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A Preliminary Model Independent Study of the Reaction pp  qqWW  qq ℓ n qq at CMS

A Preliminary Model Independent Study of the Reaction pp  qqWW  qq ℓ n qq at CMS. Gianluca CERMINARA (SUMMER STUDENT) MUON group. The Project. A Study of the WW-Fusion Channel in a Model Independent way

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A Preliminary Model Independent Study of the Reaction pp  qqWW  qq ℓ n qq at CMS

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  1. A Preliminary Model Independent Study of the Reaction ppqqWWqqℓnqq at CMS Gianluca CERMINARA (SUMMER STUDENT) MUON group

  2. The Project A Study of the WW-Fusion Channel in a Model Independent way • Purpose: The aim of my work is to verify if it’s possible to extract thesignalfrom thebackgroundfor the process ppqqWLWLqqℓnqq • Tools: • PYTHIA for the event generation • CMSJET for the detector simulation • ROOT for the data analysis • … a complete simulation will follow… Gianluca CERMINARA

  3. Why am I studying this channel? A Model Independent Study of the WW Fusion in order to clarify the Symmetry Breaking Mechanism. The Standard Model predicts that without a Higgs the scattering amplitude of the WW fusion process violates unitarity at about 1.5 TeV… …for this reason something must happen: • In the Higgs case we will observe a resonance at MHiggs= MWW otherwise • the cross section will deviate from the SM prediction. We want to know with which resolution we can study the cross section as a function of the invariant mass of the two scattered W bosons! We are looking for everything that may happen in this channel!!! Gianluca CERMINARA

  4. What is the signal? • Topology Two quarks of the proton emit a W boson, the two bosons interact giving in the final state two other W bosons: one of them decays leptonically and the other decays into a pair of quarks. • Signature: • One muon in the barrel with high ptand missing energy of the neutrino (from the W decay) • two jets in the forward region of the detector (from the parton hadronisation) . • Two jets in the central region with high Pt coming from the quarks of the W decay 6 fermion final state! Gianluca CERMINARA

  5. What are the main backgrounds? t-tbar background • Topology From the interaction of a quark and an anti-quark or of two gluons of the proton we have at and anti-t quarkpair.They immediately decay into a b and a W. • Signature Since the W decays both leptonically and hadronically we have the same final state as the signal:4 jets(2 from the b and 2 from the W) anda muon. Gianluca CERMINARA

  6. + What are the main backgrounds? W+jets background • Topology A quark and a gluon/anti-quark give a W and a quark/gluon.When the W decays leptonically, the final state is similar to the one of the signal. • Signature if during the hadronisation the gluon gives origin to more than one jet this background can be very “dangerous”. Gianluca CERMINARA

  7. What are the main backgrounds? WTWTℓnqq background • Topology A quark and an anti-quark give two W bosons in the final state. One of them decays hadronically, the other decays in a muon and a neutrino. • Signature The final state is very similar to the one of the sinal: we have a muontwo jets and missing energy from the neutrino. Only the two scattered quarks are missing. Gianluca CERMINARA

  8. Event Generation Events generated with PYTHIA Monte Carlo package. PYTHIA 6.158 Only a little Monte Carlo statistics was available. Gianluca CERMINARA

  9. Detector Simulation CMSJET Fast Simulation package. • The leptons can be identified in the range –2.4 < h < 2.4 • Jet reconstruction: • range –5 < h < 5. • Cone algorithm with DR = 0.5 on the whole range of h of the detector. • pt >10 GeV. • No event pile-up. CMSJET 4.801 Gianluca CERMINARA

  10. Signal Kinematics Analysisof the Parton Levelkinematics. • The two scattered partons have pseudo-rapidity above 2.5 and they will give origin to forwadjets. • The quarks from the W decay are mainly produced in the central region of the detector. Gianluca CERMINARA

  11. Event Reconstruction Leptons fromWmn Muon The request of an isolated muon is unavoidable in order to identify a leptonic W decay. • Selection criteria: • Max isolation. • pt > 10 GeV • Efficiency: ~96% Neutrino Reconstruction of neutrino four-momentum: • ptn = system missing pt. • pz calculated imposing the constraint: mW = 80.45 GeV GW = 2.14 GeV (pm + pn )2 = mW2 • Smallest pz chosen. • Efficiency: ~82% Gianluca CERMINARA

  12. Event Reconstruction Jets from the W decay : Wqq • Selection criteria: • |h| < 3 • pt > 10 GeV • Combination of 2 or 3 or 4 jets with invariant mass closest to mW = 80.45 GeV • Efficiency: ~96% The possibility of a good reconstruction of the W boson is basically linked to the number of detected jets. Gianluca CERMINARA

  13. Event Reconstruction Jets from the W decay : Wqq • Selection criteria: • |h| < 3 • pt > 10 GeV • Combination of 2 or 3 or 4 jets with invariant mass closest to mW = 80.45 GeV • Efficiency: ~96% The possibility of a good reconstruction of the W boson is basically linked to the number of detected jets. Gianluca CERMINARA

  14. CUT Event Reconstruction Forward jet tagging. • Selection criteria: • pt > 10 GeV; • hj1x hj2< 0; • 1.5 < | h | < 5; • | hj1– hj2| > 3. • Efficiency: ~50.8% Tagging of two forward jets. (Parton Level) Gianluca CERMINARA

  15. Signal to Background ratio Efficiencies of applied cuts for the identification of the signal topology: The forward jet tagging is a powerful criterion to improve the signal to background ratio. Gianluca CERMINARA

  16. CUT CUT Signal to Background ratio After the first set of cuts all the backgrounds are still important. For this reason others variables have been used for the discrimination: • Pseudo-rapidity W which decays leptonically Applied cut: |hWlept|  3 Gianluca CERMINARA

  17. CUT CUT Signal to Background ratio • Transverse momentum of the W boson which decays leptonically Applied cut: ptWlept > 10 GeV • Transverse momentum of the W boson which decays hadronically Applied cut: ptWqq > 10 GeV Gianluca CERMINARA

  18. CUT CUT Signal to Background ratio Cuts on the tagging jets. • Transverse momentum of the tagging jet with max Pt Applied cut: ptjtag > 20 GeV • Invariant mass of the tagging jet system Applied cut: M(jt1+jt2) > 550 GeV/c2 Gianluca CERMINARA

  19. Signal to Background ratio Efficiencies of applied cuts : Again the cuts on the forward tagging system are the most effective. Gianluca CERMINARA

  20. Preliminary Results Even if theW+jetsbackground isstill importantat high invariant masses the signal to background ratio is quite good. The high energy regionis the most interesting for thenew physicswe are looking for. 1 year “Low Luminosity” = 10 fb-1 1 year “High Luminosity” = 100 fb-1 S/B = 2.1x104/8.9x105 S/B = 2.9x103/4.3x103 Gianluca CERMINARA

  21. MWWrec - MWWgen drWW = MWWgen Preliminary Results Resolution of the WW system invariant mass reconstruction. The resolution in the reconstruction of the WW invariant mass at this stage is : ~15% Fitting the histogram with the sum of two gaussian curves the resolution in the central peak is: ~10% Gianluca CERMINARA

  22. Conclusions At this stage the measurement appears possible: • Good signal to background ratio at high WW invariant masses S/B  1 • Very good resolution on MWW energy scale of the process ~10 15% Gianluca CERMINARA

  23. Future Projects A more complete study of this process using a “Full Simulation” of the CMS detector. • 20 k signal • 30 k W+jet • 20 k t-tbar …are coming soon! Gianluca CERMINARA

  24. A Preliminary Model Independent Study of the Reaction ppqqWWqqℓnqq at CMS Gianluca CERMINARA (SUMMER STUDENT) MUON group

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