1 / 20

Prospects for leptoquark searches with ATLAS at the LHC

Prospects for leptoquark searches with ATLAS at the LHC. N. Benekos ( CERN) V. A. Mitsou ( IFIC –Valencia) I. Panagoulias, Th. Papadopoulou (NTUA Athens). Physics at LHC 13-17 July 2004, Vienna, Austria. Outline. Introduction Theoretical motivation Phenomenology

phuc
Download Presentation

Prospects for leptoquark searches with ATLAS at the LHC

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. Prospects for leptoquark searches with ATLAS at the LHC N. Benekos (CERN) V. A. Mitsou (IFIC –Valencia) I. Panagoulias, Th. Papadopoulou (NTUA Athens) Physics at LHC 13-17 July 2004, Vienna, Austria

  2. Outline • Introduction • Theoretical motivation • Phenomenology • Production of leptoquarks at LHC • ATLAS sensitivity • 2 leptons + 2 jets topology • ETmiss + 2 jets topology • Conclusions Physics at LHC 2004, Vienna

  3. Leptoquarks (LQ) are hypothetical particles which appear in many SM extensions to explain symmetry between leptons and quarks SU(5) GUT model superstring-inspired models ‘colour’ SU(4) Pati-Salam model composite models technicolor LQs are coupled to both leptons and quarks andcarry SU(3) color, fractional electric charge,baryon (B) and lepton (L) numbers LQs can have: spin 0 (scalar)► couplings fixed, i.e., no free parameters spin 1 (vector)► anomalous magnetic (κG) and electric quadrupole (λG) model-dependent couplings Yang-Mills coupling: κG=λG=0 Minimal coupling: κG=1, λG=0 Experimental evidence searched: indirectly: LQ-induced 4-fermion interactions directly: production cross sections at collider experiments Theoretical motivation Physics at LHC 2004, Vienna

  4. Buchmuller, Rückl, Wyler (BRW) model (1987) Assumptions: LQs only couple to quarks, leptons and gauge bosons (with dimensionless couplings) LQ interactions invariant under SM gauge group SU(3)C SU(2)L  U(1)Y LQs are classified by: fermion number, F=3B+L ► F = 0, 2 spin ► J=0 (scalar) or J=1 (vector) charge ► Qem= ±1/3, ±2/3, -4/3, -5/3 Intergenerational mixing is severely restricted by FCNC dataLQ appear in3 quark/lepton generations LQ-mediated π and K helicity-suppressed decays not observedchiral LQ couplings to fermions Leptoquark classification 14 chiral LQ species per generation: 7 scalar LQs (3 singlets, 3 doublets, 1 triplet) 7 vector LQs (3 singlets, 3 doublets, 1 triplet) Physics at LHC 2004, Vienna

  5. Decays: LQs decay to l±q and/orνq with branching ratios βℓ, βν = 0, 0.5, 1(depending on the quantum numbers) Scalar LQs decay isotropically Vector LQs decay ~ (1+cosθ*)2 Each LQ characterized by two parameters: LQ massMLQ LQ-l-q Yukawa coupling,λ Resonance widthΓ~ λ2·mLQ couple to ℓ-q, νq - couple to ℓ+q, νq Phenomenology labeled by weak isospin and lepton helicity Physics at LHC 2004, Vienna

  6. Single production strongly depends on λ possible signatures: ℓ+ℓ- + jet ℓν+ jet νν + jet Main background: Zjet & tt Pair production Practically independent of Yukawa coupling λ (onlyg-LQ-LQvertex) Depends mainly on LQ mass LQ LQ LQ l, ν l, ν - qqLQ LQ ggLQ LQ LQ production processes at LHC qglLQ, qg ν LQ LQ • λ-dependent process • does not contributesignificantly to 2nd & 3rd generation Physics at LHC 2004, Vienna

  7. Pair production cross sections qqLQ LQ: ~30% of total production (for mLQ≈1TeV) 100 events minimal coupling 100 events 100 events Yang-Mills LQ production rates at LHC - Vector LQs Scalar LQs Blümlein et al, Z. Phys. D 76 (1997) 137 Belyaev et al, Phys. Rev. D59 (1999) 075007 Physics at LHC 2004, Vienna

  8. Scalar leptoquarks Pair production ℓℓjj channel ννjj channel independent of λ! Simulation tools: PYTHIA qq  LQ LQ gg  LQ LQ ATLAS fast simulation (ΑΤΗΕΝΑ-ATLFAST) LQ LQ  e+e-qq mLQ=1500 GeV (schematic view) Leptoquarks in ATLAS Physics at LHC 2004, Vienna

  9. Signal LQ LQ  ℓ+qℓ-q 1st and 2nd generation LQs Scalar e-u & μ-c β=1 S0R(-1/3) β=0.5  S0L(-1/3), S1(-1/3) λ ≥ 10-6 (LQ : resonance) Background QCD: huge, but eliminated after high-pT isolated leptons and high-mℓj cuts are applied Drell-Yan: eliminated by high-mℓj cut First level cuts: At least 2 jets with pT>30 GeV and |η|<5.0 2 same-flavour, opposite- sign leptons with pT>30 GeV and |η|<2.5 2 leptons + 2 jets topology Physics at LHC 2004, Vienna

  10. Signal (mLQ=1 TeV): Many high-pT jets Two high-pT leptons Background: Zℓ+ℓ- peak at mℓℓ90 GeV After first-level cuts signal backgrnd ℓℓjj: selection variables I Physics at LHC 2004, Vienna

  11. ∑ET: sum of transverse energy in the calorimeters mℓj: lepton-jet invariant mass for two leading jets (minimum- Δmℓj combination) signal backgrnd ℓℓjj: selection variables II Physics at LHC 2004, Vienna

  12. ℓℓjj: mℓj invariant mass Provides clearest signal mLQ=1 TeV (a) (b) (c) Physics at LHC 2004, Vienna

  13. Similar cuts imposed for both eejj &μμjj channels Cuts optimized to maximize significance for all leptoquark masses at least 2 jets with pT>70 GeV and |η|<5.0 2 same-flavour, opposite- sign leptons with pT>100 GeV and |η|<2.5 mℓℓ> 180 GeV(for Z peak) ETmiss< 70 GeV(for tt background) ∑ET > 570 GeV ETmiss/∑ET < 0.05 mass window: |mℓj-mLQ| < 100 GeV mLQ reconctructed from two leading jets with minimum-∆mℓj combination ℓℓjj: selection cuts (tentative) Physics at LHC 2004, Vienna

  14. After all selection criteria S+B and B is shown for 1st generation (e+e-jj) Signal can be observed for MLQ ~ 1.3 TeV Channel background-free for MLQ>1.8 TeV but signal cross section very small (<0.07 fb) ℓℓjj: signal and background Preliminary mLQ=1 TeV mLQ=1.2 TeV mLQ=1.2 TeV mLQ=1.5 TeV Physics at LHC 2004, Vienna

  15. First generation leptoquarks Integrated luminosity ∫L=30 fb-1 Signal can be clearly observed for mLQ = 1.3 TeV Similar results obtained for μμjj channel ℓℓjj: signal significance Preliminary Physics at LHC 2004, Vienna

  16. 1st and 2nd generation LQs Scalar νd & νs LQ LQ  ννqq Signal is difficult to be separated from SM background (Z jet irreducible background) 3rd generation LQs LQ LQ  νν bb β=0 S1/2(+1/3) S1(+2/3), β= 0.5  S0L(-1/3), S1(-1/3) Background Zjet background irreducible Main backgrounds: tt, ZZ, ZW(bbℓν) All other SM backgrounds areeliminated from b-tagging and lepton-veto ETmiss +2 jets topology ~ Physics at LHC 2004, Vienna

  17. ννjj: selection criteria (tentative) • Selection criteria maximize significance for high leptoquark masses • At least 2 b-jets with pT>70 GeV and |η|<5.0 • No isolated leptons • mjj > 180 GeV • ETmiss > 400 GeV • 30o<φj-j<150o for the two leading jets • φj-pTmiss>60ofor the two leading jets signal mLQ=1 TeV background Physics at LHC 2004, Vienna

  18. ννjj: selection variables • Variables shown before applied cuts (pTjet>10 GeV) • Main cut: large ETmiss due to escaping neutrinos signal mLQ=1 TeV signal mLQ=1 TeV background background Physics at LHC 2004, Vienna

  19. ννjj: significance • Third generation leptoquarks: LQ LQ  νbνb • Integrated luminosity ∫L=30 fb-1 • No mass peak is reconstructed (only excess of events) • Signal observable for masses up to mLQ=1.3 TeV • Exclusion limits (95% C.L.) up to mLQ~1.5 TeV Preliminary 95% C.L. Physics at LHC 2004, Vienna

  20. Conclusions • ATLAS at the LHC is going to explore the existence of leptoquarks with masses up to mLQ~1.5 TeV independently of the Yukawa coupling • 1st- or 2nd-generation scalar leptoquarks can be observed up to mLQ 1.3 TeV,in the LQLQℓℓqq channel (if β=1) • 3rd-generation LQs are observable up to mLQ 1.3 TeV,if they only couple to a neutrino & a b-quark, via theLQLQννbb channel • Possibility to study other species of LQs by combining/investigating other channels Physics at LHC 2004, Vienna

More Related