Higgs Physics at the Large Hadron Collider

Higgs Physics at theHiggs Physics at the

Large Hadron ColliderLarge Hadron ColliderMarkus Schumacher, Bonn University

WE Heraeus Seminar, „New Event Generators“, Dresden, January 2006

Markus Schumacher Higgs Physics at the LHC WE Heraues Seminar, Dresden, January 2006 2

Outline

the SM Higgs Mechanism and Status of Search

SM Higgs Phenomenology and Environment at LHC

Discovery Potential for SM Higgs Boson

Investigation of the Higgs Boson Profile

Phenomenology of SUSY Higgs bosons

Discovery Potential for MSSM Higgs bosons

Discriminating the SM from Extended Higgs Sectors

Conclusion and Outlook


The Higgs Mechanism in the Nut Shell

consistent description of nature seems to be based on gauge symmetry

SU(2)LxU(1) gauge symmetry no masses for W and Z and fermions „ad hoc“ mass terms spoil

The problem:

• renormalisibility no precise calculation of observables

• high energy behaviour e.g. WLWL scattering

violate unitarity

(probability

interpretation)

at ECM ~ 1.2 TeV

massive gauge bosons: 2 transverse + 1 longitudinal d.o.f.

massless gauge bosons: only 2 transverse d.o.f.


The Higgs Mechanism in the Nut Shell

The „standard“ solution:

new doublet of complex scalar fields (4 d.o.f.)

with appropiately choosen potential V

vacuum spontaneously breaks gauge symmetry

one new particle: the Higgs boson H

= v + H

(+ 3 d.o.f. for longitudinal components of W and Z)

Scalar boson restores unitarity if

gHWW ~ MW

const=f(MH)


Mass generation and Higgs couplings: = v + H

effective mass = friction of particles

with omnipresent „Äther“

v =247 GeVx

fermion

gf

mf ~ gf v Yukawa coupling

MV ~ g v gauge coupling

x x

W/Z boson

g gauge

Interaction of particles with v=247 GeV

Fermions gf ~ mf / v

W/Z Bosons: gV ~ MV / v

Interaction of particles with Higgs H

fermion

gf

x

W/Z boson

g gauge

Higgs

Higgs v

2

2VVH coupling ~ vev

only present after EWSB breaking !!!

1 unknown parameter in SM: the mass of the Higgs boson

2


50 100 200 100010-3

10-2

10-1

100

bb cc tt gg WW ZZ

Bra

nchi

ng r

atio (Higgs

)

mH (GeV)

bb

WW

ZZ

tt

ccgg

Higgs Boson Decays in SM

for M<135 GeV: H bb, dominant

for M>135 GeV: H WW, ZZ dominant

tiny: H also important

HDECAY: Djouadi, Spira et al.


Theory:

from unitarity requirement MH <~ 1TeV

„triviality“ upper bound

vacuum stability lower bound

if New=MPlanck 130 < MH<180 GeV

What do we know about the Higgs boson mass?

Direct search at LEP:

MH<114.4 excluded at 95% CL


What do we know about the Higgs boson mass?

Indirect: from EW precision measurements (LEP,SLD, TEVATRON …):

Corrections depend

on masses of heavy particles: top, Higgs

MH < 186 GeV (EW fit only)

at 95% CL ,mtop=172.7 GeV

MH<219 GeV incl. direct search

SM prefers light Higgs boson


Status of SM Higgs Searches at the TEVATRON

Expected sensitivity:

95% CL exclusion up to 130 GeV with 4fb-1 per experiment

3 sigma evidence up to 130 GeV with 8fb-1 per experiment

Current sensitivity::

Cross section limits at level of

~ 10 x SM cross section


1) mass

2) quantum numbers:

spin and CP

3) BRs, total width, couplings

4) self coupling at SLHC

Higgs Physics at the LHC

discovery of 1 neutral scalar Higgs boson

(determination of mass, spin, CP)

discrimination between SM and extended Higgs sectors

1) > 1 neutral Higgs boson

2) charged Higgs boson

3) exotic decay modes

e.g. H invisible

4) … … …

direct observation of

additional Higgs bosons

determination of Higgs profile:

deviations from SM prediction


LHC

SPPS

pp collisions at the Large Hadron Collider

LHC: proton proton collisions at ECM = 14 TEV, start in 2007

- low luminosity running: 1(2)x1033 /(cm2 s) 10(20) fb-1/year

2 to 3 overlapping events

- high luminosity running: 1034/(cm2 s) 100 fb-1/year

~ 20 overlapping events every 25 ns


A Toroidal LHC ApparatuS Compact Muon Solenoid

• el.-mag.calorimetry: H2 photons, HZZ 4 electrons

mass resolutions: : 0.7 to 1.5 % 4e: 1.3 to 1.8%

• spectrometer + tracking det.: HZZ 4 muons

mass resolution: 0.6 to 1.1 %

• vertex + tracking detectors: ttH, Hbbb-tagging performance

• overall calorimetry: H, HWWll, VBF prod. missing E. resolution, hermiticity, forward jets calorimetry to = 5


Production of the SM Higgs Boson at LHC


QCD corrections and Knowledge of Cross Sections

K = NNLO/LO~2

= 15% from scale variations

error from PDF uncertainty ~10%

Caveat: scale variations may underestimate the uncertainties!

ttH: K ~ 1.2 ~ 15% WH/ZH: K~1.3 to1.4 ~7%

VBF: K ~ 1.1 ~ 4% + uncertainties from PDF (5 to 15%)

but: rarely MC at NLO avaiable (except gluon gluon fusion)

background: NLO calculations often not avaiable

need background estimate from data

ATLAS: use K=1 and LO MC for signal and background for now

CMS: apply K-factor for GGF production a. „guestimated“ K for BG

e.g.: Gluon Gluon Fusion

Harlander et al.


Cross sections for background processes

Higgs 150 GeV: S/B <= 10-10

overwhelming background

trigger: 10-7 reduction

on leptons, photons, missing E

p pqq

q

p pqq

qq

H

WW

l

l

Background: mainly QCD driven

Signal: often electroweak interaction

photons, leptons, …

q


Considerations for Discovery Channel Choice

efficient trigger (need photon, lepton, muon, …)

no fully hadronic final states: eg. GGF, VBF: Hbb

reconstruction of Higgs boson mass possible?

yes: Hgg, ZZ, no: HWW

background suppressable and controlable

- good signal-to-background ratio, small BG uncertainty

- estimate from data possible (sidebands, control samples)

- some channels: shape prediction from MC

evaluation of discovery potential:

stable cross section prediction and MC generator avaiable

MC studies with fast detector simulation

key performance numbers from full sim.:

b/tau/jet/el.// ID, isolation, jet veto, mass resolutions, trigger, …

both collaborations plan updated evaluation with current software,

newest detector layout and MC event generators within next year


H 2 Photons

signature: two high Pt background: irreducible pp +x

reducible ppj, (jj), …

exp issues (mainly for ECAL):

, jet separation

- energy scale, energy + angular resolution

- conversions/dead material

mass resolution M/M= 0.7% dead material: (un)converted underlying event: vtx constraint

precise background estimate

from sidebands (O(0.1%)) expectedS/BG ~ 1/10

CMS 100fb-1

LO NLO: increase of S/B ~ 5060%

NLO


Gluon Fusion: H ZZ(*)4 Leptons

signature: 4 high pt isolated leptons

1(2) dilepton mass ~ MZ

irreducible BG: ZZ

mass reconstruction

reducible BG:

tt, Zbb 4 leptons

rejection via

lepton isolation and b-veto

good mass resolution M: <~1%

small and flat background easy estimate from data

CMS

CMS

100fb-1

NLO


Gluon Fusion: H WW l l

ATLAS

M=170GeV

30fb-1

signature:

- 2 high pt leptons + large missing ET

- lepton spin corrleations

- no mass peak transverse mass

transverse mass

BG: WW, WZ, tt

lepton iso., missing E resolution

jet (b-jet) veto against tt

BG estimate in data from ll

NLO effect on spin corr.

ggWW contribution signal like

Dührssen, prel.

ll


ttH with Hbb

mass resolution M: ~ 15%

50% correct bb pairings

very difficult background estimate from

data with exp. uncertainty ~ O(10%)

normalisation from side band

shape from „re-tagged“ ttjj sample

reducible BG: tt+jets, W+jets b-tagging

irreducible BG: ttbb reconstruct mass peak

exp. issue: full reconstruction of ttH final state combinatorics !!! need good b-tagging + jet / missing energy performance

S/BG ~ 1/6

30 fb-1

only channel to see Hbb

ATLAS

signature: 1 lepton, missing energy

6 jets of which 4 b-tagged


Vector Boson Fusion: ppqqH

Jet

Jet

signature:

-2 forward jets with

large rapidity gap

- only Higgs decay products in central part of detector

Forward tagging jets

Higgs Decay


Vector Boson Fusion: ppqqH

2 forward tagging jets with rapidity gap:

pT>20GeV

forward jet reconstruction

ATLASHigh Lumi

Low Lumi

jet-veto fake rate due to pile up

ATLAS

theory questions:

jet distributions at NLO?

esp. direction of 3rd jet?

efficieny of central jet veto?need NLO MC generator

for signal and BG

influence of underlying evt?

experimental issues:


signature: tagging jets +

- 2 high pt leptons + large missing ET

- lepton spin corrleations (spin10) - no mass peak transverse mass

Weak Boson Fusion: HWWll (lqq)

tt, Wt, WWjj, ...

backgrounds:

HWWeATLAS

10 fb-1

MH=160 GeV

S/BG ~ 3.5/1 BG ~10%

shape from MC

normalisation from

side bands in

MT and ll

central jet veto, b-veto

CMS

60 fb-1


Vector Boson Fusion: H tau tau ll 4 or l had 3

signature: tagging jets +

- 2 high pt leptons (1 l, 1 tau) + large missing ET

- mass reconstruction despite 4 (3) in collinear approximation

backgrounds: tt,Zjj

central jet veto reconstruction of m

large boost of tau tau, lepton, neutrino directions same

mass resolution ~ 10%(5 % from acollinear approximation)dominated by missing E. resolution


ATLAS

He

Vector Boson Fusion: H tau tau ll 4 or l had 3

expected BG uncertainty ~ 5 to 10%

for MH > 125 GeV: flat sideband

for MH < 125 normalisation from Z peak, but shape?

channel so far only studied für MH>110 GeV:how far down sensitive? mass determination possible?

30 fb-1

30 fb-1

lepton hadron lepton lepton


Vector Boson Fusion, Hestimate of BG shape from dataIdea: jjZandjjZ

look almost the same, esp. in calos

same missing energy

only momenta different

Method: select Z events

randomise momenta

apply „normal“ mass reco.

PTmiss,final (GeV) M (GeV)

promising prel. results from ongoing diploma thesis in BN (M. Schmitz)


Discovery Potential for light SM Higgs boson

excl

ud

ed b

y

LEP

• for GGF: raise of significance by ~ 50% from LO to NLO

• results for cut based analysis improvement by multivariate methods


Discovery Potential for light SM Higgs boson

For MH>330 GeV also:

VBF: H ZZ ll

VBF: WW lqq

excl

ud

ed b

y L

EP

discovery from LEP exclusion until 1 TeV

from combination of search channels with 15 fb-1 of well understood data

with individual search channels with 30 fb-1 of well understood data


Measurement of Higgs Boson Mass

1fb300L

ATLAS

M/M: 0.1% to 1%

Uncertainties considered:

“Indirect” from Likelihood fit to transverse mass spectrum: HWWllWHWWWlll

Direct from mass peak: HHbb HZZ4l

VBF with H or WW

not studied yet !

i) statistical

ii) absolute energy scale

0.1 (0.02) % for l,,1% for jets

iii) 5% on BG + signal for HWW


sensitivity through spin correlations of Higgs decay products

one possibility HZZ4 leptons

))(cos()(sin)( 22 1TLG

TL

TLR

Spin and CP Quantum Numbers: 0 even in SM

: angle btw. decay planes

:angle btw. leptons and Z

in Z rest frame

(Gottfried Jackson angle)

Higgs rest frame

observation of Hor ggH rules out Spin=1 (Young theorem)

L (T) ratio of longitudinal (tranverse) polarised Z bosons

100 fb-1


Spin and CP Quantum Numbers: discrimination power

alternative methods:

decay: H via spin correlations

production: i) ttH angle between t,t,H ii) VBF btw. tagging jets

discrimination dominated by for masses > 250 GeV

seperation power > 2 for all

spin, CP hypothesis and MH>200 GeV

currently under study:

- NLO effects

- verification with full sim. + all BGs

- lower masses HZZ*


Determination of Higgs boson couplings

Loop induced effective couplings:(sensitive to new physics)

Photon: g = gW “+“ gt “+“…

Gluon: g = gt “+“ gb “+“…

Hx

x

Born level couplings:

Fermions gf = mf / v

W/Z Bosons: gV = 2 MV / v2

couplings in production Hx= const x Hx and decay BR(Hyy) = Hy / tot experiment: rate = Nsig+NBG Nsig= L x efficiency x Hx x BR

need to know: luminosity, efficiency, background

Hx x BR ~ HX Hy

tot

prod decay

partial width: Hz ~ gHz2

tasks: - disentangle contribution from production and decay

- determine tot


ratios of BRs = ratios of = ratios of g, if only Born level couplings

W

totW

totWW

)BR(HWW)BR(H

VBF

VBF

→

→e.g.

WWHZH,

WWHWH,

WWHttH,

WWHVBF,

WWHGF,

BR)(

BR)(

BR)(

BR)(

BR)(

W

b

WWW

Z

9 fit parameters:

all rates can

be expressed

by those 9

parameters

H WW chosen as reference as best measured for MH>120 GeV

For 30fb-1 worse by factor 1.5 to 2

13 analysis used

Ratio of Partial Widths

including various exp. and theo. errors


Total Decay Width H

for MH>200 GeV, tot>1GeV

measurement from peak width in ZZ4 l

upper limit needs input from theory:

mild assumption: gV<gVSM

valid in models with only Higgs doublets and singlets

rate(VBF, HWW) ~ V2 / tot < (V

2 in SM)/ tot

tot< rate/(V2 in SM)

lower limit from observable rates:

tot > W+Z+t+g+....

for MH<200 GeV, tot<< mass resolution

no direct determination

have to use indirect constraints on tot


Absolute couplings with gV < gVSM constraint

coupling to W, Z, , b, t

g/g = ½ g2)/g2

inv for undetactable decays

e.g. c, gluons,newphoton (new), gluon (new):

non SM contribution to loops

g/g = ½ g2)/g2

Dührssen et al.

Dührssen et al.


MH2 = 2 =MPlanck

Motivation for Supersymmetry from Higgs Sector

Higgs problem in SM: large corrections to the mass of the Higgs-Boson

2

“solves” hierarchy problem: why v=246 GeV << MPl=1019GeV ?

MH2 = (MSM-MSUSY)

2 2

W W+ HH

natural value ~ MPl electroweak fit MH~O(100GeV)

SUSY solution: - partner with spin difference by ½ cancel divergence exactly if same M- SUSY broken in nature, but hierarchy still fine if MSUSY~1 TeV

H H

-

SUSY breaking in MSSM: parametrised by 105 additional parameters too many constrained MSSM with 5 additional parameters


The MSSM Higgs sector in a tiny Nut Shell SUSY: 2 Higgs doublets 5 physical bosons

real MSSM: 2 CP even h, H, 1 CP odd A, charged H+, H-

at Born level 2 parameters: tan, m A mh < MZ

large loop corrections from SUSY breaking parameters

mh < 133 GeV for mtop=175 GeV, MSUSY=1TeV

corrections depend on 5 SUSY parameters: Xt, M0 , M2, Mgluino,

fixed in the benchmark scenarios e.g. MHMAX scenario

maximal Mh conservative LEP exclusion

t b/ W/Z

h cossin -sincos sin()

H sinsin cos/cos cos()

A cot tan -----

gMSSM = gSM

• no coupling of A to W/Z

• small small BR(h,bb)

• large large BR(h,H,A,bb)

= mixing btw. CP-even neutral Higgs bosons


Discovery Potential in the tanversus MA Plane

LEP tan exclusion:

no exclusion for mt larger ~183 GeV !TEVATRON:

so far exclusion for tan > 50 MA<200GeV

ATLAS: calculations with FeynHiggs

CMS: HDECAY with SUBHPOLE up to now

no systematic uncertainties yet

main questions for LHC: At least 1 Higgs boson observable in the entire parameter space? How many Higgs bosons can be observed? Can the SM be discriminated from extended Higgs sectors?

4 CP conserving benchmark scenarios considered: Carena et al. , Eur.Phys.J.C26,601(2003)

1) MHMAX 2) No mixing 3) Gluophobic 4) small

conclusions the same due to to complementarity of search channels

Mtop=174.3 GeV


Influence of Benchmark Scenarios

reduced couplings

e.g. small scenario

small ghbb and gh

reduced sensitivity discovery via

VBF, htt tth, hbb

different Mh in same (tan,MA) point

change of sensitive channels

- FeynHiggs: maximum value 133 GeV

- SUBHPOLE: (less corrections) 127 GeV


h or H observable

with 30 fb-1

Vector Boson Fusion: 30 fb-1

studied for MH>110GeV at low lumi running

ATLAS preliminary


Small scenario versus MHMAX Scenario, h: 30 fb-1

small „hole“ covered by complementarity of search channels

ATLAS preliminary

ATLAS preliminary

remaining differences due to different Mh

(11 GeV between MHMAX and small)

-VBF, Hborder at low tan given by Mh=110 GeV contour

- tth, Hbb: significance decreasing rapidly with increasing Mh


Light Higgs Boson h

large area covered by several channels sure discovery and parameter

determination possible

small area uncovered @ mh ~ 95 GeV

300 fb-130 fb-1

VBF dominates observation

small area from bbh,H

for small Mh

ATLAS preliminaryATLAS preliminary


CMS: Light Higgs Boson h


Heavy Neutral Higgs Bosons H and A

decay modes: H/A and H/Aenhanced with tan

dominant production: bbH(A)

(NLO studies on the way:

how to handle correctly

bbH, gbbH, ggbbH)

: BR ~ 10 % M ~ 12%

BR~ 0.04% M ~ 1%

intense coupling regime:

only might resolve

several mass states

~ (tan)2

exp. challenges: b-tag, tau-tag, Emiss res. mass res.


H/A and

H/A

ATLAS 30fb-1

larger mass: also had. had.

trigger on hard tau jets

Eff.(LV1TR)= 80% =95% offline selected evt.

Tau ID: eff(tau)=55% rejection(QCD)=2500

H/Ae (only CMS)

H/Ahad had


Discovery Potenital for H and A

ATLASpreliminary

intermediate tanregion not covered by SM decay modes


Charged Higgs Bosons

gbH+-t

low mass: mH+-< mtop

ggttttH+-bW

high mass: mH+-> mtop

running bottom quark mass used, Xsec for gbtH+- from T. Plehn‘s program

Production:

transition region around mtop and from 2to2 to 2to3 process

needs revised experimental analysis, are MC generators ready?

decay modes: H(~100% below mtop, ~10% above) Htb (~90% above threshold)

ggbtH+- contributes to NLO of gbtH+-

avoid double counting

correct handling of region around mtop


Charged Higgs Bosons

ATLAS preliminary

ttbbWH+

Wqq

H+-

ATLAS


Overall Discovery Potential: 300 fb-1

at least one Higgs boson

observable for all parameters

in all CPC benchmark scenarios

significant area where only lightest Higgs boson h is observable

can H SUSY decays or

Higgs from SUSY decays

provide observation?

discrimination via h profile

determination?

similar results in other benchmark scenarios

VBF channels , H/Aonly used with 30fb-1

300 fb-1

ATLAS preliminary


Higgs Decays to Gauginos

Msleptons=250 GeV Msleptons = 110 GeV

gbtH+, H 2,30 1,2

3l+ETmissH0 2

0 20 4l+ET

miss

e.g. H0 20 2

0 10 1

0+4l

dominant background from SUSY

• results for most optimistic scenarios shown fine tuned• require small slepton masses for large BR(2 1 n leptons) • reduced sensitivity for other channels, consistent interpretation needed


ATLASprel.

300 fb-1

SM or Extended Higgs Sector e.g. Minimal SUSY ?

discrimination via rates from VBF

R = BR(h WW) BR(h )

assume Higgs mass well measured no systematic errors considered

compare expected

measurement of R in MSSM

with prediction from SM

for same value of MH

=|RMSSM-RSM|exp


The Higgs Sector in the CP Violating MSSM

mass eigenstates H1, H2, H3

<> CP eigenstates h,A,H

at Born level: CP symmetry conserved in Higgs sector

complex SUSY breaking parameters (,At) introduce new CP phases

mixing between neutral CP eigenstates

no a priori reason for real SUSY parameters baryogenesis: 3 Sacharov conditions

B violation : via sphaleron processes

CP violation : SM too less, CPV MSSM new sources fine

No therm. Equ. : SM no strong 1st order electroweak phase transition

CPV MSSM still fine (even better NMSSM) evade dipole moments via spurious cancellations or split SUSY

Why consider such scenarios?


Phenomenology in the CPX scenario

H1,H2, H3 couple to W,Z

all produced in VBF

H3

H2

H1

H2,H3 H1H1, ZH1,WW, ZZ

decays possible

no limit for mass of H1 from LEP

(compare CPC MSSM: Mh>MZ)

maximise effect CPX scenario (Carena et al., Phys.Lett B495 155(2000))

arg(At)=arg(Ab)=arg(Mgluino)=90 degree

scan of Born level parameters: tan and MH+-

LHWG-Note 2005-01


CP-Violating MSSM: Overall Discovery Potential

MH1: < 70 GeVMH2: 105 to 120 GeV

MH3: 140 to 180 GeV

small masses below 70 GeVnot yet studied in ATLAS

300 fb-1

most promising channel: tt bW bH+, H+W H1, H1bb

final state: 4b 2j l same as ttH, Hbb (study in Bonn)

revised studies for H2/3H1H1 also interesting

yet uncovered area size and location of „hole“ depends on Mtop and program for calculation

ATLAS preliminary


Very first look at new promising MC study

M H+=135 GeV, MH1=54GeV, tan=4.8 (diploma thesis M. Lehmacher, BN)

estimate of background from data seems difficults

coverage of „hole“ area incl. systematics under study!

t tH+ b W b H+W H1 H1bb

same final state as ttH, Hbb1: 4b 2q l Emiss

reconstruct top quarks combinatorics


Conclusion and Outlook

Standard model: discovery of SM Higgs boson with 15 fb-1

• requires good understanding of whole detector• multiple channels with larger luminosity Higgs profile investigaton

CP conserving MSSM: at least one Higgs boson observable • only h observable in wedge area at intermediate tan• maybe Higgs to SUSY or SUSY to Higgs observable?• discrimination via Higgs parameter determination seems promising

CP violating MSSM: probably a „hole“ with current MC studies• promising MC studies on the way

more realistic MC studies: • influence of miscalibrated and misaligned detector• improved methods for background estimation from data• use of NLO calcluations and MCs for signal and background

additional extended models + seach channels:• CPV MSSM, NMSSM, 2HDM• Higgs SUSY, SUSYHiggs• VBF, Hbb (b-trigger at LV2), VBF,Hinv. (add. forward jet trigger)

Higgs Physics at the Large Hadron Collider

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