SM HIGGS SEARCHES AT THE TEVATRON Nikos Varelas

SM HIGGS SEARCHES AT THE TEVATRON Nikos Varelas University of Illinois at Chicago http: //www-cdf. fnal. gov/physics/exotic. html http: //www-d 0. fnal. gov/Run 2 Physics/higgs/ CTEQ Meeting, Jefferson Lab Nov 2005 Nikos Varelas 1 CTEQ Meeting @ JLab

Outline l Introduction n l Understanding the background processes n Z bb W+Jets Z+Jets s(Z+b)/s(Z+jet) Wbb Production n WH and ZH Associated Production n n l l Low Mass SM Higgs Searches: High Mass SM Higgs Searches: n n l Nikos Varelas EW Constraints on the Higgs Mass Data Samples – Tevatron Run II Strategy for SM Higgs Searches H WW* WH WWW* Prospects & Summary 2 CTEQ Meeting @ JLab

Guidance from EW Fits Tevatron (future): Dmt=1. 5 Ge. V, DMW=30 Me. V l Direct searches by LEP on SM Higgs Boson: n l m. H > 114. 4 Ge. V (95% CL) Indirect limit from fits to precision EW measurements from LEP-SLC-Tevatron n m. H < 206 Ge. V (95% CL) l using previous mt=174. 3 3. 4 Ge. V (Run I+II) Latest value: mt=172. 7 2. 9 Ge. V (Run I+II) +52 n Expected value: m. H = 98 − 36 Ge. V n l Run II will provide stringent constraints to SM Higgs n n d. Mt ~ 2 Ge. V with ~2 fb-1 d. MW < 30 Me. V (currently 59 Me. V – Run I combined) Light Mass Higgs favored Nikos Varelas 3 CTEQ Meeting @ JLab

Fermilab Te. Vatron - Run. II Chicago p p 1. 96 Te. V Booster p CDF DØ Run I 1992 -1996 ECM = 1. 8 Te. V ~120 pb-1 (0. 63 Te. V ~600 nb-1) Nikos Varelas Tevatron p source Main Injector & Recycler 4 p Run IIa 2001 -2006 ECM = 1. 96 Te. V ~ 1. 3 fb-1 Run IIb 2006 -2009 ECM = 1. 96 Te. V ~8 fb-1 CTEQ Meeting @ JLab

Data Sample l Tevatron performs according to design n Record peak luminosity ~ 1. 6 x 1032 Record integrated luminosity ~ 21 pb-1 /week n 2002 -2004 ( <400 pb-1 ) n l l Data samples presented here: Detector data collection efficiency 85 -90% Expected luminosity to each experiment ~8 fb-1 by the end of 2009 We Are Here Nikos Varelas 5 CTEQ Meeting @ JLab

SM Higgs Production and Decay Excluded at LEP Production Search strategy: MH <135 Ge. V associated production WH and ZH with H bb decay Backgrounds: Wbb, Zbb, top… MH >135 Ge. V gg H (or WH) production with H WW* decay Backgrounds: WW/WZ production… Nikos Varelas 6 CTEQ Meeting @ JLab

Low Mass SM Higgs Searches l l l WH e(m) +bb ZH (ee/mm) + bb Measurements rely on n Based on signed impact parameter resolution Jet Lifetime Impact Parameter algorithm Based on decay length resolution Secondary Vertex Algorithm b-tagging Lepton identification + Missing. ET resolution Dijet mass resolution and (Signed) Track light/b-jet calibration Impact Parameter l n b-tagging Z bb Hard Scatter B Decay Length Understanding of backgrounds l W/Z + heavy-flavor/light jets Nikos Varelas 7 CTEQ Meeting @ JLab

Z bb l Dijet invariant mass of ~86 K events n n n l l l Only two jets in the events (veto other jets with ET > 10 Ge. V) Jets must be back-to-back (Df>3. 0) Both jets have a secondary vertex b-tag The background shape is computed using untagged data passing the same selection The Z bb shape is simulated with PYTHIA The two shapes are fit to the data (blue points) Fit results are shown in red Statistical errors only Nikos Varelas 8 CTEQ Meeting @ JLab

s(W( e ) + n jets) l l Based on 127 pb-1 Jets n n l Electrons n l PT > 20 Ge. V, |h|<1. 1 W’s n n l ET > 15 Ge. V, |h|<2. 4 Cone Alg, Rcone = 0. 4 Missing ET > 30 Ge. V Veto Z mass region Theory: Alpgen+Herwig (+Detector Simulation) Backgrounds (3 -40%) n n n QCD W t , top, Z multiple pp interactions Nikos Varelas 9 CTEQ Meeting @ JLab

* s(Z/ ( ee) l Based on 343 pb-1 n l 1, 646 Z+jets events 1 st Jets 2 nd Jet Selection: n l l n n l l + n jets)/s. Z/ * ET > 20 Ge. V, |h|<2. 5 Midpoint Alg, Rcone = 0. 5 3 rd Jet ALPGEN+PYTHIA (+Detector Simulation) (CTEQ 5 L) Electrons l PT > 25 Ge. V, |h|<1. 1 l 75 < Mee < 105 Ge. V Z’s Background (2 -5%) Final cross section ratios are corrected at the hadron level Good agreement with Theory: MCFM (NLO up to Z+2 partons) ME-PS (MADGRAPH + PYTHIA with matching) Nikos Varelas 10 CTEQ Meeting @ JLab

s(Z+b)/s(Z+jet) l l l Analysis combines Z ee and mm channels Based on 180 pb-1 n 3, 458 Z+jets events n At least one Jet: n n l ET > 20 Ge. V, |h|<2. 5 l PT > 15 Ge. V, |h|<2. 5/2. 0 b-PDF is important for hb and single -top production 2 Electrons/muons: Z mass cut Apply sec. vertex b-tag n n l l Z+heavy flavor is background to ZH Z+b probes the b-quark PDF Selection: n l l 42 events with 1 tag 8. 3 events from QCD background Measure inclusive ratio to cancel many systematics PRL (94), 161801 (2005) Measurement: s(Z+b)/s(Z+j) = 0. 021 0. 004(stat) 0. 002(sys) Good agreement with NLO QCD: 0. 018 Nikos Varelas 11 CTEQ Meeting @ JLab

Search for W(e )bb Production l l l Dominant bkgd for WH Based on 382 pb-1 Selection: n n n l n n 2 Jets: l ET > 20 Ge. V, |h|<2. 5 l PT > 20 Ge. V, |h|<1. 1 b-tag: n JLIP (Jet Lifetime Probability) 153 events with 1 b-tag 13 events with 2 b-tags 1 electron: Missing ET > 25 Ge. V Expect 4. 29 ± 1. 03 Wbb 0. 14 ± 0. 03 WH 5. 73 ± 1. 45 WZ, tt, W/Z+jets, single top, multijets Total 10. 2 ± 2. 4 events Observe 13 95% CL upper limit: s(Wbb) < 4. 6 pb for b-jets with p. Tb > 20 Ge. V, |hb| < 2. 5, and DRbb > 0. 75 Nikos Varelas 12 CTEQ Meeting @ JLab

From Wbb to WH l l Based on 319 pb-1 Selection (e and m channels): n n Nikos Varelas 13 2 Jets: l ET > 15 Ge. V, |h|<2 l PT > 20 Ge. V, central 1 electron or muon: Missing ET > 20 Ge. V b-tagging: Secondary Vertex CTEQ Meeting @ JLab

WH Limits In the absence of a signal, 95% C. L. limits are set on Higgs boson production cross section times branching ratio to bquarks DØ previous Wbb/WH Result – 174 pb-1 PRL (94), 091802 (2005) Nikos Varelas 14 CTEQ Meeting @ JLab

Z( )H( bb) Search (1) l An important channel for low-mass Higgs search n l Trigger on events with large missing HT n l l Large B(Z ) ~ 20% HT is defined as the magnitude of the vector sum of jets’ ET Analysis was based on 261 pb-1 Selection: P n 2 Jets: l n n l l HT PT. 2 trk Jet 1 To reject tt events Reduce “instrumental” backgrounds l PTtrk To reject leptons from W/Z HT = S|p. T(jets)| < 200 Ge. V ET … tracks dijet)| … tracks in jets Missing ET > 25 Ge. V Veto events with isolated tracks (p. T>8 Ge. V) l n ET > 20 Ge. V, |h|<2. 5 trk = – |Sp (trk)| T T PT, 2 trk = – |Sp. T(trk in Jet 2 Jet acoplanarity Df(dijet) < 165 Use various missing energy/momentum variables Form asymmetry variables Nikos Varelas 15 CTEQ Meeting @ JLab

Z( )H( bb) Search (2) No b-tag Nikos Varelas Single b-tag 16 Double b-tag CTEQ Meeting @ JLab

Z( )H( bb) Search (3) Mass (Ge. V) Window 105 [70, 120] 115 [80, 130] 125 [90, 140] 135 [100, 150] Data 4 3 2 2 Wjj/Wbb 32 Acceptance (%) 0. 29 0. 07 0. 33 0. 08 0. 35 0. 09 0. 34 0. 09 Zjj/Zbb 31 Total bkgd. 2. 75 0. 88 2. 19 0. 72 1. 93 0. 66 1. 71 0. 57 Instrumental 16 Expected limit (pb) 8. 8 7. 5 6. 0 6. 5 Top 15 Limit @95% C. L. (pb) 12. 2 9. 3 7. 7 8. 5 WZ/ZZ 6 2 Nikos Varelas 17 b- Bkgd. composition (%) jet ta gs us ing JL IP CTEQ Meeting @ JLab

Z( )H( bb) Search (4) l l Analysis was based on 289 pb-1 Selection: n 2 Jets: l n Missing ET > 70 Ge. V At least 1 b-tag n Control Regions: n l Blind analysis technique l l l 1 st jet ET>40 Ge. V, 2 nd jet ET>20 Ge. V QCD + heavy flavor EWK, Top, and QCD Signal Region: n n n Veto events with leptons Higgs mass: 120 Ge. V Missing ET and 2 nd leading jet are not in Bkgd: 4. 36 events parallel QCD: 11. 4% Cut optimization is performed in this Top : 20. 5 % region based on MC simulation before EWK: 18. 2 % looking at the real data Mistagged light flavor : 50 % Observe: Nikos Varelas 18 6 CTEQ Meeting @ JLab

High Mass SM Higgs Searches l gg H WW* ℓ+ℓ- n l B(H WW*) > 0. 9 for m. H > 160 Ge. V WH WWW* n Fermiophobic higgs enhances s B l l High B(h WW*) for mh > 100 Ge. V Measurements rely on n n Lepton identification + Missing-ET resolution Understanding of backgrounds l WZ & WW production Nikos Varelas 19 CTEQ Meeting @ JLab

gg H WW* ℓ+ℓ- (1) l l Bkgd: Z/ *, WW, ZZ, W/Z + j, QCD tt, Selection: n n 2 high-p. T leptons + E T l ee, mm, & em combined l Z and energetic jets Veto on WW Cross Section Measurements (pb) Low (<MH/2) dilepton inv mass Opening angle between leptons is useful discriminating variable l Two leptons tend to move in parallel due to spin correlation of Higgs boson decay products W+ n W- Nikos Varelas e+ DØ: (25 evts) CDF: (17 evts) NLO Theory: CDF: PRL (94), e- 12 -13. 5 pb 211801 (2005) DØ: PRL (94), 151801 (2005) 20 CTEQ Meeting @ JLab

gg H * WW + ℓ ℓ (2) s*BR(H→WW) < 3. 7 pb DØ For MH=160 Ge. V Analysis based on ~320 pb-1 Number of expected events for MH=160 Ge. V: 0. 68 ± 0. 01 H WW* 12. 3 ± 0. 3 Diboson Production 2. 8 ± 0. 9 W+jet/g 4. 0 ± 0. 7 Z/g* 0. 47 ± 0. 03 Top 0. 2 ± 0. 1 multijets Total 19. 7 ± 1. 2 events Observe 19 DØ: Submitted to PRL hep-ex/0508054 Maximum likelihood limit on the ll distributions for m. H=140 -180 Ge. V CDF Analysis based on ~360 pb-1 Number of bkgd events for MH=160 Ge. V: 0. 58 ± 0. 04 H WW* 9. 79 ± 1. 03 WW 13. 78 ± 1. 24 Total bkgd Observe Nikos Varelas 21 16 CTEQ Meeting @ JLab

WH WWW* l l ± ± ℓ ℓ’ qq’ (1) Search for associated Higgs production with W where the H WW* Selection: n n n 2 like-sign high-p. T leptons Veto events with a 3 rd high-p. T lepton Significant E T DØ Analysis based on ~370 pb-1 Data: 1/3/2 events for ee/em/mm channels bkgd: 0. 70 ± 0. 08 for ee 4. 32 ± 0. 23 for em 3. 72 ± 0. 75 for mm CDF Analysis based on ~190 pb-1 Data: 0 events bkgd: 0. 95 ± 0. 61(stat) ± 0. 18(sys) SM Higgs (160 Ge. V) expected to be ~0. 03 evts Nikos Varelas 22 CTEQ Meeting @ JLab

WH WWW* (2) CDF: 190 pb-1 DØ: 370 pb-1 Nikos Varelas 23 CTEQ Meeting @ JLab

Where we Stand Today Nikos Varelas 24 CTEQ Meeting @ JLab

SM Higgs Search Prospects l l Near term: expect at least doubling of analyzed data for Spring ’ 06 conferences Long term: reaching ~8 fb-1 by 2009 n Detector upgrades in Spring 2006 (Si (DØ), trigger/DAQ (DØ, CDF)) LEP Tevatron Higgs Sensitivity Group: Initial Report: hep-ph/0010338 (2000) Updated in 2003 in the low Higgs mass region: Fermilab-PUB-03/320 -E 2009 http: //www-d 0. fnal. gov/Run 2 Physics/higgs_sensitivity_study. html • WH l bb • ZH bb • Improvement due mainly to sophisticated analysis techniques and better detector understanding Nikos Varelas 2006 25 CTEQ Meeting @ JLab

How do we Compare to HSS-03? Ratio Dijet mass window DØ Analysis (PRL ‘ 05) 174 pb-1 WH e bb [85, 135] Prospective Study (‘ 03) normalized to 174 pb-1 and to WH bbe [100, 136] Prospective DØ Analysis R=0. 72 Dijet mass resolution 14 ± 1 % 10 % R=0. 71 Signal events (S) 0. 049 0. 145 R=3. 0 Background evts (B) 1. 07 1. 76 R=1. 6 S/ B 0. 045 0. 11 R=2. 4 We are missing a factor 2. 4 in sensitivity for this WH(e) channel. A factor of 50 is needed to reach SM expectations for ~115 Ge. V higgs (or ~450 fb-1 of luminosity!) Nikos Varelas 26 CTEQ Meeting @ JLab

So How Do We Get There? l l l Use forward electrons (+30%), Better EM-ID (+30%) Higher b-tagging efficiency (+40%) n Layer-0 upgrade, NN b-tagger l Improved di-jet mass resolution (+40%) l Better calorimeter calibration, use Cal-Track jets We can reach the expected sensitivity by Summer’ 06 n Additional factors not included in WH sensitivity: 3 (leptons) * 2 (experiments) * 2. 5 (channels) * 1. 8 (NN-selec) * 12 (lumi 2 fb-1) = 324 = 182 Combining both factor 2. 4*18 =43 consistent with 50 needed to reach SM expectations for ~115 Ge. V Higgs Nikos Varelas 27 CTEQ Meeting @ JLab

Summary l l Tevatron accelerator complex and experiments are performing well Higgs searches using 400 pb-1 of Run II data show no deviation from SM bkgd expectations n l l Good understanding of W/Z+jets processes Expect improved analyses and limits by Spring ’ 06 based on ~ 1 fb-1 of data Sensitivity to m. H>114 Ge. V starts with 2 fb-1 Exclusion up to m. H ~ 180 Ge. V with 8 fb-1 Very exciting short and long term future prospects with a lot of hard work ahead Nikos Varelas 28 CTEQ Meeting @ JLab