W.Murray PPD 1

Bill MurrayRAL, CCLRCw.murray@rl.ac.uk

WIN 07, Kolkata15th January 2007

rimental S

k Symmetr

g

What is E-W symmetry breakingWhat are the known knowns?What are the known unknowns?What about the unknown unknowns?

W.Murray PPD 2

9 years ago..

“The LHC would

certainly ferret out the

Higgs by 2007”

W.Murray PPD 3

What is E-W symmetry breaking?

This gauge symmetry predicts γ,W,Z,gluons Requires them to be massless

Symmetry breaking is needed for W/Z masses

SU(3) x SU(2) x U(1)

W.Murray PPD 4

How can it occur?

Preserver underlying symmetrySpontaneous or dynamical breakingPreserves ρ=1

(Relative strength of neutral and charged current interactions)

Higgs mechanism!

Dr Bhattacharyya will cover this in detail.

W.Murray PPD 5

Two experimental themes

Precision Electroweak dataIs ρ=1 true?Are the loop effects correctly seen?Can we predict the Higgs mass from them?Needs masses, couplings...

Direct Higgs searchWhat can we say about SM HiggsWhat does the future hold? And when?What about Super-symmetry?

W.Murray PPD 6

Precision Electroweak

Does the SM give MW, M

t and Z properties

correctly?Z properties

Largely from LEP/SLCFinal: “Phys Rept. 427 (2006) 257”

W mass/widthLEP II resultsTevatron run ICDF Run II

Top massTevatron: Runs I and II

W.Murray PPD 7

Z Properties: LEP

Mz = 91.1876±0.0021GeV/c2

Γz =2.4952±0.0023GeV/c2

Coupling example: ρ and sin2θ

eff

Leptons precise B quarks incompatibleNon-universal EW corrections observed! Born level not quite correct – ρ close to 1

Born level

W.Murray PPD 8

W mass

LEP results are close to finalM

W = 80.376±0.033

Run 1 Tevatron results:M

W = 80.452±0.059

Now: CDF Run II resultBased on 200pb-1

http://fcdfwww.fnal.gov/physics/ewk/2007/wmass/wmass_conf.psSummary follows..

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CDF lepton quality plots:

Electron material modeling excellentAs is muon tracking description

Based on fitting ψ, φ data, validated at Z

E/P, electrons Z mass muons

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Measured Transverse mass

Backgrounds very lowAgreement of data with fit looks great

For electrons, p(χ2)=5x10-7 (stat only)But the data is really very impressive

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Improvements since run I

Huge improvements in ~all systematics

Systematic (MeV)Run I Run II

Electron Muon Electron MuonLepton energy scale 75 85 30 17Lepton energy resolution 25 20 9 3Recoil energy 37 35 12 12Backgrounds 5 25 8 9pT(W) 15 20 3 3Parton distribution 15 15 11 11

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Combined W mass

New result compatible with existingMost precise single result

Only 200pb-1: much more to come

80.452±0.05980.376±0.03380.136±0.08480.392±0.02980.413±0.04880.398±0.025

W.Murray PPD 13

Top Mass measurement

A unique particle to the TevatronPair produced, top decays:

The semileptonic are often 'golden'The other decay modes contribute too.

HadronicSemileptonic e+muleptonic e+mutaus

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Semi-leptonic channel

Clear leptonic signatureWith missing energy

But enough constraints to calculate neutrino Two b jets

All tops have theseB tagging important

W+jets is main backround

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Mass Extraction

Mass is fitted along with Jet Energy Scale

MW fixes scale

Using matrix element convoluted with resolutionUses all information in the event Biggest systematic: signal description

Mass of jjj combination

166 b-tagged candidates

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Comparison of channels

Example from CDFAll contributeBut lepton plus jets dominates

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Top by channel/experiment:

CDF results based on much more dataThe lepton plus jets channels dominate the average

MT=171.4±1.2±1.8

Systematics important – future gains will be hard work

W.Murray PPD 18

Combined Electroweak

The consistency of the data can be used to test the use of EW correctionIt also constrains the Higgs mass

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The Electroweak fit:N

ote

0.2G

eV

rang

e of

sca

le

Direct and indirect agree – predicting M top!

Also suggests m

H around

100GeV

LEP said M

H>114

5th Jan 07CDF M

W

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How is this χ2?

18 observableExpect:

5 1-2 sigma1 2+ sigma

See3 1-2 sigma1 2+ sigma

No problem!(Recent M

W not

included)

W.Murray PPD 21

Why believe in a light Higgs?

Electroweak fit(Z properties, W

and top mass) give at 95%:

MH<166GeV/c2

(MH<153 with CDF MW)

MH<199GeV/c2

(including LEP bound)(189GeV with new M

W)

Summer 06

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Direct Searches

SM Higgs:Past: LEPPresent: TevatronFuture: LHC

Supersymmetry

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Higgs then: LEP SM Higgs

Final LEP result:

MH>114.4GeV(95%CL)

Excess at 115GeV would happen in 9% cases without

signal

Likelihood shown

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Higgs now: The Tevatron

Tevatron is running well, pp at 2TeV collision energy

2fb-1 deliveredRecords broken all the time

CDF and D0 are in great shapeRun II results coming out – top qualityB tagging working well (B

s oscillations!)

Entering the region of sensitivity to SM Higgs

W.Murray PPD 25

Higgs now: The Tevatron

2fb-1 enough for SM Higgs

sensitivity

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Tevatron Search channels

ZH →llbb

ZH →ννbb

WH →lνbb

WH→WWW

H→WW→lνlν

100 110 120 130 140 150 160 170 180 190 200

Approximate ranges for channels

MH, GeV/c2

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ZH→llbb search

D0 plots of 0.9fb-1

Signal is ~50 times below backgroundBut well simulated and signal has mass peak

Sensitivity possible

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ZH→ννbb search; CDF

Double tagged mass distribution:Overall small excess in dataSignal 10% of background at peak

This is the most powerful channel

for light Higgs

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WH→lνbb with CDF

Small excess around 100GeVSignal 15 times below background

1 b tag 2 b tag

HWW* : final selection

e

MH=160GeV (x10)

e

e

950pb-1

W.Murray PPD 31

Combined Higgs boson Search @ CDF

All low mass channels analyses use 1 fb-1 of data

WH (lνbb)

ZH (l+l- bb)

ZH (ννbb)

H→WW >~ 120 GeV

For mH = 115 GeV, the 95%CL Limit/SM

is

9 (expected)

13 (observed)

W.Murray PPD 32

Tevatron SM Higgs Combination

mH Limit/SM

(GeV) Exp. Obs.

115 7.6 10.4

130 10.1 10.6

160 5.0 3.9

180 7.5 5.8Essentially equivalent to one experiment with 1.3 fb-1, since the experiments have “complementary” statistics at low and high mass

Tevatron is close to SM Higgs sensitivity

All CDF and DØ results from summer 06 combined

W.Murray PPD 33

Ingredients (DØ)Equiv Lumigain (@115)

Using ~330 pb-1 - 15 9

6.0 6.1 3.7

Combine DØ and CDF 2.0

NN b-Tagger/L0 3.0 3.5

NN analysis selections 1.7 2.7 2.8

Dijet-mass resolution 1.5 2.2

Increased Acceptance 1.2 2.0 2.5

New channels 1.2 1.9 2.1

1.7Reduced Systematics 1.2

1.2 1.5

⇒At 160 GeV needs ~5 fb-1

⇒At 115 GeV needs ~3 fb-1

Xsec Factor Xsec FactormH=115 GeV mH= 160 GeV

Lumi = 2.0 fb-1

95% CL exclusion for mH= 115-185 GeV with 8 fb-1

(assuming similar improvements at DØ and CDF)

Improvements planned/expected

W.Murray PPD 34

Tevatron Likelihood curve

The Tevatron Higgs log-likelihood

Small excess at 105GeVSmall deficit at 165GeV

Nothing to see here - move along.

W.Murray PPD 35

Let's be naughty

Log-likelihood curves can be addedThat's their great beauty

So, if we ASSUME there is a Higgs, and just want to extract its mass, we can add:

EW fitLEP Higgs search llTeVatron Higgs search ll

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Combined Likelihood

A Higgs near 115GeV still best fit

60 70 80 90 100 110 120 130 140 150 160 170 180 190 200-2

-1

0

1

2

3

4

5

6

LEP llEWTevatronSum

Very crudeNo systematics

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Next: The LHC

The 14TeV pp energy raises the Higgs cross section

c/f 2TeV Tevatron

Designed for 1034 luminosityc/f 2 1032 currently at Tevatron

Decades of preparation for this search

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LHC status

1000th dipole in ring

- Out of 1230

Collisions in 2007 planned

But at 900GeV C-o-M

W.Murray PPD 39

LHC Possible runs?

Don't shoot me...just random guesses

30fb-1 often used: Nominal first 3 years

Year Energy Luminosity TeV Total

2007 0.9 0.001 0.0012008 14 3 3

2009-2010 14 10 232011-2014 14 80 343

2017+ SLHC 14 1000 3000

Luminosity, fb-1 Per year

1028

1032-33

1033

1034

1035

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Rates?

LHC backgrounds!

Every event at a lepton collider is physics; every event at a hadron collider is background

Sam Ting

1010

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Rates in channels used

Rates in major channelsNo cuts, just branching ratiosl: e or μThousands of events to look for...

Far less will pass cuts

LEP

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Boson fusion: qq→qqH→ττ

Two forward jets, PT like M

W/2

Higgs products centralNo colourflow → suppressed central jetsZ→ττ plus two jets main background

Jet

Jet

Jet

Jet

• →ll'', lν+jet final states ( hadronic ident.)•  mass reconstruction: need PT

miss

Low mass

W.Murray PPD 43

qqH(→) via VBF

Need to undestand tails in Z mass resolutionBut signal to background could be good

• S/√B~2.5 in one LHC yearCMS: 40 fb-1 for discovery in mH=120-140 GeV rangeATLAS: Maybe 20fb-1

• Measures Yukawa coupling H

mZ

W.Murray PPD 44

H→γγ

Very rare (10-3) decay mode – top loopBut trigger is goodLarge backgrounds of γγ, γ-jet and jet jet

Jet rejection 103 requiredNeed energy and angle resolution in calorimeter

Primary vertex!CMS resolution 0.5GeV best

Production mechanism may improve s/b

W.Murray PPD 45

H→ZZ→l+l-l+l-

Golden channel mH>140GeV/c2

Above ~200 two real Z'sGood mass resolution, trigger

Backgrounds:Irreducible QCD ZZ to llllReducible Zbb, tt

Multivariate (pt, η)

methods for low mH

ATLAS toroids help

W.Murray PPD 46

HWW(*)

Important for MH~170 GeV, Higgs mass not fully reconstructed, sensitive to systematics bck• Isolated leptons WW(*)→ll (l=e,μ)• Missing transverse energy ET

miss

Background t(Wb)t(Wb)

-Request central jet veto

-WW spin correlations for the signal-small l+l- opening angles

VBF qqH→qqWWPresence of forward jets allows

purer signalmost low-mass range accessible

ATL-PHYS-2003-005

W.Murray PPD 47

SM Discovery

With 30 fb-1, more than 7 for the whole range A 200GeV Higgs can be found with 2fb-1

W.Murray PPD 48

Measuring the Higgs mass

MSSM Higgs m/m (%)h, A, H 0.10.4H 4l 0.10.4H/A 0.1-1.5h bb 12 hh bb 1-2 Zh bbll 12H/A 1-10

precision of <0.3% for mH < 400 GeVno theoretical error included

W.Murray PPD 49

Branching ratio information

3 channels for almost all mH<200GeV

Comparison of rates gives coupling info.e.g. glue/W rate to 25%Hard to measure better than 10%Quark couplings rarely accessible (ttH, H to bb)

ttH

H →γγ

H →ZZ→llll

H →WW

qqH →qqττ

qqH →qqWW

WH→WWW

WH→Wγγ

100 120 140 160 180 200 220 240

Channels with four sigma for 30fb-1

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Higgs Total Width

Width:Above 200GeV large width can be measuredBelow there is no possibility

ILC can do better

A muon collider would be very useful here

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Higgs Spin/Parity

Spin? Parity?ZZ and maybe ttH allow parity reconstruction

Spin 0 established if VVH seen – should be for all masses

W.Murray PPD 52

LHC Higgs

Extended Higgs sectors ????

Nobel

Prize:

Peter

Higgs

Nobel

Prize:

Peter

Higgs

LHC can definitively test the SM Higgs sector

This model is falsifiable! Mass measurements to per cent levelCross section x Branching ratio 10's percentSelf coupling probably not addressable

W.Murray PPD 53

Extended Higgs sectors?

All previous discussion relates to simplest model; one Higgs doubletMany more complex possibilities fit EW dataSUSY is an obvious example

Requires two doubletsCan accommodate more complex possibilities

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Supersymmetry

EW fit result favours SUSY region:

Heavy SUSYSUSY has two Higgs doublets

5 HiggsesTwo parameters:

MA, tanβ

222

2222

22222222

,

0

0 2cos42

1

WAH

ZAHh

ZAZAZAhH

MMM

MMMM

MMMMMMM Including Run II CDF M

W

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LEP SUSY Higgs limit:

LEP limits in Mh

max

Reduced Mtop

extends tanβ exclusion

Tanβ > ~2.5 for 174

Benchmark – not absolute limit. Reduced by:

CPV scenariosnMSSM modelsInvisible decays

179GeV Mtop

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e.g. CPX Scenario at LEP

Designed to have h/H/A mixing

MSUSY

500GeVM

2 200GeV

μ 2000GeVm

g1000GeV

arg(A) 90o

No mass limits for moderate tanβ

Hard at LHC too

W.Murray PPD 57

TeVatron MSSM reach

TeVatron currently sensitive to modes with enhanced couplings (w.r.t. SM)tanβ in

Bbφ→bbbbφ→ττ

Therefore large tanβ and moderate mass

W.Murray PPD 58

Other MSSM searches: γγγ

Fermio-phobic HiggsD0, 0.83fb-1

No sign of signalExclude fermio-phobic Higgs below 66GeV if H+ mass 100GeV

W.Murray PPD 59

LHC expectations:

H/A similar shape to TeVatronBut hugely expandedHH can be found for most of plot

But not all CPV scenarios all Higgs may escape

W.Murray PPD 60

Conclusions

Incredible new results from Tevatronm

W precision improving

Higgs mass below 150GeV seems clearDirect Higgs searches close to sensitive

LHC will start this yearThere is a real race happening

Do NOTNOT assume the unknown is trueBut in 2010 electroweak symmetry breaking of the SM will be established – or clearly wrong

A lepton collider will be required to explore properties