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Non-Prompt Tracks with the SiD Baseline Detector

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Non-Prompt Tracks with the SiD Baseline Detector. ALCPG07 FNAL Oct 22 – 26 2007 Bruce Schumm Santa Cruz Institute for Particle Physics. Many have contributed…. SLAC: Tim Nelson. Kansas State: Dima Onoprienko, Eckard von Toerne.

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Non-Prompt Tracks with the SiD Baseline Detector


Oct 22 – 26 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)


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

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


Not so exciting.

Can we reliably reconstruct tracks that originate outside the second tracking layer?


Seeds-to-Stubs Program

Instead, 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-  +-

We’ve just started on this.



In 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.