Search of Higgs boson in vector boson fusion qq → qq H0 → qq qq eνe: a CMS simulation I.N.F.N. Turin

V-V fusion: the process “tag” quarks correlated with incoming quarks and protons, expected at higher η, one forward, the other backward q1 q2 q't,1 q't,2 qV e νe q'V ? V W leptons expected central in η, from a W decay hopefully coming from Higgs boson “central” quarks expected more central in η, from decay of the other W or Z from Higgs boson Interaction scheme and labels 13/12/2006

Software and data formats “hard scattering” qq → qq qq eνe, 4-momentum, particle ID, colour stream information, scale data PHASE: 770 bytes/event Generation hadrons and leptons from hard scattering and underlying event; 4-momentum, particle ID, history tree, vertex information PYTHIA: 13 kb/event Fragmentation ROOT tree with ORCA (C++) objects describing both generated particles and reconstructed objects, with their specific characteristics FAMOS/ExRootAnalysis: 100 kB/event Reconstruction Currently 4-momentum, charge, relations information; in our hands! “VVfusionFW”: some kB/event Analysis 13/12/2006

Software and data formats PHASE events FAMOS... FAMOS reconstructed events generated objects reconstructed objects Tagging Combinations... roles recognition χ2-like quantities roles assignment reconstruction information goodness of roles assignment 13/12/2006

PHASE Find the Truth™ q't,1 e q1 νe qV q2 q'V q't,2 H0 Higgs boson mass 200 GeV/c2 500 GeV/c2 ∞ (no Higgs) Available events 500000 500000 500000 Years with L = 100 fb-1/year 6 7 7½ Analysed events 93810 (0.89) 95558 (0.72) 96754 (0.69) Layout fitting V-V fusion 70014 (0.66) 70370 (0.53) 70252 (0.50) “topped” event 33753 (0.32) 42710 (0.32) 45099 (0.32) WWVV vertex 3062 (0.03) 2778 (0.04) 2870 (0.02) V-V fusion event 31067 (0.29) 22833 (0.17) 20236 (0.14) Higgs event 24925 (0.24) 15330 (0.12) 11804 (0.08) q1 q2 q't,1 q't,2 qV e νe q'V H0 Selection of samples and flags Starting numbers and x-sec in PHASE samples PHASE Mass windows used: W±: (80.425 ± 15) GeV/c2; Z0: (91.188 ± 15) GeV/c2; t/t: (174.3 ± 20) GeV/c2 Cross section in picobarn of each subsample is indicated in brackets. 13/12/2006

A background: p p ―> t t The most similar background with the same final status as signal is p p → t t → b b W W, where at least one W boson decays hadronically: qV ℓ νℓ/q' q'V W ℓ/q b t p W decay semileptonic fully hadronic Total cross section 100 pb 324 pb Available events 10000 10000 The sample was generated by PYTHIA from the core QCD process p p → t t . Process layout, generic cross sections 13/12/2006

Reconstruction algorithms FAMOS reconstruction computes some objects from the generated particles given as input, which are the result of fragmentation of the six fermions of PHASE event and the remnants of the protons. The following algorithms have been used in this analysis: electrons are reconstructed as ECAL superclusters (“EGSClus”); jets: HCAL and ECAL energy deposits in a cone around “seeds” are assigned to a jet; the maximum size of this cone is measured by its angular radius Δr2 = Δη2 + Δφ2 < R2 the radius used is R = 0,5; different calibrations are available, among them: no calibration (“JetIC5A”) and γ-jet calibration (“JetIC5C”), which is used here; neutrino: the starting hypotesis is that the total transverse momentum of each event is null, while nothing can be inferred about longitudinal one; we assume all transverse momentum missing for this to happen is due to just one neutrino; it is computed from the other reconstructed objects via a cone algorithm (“METIC”). To recognize which of the many objects reconstructed are direct manifestation of generated fermions (four quarks, one electron and one neutrino), for each event a χ2-like quantity is minimized: Then, each particle is labelled as “well reconstructed” if its contribution is χi < χTHR = 0,5 . The contribution for neutrino is a little simpler: χν2 = (ΔE┴/E┴)2 + Δφ2.  2 = 𝑖  𝐸 𝑖,𝑟𝑒𝑐 − 𝐸 𝑖,𝑔𝑒𝑛 𝐸 𝑖,𝑔𝑒𝑛  2    𝑖,𝑟𝑒𝑐 −  𝑖,𝑔𝑒𝑛  2    𝑖,𝑟𝑒𝑐 −  𝑖,𝑔𝑒𝑛  2   𝑖,𝑟𝑒𝑐 −  𝑖,𝑔𝑒𝑛  2 Process layout, generic cross sections 13/12/2006

Electron: ECAL superclusters Electrons are reconstructed from ECAL data only; reconstruction provides: hit, a crystal where energy has been deposited; cluster, a set of neighboring hits; super-cluster, a set of clusters along the same η ring, which can gather both an electron and its irradiated photons, which are not bent from axial magnetic field; electron candidate, a supercluster plus a pointing track from inner trackers This analysis assumes an electron to be represented well enough by ECAL superclusters. What is a cluster Number of clusters Pt rank, Pt distribution Isolation H/E, E/p 13/12/2006

Electron: reconstruction electron chi2; dE/E; dR sample good reconstruction mH [GeV/c2] full sample Higgs signal 200 9785/10000 2624/2690 500 9748/10000 1616/1656 no Higgs 9751/10000 1513/1553 13/12/2006

Electron: transverse momentum Sorting reconstructed ECAL superclusters by transverse momentum, we see that the one generated by the electron from PHASE is the one with the biggest p┴ on 65% of events, in the first two superclusters with highest p┴ in 90% of events, in the first three in 95% of events. One sample: Pt rank; all samples: Pt distribution of reconstructed electron (including backgrounds) 13/12/2006

Neutrino: reconstruction  2 ≡  𝐸 ⊥𝑟𝑒𝑐 − 𝐸 ⊥𝑔𝑒𝑛 𝐸 ⊥𝑔𝑒𝑛  2    𝑟𝑒𝑐 −  𝑔𝑒𝑛  2   𝑟𝑒𝑐 −  𝑔𝑒𝑛  2 formula! neutrino chi2; dET/ER; dPhi sample good reconstruction mH [GeV/c2] full sample Higgs signal 200 5914/10000 1563/2690 500 6008/10000 1016/1656 no Higgs 5947/10000 846/1553 13/12/2006

Missing transverse energy The ratio of missing transverse energy over the “scalar missing energy” (the sum of transverse energy of all reconstructed objects) is an indicator of how important is the measured missing energy in the energetic balance of the event. Pt distribution MET/SET 13/12/2006

Lepton-decaying vector boson W m┴ W p┴ From truth reconstruction: eta, Pt, mass, transverse mass (definition!) 13/12/2006

Cuts on leptons and W reconstruction sample PHASE p p → t t mH = 200 GeV/c2 mH = 500 GeV/c2 no Higgs leptonic hadronic not H0 H0 not H0 H0 not H0 H0 total: 68885 24925 80288 15330 84950 11804 10000 9675 events after cuts: 34887 12107 40509 6766 43096 4961 4719 795 (“purity”: 6175(51%) 3711(55%) 2485(50%) ) ε∙σ [pb] 0.331 0.115 0.304 0.051 0.307 0.035 47.190 26.705 p┴ rank < 2 e±: p┴ > 20 GeV/c νe: p┴ > 30 GeV/c m┴W є [40, 105] mW є [60, 100] MET/SET > 0.07 q1 q2 q't,1 q't,2 qV e νe q'V ? V W Tables of cuts (with purity where available). Influence of mass windows (mass and transverse mass). 13/12/2006

What is that “purity” Tables of cuts (with purity where available). In the previous slide, a “purity” is quoted; usually, the purity is defined as events of expected kind over all events in sample. In our case, we can't build such a simple ratio: PHASE sample has a certain number of events with six fermions each; let's assume we can identify each event as belonging to signal or background; generated event is reconstructed: some sets of objects (clusters, track etc.) are computed; for each event, the first step is to “connect” the generated particles to the reconstructed objects: six among the reconstructed objects must be associated to them; the way it's done (via a χ2) almost always produces a result, but sometimes that result is so different from generated data (high χ2) that we can't trust it; this event is probably beyond recognition since it's badly reconstructed, be it signal or background; then, the true analysis algorithm is applied; it splits data into two sets: signal candidates and background candidates; this is the only discrimination we have in real life; furthermore, it assigns to each role in V-V fusion event a reconstructed object; we can look into the signal candidates set, now, and see whether they were signal or not; that is the true purity; which will be very low, since we are not trying to separate signal from background yet; we can look among events known to be signal, and see what happened to them: event has been reconstructed badly, and the result of assignment will be screwed; event has been well reconstructed: algorithm has not found any suitable assignment; algorithm has found an assignment, which, alas, is the wrong one algorithm has found an assignment, which, blessed it, it's the correct one Tables of cuts (with purity where available). Influence of mass windows (mass and transverse mass). 13/12/2006

Jets Jets have been reconstructed with a iterative cone algorithm with ΔR = 0.5 around seed. The energy has been calibrated by simulating γ/jet events. Number of jets (with different Pt cuts) Eta; invariant mass; Pt ranking; eta differences Isolation 13/12/2006

Jets: reconstruction For one sample (200): central and tag jets chi2; dE/E; dR well reconstructed in full sample well reconstructed in Higgs signal [GeV/c2] both tag jets both central jets both tag jets both central jets mH = 200 7418/10000 7482/10000 1895/2690 1986/2690 mH = 500 7516/10000 7437/10000 1139/1656 1200/1656 no Higgs 7632/10000 7463/10000 1146/1553 1112/1553 13/12/2006

Jets: transverse momentum Higgs events Number of jets (with different Pt cuts) Eta; invariant mass; Pt ranking; eta differences Isolation not Higgs events 13/12/2006

Jets: transverse momentum rank Higgs events Number of jets (with different Pt cuts) Eta; invariant mass; Pt ranking; eta differences Isolation not Higgs events 13/12/2006

Jets: pseudorapidity Number of jets (with different Pt cuts) Eta; invariant mass; Pt ranking; eta differences Isolation 13/12/2006

Hadronic-decaying weak boson sample vector bosons fusion p p → t t mH = 200 GeV/c2 mH = 500 GeV/c2 no Higgs leptonic hadronic not H0 H0 not H0 H0 not H0 H0 total: 68885 24925 80228 15330 84950 11804 10000 9675 “known” events: 26474 13228 32150 8122 34280 6286 after cuts: 7310 6434 8590 3834 9196 2867 597 831 p┴ rank < 5 (“purity”: 2561(40%) 1737(45%) 1115(39%) ) ε∙σ [pb] 0.069 0.061 0.065 0.029 0.065 0.020 5.970 27.915 tags: p┴ > 30 GeV/c; 1st c: p┴ > 15 GeV/c, 2nd c: p┴ > 10 GeV/c ηFW > –1, ηBW < +1, 1stc: |ηc1| > 2.5, 2nd c: |ηc2| > 2; ηFW > {ηc1,ηc2} > ηBW tags: mj >10 GeV/c2; central jets: mj > 5 GeV/c2 |Δηtags| є [3, 8], |Δηcentral| < 1.5 mW є [60, 100] mtags > 200 GeV/c2 q1 q2 q't,1 q't,2 qV e νe q'V H0 Distributions of true W: mass, eta 13/12/2006

Hadronic weak boson resolution Distributions of true W: mass, eta 13/12/2006

Higgs (after ~2 months) Table of events with bot cuts. sample (10000 events) vector bosons fusion p p → t t mH = 200 GeV/c2 mH = 500 GeV/c2 no Higgs leptonic hadronic not H0 H0 not H0 H0 not H0 H0 total: 7310 2690 8344 1656 8447 1553 10000 9675 Higgs candidates: 250 234 296 127 293 80 191 15 ε∙σ [pb] 0.022 0.021 0.021 0.009 0.020 0.006 α×1.910 α×0.504 Table of events with bot cuts. Invariant mass of Higgs boson, transverse mass. 13/12/2006

Higgs (after ~1 year) Table of events with bot cuts. sample (~100000 events) vector bosons fusion p p → t t mH = 200 GeV/c2 mH = 500 GeV/c2 no Higgs leptonic hadronic not H0 H0 not H0 H0 not H0 H0 total: 68885 24925 80228 15330 84950 11804 10000 9675 Higgs candidates: 3592 3185 4271 1685 4536 1252 191 15 ε∙σ [pb] 0.034 0.030 0.032 0.013 0.032 0.009 α×1.910 α×0.504 Table of events with bot cuts. Invariant mass of Higgs boson, transverse mass. 13/12/2006

Biggest ToDos samples from different generators must have cross sections weighted a new sample with an Higgs mass bigger than 200 GeV/c2 is required a shy attempt to cut top background by an invariant mass cut on three jets tracker information is not extensively used yet (but it's used in jets construction anyway) pile-up must be added to make this even vaguely believable Normalization between samples 13/12/2006

Top mass Invariant mass of the two jets reconstructed as central (from W) and each of the two tag jets are plotted (two entries per event). Normalization between samples 13/12/2006