prospects for vv scattering : latest news

Prospects for VV scattering: latest news

S.Bolognesi (Johns Hopkins University)on behalf of CMS and ATLAS

Implications of LHC results for TeV-Scale physics – CERN, March 2012

Same behavior for all VV amplitudes

without Higgs, W+LW-

L->W+LW-

L would break unitarity

V

V V

V

VV -> VV

V

VV scattering is the smoking gun of the EWSB !

2Implication of LHC results for TeV-Scale physics S.Bolognesi (JHU)€

1v 2 −s − t +

s2

s −mH2 +

t 2

t −mH2

⎛ ⎝ ⎜

⎞ ⎠ ⎟

LLLL WWWWA

2

2

2

2

2

1

HHLLLL mt

tmssts

vWWWWA

S channel T channel QGC

W,Z mass (-> longitudinal degrees of freedom) arise from the Higgs mechanism:

VV scattering: unitarity violation

LSB<1TeVSB sector weakly coupled

SB sector strongly coupled

eg, strongly interacting light Higgs

SM No-HiggsLSB>1TeVUnitarity violation

other scenarios possible:

VV scattering spectrum s(VV->VV) vs M(VV) is the fundamental probe to test nature of Higgs boson or to find alternative EWSB mechanism

VV scattering as probe for EWSB

3Implication of LHC results for TeV-Scale physics S.Bolognesi (JHU)

talk at First LHC to Terascale Workshop (Sept 2011):Personal adaptation from “Boson Boson scattering analysis” by A.Ballestrero (INFN Torino)

Experimental signature

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

JHEP 0704 (2007) 052

ggH + 2jets ggH + 2jets


VV scattering in real life (1) In no Higgs case: 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

• PDF• offshell bosons• unpolarized bosons

SILH


W±W± W±W±

PHANTOM MC PHANTOM MC

talk

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Longitudinal vs Transversal

mH 500 GeVnoHiggs (unitarity violation)

WW tail (TT): neutrino WW tail (TT): lepton

Higgs peak (LL): neutrino Higgs peak (LL): lepton

Transverse distributionLongitudinal distribution

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

partonic study in the center of mass of W


VV scattering in real life (2)

WW approximated without interference

JHEP 0603 (2006) 093

WW signal with “a posteriori” cuts

...2signal

irreducible background (aEW6)


hep-ph/0505225v1

Outline Review of theoretical tools

Experimental status: no new results but similar issues under study in other analyses

(short!) historical review and comparison with recent results for similar final states: graviton and higgs searches at high mass

• fully leptonic• semi-leptonic: V+jets control

jet merging for high pt V->jj

tag jets and central jet veto• VBF Higgs search• Z VBF analysis• first (QCD) measurements of FWD jets and jet veto


Theoretical toolsVarious complementary MC

• PHANTOM qq->6f @ aEW6 + aEW

4 × aS2

LO, full description of irreducible background with correct interference

• VBF@NLO

QCD+EW NLO for VBF Higgs production

• HAWK

• POWHEG

• LO ME MC + PS (Madgraph, Pythia, Herwig)


QCD NLO for VV scattering

QCD+EW NLO for VBF+HiggsStralung Higgs production

QCD NLO for VBF+HiggsStralung + PS matching

ratio btw scales

hep-ph/0701105v2

Any news from experiments?

higher mass

higher sensitivity

BSM search for VV resonance @ 1 TeV(DY production)

VBF dedicated search

No dedicated analysis yet (low lumi) -> but arriving to VV scattering in 2 ways

-> studying same final states as VV scattering


-> characterization of tag jets signature

HIG-12-008

low statistics

MET control V+jetsZZ→4l ZZ→llnn Search for G→ZZ: same features discussed for high mass Higgs

ZZ→lljj: large V+jets

Graviton->ZZ search


CMS is working on

ZZ->2l2j (angular analysis)

ZZ->2l 1j (jet merging)

ZZ→4l ZZ→lljj

hep-

ex a

rXiv

:120

3.07

18Ph

ys. R

ev. D

83, 1

1200

8 (2

011)

VV scattering: fully leptonicOnly background VV+jets, very low xsec

B~ 80S~ 200

Latest results:B~ 6S~ 10

Number of events for 20 fb-1 (fully MC based, no systematics, 14 TeV)

500 GeV

>1 TeV

2.2

0.1

1.9

0.2

CMS ZZ->4e, 4m

6.4 3.0

ATLAS ZZ->2l2n

>1 TeV 0.9 0.8

CMS ZW->mmmv 500 GeV 8 5

ATLAS ZW->lllv

1.1 TeV 1.4 0.4

• reso m(ll) as expected• improved reco-id efficiencies(eg ele ID: TDR time 85-90% -> today 95%)


N sign. N back.

14 TeV, 30 fb-1

500 GeV

N sign. N back.

N sign. N back.

N sign. N back.

Example: ggF Higgs 300 GeV

CERN-OPEN-2008-020

hep-ex arXiv:1202.1415

CMS

AN 2

007-

005

CERN

-OPE

N-2

008-

020

VV scattering: semileptonicSemileptonic is most promising: reasonable signal yield

Number of events for 20 fb-1 (fully MC based, no systematics, 14 TeV)

• more sophisticated analysis developed(btag categories, angular analyses, m(jj)=mZ kinematic fit)

• data driven background

Improved JES: mjj reso from 20-25% to 10-15% !

WV -> lnjjZV -> lljj

ATLAS

500 GeV

800 GeV

1.1 TeV

6.2

13

4.8

16

17

9.2

CMS

500 GeV

>1 TeV

337

45

20759

3281

Implication of LHC results for TeV-Scale physics S.Bolognesi (JHU)

N sign. N back. N sign. N back. CMS

500 GeV

>1 TeV

62

5

3415

348

N sign. N back.

For recent inclusive Higgs search: Z->jj mass forH->ZZ->2l2q

13

HIG-11-027

CERN

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N-2

008-

020

CMS

AN 2

007-

005

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• test them where we have statistics

-> Angular analysis to boost sensitivity -> angular correlations in Z+jets !!

Implication of LHC results for TeV-Scale physics S.Bolognesi (JHU) 14

PRL

106,

1718

01 (2

011)

V+jets measurements QCD measurement (jet pT>20-30 GeV):

syst. dominated by jet scale + PileUp removal, but good status at LHC

→ Tevatron: angular variables

D0 novel measurement: angular correlations have much lower systematics

-> LHC: very high statistics even at high multiplicity -> differential distributions

Implication of LHC results for TeV-Scale physics 15

hep-

ex a

rXiv

:120

1.12

76

X->ZZ->2l2q signal

Z+jets

Jet merging

DR 0.8 (CA) → MX>600 GeVDR 0.5 (Akt) → MX>900 GeV

approx

1(1 )

Zqq T

Z

MRpz z

D

( | | / | |)q Zz p p

Issue under study for EXO searches (boosted top, gravitons) WW scattering

(1.1 TeV resonance) @14 TeV

AkT 0.6

jet mass

jet radiation (sub-jet structure) -> pruning

Handles to distinguish V->j wrt to jets from QCD (Z+jets):


ww

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oups

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Any news from experiments?

higher mass

higher sensitivity

BSM search for VV resonance @ 1 TeV(DY production)

VBF dedicated search

No dedicated analysis yet (low lumi) -> but arriving to VV scattering in 2 ways

-> studying same final states as VV scattering


-> characterization of tag jets signature

HIG-12-008

WHY? Ex of (light) composite higgs:

Fermiophobic-like

“State of the art”

• NO dedicated VBF analysis yet for ZZ !!

• gg at low mass, WW at high mass


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t LHC

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HIG-12-008 HIG-12-008

First look at tag jets

control of VV background in jet-multiplicity bins

Z prodution in VBF: a candle for jet tagging and jet veto efficiency?

MC tools to describe FWD jets and gap events -> related with description of UE, MPI and QCD at wide angle

Starting to face issues related with tag jets topology and jet vetoing -> very relevant for VV scattering:

-> theoretical systematics (no control regions for ZZ, WW at high mass)

-> (after feasibility) real data analysis ongoing

-> many useful measurements can be done NOW to constraint FWD jets modeling


-> TO BE REVIEWED THIS YEAR WITH MUCH HIGHER PU

FWD jet

FWD jet

no color flow -> jet veto

19

WW backgr. in jet multiplicity bins

Uncertainty from MC@NLO scale variation (2nd jet from PS) + ALPGEN comparison

Exclusive computation have huge errors due to higher pertubative orders different treatments of

the uncontrolled higher-order O(α3

s) terms

i.e., different NNLO expansions

ex for H signal:

Inclusive xsec (σ≥Njets), as source of perturbative uncertainties-> uncert. on σN = σ≥N − σ≥N+1

with error propagation

Acceptance evaluated in each exclusive jet bin (uncert~5%) + PDF uncertainty (~2%)


Higg

s xse

c W

G: h

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Xiv:

1201

.308

4

Z in VBF as a candle? VBF Z production as reference: feasibility study at parton-level @ 10 TeV

Z+qq (4 pb) :

signal (~5%) isolated “a posteriori” with partonic cuts

-> 2700 events @ 15 fb-1

irreducible background

-> 45% eff for VBF-specific cuts

S/B improved of a factor 100: 600/78k events @ 15 fb-1 (S/sqrt(B)~ 2)

• Observation feasible but to use as reference need high lumi and to know Z+jets with high precision• Central jet veto suppress only 10% of Z+jets (~useless!)


-> 23% tighter cuts against Z+jets QCD (2700 pb)

21

hep-

ex a

rXiv

:100

1.43

57

Jet veto 3rd jet not well modeled by PS, central veto De btw Pythia and Herwig ~ 40%

-> POWHEG NLO: remaining uncertainty ~%

Check with dijet events + rapidity gap (in low PU)(at large pTjet/pTveto or Dy -> fixed order fails)• NP effects<2% (pTveto > LQCD)• HEJ all-order resummation for wide-angle emissions of similar pT-> fails for pT jet>>pTveto

• POWHEG+Pythia good agreement with data-> differences btw Herwig and Pythia


Similar study in ttbar events !

Higgs xsec WG: hep-ex arXiv:1201.3084



FWD jets modeling

useful also to commission our detector -> especially in view of PU

FWD jet spectrum (|h|3.2-4.7) with low PU events

NLO+NP and Powheg+Pythiacatch the dependence, not the xsec

Herwig does a better job than pythiaPythia Z2 tuned to LHC UE

Non-perturbative effects:• energy lost from jets due to hadronisation • energy added to jets from UE


central + forward jet

hep-

ex a

rXiv

:120

2.07

04

Summary

Start studying VV-scattering related issues in different frameworks:

• high mass general X->VV search (Higgs SM or BSM, eg graviton)

• tag jets and jet veto

improve V+jets control

understanding VV in jet multiplicites

studying jet merging

exercising the reconstruction and identification of same final states

testing FWD jets modeling and jet vetoing in data


BACK-UP:

prospects for VV scattering: latest news

S.Bolognesi (Johns Hopkins University)on behalf of CMS and ATLAS

Implications of LHC results for TeV-Scale physics – CERN, March 2012

Di-boson backgroundqq→ZZ NLO + gg→ZZ

PDF+as

scale

qq

qq

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+1with error propagation

LHC To Terascale Physics WS S.Bolognesi (Johns Hopkins University)41

WW same sign

10 TeV 60 fb-1

Final state with largest effects from unitarity violation


10 TeV 60 fb-1

15

Eur.P

hys.

J.C71

:151

4,20

11.

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

RE-DO all the analyses in VBF mode

with much less background:

summer2011


HIG-11-011

Looking forward to VV scattering

V+jets control

fully leptonics: much lower stat, much cleaner

Same issues (as Higgs search and) as expected in VV scattering search

semileptonic: larger yields, huge background

high VV mass -> boosted V -> jet merging

uncertainty on VV+2j production


first look at fully hadronic final state ongoing

SUSY-like discriminators (eg, Razor)

14 TeV, 60 fb-1qqmmmm

14 TeV, 60 fb-1qqqqmm

Historical references

CMS model independent-approach


Higgs resonance @ 500 GeV

ATLAS Chiral Lagrangian with Pade’ unitarization

-> higher xsec with resonance peak

14 TeV !!!!

CMS AN 2007-005

CERN-OPEN-2008-020

most conservative scenario: SM with no Higgs (mH->inf)

xsec ~ 100 fb


VBF H->WW->lnjj(electron channel)

H->ZZ->lljj

VBF 14 TeV vs recent inclusive results

Comparing to recent

results

14 TeV, 60 fb-1

B~ 2000S~ 300

14 TeV, 60 fb-1(muon channel)

B~ 5000S~ 80

ggF (2btag)B~ 20S~ 8

B~ 20S~ 2

14

HIG-11-027

ATLAS-CONF-2012-018

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

• MG 1500 GeV

• RS Graviton

• CA 0.8

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


prospects for vv scattering : latest news

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