The road to the ElectroWeak Symmetry Breaking

The road to the ElectroWeak Symmetry Breaking

18th January 2012Seminar at Johns Hopkins University

S.Bolognesi (Johns Hopkins University)

Outline

Status: CMS results in a nutshell, focusing on high mass H->VV

move to larger mass (>600 GeV beyond SM)

improve sensitivity to smaller xsec -> Vector Boson Fusion

The final arbiter: VV scattering

01/18/2012 seminar S.Bolognesi (Johns Hopkins University)2

The Higgs boson and the ElectroWeak Symmetry Breaking (EWSB)

• control of V+jets background• jet merging• signal characterization (angular analysis)

What’s next ?

• control of VV background

Why we need the Higgs

The Higgs boson provides

1) an EXPLICATION of the W,Z mass (ie EWSB)

2) a DESCRIPTION of the fermions masses

1 is really fundamental to make the SM “working” (next slides) … even if not less arbitrary!

2 is just another way of formulating the same question:

why the fermions have those particular masses?

why the fermions have those particular Higgs couplings?

(SM works well without 2: just the fermio-phobic Higgs)


EWSB and the W, Z mass

BBmWWmBBWWL iiiigauge

22

2

1

2

1

4

1

4

1

kjijkiii WWgWWW

BBB Gauge invariance

SU(2)

U(1)EM

complex scalar doublet of SU(2)scalar potential (l>0, m<0) 22 V

0

v

0

2

1

02

1 vwith minimum (= empty state) atSU(2)

3 Goldstone bosons wi

hv

e vi

ii

0

2

1 2

1 physical scalar field 0h

(v = empty expectation value)

generic Gauge

Gauge unitario

4 Gauge fields combined into known vector bosons: W,Z with mass, photon massless

1 physical scalar field -> Higgs

hv

0

2

1

21

2

1 iWWW

22

3

gg

gWBgZ

4 Gauge fields Wim,Bm

22

3

gg

WggBA

222

4

1vgMW

2222

4

1vggM Z

02 AM

U(1)

or

×

01/18/2012 seminar 4

2

2

2

2

2

1

HH mt

t

ms

sts

vV V

Higgs and unitarity in VBF

VBF is the smoking gun of the EWSB !

Same behavior for all VV amplitudes

(s channel only)

(t channel only)

(t and u channels)

2

2

2

1

HLLLL ms

ss

vWWZZA

2

2

2

1

HLLLL mt

tt

vWZWZA

2

2

2

2

2

1

HHLLLL mt

t

mu

utu

vWWWWA

LLLL WWWWA

2

2

2

2

2

1

HHLLLL mt

t

ms

sts

vWWWWA

canale S canale T QGC

V V

V

VV -> VV

Vector Boson Fusion (VBF)

W,Z mass (-> longitudinal degrees of freedom) arise from the Higgs mechanism:without Higgs, W+

LW-L->W+

LW-L would

break unitarity

V


VBF and VV scattering VV scattering spectrum s(VV->VV) vs M(VV)

Whatever we will see or not see at low mass (<2×mW), the EWSB mechanism must be probed in the VV final state

search for possible resonances in VBF measurement of VV scattering spectrum

is the fundamental probe to test nature of Higgs boson or to find alternative EWSB mechanism

LSB<1TeVSB sector weakly coupled

SB sector strongly coupled

eg, strongly interacting light Higgs

SM No-HiggsLSB>1TeVUnitarity violation

other scenarios possible:


Higgs production and decay


CMS results

WW→lnqq, ZZ→llqq limited by huge V+jets background, taken from simu/data with large theoretical/statistical error

ZZ→llnn:

WW→lnln at high mass limited by signal << WW background (Df not effective)

• >400 GeV limited by Z+jets tail at high MET: not large but not well known (controlled with g+jets → statistical error+met uncertainty)

• 200-400 GeV limited by non-Z background (top, W+jets, WW)

ZZ→4l limited by statistics (only ZZ background: small and well known)

drives the UL for mH>300-400

drives the UL for mH 200-300

Future improvements ?

Combination of >5 different channels (ele, mu, btag, …) Robust!

Very optimized analyses, some space for further improvement. With higher lumi:• use shape analyses (where not yet done)

• extract background (norm and shape) from data with lower uncertainty

• extract signal with multidimensional fit (now only mZZ fit)


What’s next ?

higher mass

lower xsec


1 TeV masses: not anymore “the” Higgs→ General search for X→VV→4f:

→ importance of semileptonic final states

xsec larger than Higgs:

at high mass still very low number of events per fb-1

RS Graviton vs SM Higgs:

exotic models (eg, Technicolor, ExtraDimension, …)

first, repeat “Higgs” search for different spin, width resonance

CMS AN-2010-35: Angular Analysis of Resonances pp → X → ZZ


Available results: ZZ

low statistics

MET control V+jetsZZ→4l ZZ→llnn

CDF search for G→ZZ: same features discussed for high mass Higgs @ LHC

ZZ→lljj: large V+jets

arXiv:1111.3432v1

Available results: W+2jetsCDF “bump”

ATLAS & D0 xchecks

S.Bolognesi (Johns Hopkins University)13

Control of V+jets

Improving theoretical tools (Blackhat, Madgraph, …)

Control region (eg, Z→jj sidebands) has very low stat for M(lljj)~1 TeV

• rely on them to extrapolate at higher energy/multiplicity

• test them where we have statistics


QCD measurement (jet pT>20-30 GeV):

→ syst. dominated by jet scale, PileUp removal

V+jets Data unfolded for detector effects → compared to NLO (“hadron level”)

ATLAS:

01/18/2012 seminar 15

V+jets at Tevatron

At low pT, low multiplicity:

but results limited by systematics

interesting discrepancy data-NLO observed

→ new variables

D0 novel measurement: angular correlations have much lower systematics


High mass: what’s new ?

Can we simply keep the same Higgs analysis strategy? Not at very high masses!

New experimental issues at very high mass (1 TeV and above)

X → boosted VV → jet merging (and nearby leptons)

Unknown signal and very small background → no point in pushed optimization! Keep model independent approach as much as possible

How to disentangle the various models?

• peak → mass and width, xsec and BR

• spin! → angular analysis


>1 TeV M(ZZ)→4f : jet merging (1)

Jet merging: DR 0.8 (CA) → MX>600 GeV

DR 0.5 (Akt) → MX>900 GeV

approx

Handles to distinguish wrt to jets from QCD (eg, X→ZZ→2l2j VS Z+jets):

jet massttbar → WW→ln (jj) CMS EXO-11-006

1

(1 )Z

qq TZ

MR

pz z

( | | / | |)q Zz p p


jet radiation:

soft/collinear singularity in QCDno singularity, just decay!

Jet merging (2)

by David Krohn (Harvard)JHU seminar: Path-Integral Jetswww.pha.jhu.edu/groups/particle-theory/seminars/talks/F11/talk.khron.pdf

Handles to distinguish wrt to jets from QCD (eg, X→ZZ→2l2j VS Z+jets):


Jet pruning Remove all parts of the jet which are soft and wide angle

Boosted objects mass reconstruction improved

QCD jets mass substantially decreased -> lower backgrounds

Typically used for boosted top or boosted H→bb …

arXiv:0912.0033v1


Example in X→ZZ→2l2jFirst look at Z boosted (no numbers yet) … • MG 1500 GeV

• RS Graviton

• CA 0.8preliminary, A.Bonato, R.Covarelli

X->ZZ->2l2q signal Z+jets

before jet pruning

after jet pruning

before jet pruning

after jet pruning


Angular analysis (1) X→ZZ→4f decay kinematic fully defined by 5 angles

signal (MX 250):

MC from

Johns Hopkins

0+ , 0-

1+ , 1-

2+m , 2+L , 2-

X→ZZ Z decays


Can be clearly used to disentangle different signals… but what about background?

Already used in H→ZZ→2l2q: cut on likelihood

• Z+jets from MC: no correlations,

To optimize further (multidimensional fit), need full theoretical description of background:

qq → ZZ:

gg also available → can be used to disentangle qq-gg!!

• signal: ideal × uncorr. accept

(background from jj sidebands)

Angular analysis (2)CMS PAS -11- 017


What’s next ?

higher mass

lower xsec


Improve sensitivity

Improve theoretical control of • signal: → NNLO&NNLL effects, precise mass shape prediction, signal-background interference (back-up)

• background: → control of ZZ, WW ewk continuum

Factor 5 in luminosity wrt to present results

WHY? Models with lower xsec

HOW?

Ex of (light) composite higgs:

(studied in the Higgs Xsec WG and documented in 2 Yellow Report)

First LHC to Terascale Workshop (Sept 2011):LCH at LHC by J.R. Espinoza


Diboson production (WW,WZ,ZZ)

SM test: TGC fixed by ewk gauge structure

→ any deviation from SM in VV xsec is direct hint of NP in bosonic sector

Backgrounds for high mass Higgs→VV

gg→ VV

(LHC: few % of xsec with ~50% uncertainty)

qqbar → VV

WW,WZ,ZZ forbidden for ZZ

+ NLO qqbar +

forbidden for ZW

TGC

LHC focused on leptonic final state, Tevatron looked at semileptonic but limited by systematics (V+jets)


VV: theoretical prediction

qq→ZZ NLO + gg→ZZ

Uncertainty dominated by QCD part

01/18/2012 seminar 27

PDF+as

scale

WW in jet bins: uncertainty on (s >=N) + modeling: MC@NLO vs ALPGEN

qq

qq

ZZ→4l: measurement 4l is 0.5% of ZZ xsec but very clean

1.51.2( ) 3.8 ( ) 0.2( )ZZ stat syst

0.2( )lumi pb

observed events: 8expected events: 12.5±1.1

Dedicated EWK analysis with very low luminosity, Higgs results much beyond that

39%

16%


WW->lnln: measurement


Dedicated EWK results only with very low luminosity,

Higgs analysis much beyond that:

stat. and syst. errors included

37%

First search for a VBF resonance, feasible in 2012

Measurement of VV scattering spectrum with higher lumi (>50 fb-1)

From VBF to VV scattering

Tipical signature: forward-backward “spectator” jets with very high energy

JHEP 0704 (2007) 052

VBF ggH + 2jets

VBF ggH + 2jets


Higgs-like resonance in VBF

Today only WW→lnln. Expectations for next year:

• lumi > 10 fb-1• s(vbf) ~ 0.1×s(gg)• 0.5 effic. VBF cuts

VBF yields in 2012 ~ 0.5 gg yields of 2011 summer results,

ZZ→4l will be still limited by statistics

WW→lnln will improve S/B (signal/10, WW*as2)

semileptonic final states will have reasonable signal yields + much lower background than inclusive analysis

eg, ZZ→lljj : • signal yields for mH 300-500 ~ 15 – 5 events• V+(N+1)jets/V+N jets ~ 0.15 → asking 2 jets reduces background to 2%!• S/B may increase of a factor 2 (eff 0.5 × s 0.1 / 0.02)

RE-DO all the analyses in VBF mode (eg, fermiophobic)


with much less background:

summer2011

VV scattering spectrum In no Higgs case:

BUT increasing of xsec at high VV is suppressed by

→ small difference btw SM and violation of unitarity (no Higgs)

→ with proper cut (eg Dh jets) can be enhanced -> selection of the longitudinal W

SILH

W±W± scattering

• PDF• offshell bosons• unpolarized bosons

2

2

2

2

2

1

HH mt

t

ms

sts

v

LLLL WWWWA

reducible background


Longitudinal polarization

ud->udWW->udcs ud->udWW->udcs

mH 500 GeV noHiggs (unitarity violation)

WW tail (TT): neutrino

WW tail (TT): lepton

Higgs peak (LL): neutrino

Higgs peak (LL): lepton

Transverse distribution

Longitudinal distribution

Angular analysis can boost LL-TT separation (new!):

partonic study in the center of mass of W


VV scattering: interference effects


...

2signal

irreducible background (aEW6)qq->6f O(aEW

6)

WW approximated without interference

Big interference effects considered only in PhantomJHEP 0603 (2006) 093

Accomando, Ballestrero, Bolognesi, Maina, Mariotti

=

WW signal with “a posteriori” cuts

Summary

experimental issue: control of V+jets (jet pruning) several theoretical uncertainties on VV EWK continuum

angular analysis

Ingredients along the EWSB road:

search for VBF resonance and measuring of VV scattering spectrum

search for generic resonance X->ZZ->4f

Main steps:

The first aim of the Higgs search is the understanding of the EWSB-> focus on H->VV final state


BACK-UP

18th January 2012Seminar at Johns Hopkins University

S.Bolognesi (Johns Hopkins University)

The road to the ElectroWeak Symmetry Breaking

Sources

First LHC to Terascale Workshop (Sept 2011):

LCH at LHC by J.R. Espinoza

CMS AN-2010-35: Angular Analysis of Resonances pp → X → ZZ

by David Krohn (Harvard)JHU seminar: Path-Integral Jetswww.pha.jhu.edu/groups/particle-theory/seminars/talks/F11/talk.khron.pdf

Boson Boson scattering analysis by A.Ballestrero (INFN Torino)

LHC To Terascale Physics WS S.Bolognesi (Johns Hopkins University)37

Mass shape From Passarino talk at last LHC to Terascale WS

Present approx:• xsec for on-shell Higgs production and decay in zero width approx

• acceptance from MC with ad-hoc BW distribution

10-30% uncertainty on xsecfor mH 400–600 GeV

Study with QFT-consistent Higgs propagator in the YR2

Higgs qTqT > mH NNLO

qT << mH NNLL (resumming ln(mH2/qT

2))

HqT:

Uncertainties: • factor/renorm scale

• PDF • large mt approximation

• non perturb. effects(smearing with NP form factor)


Reweight to HqT

Very small effect on acceptance in 4l: 1-2%

HqT used to reweight full event generators (POWHEG at NLO)

mH 120 GeV mH 500 GeVH pT

H ymH 120 GeV mH 500 GeV

Powheg

Powheg re-weighted to Hqt

HNNLO

(larger if jet veto!)


(to be redone before PS)

Signal: jet counting Analysis in exclusive jet bins

(ex, WW+0,1,2 jets)

• if background depends on Njets• for VBF

→ theoretical uncert in jet bins to be combined with correlations

varying renormalization and factorization scales in the fixed-order predictions for each exclusive jet cross section σN

(results as 100% correlated)

different treatments of the uncontrolled higher-order O(α3s) terms

i.e., different NNLO expansions

inclusive xsec (σ≥Njets), as source of perturbative uncertainties

σN = σ≥N − σ≥N+1

with error propagation


Signal: jet veto Resummation of jet-veto logarithms ( ln(pcut/mH) ), induced by jet cut parameter pcut

direct exclusive prediction

from inclusive to exclusive prediction


Presently doable only on beam thrust variable (~raw approx of pcut)

and used to reweight MC@NLO

Signal-background interference Recent results for WW, but focused on low mass

Effect on gg→H→WW at LO

mT < mH

( arXiv:1107.5569v1 )

non-resonant diagrams can be large for mT > mH

Worth to investigate further at high mass?

also shape effects!


ZZ: theoretical prediction Single resonant contribution

qq→ZZ NLO + gg→ZZ

ZZ fully from MC, well under control

Interference in the final state with identical leptons


ZZ: t

heor

etica

l unc

erta

intie

s PDF+as

scale

qq gg

qq gg

01/1

8/20

12 s

emin

arS.

Bolo

gnes

i (Jo

hns

Hop

kins

Uni

vers

ity)

45

WW: theoretical uncertainties

WW taken from MC for large mH

→ gg+qq NLO available (MCFM)

WW from control region for mH<200 GeV (mll, Dfll)

in jet bins using uncert on (s >=N) + modeling: MC@NLO vs ALPGEN

PDF+as and scale uncertainty dominates


WW→lnln measurement

Background Cuts

Complex analysis (no mass peak→counting experiment, many backgrounds)

background estimate:

signal acceptance:

leptonic efficiency

jet-veto efficiency

missing ET uncertainty

theoretical (gg box, PDF)

W+jets tight lepton quality

top (b-)jet veto

Drell-Yan Z mass vetomissing ET

WZ, ZZ, Wg 2 leptonsestim

ated from

data→ estimated from MC


Main systematics:

50100150200

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eV/c

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)-1Data (3.9 fbWW/WZW/Z+jetsQCDTop

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)2 (GeV/cjjM50100150200

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100

200 (b)

WW/WZ→ln2j at CDF First observation: 5.4s (first evidence at D0 with 4.4s in 2008)

Much larger backgrounds, no resolution to distinguish W/Z→jj

fit to Mjj (3.9 fb-1) + matrix element method: (2.7 fb-1)

• discriminant exploiting full kinematic information, based on calculations of differential xsec of signal and background

QCD from data

• data-MC validation of input kinematic variables

• fit to shape of discriminant

(NLO expected )16.1 0.9pb( ) 16.0 3.3( )WW WZ stat syst pb

Sara Bolognesi (CERN) Physics in Collisions, August 201148

WZ/ZZ→l / +n nn 2b at Tevatron

• WZ → lnbb + ZZ → nnbb b-tag jets + missing ET (+ topological cuts)

Crucial for Higgs search (ZH→nnbb). Very complex analysis!

• No leptons! → huge background: multijets QCD, V+jets (from data)• very sophisticated techniques: b-tag probability with Boosted Decision Tree or Neural

Network which exploits much info and different variables

different channels combined (0,1,2 b-tag)CDF (2b-tags)

3.63.0( , ) 5.8WZ ZZ pb

( , ) 6.9 1.3( ) 1.8( )WZ ZZ stat syst pb D0:

CDF: (expected 4.6 pb)

(expected 5.1 pb)


ZZ→2l2n (5.9 fb-1)Shape analysis with fit to neural network

ZZ at CDF ZZ→4l (6 fb-1) excess of events at high MZZ (eg Randall Sundrum Graviton)

• But xsec still compatible with SM

• No excess in other final states

ZZ→2l2j

Control of Z+jets very challenging to measure ZZ xsec

control of Z+jets is crucial

Sara Bolognesi (CERN) 50

(NLO expected )

WZ→3l+n at LHC Very clean, low background

( ) 17.0 2.4( )WZ stat 1.1( ) 1.0( )syst lumi pb (NLO expected )

3.1 0.92.8 0.8( ) 21.1 ( ) 1.2( ) ( )WZ stat syst lumi pb

CMS:

ATLAS:

1.20.817.2 pb


1.10.818.75 pb

(NLO expected )

Recent WZ→3l+n at Tevatron

D0 with 4.1 fb-1

Possible only at hadron colliders (charged final state)

statistics 2 times smaller than LHC, while xsec is 6 times smaller

Shape analysis with fit to neural network

3.25 0.19pb

1.060.90( ) 3.90WZ pb

(NLO expected )

CDF with 7.1 fb-1

0.6 0.60.5 0.4( ) 3.9 ( ) ( )WZ stat syst pb 3.46 0.21pb


observed events: 34

expected signal: 23.3±1.5

expected background: 6.0±0.6

V+jets: ratios

Very well known theoretically → any deviation is hint of NP

Use high statistics W sample to predict Z+jets background for NP

CMS PAS EWK-10-011

Many systematics cancel out


Z+b jets

• b-tagging with Secondary Vertex requirement or more sophisticated (eg Neural Network in D0)

• b-tag eff. measured separately from data• b-tag purity extracted from data (eg SV mass fit)

PDF of b quarks

fixed flavor scheme b only from gluon splitting

variable flavor schemegluon splitting integrated into the PDF

Benchmark for MSSM Higgs: fbbbar (large theoretical uncertainty on xsec)

Background to ZH(H→bbar), NP search with lept+b-jets

b-jets analysis:

(expected to coincide at NLO)

measurement of Z+b / Z+jets to cancel other (non-btag) systematics

Sara Bolognesi (CERN) 54)2Secondary vertex mass (GeV/c

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5

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ents

/ ( 0

.167

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/c

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Datab-jetsc-jetsl-jets

-1 = 7 TeV, L = 36 pbs

CMS Preliminary

High efficiency b-tagging


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CMS Preliminary

High purity b-tagging

(GeV/c)b-leadT

p50 100 150 200 250

Even

ts/2

0GeV

/c

0

5

10

15

20

25

30

Datatt

Z+bZ+cZ+l

-1 = 7 TeV, L = 36 pbsCMS Preliminary

High Purity b-tagging

(Z,b-lead)0 0.5 1 1.5 2 2.5 3

Even

ts/0

.2

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p50 100 150 200 250

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0GeV

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(Z,b-lead)0 0.5 1 1.5 2 2.5 3

Even

ts/0

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10

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Z+jets



Z+b results

(corrected for geometrical acceptance)

CDF (7.86 fb-1)

D0 (4.2 fb-1)NLO (mZ

2) 0.0192 +/- 0.0022

CMS

(fixed flavor)(variable flavor)

Similar results for muons

No statistical power yet to disentangle fixed VS variable flavor scheme

variable schemafixed

schema

0.9 data/MC b-tag eff.

b-tag eff. corrected results:


TO BE UPDATED soon with 1fb-1 → much better precision!

SSVHED-6 -4 -2 0 2 4 6

num

ber o

f eve

nts/

0.24

0

10

20

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40

50

60

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90

Data

+charm+W

+light+W

top

Other bckg.

CMS preliminary

= 7 TeVs at-136 pb

SSVHED-6 -4 -2 0 2 4 6

num

ber o

f eve

nts/

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20

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40

50

60

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80

90

Data

+charm-W

+light-W

top

Other bckg.

CMS preliminary

= 7 TeVs at-136 pb

[GeV]TM60 80 100 120 140 160

num

ber o

f eve

nts/

2 Ge

V

0

200

400

600

800

1000

1200

Data

+charm+W

+light+W

top

Other bckg.

CMS preliminary

= 7 TeVs at-136 pb

[GeV]TM60 80 100 120 140 160

num

ber o

f eve

nts/

2 Ge

V

0

100

200

300

400

500

600

700

800

900

1000

Data

+charm-W

+light-W

top

Other bckg.

CMS preliminary

= 7 TeVs at-136 pbW+c Dominated by sg→Wc• dg→Wc Cabibbo suppressed• W+b even more suppressed

LHC: W+c ~ 10% W+jets (W+b negligible)

→ Wcbar (Wc) measures the sbar (s) PDF

MC predictions fit

lifetime-tagging

CMS (unexpected! just a first go):

Tevatron: W+c ~ 5% W+jets

semileptonic charm decay + opposite charge W and c

CDF (4.3 fb-1):

(NLO calculation )

( ) ( ) 33.7 11.4( ) 4.7( )Wc BR W l stat syst pb

16.5 4.7 pb


Documents

The road to the ElectroWeak Symmetry Breaking