148 11s5 14p30 kajfasz

Search For New Physics with the D0 Detector : Search For New Physics with the D0 Detector Eric Kajfasz CPPM, Marseille on behalf of the D0 collaboration ICHEP 2006, Moscow [Only the most recent results not shown elsewhere at this conference]


Standard Model : Based on: - 4-D space-time - Poincaré group - SU(3)c x SU(2)L x U(1)Y 3 generations of quarks and leptons - Higgs mechanism Phenomenologically successful so far, but many questions unanswered... Higgs field filling our Universe and slowing down elementary particles. Is it elementary? If so, some drawbacks: no dynamical explanation to EWSB unnatural, requires fine tuning -> MH unstable against rad. corr. in GUTs, leads to hierarchy problem -> 2 very different scales no insight to flavor physics Standard Model


Some Ways to go Beyond ... : - Alternative EWSB mechanisms -> Technicolor rT -> pTW - Relate quarks and leptons -> Leptoquarks - jets+MET - b-jets+MET - Extend Poincaré -> Supersymmetry and include gravitation (Supergravity) Increase the number of dimensions - Enlarge the gauge group - Repeat History (compositeness) Some Ways to go Beyond ... Numerous D0 results given in other talks at this conference Notes and results on New Physics can be found at: http://www-d0.fnal.gov/Run2Physics/WWW/results/np.htm http://www-d0.fnal.gov/Run2Physics/WWW/results/higgs.htm To answer some of the questions ... new theories and models


The Tevatron @ Fermilab : Luminosity: Peak: > 1.7 1032 cm-2s-1 Delivered: > 1.5 fb-1 On tape: > 1.2 fb-1 Design goal 8 fb-1 (end of 09) In this talk: 0.3 to 0.4 fb-1 The Tevatron @ Fermilab


Technicolor : Technicolor Technicolor (TC - first introduced by Weinberg and Susskind): New strong dynamics ‘a la QCD’ SU(NTC) -> TC condensates of technifermions Coupling of condensates with unbroken electroweak gauge fields -> mass to W&Z Extended TC (ETC) [mass and mixing to quarks and leptons] Walking Technicolor (WTC) [flavor changing neutral current in ETC] Topcolor-assisted Technicolor (TC2) [high value of mtop] Technicolor Straw Man Model (TCSM2): Framework to search for light technihadrons (relevant for Tevatron searches). lightest technifermions expected to be an isodoublet of color singlets -> color-singlet vector mesons: rT and wT -> color-singlet pseudo-scalar mesons: pT0 and pT+/- produced with substantial cross-section at the Tevatron cross-sections and branching fractions depend on: masses of rT and wT technicolor charges of the technifermions mass difference between vector mesons and technipions 2 mass parameters: MA for axial-vector and MV for vector couplings Implemented in PYTHIA [S. Mrenna] K. Lane, S. Mrenna Phys. Rev. D 67 (2003) Analysis focuses on rT +/-  W+/- pT0 | bb and rT 0  W-/+ pT+/- | bc,bc MA = MV = 500 GeV


W(en)T(bb/c) event selection : W(en)T(bb/c) event selection One isolated electron (EM TRIGGER) pT > 20 GeV, |h| < 1.1 select W(e) events veto on other electrons to suppress Z Missing ET > 20 GeV, MT > 30 GeV select W(e) events eliminates multi-jets events Two jets pT > 15 GeV, |h| < 2.5 At least one jet has to be associated with a Secondary Vertex (b-tagging) Veto on a third jet, suppresses tt background multijet production (mis-IDed electron) W + light flavored jets (mistag) Instrumental Background estimated from data Select W(en)+Heavy Flavor events SM Background Signal


Slide7 : backgrounds Instrumental (W+Heavy Flavor)-like events SM 2 strategies to extract the signal: - Cut based (CB) - Neural Net based (NN)


Cut based analysis : Cut based analysis Define kinematic and topological quantities to extract the WT signal HTe (electron pT + ∑ jet pT) discriminates against tt pT(jj) (pT of the dijet system) discriminates against tt (jj) and (e,MET) against multijet and W + light quarks M(jj) (inv. mass of the dijet system) -> indication of T narrow resonance M(Wjj) (W + dijet system) -> indication of T narrow resonance Mass dependant optimization of cuts on S/√B D0 Run II Preliminary 388 pb-1 M(T) = 105 GeV M(T) = 200 GeV MV = 500 GeV M(T) = 110 GeV M(T) = 210 GeV M(T) = 105 GeV M(T) = 200 GeV MV = 500 GeV Data: 12 Bkg: 12.7 ± 0.9 Signal: 10.3 ± 1.0 no excess seen ... M(jj) M(Wjj)


Neural Net analysis : Neural Net analysis M(T) = 105 GeV M(T) = 200 GeV MV = 500 GeV D0 Run II Preliminary 388 pb-1 no excess seen ... 2 stage NN using 8 kinematic and topological variables HTe, pT(jj), (jj), (e,MET), pT(j1), pT(j2), pT(e), MET Mass dependent optimization on S/√B


Result of the WT analyses : Result of the WT analyses First measurement done with TCSM2 model (cannot be compared with the now obsolete TCSM) No evidence was found for T, T production for the parameters used with 388 pb-1 > 1 fb-1 is now available Add  channels soon Possibility of exploring larger TC parameter space D0 Run II Preliminary 388 pb-1 Observed Excluded (NN) Expected Excluded (NN) Observed Excluded (CB) Expected Excluded (CB) Forbidden Region 95% CL Limits computed using: Bayesian statistics (CB) 2D maximum likelihood using (M(Wjj),M(jj)) correlations (NN)


Leptoquarks : Leptoquarks Predicted by many extensions of the SM Carry both lepton and quark quantum numbers => connection of lepton and quark sectors Description with effective couplings invariant under SU(3)CxSU(2)LxU(1)Y conserve lepton and baryon number separately (proton lifetime) couple to lepton and quark in the same family (FCNC) scalar and vector leptoquarks are possible but only limits for scalar leptoquarks will be shown (lower cross-sections and less model dependant)


Leptoquarks : Leptoquarks Pair production modes: - quark anti-quark annihilation - gluon fusion Decay: parameterized by b the LQ branching fraction to charged lepton + quark Topology: 2 (light/b)-jets + missing energy ‘QCD’ or instrumental: - multijet production determined from data Standard Model (SM) : (ALPGEN interfaced with PYTHIA) - Vector boson production associated with jets - Z + 2 jets   + 2 jets (irreducible) - W + 2 jets l + 2 jets (l = e, ,) (lepton not reconstructed) - W + 1 jet  l + 1 jet (l = e, ) (lepton identified as a jet) - diboson production : WW, WZ, ZZ - top production (single and pair) SIGNAL BACKGROUNDS reported on in this talk


Leptoquarks in acoplanar jet topology : Leptoquarks in acoplanar jet topology Start with ~ 14 million events collected with the Jets+MET trigger Initial cuts: - MHT = > 40 GeV - DF(2 leading jets) < 165o - MET > 40 GeV - |zPV| < 60 cm - at least 2 jets - data quality cuts mLQ = 140 GeV Selection


Angles between jets and MET : Angles between jets and MET (Δφmax – Δφmin) cut at 120° removes almost all of QCD with minor induced signal inefficiency (Δφmin + Δφmax) cut at 280° removes a good fraction of the SM bkg with moderate added signal inefficiency mLQ = 140 GeV


QCD background estimation : QCD background estimation mLQ = 140 GeV


leptoquarks in acoplanar jet topology : leptoquarks in acoplanar jet topology no excess seen ... After all cuts


leptoquarks in acoplanar jet topology : leptoquarks in acoplanar jet topology b = 0 what about the 3rd generation? Most stringent limit for 1st and 2nd generation scalar leptoquarks decaying exclusively in a quark and a neutrino (b=0) mLQ > 136 GeV @ 95% CL


3rd gen. LQ : 3rd gen. LQ Decay: BR(LQ3->bn) = 1 as long as M(LQ3) < M(t)+M(t) Phase space suppression factor Fs for higher masses BR(LQ3->bn) = 1 – 0.5*Fs Selection Signal charge 1/3 Use b-tagging to increase sensitivity to signal


Before b-tagging : Before b-tagging SM background (W/Z + jets and top) normalized to the integrated luminosity (310 pb-1) reproduces the data well => contribution of QCD multijet processes is small mLQ = 200 GeV


Using b-tagging : Two taggers used: Jet LIfetime Probability (JLIP): based on impact parameter of tracks in jet m-tag: if muon within a cone DR = 0.5 around the jet axis 2 b-tags are required: at least 1 m-tag and at least 1 JLIP-tag 2 JLIP-tags and Xij > 0.8 ( ) Using b-tagging no excess seen ...


3rd generation leptoquarks : 3rd generation leptoquarks if LQ decays in tt: mLQ > 213 GeV @ 95% CL if not: mLQ > 219 GeV @ 95% CL [B(LQ -> bn) = 1]


Conclusions and Outlook : Conclusions and Outlook So far, no convincing hint of physics BSM at D0 But, substantially improved limits ... ... and we are still hopeful for discoveries! Results presented were obtained with < 0.4 fb-1 ~1.2 fb-1 already available and being analyzed More integrated luminosity is on its way ... design goal of 8 fb-1 likely to be achieved ... Stay tuned ... СПАСИБO! D0 is open to new physics ideas that can be tested with our data, so do not hesitate to get in touch with us!