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HEP 2008, Olympia, Greece

Ariadni Antonaki Dimitris Fassouliotis Christine Kourkoumelis Konstantinos Nikolopoulos University of Athens S tudies for the detection of new heavy bosons with the ATLAS detector. HEP 2008, Olympia, Greece. Search motivation.

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HEP 2008, Olympia, Greece

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  1. Ariadni Antonaki Dimitris Fassouliotis Christine Kourkoumelis Konstantinos Nikolopoulos University of Athens Studies for the detection of new heavy bosons with the ATLAS detector HEP 2008, Olympia, Greece

  2. Search motivation • Several theoretical models beyond SM predict the existence of new, heavy gauge bosons • GUTs • E6 models • Left-Right Symmetric models • Little Higgs models • Kaluza-Klein models • Z’ (neutral) / W’ (charged)

  3. Mass limits Not well defined by the theoretical models  experiment searches in a broad mass region Current Limits (Tevatron): • Z’ mass > 850GeV@ 95% C.L. • W’ mass > 1 TeV @ 95% C.L. LHCwill search up to ~4TeV. The reference model For our analysis we use the Sequential Standard Model (SSM)  Z’,W’identical to Z,W (same couplingsto fermions) but with much larger mass We have worked with two different mass samples for each case : 1TeV and 2 TeV

  4. What’s new in this analysis • All samples with Full Simulation • Initial Detector Layout • MS Trigger Study (Isol. μ, PT>20GeV)  90% eff. W’, 95% eff. Z’ (first time) • x-sections @ NLO • Evaluation of systematic effects

  5. W’, Z’ cross sections (LO)

  6. 1TeV 2TeV W’ μν(MSc thesis of Zacharias Roupas) Transverse mass distribution (MT) Background to W’ decay: W-boson tail, ttbar production, di-jets…

  7. W’ boson W’->μν: clear signature, consisting of high-energy isolated muon + large ETmiss Event Selection

  8. Transverse Mass (after all Cuts) --- W tail : dominant

  9. Significance Integrated Luminosity for a 5σ W’ discovery ~70pb-1 ~3pb-1

  10. Z’μμ The most distinctive signature comes from dileptondecay. The dominant background is the (irreducible) Drell-Yan process to muons. Other contributions (ttbar prod., Zττ, dijets e.t.c.) negligible in high-mass region & after appropriate selection criteria

  11. Z’ boson Event Selection At least 2opposite charged muons with: Cut Efficiency (NO isol. Cut)

  12. M(GeV) Mass Plots (after Cuts) * Drell-Yan * Zprime 1TeV * Zprime 2TeV

  13. Significance Studies • The main goal is to test two hypotheses: • the data is compatible with non-signal SM background (“null hypothesis” - H0 ) • the data is compatible with signal+background (“alternative/test hypothesis” – H1 )

  14. Significance Studies (methods) 1). Mass Integral Input: Total number of signal and bkg events in the same mass region (normalized at luminosities under study). Output: signal significance for several luminosities under study. Systematics (PTmuon resolution, ±5% efficiency) can be included. 1). Mass Spectrum Input: Mass distributions for signal and bkg, normalized at the luminosities under study. Output: FFT signal significance for several luminosities under study. Systematics (Ptmuon resolution, ±5% efficiency) can be included. 2). Mass Spectrum Input:Mass distributions for signal and bkg, normalized at the luminosities under study. Constructs the p.d.f.’s (FFT) for the signal and the bkg for some discriminant variable (e.g. Inv.Mass) and counts the Likelihood Ratio Output: signal significance for the several luminosities under study. Systematics (PTmuon resolution, ±5% efficiency) can be included.

  15. (s+b) median (20pb-1) fixed mass Significance Studies (methods) • 3).Toy MC • Input: The signal and bkg distributions, normalized at 1pb-1. Perform an expo fit for the bkg and assume gaussian for the signal. • Perform pseudo-experiments and count the integral of signal Gaussian and bkg. The Gaussian can be performed in a fixed region (“fixed mass”) or everywhere (“floating mass”). For each hypothesis, we produce: Count how many b aboves+b median • Output: Significance for “fixed mass” and “floating mass” case. * Expo fit(DY) * Gaussian(1TeV) * Gaussian(2TeV) H1 H0 Likelihood Ratio

  16. Significance for 1TeV (SM-like) Zprime For 5σ : Luminosity 12-13pb-1

  17. Significance for 2TeV (SM-like) Zprime For 5σ : Luminosity ~300pb-1

  18. Significance for several Z’ models Z’e+e- SSM: most optimistic case Difference < factor of 10  stable in all mass range

  19. Conclusions & Future Work SM-like Z’ and W’ bosons can be detected in ATLAS, even in early data taking (~10pb-1 after a month) The expected luminosities for SM-like Z’ and W’ at 5σ discovery have been estimated: • A SM-like Z’ μμ 1TeV mass at ~13pb-1, 2TeV mass ~300pb-1 • A SM-like W’ μν 1TeV mass at ~3pb-1, 2TeV mass ~70pb-1 Future: • W’ : Mass measurements • Z’ : More masses, different Z’ models (when produced)

  20. Back up Slides

  21. W’ boson data samples W’μν Process Generator σ ΧBR [fb] Comments Events 1TeVW →lνPYTHIA 9430 min(√s) = 300GeV 30K 2TeVW →lνPYTHIA 437 min(√s) = 300GeV 30K 3TeVW →lνPYTHIA 54 min(√s) = 300GeV 10K SMW →ν PYTHIA 18721.1 200GeV< m(W) <500GeV 20K SMW →ν PYTHIA 708.26 m(W) >500GeV20K t ¯t MC@NLO 452000 340K Dijet J0 PYTHIA 1.76Χ1013 pˆT = 8−17GeV 380K Dijet J1 PYTHIA 1.38Χ1012 pˆT = 17−35GeV 380K Dijet J2 PYTHIA 9.33Χ1010 pˆT = 35−70GeV 390K Dijet J3 PYTHIA 5.88Χ109 pˆT = 70−140GeV 380K Dijet J4 PYTHIA 3.08Χ108 pˆT = 140−280GeV 390K Dijet J5 PYTHIA 1.25Χ107 pˆT = 280−560GeV 370K Dijet J6 PYTHIA 3.60Χ105 pˆT = 560−1120GeV 380K Dijet J7 PYTHIA 5.71Χ103 pˆT = 1120−2240GeV 430K

  22. W’ boson W’μν PT-1 Resolution 1TeV 2TeV ETmiss Resolution

  23. Systematics (theor.) Systematics (exp.) ---- : Coulomb scattering, low energies ---- : Alignment, high energies (PTResolution Uncertainty: 10->20%)

  24. Cut Flow

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