Experimental and theoretical Group Torino + Moscow A Preliminary Model Independent Study of the Reaction ppqqWWqqℓnqq at CMS Experimental and theoretical Group Torino + Moscow Gianluca CERMINARA

We are looking for everything that may happen in this channel!!! ppqqWLWLqqℓnqq 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 measure 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!!! 14/02/2003 Gianluca CERMINARA

Model Independent Standard Model Cross Section (PYTHIA) to generate the signal sample for the study. NO non-standard Symmetry Breaking Mechanism was assumed!!! Measurement of the s(WW) vs M(WW) up to ~2 TeV 14/02/2003 Gianluca CERMINARA

What is the signal? fwd q m p W n q sVV fwd q 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 pt and missing energy of the neutrino (from the W decay) two jets in the forward region of the detector (from the parton hadronisation) . 6 fermion final state! W p fwd q q m n sVV Two jets in the central region with high pt from the W decay fwd q 14/02/2003 Gianluca CERMINARA

What are the main backgrounds? pp tt WWbb t-tbar background Topology From the interaction of a quark and an anti-quark or of two gluons of the proton we have a t and anti-t quark pair.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) and a muon. ℓnℓ qq 14/02/2003 Gianluca CERMINARA

What are the main backgrounds? W+2jets background Topology Two quarks/gluons from the protons give a final state with a W and two quarks/gluons.When the W decays leptonically, the final state is similar to the one of the signal. pp W+q/g+q/g mn Signature if during the hadronisation quarks or gluons give origin to more than one jet this background can be very “dangerous”. m n W p q/g 14/02/2003 Gianluca CERMINARA

What are the main backgrounds? pp W ℓnℓ qq-bar Single W background Topology All processes with a single W boson in the final state can be considered backgrounds for our study. Signature From the W decay we can have two jets in the central region of the detector or a lepton with missing Et from the neutrino. p W 14/02/2003 Gianluca CERMINARA

Event Generation Events generated with PYTHIA and CompHEP Monte Carlo packages. Signal t-tbar W+2jets Single W Cross section 18 pb 624 pb 770 pb 184885 pb Number of generated events 24153 46229 300000 596618 Monte Carlo PYTHIA CompHEP PYTHIA 6.158 CompHEP 41.10 14/02/2003 Gianluca CERMINARA

PYTHIA vs CompHEP Comparison the two generators for W+jets backgrounds. PYTHIA: it calculates diagrams for 2  2 processes (e.g. qq  gW and qq  qW ). Other diagams like W+many partons are taken into account with showering procedure; CompHEP is able to calculate a complete set of diagrams W+1,2,3 partons (W+4 with showering procedure) pt distribution W Eta distribution W Harder pt(W) More central W A. Krokhotine + CompHEP group 14/02/2003 Gianluca CERMINARA

Detector Simulation CMSJET CMS detector 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 >20 GeV. No event pile-up. CMSJET 4.801 14/02/2003 Gianluca CERMINARA

Event Reconstruction Leptons from Wmn Muon The request of an isolated muon is unavoidable in order to identify a leptonic W decay. Selection criteria: Max isolation. DR > 0.1 pt > 20 GeV Efficiency: ~77% 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: ~61% 14/02/2003 Gianluca CERMINARA

Event Reconstruction Jets from the W decay : Wqq The possibility of a good reconstruction of the W boson is basically linked to the number of detected jets. Selection criteria: |h| < 3 pt > 20 GeV Combination of 2 or 3 or 4 jets with invariant mass closest to mW = 80.45 GeV Efficiency: ~90% 14/02/2003 Gianluca CERMINARA

Event Reconstruction Jets from the W decay : Wqq The possibility of a good reconstruction of the W boson is basically linked to the number of detected jets. Selection criteria: |h| < 3 pt > 20 GeV Combination of 2 or 3 or 4 jets with invariant mass closest to mW = 80.45 GeV Efficiency: ~90% 14/02/2003 Gianluca CERMINARA

Event Reconstruction CUT Forward jet tagging. Tagging of two forward jets. Selection criteria: pt > 20 GeV; hj1 x hj2 < 0; 1.5 < | h1 | < 5 or 1.5 < | h2 | < 5 | hj1 – hj2| > 3. Efficiency: ~41% (Parton Level) 14/02/2003 Gianluca CERMINARA

Efficiencies Efficiencies of applied cuts for the identification of the signal topology: Cuts Signal t-tbar W+2jets Single W Isolated muon pt > 20 GeV 76.7% 34.3% 84.5% 52.0% Reconstruction neutrino pz 60.9% 24.7% 70.5% 45.8% Reconstruction W from jets 90.1% 98.2% 86.4% 21.0% Tagging jets 40.6% 24.2% 11.0% 2.7% The forward jet tagging is a powerful criterion to improve the signal to background ratio. 14/02/2003 Gianluca CERMINARA

Signal to Background ratio CUT Transverse momentum of the W boson Applied cut: ptWlept > 10 GeV ptWqq > 15 GeV Pseudorapidity of the W boson which decays hadronically: |hWlept| < 3 Very powerful cut on higher Pt ptWlept < 130 GeV Not to apply in high mass resonance case!!! 14/02/2003 Gianluca CERMINARA

Signal to Background ratio CUT Cuts on the tagging jets. Difference of pseudo-rapidity between muon from W and tagging jets (rapidity gap cut) Applied cut: Dhm-jt > 1 CUT Invariant mass of the tagging jet system Applied cut: M(jt1+jt2) > 550 GeV/c2 14/02/2003 Gianluca CERMINARA

Efficiencies |hWlept| < 3 Efficiencies of applied cuts : Cuts Signal t-tbar W+2 jets Single W |hWlept| < 3 97.7% 99.4% 100% 89.3% ptWlept > 10 GeV 97.8% 98.6% 90.8% ptWadron. > 15 GeV 94.1% 96.2% 96.9% 74.8% 60 GeV < mWqq < 100 GeV 82.1% 86.4% 70.2% 71.0% M(jt1+jt2) > 550 GeV/c2 66.5% 30.0% 46.8% 11.5% Dh(m-jt) > 1 79.5% 49.0% 46.3% 57.1% ptWlept < 130 GeV 87.6% 75.8% 38.4% 75.0% Total efficiency 6.7% 0.4% 0.01% Again the cuts on the forward tagging system are the most effective. 14/02/2003 Gianluca CERMINARA

With higher pt cut (ptWlept < 130 GeV) Preliminary Results With higher pt cut (ptWlept < 130 GeV) Even if the W+2jets background is still important at high invariant masses, the signal to background ratio is quite good. 1 month “low” luminosity Without higher pt cut (ptWlept < 130 GeV) 1 month “low” luminosity S/B  0.41 S/B  12/~0 The high energy region is the most interesting for the new physics we are looking for. S/B  0.32 S/B  0.23 14/02/2003 Gianluca CERMINARA

Preliminary Results With the 20k WLWL events generated with PYTHIA the maximum M(WW) achieved is 2 TeV Assuming a flat efficiency vs M(WW) we can estimate to have: 10 events with 1.5 TeV < M(WW) < 1.6 TeV in 1.5 years at “low” luminosity. 10 events with 1.8 TeV < M(WW) < 2.0 TeV in 3 years at “low” luminosity. But New Physics will manifest itself through increasing s(WW) for the signal at the energy scale (M(WW)) where the Symmetry is broken. 1 year “Low Luminosity” = 20 fb-1 1 year “High Luminosity” = 100 fb-1 14/02/2003 Gianluca CERMINARA

Preliminary Results Resolution of the WW system invariant mass reconstruction. MWWrec - MWWgen MWWgen drWW = 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: ~8% 14/02/2003 Gianluca CERMINARA

Conclusions At this stage the measurement appears possible: Good signal to background ratio at high WW invariant masses S/B  good Very good resolution on MWW  energy scale of the process ~10 15% 2 TeV region reached in 3 years at “low” luminosity 14/02/2003 Gianluca CERMINARA

Future Projects A more complete study of this process using a “Full Simulation” of the CMS detector. A new Monte Carlo for our signal (by A. Ballestrero, E. Accomando, E. Maina –Torino group-) New backgrounds: W+1 jet, W+3jets, W+4jets (Moscow + CompHEP Group) …are coming ! 14/02/2003 Gianluca CERMINARA

Experimental and theoretical Group Torino + Moscow A Preliminary Model Independent Study of the Reaction ppqqWWqqℓnqq at CMS Experimental and theoretical Group Torino + Moscow Gianluca CERMINARA