1 / 19

Charles Plager UCLA For the CDF and D Ø Collaborations

Top Properties at Tevatron Run II 2008 QCD Conference. _. Charles Plager UCLA For the CDF and D Ø Collaborations. New Era of Top Precision Physics!. CDF and D Ø now have more than thirty ( 30 !!!) times as much integrated luminosity as we did when we discovered the top quark in Run I!

gabrieltejada
Download Presentation

Charles Plager UCLA For the CDF and D Ø Collaborations

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. Top Properties at Tevatron Run II 2008 QCD Conference _ Charles Plager UCLA For the CDF and DØ Collaborations QCD 2008 – July 11

  2. New Era of Top Precision Physics! • CDF and DØ now have more than thirty (30 !!!) times as much integrated luminosity as we did when we discovered the top quark in Run I! • With the data we have recorded, we are now able to have large, very pure top samples. • For example, of the almost 50 results that CDF sent to the winter conferences, more than half were in top physics! Double B-Tag W + Jets Candidates QCD 2008 – July 11

  3. Top Quark Review • Fundamental question: Is it the truth, the Standard Model (SM) truth, and nothing but the truth? • Did we really find the top quark? • Is it the SM top quark? • Is it only the SM top quark? • The top quark is an ideal place to look for Beyond the Standard Model Physics! - tt Pair Lepton + Jets Decay _ QCD 2008 – July 11

  4. What Can We Study About Top Quarks? _ Top physics is very rich. Branching ratios Rare decays Non-SM decays Decay kinematics W helicity |Vtb| Production cross section Production mechanism Resonance production Production kinematics Spin polarization Top charge Top spin Top mass Top width In today’s talk. Public Tevatron analyses. QCD 2008 – July 11

  5. Top Pair Decay Modes • According to the SM, top quarks almost (?) always decay to Wb. • When classifying the decay modes, we use the W decay modes: • Leptonic • Light leptons (e or ) • Tauonic () • Hadrons QCD 2008 – July 11

  6. _ Search for tt Resonances • Uses “lepton + jets” event selection • B-tag. • Invariant mass reconstruction: • Assume pT= MET • Solve for Pz assuming W mass. • Allows for events with less than three jets. QCD 2008 – July 11

  7. _ Search for tt Resonances, cont. • For Z’ limits, assuming a lepto-phobic Z’ • Br (Z’ ! tt) = 100% • MZ’ > 760 GeV _ World’s Most Precise Measurement! QCD 2008 – July 11

  8. It is the relative reconstruction efficiency  acceptance that determines the relative yield. • is the relative acceptance when one top decays to the Wb while the other decays to the new decay, XY. • is the relative acceptance when both top quarks decays to the new decay, XY. • Compare expected yield to observed number of candidate events. • Create Feldman-Cousins acceptance bands using number of observed events. • t ! Zc, t ! gc, t !c, t ! Invisible. Search for Invisible Top Decays XY • What do we mean by “invisible?” • Not (well) reconstructed as double b-tag lepton + jets. • What would happen if there were a large branching fraction to an invisible decay? For example, Br (t !Invisible) = 10%? • Br (t ! Wb) = 90% • P (tt ! Wb Wb) = 81% ) For a purely invisible decay, we should have an 19% deficit when we look at the L + J event yield for a given theoretical cross section. Charles Plager

  9. Feldman-Cousins Acceptance Bands QCD 2008 – July 11

  10. Search for Invisible Top Decays, cont. From Cacciari et al. (hep-ph: 0804.2800) assuming CTEQ PDFs. World’s First Measurement! QCD 2008 – July 11

  11. Search for the Top FCNC Decay t → Zq • Top FCNC extremely rare in the SM: B(t → Zq) = O(10–14) • Beyond SM: B(t → Zq) up to O(10–4), • Any signal at Tevatron or LHC: New Physics. • Signature: tt → Wb Zq (Z + ≥4 Jet). • Dominant SM background: SM Z + Jets. QCD 2008 – July 11

  12. Search for t → Zq: Ingredients ’ QCD 2008 – July 11

  13. Search for t → Zq: Results • Analysis method: Fit mass 2 in 3 regions: • Signal (B-tagged and Anti b-Tagged) • Control ) Constrain shape & normalization of Z + jets background. • Data compatible with background only. • Feldman-Cousins limit with systematic uncertainties: • 3.5 times better than best published limit (L3) World’s Best Measurement! QCD 2008 – July 11

  14. Looking Forward • Top quark physics is becoming precision field. • Almost all analyses (except mass) are still statistics limited. • So far, most (but not all) things are frustratingly consistent with the SM. • CDF and DØ each have many of the world’s best measurments: • http://www-cdf.fnal.gov/ physics/new/top/top.html • http://www-d0.fnal.gov/Run2Physics/ WWW/results/top.htm • MZ’ (leptophobic) > 760 GeV (95% C.L.) • Br (t ! Zq) < 3.7% (95% C.L.) • Br (t ! Invisible) < 9% (95% C.L.) • … • Lots of exciting top physics happening at the CDF and DØ. • CDF, DØ,and the Tevatron are all running very well. • A lot of room to grow. 2 fb-1 8 fb-1 QCD 2008 – July 11

  15. New Era of Precision Top Physics! 2006 PDG Top Entry 2008 PDG Top Entry 2010 PDG Top Entry QCD 2008 – July 11

  16. Thank You! QCD 2008 – July 11

  17. Backup Slides QCD 2008 – July 11

  18. Top Physics Finally Makes Prime Time The Big Bang Theory! Mondays at 7:00 on CBS. Top Branching Fractions Top FCNC QCD 2008 – July 11

  19. QCD 2008 – July 11

More Related