC FLTs operate at 40 MHz ?
  • Concept of readout time frames
  • FLT identifies pair of crossings (or more) for
    read out
  • e.g. PEP II / BABAR
  • PEP II runs at 250 MHz (4 ns).
  • BABAR system clock 60 MHz (16 ns).
  • L1T runs at multiples of 16 ns.
  • DAQ reads out time frames as large as few
    microsec, as appropriate to subdetector
    technology.
  • May not be possible for many FEE systems
  • Increases data volume on FEE links through DAQ
  • Yes, SLHC FLTs could operate at 40 MHz,
  • But, 40MHz FLTs will generally suffer more from
    pile-up.

15
FLT Should SLHC FLTs operate at 80 MHz ?
  • Advantages
  • Reduced pile-up effects
  • more effective algorithms
  • less data volume (for detectors that identify
    Xing during r/o)
  • Ability to identify crossing that caused trigger
  • Allows more processing steps within fixed latency
  • 80 MHz electronics feasible (Portions already at
    80MHz.)
  • Disadvantages
  • Requires FLT upgrades
  • Increased data bandwidth into within FLT
  • FEE may not be able to deliver data to FLT at
    80MHz
  • Study (cost/benefit) needed.

16
FLT Can SLHC FLTs operate at both 40 80 MHz ?
  • Portions of FLT could operate at 40 MHz while
    other portions operate at 80 MHz.
  • Note Identification of 12.5 ns crossing can be
    derived from 40 MHz samples for calorimeters.
  • Time resolution of calorimeter pulses is much
    better than 25 ns.
  • Timing of pulses is derived by digital filtering
    of multiple samples.
  • Such a scheme already used in ATLAS CSCs w/
    sampling at 20 MHz
  • Some such hybrid likely to be a good solution.

17
High-Level Triggers Data Acquisition
  • Commercial computing networking technologies
    will provide the advances necessary for High
    Level Triggers (HLTs) and Data Acquisition (DAQ)
    systems to perform at SHLC rates.
  • e.g. Moores Law will provide x10 improvement in
    priceperformance ratio wrt LHC start-up 5 years
    after start-up.
  • e.g. Appetite for high-bandwidth graphical
    computing applications will drive networking
    capabilities up and costs down.
  • RD is necessary to develop technology advances
    for HEP applications.
  • Data transfer
  • Data links
  • HLT/DAQ networks
  • Data Sources / Readout Buffers
  • Data processing
  • New HLT algorithms to maintain HLT selectivity
    with increased pile-up
  • Complexity handling

18
Data Links
  • New challenges at SLHC
  • for data links from Front-end Electronics to
    Trigger DAQ
  • Higher bandwidths due to higher occupancies (
    FLT rates?)
  • Radiation effects at transmitting end
  • for some subdetectors, e.g. systems optimized for
    LHC
  • Also to increase input capabilities of FLTs
  • Limitations on data input often limit FLT
    capability.
  • RD needed
  • Applications of commercial developments
  • Possible custom developments

19
HLT/DAQ Networks
  • Networks connect HLT processors to data sources.

CMS/Cittolin
  • Every processor connects to every source.
  • Data moves from sources to processors in parallel
    (parallel event building) to handle high
    trigger rates.

20
HLT/DAQ Networks
  • Commercial networking equipment provides the
    infrastructure for interconnection (switches) and
    data transfer (links).
  • At present, the cost of this equipment determines
    how much data experiments can afford to move to
    HLT processors.
  • Thus, cost can limit trigger rate capability.
  • ATLAS has adopted an RoI-based Level 2 trigger
    in order to reduce overall data bandwidth
    requirements.
  • CMS has developed a scaleable event building
    architecture.
  • SLHC network bandwidth at least 5-10 times LHC
    b/w.
  • Even if SLHC FLTs can provide same rate as at LHC
  • Network bandwidth requirements grow with
    occupancy.

21
HLT/DAQ Networks
Complete HLT/DAQ systems require large networks.
Individual network switches not yet of size
required for full interconnectivity.
22
HLT/DAQ Networks RD
  • RD should track evolution of network technology
  • Seek switches with requisite number of ports to
    avoid multiple switches extra ports
  • Technical challenge to manufacture of switches
    with many high-speed ports is bandwidth
    capability of switch fabric (backplane) that
    interconnects ports.
  • Switches from different vendors behave
    differently within HEP systems
  • Due to internal differences (e.g. buffer sizes)
  • RD will sometimes require very large-scale
    testbeds, which could be provided by large farms
    foreseen for LHC computing and Grid projects.
  • If we desire to use commodity technologies, then
    anticipate use of 10 Gbit Ethernet, as well as
    Gigabit Ethernet in SLHC systems.

23
Data Sources / Readout Buffers
  • This is electronics that buffers detector data at
    the input of HLT/DAQ systems and that sources
    data into HLT/DAQ networks.
  • They tend to operate at highest rates
  • (relative to other HLT/DAQ components).
  • Cannot benefit from event parallelism,
  • as exploited by other components
  • Each data source must function at full FLT rate.
  • Increased occupancy (and increased FLT rate)
    increase data source internal bandwidth
    requirements.
  • These elements likely to need upgrade for SLHC
    rates.
  • Compare performance with SLHC requirements

24
Data Sources / Readout Buffers RD
  • Upgrade directions
  • Internally, these elements tend to employ busses
    for data transfer.
  • Reasonable for O(80Mword/sec) on circuit board
  • Challenging for higher bandwidths between groups
    of modules (e.g. on backplanes)
  • High-speed serial connections may provide better
    data transfer in upgrades.
  • Technology trends in this direction
  • FEE inputs to these elements already on serial
    links.
  • Serial output links to HLT/DAQ network with
    bandwidth comparable to bandwidth of input links
    will remove bottleneck.
  • I.e., push network technology closer to FEE, to
    exploit
  • High-speed serial links
  • Parallelism afforded by networking

25
HLT Algorithms
  • New HLT algorithms needed
  • To maintain selectivity in face of increased
    occupancy and pile-up
  • e.g. Electron triggers
  • Dominate FLT output rate, unless thresholds
    raised high
  • FLT rate 22 kHz _at_ 30 GEV threshold at LHC
  • FLT selectivity degraded because pile-up blurs
    isolation
  • HLT algorithms must recovery selectivity despite
    degraded isolation.
  • How can this be accomplished? Will refined
    tracking information need to brought to bear
    early in selection sequence?
  • e.g. Muon triggers
  • Degraded by occupancy
  • Degraded by loss of momentum-resolution at higher
    threshold
  • HLT algorithms must recover selectivity.
  • HLT algorithms must accommodate upgraded muon
    detectors.
  • Moores Law will provide data processing power
    for new algorithms.

26
Complexity Handling
  • HLT/DAQ systems are extremely complex.
  • Large numbers (thousands) of processors
  • Even larger numbers of software processes tasks
  • Highly distributed, heterogeneous system
  • Real-time demands not present in offline
    systems
  • Complex control (e.g. startup shutdown)
    procedures
  • Remote access required for monitoring
    troubleshooting
  • Very high reliability required
  • Robustness, redundancy, fault tolerance
  • Including robustness of complex selection
    algorithms
  • Note Technology evolution may mean that SLHC
    HLT/DAQ systems are no larger than for LHC. In
    this case, SLHC complexity stays same as LHC

27
Complexity Handling RD
  • RD can develop solutions to manage complexity.
  • RD can track development of tools for
    complexity handling in very large commercial
    and other applications.
  • E.g. web tools from e-commerce for high-level
    controls and user interfaces
  • Similar remote access, security, database issues

28
Summary
  • Higher Luminosity gt
  • Increased event pile-up detector occupancy
  • Increased trigger rates data volume
  • Increased radiation effects
  • Enabling technologies
  • Integrated circuits custom, FPGAs, memories,
    etc.
  • Commodity computing networking
  • Challenges arise in data transfer in data
    processing
  • Processing challenges felt mainly in First Level
    Triggers
  • Data transfer challenges felt in both FLTs and
    HLT/DAQ
  • Trigger rates manageable by
  • Increasing thresholds on inclusive triggers
  • Using exclusive triggers where low thresholds
    needed
  • Technical solutions exist, but RD is required.

29
RD Summary
  • First Level Triggers
  • Operation with 80 MHz crossing rate
  • Coping with increased occupancy (muons) pile-up
    (calorimeter)
  • Adapting to new sub-detectors or readout
  • Radiation-tolerant on-detector FLT electronics
  • Input data links from Front-end Electronics
  • High Level Triggers Data Acquisition
  • Coping with increased data bandwidth
  • Input data links, HLT/DAQ networks, data sources
    / readout buffers
  • Coping with increased occupancy pile-up ( new
    detectors or r/o)
  • New HLT algorithms
  • Complexity handling
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