1. E.Nagy - Low Mass Higgs 8/9/2011 Update on the ZZ-->llbb search1 Update on the ZZ  llbb search E. Nagy CPPM/Fermilab for the zh-llbb Team S.B. Beri, S. Caughron, M.-C. Cousinou, S. Desai, S. Dutt, M. Mulhearn, E. Nagy, H. Nguyen, L. Welty-Rieger, T. Yasuda

2. E.Nagy - Low Mass Higgs 8/9/2011 Update on the ZZ-->llbb search2 The principal goal of this analysis is to validate the Higgs search ZH  ll+bb on an existing signal of the same or similar topology: ZZ  ll+bb (+qq = uu/dd/ss/cc suppressed by b-tag) ZW  ll+qq’ (qq’ = ud/cs suppressed by b-tag) WW  lv+qq’+l(fake) considered as background Therefore: Same analysis as the ZH  llbb search until the RF training RF training (only Run2b, since Run2a is not retrained) WZ and ZZ considered as signal instead of background We use collie to assess the signal (exampleLimitCalculation.cc) to evaluate the xsection (exampleXsecMeasurement.cc) with final variables RF (Run2b) and separately M bb (Run2a+b)

3. E.Nagy - Low Mass Higgs 8/9/2011 3 Last time (August 4 th ) we have shown result only on M bb (Run2a+b) since RF has shown serious miss-modeling in single b-tag (st) Having applied cuts: MET > 50 GeV ΔΦ(Z,jj) > 1.7 the miss-modeling Is largely improved Today’s Update: Results using RF (Run2b) Comparison w/ M bb (Run2b) and w/ M bb (Run2a+2b) Effect of cuts on ZH search by applying the cuts Update on the ZZ-->llbb search

4. E.Nagy - Low Mass Higgs 8/9/2011 Update on the ZZ-->llbb search4 http://www-d0.fnal.gov/Run2Physics/higgs/zh_llbb/d0_private/plots/latest_summer2011/mva/all/1t/ http://www-d0.fnal.gov/Run2Physics/higgs/zh_llbb/d0_private/plots/archive/analysis_v3.15/mva/all/1t/ All plots w/ MET > 50 GeV and ΔΦ(Z,jj) > 1.7 cuts All plots without the above cuts

5. E.Nagy - Low Mass Higgs 8/9/2011 Update on the ZZ-->llbb search5 Xsection calculation and fittest on to_collie RF files with: MET > 50 GeV ΔΦ(Z,jj) > 1.7 Only Run2b data Prefit BgOnly: Sg+Bg: Data: 1277 1277 1277 Bkg: 1235.8 1269.6 1269.4 Sig: 42.8 0. 3.7 Χ 2 : 314.6 314.6 SigSc: 0.09+/-0.64(stat) Observation is more background-like but compatible w/ both signal (1) and no signal (0)

6. E.Nagy - Low Mass Higgs 8/9/2011 Update on the ZZ-->llbb search6 The SM xsection value (4.8 pb) cannot exclude the b-only hypothesis w/ the present statistics (Run2b)

7. E.Nagy - Low Mass Higgs 8/9/2011 Update on the ZZ-->llbb search7 Observation: 1-CL b = 4.1x10 -1 1-CL sb = 9.1x10 -1 1-CL s = 0.84 Separation: S=1.05

8. E.Nagy - Low Mass Higgs 8/9/2011 Update on the ZZ-->llbb search8 Bg subtracted data vs RF

9. E.Nagy - Low Mass Higgs 8/9/2011 Update on the ZZ-->llbb search9 Xsection calculation and fittest on to_collie M bb files with: MET > 50 GeV ΔΦ(Z,jj) > 1.7 Only Run2b data Prefit BgOnly: Sg+Bg: Data: 1213 1213 1213 Bkg: 1167.1 1206.7 1206.0 Sig: 41.8 0. 33.8 Χ 2 : 338 337 SigSc: 0.78+/-0.79 ( 0.56(stat)+/-0.56(syst)) Observation is compatible w/ both bg-like and sg-like

10. E.Nagy - Low Mass Higgs 8/9/2011 Update on the ZZ-->llbb search10 The RMS values are ~20% larger than in the RF case

11. E.Nagy - Low Mass Higgs 8/9/2011 Update on the ZZ-->llbb search11 Observation: 1-CL b = 2.1x10 -1 1-CL sb = 6.7x10 -1 1-CL s = 0.58 S = 0.85 (worse than in the RF case) Separation:

12. E.Nagy - Low Mass Higgs 8/9/2011 Update on the ZZ-->llbb search12 Bg subtracted data vs M bb

13. E. Nagy - General Higgs 4th of August 2011 Status of the ZZ-->llbb search13 Comparison w/ Run2a+Run2b M bb analysis (w/o cut) Same sensitivity (RMS) for the bg-only hypothesis: 2.20 pb Slightly smaller error (RMS) for the xsection: 3.46 vs 3.52 pb

14. E.Nagy - Low Mass Higgs 8/9/2011 Update on the ZZ-->llbb search14 Effect of MET > 50 GeV, ΔΦ(Z,jj) > 1.7 cuts for low mass Higgs search M H = 100 GeV M H = 105 GeV

15. E.Nagy - Low Mass Higgs 8/9/2011 Update on the ZZ-->llbb search15 Mass Exp. Lim. Obs. Lim. GeV w/ cut w/o cut w/ cut w/o cut 100 3.5 3.4 2.3 2.1 105 3.8 3.7 2.4 2.5 110 4.4 4.2 3.2 3.0 115 5.0 4.8 4.3 4.3 120 5.5 5.3 5.9 5.5 125 6.8 6.5 8.6 8.4 130 8.8 8.4 10 8.9 135 12 11 15 14 140 15 14 22 22 145 23 22 32 34 150 36 34 48 38 3-5% deterioration of the sensitivity

16. E.Nagy - Low Mass Higgs 8/9/2011 Update on the ZZ-->llbb search16 Conclusions Concerning the ZZ/ZW signal: with the present statistics and selection - we cannot rule out the absence of the ZZ/ZW signal expected p-value: 0.07 expected b-only and s+b separation: ~1 st.dev. - the observed signal is compatible with the SM xsection - the expected xsection error is ~60% - the RF final variable results in ~20% better limit Concerning the ZH search: The study of the ZZ/ZW signal revealed some miss-modeling in the ST RF distribution This miss-modeling could be mitigated by a simultaneous MET > 50 GeV and ΔΦ(Z,jj) > 1.7 cut These cuts didn’t change the preliminary limit values however they deteriorated the previous sensitivity by ~3-5%

17. E.Nagy - Low Mass Higgs 8/9/2011 Update on the ZZ-->llbb search17 Backup slides

18. E.Nagy - Low Mass Higgs 8/9/2011 Update on the ZZ-->llbb search18 Collie Xsec measurement: Minimizing the “profile likelihood” (difference of Χ 2 for s+b and b-only hypotheses) wrt the nuisance parameters θ k and the xsection scalefactor, f d i – data p i – predicted number of events = s i + b i (signal + background) f = s i /s i SM s i SM – predicted signal of the SM in bin i R k – prior of θ k

19. E.Nagy - Low Mass Higgs 8/9/2011 Update on the ZZ-->llbb search19 RF distributions Run2b1 Run2b23 ST DT

20. E.Nagy - Low Mass Higgs 8/9/2011 Update on the ZZ-->llbb search20 M bb /(200 GeV) distributions ST DT ST DT Run2b1 Run2b23

21. E.Nagy - Low Mass Higgs 8/9/2011 Update on the ZZ-->llbb search21