On behalf of the

Maxim Titov, CEA Saclay, France

COLLABORATIONS

18 August 2011, Moscow, Russia

• Introduction • Challenges and Analysis strategies • Standard Model Higgs Searches • New Tevatron combined result• Beyond Standard Model Higgs

The excellent performance of the Tevatron during last few years has

sparked the realisation that a Higgs might be observed at Tevatron, thus

ensuring a complimentarity of Tevatron and LHC Searches

Exciting interplay of Higgs physics and direct supersymmetry searches

A light Standard Model Higgs hypothesis is in agreement with all indirect tests

MW mt2, logmH

mH< 161 GeV (95% CL)

mH 92 2634 GeV

Indirect constraints• Precision electroweak observables

are sensitive to the Higgs boson mass via quantum corrections.

First the Higgs Boson

has tobe discovered !!!

Is it a Standard Modelor MSSM Higgs...?

Mass: determines SM Higgs profile

Width/partial width/ couplings

Spin and CPquantum numbers

Higgs self-coupling

Tevatron/ LHC

Higgs is a journey,not a destination

LHC/sLHC/

Linear Collider

The absence of a light Higgs implies New Physics beyond SM

7.02.52.5# int./ crossing

3963963500Bunch crossing (ns)

50-6015-203 Ldt (pb-1/week)

4.0 10321x10321.6 1030Typical L (cm-2s-1)

1.961.961.8s (TeV)

36 3636 366 6Bunches in Turn

Run IIbRun IIaRun I

World’s highest energy proton-antiproton collider

Expect > 10 fb-1 analyzable data by end of September 2011

Results today using

up to 8.5 fb-1

Two general purpose detectors:

• Central tracking system embedded in a solenoidal magnetic field:

• Silicon vertex detector • Tracking chamber (CDF)

• Fiber tracker (DØ)

• Preshowers• Electromagnetic and hadronic

calorimeters• Muon system

Rapidity coverage: CDF DzeroTracking 2.0 2.5 Calorimeter 3.6 4.0 Muon 1.0 2.0 B-field 1.4 T 2.0 T

Main production mechanisms (115<mH<180 GeV):

• Gluon fusion (gg H): ~0.8-0.2 pb• Associated production (VH, V=W,Z): ~0.2-0.02 pb• Vector boson fusion (VBF): ~0.1-0.02 pbs

mH < 135 GeV:

VH (V=W,Z) production with H→bb decay

mH > 135 GeV:

gg→H production with H→WW→lnln decay

Analyze all decay channels to achieve the best sensitivity (e.g.):

• Direct: gg H tt, gg• VBF: qqH qqbb, qqH qqWW • ttH l+jets, ttH all jets

Combine all CDF/DO channels

~ 400 -700 Higgs events

produced with 10 fb -1

• QCD Multijets (data driven methods) Jets faking leptons, ET

miss from mismeasured jets

• Z/g + jets (ALPGEN/PYTHIA, NNLO theory cross-section, data-based corrections to model pT(Z)) mismeasured jets or leptons yielding MET • W+jets, W+g(ALPGEN/PYTHIA, NNLO theory cross-section, data-based corrections to model pT(W) and/or data driven methods) jets or gfaking lepton

• Diboson - WW, WZ, ZZ (PYTHIA, normalized to NLO cross-section; NLO correction for pT and di-lepton opening angle)

• ttbar, single top (ALPGEN/PYTHIA, COMPHEP; normalized to NNLO)

• gg H bb final state overhelmed by QCD

• Main channel: associated production WH / ZH with H→bb

Extremely challenging (requires Excellent b-tagging, dijet mass resolution, bkgds understanding)

WH lnbb ZHnnbbZHl l bb

WH→lnbb: lepton+MET+2 b-jets Largest signal rate Larger V+jets background

ZH→llbb: dilepton+2 b-jets Smallest Higgs signal rate Low background Kinematically constrained

ZH→lnbb: MET+2 b-jets Comparable signal rate to WH(+WH→lnbb with missing lepton) Challenging instrumental background

Step 1: Identify events consistent with leptonic W/Z decays and >= 2 jets

Trigger on high pT electrons, muons or ETmiss

• Wln: e or m and high ETmiss

• Zll: ee or mm consistent with Z resonance • Znn: no charged leptons; high Et

miss and 2 acoplanar jets

Step 2: b-tagging (reduces backgrounds by two orders of magnitude) B-tagging exploits information on:

• Lifetime: displaced tracks and/or vetices• Mass: secondary vertex mass• Soft leptons

Use MVA for improved performance: NN for b-to-c discrimination after

secondary vertex tagging; NN for b-to-light: continuous tagger

(multiple operating points)

13131313

S:B ~ 1:4000 S:B ~ 1:75S:B ~ 1:400

Before b-tagging =1 tightb-tag

≥2 looseb-tags

e.g. DO: NIMA620 490-517 (2010)

b-jet eff. ~ 50%mis-tag rate ~ 0.5%

Step 3: Validate background modelling in control regions

Similar control regions for other final states and heavy flavour enhanced samples

Multijet enhanced:

loosening missing ETmiss

(and related variables)

W+jets enhanced:

require isolated lepton

Top enhanced:

require isolated leptonand two 2b-tag jets

• The invariant mass of the bb pair is the most sensitive variable to the Higgs

• An improvement in resolution has a direct impact on the search sensitivity

Exploit information from tracker,preshower, jet shape variables,semileptonic b-decays with the NN

15% resolution improvement

How to choose 2jets from 3jets or more?

Instead of using two largest pT jets, use two most b-like jets from bID information.

S/B remains small, need advanced (multivariate) analysis techniques

Step 4: Optimize separation via multivariate technique• Exploit information from several discriminant variables and their correlations

• Improves sensitivity compared to cut-based analysis by ~15-20%

• However, must be very careful with the choice of training sample

• Many checks performed in different kinematic regions to validate the modeling of the inputs to the MVA method and its output;

Same optimization/techniques in similarfinal states as for Higgs searches:

• Single top

• Diboson hadronic decays

VS

WZ+ZZnnbb,nncc:

17171717

WZ ZZmeas 6.9 1.3(stat.) 1.8(syst.) pb

WZ ZZtheo 4.6 0.3 pb

D0 NOTE-6223 (2011)For mH=115 GeV• WH→lnbb: σ = 26 fb• ZH→nnbb: σ = 15 fb• ZH→llbb: σ = 5 fb Total VH: σ = 46 fb

Replace Z with H• WZ→lnbb: σ = 105 fb• ZZ→nnbb: σ = 81 fb• ZZ→llbb: σ = 27 fb Total VZ: σ = 213 fb

• Use the final discriminant distribution (e.g. NN output) to perform hypothesis testing (S+B vs B-only)

In the absence of excess, set limits using:

A Bayesian method (flat prior signal, credibility intervals) The CLS method (log-likelihood test statistic CLS = CLS +B /CLB)

Upper cross section limit for Higgs production relative to SM prediction

Observed limit

(solid line)from data

Expected limit (dot dashed line) and predicted 1σ/2σ (green/yellow bands)variations from background only pseudo-experiments

ZHllbb

WHlvbb

(7.9 fb-1) (7.5 fb-1 ) (7.8 fb-1)

VHvvbb

Exp (obs) - 3.9 (4.8) x SM @ MH=115 GeV

CDF NOTE-10583 (2009)CDF NOTE-10596 (2011)

CDF NOTE-10593 (2011)

CDF NOTE-10572 (2011)

Exp (obs) – 2.7 (2.6) x SM @ MH=115 GeV

Exp (obs) – 2.9 (2.3) x SM @ MH=115 GeV

ZHllbb

WHlvbb

(8.6 fb-1) (8.5 fb-1 ) (8.4 fb-1)

VHvvbb

D0 NOTE-6166 (2011)

Exp (obs) – 4.8 (4.9) x SM @ MH=115 GeV

D0 NOTE-6220 (2011)

Exp (obs) – 3.5 (4.6) x SM @ MH=115 GeV

D0 NOTE-6223 (2011)

Exp (obs) – 4.0 (3.2) x SM @ MH=115 GeV

95% CL Limits at mH = 115 GeV:

Channel Exp/obs Limit (/SM)

WHlnbb (7.5 fb-1) 2.7/2.6

ZHnnbb (7.8 fb-1) 2.9/2.3

ZHl+l-bb (7.9 fb-1) 3.9/4.8

WHlnbb (8.5 fb-1) 3.5/4.6

ZHnnbb (8.4 fb-1) 4.0/3.2

ZHl+l-bb (8.6 fb-1) 4.8/4.9

VH/VBFjjbb (4.0fb-1) 17.8/9.1

ttHl+jets (7.5 fb-1) 11.722.9

ttHjets (5.7 fb-1) 20.2/28.1

Tevatron Combination H gg:

D0: arXiv: 1107.4960

Channel Exp/obs Limit (/SM)

tt+1j,2j (6.0 fb-1) 15.2/14.7

lltt/lntt(6.2 fb-1) 17.3/18.5

tt+2j (5.4 fb-1) 12.8/32.8

Dominant decay mode for mH> 135 GeV: H WW

Clean environment can takeadvantage of gg → H production:

• 2 opposite charge high pT leptons

• Missing ET (E T miss)

Signal contribution also from associated production (W/Z+H) and VBF (qqH):

~ 35 % more signal

Consider all final states with 2 high-pT leptons and ETmiss

Step 1: Preselect events with two isolated high-pT leptons

Split analysis according to:

• D0: Lepton flavor: ee, em, mm • CDF: Signal purity based on lepton

quality• CDF: Low (<16 GeV) di-lepton mass

Different instrumental/fake backgrounds Different background compositions

Suppress the dominant Z/g background:

Use kinematics, in particular ETmiss

based variables that ensure ETmiss is

significant and not due to mis-measured object.

DO (ee, mm) employs Decision Trees trained against Z/g

Step 2: Validation of background modelling and search techniques that share characteristics of the signal

Define control regions to testmodelling for different backgrounds:

W+jets :

same-signdileptons

t-tbar :

opposite-sign

dileptons, >= 2 jets,

b-tag

Diboson cross section measurements:

CDF NOTE-9753 (2009)

CDF NOTE-10358 (2010)

Split analysis according to jet multiplicity:better sensitivity to H+jets final states: qqH, WH, ZH (important for low mass)

Each multiplicity bin correspond toa different dominant background:

• 0 jet: WW• 1 jet: WW; Z/g• ≥2 jets: ttbar MVA optimized for

each channel & mass hypothesis.

Input MVA variables (e.g. D0):

0-jet

1-jet

2-jet

mH = 165 GeV

D0 NOTE-6219 (2011)

CDF NOTE-10599 (2011)

Step 3: Multivariate analysis

Additional sensitivity ( ~ 10%) from same charge dilepton selection

W/ZW/Z Main backgrounds are instrumental:

• Lepton charge mis-ID (Z/g*l+l-)• Jets faking leptons (multijet, W+jet/g)

Final multivariate (BDT, NN) discriminants to analyze data

Exploit: Event topology, lepton kinematics, jet content, relation betweenlepton and ET

miss …

CDF NOTE-10599 (2011)D0: arXiv 1107.1268 (2011)

• Data consistent with the background-only hypothesis within the systematic uncertainties.

• Significant sensitivity at high mass!

CDF Combination: D0 Combination:

Tevatron (CDF + D0) Combination:

S+B versus B-only Hypotheses (LLR = -2lnQ, where Q = Ls+b/Lb)

Most “signal-like’ excess consistent with Higgs of 130 GeV but alsoconsistent with background-onlyhypothesis

D0 NOTE-6229 (2011)

Tevatron Combination:

mH Limit/ SM(GeV) OBS. EXP.

115 1.22 1.17130 2.02 1.37165 0.48 0.58 180 1.17 1.98

July 2011 Tevatron Combination: arXiv:1107.5518

SM Higgs excluded @ 95 % CL:

Observed Exclusion: 100 < mH < 108 and 156 < mH <177 GeVExpected Exclusion: 100 < mH < 109 and 148 < mH < 180 GeV

Observedlimit (data)

• Best current limit for mH<130 GeV

• Unique window into H bb

• H WW analysis sensitive to different signals and backgrounds than LHC around 130-140 GeV

1-3 * SM

Including ongoing analysis improvements and morechannels:

• Exclusion potential for mH < 190 GeV

• 2-3 sensitivity for mH ~ 115-130 GeV

MSSM requires exactly 2 Higgs doublets:• one couples to up-type quarks (vev vu)• another couples to down-type quarks (vev vd)

Important parameter: tan b = vu/vd

tan b ~ 35 = mt/mb is appealing (large tan b)

After EW breaking: 5 physical states ‣ 3 neutral Higgs bosons: h/H (CP-even)

and A (CP-odd) (convention: mh < mH, h/H/A generically denoted j)

‣ 2 charged Higgs bosons: H±

• At tree level: EW breaking controlled by MA and tanβ. Radiative corrections make it more model dependent.

• There must be a light Higgs (h): mh ≤ 135 GeV

H/A/H+ nearly equal masswhen mA large

Higgs coupling to b-quarks enhanced by tan β PROD ~ tan2 b

OverwhelmingQCD background Relatively clean signature

low BR ~10%

High BR ~90%Large multijet background

Reduced backgroundAdditional sensitivity at low mA

Three complimentary channels:

• Both CDF and DØ see ~2 excesses around mA~120-150 GeV

CDF: arXiv: 1106.4782 (2011)

D0: PLB698, 97 (2011)

35

bfbtt

• Tevatron searches does not observe any significant excess

ftt

arXiv: 1106.4555 (2011)

D0 Note 6227 (2011)

• CDF and D0 have paved the way and brought sophistication and maturity into Higgs boson searches at hadron colliders.

• Tevatron is on track to deliver Higgs search results in spring 2012 based on the full 10 fb-1 datasets with promised sensitivity goals

NATURE W

ILL, IN

ALL

LIKEL

IHOOD, S

URPRISE

US !

• Consider main low mass analyses (WHlnbb, ZHnnbb, ZHllbb) at 6 fb-1 and evaluate expected LLR after injecting a SM-like signal at mH=115 GeV

observed limit consistent with a what would be expected from signal+background (but also consistent with background-only)

Tevatron Observed Limit: Signal Injection Test (6 fb-1):

A. Juste, 2011 DPF Meeting, August 2011