060217 CLEMENT B talk

Slide1: 

Selected results on top physics at DØ Benoit Clément Institut de Recherches Subatomiques, Strasbourg On behalf of the DØ Collaboration

What can be studied on top ?: 

What can be studied on top ? Production cross section Heavy resonance decay W helicity Anomalous coupling CP violation Spin Charge Width Mass Production kinematics Polarization Rare or BSM decays Branching ratios CKM :|Vtb|

Top production modes: 

Top production modes Strong interaction : tt pair production Dominant mode σNNLO=6.77±1.2 pb Used to study top properties Electroweak interaction : Single top Larger background, smaller cross section -andgt;not yet observed t-channel σNLO = 1.98 ± 0.30 pb s-channel σNLO = 0.88 ± 0.14 pb Allow direct measurement of CKM |Vtb| tt production s-channel single top - - t-channel single top

Top pair final states: 

Top pair final states Top quark decays in : t-andgt;Wb Analysis channels are characterized by the W bosons decays modes. All-jet : BR ~ 44 % (6 jets) Large statistics Dominated by QCD multijet bkg Lepton+jets : BR ~ 30 % (4 jets) e+jet, μ+jet Best compromise signal/bkg Main background : W+jets Always 2 b jets single / double b-tagging significantly reduce backgrounds. No results on t+X Dilepton : BR~5% (2 jets) ee, eμ, μμ Very clean signature, low rate Main background : Z/W+jets

Cross section measurements: 

Cross section measurements All-jet : Topological (NN) + b-tag (SVT). Dilepton : Topological selection, no b-tagging. Lepton+jets : Topological (LH) Or b-tagging (SVT). 350 pb-1 370 pb-1 370 pb-1 230 pb-1

Cross sections summary: 

Cross sections summary

Single top production: 

Single top production Select : 2-4 jets, 1 lepton, Missing transverse energy Multivariate analysis : NN or Likelihood discriminant t-channel/tt filter - t-channel/W+jets filter Use 2 filters to discriminate signal from main backgrounds s and t channel searches

95% CL Bayesian limits: 

95% CL Bayesian limits Use full 2D LH distribution to compute bayesian limits s- and t-channel simultaneous fit : constraint on BSM (NN analysis, 230pb-1) Best world limits Projections: towards observation ?

Simultaneous fit of σtt and R : 

Branching ratio B(tWb)/B(tWq): Compare events with 0, 1 and 2 b-tagged jet. Use topological likelihood discriminant for 0 tags Lepton+jets (~230 pb-1) SM unitarity triangle constraint Simultaneous fit of σtt and R

W helicity in top decays: 

W helicity in top decays Left-handed WF-=0.3 t b W +1/2 -1/2 +1 Right-handed W F+= 0 t Longitudinal W F0=0.7 W b +1/2 +1/2 0 F+= 0.00±0.13±0.07 F+andlt; 0.25 @ 95% CL Mtop andgt;andgt; Mb, MW Right-handed W suppressed by V-A coupling. 230 pb-1

Other properties: 

Other properties Heavy resonance X-andgt;tt (GUT, ED): Reconstruct invariant mass of tt system in lepton +jet events. Small excess at mX~450 GeV Not statistically significant Top charge : is it top or some exotic quark with Q=4/3 ? (compatible with EW data) W.-F. Chang et al.,hep-ph/9810531, E. Ma et al. , hep-ph/9909537 Use lepton charge + jet charge algorithm: Exclude Q=4/3 at 94% CL 370 pb-1

Top quark mass: 

Dilepton (230pb-1): Lepton+jet: Templates topological (230pb-1): Template btag (230pb-1): Matrix element (370pb-1): Top quark mass Lepton+jets : Dynamic fits (matrix elements) : use all reconstructed information in event by event likelihood Topological fits (templates) Dilepton : Dalitz and Goldstein, RunI method Reducing Jet energy scale systematics Simultaneous fit of top mass and JES on hadronic W in lepton+jet events Matrix elements

Top Mass results and prospects: 

Top Mass results and prospects Prospect for RunII (CDF+D0) Δmtop andlt; 1.5 GeV/c2 with 2 fb-1 Run I+II mW = 80.425 ± 0.038 GeV/c2 (LEP2) mtop = 172.7 ± 2.9 GeV/c2 (DØ+CDF)

Conclusion: 

Conclusion Top physics is a sector to probe the standard model at the energy of the EW symetry breaking (Yukawa coupling~1). New physics could appear in top properties : need precise studies -andgt; W helicity, top kinematics, rare decays,… Can only be studied at the Tevatron (until LHC shows up…) Updated results in a few weeks/months : ~1 fb-1 of data - reduced top mass uncertainties - towards single top observation - top properties : charge, W helicity Many exciting results coming…

Backup: 

Backup

Tevatron pp collider: 

Tevatron pp collider Increase anti-proton production: antiprotons recycler (fall 2004) electron cooling (summer 2005) 8 2.3 2.5 Interactions/crossing 396 396 3500 Crossing time (ns) 50 17 3  Ldt (pb-1/week) 3 1032 1 1032 1.61030 Luminosity (cm-2s-1) 1.96 1.96 1.8 s (TeV) 36 36 36  36 6  6 Bunches / turn Run IIb Run IIa Run I 06/09 01/06 92/96 Duration -

Luminosity: 

Design Base Luminosity 2006 2005 2004 2003 2002 100 pb-1 500 pb-1 Start physics data taking in april 2002: ~1.4 fb-1 delivrered ~ 1.15 fb-1 recorder Efficiency : ~83% andlt;- Number of antiprotons available 300.1010 100.1010

The DØ detector: 

The DØ detector Scintillating Fibers (CFT) Solénoïd : 2 Telsa Vertex detector : silicon microstrip tracker (SMT) Calorimeter : Cu / U – Liquid argon Tracker Toroïd magnet Muons chambers : Drift tubes and scintillators

Jet reconstruction: 

Jet reconstruction Calorimètre organised in pseudo-projective towers: ΔηxΔφ = 0.1x0.1 Coverage : || andlt; 4.2 Jets are reconstrucetd from calorimeter towers using a fixed cone algorithm : R= √(Δη²+Δφ²) = 0.5 Jet Energy Scale correction (JES) Calorimeter jet -andgt; particle jet Eoffset : Energy not originating from the hard scatter vertex (uranium noise, underlying event). Rjet : Calorimeter response. Scone: Out of cone showering.

From the collison to the detector: 

From the collison to the detector pp collision: only internal structures of the proton (partons) interact: Quark of valence (u,d) Quark from the see (u,d,s,c,b,t) Gluons ISR, FSR : Initial/Final state radiation (gluons and photons) Fragmentation / hadronisation : Quarks et gluons -andgt; hadrons -andgt; jet. In the detector : Tracker : Identify charged particles Calorimètre EM : electrons, photons, jets Calorimètre HAD : jets Système à muons : muons Neutrinos don’t interact : missing energy -

Cross section at Tevaton: 

Cross section at Tevaton ~ 3 tt / hour ~ 20.106 bb / hour - - 70 mb 7 pb ~ 7.106 events / second Parton density functions (PDFs) Parton cross sections (pQCD) L=1032 cm-2s-1 Only record 50 events/second : Crucial role of trigger criteria

b-jets identification: 

b-jets identification Very important in top physics, Higgs search (H-andgt;bb) and some SUSY channels (sbottom, stop) m Bottom hadrons charactristics Decay through weak interaction with change of family : large lifetime(~10-12s) - Tracks with large impact parameters (IP) wrt. PV -andgt; JLIP - Secondary decay vertex (decay length ~ a few mm) -andgt; SVX High mass (~4.5 GeV/c2) : - Large invariant mass of tracks in SV. - Hard fragmentation : open jets. Large semi-leptonic decay rate (~20%) : - Muons or electrons within jets. -andgt; SLT IP -

B-tagging algorithms: 

B-tagging algorithms 50% 1% Three algorithms at DØ : SLT : Soft Lepton Tagger, identify muon/electron within a jet. SVX : Reconstruction of secondary vertices with large dacay length JLIP : Jet LifeTime Probability, combine IP of tracks within a jet into a probability for the jet to originate from the primary vertex. Both efficieny and mistag are measured in real data. JLIP efficiency Mistag rate

Top mass and Higgs mass: 

Top mass and Higgs mass Radiative correction to the W mass : mW and mtop -andgt; mHiggs

Single top analysis strategy: 

Single top analysis strategy 2 analyses : s/t-channel. 4 orthogonal channels for each analysis : - electron/muon - single/double b-tag B-tagging : JLIP Use asymetric b-tagging to increase double tag statistics: Single tag : exactly 1 Tight b-tagged jet and no extro Loose b-tag. Double tag : at least 1 Tight and 1 Loose b-tagged jets. Enhance s/t-channel separation W boson leptonic modes (e or mu) 1 lepton, missing energy, 1 b-jet (top), 1 to 3 extra jets.