Search for Heavy Resonances Decaying to Bosons with the ATLAS and CMS Detectors

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Search for Heavy Resonances Decaying to Bosons

with the ATLAS and CMS Detectors

Francesco Santanastasio

(Sapienza, University of Rome and INFN)

On behalf of the ATLAS and CMS Collaborations ICHEP 2014, July 4 th - Valencia

7/4/14 Francesco Santanastasio (CERN) 1

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New Physics at LHC

•  Many theories of new physics beyond the Standard Model

•  One of the most direct ways to find new physics at TeV scale is to search for new resonances

Number of Events

Invariant Mass

Courtesy of Hitoshi Murayama

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Discovery of Resonances in Hadron Collisions

•  In early 60s, the energy of hadron collisions increased to √s ~ few GeV  new resonances appeared!

•  Known properties of π s and Ks (mass, decays, quantum numbers) were exploited to study these new particles

1961: ρ (770) ππ 1961: K*(892)K π

and many more after…

1961: φ (1020)KK

PhysRevLett.6.628 PhysRevLett.6.300

PhysRevLett.9.180

A classic example:

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Diboson Final State

•  Theories of new physics predict existence of

resonances with a mass of ~ TeV that decay to pairs of massive bosons

•  Clear experimental signature

–  Known properties and decay kinematics

•  In case a new resonance is discovered, possible to

measure its properties from the angular distributions of the decay products

New resonance

V / H

M

_W

~ 80.3 GeV Mz ~ 91.2 GeV M

_H

~ 125 GeV Wqq ~ 67% Zqq ~ 70% Hbb ~ 57%

W lν ~ 33% Zνν ~ 20% HWW ~ 21%

HZZ ~ 2.5%

Z ll ~ 10% H ττ ∼ 6%

H γγ ~ 0.2%

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Exotica Diboson Searches at 8 TeV LHC

Final State Note Number Presented in

l / γ

WZ  lνll ATLAS arXiv:1406.4456 This talk

WZ  lνll CMS-EXO-12-025 This talk

HH/ZHmulti-lept.

and/or diphotons CMS-HIG-13-025

O. Bondu’s talk (Jul 5, Higgs session)

γγ (high mass) CMS-HIG-14-006

M. Kenzie’s talk (Jul 3, Higgs ses.)

W γ  lνγ / Z γ  llγ ATLAS – to be submitted

to PLB

K. Terashi’s talk (Jul 4, this ses. )

l / γ + Jets

WV  lν + V-jet CMS arXiv:1405.3447 This talk ZV  ll + V-jet CMS arXiv:1405.3447 This talk ZV  ll + jj or V-jet ATLAS-CONF-2014-039 This talk

HH  γγ + bb CMS-HIG-13-032

O. Bondu’s talk (Jul 5, Higgs session)

HH  γγ + bb ATLAS arXiv:1406.5053 This talk

Jets HH  4b ATLAS-CONF-2014-005 This talk VV  V-jet + V-jet CMS arXiv:1405.1994 This talk

NEW Updated

⌘ Order of presentation: from low-mass to high-mass sensitivity ⌘

NEW NEW NEW

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•  Standard H γγ sel. + 2 b-jets

–  |m

_γγ

-m

_H

|<2 σ

_m

& 95<m

_jj

<135 GeV

–  |m

_γγbb

-M

_X

|< optimized cut, M

_X

dependent

•  Counting experiment

–  Background estimated from m

_γγ

sideband and events with <2 b-jets

•  Results

–  Broad excess in m

_γγbb

distribution

–  Not confirmed by CMS-HIG-13-032 result

ATLAS

HH  γγ bb NEW

drawing More details on HH γγ bb searches in:

- ATLAS: S.Laplace & M. Neubauer’s talk (Jul 3-5, Higgs session) - CMS: O. Bondu’s talk (Jul 5, Higgs session)

A TLAS arXiv:1406.5053

H

H X

γ γ b

b

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HH  4b

•  Event selection

–  4 b-jets

–  2 dijets with M

_jj

~M

_H

–  ttbar veto

•  Multijet background (from data)

–  2-btag  4-btag extrapolation

–  Validation in signal-depleted sidebands

•  M 4b resolution ~15% at 1 TeV

•  No excess in data above SM prediction

A TLAS-CONF-2014-005

H

H X

b b b b

Sideband

HH HZ ZH ZZ

Control

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W`  WZ  l ν ll

•  Fully leptonic final state

–  4 channels: e νµµ , e ν ee, µν ee, µνµµ

–  Irreducible Background from MC  non -resonant WZ production

–  Low BR (~1.5%)  low signal yield

•  Analysis Strategy

–  Search for bump in M

_WZ

spectrum –  Neutrino p

_z

from W mass constraint –  Only one neutrino  acceptable mass

resolution (~10% at 1 TeV)

ATLAS arXiv:1406.4456 CMS-EXO-12-025

l

ν

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W`  WZ  l ν ll - Limits

•  Put constraints on various models

–  Sequential SM, Heavy Vector Triplet, Technicolor

•  Comparable sensitivity for ATLAS and CMS

CMS-EXO-12-025

W`

_SSM

W`

_SSM

ATLAS arXiv:1406.4456

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WV / ZV

Final States with Jets

•  Physics observable: invariant mass of diboson system

•  Signal over background changes depending on the channel

l ν

q q X

W

W/Z

l l

q q X

Z

W/Z

q q

q q X

W/Z

Signal (BR) Background

Signal from VV resonance Background from

SM processes

(data-driven methods)

Typical mass scale >=1 TeV

~20%

~45%

~3% 1X

5X

30-50X

Number of Events

Invariant Mass of VV system

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Boosted V Topology

•  Low p T boson

–  Large opening angle

•  Energetic boson

–  M resonance = 2 TeV –  p T,V ~ 1 TeV

–  M V ~ 100 GeV

V

€

Δ R qq min ≈ 0.2

quark

anti-quark

V Y

Δ R ~ 0.2

€

Δ R qq min ≈ Δ θ qq min ≈ 2 M V p T , V

Vqq decay:

Jet Merging

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Jet Substructure

•  1) Jet trimming, pruning, filtering, …

–  Remove soft component of jet, reducing effects of pileup and UE

•  2) Substructure variables

–  Built from subjets after jet declustering m

_jet

~ m

_q

~ 0

BACKGROUND m

_jet

~ m

_W

~ 80 GeV +

Dipolar structure

SIGNAL

Jet mass N-subjettiness τ

_N

(topological

compatibility with N subjets)

CMS arXiv:1405.1994 ATLAS-CONF-2014-039 CMS arXiv:1405.1994

Momentum Balance

Plenty of alternatives at CMS-JME-13-006 and ATL-PHYS-PUB-2014-004

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ZV  ll+qq

•  Resolved low-p

_T

region

–  2 jets , p

_T^V

>100 GeV

•  Resolved high-p

_T

region

–  2 jets , p

_T^V

>250 GeV

•  Merged region

–  1 V-jet , p

_T^V

>400 GeV –  Use jet substructure

•  Z+jets Background –  MC shape/norm.

corrected using data events in jet mass sideband

•  No significant excess in data above SM prediction

ATLAS NEW

ATLAS-CONF-2014-039

Signal Efficiency

m

_ZV

spectra:

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CMS VV Searches

- V+jets background from jet mass sideband in data -  ttbar and VV from corrected simulation

-  m

_VV

resolution ~3-6%

-  Background from fit to data with smoothly falling function -  m

_VV

resolution ~5%

CMS arXiv:1405.3447 CMS arXiv:1405.1994

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Combined Limits:

G bulk WW/ZZ

Combination assuming BRs and efficiencies of narrow bulk graviton model Largest excess at M~1.8 TeV (<1.5 σ)

CMS arXiv:1405.3447

Bulk graviton (arXiv:hep-ph/

0701186)

CMS NEW

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Comparison of G bulk Limits

HH  4b WWl ν +V-jet

ZZll+V-jet

CMS arXiv:1405.3447

k/M

_pl

=1.0 ( Γ /M~5%)

Caveat: approximate comparison since the resonance width increases with (k/M

_Pl

)

²

, while this CMS limit plot is strictly valid only for a narrow G

_bulk

(see next slide for analysis extension)

WW2 V-jets ZZ2 V-jets +

k/M_pl=1.0

ZZll+qq

ATLAS NEW

ATLAS

CMS

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CMS VV Searches -

Model Independent Interpretation

•  Interpret results for a generic XVV resonance model

–  Narrow/Wide resonances

–  Different charge/spin hypotheses –  Different V polarization

•  1) Generate events for a generic resonance model

•  2) Apply acceptance cuts of the analysis at generator level

•  3) Reweight events using V tagging efficiency tables

•  4) Test model by comparing

expected signal yield with upper limits on number of signal events in M X vs Γ /M plane

Reconstruction efficiencies: Ex. Wqq

Upper limits on N

_signal

(l ν + V-jet)

Gen. | η

V

|

Gen. p

_T,V

Γ /M=40%

Γ /M<1%

50 250

CMS arXiv:1405.3447

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Conclusion

•  Search for heavy

resonances is one of the most direct ways to find new physics at TeV scale

•  Diboson final state provides clear

experimental signature and allows cross check among different channels

•  No significant excess observed in data

•  Several searches not yet done  more to come at 8 TeV in next few months…

W‐>lv W‐>qq Z‐>ll Z‐>vv Z‐>qq H‐>γγ H‐>ττ H‐>bb

W‐>lv 7TeV 8TeV 8TeV 8TeV

W‐>qq 8TeV 8TeV 7TeV 8TeV

Z‐>ll 8TeV

Z‐>vv 7TeV

Z‐>qq 8TeV

H‐>γγ 8TeV

H‐>ττ

H‐>bb 8TeV

CMS ATLAS Dedicated Exotica “Bump” Searches (excluding HiggsVV searches)

ZH / WH VV

HH

⌘ Large increase in sensitivity at √s=13 TeV!!

⌘ Jet substructure will become more important

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BACKUP SLIDES

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Search at High Energy

2010 2013 2015

STOP1

Run1 Run2

2017 2019 2022-23

STOP2 Run3 High-Luminosity LHC (HL-LHC)

2030

…

7/8 TeV 13-14 TeV

20 fb

^-1

~100 fb

^-1

~200 fb

^-1

3000 fb

^-1

2 TeV resonance

•  The LHC will run at its design energy of 13-14 TeV starting from 2015

•  Large potential for discoveries of new heavy particles at LHC in the next few years

signal cross section

~10 times larger

Caveat: approximate luminosity/period estimates

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Event Displays

X  VV  V-jet + V-jet? X  HH 4b?

M

_4b

= 834 GeV

M

_4b

~ 2150 GeV

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HH  γγ bb - CMS

•  Standard cut-based H γγ reconstruction

•  Two categories: 1 or 2 b-jets p

_T

>25 GeV

•  Kinematic fit to improve m

_γγ_bb

resolution

•  Low-mass analysis (260 < m

_X

< 400 GeV)

–  Require m

_jj

~m

_H

and m

_γγbb

~m

_X

–  Bump search in m

_γγ

distribution

•  High-mass analysis (400 < m

_X

< 1100 GeV)

–  Require m

_γγ

and m

_jj

compatible with m

_H

–  Fit to m

_γγbb

distribution

drawing

Compare with ATLAS after dividing CMS limit by BR(HH γγ bb) mX = 300 GeV

selection

CMS-HIG-13-032 A TLAS arXiv:1406.5053

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HH  4b

•  Event selection

–  4 b-jets: p

_T

>40 GeV, | η |<2.5

–  2 dijets: Δ R<1.5, pT

_dijet

>200 GeV

–  ttbar veto (reconstructed m

_W

and m

_top

)

H

H X

b b b b

•  m jj used to define signal,

sideband, and control regions

•  Exclude HZ and ZZ regions

Efficiency drop above 1 TeV  jet merging

Sideband

HH HZ ZH ZZ

Control

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WZ  l ν ll

Coupling to fermions NEW

Coupling to H / W / Z

Model A = weakly coupled model from SM extension Model B = strongly coupled model (composite Higgs)

Ex. Heavy Vector Triplet, use phenomenological Lagrangian defined at arXiv:1402.4431

W`

_SSM

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XZV searches (ll + V-jet)

HP ( τ

₂₁

<=0.5) LP (0.5< τ

₂₁

<0.75)

e µ

CMS arXiv:1405.3447

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XWV searches (l ν + V-jet)

HP ( τ

₂₁

<=0.5) LP (0.5< τ

₂₁

<0.75)

e µ

CMS arXiv:1405.3447

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XVq searches (V-jet + jet)

HP ( τ

₂₁

<=0.5)

LP (0.5< τ

₂₁

<0.75)

q

q*Wq q*Zq

CMS arXiv:1405.1994

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XVV searches (V-jet + V-jet)

HP ( τ

₂₁

<=0.5)

LP (0.5< τ

₂₁

<0.75)

Bulk Graviton RS1 Graviton

W’WZ

CMS arXiv:1405.1994

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Background Estimation (example: WVl ν +V-jet)

•  V+jets background from data in signal-free control region

•  VV and top background from simulation (corrected)

Sideband region (SB) : m

_jet

[40,65] GeV Signal region (SIG) : m

_jet

[65,105] GeV

2) α Function (W+jet MC) 3) Bkg prediction in SIG 1) Data in SB

€

α = N

_SIG^MC^−Wjets

N

_SB^MC^−Wjets

CMS arXiv:1405.3447

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V-tag efficiencies - Zll , Zqq

CMS arXiv:1405.3447

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V-tag efficiencies - Wl ν , Wqq

CMS arXiv:1405.3447

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Model Independent Limits

CMS arXiv:1405.3447

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Comparison of ZZllqq searches

•  Comparable sensitivity

k/M_pl=1.0

NEW

k/M

_pl

=1.0 ( Γ /M~5%)

Caveat: approximate comparison since the resonance width increases with (k/M

_Pl

)

²

. The ATLAS plot is done for a resonance with Γ /M ~5% (k/m=1) while the CMS limit plot is strictly valid only for a narrow G

_bulk

(<1%).

Still mass resolution is of the order of 5% for both searches  so the comparison is meaningful

ATLAS goes below 600 GeV thanks to

resolved 2 jets topology

CMS arXiv:1405.3447

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W’WZ limits

W`

_SSM

lvll llqq

W`

_SSM

ATLAS-CONF-2014-039

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Composite Higgs

•  Possible answer: The Higgs boson is a bound state of a new strong dynamics at the TeV scale

•  The new strong sector includes composite states:

–  the Higgs boson (h), the vector bosons (W

_L

and Z

_L

) –  NEW spin-1 resonances decaying to h, W

_L

, and Z

_L

•  New spectroscopy at LHC in diboson final state

A naive

example, QCD:

π

⁺

, π

^-

, π

⁰

ρ

⁺

, ρ

^-

 π

^+/^-

π

⁰

ρ

⁰

 π

⁺

π

^-

h, W

_L

, Z

_L

ρ ’

⁺

, ρ ’

^-

 W

_L

h, WZ

ρ ’

⁰

 W

_L

W

_L

, Z

_L

h

New strong sector:

π , ρ of QCD are composite

states of quarks

Roberto Contino, et al.:

JHEP 05 (2007) 074 [1]

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Extra Dimensions

Why ElectroWeak (10 2 GeV) and Gravity (10 19 GeV) scales are so different?

•  We live in a warped 5-dimension universe (Randall-Sundrum [RS] model, 1999)

•  Gravity propagates in extra dimension

•  Gravity is weak from “4D point of view”

Bulk Graviton

Ref. : Phys. Rev. D 76, 036006 (2007) [5]

•  Extension of original RS model

•  Also justifies fermion masses

•  Predicts neutral spin-2 resonances (gravitons)

Graviton wave function

TeV brane Planck brane

Bulk Graviton (G) decay G  qq/ggdijets

G  γγ G  l

⁺

l

^-

G  ttbar G  hh

G  WW/ZZ

Suppressed decays

Enhanced decays

Another interest for the diboson final state:

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W-jet Control Sample

•  Use known process to calibrate and test algorithms

 W bosons from top pair production

•  The W mass is well reconstructed

•  Substructure variables are well modeled

CMS-JME-13-006 A TL-PHYS-PUB-2014-004

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Jet Substructure

m

_jet

~ m

_q

~ 0

m

_jet

~ m

_W

~ 80 GeV +

Dipolar structure

€

z = min( p

_T_,i

, p

_T_,_j

)

p

_T_,_jet

> 0.1

€

ΔR

_ij

< M

_jet

p

_T_,_jet

Jet Pruning (arXiv:0903.5081)

-  Filter out soft and large angle QCD emission

N-subjettiness (arXiv:1011.2268)

-  Topological compatibility with N subjets

€

τ

N

= 1

d

₀

p

_T_,k

k

∑ min [ ΔR

^1,k

,ΔR

^2,k

,...,ΔR

^N^,k

]

BACKGROUND SIGNAL

CMS arXiv:1405.1994

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VH Resonances

X

Z  ll W lν W/Zqq

b

bbar Higgs-jet

•  Use Higgs as a tool to search for new Physics

–  Known mass and decays

•  hbbar ~ 60%  jets – Subjet b-tagging

•  M h > M V

–  Cleaner experimental signature

•  Cross section of this process is comparable with the one

discussed before (VV, HH)

–  Search can be performed already

with 8 TeV data

Search for Heavy Resonances Decaying to Bosons with the ATLAS and CMS Detectors