Daniela Bortoletto Purdue University 1 D. Bortoletto Moriond QCD

THE STANDARD MODEL HIGGS 2 D. Bortoletto Moriond QCD Experimentally: weak gauge bosons are massive  EWK symmetry breaking BEH mechanism SM unifies weak and electro-magnetic interactions ● Finding the Higgs boson is essential to confirm the validity of the BEH mechanism ● The search is difficult since m H is not predicted in SM ● Since the Higgs decays very quickly ( s)  it can be observed only through its decays into other particles ● The Higgs couples to mass and decays preferentially to the heaviest objects kinematically allowed

Higgs boson phenomenology D. Bortoletto Moriond QCD 3 D. Bortoletto, RPM, Berkeley  Higgs decay modes and searches in 1975: 3

Fermilab Tevatron THE TEVATRON  Proton-antiproton collider with 1.96 TeV center-of-mass energy  396 ns between bunches 4 1 km Peak instantaneous luminosity L=4.31  cm -2 sec -1 End of operation September 2011 ≈ 12 fb -1 delivered ≈ 10 fb -1 acquired by the experiments ≈ 12 fb -1 delivered ≈ 10 fb -1 acquired by the experiments CDF D0 D. Bortoletto Moriond QCD

HIGGS PRODUCTION AND DECAY  Four main production mechanisms at hadron colliders 5 D. Bortoletto Moriond QCD gg  Hqq  WH qq  ZH qq'  qq' H (VBF) GeV 135 GeV 1 TeV HIGH MASSLOW MASS Branching fraction too small for discovery at the TEVATRON

The Higgs challenge S/B D. Bortoletto Moriond QCD 6 Many of the background processes have cross section orders of magnitude larger than the Higgs Potential Higgs signal is TINY  Maximize signal acceptance  Excellent modeling of background processes  Use multivariate analysis techniques (MVA) to fully exploit all kinematic differences Expect 167 SM Higgs events (reconstructed and selected) and ~200,000 events from SM backgrounds for m H =125 GeV/c 2 W Z Wγ Zγ WW tt WZ t ZZ

WH  l bb Low Mass M H < 135 GeV/c 2 Main Higgs channels at the Tevatron D. Bortoletto Moriond QCD 7 7 ZH  bb WH  l) bb  Maximize lepton reconstruction and selection efficiencies  Maximize efficiency for tagging b-quark jets  Optimize dijet mass resolution Select: Strategy:  0,1,2 leptons and/or missing E t  Two or three high E t jets ZH  llbb 7 High Mass M H > 135 GeV/c 2 Main channel: gg  H  WW which is also important at low mass High P T leptons and Missing transverse energy

Tevatron Higgs searches 8 ZH  llbb ZH  bb WH  l bb H  WW  l l Total D. Bortoletto Moriond QCD

Higgs analyses strategies 9 Select data sample Apply loose selections Verify modeling of background Control regions Signal region Separate into channels based on S/B Multivariate techniques Channel 1Template 1 Template 2 Channel 2 ……. Systematics and correlations Limits or signal significance Improve S/B D. Bortoletto Moriond QCD

Improvements since summer 2011  Both experiment are:  Validating the Higgs search techniques in WZ/ZZ → X + bb searches (talks on Thursday)  Cross section is ~5 times higher  Using 25% more luminosity in many analysis  New techniques, improved MVA and modeling to increase the sensitivity  Additional triggers and leptons  CDF  New multivariate b-tagger optimized for H  bb jets (HOBIT) with ~20% more acceptance D. Bortoletto Moriond QCD 10 mistag rate SecVtx efficiency HOBIT efficiency ~1%39%54% SECVT X HOBIT b-jetsLight Jets

ZHllbb MVA Improvements Many backgrounds processes are present the llbb selection The individual processes have different kinematics We utilize the three expert networks to assign events to distinct regions in the final event discriminant used in the extraction of upper limits. D. Bortoletto Moriond QCD 11 tt-likeother Z+qq - likeother WZ, ZZ - like ZH - like

ZHllbb D. Bortoletto Moriond QCD 12 WZ, ZZ Z+ qq tt ZH YES NO YES Tagged events Is the event tt-like? NO Z+qq like? WZ/ZZ like? Region 1 Region 2 Region 3 Region 4 Identify events with enhanced S/B s/b=1/1

MET+bb D. Bortoletto Moriond QCD 13  Use Missing p T TRK to suppress multijet background  Exclude isolated tracks from Missing p T TRK to improve WH acceptance by 10%  50% of signal is fromWH with lost leptons Add together b-tagger outputs for both jets Cut on the sum instead of per jet cuts 25% improvement in sensitivity expected from additional data: 6% Increasing purity Tight b Medium b s/ b=0.3%s/ b=1.5%

Met +bb D. Bortoletto Moriond QCD 14  Improve jet energy resolution with Neural network which correlates jet- related variables and returns most probable jet energy based on bottom quark hypothesis  Jet energy is currently used only to determined corrected MET. Selection improves S/B separation b-targeted corrections Signal mass resolutio n Analysis does not yet use HOBIT. Further improvements expected S/B=1/5 Multi- jet Higgs

Limits for Hbb D. Bortoletto Moriond QCD 15 Limits at MH = 115 GeV: Exp: 1.71 x σ(SM) Obs: 1.79 x σ(SM) Limits at MH = 125 GeV: Exp: 2.49 x σ(SM) Obs: 3.29 x σ(SM) TEVATRON Broad excess observed in H→bb Largest Excess: 135 GeV LEE of 2 for range from 100 to 150 GeV/c 2 CDFChannelLocal P- value Global P- value M H =135H->bb2.9σ2.7σ

Limits for Hbb D. Bortoletto Moriond QCD 16 Limits at M H = 115 GeV: Exp: 1.71 x σ(SM) Obs: 1.79 x σ(SM) Limits at M H = 125 GeV: Exp: 2.49 x σ(SM) Obs: 3.29 x σ(SM) TEVATRON Broad excess observed in H→bb Largest Excess: 135 GeV LEE of 2 for range from 100 to 150 GeV/c 2 CDFChannelLocal P- value Global P- value M H =135H->bb2.9σ2.7σ

Tevatron combination: WZ and ZZ D. Bortoletto Moriond QCD 17 W/Z+Z→bb: σ obs = (1.01 ± 0.21) x σ SM  same final state  same set of tagged events  different MVA optimized for WZ and ZZ events

TEVATRON COMBINATION SM HIGGS D. Bortoletto Moriond QCD 18 TEVATRON 95% C.L. upper limits on SM Higgs boson production − Expected exclusion: 100 < MH < 120 GeV, 141 < MH < 184 GeV − Observed exclusion: 100 < MH < 106 GeV, 147 < MH < 179 GeV

D. Bortoletto Moriond QCD 19 High s/b region M H =125 GeV M H =165 GeV Fits to data, with background subtraction Right-to-left Integral of S/B distribution Log 10 (S/B)

The excess D. Bortoletto Moriond QCD 20 Local p-value distribution for background only expectation Minimum local p-value: 2.7 standard deviations Global p-value with LEE factor of 4 range from 100 to 200 GeV/c 2 : 2.2 standard deviations  Simple overlay of H→bb signal prediction for the dijet invariant mass (M H = 120 GeV)  Data and diboson prediction from Tevatron low mass WZ/ZZ measuremen t  Additional signal is not incompatible

The excess D. Bortoletto Moriond QCD 21 Local p-value distribution for background only expectation Minimum local p-value: 2.7 standard deviations Global p-value with LEE factor of 4 range from 100 to 200 GeV/c 2 : 2.2 standard deviations  Simple overlay of H→bb signal prediction for the dijet invariant mass (M H = 120 GeV)  Data and diboson prediction from Tevatron low mass WZ/ZZ measuremen t  Additional signal is not incompatible

Conclusions D. Bortoletto Moriond QCD 22  For additional details see  Tevatron:  CDF:  D0: Thank you to Michelle Stancari, Joe Haley, Homer Wolfe, Satish Desai, Wade Fisher, Tom Junk, Eric James, Karolos Potamianons, Quiguna Liu, and many others  Tevatron experiments are now analyzing full data set in most channels  More improvements are expected in the near future  The data appears to be incompatible with the background, with a global P-value of 2.2 s.d. ( 2.7 local )  H→bb only: 2.6 s.d. ( 2.8 local )  Higgs mass range of 115 < M H < 135 continues to be very interesting  Let us hope that 2012 is the year of the Higgs boson

 BACKUP D. Bortoletto Moriond QCD 23

CONSTRAINTS ON THE HIGGS D. Bortoletto Moriond QCD M H <145 95% CL M H = GeV Many direct searches at the Large Electron Positron Collider, TEVATRON proton anti-proton collider, nd the LHC SM parameters ( M W, M t, Z pole measurements etc) New CDF 2012 W mass M W = ± 12 stat ± 15 syst MeV/c 2 New World Average M W = ± 16 MeV/c 2 Exclusions of M H : − LEP < 114 GeV (arXiv: v1) − Tevatron [156,177] GeV ( arXiv: ) − LHC [~127, 600] GeV arXiv: (ATLAS) arXiv: (CMS) 24

Modeling D. Bortoletto Moriond QCD 25 llbb final discriminant in the pretag region which is background dominated

H → WW D. Bortoletto Moriond QCD 26 Limits at MH = 125 GeV: Exp: 3.14 x σ(SM) Obs: 3.50 x σ(SM) Limits at MH = 125 GeV: Exp: 3 x σ(SM) Obs: 3 x σ(SM)

Limits for H->WW D. Bortoletto Moriond QCD 27 Final states: ee, μμ and eμ Exploit spin correlations to control backgrounds Z → ll is major background for ee and μμ channels Use Boosted Decision Trees to control backgrounds from Z → ee, μμ Signal and background composition vary with jet multiplicity Consider multiple signals: Gluon fusion, Vector boson fusion,H → ZZ...

CDF and D0 Individual results D. Bortoletto Moriond QCD 28 Winter 2012 Summer 2011

ZHbb D. Bortoletto Moriond QCD 29  21% additional luminosity  Small improvements in background rejection  Limits show same basic behavior with 0.5 to 1.0σ increases in significance of excess Summer 2011 Winter 2012

D. Bortoletto Moriond QCD 30

WHlbb D. Bortoletto Moriond QCD 31  26% (69%) additional luminosity for 2-jet (3-jet) channels  5-10% level lepton acceptance/trigger efficiency improvements  New HOBIT b-tagger equivalent to adding another 20% in additional luminosity  Limits show same basic behavior with 1.0 to 1.5σ increases in significance of excess Summer 2011 Winter 2012

ZHllbb D. Bortoletto Moriond QCD 32  23% additional luminosity  More gain from HOBIT in this analysis than WH (original tagging not as sophisticated)  56% of data events in current analysis were not included in previous analysis!  37% sensitivity improvement (4.67  2.95 at m H =120 GeV/c 2 ) Summer 2011 Winter 2012

ZHllbb D. Bortoletto Moriond QCD 33  Electron channels  Here we observe a significant change Summer 2011 Winter 2012

ZHllbb D. Bortoletto Moriond QCD 34  ZH  llbb channel has...  lowest backgrounds  smallest expected signal yields (9 events for m H =120 GeV/c 2 )  Some discriminant bins with large S/B  Low probability for observing events in these bins  A few such events can have substantial effects on observed limits S = 0.16 events, B= 0.06 events

H → WW D. Bortoletto Moriond QCD 35 Summer 2011 Winter 2012  18% additional data  Small signal acceptance improvements (0.1 < ΔR ll < 0.2)  No appreciable change in behavior of limits

H->ZZ D. Bortoletto Moriond QCD 36

D. Bortoletto Moriond QCD 37

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Measurement of WZ and ZZ D. Bortoletto Moriond QCD 39 WZ and ZZ events  same final state  same set of tagged events  different MVA optimized for WZ and ZZ events  (WZ+ZZ)= 4.08 ± 1.32 pb Significance 3.2σ  (WZ+ZZ)= 5.0±1.0±1.3 pb Significance: 3.3σ  (WZ+ZZ): Theory= 4.4±0.3 pb