1 / 16

Soft Electron Tagging

Soft Electron Tagging. John Paul Chou DOE Review 2008 Thursday, August 14, 2008. Overview. Soft Electron b-tagging (SLT e ) Algorithm Simulation Applying the Tagger Top Pair Cross Section W+Charm Cross Section Top Charge. Soft Electron b-Tagging.

kin
Télécharger la présentation

Soft Electron Tagging

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Soft Electron Tagging John Paul Chou DOE Review 2008 Thursday, August 14, 2008

  2. Overview • Soft Electron b-tagging (SLTe) • Algorithm • Simulation • Applying the Tagger • Top Pair Cross Section • W+Charm Cross Section • Top Charge DOE Review 2008 -- JPC

  3. Soft Electron b-Tagging • Look for soft electrons from heavy flavor decay • BF(b→eνX) ~ 10% • BF(b→c→eνX) ~ 10% • ~35% of top events have a soft electron from HF • High PT Electrons • Charged track • Associated with electromagnetic shower • Little to no hadronic energy • No other tracks nearby (i.e. isolated) • Question: How do we ID electrons when the electron is embedded in a jet? • Specifications: • b-jets from top decay are high PT and dense, but the tagger must work over a couple decades in scale • To be useful, we need ~100:1 e:π/k/p separation DOE Review 2008 -- JPC

  4. Soft Electron Algorithm • Begin by using calorimeter quantities: • E/P: Electromagnetic energy on par with track P • Had/Em: Cluster dominated by EM component • Not finely segmented: very sensitive to local environment • Main engine of the tagger: CES • Wire and strip chambers located at approximately shower maximum within the EM calorimeter • Measures transverse EM shower profile in two orthogonal directions • Advantage: less environmental dependence • Finely segmented: ~2-3 mm resolution • Measure position and shape of shower (not amplitude) • Disadvantage: not well modeled in MC • Combine CES elements into a likelihood and cut DOE Review 2008 -- JPC

  5. Conversions • Conversion electrons are also a significant background • Conversions dominate signal at low PT • ~3 times as many candidate tracks in top are from conversion photons than from HF • Two techniques for removal • Locate partner electron track geometrically • But partner track may not be reconstructed • Low PT threshold for candidate electrons • Asymmetric energy sharing • Use material interaction behavior to identify conversions • Extrapolate track through silicon detector • Use double-sided silicon layers • Reject tracks with more than three layers expecting hits on each side but having none • 70% efficiency for low PT conversion electrons in jets • 7% over-efficiency to misidentify prompts as conversions DOE Review 2008 -- JPC

  6. Simulation B enriched dijets • Calorimeter variables are well-modeled, but CES variables are not • Parameterize data and apply it to MC • Consider the effects of • Kinematics (PT) • geometry (η) • and local environment (track isolation) • Cross check as many places as we can • (Z’s, b-jets, etc.) • Tag Matrix – predicts the tagging rate of electrons • Use conversion electrons as a template • Correct tag matrix for jet environment since most conversion electrons are not in jets • Fake Matrix – predicts the tagging rate of non-electrons (a.k.a. fakes) • Use tracks from generic jets (20/50/70/100) as a template • Correct Fake matrix for real electron contamination (HF, conversions, Dalitz, etc.) • Use conversion (over-)efficiency Scale Factors to adjust MC • Measured in generic jet data DOE Review 2008 -- JPC

  7. Top Production Cross Section • The cross section is a cross check of the tagger itself • We extrapolated the SLTe tagger into a High PT, dense environment • Second order effects could come into play: should check that it works • Lepton+Jets event selection • 1 isolated, high PT lepton (electron or muon) with PT/ET > 20 GeV • ≥ 3 jets (Corrected ET > 20 GeV, |η| < 2.0) • Missing ET > 30 GeV • Scalar sum of transverse energy, HT > 250 GeV • ≥1 soft electron tag • Missing ET, HT, and SLTe likelihood cut optimized for total uncertainty Background method similar to secvtx xs Luminosity = 1.7 fb-1 Acceptance*Efficiency DOE Review 2008 -- JPC

  8. Cross Section First measurement of cross section with soft electron tags in run II Moving towards PRD DOE Review 2008 -- JPC

  9. Kinematics DOE Review 2008 -- JPC

  10. W+Charm • Measure W+Charm production cross section • Important background in W+1,2 jet sample (Higgs, etc.) • Charges of W lepton and soft lepton are anti-correlated • Count Opposite Sign (OS) minus Same Sign (SS) events • Use 1, 2 jet bin of top cross section measurement as control region • Plan: precision measurement combining soft electron and soft muon channels with 3.0 fb-1 DOE Review 2008 -- JPC

  11. Top Charge (I) • Theoretically, exotic top model with mass near 175 GeV/c2 could have -4/3 charge • Decays into W- and b, instead of W+ and b • PRD59(091503) • Measurement techniques • Measure associated photon production cross section • Not practical at Tevatron, but possible at LHC • Use jet charge algorithm to determine b-jet charge • Kinematic fitter determines which jets are “leptonic b” and “hadronic b” • Assign top charge based on b-jet charge and lepton charge • high efficiency, low purity • Exotic quark model excluded at 87% confidence level • Use soft lepton tagging instead of jet charge • Want to maximize εD2 (Dilution, D≡2P-1) • Lower efficiency, higher purity: competitive, orthogonal measurement DOE Review 2008 -- JPC

  12. Top Charge (II) • Increase purity by selecting high PT soft lepton tags • Optimizing on separate channels triples measurement significance: • SecVtx + SLT (different jets) • Use SLT tag in kinematic fitter to enhance fitter purity • SecVtx + SLT (same jet) • Low purity high efficiency channel • 2 SecVtx + SLT (in same a SecVtx jet) • Best εD2 • Electrons are better than muons! • Can tune S/B with different operating points • Less efficiency but higher fake rejection at high PT ~80% purity at PT>8 GeV/c DOE Review 2008 -- JPC

  13. Summary • We have implemented a soft electron tagger at CDF • Tagger used to measure top cross section • Godparent committee has been chosen • W+charm measurement is in the works • Top charge measurement with soft lepton tags shows promise DOE Review 2008 -- JPC

  14. Backup Slides

  15. Figures of Merit • Environment overstates HF electron tagging efficiency • In top events, tagging efficiency for HF electrons ~40% per track (L1) • Electron contamination overstates non-electron tagging rate • In top events, per track non-electron tag rate ~0.5% per track (L1) Per track tagging efficiency for conversion electrons and tracks in generic jets DOE Review 2008 -- JPC

  16. Schematic Data Tag/Fake Matrix Depend on choice of Likelihood cut MC Both DOE Review 2008 -- JPC

More Related