1. La Thuile, March, 15 th, 2003 f Makoto Tomoto ( FNAL ) Prospects for Higgs Searches at DØ Makoto Tomoto Fermi National Accelerator Laboratory (For the DØ Collaboration) La Thuile 2003, La Thuile, Italy

2. Makoto Tomoto ( FNAL )La Thuile, March, 15 th, 2003 f Outline Introduction DØ Run II Run II Data –W + jets –Z + jets –H  WW Summary

3. Makoto Tomoto ( FNAL )La Thuile, March, 15 th, 2003 f Introduction Major goal of the Tevatron Run II is the search for Higgs bosons. Direct SM Higgs search at LEP: m H > 114.4 GeV at 95% C.L. ( hep-ex/0211058) Indirect limit of the global SM fit: m H < 196 GeV at 95% C.L. Fit minimum is at 85 GeV (hep-ex/0212036) 200 GeV

4. Makoto Tomoto ( FNAL )La Thuile, March, 15 th, 2003 f Production Process & Decay Channel H  bb H  WW gg  H …  gg  H) ~ 1 pb For masses below ~140 GeV, Background hides H  bb signals For higher masses; m H > 120GeV, Combination with H  WW decay process can be useful HW, HZ …  (HW/HZ)  ~ 0.1 pb Leptonic decays of W/Z help background rejection Hqq …  (Hqq) ~ 0.1 pb Background too high Hbb …  (Hbb) ~ 5 fb SM extensions may enhance  b/bb (  =h,H,A)

5. Makoto Tomoto ( FNAL )La Thuile, March, 15 th, 2003 f Tevatron Higgs Working Group Study The Higgs discovery potential for the Tevatron RunII has been evaluated. –hep-ph/0010338 A joint effort of theorists and both experimental groups, CDF and DØ. Simulation performed using a parameterized fast detector simulation. Main conclusion : –Discovery at 3-5  can be made, –Combine all channels. –Combine the data from both experiments, CDF and DØ –Must improve understanding of signal and background processes and detector performance. –b-tagging, resolution of M bb LEP excluded at 95% C.L. Results of studies with full simulations for selected signal process are consistent with SHWG expectations. – Advanced analysis techniques are vital – Largest luminosity required to discover Higgs

6. Makoto Tomoto ( FNAL )La Thuile, March, 15 th, 2003 f DØ Run II Tevatron Run II in progress –Collider energy : 1.8 TeV  1.96 TeV  Higgs production cross section increases by 20~30% –Target Luminosity : 6  11 fb  1 or more –Peak luminosity now better than Run I : 3.7 x 10 31 cm  1 s  1 DØ upgraded for Run II –New tracking system fully working well.  Important for b-tagging –D0 recorded over 80 pb -1 with full detector (Operating at >85% efficiency) Analysis in this talk based on 30~50 pb  1 (Collected from August 2002 to January 2003)

7. Makoto Tomoto ( FNAL )La Thuile, March, 15 th, 2003 f Current Activity Study of the W/Z(  lepton) + jets production –First step towards W/Z (  leptons) +H (  bb) measurement –The W/Z + b-jets can be related to W/Z+ jets properties –Try to understand major background source from W/Z + di-jets Search for H  WW (*) (  ee /  /e  ) decays –Lot of interesting physics in WW (*) production –Important to keep an eye Others Search for H  decays WH(  l  + bb) ZH(  l  l  or  bb)  b/bb,  bb/  (  = h, H, A ; SUSY Higgs)

8. Makoto Tomoto ( FNAL )La Thuile, March, 15 th, 2003 f Object Identification missing E T electron E T MTMT W p T Dot : Data Line : MC Z  W  e DØ Run II Preliminary Z  W characteristics are represented by MC Clear mass peak of Z(ee) and Z(  ) : Data : MC DØ RunII Preliminary Z  ee QCD : Data : MC

9. Makoto Tomoto ( FNAL )La Thuile, March, 15 th, 2003 f W/Z + jets production First step towards W/Z (  leptons) +H (  bb) measurement. W/Z + b-jets properties can be related to W/Z + jets properties. –Major background source to Higgs searches Analysis utilized 35 pb  1 Data samples triggered by lepton –No bias for jets distribution. Basic Selection: –Isolated lepton and large E T (for W) –2 high p T leptons and m ll consistent with m z (for Z) –Plus jets

10. Makoto Tomoto ( FNAL )La Thuile, March, 15 th, 2003 f W+jets production (1) Selection –W(  e ) Isolated e : p T > 20 GeV |  | < 0.8 Missing E T > 25 GeV –W(   ) Isolated  : p T > 25 GeV |  | < 1.5 missing E T > 20 GeV –Jets p T > 20 GeV |  | < 2.5 Compare PYTHIA MC with DATA Normalized by area Error includes stat. error and dominant syst. error from JES 2 nd leading jets 1 st leading jets GeV W(e )+jets QCD BKG : Data : MC : Data : MC

11. Makoto Tomoto ( FNAL )La Thuile, March, 15 th, 2003 f W+jets production (2) Di-jet Mass  R between di-jets W(e )+jets Reconstructed di-jet mass and  R(=  2 +  2 ) between jets –MC reproduces jet distributions well –First step towards study of W(  leptons)H(  bb) decay process QCD BKG M jj (GeV)  R jj : Data : MC : Data : MC

12. Makoto Tomoto ( FNAL )La Thuile, March, 15 th, 2003 f W+jets production (3) Di-jet mass and  R jj distribution for W(   ) + jets event M jj (GeV)  R jj Di-jet Mass  R between di-jets W(  )+jets : Data :MC QCD BKG W(  )+jets : Data :MC

13. Makoto Tomoto ( FNAL )La Thuile, March, 15 th, 2003 f Z+jets production (1) Selections – 2 muons from Z(   ) p T > 15 GeV |  | < 2 – 2 electrons from Z(  ee) p T > 20 GeV |  | < 2.3 – Jets p T > 20 GeV |  | < 2.5 1 st leading jets 2 nd leading jets Compare PYTHIA MC with DATA Normalized by area Combined Z(ee)+jets and Z(  )+jets Error includes stat. error and dominant syst. error from JES

14. Makoto Tomoto ( FNAL )La Thuile, March, 15 th, 2003 f Z+jets production (2) Number of jets in Z + jets final states Reconstructed di-jet mass and  R(=  2 +  2 ) between jets –MC describes jet distributions well –First step towards Z(  leptons)H(  bb) study Di-jet Mass  R between di-jets #jets in Z+jets Combined Z(ee)+jets and Z(  )+jets

15. Makoto Tomoto ( FNAL )La Thuile, March, 15 th, 2003 f b-tagging (1) Next step in searches for Higgs would be b-jet identification Crucial to keep signal efficiency high and suppress non-b jets b-tagging efficiency determined by Impact Parameter (IP) resolution Measured IP resolution after 1 st pass in SMT alignment IP resolution as the function of P T IP resolution Mean = 0.9  2.2  m Sigma = 36.3  1.8  m Beam ~ 30  m  IP resolution ~ 20  m

16. Makoto Tomoto ( FNAL )La Thuile, March, 15 th, 2003 f  + jet sample b-tagging (2) b-tagging explores IP significance method Lepton from semileptonic decay of b is very useful Positive IP Negative IP Impact Parameter > 0  track crosses jet axis after primary vertex Jet track Resolution b enhanced Interaction point Impact Parameter < 0  track crosses jet axis before primary vertex DØ Run II Preliminary Significance = IP/  IP

17. Makoto Tomoto ( FNAL )La Thuile, March, 15 th, 2003 f H  WW (*)  l  l   decays Lot of interesting physics in WW production –SM Higgs at high mass region (m H > 120 GeV) –4 th fermion family enhances SM Higgs cross section (factor ~8.5 for m H =100 – 200 GeV) –Fermiophobic/Topcolor Higgs –(Br(H  WW)>98% for m H > 100 GeV) –Non Higgs-related … Tri-linear couplings, New Phenomena Look at ee/  /e  plus missing E T events Backgrounds include Z/  *, WW, tt, W/Z+jets, QCD Cannot directly reconstruct mass –Transverse mass (m T ) computed using m ll and E T Opening angle between leptons (  ll ) is useful discriminating variable –Two leptons from Higgs tend to move in parallel (small  ll ), due to spin correlations in H  WW decay products –Leptons from Z/  *, multijets are emitted back to back (large  ll )

18. Makoto Tomoto ( FNAL )La Thuile, March, 15 th, 2003 f H  WW (*)  e  e   final states Expected backgroundDATA Lepton ID, p T >10, 20 GeV 2748  42  245 2753 m ee < m H /2 264  18.6  4.3 262 E T > 20 GeV 12.3  2.5  0.7 11 m T <m H + 20 GeV 3.6  1.4  0.2 1  ee < 2.00.7  1.4  0.1 0 Event Selection L=44.5 pb  1 Selection optimized for m H = 120 GeV Expected Backgrounds (H  WW  e  ) x 50 After basic kinematics cuts After all selection but  ee  signal = ~ 8%

19. Makoto Tomoto ( FNAL )La Thuile, March, 15 th, 2003 f H  WW (*)  e  final states Expected backgroundDATA Lepton ID, p T >10, 20 GeV 22  2.1  2.2 22 E T > 20 GeV 3.1  1.7  0.1 4  (E T,jets)>0.5, |E T +p T |>50 GeV 1.4  1.5  0.1 2  e  < 2.00.9  1.5  0.1 1 Event Selection After basic kinematics cuts After all selection but  ee (H  WW  e  ) x 20 Expected Backgrounds L=34 pb  1 Selection optimized for m H = 160 GeV  signal = ~ 12%

20. Makoto Tomoto ( FNAL )La Thuile, March, 15 th, 2003 f Candidate of H  WW (*)  e  e  ETET e e ETET e e e p T = 31.1 GeV p T = 27.3 GeV E T = 31.2 GeV m T = 106.8 GeV M ee = 36.1 GeV  ee =1.43 Selection optimized for m H =160GeV e

21. Makoto Tomoto ( FNAL )La Thuile, March, 15 th, 2003 f Summary DØ is taking physics quality data. Background to Higgs production are under study. –W+jets –Z+jets –WW More to come in the near future!!