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BTeV Trigger and Data Acquisition System

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BTeV pixel detector with its exceptional pattern recognition capabilities ... With new data arriving at a rate of 7.6 MHz, the L1 trigger must produce a ... – PowerPoint PPT presentation

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Title: BTeV Trigger and Data Acquisition System


1
BTeV Trigger andData Acquisition System
Presentation to the DOE/Fermi Group, January 11,
2001
2
Overview
  • The challenge for the BTeV trigger and data
    acquisition system is to analyzeparticle tracks
    and interaction vertices for every interaction
    that occurs in the BTeV detector (15 million per
    second), and to select interactions with Bs.
  • The trigger performs this task using 3 stages,
    referred to as Levels 1, 2 and 3L1 looks at
    every interaction, and rejects 99 of
    uninteresting dataL2 uses L1 results and
    performs a more refined analysis for data
    selectionL3 performs a complete analysis
    that uses all of the data for an interaction
  • Reject 99.8 of background. Keep gt 50 of
    signal.
  • The data acquisition system saves all of the data
    in memory for as long as isnecessary to analyze
    each interaction ( 1 millisecond on average),
    and movesdata to processing units and data
    storage for selected interactions.
  • The key ingredients that make it possible to meet
    this challenge
  • BTeV pixel detector with its exceptional pattern
    recognition capabilities
  • rapid development in technology FPGAs, DSPs,
    microprocessors
  • good ideas

FPGAs field programmable gate arrays DSPs
digital signal processors
Erik Gottschalk f
3
Trigger/DAQ
Erik Gottschalk f
4
Vertex Trigger
  • The vertex trigger is the primary physics trigger
    for BTeV. The trigger looks forparticles that do
    not come from the main interaction, but appear to
    come from aB-decay vertex close to (of order 1
    10 mm) the main interaction vertex.
  • The first stage of the trigger, L1, reconstructs
    tracks and vertices for every beamcrossing (7.6
    million beam crossings per second), and every
    interaction (averageof 2 interactions per beam
    crossing). L1 handles 15 million
    interactions/second!
  • With new data arriving at a rate of 7.6 MHz, the
    L1 trigger must produce atrigger decision
    (accept or reject) every 132 ns.
  • To accomplish this the L1 trigger uses
    parallelism pipelining
  • data for each beam crossing is subdivided and
    processed in parallel
  • processor farms use parallelism to handle
    multiple crossings simultaneously
  • data can remain in the processing pipeline for
    as long as a millisecond, but trigger decisions
    occur at most every 132 ns, on average

Erik Gottschalk f
5
Simulated Pixel Data (compressed along beam
direction by 10)
  • pixel data for a beam crossing (an interaction
    with B-decay vertices) input to L1
  • data are subdivided and processed in parallel

Erik Gottschalk f
6
Track segments found by the L1 vertex trigger
A key feature of the L1 vertex trigger is that
partial track reconstruction issufficient at
this stage of the trigger. Therefore, we find
tracks as the enterthe pixel detector (close to
vertex), and as they exit (momentum measurement).
entering track segment exiting track segment
Erik Gottschalk f
7
L2 and L3 Vertex Trigger
  • Unlike the L1 trigger, which is built with field
    programmable gate arrays (FPGAs)and digital
    signal processors (DSPs), the L2 and L3 triggers
    are implemented as afarm of commercial
    processors (e.g. INTEL processors running LINUX).
  • L2 trigger (data for one beam crossing are sent
    to a single processor)
  • starts with tracks and vertices found by the L1
    trigger
  • requests data from other detectors (such as the
    forward tracking system)
  • improves the track and vertex reconstruction
  • imposes more selection criteria to reject 80
    90 of crossings that pass L1
  • L3 trigger (L3 begins when all data for a beam
    crossing are sent to a processor)
  • further refinement of selection criteria
  • reject 50 75 of crossings that pass L2
  • reduce the amount of data that will be recorded
  • Output 4000 crossings per second, with an
    average size of 50 Kbytes 200 Mb/sec

Erik Gottschalk f
8
Final Remarks
  • The BTeV trigger and data acquisition system is
    an ambitious project.
  • We benefit from new technologies that help us
    meet the challenge
  • pixel detectors
  • rapid development of FPGAs, DSPs,
    microprocessors
  • BTeV trigger rejects 99.8 of background, keeps gt
    50 of signal.

Erik Gottschalk f
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