1 / 78

New Electroweak Results from DZero

Chicago . DØ. Tevatron. Main Injector. New Electroweak Results from DZero. Z -> tt Observation and Cross Section times Branching Fraction Diboson Studies: W g , Z g , WW, WZ. “Wine + Cheese” January 28, 2005. For the D Ø Collaboration. Tom Diehl

brad
Download Presentation

New Electroweak Results from DZero

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. Chicago  DØ Tevatron Main Injector New Electroweak Results from DZero • Z -> tt Observation and Cross Section times Branching Fraction • Diboson Studies: Wg, Zg, WW, WZ “Wine + Cheese” January 28, 2005 For the DØ Collaboration Tom Diehl Fermi National Accelerator Laboratory

  2. Outline • DØ Run II Data • The DØ Detector • Inner tracker, calorimeter, & muon systems • s*Br(Z->tt) at 1.96 TeV • Motivation • Event Selection • Tau reco, classification, & ID • Cross Section measurement • Dibosons: WW, WZ, Wg, Zg • Motivation • WWg and WWZ Couplings & Anomalous Couplings • WW (Dileptons) • Cross Section @ 1.96 TeV • WZ (Trileptons) • Limit on s(WZ)s(WZ), and AC limits. • Wg in e and m channels • Wg Cross Section, Photon ET Spectrum, and limits on AC. • Progress on Rad. Zero • Zg in ee and mm channels • Zg Cross Section, Photon ET Spectrum, Event Characteristics, and limits on ZZg and Zgg AC. • Summary

  3. The DZero Collaboration • 19 Countries • 86 institutions • ~620 physicists

  4. DZero Run II Data • ~700 pb-1 pp collisions at sqrt(s) = 1960 GeV since the start of Run II. • Since the end of the 2004 shutdown the Tevatron has returned to high-performance operation. • Stores routinely in the 80-100e30 cm-1 s-1 range. • Peak luminosity increases due to effort in A.D. • Challenges DZero to adapt to increasingly higher luminosities • Trigger List • Reconstruction • So far, so good. pp collisions at sqrt(s) = 1960 GeV 650 pb-1 Analyzed to here: 520 pb-1 Monthly Eff’y

  5. SMT SMT SMT The DZero Detector in Run II: Inner Tracker Tracker

  6. The DZero Detector in Run II: Calorimeter Fine Longitudinal and Transverse Segmentation • Fitted Z(ee) peak has 3.7 GeV/c2 mass resolution in Run II.

  7. No Shielding D0 Shielding The DZero Detector in Run II: MUONS • Fitted Z(mm) peak has 8.1 GeV/c2 mass resolution in Run II. Simulation m’s in Central Scint. Counters Run II Data Unbiased Triggers t(ns) Run II Run Ia

  8. Physics Motivation • Test consistency of SM couplings to all leptons • Benchmark our level of understanding of the experiment. • Tau is most difficult lepton to ID • Develop Tau ID, Efficiencies, backgrounds • We use this signal to tune up our triggers and algorithms for non-SM searches such as • certain parts of SUSY space • New Phenomena such as heavy resonances that decay with enhanced coupling to 3rd generation. • What do we know about this? • NNLO calculation* predicts s(Z) =242+-9 pb. • Br(Z->tt) is well measured. *from Hamberg, van Neervan, and Matsura, Nucl. Phys. B359, 343 (1991), using CTEQ6L

  9. The analysis is complicated. Start Divide Events into OS and SS (For BKGD Estimate) Lepton Pairs Preselection: single muon events Reconstruct taus Final Event Selection Classify tau candidates Extract Cross Section

  10. Event Selection Tau Decay Signature • L=226 pb-1DL/L = 6.5% For reference: • One t must decay to mnn. • Event Selection startswith an isolated muon • One m w/ pT(m)>12 GeV/c • This muon carries the sign of it’s tau lepton • The other t can go to any of 3 decay modes

  11. Cones of size R=0.3 and 0.5 Charged Particle I.P. Reconstruct Tau Candidates • Start with the Calorimeter • CAL. ET (R=0.5) > 5 GeV & ET (R=0.3) > 3 GeV • Taus have narrow jets • Then use the Tracker • N(tracks w/ pT>1.5 GeV/c in the narrow cone) > 0 • Start with the highest pT track • If there’s a second track such that Mass(2-tracks)<1.1 GeV/c2, add that track to the tau list • If a third track such that Mass(3-tracks)< 1.7 GeV/c2, add it unless total charge = 3 or -3. • If total charge = 0, discard the tau candidate. • Require |f(m)-f(t)| > 2.5 (These are low pT Z’s) • Reconstruct EM subclusters with ET > 800 MeV

  12. “One-Prong + EM” “One-prong” “Multi-Prong”  TRK + CAL Type 1    no TRK, but EM sub-cluster o  Type 2    TRK + CAL   • 1 TRK + wide CAL cluster Type 3     Tau Identification: Classification • Classify the tau candidates into three types • “One-prong”, a single track w/ no EM subclusters • “One-prong” + EM, a single track w/ EM subclusters (cleanest) • “Multi-prong”, more than one track And there are selection criteria discriminating them from each other And rejecting background.

  13. “One-Prong + EM” “One-prong” “Multi-Prong”  TRK + CAL Type 1    no TRK, but EM sub-cluster o  Type 2    TRK + CAL   • 1 TRK + wide CAL cluster Type 3     Gets rid of events w/ extra m’s Tau Identification: Classification • Classify the tau candidates into three types • “One-prong”, a single track w/ no EM subclusters • “One-prong” + EM, a single track w/ EM subclusters (cleanest) • “Multi-prong”, more than one track

  14. “One-Prong + EM” “One-prong” “Multi-Prong”  TRK + CAL Type 1    no TRK, but EM sub-cluster o  Type 2    TRK + CAL   • 1 TRK + wide CAL cluster Type 3     Gets rid of events w/ extra m’s Tau Identification: Classification • Classify the tau candidates into three types • “One-prong”, a single track w/ no EM subclusters • “One-prong” + EM, a single track w/ EM subclusters (cleanest) • “Multi-prong”, more than one track • No attempt to separate hadron channels from electron channels. • At this point we have the charge sign of m and t.

  15. Jet-Background • 1 TRK + wide CAL cluster + EM sub-cluster  o  q o  Tau Identification: Neural Network • Divide 29,021 events into SS and OS lepton-lepton candidates. • We still have a large background from multijets. Jets tend to • be wider than t’s • have higher track multiplicity • have higher mass than M(t) • be less isolated from other hadronic energy than are tau’s from Z’s. • A Feed-forward neural network • 8 input nodes (each a new criteria), a single hidden layer with 8 more nodes, and a single output (the answer). Not all inputs for all tau types. • Train the 3 types separately on expected signal and backgrounds. “One-Prong”+ EM “One-Prong” “Multi-Prong” “All Types”

  16. Tau Identification: # Candidates TOTAL Number of Events • Events predicted and events observed before and after P(NN)>0.8 criteria for all 3 types. • QCD background is scaled from same-sign data • The other bkgds and expected Z(tt) from MC. • Eff’y(NN)=0.78 Signal/Bkgd ~ 0.82 • #Z(tt) Observed = 865+-55 after M(tt)>60 GeV/c2 • P Eff’y = 1.52% for M(tt) > 60 GeV/c2. Before NN QCD 13881+-264 Z/g -> mm 100+-24 W->mn 434+-153 Z/g*->tt 1174+-43 SUM 15589+-309 OS Events 15911 QCD 984+-46 Z/g -> mm 70+-16 W->mn 58+-20 Z/g*->tt 914+-24 SUM 2026+-57 OS Events 2008 After NN • type contribution to signal: 13% Type1, 58% Type 2, 29% Type 3

  17. ET(t) ET(t) PT(m) PT(m) Systematic Uncertainties UNCERTAINTY IN • Energy scale 2.5% • NN MC inputs 2.6% • Backgrounds 4.6% • PDF’s 1.7% • Eff’y & Accept. 2.6% • Trigger Eff’y 3.5% • Total 7.5% • Figures show ET(t) and pT(m) for: Z->tt MC vs. background subtracted data

  18. Cross Section Calculation • For m(tt)>60 GeV/c2 • After removing the g* contribution Theory: Matsura + van Neervan Submitted to PRL. hep-ex/0412020 FERMILAB-PUB-04/381-E

  19. What else can we say about Taus? • Z->tt mass peak • We can find states that decay to tau’s. • Not some other large source of tau pairs. • Searches for Higgs, SUSY etc with tau final states are available and more are coming • Lepton Universality • Use DØ’s Run II preliminary muon and electron results Upper Left: Mass(m,t) for Bkgd vs. Signal MC for type 1 and type 2 tau tracks Upper Right: Mass(m,t) for (OS events - Bkgd) vs Signal MC 1.96 TeV

  20. Dibosons (Outline) • Dibosons: WW, WZ, Wg, Zg • Motivation • WWg and WWZ Couplings & Anomalous Couplings • WW Dileptons • Cross Section @ 1.96 TeV • WZ Trileptons in Run II • Limit on s(WZ), s(WZ), and AC limits. • Wg in e and m channels • Wg Cross Section, Photon ET Spectrum, and limits on AC. • Progress on Rad. Zero • Zg in ee and mm channels • Zg Cross Section, Photon ET Spectrum, Event Characteristics, and limits on ZZg and Zgg Anomalous Couplings.

  21. Dibosons: Introduction • Motivations • Multiple vector bosons provide a high-pT Standard Model process with a cross section and interesting physics • Cross sections are useful for New Phenomena search analyses. • a SM parameter to measure: the gauge boson “self-couplings” SM Higgs Branching Fractions • More Motivation • We are on the lookout for very massive particles that decay to the heaviest gauge bosons. • Like the Higgs. • Or the Higgs that doesn’t decay to fermions. • Or whatever. hep-ph/9704448

  22. WWgCoupling WWZ Coupling t-channel u-channel s-channel WWg and WWZ Couplings • Self-interactions are direct consequence of the non-Abelian SU(2)L x U(1)Y gauge symmetry. SM specific predictions. • Cancellation of t- and u-channel by s-channel amplitude removes tree-level unitarity violation (in Wg, WW, and WZ, too). Textbook example • t-channel: At high energy limit and with massless quarks (simpler calculation). s violates unitarity. • s-channel: Term of opposite sign cancels unitarity violating part.

  23. WWg and WWZ Anomalous Couplings • Characterized by effective Lagrangian • 5 CP Conserving SM Parameters: lZ = 0 lg = 0 DkZ = 0 Dkg= 0 (Dk = k-1) Dg1Z = 0 (Dg1Z = g1Z -1) In Wg production, only the WWg couplings. In WZ, only WWZ couplings. In WW, both and one has to make an assumption as to how they are related. W+ Boson Static Properties mW =e(1+k+l) / 2MW QeW = - e (k-l) / M2W

  24. WW Production Effect of Non-SM WWg and WWZ Couplings • Cross section increases especially for High ET bosons (W/Z/g). • Unitarity Violation avoided by introducing a form-factor scale L, modifying the A.C. at high energy. e.g.: # Events/20 GeV/c PT(W) (s^(0.5)=1800 GeV)

  25. Anomalous Couplings – LEP and Tevatron • DØ and CDF put limits on anomalous WWg and WWZ Couplings in Run 1. • WWg and WWZ couplings from WW • WWg couplings from Wg analyses * • WWZ couplings from WZ * • DØ Combined Wg, WW, WZ (1999) Tightest from the Tevatron • LEP Combined (1D 95% CL) LEP EWK Working Group hep-ex/0412015 “HISZ” SU(2)xU(1) coupling relations *(complementary in several ways) Didn’t use a form-factor dependence in their couplings.

  26. Dileptons Lepton+jets All-jets emnn and mmnn en+jets, mn+jets All-jets Br = 2.5 and 1.2% Br = 15% Br = 47% Pure and efficient Low branching Frac. Efficient Not very pure Very Efficient Never Mind WW Production and Decay • Decay Modes are named like top pairs. In fact, WW is one of the top backgrounds. Campbell & Ellis • s(WW) ~ 13.5 pb-1 at Run II Tevatron energy*. * Ohnemus (1991), (1994) and Campbell & Ellis (1999).

  27. WW to Dileptons in Run I • WW to dileptons @ DØ and CDF • Cross section limit and anomalous coupling limits @ DØ (PRL and several PRDs) • Evidence for WW Production and anomalous coupling limits @CDF in 1997 PRL. • Leptons + jets channels provided more restrictive A.C. limits than dileptons at DØ andCDFbut we couldn’t isolate a signal from the much bigger W+jets background. 1D AC limits

  28. D0 D0 D0 em Channel ee Channel mm Channel Run 2: WW -> Dileptons Event Selection • Preselection Criteria • Two oppositely-charged e or m w/ pT>15 GeV/c. At least one has pT>20 GeV/c. • MET > 30, 40, & 20 GeV/c2 in ee, mm, & em channels to remove Z/g*. Missing Transverse Energy After Preselection Criteria Shows agreement between data and signal plus backgrounds. mm channel

  29. WW ->emnn Event Selection • em channel criteria • No third lepton so that 61< M(l+l-) < 121 GeV/c2. • Minimal Transverse Mass > 20 GeV/c2. • “Scaled MET” > 15 rootGeV • HT(jets w/ ET>20 &|h|<2.5) <50 GeV. • 3+ silicon hits on electron if MT(mn)~MT(W). • Background is 3.81+-0.17 events and is 71% W+j or g. • Eff’y is 15.4+-0.2%. • Expected signal is 11.1+-0.1 events. • 15 Candidates Observed. REMOVES WZ & ZZ multijets & Z/g* All Cuts except MT(min) Z/g* ->tt D0 Top pairs Wg

  30. WW (Dileptons) Quick Summary • The dielectron and dimuon channels have selection criteria along the same lines but with much more emphasis on rejecting Z bosons. • As a result, the efficiency isn’t as high in these channels as in electron+muon.

  31. WW Cross Section – Systematic Unc’ys • These are mostly correlated between channels (horizontally). • These are added in quadrature for each channel (vertically). Bottom Line Systematic Unc’y: +8.7% -6.5%

  32. WW-> Dileptons Cross Section • For each channel • We combine channels to extract s as minimum in D0

  33. WW-> Dileptons Cross Section • Submitted to PRL hep-ex/0410066 CDF Run II: hep-ex/0501050 Also submitted to PRL

  34. Trileptons Lepton+jets All-jets e’s and m’s e+jets, m+jets All-jets Br = 15% Br = 49% Br = 1.5% Efficient Not very pure Use B-tagging Very Efficient Never Mind Pure and efficient Very Low branching Frac. • Measure s(WZ) with “trileptons” • “Leptons + jets” is stepping stone for WH where H decays to bb. WZ Production and Decay • s(WZ) ~ 4.0 pb at Run II Tevatron energy. Campbell & Ellis

  35. WZ @ Tevatron in Run I • DØ Trileptons Results (92 pb-1) • mnee and enee channels • 1 candidate w/ background of 0.50+-0.17 events (mostly Z+jets). • Expected 0.25+-0.02 WZ events • Model independent limits on Anomalous WWZ couplings in 1999 PRD. • DØ + CDF Results (leptons + jets) • Cannot distinguish between W+jets, WW, and WZ in those analyses. • Limits on anomalous WWg and WWZ couplings using the ET spectrum of the dijets from WW and WZ combined. • 1996 PRL (CDF) and 1996 + 1997 PRLs (DØ) and several PRD’s -> 1999 (DØ) 1D limits

  36. 32222 entries 24552 entries Run 2: WZ -> Trileptons Event Selection • At least 2 isolated e’s and/or m’s with ET>15 GeV that make a Z boson • 71<M(ee)<111 GeV/c2 or 50<M(m+m-)<130 GeV/c2. • A third isolated e or m with Et>15 GeV • DR(leptons)>0.2 mm Identify a Z boson Only 65 events with 3 ee Rejects Brems, W/Z+g, Z->taus WZ efficiency after these criteria is ~15%.

  37. WZ -> Trileptons Event Selection + BKGD. • MET>20 GeV • ET(had) < 50 GeV Z/g*+jet Background M.C. WZ (Z->mm) * 3e Event For a W boson Remove Top with B-> isol. lepton DiElectron Channel MET • Background (Mostly Z+X) Total = 0.71+-0.08 bkgd.expected. • 2 mmmn and 1 eeen Candidates WZ efficiency after these criteria is ~13%. M(ll) *s(ZZ)=1.43 pb (Ellis+Campbell,Ohnemus)

  38. WZ -> Trileptons Event Selection + BKGD. • MET>20 GeV • ET(had) < 50 GeV Z/g*+jet Background M.C. WZ (Z->mm) * 3m Events For a W boson Remove Top with B-> isol. lepton MET Dimuon Channel • Background (Mostly Z+X) Total = 0.71+-0.08 bkgd.expected. • 2 mmmn and 1 eeen Candidates WZ efficiency after these criteria is ~13%. M(ll) *s(ZZ)=1.43 pb (Ellis+Campbell,Ohnemus)

  39. WZ Cross Section • Cross section limit Combined Ln(Likelihood) D0 Prelim. • “Evidence” for WZ Production • P(0.71 bkgd) -> 3 Candidates is 3.5% • Interpreting the Events as Signal + Background: D0 Preliminary CDF Run II: hep-ex/0501021 submitted to PRD

  40. WWZ Anomalous Trilinear Couplings • Generate a grid of WZ MC using Hagiwara, Woodside, + Zeppenfeld LO generator => Fast Detector Simulation. • Form ln(Likelihood) for each grid point to match the observations using the BKGD-subtracted number of events. • Intersect the ln(Likelihood) with a plane at Maximum-3.0 to form 2D Limits @ 95% C.L. -Ln(Likelihood) L=1 TeV Dg1z vs. lz

  41. WWZ Anomalous Trilinear Couplings 1D Limits (holding the other to 0) • Inner contours: our 2D limits. Outer contours are from s-matrix unitarity. • Best limits in WZ final states. • First 2D limits in Dkz vs. lz using WZ. • Best limits available on Dg1Z, Dkz, and lz from direct, model-independent measurements. • The DØ Run II 1D limits are ~ factor of 3 better than our Run I limits. DØ Preliminary 95% C.L. L=1.5 TeV L=1 TeV

  42. Wg Production • Sensitive only to WWg couplings • Identify W boson decay to en or mn. • We don’t bother with hadronic W channel. The background from QCD photons (qq annihilation and Compton at L.O.) and from “phony” photons swamps it. • Final state radiation is sort of a “background” w/ a collinear divergence @ low-ET. Initial State Radiation Final State Radiation WWg Vertex Monte Carlo Prediction Baur & Berger (1990)

  43. Wg @ Tevatron in Run I • D0 (1995 and 1997 PRL’s) + CDF(1995 PRL) • s agrees w/ SM and Limits on Anomalous WWg couplings using the photon ET spectrum. DR(lg)>0.7 & ET(g)> 7 GeV (CDF) DR(lg)>0.7 &ET(g)> 10 GeV (DØ) Anomalous Coupling Limits DØ Tightest WWg limits at hadron collider, (UP TO NOW)! 1D limits

  44. Run 2: Wg Event Selection: en and mn ID a W boson • An isolated electron w/ ET>25 GeV in |h|<1.1 • MET>25 GeV • MT(en)>40 GeV/c2. • .NOT. 70<M(eg)<110 GeV/c2. • One m, isolated, w/ pT > 20 GeV/c. • MET > 20 GeV • No MT cut at this stage Eliminate Z bosons Lum’y: eg (mg):162 (134) pb-1 ID a Photon (Both Channels) ET(photon)>8 GeV DR(l,g)>0.7 |hg|<1.1 • An isolated EM object • No track match (spatial) • (Calorimeter j -width)2 < 14 cm2 • If photon has tracks in a hollow cone of size 0.05<DR<0.4 require For g within fiducial coverage, Efficiency(ID) = 0.81+-0.03

  45. Run 2 Wg: Expected Backgrounds Wg->eng Wg->mng • W+jet (jet mimics g)* 58.7+- 4.5 61.8+-5.1 events • “leX” (Z’s) 1.7+-0.5 0.7+-0.2 • Wg->tng0.42+-0.02 1.9+-0.2 • Zg (lost lepton) 0 6.9+-0.7 Total BKGD 60.8+- 4.5 71.3+-5.2 events # Observed 112 161 candidates * Probability(jet mimics g) ~ 5x10-3 anddecreases with ET(jet). # Observed – Background = 141 Wg 1.7x as many Wg as in Run 1 1.6x as much luminosity as in Run 1 (analyzed so far)

  46. Wg Cross Section & Event Characteristics Decay Channel eng mng Lum’y 162 (6.5%) 134 (6.5%) pb-1. # Observed 112 161 candidates Total BKGD 60.8+- 4.5 71.3+-5.2 events Eff’y*Acc. 0.023+-0.001 0.044+-0.002 Three-body Transverse Mass en channel D0 Prelim. D0 Prelim. mn channel ET(g) >8 GeV DR>0.7 D0 Prelim. 323 Candidates w/ ~114 BKGD. ~200 pb-1.DR>0.7 CDF FERMILAB-PUB-04-246-E => PRL ET(g)>7 GeV Scales adjusted to same.

  47. Wg Anomalous Couplings • Photon ET agrees w/ S.M. (last is overflow bin). Baur + Berger MC w/ A.C. • Form a binned-likelihood based on pT(g) in a lg vs. DKg grid including bkgd on events w/ MT(3)>90 GeV/c2. Combined channels ET(g) D0 Prelim. D0 Prelim. @ 1.96 TeV 1D limits @ 95% C.L. 2D limits 1D limits Still the tightest at any Hadron Collider!

  48. Wg Radiation Amplitude Zero • For COS(q*), the angle between incoming quark and photon in the Wg rest frame, = -1/3, SM has “amplitude zero”. • For events w/ MT(cluster)>90 GeV/c2. One could guess the Wg rest frame. We use charge-signed Dh(l,g) D0 Preliminary Muon Channel M.C. • We plot the background-subtracted muon data vs. MC Dh(l,g) => hints of the Rad. Zero. • It will help to extend the eta-coverage of electrons and especially of photons.

  49. Zg Production Initial State Radiation Final State Radiation No SM ZZg or Zgg interaction. Monte Carlo Prediction Baur & Berger (1993) • Initial and final state radiation. • Identifying Z boson decay to e+e- or m+m- is easiest. • Zg->nng was done in Run 1A. It might be possible to do it in Z->bbar. We don’t bother with hadronic Z channel.

  50. ZZg/Zgg Anomalous Couplings • Non-SM Characterized by an effective Lagrangian w/ 8 form-factor coupling parameters called h1V, h2V, h3V, and h4V whereV stands for g and Z. CP Violating h1V and h2V CP Conserving h3V and h4V • In SM all these couplings =0. • Transition Moments

More Related