fasttrack: real time silicon tracking for lhc
DESCRIPTION
FastTrack: Real Time Silicon Tracking for LHC. Alessandro Cerri (borrowing from several talks…). Outline. What are we talking about? ATLAS trigger (quick!) overview What’s missing? Does it work? How? CDFII experience Evolving towards LHC Why would one want to use it? - PowerPoint PPT PresentationTRANSCRIPT
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FastTrack: Real Time Silicon Tracking for LHC
Alessandro Cerri(borrowing from several
talks…)
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Outline
• What are we talking about?– ATLAS trigger (quick!) overview– What’s missing?
• Does it work? How?– CDFII experience– Evolving towards LHC
• Why would one want to use it?– Selected physics cases
• Think outside the box!
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The ATLAS Trigger
• High rate pp collisions force us to throw away events: 40MHz ~100Hz
• You want to throw away uninteresting* stuff
• How?• Combine trigger primitives:
“crude” approximations of analysis objects, like:– Jets– e/– Tracks
– Et (and lack thereof)
– EM
• Where is the 3rd generation???
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FastTrack• L2 is designed to be basically a
commercial CPU farm• …not enough time to reconstruct tracks
at full resolution• Why would I want to do that?
– b tagging – … but keep your mind open: you can do a
lot more with a little fantasy!• Is there money (physics reach) to gain?
3rd generation is the closest to new physics!
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30 minimum bias events + H->ZZ->4
Tracks with Pt>2 GeV
Where is the Higgs?
FTK
FastTrack to the rescue!
Where is the Higgs?
Help!
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ATL-DAQ-2000-033
with Fast-Track offline b-tag performances early in LVL2. You can do things 1 order of magnitude better
ATLA
S T
DR
-016
0.6
100
10
1000
b
Ru Calibration sample
bbH/A bbbb
tt qqqq-bb
ttH qqqq-bbbb
H/A tt qqqq-bb
H hh bbbb
H+-
tb qqbb
Z0 bb
The case for offline-like b-tagging
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FastTrack/LHC: access to the 3rd generationA
TLA
S +
FTK
4ET200 +
j70 + j50 + j15 (||<2.5)
““
““
2.66 + j25 + j10 (||<2.5)
ATL-
CO
M-D
AQ
-20
02-
02
2
F. G
ianott
i, L
HC
C, 0
1/0
7/2
002
CM
S T
DR
6 &
Scenario: L= 2 x 1033 deferralA
TLA
S
CMS 5b-jet 237Inclusive b-jet
50mini ev.
2 b-jets +Mbb > 50
160mini ev.
2 b-tags +Mbb > 50
0.20.20.2
j2003j904j65
4020210
0.80.2
2026
HLT rate (Hz)
HLT selection
LVL1 rate (KHz)
LVL1selection
25
j4003j1654j110
13b leading
43 b-tags
Even better strategies: see ‘physics cases’
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Is it feasible?• We are talking about something
capable of digesting 100000 evts/second and identifying tracks in the silicon
• What on earth would be able to do that?
~ 48 m
Single Hit
Superstrip
Road
Dete
ctor
Laye
rs
•… it turns out CDFII has been doing something similar since day 0•The recipe uses specialized hardware:
1)Clustering Find clusters (hits) from detector ‘strips’ at full detector resolution
2)Template matching Identify roads: pre-defined track templates with coarser detector bins (superstrips)
3)Linearized track fitting Fit tracks, with combinatorial limited to clusters within roads
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Is it effective?
2 b-jets (Zbb)MET + disp. tracks (ZH)lepton + disp. track (SUSY)gamma + disp. track (SUSY)
Many high-pt triggers based on SVT are taking
data.
SVT
SVT rejection:3 orders of magnitude
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Can we scale to the ATLAS complexity?
• Not easy:– 500K channels O(100M)– 20s2s
• But feasible:– SVT has been designed in
~1990 with (at the time) state of the art technology
– We have been thinking a lot on how to improve the technology
– The SVT ‘upgrade’ (2005) is in fact partly done with hardware capable of LHC-class performance!
1998: Full custom VLSI “Associative Memory” chip:
128
patterns
2004: Standard Cell “Associative Memory” chip:
~5000
patterns
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1/2
A
M1
/2
AM
Divide into sectors
6 buses 40MHz/bus
ATLAS Pixels + SCT
Feeding FTK @ 50KHz event rate
Pixel barrel SCT barrel Pixel disks
6 Logical Layers: full coverage
2 sectors
~70MHz cluster/layer(Low Luminosity, 50KHz ev.)
ATLA
S-T
DR
-11
Allow a small overlapfor full efficiency
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How to pick the ATLAS data?
Fast Track + few(Road Finder) CPUs Fast Track + few(Road Finder) CPUs
ROBROB
offlinequalitytracks:Pt >1 GeV
Ev/sec = 50~100 kHz
~NO impact on DAQ
PIPELINE
LVL1LVL1
Fast network connectionFast network connection
CPU FARM (L2 Algorithms)CPU FARM (L2 Algorithms)
CALO MUON TRACKERCALO MUON TRACKER
BufferMemory
ROD
BufferMemory ROB
FEFE
S-link
Two outputs!
~40 9U VME boards
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Selected Physics Cases
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Lots of ideas, limited energy:
Zbb Better acceptance (calibration samples)
bbH/A Hbb,
Low Pt b-jets
Hhh bb bb
l Lower thresholds (calibration sample)W
Multi-prong triggers Improved acceptance
B Lower thresholds
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Example 1: Zbb•Important calibration tool to measure jet response/resolution (-jet and z-jet balance have theo/exp issues)
•Standard trigger: Large L1 rate higher Et threshold high Mjj turn-on
•With FastTrack: qgZqbbq (3jet + btag) advantages:
•Better Mjj acceptance, improved rejection
•Highest Et jet needs not be tagged!LVL1 LVL2 S/B
MU6+ 2J 2.6 KHz Mbb > 50 160 Hz 60 (@20 fb-1)
3J + SE200 4 KHz Mbb > 50 50 Hz 20 (@20 fb-1)
J190 5 KHz 1 non-b, 2b
10 Hz 21 (@30 fb-1)
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Example 2: bbH/A bbbbA
TLA
S-T
DR
-15
(1
99
9)
MA (Gev)
tan
200
Optimized Analysis (not very recent though):4 b-jets |j|<2.5 PT
j > 70, 50, 30, 30 GeV efficiency 10%Effect of trigger thresholds (70,50,30,30)->4x110 !!!
ATLAS + FTK triggers
13%3b leading3j + ET200
8%3 b-tagSoft6 + 2j
Effic.LVL2LVL1 As efficient as offline selection:full Higgs sensitivity
ATL-
CO
M-D
AQ
-20
02
-0
22
Standard trigger limits tan reach at low MA !!!
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Example 3: @ CMS
L=2x1033 cm-2 sec-1
0.4
0.5
0.6
0.7
0.8
0.9
1.
0 0.02 0.06 0.1 0.14
(QCD 50-170 GeV)
(H
(20
0,5
00
GeV
)
1
,3h+
X)
mH=500
mH=200
TRK tau on first calo jets
Pix tau on first calo jet
Staged-Pix tau on first calo jet
TRK tau on both calo jets
Calo tau on first jet
0.0070.004
Efficiency & jet rejection could be enhanced by using tracks before
calorimeters.
L2/L1
Default algorithm: calorimetric search first, then tracking
Isol: R~0.2-0.45
Tag tracks: R~0.07
Lead. Track: R~0.1
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Q: Which of these represents an actual trigger rate vs luminosity?
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Be careful!
•CDF misunderestimated( GWB) the background rates by large (~2x) factors. Not for ingenuity but for lack of better ways of extrapolating to the High Energy Frontier! Expect something similar!
•Rates and rejections must be understood at our best NOW:
•Anything too loose will be cut out/removed
•Trigger rates are *not* dominated by physics:
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Where would I put effort•Simulating background requires HUGE resources: billions of MC events @ 5 minutes/event ?!??
•Revert to fast simulation
•Calibrate (e.g. jet response and trigger efficiencies) from full simulation
•Parameterize in AtlFast!
•Need to strengthen the physics case:
•Ideas
•Other physics cases
•Applications
•Tools
•Fast simulation is basically there (but still not 100%)
•There is a substantial setup time: the sooner the better
•Brainstorming!
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Beyond b tagging?• FastTrack is extremely modular• With little interfacing, any detector can in principle
be used as seed for FastTrack objects:– Muons– Calorimetry– TRT
• What would you be able to do with those at trigger level?
• Any other wild dream of yours?• Mine: FastTrack can do more complicated pattern
recognition than just tracks– Vertices?– Topological triggers?
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perform b tagging. ol that allows good
trigger
Some References:
http://www.pi.infn.it/~orso/ftk/
http://www.pi.infn.it/~annovi/
http://hep.uchicago.edu/cdf/shochet/ (under ftkxxx)
http://www-cdfonline.fnal.gov/svt/
physics
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IEEE Trans. Nucl. Sci. 51, 391 (2004)