The Silicon Track Trigger STT at D

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The Silicon Track Trigger (STT) at DØ
Beauty 2005 in Assisi, June 2005
Tag
fast
beauty
Sascha Caron for the DØ collaboration
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The Silicon Track Trigger at DØ

• OUTLINE
• - D0 detector
• D0 trigger
• What is the STT?
• dataflow
• clustering and tracking
• B identification
• Performance
• Summary

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Sascha Caron
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The Silicon Track Trigger at DØ
D0 in Run II
The Silicon Track Trigger is based on
information of the Silicon Microstrip
Tracker Central Fiber Tracker

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Sascha Caron
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The Silicon Track Trigger at DØ
D0 in Run II
The Silicon Track Trigger is based on
information of the Silicon Microstrip
Tracker Central Fiber Tracker

• 50 µm pitch strips (parallel to beam)
• 800000 readout channels
• Only axial strips used for STT tracks

• Scintillating fibers
• Coverage Rapidity lt 1.7

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Sascha Caron
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The Silicon Track Trigger at DØ
QCD ETgt30 GeV dijet production
Events per second
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Aim High ET Z-gtbb, HZ-gtbbvv, H-gtbb,
etc. Hopefully B physics
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b-jets ETgt30 GeV
Find b-events early to keep high efficiency at
an acceptable rate
0.1
0.01
Z-gt b bbar
0.001
Higgs-gtb bbar
Events for L100 E30 cm-2/s about 8 pb-1/day
0.0001
ZH-gt bbvv, bH-gtbbb etc.

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The Silicon Track Trigger at DØ
Principal Idea
B decay products
B decay length is mm
Interaction point is mean beam spot
Impact parameter (2d in x-y plane)

• Silicon Improved Tracks with
• 2d impact parameter
• Select events with large impact parameter tracks

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The Silicon Track Trigger at DØ
Trigger System
p p bunch crossing frequency

L1 Trigger decision time about 4 µs
(1500) 5000 Hz
(700) 1000Hz
L2 Trigger decision time about 200 µs
L3 Trigger decision time about 50 ms
50 Hz
2.5MHz

• Hardware based
• CTT tracks, calorimeter towers, muons

• Hardware/Software
• simple jets, electrons, muons, taus
• Silicon Microvertex improved tracks (STT)
• global processor to combine information
• (e.g. STT tracks for Bid)

• Software based
• partial event
• reconstruction

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The Silicon Track Trigger at DØ
other L2 pre- processors
Data flow chart L2 tracks
L2 CTT
L2 Global
Central Fiber Tracker
L1 CTT
L2 STT
Silicon Micro Detector
Detector
Level 1
Level 2
Level 1
Detector

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Sascha Caron
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The Silicon Track Trigger at DØ
How is the tracking improved?

• Tracks found at L1 with the Central Fiber
  Tracker are used to define roads into the Silicon
  
• Silicon hits are clustered
• Track is re-fit within the road

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The Silicon Track Trigger at DØ
Silicon Track Trigger cards
Road data to Fiber Road Card
Fitting done in Track Fit Card
Done in parallel for each of the 12 sectors 2
sectors in 1 crate -gt 6 Crates with 1 Fiber Road
Card 9 Silicon Trigger Cards 2 Track Fit Cards

SMT data to 9 Silicon Trigger Cards

L2CTT

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The Silicon Track Trigger at DØ
Silicon Track Trigger cards
Road data to Fiber Road Card

• - Receives and distributes L1 tracks
• Communicates with Trigger
• framework

SMT data to Silicon Trigger Cards
Fitting done in Track Fit Card
- Perform clustering and cluster-road matching -
Clusters SMT hits pedestal correction - Axial
clusters are matched to the roads

• - receives road and axial clusters
• convert to physics coordinates via LUT
• perform track fit f(r) b/rkrf0
• beam spot correction
• output tracks to L2CTT

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The Silicon Track Trigger at DØ
Performance studies STT tracks
Impact Parameter resolution
Correlation to RECO
Resolution in µm
pT(GeV)
Purity
Including beam spot size 35 µm and 15 µm SMT
resolution

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The Silicon Track Trigger at DØ
B identification
Signal to Background ratio
Ri
Store 2d signal (b events) to background (light
quarks) ratio into a lookup table
1.5 mm
b/db
- Fast, simple and efficient technique - Time
needed is 2 operations per track and goes linear
with the number of tracks -gt about 1-5 µs -
Degrades bad tracks without cutting them

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The Silicon Track Trigger at DØ
Performance studies
efficiency Z-gtbb
L2 B-id likelihood
Red Simple Cut Blue/Green B-id
Very well separation of signal and background
events
Large background reduction with L2 b-ID algorithms

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The Silicon Track Trigger at DØ
First studies using data
Using MC pdfs
DØ preliminary
Jet data Offline B-tagged data
DØ preliminary
Likelihood shifted to higher values due to e.g.
min bias effects
Max IP Significance
Likelihood
L2 data well correlated with offline data -gt
proof of b-id principle -gt Much more studies on
their way

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The Silicon Track Trigger at DØ
Summary

• The STT is operating routinely and smooth
• High Impact Parameter resolution
• Data is understood
• Very fast L2 b-id is (almost) implemented
• We expect a high potential for
• Z-gtbb and Higgs physics now and at
  L200E30cm-2/s

Outlook

• Implementation of new Layer 0 (r22mm) into STT
  
• -gt further increase in precision and
  stability

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Sascha Caron