LHC Searches from a Heavy Light Higgs

Jessie SheltonYale University

arXiv:1112.4996 with Y. Bai, P. Draper work in progress with M. Graesser

U. Michigan Higgs Symposium, April 19, 2012

What we’ve learned after 5 fb-1

• (Hints of) a SM-like Higgs boson around 125 GeV...

• ...and not much else

What we’ve learned after 5 fb-1

Mass scale [TeV]-110 1 10 210

Oth

erEx

cit. f

erm

.Ne

w qu

arks

LQV'

CIEx

tra d

imen

sions

llqmVector-like quark : NC, q!lmVector-like quark : CC, jjmColor octet scalar : dijet resonance, µµ

m)=1) : SS dimuon, µµ"L±± (DY prod., BR(HL

±±H (LRSM, no mixing) : 2-lep + jetsRW

Major. neutr. (LRSM, no mixing) : 2-lep + jets,WZT

mlll), !Techni-hadrons : WZ resonance (µµee/mTechni-hadrons : dilepton, #µ

m resonance, #-µExcited muon : #em resonance, #Excited electron : e-jjmExcited quarks : dijet resonance,

jet#m-jet resonance, #Excited quarks : ,missTE : 1-lep + jets + 0A0 + At t" exo. 4th gen.TT

Zbm Zb+X, "'bNew quark b' : b'

WtWt"4d4

generation : dth4 WbWb"4u

4 generation : uth4

WqWq"4Q4

generation : Qth4jj!µjj, µµ=1) : kin. vars. in !Scalar LQ pairs (jj!=1) : kin. vars. in eejj, e!Scalar LQ pairs (µT,e/mSSM W' : µµee/mSSM Z' :

,missTEuutt CI : SS dilepton + jets + ll

m combined, µµqqll CI : ee, )

jjm($qqqq contact interaction :

)jjm($

Quantum black hole : dijet, F Tp%=3) : leptons + jets, DM /THMADD BH (

ch. part.N=3) : SS dimuon, DM /THMADD BH (jetsN,

Tp%=3) : multijet, DM /THMADD BH ( tt

m l+jets, " t=-0.20 : tsg/qqgKK

gRS with llll / lljjm = 0.1 : ZZ resonance, PlM/kRS with

llm = 0.1 : dilepton, PlM/kRS with ##m = 0.1 : diphoton, PlM/kRS with

,missTE + ##UED :

Large ED (ADD) : diphotonLarge ED (ADD) : monojet

)Q/m! = qQ&Q mass (coupling 760 GeV (2011) [1112.5755]-1=1.0 fbL

)Q/m! = qQ&Q mass (coupling 900 GeV (2011) [1112.5755]-1=1.0 fbL

Scalar resonance mass1.94 TeV (2011) [ATLAS-CONF-2012-038]-1=4.8 fbL

massL±±H355 GeV (2011) [1201.1091]-1=1.6 fbL

(N) < 1.4 GeV)m mass (RW2.4 TeV (2011) [Preliminary]-1=2.1 fbL

) = 2 TeV)R(WmN mass (1.5 TeV (2011) [Preliminary]-1=2.1 fbL

))T'(m) = 1.1 T(am, Wm) + T((m) =

T'(m mass (

T'483 GeV (2011) [Preliminary]-1=1.0 fbL

) = 100 GeV)T((m) - T)/T'(m mass (T)/T

'470 GeV (2011) [ATLAS-CONF-2011-125]-1=1.1-1.2 fbL

*))µ = m(** mass (µ1.9 TeV (2011) [ATLAS-CONF-2012-023]-1=4.8 fbL

= m(e*))*e* mass (2.0 TeV (2011) [ATLAS-CONF-2012-023]-1=4.9 fbL

q* mass3.35 TeV (2011) [ATLAS-CONF-2012-038]-1=4.8 fbL

q* mass2.46 TeV (2011) [1112.3580]-1=2.1 fbL

) < 140 GeV)0(AmT mass (420 GeV (2011) [1109.4725]-1=1.0 fbL

b' mass400 GeV (2011) [Preliminary]-1=2.0 fbL

mass4d480 GeV (2011) [Preliminary]-1=1.0 fbL

mass4u404 GeV (2011) [1202.3076]-1=1.0 fbL

mass4Q350 GeV (2011) [1202.3389]-1=1.0 fbL

gen. LQ massnd2685 GeV (2011) [Preliminary]-1=1.0 fbL

gen. LQ massst1660 GeV (2011) [1112.4828]-1=1.0 fbL

W' mass2.15 TeV (2011) [1108.1316]-1=1.0 fbL

Z' mass2.21 TeV (2011) [ATLAS-CONF-2012-007]-1=4.9-5.0 fbL

*1.7 TeV (2011) [1202.5520]-1=1.0 fbL

(constructive int.)*10.2 TeV (2011) [1112.4462]-1=1.1-1.2 fbL

*7.8 TeV (2011) [ATLAS-CONF-2012-038]-1=4.8 fbL

=6)+ (DM4.11 TeV (2011) [ATLAS-CONF-2012-038]-1=4.7 fbL

=6)+ (DM1.5 TeV (2011) [ATLAS-CONF-2011-147]-1=1.0 fbL

=6)+ (DM1.25 TeV (2011) [1111.0080]-1=1.3 fbL

=6)+ (DM1.37 TeV (2010) [ATLAS-CONF-2011-068]-1=35 pbL

KK gluon mass1.03 TeV (2011) [ATLAS-CONF-2012-029]-1=2.1 fbL

Graviton mass845 GeV (2011) [1203.0718]-1=1.0 fbL

Graviton mass2.16 TeV (2011) [ATLAS-CONF-2012-007]-1=4.9-5.0 fbL

Graviton mass1.85 TeV (2011) [1112.2194]-1=2.1 fbL

Compact. scale 1/R (SPS8)1.23 TeV (2011) [1111.4116]-1=1.1 fbL

(GRW cut-off)SM3.0 TeV (2011) [1112.2194]-1=2.1 fbL

=2)+ (DM3.2 TeV (2011) [ATLAS-CONF-2011-096]-1=1.0 fbL

Only a selection of the available mass limits on new states or phenomena shown*

-1 = (0.04 - 5.0) fbLdt, = 7 TeVs

ATLASPreliminary

ATLAS Exotics Searches* - 95% CL Lower Limits (Status: March 2012)

A heavy light Higgs and physics beyond the Standard Model

• Physics beyond the SM so far is not showing up in easy and/or standard channels.

• Higgs: most sensitive piece of SM to new physics

• If we believe 125 GeV excesses are a SM-like Higgs, what channels does this suggest for new physics in 2012?

(Everyone in this room has their own answers!)

H

125 GeV + nothing else (yet)

• Heavy: no LEP constraints; (almost) anything goes!

Picture I:

New physics is SM-singlet, communicates only through Higgs portal

• Light Higgs: chance to observe light hidden degrees of freedom directly

H

125 GeV + nothing else (yet)

Picture II:

Weakly coupled EWSB, but SUSY EW scale stabilization mechanism is either tuned or non-standard

• Light Higgs: SUSY models are still sensible

• Heavy: ...but many minimal models look strained

I. Rare decays of a light Higgs

A light Higgs is narrow

• For , total width of SM Higgs is tiny:

[GeV]HM100 120 140 160 180 200

Bran

chin

g ra

tios

-310

-210

-110

1bb

cc

gg

Z

WW

ZZ

LHC

HIG

GS

XS W

G 2

010

[GeV]HM100 200 300 1000

[GeV

]H

-210

-110

1

10

210

310

LHC

HIG

GS

XS W

G 2

010

500

• light SM-like Higgs very sensitive to existence of new light degrees of freedom

mH<∼ 2mW

⇒

Rare decays of a light Higgs

Λ � m2 � v2

Λ = 0.05Λ = 0.1

0 20 40 60 800.0

0.2

0.4

0.6

0.8

1.0

ma

BR�SM�

• Even relatively small couplings to new sectors can disrupt Higgs branching fractions by

• New physics may well show up at the LHC first in rare decays of the Higgs

• Not necessarily hopeless! SM sensitivity is driven by rare modes

O(1)

Lint = λa2|H|2

Higgs to invisibles

• Will study invisibles: comprehensive update

• aim: estimate LHC sensitivity in low (i.e: not 14 TeV) run

• Example of many issues generic to study of rare decays:

• trigger considerations

• systematic uncertainties

H →

Spotting an invisible Higgs

• Weak boson fusion offers best signal to background (Eboli, Zeppenfeld ’00)

• Final state :

• Large GeV triggerable

• jet kinematics are set by EW process and distinctive

• WBF reference cuts:

• jets are energetic, GeV, TeV

• jets are widely separated,

• dominant scattering process does not involve QCD relatively little other jet activity

2j + E/T

E/T >∼ 100

pT >∼ 30 Mjj>∼ 1

∆ηjj > 4

⇒

Signal and backgrounds

• Dominant physics background: jets,

• both Drell-Yan and WBF processes are important

• jets where the lepton is lost is numerically as important

• Mismeasured QCD background is challenging to estimate

• suppress by MET quantity ( 100 GeV) and quality (Min 0.5) cuts

• finally, rate is so large that it contributes to reach despite small acceptance

Z+ Z → νν̄

W+

gg → H

E/T >∼∆φ(ji, �p/T ) >

Setting Limits

• Purely a counting experiment: systematic uncertainties critical for setting limits

• Theoretical predictions for WBF processes under excellent control

• Theoretical uncertainties on Z + jets still uncomfortably large: model from data

• But: natural control sample Z + jets, Z statistics limited

• New idea pioneered by jets + MET SUSY searches at CMS: use reweighted photon + jets

→ �+�−

Reweighting photons for Z+jets

from Bern et al. ’11

RatioZ + 2j +X

γ + 2j +Xis stable (Bern et al, ’11)

Expect we are in the region where this works:

• MET requirement similar to existing studies

• MET quality cut removes collinear region

Allows 10% precision on V+jets backgrounds

∆φ

Sensitivity to invisible Higgs

120 130 140 150 160 170

1.00

0.50

0.20

0.30

0.70

mH

!"

BR

inv!!

SM

95# CL limits with 20 fb$1

at 7 TeV

Projected 95% CL limits on for 20 fb-1 at 7 TeVassuming 10% uncertainty on V+jets and 5% uncertainty on WBF processes

σ ×BR(h → inv)

stat only

theory syst.

20% syst

30% syst

120 130 140 150 160 170

1.00

0.50

0.20

0.30

0.70

mH

!"

BR

inv!!

SM

Sensitivity to invisible Higgs

Projected 95% CL limits on for 20 fb-1 at 7 TeVas a function of systematic error

σ ×BR(h → inv)

Update to 8 TeV coming...

Final comments about an invisible Higgs

• LHC experiments will be able to probe significantly below 1 in 2012

• ZH associated production can help extend reach

• enough to be interesting? Getting started...

• Invisible decay mode has two challenges: large EW background and lack of a mass feature

• Other rare decay modes may be more striking: 10% branching fractions not necessarily out of reach

• Triggers are not automatic (Strassler)

BR(H → inv)

II. Natural SUSY Spectra and Direct Stop Pair Production

A light Higgs and no SUSY signals

• Evidence for SM-like elementary Higgs, but gluinos and (degenerate) light squarks constrained to be TeV

• Main motivation for weak scale supersymmetry is electroweak hierarchy. Little hierarchy?

• Natural SUSY: particles tied directly to the weak scale

>∼

__________________

__________________

______

200

500

1200

200

500

1200

m�GeV

�

H̃

t̃1, t̃2b̃1

g̃

Searches in a natural SUSY spectrum

• If gluino is out of reach: direct stop pair production, more challenging (rate!)

• Near-degenerate Higgsinos all appear as (mostly) MET

• Charged and neutral branching fractions of squarks are similar:

�1.0 �0.5 0.0 0.5 1.0

0.2

0.4

0.6

0.8

cos Θt

BR�t 1�

b

t

left rightright

µ = 200tanβ = 20

�1.0 �0.5 0.0 0.5 1.0

0.2

0.4

0.6

0.8

cos Θt

BR�t 2�

right leftleft

b

t

µ = 200tanβ = 20

• If gluino is out of reach: direct stop pair production, more challenging (rate!)

• Near-degenerate Higgsinos all appear as (mostly) MET

• Charged and neutral branching fractions of squarks are similar:

Searches in a natural SUSY spectrum

�1.0 �0.5 0.0 0.5 1.0

0.2

0.4

0.6

0.8

cos Θb

BR�b 1�

left rightright

⇒ t b+ E/T

b

t

µ = 200tanβ = 20

• If gluino is out of reach: direct stop pair production, more challenging (rate!)

• Near-degenerate Higgsinos all appear as (mostly) MET

• Charged and neutral branching fractions of squarks are similar:

Searches in a natural SUSY spectrum

Direct stop pair production

t̃1

χ0 χ0

t̃∗1t̄

b̄

�+

ν

b

χ−Final state: b b �+ E/T

Unlike SM backgrounds (and unlike searches) the signal has asymmetric kinematics

t t̄+ E/T

0.0 0.2 0.4 0.6 0.8 1.0r�pT�

stops

top

r(pT ) =pT1 − pT2

pT1 + pT2

Top background

0 100 200 300 400mT�l,MET�

stops

dileptonic tops

semileptonic tops Main background: dileptonic tops with a missed lepton

• semileptonic tops, as well as Wbb, eliminated after cutting on mT

Unit-normalized transverse mass distributions

Strategies to suppress dileptonic top? (Kats, Meade, Reece, Shih ’11; Bai, Cheng, Gallicchio, Gu ’12)

Reducing dileptonic top background

Dileptonic top: have enough mass shell constraints to completely reconstruct the event

Reducing dileptonic top background

Dileptonic top: have enough mass shell constraints to completely reconstruct the event

After losing a lepton, no longer true.

Can instead choose solutions that minimize:• •

√s

Meff

• Discriminant based on goodness of reconstruction efficiently separates signal and background

Reducing dileptonic top backgrounds

-based discriminant evaluated on showered events takes b-tagged jet and leading non-tagged jet as input; keeps best assignment

�10 �5 0 5 10 15Log S

t b+ E/T

t t̄+ E/T

t t̄

√s

Concluding comments about light stops

• Direct stop pair production is challenging, but one of the most motivated targets

• Minimal natural SUSY spectrum has unique collider phenomenology which can be exploited

• Ideas for controlling large dileptonic top backgrounds can help in many similar searches

• Stay tuned for more results!

Backup: Rates