Higgs Searches at Tevatron

Kazu HanagakiKazu Hanagaki 11

Higgs Searches at TevatronHiggs Searches at Tevatron

MotivationMotivationExperimental strategy (and Experimental strategy (and

detector)detector)Higgs search statusHiggs search statusProspectsProspectsConclusionsConclusions

花垣和則 (Kazunori Hanagaki) / Fermilab for the CDF & DØ collaborations

MotivationMotivation


Electroweak Symmetry BreakingElectroweak Symmetry Breaking Gauge invariant Gauge invariant no mass term no mass term Higgs mechanism [with U(1) vector field]Higgs mechanism [with U(1) vector field]

L = (DL = (DDD – V( – V(- ¼ F- ¼ FFF D D ∂∂+ieA+ieA, F, F ∂ ∂AA - ∂ - ∂AA

V(V() = ) = 22 + | + ||(|())22

is complex scalar doublet: Higgs fieldis complex scalar doublet: Higgs field ee22AAAAin (Din (DDD

(e(e22vv22)/2·A)/2·AAA mass term!! mass term!! One Higgs doublet in SMOne Higgs doublet in SM

4 degree of freedom – 3 x (gauge boson) 4 degree of freedom – 3 x (gauge boson) one Higgs boson one Higgs boson

Spontaneous symmetry breakingSpontaneous symmetry breaking22>0 (hot) potential minimum at >0 (hot) potential minimum at =0=022<0 (cold=present world) at <0 (cold=present world) at 00

<<> = > = v/sqrt(2)v/sqrt(2)


Why is Higgs Preferred?Why is Higgs Preferred?

Unitarity: individual diagraUnitarity: individual diagram diverges with sqrt(s)m diverges with sqrt(s) gauge cancellationgauge cancellation

spin 1 intermediate statespin 1 intermediate state spin 0 componentspin 0 component due to w due to w

rong helicity state of erong helicity state of e++ee-- must be canceled by spi must be canceled by spin 0 particlen 0 particle

proportional to mass proportional to mass Higgs coupling!Higgs coupling!

WW-- WW++

ee-- ee++

WW-- WW++

ee-- ee++

ZZ

WW-- WW++

ee-- ee++

WW-- WW++

ee-- ee++

HH


Needs to be light (160-180 GeV) for a theory valid up to Needs to be light (160-180 GeV) for a theory valid up to Plank scalePlank scale

Finding a Higgs at MFinding a Higgs at MHH ~ 120 GeV would be an evidence o ~ 120 GeV would be an evidence of new physicsf new physics

115-200 GeV is our target mass range115-200 GeV is our target mass range

Higgs MassHiggs Mass

unstable unstable vacuumvacuum

Higgs self-Higgs self-coupling coupling divergesdiverges

energy scale (GeV)energy scale (GeV)

MMHH > 114.4 GeV @95% CL sear > 114.4 GeV @95% CL search by LEP2ch by LEP2

MMH H < 175 (207) GeV @95% CL < 175 (207) GeV @95% CL global EW fittingglobal EW fitting


Fermion remains masslessFermion remains massless Nucleon mass almost unchanged, but proton woNucleon mass almost unchanged, but proton wo

uld be heavier than neutronuld be heavier than neutron Spontaneous symmetry breaking by QCD Spontaneous symmetry breaking by QCD W/Z W/Z

mass ~1/2500 (W,Z vs mass ~1/2500 (W,Z vs ) ) very rapid inversed very rapid inversed beta decay (pbeta decay (pn+en+e++++))

Unstable proton Unstable proton no hydrogen atom no hydrogen atom

Completely different world !!Completely different world !!

If the symmetry is not broken…?If the symmetry is not broken…?

Mechanism of electroweak symmetry breaking isMechanism of electroweak symmetry breaking is

the mystery relevant for existence of ourselves the mystery relevant for existence of ourselves

Experimental Strategy and Experimental Strategy and DetectorDetector


Search StrategySearch Strategy

MMHH < 135 GeV < 135 GeV H H b b-bar dominant b b-bar dominant too much BG in too much BG in

gg gg H H b b-bar b b-bar qqqqW/Z+H(W/Z+H(bb)bb)

For high MFor high MHH range range H H WW dominant WW dominant gg gg H H WW WW

For medium MFor medium MHH range range W/Z+H(W/Z+H(WW) helpsWW) helps


The DetectorThe Detector

= -ln[tan(= -ln[tan(/2)]/2)]


Silicon Tracker for b-jets IdentificationSilicon Tracker for b-jets Identification

Silicon micro-strip detector for preciseSilicon micro-strip detector for precisemeasurement of charged particle trajectorymeasurement of charged particle trajectory

New silicon detector in DØ for New silicon detector in DØ for improvement of b-jet IDimprovement of b-jet ID installed and tested in this shuinstalled and tested in this shu

tdown periodtdown period


Identification of b-jetsIdentification of b-jets

ccb-hadronb-hadron ~ 400-500 ~ 400-500 m m tra travel by a few mm from primarvel by a few mm from primary vertexy vertex S(Lxy) = Lxy/(Lxy) or S(IP) S(IP)

= d= d00//dd00 with V0 (Ks etc.)

removal

prim

ary

verte

x seco

ndar

y

verte

xL xyd 0

DØDØ

CDFCDF

sec.vertex basesec.vertex base

Higgs Search StatusHiggs Search Status

Standard ModelStandard Model MSSMMSSM


Standard Model – Low Mass HiggsStandard Model – Low Mass Higgs

W/Z identificationW/Z identification WWll: high p: high pTT isolated lepton + isolated lepton +

missing Emissing ETT W mass W mass ZZ: large missing E: large missing ETT

ZZll: high pll: high pTT isolated dilepton isolated dilepton Z massZ mass

High pHigh pTT dijets with b-ID dijets with b-ID dij dijet masset mass

qq

q(’)q(’) W*/Z*W*/Z*

HH

W/ZW/Z

xBr(W/ZxBr(W/Zff) = 0.015-0.003 ff) = 0.015-0.003 pbpb

BackgroundsBackgrounds W/Z+bb/cc/jj, top, W/Z+Z(W/Z+bb/cc/jj, top, W/Z+Z(bb), bb),

QCD…QCD… b-jet ID, jet energy resolution arb-jet ID, jet energy resolution ar

e importante important

bb

bb

ff

ff

Z(Z()H()H(bb) Lbb) Lintint = 261 pb = 261 pb-1-1


W(W(ll)H()H(bb)bb) ppTT(e or (e or ) > 20 GeV) > 20 GeV Missing EMissing ETT > 20 GeV (CDF) > 20 GeV (CDF)

> 25 GeV (DØ) > 25 GeV (DØ) CDF: jet ECDF: jet ETT>15 GeV, |>15 GeV, ||<2|<2 DØ: jet EDØ: jet ETT>20 GeV, |>20 GeV, ||<2.5|<2.5 b-jet taggingb-jet tagging

Consistent Consistent with SM with SM background background expectationsexpectations backgroundbackground

s well s well understoodunderstood


Standard Model – High MassStandard Model – High Mass

Two isolated high pTwo isolated high pTT leptons leptons + missing E+ missing ETT

Dominant background is qqDominant background is qqWWWW different decay angular correlatiodifferent decay angular correlatio

n with Higgs signaln with Higgs signal

DØ Run II Preliminary Lint = 950 pb-1

W+ e+

W- e-


The Other AnalysesThe Other Analyses WH(WH(WW) WW) l l±±ll±±XX

high phigh pTT isolated isolated like signlike sign dil dilepton (ee,epton (ee,,e,e))

large missing Elarge missing ETT diboson production is the mdiboson production is the m

ain background due to charain background due to charge mis-identificationge mis-identification

t(t(bW)t(bW)t(bW)H(bW)H(bb)bb) exactly one e or exactly one e or missing Emissing ETT 5 or more jets5 or more jets 3 or more b-jets3 or more b-jets


Standard Model Higgs SummaryStandard Model Higgs Summary

~1~155

First DØ combined result First DØ combined result Z(Z(ll)H not yet includedll)H not yet included


MSSM HiggsMSSM Higgs

t

0

b

0

Amplitude 1/tan Amplitude tan

+

b

b

0

Amplitude tan

Two Higgs doublet in MSSM to avoid anomalyTwo Higgs doublet in MSSM to avoid anomaly 8 degrees of freedom – 3 x (longitudinal polarization of 8 degrees of freedom – 3 x (longitudinal polarization of

WW± ± and Z) and Z) 5 scalars ( 5 scalars (h, H, Ah, H, A, H, H±±)) tantan = <H = <Huu>/<H>/<Hdd>>

At high tanAt high tan, , (h or H, A) is enhanced(h or H, A) is enhanced Br(ABr(Abb)~90%, Br(Abb)~90%, Br(A)~10%)~10%

00


MSSM Higgs Search StatusMSSM Higgs Search Status

CDF: CDF: ; DØ: b(b); DØ: b(b)b(b)bb, b(b)bb,

ProspectsProspects


LuminosityLuminosity

4-8 fb4-8 fb-1-1 by 2009by 2009

100E3100E300

200E30200E30 Improvement by the recycler Improvement by the recycler as a storage ring of p-baras a storage ring of p-bar

Electron cooling at the recyclerElectron cooling at the recycler


Improvement of b-tag at DØImprovement of b-tag at DØQCD data (fake rate)

SVT JLIP CSIPSVT JLIP CSIP

SV

T JLI

P

C

SIP

SV

T JLI

P

C

SIP + jet data

(efficiency)

SVT JLIP CSIPSVT JLIP CSIP

SV

T JL

IP

CSIP

SV

T JL

IP

CSIP

correlation coefficientcorrelation coefficient

Three b-tag algorithms in Three b-tag algorithms in DØ; SVT, JLIP, and CSIPDØ; SVT, JLIP, and CSIP correlated in efficiencycorrelated in efficiency small correlation for fakesmall correlation for fake significant improvement by significant improvement by

combination by Neural combination by Neural Network (~30% per jet)Network (~30% per jet)


The Future of SM Higgs SearchThe Future of SM Higgs Search

Comparison w.r.t. Comparison w.r.t. old old sensitivity studysensitivity study For MFor MHH=115GeV: =115GeV:

Limit/Limit/ =15 @~330pb =15 @~330pb-1-1 by by DØ aloneDØ alone vs vs 95% CL exclusion 95% CL exclusion @2fb@2fb-1-1

We can reach very close to the sensitivity studyWe can reach very close to the sensitivity study

itemitem gaingain cross efficiencycross efficiency 1.11.1lum(2/0.33)lum(2/0.33) 2.42.4 L0/L1calL0/L1cal 1.11.1

NN b-tagNN b-tag 1.41.4 multivariate multivariate selectionselection 1.51.5

jet resolutionjet resolution 1.21.2 reduced syst.reduced syst. 1.11.1new channelsnew channels 1.11.1 combine with CDFcombine with CDF 1.41.4increased increased acceptanceacceptance 1.11.1 grand totalgrand total 1414

ConclusionsConclusions


ConclusionsConclusions Mechanism of electroweak Mechanism of electroweak

symmetry breaking is a symmetry breaking is a profound mysteryprofound mystery

Searches have been carried Searches have been carried out with 194-950 pbout with 194-950 pb-1-1 of data of data Remaining events consistent Remaining events consistent

with SM backgroundswith SM backgrounds If the (SM) Higgs exists and If the (SM) Higgs exists and

is light, there is a great is light, there is a great potential to find the Higgspotential to find the Higgs

Now is the Time to Search for Now is the Time to Search for Higgs at TevatronHiggs at Tevatron

BackupBackup


Projection of MSSM Higgs SearchProjection of MSSM Higgs Search Tevatron will prob

e below

b

t

m

mtan


MSSM ParametersMSSM Parameters

22

2

19

9

1

tan2

bb

SMSUSYBR

radiative correction depending oradiative correction depending on many parametersn many parameters

GeVGeVmGeVGeVGeVGeVM

TeVXTeVTeVMmixingnom

g

t

SUSY

h

160080020020020020002

21max

2

HhA


New Technique of Jet ReconstructionNew Technique of Jet Reconstruction Charged track information in jet reconstructionCharged track information in jet reconstruction

EEcalcal = E(e/ = E(e/) + E(neutral hadron) + E(chrgd had)) + E(neutral hadron) + E(chrgd had) EEtrkcaltrkcal = E = Ecal cal – E– Eexpectexpect(chrgd had) + E(chrgd had) + Etrktrk(chrgd had)(chrgd had)

resolution measured in resolution measured in +jet data+jet dataDØ Run II PreliminaryDØ Run II Preliminary

similar similar improvemenimprovement at CDF as t at CDF as wellwell


b-tag efficiency measurement at b-tag efficiency measurement at DØDØ

Solve 8 equations for 8 unknownsSolve 8 equations for 8 unknowns

unknownunknownss

+jet+jet+jet && opposite tag+jet && opposite tag

number of number of eventsevents

before b-tagbefore b-tag

b-tag by muonb-tag by muon

b-tag by tagger under b-tag by tagger under testingtesting

b-tag by both taggerb-tag by both tagger

example to measure JLIP effiexample to measure JLIP efficiency with the combinatiociency with the combination of muon tagn of muon tag


Low Mass Higgs Search at DØLow Mass Higgs Search at DØ

W(W(e/e/++)H()H(bb): bb): xBR = 0.015 pbxBR = 0.015 pb Z(Z(ee/ee/)H()H(bb): bb): xBR = 0.003 pbxBR = 0.003 pb Z(Z()H()H(bb): bb): xBR = 0.015 pbxBR = 0.015 pb

for 261-389 pbfor 261-389 pb-1-1 effeff SS BB S/sqrt(B)S/sqrt(B)

W(W(ee)H)H 3.4%3.4% 0.180.18 4.74.7 0.080.08

W(W()H)H 1.7%1.7% 0.100.10 4.04.0 0.050.05

Z(Z(ee)Hee)H 4.5%4.5% 0.050.05 1.41.4 0.040.04

Z(Z()H)H 5.9%5.9% 0.050.05 3.13.1 0.030.03

Z(Z()H)H 5.2%5.2% 0.210.21 9.09.0 0.070.07

W(W()H miss lep.)H miss lep. 4.2%4.2% 0.150.15 9.09.0 0.050.05

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Higgs Searches at Tevatron