Non-Prompt Tracks with the SiD Baseline Detector

6th SilC Meeting Torino, Italk

December 17 2007

Bruce Schumm

Santa Cruz Institute for Particle Physics

Many have contributed…

SLAC: Tim Nelson

Kansas State: Dima Onoprienko, Eckard von Toerne

Santa Cruz: Chris Betancourt, Chris Meyer, Tyler Rice, Lori Stevens, Bruce

Schumm, Eric Wallace

In all its glory:The SiD Tracker

“Inside-Out” Tracking requires 4 VXD layers

For e+e- qq, 5% of charged tracks originate outside of rorg = 2cm

“Cheat” these particles and their hits away (remove them from the banks). How well can we do on remaining “non-prompt” tracks?

Initial Tool: Axial Barrel Track Finder (ABTF)

Originally written by Tim Nelson to find tracks when VXD is tired or sick.

Finds tracks in 5-layer central tracker by extending three-hit seeds inward.

Optimized for non-prompt tracks (relax IP constraint, add a few tricks) by UCSC students.

UCSC students also added capability to use modular z information

Apply to qq events at Z Pole and at Ecm = 500 GeV (require at least 4 hits; all fakes are 4-hit)

pythiaZPolebbbar-0-1000_SLIC_ v1r9p3_sidaug05.slcio, no beam no brem

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Log base 10 of segmentation length (in cm)

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Found 5

Found 4

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Fake

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Combining all three 500GeV data sets

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Log base 10 of segmentation length (in cm)

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Kansas State’s “Garfield” Algorithm

Extrapolates calorimeter “stubs” into tracker, attaching hits as appropriate

Adapted by UCSC students to run as third-pass tracker, after “cheating” and ABTF

Goal: improve efficiency and/or clean up 4-hit tracks and, if we can, reconstruct the 3-hit tracks.

Start with Z-Pole Events

Axial Barrel4 Hit Tracks

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Z Segmentation

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AB Found

AB Fake

Missing

ABTF 4-hit tracks already fairly pure; can Garfield help with leftovers?

Garfield gets a few more. But what about 3-hit tracks?

Garfield4 Hit Tracks

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Z Segmentation

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GAR Found

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Not so exciting.Can we reliably reconstruct tracks that originate outside the second tracking layer?

3 Hit Tracks

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Z Segmentation

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GAR Found

GAR Fake

Missing

Seeds-to-Stubs ProgramInstead, UCSC students proposed matching precise three-hit tracker seeds to Garfield stubs

Helix – Stub Matching (optimized for Z qq)• Base Difference < 2 mm• Phi Difference < 100 milliradians• Curvature Ratio ( (seed - stub)/ seed ) < 10

e.g.: Position-matching for isolated muons

(mm)

Seed-to-Stubs Performance; Z qq

Of a total of 20 3-hit particles:

• 12 were reconstructed as 3-hit tracks, with only 4 fakes

• Two additional 4-hit particles were found

BUT: Performance vastly worse for e+e- qq at Ecm = 500 GeV. Could optimize for this type of event, but do we want to?

Algorithm tuning dependent on signature under exploration

Next Steps: GSMB?

With Jonathan’s help, will generate meta-stable e+e- stau+ stau- with stau+ +

+ gravitino

Signature will be stiff charged track with kink (1-prong tau) or star (3-prong tau) in midst of tracker

Challenge will be to reconstruct kink again SM background of e+e- +

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We’ve just started on this.

3-Hit Tracks & Non-Prompt Signatures

Probably need 5+1 layers for prompt track

If we require 4 hits for non-prompt tracks, sensitive region for kinked tracks is very limited.

ConclusionsIn the abstract, four-hit tracks (Rorg < 46 cm, compared to Rmax = 125 cm) seem possible with tracker + cal assist

Three-hit tracks (Rorg < 72 cm) very scenario-dependent, so trying to look at meaningful signature (GSMB)… what else?

Use these signatures to pin down value of z segmentation

What about detector concepts other than SiD?

Note: Much of this work done with junior and senior UG physics majors.