Searches for the Standard Model Higgs at the Tevatron presented by Per Jonsson Imperial College London On behalf of the CDF and DØ Collaborations Moriond QCD 2006 La Thuile, Aosta Valley, Italy, March 18-25, 2006

Per Jonsson - Imperial College London Moriond QCD Per Jonsson - Imperial College London Outline Introduction Higgs  bb (low mass) –ZH  bb –WH  l bb Higgs  WW (high mass) –WH  WWW –H  WW Limits: –combination Main Injector & Recycler Tevatron Chicago   p source Booster pp p p pp 1.96 TeV CDF DØ 36×36 bunches 396 ns bunch crossing Thanks to all colleagues at the Tevatron for their contributions to this talk New results! New result! Only new results since last year’s Moriond are shown

Per Jonsson - Imperial College London Moriond QCD Per Jonsson - Imperial College London Tevatron Performance 80-85% Average Efficiency Currently in shutdown: Silicon and Trigger upgrades Run I 4-8 fb -1 expected by end of 2009 This talk: pb -1

Per Jonsson - Imperial College London Moriond QCD Per Jonsson - Imperial College London The DØ and CDF detectors The Standard Model Higgs Boson is: Key part of Electro-Weak symmetry breaking A scalar with the Higgs mass as the only free parameter DØ and CDF constrain the SM Higgs boson mass: Indirectly: Top and W mass measurements Directly: Search for Higgs boson production

Per Jonsson - Imperial College London Moriond QCD Per Jonsson - Imperial College London EW constraints on Higgs m H constrained in the Standard Model m H = GeV Direct searches at LEP2: m H >114.4 m H <175 (< 207 GeV if LEP2 limit incl.) A light Higgs is favored 68% CL [GeV] LEPEWWG 18/03/06

Per Jonsson - Imperial College London Moriond QCD Per Jonsson - Imperial College London SM Higgs Production Production cross sections are small: pb depending on m H : ~1 in pp events is a Higgs M H < 135 GeV: decay to bb –gg  H  bb overwhelmed by QCD background searches can be performed in W/Z associated production with lower background Best channels: –WH  l bb, ZH  bb M H > 135 GeV: decay to WW –gg  H  WW (*)  l + l - –WH  WWW (*) final states can be explored We probably have a Higgs in our data already! H  bb H  WW (*) Dominant decay modes

Per Jonsson - Imperial College London Moriond QCD Per Jonsson - Imperial College London Backgrounds and Tools Lepton identification Missing transverse energy Measurements also rely on: Jet reconstruction B-tagging: –Use track impact parameter (IP) measurements or secondary vertex reconstruction IP Both detectors are delivering the excellent performance needed Understanding and modeling of background is critical: Especially so for advanced analysis techniques Electroweak backgrounds (W, Z, WZ, WW, Top): – Monte Carlo distributions normalized to (N)NLO cross sections QCD and instrumental background taken from real data control samples

Per Jonsson - Imperial College London Moriond QCD Z/    ee + jets Comparison of jet multiplicities and distributions in data and MC: –Pythia vs. Sherpa –Sherpa : Matrix Element + Parton showers, using CKKW algorithm Event selection includes: –Electron p T > 25 GeV,  –70 GeV < M ee < 120 GeV New result! Sherpa agrees well with data upto njet=4 L=~950 pb-1 For details see Gavin’s talk yesterday.

Per Jonsson - Imperial College London Moriond QCD ZH  bb Event selection includes: –≥ 1 tagged b-jets –Two jets with E T > 60/25 GeV –E T miss > 70 GeV Backgrounds: – W/Z + heavy flavour jets – QCD – Di-bosons – Mis-tagged b-jets – Top pairs M H = 120 GeV, 80 < m jj < 120 GeV – 6 events observed – / predicted –    pb E T 1 = GeV E T 2 = 54.7 GeV E T miss = GeV M jj = 82.1 GeV

Per Jonsson - Imperial College London Moriond QCD New result! L=261 pb -1 1 b-tag2 b-tags Improved event selection includes: –Two acoplanar jets with: E T > 20 GeV –E T miss > 50 GeV –Sum of scalar jet E T < 240 GeV Separate analysis for single and double b- tagged events: –Increased statistics m H = 115 GeV, 75 < m jj < 125 GeV: –11 events observed –9.4 +/- 1.8 predicted –    pb Same analysis for WH  l bb with missed lepton improves the WH limit ZH  bb

Per Jonsson - Imperial College London Moriond QCD Muon and electron channel combined: – 1 or 2 tagged b-jets – electron or muon with p T > 20 GeV – E T miss > 20 GeV Per Jonsson - Imperial College London Main backgrounds: W + jets Top pairs di-bosons (WW, WZ etc.) e/  b jet WH  l bb, (l=e, 

Per Jonsson - Imperial College London Moriond QCD New muon analysis Re-optimized electron analysis Separate single and double b-tag analysis Event selection includes: –Central isolated e/   p T > 20 GeV –Missing E T > 25 GeV –≥ two jets: E T > 20 GeV, |η| < 2.5 –One or two tagged b-jets Limit from combined channels: –m H = 115 GeV, 85 < m jj < 140 GeV: 6 (32 ST) events observed 9.3 (45.1 ST) predicted    pb New result! WH  l bb, (l=e,  Per Jonsson - Imperial College London

Moriond QCD Event selection includes: –Two isolated like signed leptons (ee,e  –p T > 15 GeV –E T miss > 20 GeV    m H =115 GeV)  pb WH  WWW (*)  ll  qq,  (l=e,  Per Jonsson - Imperial College London Mainly di-bosons (WZ) CDF 194 pb -1 L=363 pb -1 observedexpected ee / ee /  /- 0.75

Per Jonsson - Imperial College London Moriond QCD Per Jonsson - Imperial College London Higgs mass reconstruction not possible due to two neutrinos Employ spin correlations to suppress the background –  (ll) variable is particularly useful –Charged leptons from Higgs are collinear Event selection includes: –Two leptons (e/  p T > 20/10 GeV –Missing E T greater than M H /4 –Di-lepton invariant mass > 16 GeV < M H /2-5 GeV  ll distribution fitted to extract 95% CL limit SM cross section still far away, but 4 th generation models getting closer m H = 130 GeV m H = 160 GeV W+W+ e+e+ W-W- e-e- H  WW (*)  l + l -, (l=e, 

Per Jonsson - Imperial College London Moriond QCD L= 950 pb -1 ee and e  channels Event selection includes: –Isolated e/  p T (e 1, e 2 ) > 15, 10 GeV p T (e/  1 ) > 15 GeV, p T (e/  2 ) > 10 GeV –Missing E T greater than 20 GeV (ee, e  ) –Veto on Z resonance Energetic jets M H = 120 GeV: –31 events observed –32.7 +/- 2.3 (stat) predicted –Bkg systematic uncertainty: 15% –    pb Per Jonsson - Imperial College London New result! ee ee After cuts 160 GeV Higgs (x 10) H  WW (*)  l + l - (l=e, 

Per Jonsson - Imperial College London Moriond QCD Currently a factor 15 away from m H =115 GeV With L= 2 fb -1, both experiments, NN b-tagging, NN analyses, track- cal jets, increased acceptance, new channels, full cross efficiency, and reduced systematics: –Cross section factor = 1.2 New result! Combined limit New combined limit from all SM Higgs search channels! 14 orthogonal search channels (incl. single and double-tag analyses and WH  l bb w. missed lepton) Full account taken of systematic uncertainties High mass region benefits from H  WW analyses

Per Jonsson - Imperial College London Moriond QCD Limits

Per Jonsson - Imperial College London Moriond QCD Per Jonsson - Imperial College London Summary Many results already and more with increased stats are coming soon! The Tevatron and the experiments are performing well A wide range of Standard Model Higgs searches have been performed by both CDF and D0 with up to 1 fb -1 RunII data: –No deviation from the SM background expectation observed Work underway to improve sensitivity: –First combination of all channels from D0 Very exciting prospects for the future: –Sensitivity to m H > 114 GeV starts at ~2 fb -1 –Exclusion up to 180 GeV possible with 8 fb -1

Per Jonsson - Imperial College London Moriond QCD Back-up slides

Per Jonsson - Imperial College London Moriond QCD Per Jonsson - Imperial College London SM Higgs Sensitivity New Higgs sensitivity study from CDF + DØ in 2003: Statistical power only Systematics not included Improved sensitivity from refined analysis and detailed simulation No systematics The SM Higgs is a challenge, understanding of bkgs critical!

Per Jonsson - Imperial College London Moriond QCD Major Improvements 6x more lumi (2 fb -1 ): 2.4 We need both CDF and D0: 1.4 Multivariate analysis: 1.7 NN b-tagging: 1.35 Di-jet mass resolution: 1.2 Additional search channels: 1.15