# Presentation: 950486

## 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?
- Selected physics cases
- Think outside the box!

## 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???

## 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!

## FastTrack to the rescue!

- Where is the Higgs?

- Help!

## The case for offline-like b-tagging

- ATL-DAQ-2000-033

- with Fast-Track offline b-tag performances early in LVL2. You can do things 1 order of magnitude better

- ATLAS TDR-016

- 0.6

- 100

- 10

- 1000

- b

- Ru

-  Calibration sample

## FastTrack/LHC: access to the 3rd generation

- ATL-COM-DAQ-2002-022

- F. Gianotti, LHCC, 01/07/2002
-  CMS TDR 6 &

- Scenario: L= 2 x 1033  deferral

- ATLAS

- 40

- 20
- 210

- 0.8
- 0.2

- 20
- 26

- HLT rate (Hz)

- HLT
- selection

- LVL1 rate (KHz)

- LVL1
- selection

- Even better strategies: see ‘physics cases’

## 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?

- ... it turns out CDFII has been doing something similar since day 0

- The recipe uses specialized hardware:
- Clustering
-       Find clusters (hits) from detector ‘strips’ at full detector resolution
- Template matching
-       Identify roads: pre-defined track templates with coarser detector bins (superstrips)
- Linearized track fitting
-       Fit tracks, with combinatorial limited to clusters within roads

## Is it effective?

- 2 b-jets (Zbb)
- MET + disp. tracks (ZH)
- lepton + disp. track (SUSY)
- gamma + disp. track (SUSY)

- Many high-pt triggers based on SVT are taking data.

- SVT rejection:
- 3 orders of magnitude

## Can we scale to the ATLAS complexity?

- Not easy:
- 500K channels  O(100M)
- 20s2s
- 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

## 1/2  AM

- 1/2  AM

- 1/2  AM

- Divide into
-  sectors

- 6 buses 40MHz/bus

- ATLAS Pixels + SCT

- Allow a small overlap
- for full efficiency

## How to pick the ATLAS data?

- Fast Track   + few
- (Road Finder)  CPUs

- ROB

- offline
- quality
- tracks:
- Pt >1 GeV

- Ev/sec = 50~100 kHz

- ~NO impact on DAQ

- PIPELINE

- LVL1

- Fast network connection

- CPU FARM (L2 Algorithms)

- CALO       MUON    TRACKER

- Buffer
- Memory

- ROD

- Buffer
- Memory

- ROB

- FE

- FE

- S-link

- Two outputs!

- ~40 9U VME boards

## Selected Physics Cases

## Lots of ideas, limited energy:

| Zbb | Better acceptance (calibration samples) |
| --- | --- |
| bbH/A
       Hbb, | Low Pt b-jets |
| Hhh bb bb |  |
| l | Lower thresholds (calibration sample) |
| W |  |
| Multi-prong  triggers | Improved acceptance |
| B | Lower thresholds |

## Example 1: Zbb

- 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: qgZqbbq (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) |

## Example 2: bbH/A  bbbb

- ATLAS-TDR-15 (1999)

- MA (Gev)

- tan

- 200

- Standard trigger limits tan reach at low MA !!!

## Example 3:  @ CMS

- L=2x1033 cm-2 sec-1

- 0     0.02        0.06          0.1          0.14
- 	           (QCD 50-170 GeV)

-  (H(200,500 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

- 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

## Q: Which of these represents an actual trigger rate vs luminosity?

**Q: Which of these represents an actual trigger rate vs luminosity?**

## 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:

## 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!

## 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?

## Some References:

- perform b tagging.

- ol that allows good

- trigger

- 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

## IEEE Trans. Nucl. Sci. 51, 391 (2004) 

- IEEE Trans. Nucl. Sci. **51**, 391 (2004)