Search for single production of vector-like quarks decaying into a W-boson and a b-quark at 13 TeV

Transcription

1 Search for single production of vector-like quarks decaying into a W-boson and a b-quark at 3 TeV Dustin Biedermann Humboldt-Universität zu Berlin Top 06 Olomouc, 0th September 06

2 Vector-like Quarks Introduction Vector-like Quarks (VLQ) predicted by several BSM models (little Higgs, composite Higgs,...) addressing Hierarchy problem, tension in A b FB,... Appear in different SU() multiplets: Singlets: T, B Doublets: (XT), (TB), (BY) Triplets: (XTB), (TBY) Y/T most promising Pair production: mass constraints (m(t /Y ) GeV) Single production: coupling constraints Maximally allowed single production cross sections from electro-weak bounds Phys.Rev. D88.9 (03) / 8

3 Principal analysis idea Analysis Singly-produced VLQ Y 4 3 and T 3 (05 data, 3. fb ) Production: Weak t-channel bw fusion Decay process: Y /T Wb BR(Y Wb) = 00%; T-singlet: BR(T Wb) 50% at high masses q q W Y /T W c L/R or sin θ L/R c L/R or sin θ L/R g b b b Measure/set limits on single production cross-section and couplings (c L/R, sin θ L,R ) c L/R : Matsedonskyi, Panico and Wulzer, JHEP (04) 097 sin θ R/L : Aguilar-Saavedra et al., PRD 88.9 (03) / 8

4 Analysis Strategy Analysis Strategy Exactly one e or µ ET miss > 0 GeV b-tagged jet (R = 0.4) p T > 350 GeV Large φ(l,b-jet) Veto hard central jets ( η <.5, p T > 75 GeV) Forward jet (.5 < η < 4.5) ( ) Discriminant: m(vlq) = l,ν,b p i i Main backgrounds: W+jets, tt, single top 4 / 8

5 Results Signal extraction with profile likelihood fit in m VLQ Events / 00 GeV 0 ATLAS Preliminary s = 3 TeV, 3. fb 8 Q Wb, Q = T or Y 6 SR Pre Fit 4 Data Single top Other SM bkg. Yq(b) (. TeV, tt W+jets Total unc. c+c L R =/ ) Events / 00 GeV 0 ATLAS Preliminary s = 3 TeV, 3. fb 8 Q Wb, Q = T or Y 6 SR Post Fit 4 Data tt Single top W+jets Other SM bkg. Total unc Data / Pred m VLQ [GeV] Data / Pred m VLQ [GeV] Good data/mc agreement in SR and in ttbar and W+jets CR (backup) Good data/mc agreement in other distributions too (backup) No significant excess observed limit setting 5 / 8

6 Results Limit on cross section times branching ratio for Y and T BR [pb] σ 0 Observed 0 ATLAS Preliminary s = 3 TeV, 3. fb 95% CL Exclusion Limits on σ BR Expected Expected ± σ Expected ± σ Theory (NLO), BR(Q >Wb)= σ th, σ th, σ th, c L c L c L + c R = / + c R = + c R = m Q [TeV] m(y ) <.44 TeV excluded at 95% CL for c L + c R = / 6 / 8

7 Limits on couplings Results L sinθ ATLAS Preliminary - s=3 TeV, 3. fb T Singlet 95% CL Exclusion Limits on Mixing Angle Observed Expected Expected ± σ Expected ± σ Indirect EW constraint (S,T) R sinθ ATLAS Preliminary - s=3 TeV, 3. fb (B,Y) Doublet 95% CL Exclusion Limits on Mixing Angle Observed Expected Expected ± Expected ± σ σ Indirect EW constraint (S,T) Indirect EW constraint R b [TeV] m T [TeV] m Y Limits are close to electro-weak precision bounds for Y masses between 900 and 00 GeV (More coupling limits in backup slides) 7 / 8

8 ] 7/6 calibration Conclusion Conclusion Summay Search for singly produced Y/T VLQs using 3. fb ( s = 3 TeV) Observed limit for Y/T(m = 900 GeV): σ < 0.33 pb Y mass exclusion for cl + c R = / : m(y)<.44 TeV sin θ R limits for (BY) doublet close to EW precision bounds Results are public: ATLAS-CONF More data is coming in fast perhaps VLQs are discovered soon! Delivered Luminosity [fb ATLAS Online Luminosity 0 pp s = 7 TeV 0 pp s = 8 TeV 05 pp s = 3 TeV 06 pp s = 3 TeV 5 0 Jan Apr Jul Oct Month in Year 8 / 8

9 Conclusion Thank you! 9 / 8

10 Backup Backup 0 / 8

11 Couplings Backup Model-independent aproach (JHEP (04) 097) L W = g ) (c L Q L γ µw µ b L + c R Q R γ µw µ b L +... () σ sing (Qb) = ( cl + R) c σwb (M) () σ limit = c σ theory ( c L + cr = ) L + c R (3) Model-specific aproach (PRD 88.9 (03) 09400) L W = g ( V L Qb Q Lγ µw µ b L + V R Qb Q Rγ µw µ b L ) +... (4) The mixing V depends on the multiplett, e.g. for (BY) it is V R/L Yb = sin θ R/L e iφ possible to translate limit on cl + c R to model specific mixing parameter sin θ R/L / 8

12 Backup Coupling determination in single production Single production cross section is coupling dependent Strong Pair production mass constraints (less model-dependent) Electroweak Single production coupling constraints (more model-dependent) u d c Wb L/R or sin θ L/R W Y W c Wb L/R or sin θ L/R g b b b Models considered in this analysis: Matsedonskyi, Panico and Wulzer, JHEP (04) 097 Model-independent non-renormalizable Lagrangian w/o specific multiplet structure Couplings: c Wb L/R Aguilar-Saavreda et al., PRD 88.9 (03) Renormalizable Lagrangian, multiplet realizations, also limits from EW precision obs. Couplings: sin θ L/R with sin θ L = f (sin θ R ) Translation: c Wb L/R = sin θ L/R / 8

13 Systematics Backup Considered Systematics JES/JER E miss T Electron / muon Lepton SF Flavour tagging tt generator, shower/hadronisation, ISR/FSR Single top generator, shower/hadronisation, ISR/FSR Luminosity uncertainty:.% V+jets and Diboson cross section: 5% Single top cross section : 6.8% Top pair production cross section: +5.7% and 5.3% Fakes: 50% (flat) PDF systematics for W+jets and signals 3 / 8

14 Selection cuts Backup Preselection Exactly one e or mu (single lepton trigger) Number of j4 (p T > 5 GeV): >, leading jet (lj): η <.5 Veto events with fwd jets (.5 < η < 4.5) of p T < 40 GeV E miss T > 0 GeV Y/T signal region lj: b-tagged lj: p T > 350 GeV veto hard central jet (hj) (p T > 75 GeV ) with R(hj,lj) <. and R(hj,lj) >.7 φ(lep,lj) >.5 number of fwd. jet Wjets control region Same cuts as in SR except: lj: not b-tagged lj: p T > 50 GeV ttbar control region Same cuts as in SR except: lj: p T > 00 GeV Require at least one hj with R(hj,lj) <. or R(hj,lj) >.7 Cuts are optimized to obtain maximal S/ B for m(y ) = 900 GeV in SR 4 / 8

15 Signals in signal region Backup Events / 00 GeV ATLAS Simulation Preliminary - s=3 TeV, 3. fb Total background Y 700 GeV Y 900 GeV 0 Y 00 GeV m VLQ [GeV] Assumed coupling for all three signals is c L + c R = / 5 / 8

16 Backup Control regions - Data/MC - Pre-fit Events / 00 GeV ATLAS Preliminary s = 3 TeV, 3. fb Q Wb, Q = T or Y W+jets CR Pre Fit Data Single top Other SM bkg. tt W+jets Total unc. Yq(b) (. TeV, c+c L R =/ ) Events / 00 GeV 00 ATLAS Preliminary s = 3 TeV, 3. fb Q Wb, Q = T or Y tt CR 80 Pre Fit 60 Data Single top Other SM bkg. tt W+jets Total unc. Yq(b) (. TeV, c+c L R =/ ) Data / Pred m VLQ [GeV] Data / Pred m VLQ [GeV] 6 / 8

17 Backup Control regions - Data/MC - Post-fit Events / 00 GeV ATLAS Preliminary s = 3 TeV, 3. fb Q Wb, Q = T or Y W+jets CR Post Fit Data tt Single top W+jets Other SM bkg. Total unc. Events / 00 GeV 90 ATLAS Preliminary s = 3 TeV, 3. fb 80 Q Wb, Q = T or Y tt CR 70 Post Fit 60 Data tt Single top W+jets Other SM bkg. Total unc Data / Pred m VLQ [GeV] Data / Pred m VLQ [GeV] 7 / 8

18 Backup Limit on YbW coupling ( model independent ) 8 TeV 3 TeV Wb ) R + (c Wb ) L (c ATLAS Preliminary - s=3 TeV, 3. fb (B,Y) Doublet 95% CL Exclusion Limits on Coupling Observed Expected Expected ± Expected ± σ σ [TeV] m Y 8 / 8

19 Backup Limit on YbW coupling in a BY-doublet model 8 TeV 3 TeV R sinθ ATLAS Preliminary - s=3 TeV, 3. fb (B,Y) Doublet 95% CL Exclusion Limits on Mixing Angle Observed Expected Expected ± Expected ± σ σ Indirect EW constraint (S,T) Indirect EW constraint R b [TeV] m Y 9 / 8

20 Backup Limit on TbW coupling (for a T singlet) 8 TeV 3 TeV L sinθ ATLAS Preliminary - s=3 TeV, 3. fb T Singlet 95% CL Exclusion Limits on Mixing Angle Observed Expected Expected ± σ Expected ± σ Indirect EW constraint (S,T) [TeV] m T 0 / 8

21 Kinematic variabels - I Backup Events / 00 GeV ATLAS Preliminary s = 3 TeV, 3. fb Q Wb, Q = T or Y SR Post Fit Data tt Single top W+jets Other SM bkg. Total unc. Events / 00 GeV ATLAS Preliminary s = 3 TeV, 3. fb Q Wb, Q = T or Y SR Post Fit Data tt Single top W+jets Other SM bkg. Total unc Data / Pred Lepton p [GeV] T Data / Pred Leading b tagged jet p [GeV] T / 8

22 Kinematic variabels - II Backup Events / 00 GeV 45 ATLAS Preliminary s = 3 TeV, 3. fb 40 Q Wb, Q = T or Y SR 35 Post Fit 30 Data tt Single top W+jets Other SM bkg. Total unc. Events / 00 GeV ATLAS Preliminary s = 3 TeV, 3. fb Q Wb, Q = T or Y SR Post Fit Data tt Single top W+jets Other SM bkg. Total unc Data / Pred Missing E [GeV] T Data / Pred W boson p [GeV] T / 8