forward tracking in a linear collider detector robin glattauer rudolf frühwirth winfried a....

Forward Tracking in aLinear Collider Detector

Robin Glattauer

Rudolf Frühwirth

Winfried A. Mitaroff

Annual Meeting of ÖPG-FAKT

Univ. Graz, 18–21 Sept. 2012

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• Physics motivation• Experimental environment:

– International Linear Collider (ILC)– International Large Detector (ILD)

• Track reconstruction:– Strategy– Forward tracking– Performance

• Summary and outlook

Winni Mitaroff: ÖPG-FAKT21 Sept. 2012


Collisions at the TeV scale

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Cross sections at the TeV scale

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p p e– e+

Winni Mitaroff: ÖPG-FAKT

LHC ILCe– e+ Z H Z e– e+, H b b …

Example: simulated Higgs event

–

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The International Linear Collider (ILC)

– 3 stages: collision energies 250 GeV (“Higgs Factory”), 500 GeV, eventually 1 TeV (adjustable for scans in range 200 – 500 GeV);– Stability and precision of the beam energies to be below 0.1 %;– Peak luminosity of ≈ 2×1034 cm-2s-1, with an integrated luminosity of 500 fb-1 to be achieved within the first 4 years of operation;– Electron polarization at least 80%, positron polarization an option;– Options: Z0 factory (“GigaZ”), e–e–, e–γ, γγ (“photon collider”).

The ILC basic design is a worldwide consent since autumn 2004;Technology is based on superconducting RF cavities at 1.3 GHz,average field gradient is 31.5 MV/m in the first stages ≤ 500 GeV; The project is pursued by the “Global Design Effort” since 2005.

Beam crossing angle 14 mrad;Only 1 experimental zone with2 detectors operated in “push/pull”.

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The International Large Detector (ILD)

• Central tracking detector: large TPC– excellent pattern recognition in a dense track environment,– proven technology;

• Silicon tracker: pixels and ss/ds strips– extended tracking coverage,– improved track momentum resolution;

• High-precision Si vertex detector– close (16 mm) to the beam interaction point,– best possible heavy flavour tagging;

• Fine-granularity calorimeters– particle flow (PFA) calorimetry is an asset,– provides necessary jet energy resolution;

• Solenoid magnetic field of 3.5 T– upgradable to 4 T (for the ILC 1 TeV stage);

• Almost 4π geometric acceptance– to the benefit of tracking & calorimetry.

Basic design parameters (ILD_00):

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HEPHY Vienna is founding member of the ILD proto-collaboration.ILD is one of two ILC detector concepts “validated” by IDAG in April 2009.


The ILD silicon trackers

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Domain of HEPHY Vienna’shardware contributions !


ILD Forward Tracking Detector (FTD)

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Forward track reconstruction in ILD

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Stage 1: Cellular Automaton (CA),Stage 2: Kalman Filter (KF),Stage 3: Hopfield Neural Network (HNN).

Embedded in ILD’s software framework Marlin.

New stand-alone software package ForwardTracking:

Fast semi-global track finding method: Takes all hits into account simultaneously, but

situation evolves based on local rules; Track segments interact with connected ones and are

tested for compatibility.

Stage 1: the Cellular Automaton (CA)

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Stage 2: the Kalman Filter (KF)


Two main goals: Track parameter determination, Chi-squared probability gives feedback about

the track quality; Chi-squared probability cut value = 0.005; Algorithms called:KalTest + KalDet + MarlinTrk.

Note: an ultimate track fit by a KF + smoother will alsobe performed, after track search, on the final sample !

Stage 3: Hopfield Neural Network (HNN)

Ambiguity resolving:this is the last stage in forward track search;

Tracks sharing hits are incompatible:overlap comes from combinatorics in reconstruction

ghosts and clones:⇒


How does the HNN work ?

Tracks are assigned a quality and an activation state, and they do dynamically interact;

Compatible tracks amplify each other, whereas incompatible ones weaken each other;

In order to prevent oscillation between states, updating is done asynchronously;

A global extremum is searched for – in order to avoid falling into a local one, an annealing scheme is used (by assigning the system a “temperature” being cooled down).


ForwardTracking: new forward tracking package, SiliconTracking: old package (still used in barrel), TrackSubsetProcessor: combines results of both.

Performance: efficiency


ForwardTracking: new forward tracking package, SiliconTracking: old package (still used in barrel), TrackSubsetProcessor: combines results of both.

Performance: ghost rate


ForwardTracking: new forward tracking package, SiliconTracking: old package (still used in barrel).

Performance: processing time


Background scaled conforming to the LoI with 500 GeV !

Conclusions and Outlook

A new software package for stand-alone track reconstruction in the forward region of ILD has been successfully developed and implemented;

It shows superior performance w.r.t. the old ILD software (originally developed for the barrel);

Our ForwardTracking package is on board for benchmark processing for ILD’s “Detailed Base-line Design” (DBD) report, due by Dec. 2012;

Our package will also be used for a modified ILD detector at the “Compact Linear Collider” (CLIC).


Backup Slides

19Winni Mitaroff: ÖPG-FAKT21 Sept. 2012


Toy detector: true tracks

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True hits (green) + background hits (red)


CA: building segments (“cells”)



CA: iteration #1 (red states)

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CA: iteration #2 (orange states)

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CA: iteration #3 (green states)

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CA: iteration #4 (blue states)

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CA: after clean-up of bad states


KF + HNN: final tracks found


Two machine studies: ILC and CLIC


The CERN Linear Collider Detector Project: adapting the ILC detector concepts for the higher CLIC energies (CLIC_ILD, CLIC_SiD), and using the software developed by the ILC collaborations for simulation and optimization studies.The decision ILC vs. CLIC will be based on “new physics” results from LHC. If it will be in favour of CLIC, the ILC detector collaborations will move.

Detector performance requirementsof ILC / CLIC vs. those of LHC


○ Inner vertex layer ~ 3 - 6 times closer to IP

○ Vertex pixel size ~ 30 times smaller

○ Vertex detector layer ~ 30 times thinner

Impact param resolution: Δd ≤ 5 μm + 10 μm / [ (p/GeV) x sin3/2 θ ]

○ Material in the tracker ~ 30 times less

○ Track momentum resolution ~ 10 times better

Momentum resolution: Δp / p2 ≤ 5 x 10-5 / GeV “barrel region”,

Δp / p2 ≤ 3 x 10-5 / GeV “forward region”

○ Granularity of EM calorimeter ~ 200 times better

Jet energy resolution: ΔE / E ≤ 0.3 /√Eo Forward hermeticity down to θ ≥ 5 - 10 mrad

Forward region of ILD_00 layout


ϑ = 900

36.70

25.50

16.50

11.50

80

50

10 padrows →

FTD 1 2 3 4 5 6 7

Very forward region:– 5.00 < ϑ < 11.50: only FTD measuremts. contributing,– Range of FTD 1 (2) starts where that FTD 6 (7) ends.Intermediate region:– 11.50 < ϑ < 25.50: complex mix of VTX + FTD + TPC,– FTD: only FTD 1 … 3, plus FTD 4 until ϑ < 16.50,– TPC: 10 pad-rows @ 11.50 … 100 pad-rows @ 25.50.Barrel + FTD 1 only:– 25.50 < ϑ < 36.70: VTX + FTD 1 + SIT + TPC.ETD: ignored by track fitting (no more precision)– 9.80 < ϑ < 36.90: PR link to fwd. ECAL, useful in PFA.

Pixel disks Double-sided (stereo angle) strip disks

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Spurrekonstruktion für FTD

Jeder Detektor ist anders Hintergrund

Paarbildung (Photonen) Pixels: aufintegrierte Events Strips: Ghost Hits

Geschwindigkeit Efficiency und Ghost Rate Wart- und Lesbarkeit

TPC

FTD

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Processors in ILD’s framework “Marlin”

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For compatibility cut off criteria are needed

Cut offs rely on analysis of true tracks

Efficiency vs. ghost rate & computing time



Conways Spiel des Lebens

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forward tracking in a linear collider detector robin glattauer rudolf frühwirth winfried a....

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