# Presentation: 080190

## The Silicon Track Trigger (STT) at DØ

- Beauty 2005  in Assisi, June 2005

- Sascha Caron
- for the DØ collaboration

- Tag

- beauty

- fast ...

##                                                                                       page 1

- The Silicon Track Trigger at DØ

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

-                      Sascha Caron

##                                                                                       page 2

- The Silicon Track Trigger at DØ

-                      Sascha Caron

**D0 in Run II**

- The Silicon Track Trigger is based
- on information
- of the :
- Silicon Microstrip
- Tracker
- Central Fiber Tracker

##                                                                                       page 3

- The Silicon Track Trigger at DØ

-                      Sascha Caron

**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| < 1.7

##                                                                                       page 4

- The Silicon Track Trigger at DØ

-                      Sascha Caron

- Events for
-  L=100 E30 cm-2/s
- = about 8 pb-1/day

- 10

- 1

- 0.1

- 0.01

- 0.001

- Higgs->b bbar

- ZH-> bbvv, bH->bbb etc.

- Z-> b bbar

- QCD ET>30 GeV
- dijet production

- b-jets ET>30 GeV

- 0.0001

- Events
- per
- second

- Find b-events
- early to keep
- high efficiency
- at an acceptable
- rate

- Aim: High ET
-  Z->bb, HZ->bbvv, H->bb, etc.
- Hopefully B physics

##                                                                                       page 5

- The Silicon Track Trigger at DØ

-                      Sascha Caron

**Principal Idea**

- B **decay length is mm**

**Impact parameter**
**(2d in x-y plane)**

**B decay products**

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

**Interaction point **
**is mean beam spot**

##                                                                                       page 6

- The Silicon Track Trigger at DØ

-                      Sascha Caron

- L1 Trigger
-  decision time
- about 4 μs

**(1500) 5000 Hz**

**(700)**
**1000Hz**

**50 Hz**

**2.5MHz**

- L2 Trigger
-  decision time
- about 200 μs

- L3 Trigger
-  decision time
- about 50 ms

**Trigger System**

- p p bunch	 crossing frequency

-  ̄

-  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

##                                                                                       page 7

- The Silicon Track Trigger at DØ

-                      Sascha Caron

- Silicon
- Micro
- Detector

- Central
- Fiber
- Tracker

**L2**
**STT**

- L1
- CTT

- L2
- CTT

- L2
- Global

- other
- L2 pre-
- processors

**Detector**

**Level 1**

**Level 2**

**Level 1**

**Detector**

**Data flow chart L2 tracks**

##                                                                                       page 8

- The Silicon Track Trigger at DØ

-                      Sascha Caron

**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

##                                                                                       page 9

- The Silicon Track Trigger at DØ

-                      Sascha Caron

**Silicon Track Trigger cards**

- Road data to
- Fiber Road Card

- SMT data to
- 9 Silicon Trigger
-  Cards

- Fitting done
- in Track Fit Card

- L2CTT

- Done in parallel for each
- of the 12 sectors
- 2 sectors in 1 crate
- -> 6 Crates with
- 1 Fiber Road Card
- 9 Silicon Trigger Cards
- 2 Track Fit Cards

##                                                                                       page 9

- The Silicon Track Trigger at DØ

-                      Sascha Caron

**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

- - Perform clustering and cluster-road matching
- - Clusters SMT hits + pedestal correction
- - Axial clusters are matched to the roads

- Fitting done
- in Track Fit Card

- - receives road and axial clusters
-  convert to physics coordinates via LUT
-  perform track fit φ(r)= b/r+kr+φ0
-  beam spot correction
-  output tracks to L2CTT

##                                                                                       page 10

- The Silicon Track Trigger at DØ

-                      Sascha Caron

**Performance studies STT tracks**

- Impact Parameter resolution

- Correlation to RECO

- pT(GeV)

- Resolution in μm

- Purity

- Including beam spot size 35 μm
- and 15 μm SMT resolution

##   B identification                  

-                                                                                       page 11

- The Silicon Track Trigger at DØ

-                      Sascha Caron

- - Fast, simple and efficient technique
- - Time needed is 2 operations per track and goes linear with the number of tracks -> about 1-5 μs
- - Degrades bad tracks without cutting them

- Store 2d signal (b events) to background (light quarks) ratio into a lookup table

**  ****B ****identification                  **

- Signal to Background ratio

-  b/db

- 1.5 mm

- Ri

##                                                                                       page 12

- The Silicon Track Trigger at DØ

-                      Sascha Caron

**Performance studies**

**Very well separation of signal and **
**background events**

**Large background reduction**
**with L2 b-ID algorithms**

- efficiency Z->bb

- L2 B-id likelihood

-  Red :
- Simple Cut
- Blue/Green:
- B-id

##                                                                                       page 13

- The Silicon Track Trigger at DØ

-                      Sascha Caron

**First studies**
**using data**

- Max IP Significance

- Likelihood

- L2 data well correlated with offline data
- -> proof of b-id principle -> Much more studies on their way

- Jet data
- Offline B-tagged data

- Likelihood shifted to
- higher values due
- to e.g. min bias effects

- DØ
- preliminary

- Using MC pdfs

- DØ
- preliminary

## Summary

- The Silicon Track Trigger at DØ

-                      Sascha Caron

**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->bb and Higgs physics now and at L=200E30cm-2/s

**Outlook**

-   Implementation of new Layer 0 (r=22mm) into STT
-     -> further increase in precision and stability