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Higgs @ LHC

Higgs @ LHC. S. Bolognesi (1) from CMS. A. Di Simone (2) from ATLAS. V workshop italiano sulla  fisica p-p ad LHC Perugia, 30 Gennaio - 2 Febbraio, 2008. 1 Università di Torino ed INFN Torino. 2 Università di Roma Tor Vergata ed INFN Roma 2. Outline. Higgs at Tevatron Higgs in Italy

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Higgs @ LHC

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  1. Higgs @ LHC S. Bolognesi(1) from CMS A. Di Simone(2) from ATLAS V workshop italiano sulla fisica p-p ad LHC Perugia, 30 Gennaio - 2 Febbraio, 2008 1 Università di Torino ed INFN Torino 2 Università di Roma Tor Vergata ed INFN Roma 2

  2. Outline • Higgs at Tevatron • Higgs in Italy • Low mass searches • ttbb • H → gg • H → tt • H → VV channels • H → ZZ(*) → 4l • H→WW→lnln • MSSM Higgs • Combined results • Discussion V workshop italiano su LHC - Perugia Sara Bolognesi - CMS Torino 2

  3. Projected Integrated Luminosity in Run II pessimistic scenario → 5.83 fb-1 (same performance of 2007) 7 realistic scenario → 6.75 fb-1 6 5 Integrated luminosity [fb-1] 4 3 2 1 0 01/03 01/04 02/05 03/06 02/07 04/07 04/08 05/09 expected 2009 analyzed data Higgs @ Tevatron Exclusion Limit: Tevatron Run II Preliminary • Collected >3 fb-1, expected 6 or 7 fb-1 by the end of 2009 • With 1.9 fb-1 analysis close to exclude wide range MH≈ 160 GeV • Sensitivity lower than expected in low MH region V workshop italiano su LHC - Perugia Sara Bolognesi - CMS Torino 3

  4. Higgs in Italy!! CMS ATLAS old analysis from Pavia; Perugia, Napoli Genova ttH → ttbb Roma not yet started Milano H→gg SM Pisa, SM Pavia, Pisa; H→tt MSSM: Roma1, Milano MSSM Pisa Milano, Roma Torino, Bari, (e.o.i Bologna, Padova, Trieste) Roma1, Roma2, LNF H→ZZ Genova, Cosenza, Pavia Padova, Roma, Milano (e.o.i Bologna, Trieste) Roma1 in the next future H→WW Milano, Bologna, Perugia, Pisa higgs MSSM and BSM LNF, Roma1 V workshop italiano su LHC - Perugia Sara Bolognesi - CMS Torino 4

  5. Low-mass searches • Low Higgs mass favoured by EW precision measurements • Most difficult mass region: • with mH<130 GeV the most promising decay channels are intophotons and taus(≈ 50 and 100 fb) • very high background rate (also from fakes) • VBF production channel gives the best s/b ratio • in MSSM the di-photon decay channel is suppressed analyses focus on di-tau final state • at low mass BR(H→bb) ≈ 70% but it cannot be a low lumi discovery channel: • huge QCD background associated production ttH (× BR ≈ 0.3 pb) • very complex final state, many systematics involved • NEW IDEA:VBF Higgs with H→bb + request of a high pT central photon pioneer parton level study shows s/b increases of more then one order of magnitude (destructive interference in central g emission in QCD bbjj): E.Gabrielli, F.Maltoni, B.Mele, M.Moretti, F.Piccinini and R.Pittau, “Higgs boson production in association with a photon in vector boson fusion at the LHC,'‘ Nucl. Phys.781 (2007) 64 [arXiv:hep-ph/0702119] V workshop italiano su LHC - Perugia Sara Bolognesi - CMS Torino 5

  6. ttH → ttbb (MH ≈ 120 GeV) • Complex final state (2W,4b) • good detector control (b-tag, jet reco/calib,…) • full simulation ATLAS preliminary • control samples (align, jet calib) (after likelihood analysis) • combinatorial background multivariate technique • Big QCD background (ttjj, ttbb) dedicated study on background normalization and shape from data • CMS: S/√B <0.1 with 60 fb-1 (NO discovery channel) [≈ 3 without syst.] WW→lnjj WW→jjjj WW→lnln • low trigger efficiency more sophisticated trigger needed 77% 63/52% 25% • b-tag performance at best for pTjet≈ 80 GeV (while ttbb contains many low pT jets) energy flow / jets with tracks needed (they would improve also b-tag) • jet reco/calib. performance still poor V workshop italiano su LHC - Perugia Sara Bolognesi - CMS Torino 6

  7. ATLAS: S/√B ≈ 2.3 with 30 fb-1 (only semilept., NO systematics included) • slightly worse efficiencyVSfake leptons performance … • … similar btag performance … M(t→bjj) • … but better jet resolution: LmjjbG=174GeV M(H→bb) sm = 11.7 GeV LmbbG=98GeV sm = 20.0 GeV ATLAS sm≈16 GeV if soft muons added to b-jet ATLAS CMS CMS V workshop italiano su LHC - Perugia Sara Bolognesi - CMS Torino 7

  8. H → gg(MH≈ 130 GeV) • Vertex reco is crucial for correct mass measurement • CMS: vertex fitted from high-pT tracks CMS resolution 5mm (low lumi) • ATLAS: calorimeter transverse granularity s≈ 1.6cm exploited vertex from other tracks can be added too s ≈40mm • g/p0 and g/jet discrimination needed to suppress huge reducible background (sgj≈ 103sgg , sjj ≈ 106 sgg) • ATLAS: using hadronic leakage and shower shapes, exploiting calorimeter granularity (total rejection of ~3000 for g efficiency of 80%) • CMS: isolationagainst jets p0 rejection with Neural Network with input variables related to shower shape + silicon preshover info in the EndCaps V workshop italiano su LHC - Perugia Andrea Di Simone - ATLAS Roma 8

  9. H → (2) • Photon conversions are important, due to material balance in inner detectors • ATLAS: ~30%s convert in the barrel • CMS: 42% in the barrel, 59.5% in the endcap • Trigger based on detections of high-energy isolated photons • ATLAS: 220i, 60, 2d20i||60 • CMS: efficiency (212i) is 89.2% at L1 and 87.4% at HLT. • no veto on tracks → high trigger also for di-electron events • Associated production allows to improve s/b ratio. Both ATLAS and CMS are studying several channels • “Advanced” analyses (NN, Likelihood, categories) allow to improve results with low statistics CMS NN 7.7 fb-1 signal × 10 CMS: 6.0 cut based, 8.2 NN Significances@30fb-1: ATLAS: 6.3 cut based V workshop italiano su LHC - Perugia Andrea Di Simone - ATLAS Roma 9

  10. H → (MH≈ 130 GeV) • Both experiments are focusing on VBF production channel, since it allows to improve s/b ratio. • ATLAS performing studies on all final states (ll, lh, hh), while CMS focused in the recent past on lh decay channel. • Main background: • irreducible Zjj (QCD), help by CJV • irredicible Zjj (EW) help by mass reconstruction • reducible: QCD multi jet, W+jet, Z/g+jet, tt • Trigger: • ATLAS: • e25i and mu20i for lh or ll final states. More complex trigger schemas (tau+mu or tau+e) are also under study. Single tau trigger exposes to huge QCD background, so for hh final state tau+METseems the most promising trigger choice • CMS: • single e || single mu || e+tau|| mu+tau at L1 and HLT V workshop italiano su LHC - Perugia Andrea Di Simone - ATLAS Roma 10

  11. Central jet veto H → (2) • Forward jet tagging: identifying the quark-initiated jets from VBF: typically in opposite hemispheres and high-pT • CMS: selects the two highest Pt jets and requests opposite h sign • ATLAS: like CMS or choose the highest pT one and couple it with the highest found in the opposite hemisphere ATLAS • Central jet veto: no additional hard jets • challenge is to make it robust against additional pileup/fake jets CMS Significances at 30 fb-1 • ATLAS: • lh MH=130 GeV , Sign. 4.4 • lh + ll MH=130 GeV Sign. 5.7 • CMS: lh MH=135 GeV , Sign. 3.98 V workshop italiano su LHC - Perugia Andrea Di Simone - ATLAS Roma 11

  12. H→VV channels • For MH>130 GeV,H→VV most promising channels: effectiveness of ZZ and WW channels follows closely the BR shape • mH 150 high ZZ BR and low backgrounds • mH 170 low ZZ BR while H→WW turns on • mH 200 strong enhancement of ZZ BR for mH > 2mZ (suppression of WW) • mH > 350 lower signal xsec and BR (due to H→tt) • VBF VV→VV interesting ‘per se’ as a probe of EWSB mechanism: • Higgs in s-channel → mass peak • no Higgs → SM unitarity violation V workshop italiano su LHC - Perugia Andrea Di Simone - ATLAS Roma 12

  13. H → ZZ(*) → 4l channels • Interesting over a wide mass range, mainly for their very clean signature: most critical mass region is 125-150 GeV, where one Z is off-shell, leading to low pT leptons • Backgrounds: • ZZ*/g*→ 4leptons: irreducible background, cross section ~ tens of fb (big uncertainty on gg→ZZ) • → the biggest one after analysis selection • Zbb: reducible (lepton isolation and impact parameter), cross section ~hundreds of pb, rejection factor ~O(103) needed: • tt: reducible, rejection factor ~O(105) needed • Reduce PDF, luminosity and background uncertainties normalizing from sidebands orusing s(ZZ → 4l) / s(Z → 2l) • Lepton identification and reconstruction are crucial for selection efficiency and H mass reconstruction: lepton performance measured from Z →2l V workshop italiano su LHC - Perugia Andrea Di Simone - ATLAS Roma 13

  14. H → ZZ(*) → 4l (2) • Trigger: inclusive single mu/e, double mu, double e, have good signal efficiency and bg rejection ATLAS mu reco • Main systematics come from lepton energy scale/resolution and lepton-id efficiency results from single Z→ll (e.g. tag and probe) crucial for systematics control CMS e reco CMS ATLAS Preliminary V workshop italiano su LHC - Perugia Andrea Di Simone - ATLAS Roma 14

  15. H→WW→lnln(MH≈130-180 GeV) • No mass peak: • alternative variable ll) • to be carefully monitored: ATLAS preliminary • bkgr normalization from real data extrapolation from control regions (ad hoc for tt and WW) • systematic effects on background shape and normalization • ATLAS documented work mainly about: • MC physics model description: MC@NLO for signal and most backgr. • detailed background normalization procedure and evaluation of theoretical uncertainties: Ex: • dedicated MC for gg→WW (10% of qq→WW after cuts and different shape) but pT(WW) modeled by PS (no NLO available) • interference between single top (produced in association with b) and double top 5.3% uncertainty on WW normalization (theoretical systematic dominates) 12.2% uncertainty on tt normalization (theor. syst. and jet energy scale) V workshop italiano su LHC - Perugia Sara Bolognesi - CMS Torino 15

  16. H → WW → lnln: experimental systematics (e,MET) • CMS more focused on: from MC from “data” • simulation of real detector and real data workflow (trigger, skimming) different pT, spectra • detector performance measurement from data: • electron identification efficiency extrapolated from Z→ee (tag & probe) • lepton fake rate measured from QCD multi-jets events to evaluate the W+jets impact CMS (different jet flavour decomposition under study) • MET systematics • from W mass measurement → 5% on resol, 2% on scale • comparison of W and Z with one lepton removed V workshop italiano su LHC - Perugia Sara Bolognesi - CMS Torino 16

  17. MSSM Higgs discovery potential • Light neutral h (same analysis of SM): particularly effective VBF with h→ complemented by VBF/ggF with H→VV in the small  scenario (low H- coupling) • Heavier neutral A/H: • high tg: bbH with h→ (, low BR but clean) • low tg: GGF with A → Zh → llbb A/H → 0202 → 4l + MET • Charged H±: tt→tHb with H→ • mH<mt: gg→tbH H→tb • mH>mt: with gb→tH H→ (lower BR but cleaner) high background (QCD, tt, tt+(b)jets, W+(b)jets) also combinatorial • At intermediate tg, sensitivity only to h also with 300 fb-1→ difficult to disentangle MSSM and SM V workshop italiano su LHC - Perugia Sara Bolognesi - CMS Torino 17

  18. NZ→ NZ→ee MSSM study for low lumi • ATLAS: bbh → bb with Mh≈ MZ (only slightly different angular distrib. because Z vector, h scalar) Z/*bb background ( ≈ 102 signal ) has same diagrams! difficult to be removed bbZ → bbee as control sample: ATLAS detector response differences >e→ more fake combinations with  from b different inner brehmsstralung good control sample to measure detector performance on signal: ATLAS •  reco efficiency • M() resolution ) ( • b-tag performances V workshop italiano su LHC - Perugia Sara Bolognesi - CMS Torino 18

  19. Summary V workshop italiano su LHC - Perugia Sara Bolognesi - CMS Torino 19

  20. Combined results • For mH>140 GeV, ~1 fb−1 might be sufficient • For low mass higgs (< 140 GeV) situation more complex: ~5 fb-1 needed and several channels must be combined 5s discovery Exclusion limit @ 95% confid. level • These are inverse fbs ofwell understood data!! • detector systematics: jets, g/p0, MET CMS + ATLAS (e and m from Z→ll) • multiple jets background xsec: V+jets, VV+jets, tt Plot from: J.J.Blaising, A.De Roeck, J.Ellis, F.Gianotti, P.Janot, G.Rolandi and D.Schlatter "Potential LHC contributions to Europe's Future Strategy at the High Energy Frontier" V workshop italiano su LHC - Perugia Sara Bolognesi - CMS Torino 20

  21. Further reading… • CMS physics TDR • ATLAS physics TDR • CMS note 2006/119 (ttH→ttbb) • CMS notes 2006/078, 2006/97, 2006/112 (H→gg) • CMS note 2006/088 (H→tt) • CMS note 2007/037 (H→WW) • CMS notes 2006/136, 2006/130, 2006/115, 2006/122 (H→4l) • ATLAS: "Prospect for a Higgs discovery in the channel H→WW→lnln with no hard jets" Mellado, Quayle, Wu • ATL-PHYS-PUB-2006-019 (Z→mm/Z→ee) V workshop italiano su LHC - Perugia Sara Bolognesi - CMS Torino 21

  22. Higgs @ LHC A. Di Simone from ATLAS S. Bolognesi from CMS Discussion V workshop italiano sulla fisica p-p ad LHC Perugia, 30 Gennaio - 2 Febbraio, 2008

  23. Avoid fake discovery If we have a deviation from the SM expectations, how we should react? • necessary prerequisites • good comprehension of the detector (commissioning and integration) • control of the systematics from standard candles (ex. Z,W for leptons) • good comprehension of the MC tools (comparison between MCs, close dialogue with theoreticians) • measure background (normalization and shape) from data • clever tools to cross-check: • comparison between similar channels (ex. e and m) • work with ratios (ex: 4m/2m, 2m/2e) prepare the analysis to make it possible!! V workshop italiano su LHC - Perugia Andrea Di Simone - ATLAS Roma 1

  24. Weak points • Channels still to be addressed or just started • H → ZZ → mmnn (CMS just starting, ATLAS done in the physics TDR) DISEGNO qqbbg • qqH → qqbb (VBF) Theoretical study with additional g Experimental study: g (also fake) from fragmentation are not an issue (CMS Bologna using Pythia QCD sample) • ttH → tttt • ATLAS missing points: • analysis sometimes based still on fast simulation • Pileup & Cavern background effects often included but need to be studied systematically • CMS missing points: • jet reco performance still too low (energy flow work on-going) • SUSY analysis should be more focused on real detector and low lumi scenarios V workshop italiano su LHC - Perugia Andrea Di Simone - ATLAS Roma 2

  25. Normalisation to ppZ2l • SM single Z2l production cross-sections measured with great precision in an experiment which will have L ~ 10 fb-1. • Calculate from MC the ratio Rs = s(ZZ)/ s(Z) • Full cancellation of LHC luminosities uncertainties • Partial cancellation of PDFs and QCD-scales uncertainties • Partial cancellation of experimental uncertainties • sZZ(extrapolated) = Rs •s(Z)exp • Discussion about using a similar approach in ATLAS too V workshop italiano su LHC - Perugia Andrea Di Simone - ATLAS Roma 3

  26. Theoretical and experimental uncertainty estimations for evaluation of background from single Z2e measurements Normalisation to ppZ2l V workshop italiano su LHC - Perugia Andrea Di Simone - ATLAS Roma 4

  27. Work on-going Focus on • real detector and LHC environment (PU) simulation • develop strategy to measure from data: • detector performances and systematics (standard candles as W and Z) (tt,V+jets,VV+jets) • backgrounds shape and normalization CMS: • usage of CSA07 samples with misalignment/miscalibration in 10 pb-1 (100 pb-1) scenarios • study of lepton systematics from data in Z/W events (“2007 Notes”) to be extrapolated in the various Higgs channels ATLAS: several issues (systematics, trigger, bkg from data) are being addressed for all the channels in the latest analysis results to be published in the near future (“CSC Notes”) V workshop italiano su LHC - Perugia Andrea Di Simone - ATLAS Roma 5

  28. Beyond start-up • Mass and width Ex. CMS: H→gg e →ZZ estimated precision <0.3% up to 350 GeV (stat error only) with 30 fb-1 Ex. CMS + ATLAS: H→ZZ direct measurement with reasonable accuracy can be performed only above ~250 GeV (better than 10% for MH>300 GeV with 300 fb-1) if Higgs found • Coupling to EW bosons through VBF Ex. ATLAS: qqH → qqlnln / qqtt: • possible to distinguish SM from purely CP odd/even H to VV coupling • possible to increase the limit on anomalous coupling • CP,spin through VBF Ex. ATLAS: qqH → qqlnjj: • Test of EWSB mechanism through VBF Ex. CMS: qqVV → qqVV → 6 fermions V workshop italiano su LHC - Perugia Andrea Di Simone - ATLAS Roma 6

  29. Higgs @ LHC A. Di Simone from ATLAS Back-upslides S. Bolognesi from CMS V workshop italiano sulla fisica p-p ad LHC Perugia, 30 Gennaio - 2 Febbraio, 2008

  30. Higgs @ Tevatron back-up 1

  31. Slide by F. Gianotti back-up 2

  32. Higgs @ CMS early discovery channels • H→ZZ*→4l measure Higgs properties (mass, width, xsec) already with 30 fb-1 !! • H→WW*→lnln significance > 5(3) with 30 fb-1 • H→WW*→jjln / lnln in VBF but good comprehension of detector needed (jet, MET, t in lept. and hadr. decay) • H→tt in VBF very difficult analysis with still quite unpredictable background • H→gg at least 60 fb-1 • ttH→ttbb (many jets also with low pT (<30 GeV) → bad reso/eff) • other channels (mainly associated production) can help EXCLUDING Higgs (e.g. WH→WWW*→Wlnln) channel studied MH • Analysis focusing on H→ ZZ*→4l 5-100 fb 130-500 GeV • improvement of the reconstruction H→ WW*→lnln 0.5-2.5 pb 120-200 GeV 200-900 fb 120-250 GeV H→ WW*→jjln • backgr. and syst. from data VBF 50-250 fb 120-200 GeV H→ WW*→lnln • correct statistical treatment of results 50-150 fb 115-145 GeV H→tt H → gg 50-100 fb 115-150 GeV back-up 3

  33. H →ZZ(*)→ 4l • very sensible for M(H) = 130 to 500(except 150-190 where WW open) • early discovery: statistical observation involving a small number of events • compatibility with SM expectation: preserving the phase space for more involved characterization measuring xsec, MH, width (spin, CP …) M(H)=130 GeV • usual cuts • isolated lepton from primary vertex with high pT(trigger) greater than 50% for M(H)>115 • one on-shell Z greater than 85% for M(H)>150 • three channels • 4m: golden channel • 2e 2m: highest BR but lower reso/effic on electrons • 4e: most difficult (important to recover low pT electrons) back-up 4

  34. backgrounds: ZZ(*)/g*, tt, Zbb (Zcc found to be negligible) 2e2m analysis • reconstruction offline selection • likelihood approach to discriminate real / fake e+/- mH=140GeV mH=200GeV • ECAL-Tracker matching, shower shape before • e+e- with highest likelihood selected • internal bremsstrahlung recovery: 10 fb-1 10 fb-1 • 40%-10% events with g (pT>5 GeV) radiation from lepton (1/3 from m) after Nsign≈ 12 Nsign≈ 36 Nback≈ 2 Nback≈ 16 • recovered g with DR(g,l) < 0.3 back-up 5

  35. 2e2mresults • Background normalized from sidebands DB = DB stat DB theory DB stat increases with mHfrom 2% (mH 120) to 30% (mH 600) because of events decreasing in sidebands w.r.t. signal window DB theory from PDF, QCD scale, NLO ZZ xsec →0.5% - 4.5% • Luminosity VS mH(same shape of 4m and 4e) • mH 150 high BR and low backgrounds • mH 170 low BR at the H→WW turn on • mH 200 strong enhancement of BR for mH > 2mZ • mH 250 decreasing of signal while ZZ background remains high • mH 250-350 decreasing of ZZ background • mH > 350 decreasing of signal xsec and BR (due to H→tt) back-up 6

  36. 4m analysis MC generated sample Reconstructed M(4m) after selection s channel Z g* t channel mh150 Half of the events used to optimize cuts with GARCON* which allows to obtain smooth M(4m) dependent cuts: • muon isolation three main critical cuts uncorrelated: • pT of the second lowest pT muon • M(4m) window (≈ 2s where s ≈GH + reso) other half of the events used to compute significance *Genetic Algorithm for Rectangular Cuts OptimizatioN allows to check effectively a large set of cuts which, in a straightforward approach, would take an astronomical amount of time back-up 7

  37. 4m background systematics Ratio H→ 4m to Z→2m (≈ 1 fb-1) Normalization from sidebands deep when b biggest (lower systematics but bigger statistical error) • new process NNLO gg→ZZ ≈ (20±8)% LO xsec(different initial state so variations of QCD scale do not necessary give a feel for its relative importance) back-up 8

  38. 4m results • problem of significanceoverestimatimation of a local discovery in searching for a localized new phenomenon in a wide phase space complementary approaches • check the consistency with expected properties: • xsec and variables not used in the analysis • M(4m) shape consistency with sign+back hypothesis • decrease a priori the open phase space: • MH prior probability could be forced to be consistent with the fit to precision EW measurements • use the early data for a first hint and then discard them from analysis back-up 9

  39. 4e analysis After trigger and preselection After full analysis selection 30 fb-1: Nsignal≈ 17 Nbackg≈ 4 • Optimization of low pT e+/- reco • cuts to reject fakes are separately optimized for different Bremsstr. e+/- classes back-up 10

  40. 4e: systematics & reults • Use Z→e+e- with one golden e+/-, second e+/- used to estimate uncertainties • 1% uncertainty on reco, isolation and identif.efficiency • 0.5% barrel (1% endcaps) uncertainty on energy scale (best resolution on the Jacobian peak: pT ≈ mZ/2, low |h|) • Tracker “radiography”measuring the amount of e+/- Bremsstralhung • (2%material budget with 10 fb-1 ) back-up 11

  41. H→WW(*)→lnln [M(H)=150-180] • No narrow peak → • high S/B needed • good background shape control necessary (normalization from data) • mass independent cuts • signal: all leptonic W decays (0.5 - 2.3 pb with a peak at MH≈160 GeV) • backgrounds: tt, tWb (≈ 90 pb) WW, WZ, ZZ (≈ 15 pb) (ggWW) Z Drell-Yan not considered but checked that after selection should be < 2% of the total background back-up 12

  42. lnlnanalysis • central jet veto (|h|<2.5, ET>20 GeV) • no calibration (energy is not needed) • discrimination between real and fake jets (PU, UE, FSR, ISR, detector noise) a > 0.2 for jets with 15 < ET < 20 GeV • high MET (> 50 GeV) • ee, em, mm reconstruction and selection • intermediate m(ll) • little f(ll) in the transverse plane back-up 13

  43. lnlnresults • DB from data defining free signal region varying the analysis cuts • DB (tt) ≈ 16% dominated by jet energy scale • DB (WW) ≈ 17% dominated by statistic • DB (WZ) ≈ 20% dominated by the presence of tt also (values for 5 fb-1) • tWb, ggWW small fraction of B: • normalization region difficult to find • syst uncertainties from MC theoretical error dominates (20%, 30%) Similar promising analysis specifically in VBF channel: background normalized to signal free region (M(ll)>110) back-up 14

  44. qqHwith H→WW→lnjj [M(H) = 120-250] + BR ≈ 5.5 BR(lnln) → xsec ≈ 0.02 - 0.8 pb + you can reconstruct the Higgs mass - big amount of background → strong cuts → good knowledge of physics needed (measure backgrounds from data) : • tt + jets (≈ 840 pb) 16% detector systematics • Wtb (≈ 100 pb) 30 fb-1 • VV + jets (≈ 100 pb) • V + jets (≈ 700 pb) • multiple jets xsec will be precisely measured from data • many systematicsabout jets will be understood and resolved from data Extra Jet Veto Loose Extra Jet Veto back-up 15

  45. CMS qq + H→lnjj : jets (1) • Strong ET cuts needed • for keeping an acceptable resolution (jets with ET<30 GeV very difficult to calibrate) • for eliminating fake jets (most of PU jets with ET<30 GeV) • Strong ET cuts affect efficiency: • Efficiency of requiring at least 4 jets • Parton-jet matching efficiency tt + jets signal forward quarks signal W + 4 jets signal quarks from W decay W + 3 jets mH = 170 mH = 170 (efficiency normalized to 1 for jet ET threshold of 20 GeV) (efficiency normalized to 1 for jet ET threshold of 16 GeV) back-up 16

  46. CMS qq + H→lnjj : jets (2) • tag jets misidentified with jets from FSR, ISR, PU, UE, detector noise … In the signal this increases the chance of misidentification central jets from W M(W→jj) using parton-jet matching • jets from W: mH = 170 • best possible resolution of 15 GeV !! • other central jets (ET>20 GeV in 60% of events) often (20%) with higher ET than jets from W • MC calibration from QCD jet samples • Iterative cone algorithm (DR=0.6) • Fast Simulation for some backgrounds back-up 17

  47. qqH with H→tt→lep + jet [M(H)< 150] • Z/g* + jets (irreducible), • backgrounds: • W→ln + jets with one jet misidentified as t-jet • tt→blnbln • complex signal kinematics: • forward jets with high rapidity gap (no color exchange) • MC calibration • central jet veto applied (with cut on a parameter) • high pT lepton (e or m) • MET: resolution 20% after correction • t-jet identification • trigger on little (DR) isolated jet • offline impurity 2.7% efficiency 30% (mainly due to pT, h cuts and request of isolation) • energy resolution 11.3% back-up 18

  48. H→tt results • M(tt) computed using collinear approximation of visible part of t decay products and neutrinos relaxed cuts • M(tt) overestimated 5 GeV because of over-corrected MET • M(tt) resolution of 9.1% • Significance exceeds 3s at 30 fb-1 • number of events computed from data using the M(tt) fit (envisaged to do it in a region unaffected from signal) • error (sB) only from the fit: • 10k toy MC data distributions following the fit (with the number of events equiv. to 30 fb-1) • each sample refitted with free scale factors for the three independent fit • uncertainty = spread of the number of background events in the 10k samples back-up 19

  49. Inclusive H→gg [M(H)=115-150] • inclusive signal production but with very low BR≈0.002 • pp→ gg (irreducible) very big background and very detector dependent + not well known QCD physics (big k factor in g+jets events) pp→ jets / g + jets (reducible) with one jet misidentified as g Drell-Yan e+e- Great deal of uncertainty in the benchmark estimate of luminosity … … this will not be a systematic error on real data since the background will be measured from data (thanks to the big sidebands signal free) • Analysis based on NN trained (1% systematic error on the background interpolation under the Higgs peak) • on sidebands for backgr. • on MC for signal back-up 20

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