Theodora D Papadopoulou NTU Athens 1 rst ECFACERNLHe

Theodora D. Papadopoulou NTU Athens 1 rst ECFA-CERN-LHe. C Workshop September 1 -3 / 2008 1 st LHe. C Workshop 1 Th. D. Papadopoulou

Outline Ø About theoretical motivation on LQ studies Ø Pair and LQ production at LHC Ø Comparison of Single and Pair LQ aspects Ø Single LQ studies at LHC Ø Preliminary results ØOutlook Ø As an Epilogue 1 st LHe. C Workshop 2 Th. D. Papadopoulou

Theoretical Motivation LQs: b e(μ) LQ s 1 st LHe. C Workshop 3 μ(e) Th. D. Papadopoulou

BRW model 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=3 B+L F = 0, 2 – spin J=0 (scalar) or J=1 (vector) – charge Qem= ± 1/3, ± 2/3, -4/3, -5/3 1 st LHe. C Workshop • Intergenerational mixing is severely restricted by FCNC data LQ appear in 3 quark/lepton generations LQ-mediated π and K helicitysuppressed decays not observed chiral LQ couplings to fermions 14 chiral LQ species per generation: 7 scalar LQs (3 singlets, 3 doublets, 1 triplet) 7 vector LQs (3 singlets, 3 doublets, 1 triplet) 4 Th. D. Papadopoulou

About LQ Coupling • 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 • Resonance width Γ~ λ 2·m. LQ • Yang-Mills coupling κG=λG=0 • Minimal coupling κG=1, λG=0 1 st LHe. C Workshop 5 Th. D. Papadopoulou

LQ species and decays couple to ℓ-q, νq couple to ℓ+q, νq labeled by weak isospin and lepton helicities Decays: • LQs decay to l±q and/or νlq’ with branching ratios βℓ, βν = 0, 0. 5, 1 (depending on the quantum numbers) • Scalar LQs decay isotropically • Vector LQs decay ~ (1+cosθ*)2 1 st LHe. C Workshop 6 Th. D. Papadopoulou

Overview of LQ production mechanisms 1 st LHe. C Workshop 7 Th. D. Papadopoulou

LQ production at LHC • Pair production – Practically independent of Yukawa coupling λ – Depends mainly on LQ mass • Single production – strongly depends on λ – possible signatures: • ℓ+ℓ- + jet • ℓν + jet • νν + jet LQ LQ LQ l, ν v Both categories (Pair and Single) LQs are complementary for LHC searches 1 st LHe. C Workshop 8 Th. D. Papadopoulou

LQ cross sections at LHC Pair Scalar LQ production Single Scalar LQ production • Single LQ valence quarks • Single sea quarks ~10 fb A. Belyaev, C. Leroy, R. Mehdieyev, A. Pukhov, Phys. Rev. D 59 (1999) 075007 v If the LQ Coupling is of the order of single LQ production should 1 st LHe. C Workshop 9 Th. D. Papadopoulou be combined with the studies of LQ pair production

Single LQ studies with ATLAS We will probe distances up to 10 -19 m ! 1 st LHe. C Workshop 10 Th. D. Papadopoulou

First LQ study in ATLAS Pair LQ production -ATLAS LQ LQ e+e-qq (m_LQ=1500 Ge. V) • 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) V. Mitsou, N. Benekos, I. Panagoulias, Th. Papadopoulou, ATL-COM-PHYS 2004 -071, Cz. J. of Physics, Vol. 54(2004), Suppl. A 1 st LHe. C Workshop 11 Th. D. Papadopoulou

lljj Signal and Background L=30 fb-1 Signal can be observed for MLQ ~ 1. 3 Te. V (5σ) Results are presented by V. Mitsou in “Physics at LHC” Conference, Vienna 2004 1 st LHe. C Workshop 12 Th. D. Papadopoulou

Single LQ at LHC LQ LQ LQ l, ν Interesting aspects !! v it is possible to probe LQ masses greater than half of the center-of-mass-energy of the experiment ( Ecm/2) v this process gives high PT leptons and jets (clear signal) BUT v the signal extraction is very difficult due to low cross-section ! 1 st LHe. C Workshop 13 Th. D. Papadopoulou

Single LQ production with ATLAS PRELIMINARY RESULTS Evgenia Panagiotopoulou Ph. D studies-NTU Athens Ø reconstruction of invariant mass LQ (1) Study of the 2 nd gen 0. 8 Te. V 1. 0 Te. V Single LQ c μ Topology : μ μ jet and (later) (2) Study of the 1 st gen 1. 2 Te. V 1. 4 Te. V Single LQ u e , d e Topology : e e jet • ATLFAST studies 1 st LHe. C Workshop 1 st • Studies with fully simulated events 2 nd step 14 Th. D. Papadopoulou

Baseline selections (common for all ATLAS LQ analyses) Muons Combined muons (reconstructed containing track in both inner + muon detectors) Muon p. T ≥ 20 Ge. V Muon |η| ≤ 2. 5 Jets Reconstructed calorimeter towers with ΔR = 0. 4 cone algorithm Jet p. T ≥ 20 Ge. V Jet |η| ≤ 4. 5 Individual analysis cuts Select the 2 highest p. T muons (p. Tmaxμ 1, p. Tmaxμ 2) and the highest p. T jet (p. Tmaxj) all max p. Ts ≥ 170, 230 Ge. V for high LQmass all max p. Ts ≥ 100 Ge. V for low LQmass (300, 400 Ge. V) (600, 800 Ge. V respectively) Cut b-jets (jets who’s weight is > 4) Invariant mass of the 2 selected muons Mμμ ≥ 200 Ge. V Sum of max p. Ts: SPT = p. Tmaxμ 1 + p. Tmaxμ 2 + p. Tmaxj 1 st LHe. C Workshop SPT ≥ LQmass+100 Ge. V 15 Th. D. Papadopoulou SPT ≥ LQmass+200 Ge. V

Single LQ Signal efficiencies PRELIMINARY RESULTS Single LQ mass LQ → u μ LQ → c μ (Ge. V) (good statistics) (poor statistics) 300 13. 3% ± 0. 9% 12. 2% ± 2. 1% 400 12. 4% ± 0. 4% 17. 5% ± 2. 5% 600 15. 2% ± 0. 9% 11% ± 1. 6% 800 15. 7% ± 0. 7% 10. 9% ± 1. 4% Signal efficiency • for Single Scalar LQ ( Q = -1/3) 1 st LHe. C Workshop 16 Th. D. Papadopoulou

Single LQ Discovery Luminosities PRELIMINARY RESULTS MLQ (Ge. V) 5σ Discovery Generate Signa Backgroun Signal d l Expected d LQ → u μ significanc Luminosit single LQ events e (pb) y s events (fb-1) σ *B 300 1. 234 1809 1153 199 45 0. 71 400 0. 368 7541 402 132 23 1. 67 600 0. 0647 2355 59 11 10 4. 6 800 0. 0173 3476 14 3. 7 5. 1 14 1 st LHe. C Workshop 17 Th. D. Papadopoulou

Cut flow for Single LQ (m=400 Ge. V) PRELIMINARY RESULTS Physics sample Before cuts LQ p. Tmaxμ 1, 2 ≥ 100 Ge. V SPT ≥ Mμμ ≥ mass Baseline 500 200 p. Tmaxj ≥ 100 Ge. V window cuts Ge. V b-tag weight ≤ 4 (± 2σ) MLQ = 400 Ge. V 3680 2432 666 613 457 402 Z/DY ≥ 150 Ge. V 72780 33626 689 586 360 118 420000? 86581 42 28 28 14 t tbar • Single Scalar LQ u μ ( Q = -1/3) • Optimized for the smallest integrated luminosity needed for a discovery with 5σ and normalized for an integrated luminosity of 10 fb-1 • All other background are negligible 1 st LHe. C Workshop 18 Th. D. Papadopoulou

VERY PRELIMINARY RESULTS effect on signal effect on background Integrated luminosity LQ cross-section High mass DY cross-section (main background) t tbar cross-section (secondary background) Muon identification and trigger Muon resolution Jet energy scale Jet resolution Statistical uncertainty of MC B-tagging uncertainty 20% ? ? 10% - - 1. 2% - 7. 2% 10% 8% 8% 6% 7% 5% 6% 2% 6% 10% Quadratic sum of all uncertainties 28. 8% 28. 9% Systematic error 1 st LHe. C Workshop 19 Th. D. Papadopoulou

Invariant mass μj pair PRELIMINARY RESULTS Early LHC Single LQ searches ! • LQ mass from 300 – 600 Ge. V • plots are normalized to L= 10 fb-1 1 st LHe. C Workshop 20 Th. D. Papadopoulou

Beyond minimal LQs: SUSY quarks • Rp can be explicitly broken by trilinear terms in the superpotential 9 Couplings 27 Couplings 9 Couplings HERA o single sparticle production o Unstable LSP ! via a ΔL 0 or a ΔB 0 operator • Resonant squark production • l +( l ) + multijets fast proton decay is suppressed if Lepton and Baryon number Violating Couplings not simultaneously present 1 st LHe. C Workshop 21 Th. D. Papadopoulou

Outlook • Pair and Single LQ studies at LHC are complementary • First studies on Single LQ with ATLAS/LHC are underway towards the final results at early LHC • Results presented are PRELIMINARY • Use of the LHC results to predictions for the LHe. C are important for the LHe. C expectations on the potential of LHe. C New physics 1 st LHe. C Workshop 22 Th. D. Papadopoulou

Hunting LQs (!) from Single LQ at LEP 1 Th. Papadopoulou DELPHI Collaboration Phys. Lett B 316 (1993)620 1 st LHe. C Workshop 23 Th. D. Papadopoulou

LQ Exclusion Limits -- comparison with LEP and Tevatron from I. Panagoulias’ talk at DIS 2008 – work on Ph. D / NTUA & DESY HERA extends the exclusion region 1 st LHe. C Workshop 24 Th. D. Papadopoulou

Future Perspectives ! ILC LHC Tevatron HERA LEP 2 1 st LHe. C Workshop New Physics ? LHe. C Collider ? Desert ? 25 Th. D. Papadopoulou