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Exploring Higgs Boson Physics at the LHC: Italian Workshop Insights

This workshop compilation discusses Higgs boson research at the LHC, including low-mass searches, Higgs production channels, and the Italian contributions to Higgs studies. It highlights the challenges and advancements in detecting Higgs boson particles, analyzing different decay channels, and presenting projected integrated luminosity data. The findings cover analyses from CMS and ATLAS experiments, such as ttH to ttbb processes and Higgs decays into various final states.

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Exploring Higgs Boson Physics at the LHC: Italian Workshop Insights

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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 preshower 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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