1. 1 CTEQ Meeting @ JLab Nikos Varelas SM HIGGS SEARCHES AT THE TEVATRON Nikos Varelas University of Illinois at Chicago http://www-cdf.fnal.gov/physics/exotic/exotic.html http://www-d0.fnal.gov/Run2Physics/higgs/ CTEQ Meeting, Jefferson Lab Nov 2005

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

3. 3 CTEQ Meeting @ JLab Nikos Varelas Guidance from EW Fits Direct searches by LEP on SM Higgs Boson: m H > 114.4 GeV (95% CL) Indirect limit from fits to precision EW measurements from LEP-SLC-Tevatron m H < 206 GeV (95% CL) using previous m t =174.3  3.4 GeV (Run I+II) Latest value: m t =172.7  2.9 GeV (Run I+II) Expected value: m H = 98 +52 −36 GeV Run II will provide stringent constraints to SM Higgs  M t ~ 2 GeV with ~2 fb -1  M W < 30 MeV (currently 59 MeV – Run I combined)  Light Mass Higgs favored Tevatron (future):  m t =1.5 GeV,  M W =30 MeV

4. 4 CTEQ Meeting @ JLab Nikos Varelas Fermilab TeVatron - RunII Main Injector & Recycler Tevatron Chicago   p source Booster pp p p pp 1.96 TeV CDF DØ Run IIa 2001-2006 E CM = 1.96 TeV ~ 1.3 fb -1 Run IIb 2006-2009 E CM = 1.96 TeV ~8 fb -1 Run I 1992-1996 E CM = 1.8 TeV ~120 pb -1 (0.63 TeV ~600 nb -1 )

5. 5 CTEQ Meeting @ JLab Nikos Varelas Data Sample Tevatron performs according to design Record peak luminosity ~ 1.6 x 10 32 Record integrated luminosity ~ 21 pb  /week Data samples presented here: 2002-2004 (  400 pb  ) Detector data collection efficiency 85-90% Expected luminosity to each experiment ~8 fb -1 by the end of 2009 We Are Here

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

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

8. 8 CTEQ Meeting @ JLab Nikos Varelas Z  bb Dijet invariant mass of ~86K events Only two jets in the events (veto other jets with E T  10 GeV) Jets must be back-to-back (  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

9. 9 CTEQ Meeting @ JLab Nikos Varelas  (W(  e ) +  n jets) Based on 127 pb -1 Jets E T > 15 GeV, |  |<2.4 Cone Alg, R cone = 0.4 Electrons P T > 20 GeV, |  |<1.1 W’s Missing E T > 30 GeV Veto Z mass region Backgrounds (3-40%) QCD W  , top, Z multiple pp interactions Theory: Alpgen+Herwig (+Detector Simulation)

10. 10 CTEQ Meeting @ JLab Nikos Varelas  (Z/  * (  ee) +  n jets)/  Z/  * Based on 343 pb -1 1,646 Z+jets events Selection: Jets E T > 20 GeV, |  |<2.5 Midpoint Alg, R cone = 0.5 Electrons P T > 25 GeV, |  |<1.1 Z’s 75 < M ee < 105 GeV 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) ALPGEN+PYTHIA (+Detector Simulation) (CTEQ5L) 1 st Jet 2 nd Jet 3 rd Jet

11. 11 CTEQ Meeting @ JLab Nikos Varelas  (Z+b)/  (Z+jet) Analysis combines Z  ee and  channels Based on 180 pb -1 3,458 Z+jets events Selection: At least one Jet: E T > 20 GeV, |  |<2.5 2 Electrons/muons: P T > 15 GeV, |  |<2.5/2.0 Z mass cut Apply sec. vertex b-tag 42 events with  1 tag 8.3 events from QCD background Measure inclusive ratio to cancel many systematics Z+heavy flavor is background to ZH Z+b probes the b-quark PDF b-PDF is important for hb and single-top production Measurement:  (Z+b)/  (Z+j) = 0.021  0.004(stat)  0.002(sys) Good agreement with NLO QCD: 0.018 PRL (94), 161801 (2005)

12. 12 CTEQ Meeting @ JLab Nikos Varelas Search for W(e )bb Production Dominant bkgd for WH Based on 382 pb -1 Selection: 2 Jets: E T > 20 GeV, |  |<2.5 1 electron: P T > 20 GeV, |  |<1.1 Missing E T > 25 GeV b-tag: JLIP (Jet Lifetime Probability) 153 events with  1 b-tag 13 events with 2 b-tags Expect 4.29 ± 1.03Wbb 0.14 ± 0.03WH 5.73 ± 1.45WZ, tt, W/Z+jets, single top, multijets Total 10.2 ± 2.4 events Observe 13 95% CL upper limit:  (Wbb)  4.6pb for b-jets with p T b  20 GeV, |  b |  2.5, and  R bb  0.75

13. 13 CTEQ Meeting @ JLab Nikos Varelas From Wbb to WH Based on 319 pb-1 Selection (e and  channels): 2 Jets: E T > 15 GeV, |  |<2 1 electron or muon: P T > 20 GeV, central Missing E T > 20 GeV b-tagging: Secondary Vertex

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

15. 15 CTEQ Meeting @ JLab Nikos Varelas Z(  )H(  bb) Search (1) An important channel for low-mass Higgs search Large B(Z  ) ~ 20% Trigger on events with large missing H T H T is defined as the magnitude of the vector sum of jets’ E T Analysis was based on 261 pb -1 Selection: 2 Jets: E T > 20 GeV, |  |<2.5 Missing E T > 25 GeV Veto events with isolated tracks (p T  8 GeV) To reject leptons from W/Z H T =  |p T (jets)| < 200 GeV To reject tt events Reduce “instrumental” backgrounds Jet acoplanarity  (dijet) < 165  Use various missing energy/momentum variables Form asymmetry variables Jet1 Jet2 ETET HTHT P T trk P T.2 trk P T trk = – |  p T (trk)| … tracks P T,2 trk = – |  p T (trk in dijet)| … tracks in jets

16. 16 CTEQ Meeting @ JLab Nikos Varelas No b-tagDouble b-tagSingle b-tag Z(  )H(  bb) Search (2)

17. 17 CTEQ Meeting @ JLab Nikos Varelas Mass (GeV) Window 105 [70,120] 115 [80,130] 125 [90,140] 135 [100,150] Data4322 Acceptance (%)0.29  0.070.33  0.080.35  0.090.34  0.09 Total bkgd.2.75  0.882.19  0.721.93  0.661.71  0.57 Expected limit (pb)8.87.56.06.5 Limit @95% C.L. (pb)12.29.37.7 8.5 Wjj/Wbb32 Zjj/Zbb31 Instrumental16 Top15 WZ/ZZ6 Bkgd. composition (%) Z(  )H(  bb) Search (3) 2 b-jet tags using JLIP

18. 18 CTEQ Meeting @ JLab Nikos Varelas Z(  )H(  bb) Search (4) Analysis was based on 289 pb-1 Selection: 2 Jets: 1 st jet E T  40 GeV, 2 nd jet E T  20 GeV Missing E T > 70 GeV At least 1 b-tag Blind analysis technique Control Regions: QCD + heavy flavor EWK, Top, and QCD Signal Region: Veto events with leptons Missing E T and 2 nd leading jet are not in parallel Cut optimization is performed in this region based on MC simulation before looking at the real data Higgs mass: 120 GeV Bkgd: 4.36 events QCD: 11.4% Top : 20.5 % EWK: 18.2 % Mistagged light flavor : 50 % Observe: 6

19. 19 CTEQ Meeting @ JLab Nikos Varelas High Mass SM Higgs Searches gg  H  WW *  ℓ + ℓ - B(H  WW * )  0.9 for m H  160 GeV WH  WWW * Fermiophobic higgs enhances  B High B(h  WW * ) for m h  100 GeV Measurements rely on Lepton identification + Missing-E T resolution Understanding of backgrounds WZ & WW production

20. 20 CTEQ Meeting @ JLab Nikos Varelas gg  H  WW *  ℓ + ℓ - (1) Selection: 2 high-p T leptons + E ̸ T ee, , & e  combined Veto on Z and energetic jets Low (  M H /2) dilepton inv mass Opening angle between leptons is useful discriminating variable Two leptons tend to move in parallel due to spin correlation of Higgs boson decay products W+W+ e+e+ W-W- e-e- n WW Cross Section Measurements (pb) DØ: (25 evts) CDF: (17 evts) NLO Theory: 12-13.5 pb DØ: PRL (94), 151801 (2005) CDF: PRL (94), 211801 (2005) Bkgd: Z/  *, WW, ZZ, WZ, t t, W/Z + j, QCD

21. 21 CTEQ Meeting @ JLab Nikos Varelas gg  H  WW *  ℓ + ℓ - (2) Maximum likelihood limit on the  ll distributions for m H =140-180 GeV DØ Analysis based on ~320 pb -1 Number of expected events for M H =160 GeV: 0.68 ± 0.01 H  WW * 12.3 ± 0.3 Diboson Production 2.8 ± 0.9 W+jet/  4.0 ± 0.7 Z/  * 0.47 ± 0.03 Top 0.2 ± 0.1 multijets Total 19.7 ± 1.2 events Observe 19 CDF Analysis based on ~360 pb -1 Number of bkgd events for M H =160 GeV: 0.58 ± 0.04 H  WW * 9.79 ± 1.03 WW 13.78 ± 1.24 Total bkgd Observe 16  *BR(H → WW) < 3.7pb For M H =160 GeV DØ: Submitted to PRL hep-ex/0508054

22. 22 CTEQ Meeting @ JLab Nikos Varelas Search for associated Higgs production with W where the H  WW * Selection: 2 like-sign high-p T leptons Veto events with a 3 rd high-p T lepton Significant E ̸ T WH  WWW*  ℓ ± ℓ’ ± qq’ (1) DØ Analysis based on ~370 pb -1 Data: 1/3/2 events for ee/e  /  channels bkgd: 0.70 ± 0.08 for ee 4.32 ± 0.23 for e  3.72 ± 0.75 for  CDF Analysis based on ~190 pb -1 Data: 0 events bkgd: 0.95 ± 0.61(stat) ± 0.18(sys) SM Higgs (160 GeV) expected to be ~0.03 evts

23. 23 CTEQ Meeting @ JLab Nikos Varelas WH  WWW* (2) CDF: 190 pb  DØ: 370 pb 

24. 24 CTEQ Meeting @ JLab Nikos Varelas Where we Stand Today

25. 25 CTEQ Meeting @ JLab Nikos Varelas 2006 2009 LEP SM Higgs Search Prospects Tevatron Higgs Sensitivity Group: Initial Report: hep-ph/0010338 (2000) Updated in 2003 in the low Higgs mass region: Fermilab-PUB-03/320-E http://www-d0.fnal.gov/Run2Physics/higgs_sensitivity_study.html WH  l bb ZH  bb Improvement due mainly to sophisticated analysis techniques and better detector understanding Near term: expect at least doubling of analyzed data for Spring ’06 conferences Long term: reaching ~8 fb-1 by 2009 Detector upgrades in Spring 2006 (Si (DØ), trigger/DAQ (DØ, CDF))

26. 26 CTEQ Meeting @ JLab Nikos Varelas How do we Compare to HSS-03? 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] Ratio Prospective DØ Analysis R=0.72 Dijet mass resolution14 ± 1 %10 %R=0.71 Signal events (S)0.0490.145R=3.0 Background evts (B)1. 071.76R=1.6 S/  B 0.0450.11R=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 GeV higgs (or ~450 fb  of luminosity!)

27. 27 CTEQ Meeting @ JLab Nikos Varelas So How Do We Get There? Use forward electrons (+30%), Better EM-ID (+30%) Higher b-tagging efficiency (+40%) Layer-0 upgrade, NN b-tagger Improved di-jet mass resolution (+40%) Better calorimeter calibration, use Cal-Track jets We can reach the expected sensitivity by Summer’06 Additional factors not included in WH sensitivity: 3 (leptons) * 2 (experiments) * 2.5 (channels) * 1.8 (NN-selec) * 12 (lumi  2fb -1 ) = 324 = 18 2  Combining both factor 2.4*18 =43  consistent with 50 needed to reach SM expectations for ~115 GeV Higgs

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