Jets+met Triggers SM Higgs boson search in the HZ bb final state

1. Jets+met Triggers SM Higgs boson search in the HZbb final state Arnaud Duperrin (CPPM Marseille) on behalf of D0 and CDF Alexandre Zabi (Oct. 04) D0 France PhDs (on these topics) Thomas Millet (May 07) Fabrice Tissandier (Oct. 07) Samuel Calvet (Sept. 07) Bertrand Martin (Sept. 08) Christophe Ochando (Sept. 08) Florent Lacroix (Dec. 08) • TRIGGERS • Jets+MET Signals • Trigger Systems • Design • Historic • Data Trigger Efficiency • Performances ANALYSIS • Data Sample • SM Backgrounds • The Multijet Background • Selection/Systematics • Results/Improvements • CDF

2. It is challenging: 1) Which Jets+met signals do we want to TRIGGER on?

3. 2) Trigger System at D0 (online) Full reco (offline)

4. Run IIb: 31032 cm-2 s-1 • new hardware (faster) • new tools (ex MET) • new design (ex: Oring) @2401030 cm-2 s-1 Why an upgrade of the trigger system in 2006 ? Run IIa: 0.51032 cm-2 s-1 data (min bias trigger) @601030 cm-2 s-1

5. 3) Jet+MET trigger design: an example at L3 25 GeV Signal ZH (mH=115 GeV) (arbitrary normalization) Result of the L3 design of Run IIb jets+met triggers for Higgs search  cut rate to tape by ~50% while keeping trigger efficiencies constant (~85%)  Higgs and NP jets+met triggers are kept unprescaled up to highest luminosity

6. v11 v12 v13 FH EM CC EC Tower (TT) Trigger Tower 4) Jet+MET trigger: design historic 6% 23% of Fev. 2003 July 2003 June 2004 July. 2003 June. 2004 Fev. 2003 MHT30 • L1: CJT(3,5) : 3 TT with ET>5 GeV • L2: MHT>20 GeV • L3: at least 1 one jet, MHT>30 GeV, HT>50 GeV  improved the triggers as function of the instantaneous luminosity increases

7. Run IIb June 2006 June 2006 v15 • monjet+met • dijet+met • multijet+met • L1: MET>24 GeV and Jet Pt1>20 GeV and Jet Pt2>8 GeV and “no back-to-back jets” (noBB) • L2: Pt1>20 GeV, MHT>20 GeV, HT>35 GeV, noBB • L3: 2 Jets Pt>9 GeV, MHT>25 GeV, no BB (170o), (Jet1,MHT)>25o, MET>25 GeV  L1JET CSWJT(1,8,3.2)   CC   Run IIb: Oring of several complex triggers  very different from the first “MHT30” trigger (June 2006) (and I am skipping a lot of the technical difficulties which went into these designs…) design historic 38% 33% July 2005 June 2004 July 2005 June 2004 v13 v14 • JT1_ACO_MHT_HT • JT2_MHT25_HT

8. TT calibration = bring the precision readout + shifting + smearing of TT energy to match data/MC • Two approaches: • 1) Calibrate the online trigger simulator (called d0trigsim): • get the jet+met trigger response • takes the complex correlations between the objects (jets and MET) • allows to study the systematics Offline is ~OK QCD data/MC: 2 jets back-to back Jet 1 Jet 2 Results: shown for L1 Jets and L1 MET data/MC comparison for L1 objects entering in the HZ triggers looks good after calibration (work in progress) DATA MC TT calibration before after after 5) Trigger Efficiencies GEANT program does not simulate the D0 calorimeter response correctly  need to calibrate the response of the simulated trigger system with the data

9. Second approach: derive a standalone parametrization to “emulate” the jet+MET Higgs trigger response by calibrating objects directly and study possible remaining correlations (current choice for the analysis shown later) • Z+- +jets and W() + jets data: • equivalent to jets+met data from the calorimeter point of view • well understood signal and easy to collect (isolated muon trigger)  triggers Example on how to parametrize:termCSWJT(1,30,3.2) : “at least one L1 jet with ET>30 GeV & ||<3.2” Term efficiency +jets+MET triggers (both are data) 6) Trigger Performances HZ signal MC: • HZ Trigger efficiency: (for loose offline cuts) • L1: 88% • L1+L2+L3: 84% • with un-calibrated d0trigsim: 91% +jets+MET triggers “emulation” (both are data) (+ complex Oring taken into account…)

10. ZHbb WHlbb ZHl+l-bb  with WH, ZH is the most sensitive channel at low mass  same final state than many NP particles (ex. sbottom, stop, LQ3) SM Higgs boson search in the HZbb final state BR(Zl+l-) 3% BR(Z)20% (3 neutrinos flavors) (this search is also sensitive to W(l)H signal events when the lepton is not reconstructed represents 40% of the signal sample)

11. b  Z  b b q 90% 81% 2) SM Backgrounds b W (see Jean-Francois’s presentation on SM backgrounds + heavy flavors “scale factors”) q Irreducible: Z()+jets (800 pb) reducible: W(l)+jets (4500 pb) 1) Data Sample

12. jets: Jets energy fluctuate  MET multijet background contribution jet 2 MET min(Jet,MET) jet 1 • Selection: • 2 or 3 jets Pt>20 GeV • MET> 50 GeV • min(Jet,MET), Aco veto… 3) The Multijet Background Of the order of the milibarn (to be compared to signal cross section ~ 0.015 pb mH=115 GeV) …but difficult to simulate (from theory and instrumental point of view)  has to be evaluated with data (next slide)

13. MET R(jet 1, jet 2) Z+jets  in the “signal sample” at preselection level, the SM+QCD contributions (QCD obtained from data) shows a good agreement between data/MC W+jets QCD Signal x 500 Jet 1 Signal sample (</2) QCD sample (>/2) M_trkPt M_trkPt MET Jet 2 QCD SIGNAL (TrkPt, MET) is used to split the data in two samples: « QCD-like » and « signal-like »

14. Neural Network b-tagging: Dijet invariant mass Before After W+jets W+saveurs lourdes Z+jets Z+saveurs lourdes Top QCD Signal (x10) Boosted decision tree (DT): • 24 variables used: • dijet invariant mass(which is the most discriminant), • jets pT & , • R(jet 1, jet 2), (jet 1, jet 2), etc… Signal (x500) DT output 4) Selection

15. 5) Systematics 6) Results • trigger efficiencies:  5.5% • cross section:  6-16% (SM backgrounds),  6% (signal) • HF fraction:  50% • b-tagging efficiencies:  6% • Luminosity:  6.1% At mH=115 GeV, Ratio=7.5 observed (8.4 expected) (predicted by the “SM” Higgs)  most sensitive result for a low mass Higgs at D0 7) Improvements foreseen: • lower the MET cut down to 40 GeV  15% more signal (including trigger efficiencies)  work on trigger and QCD modeling • combine with “single b-tagging” and separate 2 & 3 jets bins • add an isolated track veto analysis • jet resolutions improvements • more luminosity!

16. win08 win08 At mH=115 GeV, Ratio=7.9 observed (6.3 expected) CDF improvements in sensitivity of VH->MET+bb analysis in the course of 2007-2008 8) CDF similar results (split by b-tagging categories + uses a NN to select the signal) • Single Tagged category adds ~10% to sensitivity. • Accept three jet events, where the 3rd jet is either a jet radiated off from a quark or a charged lepton => Adds sensitivity to WH->taunubb channel (hadronic  jets = 30% of selected signal events) • Multijet background shape and normalization are estimated from data => Multijet normaliztion uncertainty reduced to <20%. • Jet energies are corrected using tracking information => Improves Dijet Mass resolution. • Neural Network =>Improvement in signal acceptance with respect to cut-based selection

17. with Fermilab, Manchester, Imperial College, among others Conclusion HZbb+ set one of the most stringent limits on Higgs boson production cross-section among various Tevatron searches  many improvements still to come  combination with other channels (see Gregorio’s presentation) Jets + MET triggers are challenging but provide access to very important search channels (not only Higgs but also to SUSY)  Undoubtly a very useful experience acquired at Tevatron in a challenging but important area which can be expanded at LHC experiments