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The Origin of Mass - Exploring the Higgs Sector at the Large Hadron Collider with ATLAS

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### The Origin of Mass-Exploring the Higgs Sector at the Large Hadron Collider with ATLAS

Markus Schumacher, Universität Bonn

Particle Physics Seminar, HU Berlin/DESY Zeuthen, 9th June 2006

Outline

- Which mass? Why? The mass problem and the SM solution.
- Higgs boson phenomenology and experimental environment
- Discovery potential for a SM like Higgs boson
- Investigation of the Higgs boson profile
- Discovery potential for MSSM Higgs bosons
- Conclusions

- only ATLAS results. CMS TDR will become public very soon.

Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC

Which mass?

The nucleon mass

100%

Unknown Form

of

Dark Energy

80%

60%

O(%) due to Mu~5 MeV

and Md ~10 MeV

Rest: kinetic energy

of partons +

other QCD effects

40%

Unknown Form

of

Dark Matter

20%

0%

protons/neutrons

in stars, dust,etc.

neutrinos

Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC

Particle masses and their relevance

- electron mass: def. length scale of our world, Bohr radius a=1/aem me

me = 0 no atomic binding

me = 0.02MeV human giants 45 m, visible light in infrared

me = 105 MeV nucleon capture penn energetically possible

only helium, n + n different universe

- no/small W mass: fusion in stars: p+pD e+n GF~ (MW )-2 short burning time of sun at lower temperature no humans on earth

- quarks massless or mu=md proton mass > neutron mass

proton decay pnen possible

modified nucleosynthesis different universe

mass values of e, u, d, W and their fine tuning are

- essential for creation and development of our universe
- principle of mass generation Higgs mechanism
- origin of mass values even no theoretical explanation yet

Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC

Gauge symmetries of the SM and particele masses

- consistent description of nature based on gauge symmetries
- electroweak SU(2)LxU(1)Y symmetry forbids „ad hoc“ masses for

gauge bosons: W and Z fermions: (l = doublet, r = singlet)

- „ad hoc“ mass terms destroy

- renormalisibility no precision prediction for observables
- high energy behaviour of theory e.g. WLWL scattering

Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC

High energy behaviour of s in WWWW

violates unitarity

at ECM ~ 1.2 TeV

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

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

scalar boson H

restores unitarity, if

gHWW ~ MW

gHff ~ Mf

and MH < 1TeV

s const=f(MH)

Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC

The Higgs Kibble mechanism

The „standard“ solution:

one new doublet of complex scalar fields (4 degrees of freedom)

with appropriately chosen potential V

V = -m2 |f+f| + l |f+f|2

m2,l > 0

minimum of V not at f=0 spontaneous symmetry breaking

3 massless excitations along valley 3 longitudinal d.o.f for W+- and Z

1 massive exciation out of valley 1 d.o.f for „physical“ Higgs boson

Higgs field has two „components“

1) omnipresent, constant background condensate v= 247 GeV (from GF)

2) Higgs boson H with unknown mass MH ~ m ~ Ölv

Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC

Mass generation and Higgs Boson couplings: F = v+H

x

v =247 GeV

gf

- interaction with „ether“ v=247 GeV

MV~ gvgauge coupling

mf~ gfv Yukawa coupling

introduced „ad hoc“

Fermion

x

x

2

g gauge

W/Z boson

- interaction with Higgs boson H

Higgs

gf

fermions: gf ~ mf / v

W/Z bosons: gV ~ MV / v = g2 v

2

fermion

v

Higgs

VVH coupling ~ vev

only existent after EWSB

hint towards background condensate

x

2

g gauge

W/Z boson

1 unknown parameter in SM: MH

Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC

Decays of the Higgs boson in the SM

bb

WW

ZZ

tt

cc

tt

gg

gg

HDECAY: Djouadi, Spira et al.

for M<135 GeV: H bb,tt dominant

for M>135 GeV: H WW, ZZ dominant

tiny: H gg also important

Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC

What is the mass of the Higgs boson ?

- theory: unitarity in WW scattering MH < 1 TeV

- direct search at LEP: MH<114.4 GeV excluded with 95% CL

- indirect prediction in SM, e.g.

MW(Phys) = MW(Born) +

t

H

W

W

W

W

S. Roth

b

W

2

… mt + … ln(MH)

MH < 186 GeV (mtop=172.7 GeV)

with 95% CL

Standard Model prefers a light Higgs boson

Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC

Status of SM Higgs boson searches at 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

~ 5 to 20 x SM cross section

Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC

The Large Hadron Collider LHC

proton proton collisions at ECM of 14 TeV, start in 2007

initial luminosity: (2)x1033 cm-2s-1 10 to 20 fb-1/year

design luminosity: 1034 cm-2s-1 100 fb-1/year

Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC

AToroidal LHC ApparatuS

- MC studies with fast simulation of ATLAS detector
- key performance numbers from full sim.: b/tau/jet/el./g/m identification,

isolation criteria, jet veto, mass resolutions, trigger efficiencies, …

Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC

Production of the SM Higgs Boson at LHC

- gluon fusion dominant for all masses
- VBF roughly one order of magnitude smaller
- HW, HZ,H tt only relevant for small MH

Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC

QCD corrections and knowledge of cross sections

e.g.: gluon gluon fusion

- K = sNNLO/sLO~2
- Ds = 15% from scale variations
- error from PDF uncertainty ~10%
- caveat: scale variations may
- underestimate the uncertainties!

Harlander et al.

- ttH: K ~ 1.2, Ds~15% WH/ZH: K~1.3 Ds~7% VBF: K ~ 1.1, Ds~4%
- but: rarely MC at NLO avaiable (except gluon gluon fusion)
- background: NLO calculations often not avaiable

need background estimate from data

ATLAS policy: use K=1 for signal and background

- remark: NLO calculation for total cross section is not

NLO calculation for additional jet needs NNLO or NLO+(N)LL

Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC

Cross sections for background processes

overwhelming background: mainly QCD driven

signal: often electroweak interaction

photons, leptons, … in final state

3 level trigger system on

leptons, photons, missing energy

provides reduction by 10 000 000

no access to fully hadronic events

e.g. GGF, VBF with Hbb

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

Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC

An event at the LHC

„hard“ collision

+ ISR,FSR

+ „underlying

event“

- + ~23 overlayed pp interactions per bunch crossing at high luminosity
- ~109 proton proton collisions / second
- ~1600 charged particles enter detector per event

+ effects from „pile up“: read out time > Dt btw. bunch crossings

Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC

The challenge of event reconstruction

low lumiosity high luminosity

Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC

Which channels may provide discovery?

- efficient trigger no hadronic final states: e.g. GGF, VBF: Hbb
- Higgs boson mass reconstructable? which mass resolution?
- background reducible and controllable?

- good signal-to-background ratio

- small uncertainty on BG, estimation from data itself possible?

Status 2001

- discovery channels:

inclusive:

H 2 photons

ZZ 4 leptons

WW lnln

- exclusive:
- ttH, Hbb

VBF, HZZ,WW for large M

Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC

H 2 Photons

- signal: two highPtphotons

- background: irreducible pp gg+x

reducible pp gj, jj, …

- exp. issues (mainly for ECAL):
- - g, jet separation (Eff=80%, Reject. ~ few 1000)
- - energy scale, angular resolution
- conversions/dead material

ATLAS 100fb-1

- mass resolution sM: ~1 to 1.5%

S/BG ~ 1/20

- precise background estimate
- from sidebands (O(0.1%))
- no MC needed

- preliminary NLO study:
- increase of S/ÖB by 50%

Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC

H ZZ(*) 4 leptons

- signal:4 iso. leptons

1(2) dilepton mass= MZ

- reducible BG:

tt, Zbb 4 leptons

lepton isolation and

veto against b-jets

- irreducible BG:

ZZ 4 leptons

four lepton mass

- good mass resolution sM~1%

muon spectrometer + tracking detectors

- small and flat background

easy estimate from sidebands

no Monte Carlo needed

- preliminary NLO study indicates

significance increase by 25%

Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC

H WW ln ln

- signal:

- 2 leptons + missing ET

- lepton spin corrleations

- no mass peak transverse mass

ATLAS

M=170GeV

30fb-1

transverse mass

- BG: WW, WZ, tt

lepton iso., missing E resolution

jet (b-jet) veto against tt

Dührssen, prel.

- BG estimate in data from DFll : 5%

normalisation from sideband

shape from MC

- NLO effect on spin corr.

ggWW contribution signal like

DFll

Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC

- signal: 1 lepton, missing energy

6 jets of which 4 b-tagged

- 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

ATLAS

- mass resolution sM: ~ 15%
- 50% correct bb pairings
- difficult background estimate from
- data with exp. uncertainty ~ O(10%)
- normalisation from side band
- shape from „re-tagged“ ttjj sample

30 fb-1

S/BG ~ 1/6

only channel to see Hbb

Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC

Vektor boson fusion VBF: ppqqH

Jet

Jet

Forward tagging jets

- signature:
- 2 forward jets

with large rapidity gap

- only Higgs decays

in central part of dector

f

h

Higgs Decay

=-ln tan(q/2)

ATLAS

ATLAS

Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC

VBF: Challenges

ATLAS

- reconstruction of taggings jets

influence of

- „underlying event“ (UE) ?

- overlapping events (OE) ?

- „pile up“ (PU) ?

so far only low lumi considered

pT>20GeV

- central jet veto:

influence of UE, OE, PU?

- efficiency of jet veto at NLO?

but: no NLO MC-Generator yet

now: study started using SHERPA

Zeppenfeld et al.

Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC

- signature:tagging jets +2 leptons + large missing tranvsere energy

- background:QCD processes tt,Zjj Dh, central jet veto

reconstruction of mtt

collinear approximation

Httem

ATLAS

30 fb-1

- expected DBG ~ 5 to 10%

for MH > 125 GeV: side band

for MH < 125 normalisation from

Z-peak, shape from Zmm

- sM /M ~ 10%
- dominated by Emiss

Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC

VBF, Htt: determination of background from data

- Idea:jjZmmandjjZttmmwith identical topology
- muons are MIPS same energy deposition in calorimeters
- only difference: momentum spectra of muons
- Method:select Z mm events

„randomise“ m-momenta according to Z tt mm4n MC

apply „usual“ selection and mass reconstruction

shape of background

can be extracted precisely

from data itself

(M. Schmitz, Diplomarbeit BN 2006)

Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC

Weak Boson Fusion: HWWllnn (lnqq)

HWWlnln: VBF versus inclusive channelATLAS

M=170GeV

30fb-1

ATLAS

10 fb-1

HWWe

S/BG ~ 3.6 Signal = 82.4 S/BG ~ 0.7 Signal = 144

VBF with respect to gluon fusion

- smaller rate larger sig-to-BG ratio smaller K-factor
- more challenging for detector understanding
- order of significance depends on channel and Higgs mass

Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC

Discovery potential in SM

excluded by LEP

10 fb-1

30 fb-1

excluded by LEP

- VBF dominates discovery potential for low mass (at least at LO)
- with 15 fb-1 and combination of channels: discovery from LEP to 1TeV
- prel. NLO studies: increase of signifcance up to 50% for incl. channels
- so far: cut based improvement with multivariate techniques

Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC

Measurement of Higgs boson mass

- Direct from mass peak:

HggHbbHZZ4l

(energy scale 0.1 (0.02)% for l,g,1% for jets)

ATLAS

- “Indirect”

from transverse mass spectrum:

HWWlnln WHWWWlnlnln

S. Roth

300 fb-1

DM/M: 0.1% to 1%

- Higgs boson mass
- determines Higgs sector in the SM
- is precision observable of the SM

Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC

Determination of Higgs boson couplings

- coupling in production sHx= const x GHxand decay BR(Hyy)= GHy / Gtot

Prod.

Decay

GHX GHy

2

Partial width:GHz ~ gHz

sHx x BR ~

Gtot

- goal: - disentangle contribution from production and decay
- - determine total width Gtot

- model independent:
- only ratio of partial width

- 13 final states in global fit

(including various syst. uncertainties)

H WW used as reference as most precise determination for MH>120 GeV

Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC

Absolute Couplings with gV < gVSM

- for MH<200 GeV, Gtot<< mass resolution

no direct determination

indirect limits needed

300 fb-1

- coupling to W, Z, t, b, t

Dührssen et al.

- lower bounds from observed rates:

Gtot > GW+GZ+Gt+Gg+....

- upper bound with theoretical input

weak assumption: gV<gVSM

(true in all models with only doublets and singlets)

Gtot< Rate(VBF,HWW)/(GV2 in SM)

Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC

- SUSY “solves” hierarchy problem: why MH, v << MPl=1019GeV ?

- SUSY needs two Higgs doublets

2 vevs: v1,v2 5 Higgs bosons: h,H,A,H+,H-

- 2 parameters determine Higg sector at Born level: tanb=v2/v1, MA

+ ~100 additional, which are fixed in benchmark scenarios

- lightest Higgs boson: Mh<135 GeV (for mtop=175GeV)
- modified couplings

w.r.t. SM

- Is at least one Higgs boson observable at LHC?
- Discrimination SM MSSM ? - several Higgs bosons observable

- characteristics of h differ from SM

Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC

Discovery potential for light Higgs boson h

300 fb-1

30 fb-1

ATLAS preliminary

ATLAS preliminary

- large area covered by many channels

stable discovery and parameter

determination possible

- small area uncovered @ mh~95 GeV

- VBF, Htt covers whole plane

via observation of h or H

with 30fb-1

- VBF dominates observation
- small area from bbh,hmm

for small Mh

Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC

Overall discovery potential: 300 fb-1

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?

ATLAS preliminary

similar results in other benchmark scenarios

VBF channels , H/Att only used with 30fb-1

Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC

SM or extended Higgs Sector e.g. Minimale SUSY ?

discrimination via VBF

comparison of expected

determination of R in MSSM

with SM prediction for same MH

BR(h WW) BR(h tt)

R =

300 fb-1

ATLAS

prel.

- assumption: Mh well known
- no systematic uncertainties

D=|RMSSM-RSM|/sexp

D=|RMSSM-RSM|/sexp

Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC

The Higgs sector in the CP violating MSSM

- at Born level: CP symmetry conserved in Higgs sector
- complex SUSY breaking parameters (m,At) introduce new CP phases

mixing between neutral CP eigenstates

mass eigenstates H1, H2, H3

<> CP eigenstates h,A,H

Why consider such scenarios?

- 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)

- no absolute limit on mass of H1 from LEP

Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC

Discovery potential in CP violating MSSM

MH1: < 50 GeV, MH2: 105 to 115 GeV, MH3: 140 to 180 GeV, M H+-:130 to 170 GeV

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

final state: 4b 2j l n same as ttH, Hbb

- revised studies for H2/3H1H1 also interesting

Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC

Conclusions

- our universe needs masses of elementary particles
- Higgs Kibble mechanism allows their consistent description
- LHC: - discovery of Higgs boson in SM with 15fb-1 well understood data
- - determination of mass, width, spin, CP
- - ratio of partial width, absolute couplings only with theo. input
- - CPC MSSM: at least one Higgs boson observable
- discrimination from SM seems promising
- - CPV MSSM: so far uncovered area at low MH as not studied yet
- promising channels are investigated now
- now: prepare for data taking
- - determine background, trigger eff., id eff./rejection from data
- - improve reconstruction and MC simulation (mis. calibration, allignment)
- - perform NLO studies and investigate other „exotic“ scenarios

Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC

Higgs Physics is golden (J.Lykken 2000)

Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC

The new „Weltmeisterformel“ ???

54 x 74 – 1990 = ???

- Thanks for your attention!

Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC

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