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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.

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the origin of mass exploring the higgs sector at the large hadron collider with atlas

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
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
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
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 penn energetically possible

 only helium, n + n  different universe

  • no/small W mass: fusion in stars: p+pD 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 pnen 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
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 ww ww
High energy behaviour of s in WWWW

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 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
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
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
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
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
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

a t oroidal l hc a pparatu s
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
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
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
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 Hbb

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
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
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
Which channels may provide discovery?
  • efficient trigger  no hadronic final states: e.g. GGF, VBF: Hbb
  • 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, Hbb

VBF, HZZ,WW for large M

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

h 2 photons
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
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 l n l n
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.

 ggWW contribution signal like

DFll

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

slide23

ttH with Hbb

  • 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 Hbb

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

vektor boson fusion vbf pp qqh
Vektor boson fusion VBF: ppqqH

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
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

slide26

VBF: H tt  ll 4 n

  • signature:tagging jets +2 leptons + large missing tranvsere energy
  • background:QCD processes tt,Zjj  Dh, central jet veto

 reconstruction of mtt

collinear approximation

Httem

ATLAS

30 fb-1

  • expected DBG ~ 5 to 10%

for MH > 125 GeV: side band

for MH < 125 normalisation from

Z-peak, shape from Zmm

  • sM /M ~ 10%
  • dominated by Emiss

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

slide27

VBF, Htt: determination of background from data

  • Idea:jjZmmandjjZttmmwith 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

h ww l n l n vbf versus inclusive channel

Weak Boson Fusion: HWWllnn (lnqq)

HWWlnln: VBF versus inclusive channel

ATLAS

M=170GeV

30fb-1

ATLAS

10 fb-1

HWWe

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
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
Measurement of Higgs boson mass
  • Direct from mass peak:

HggHbbHZZ4l

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

ATLAS

  • “Indirect”

from transverse mass spectrum:

HWWlnln WHWWWlnlnln

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
Determination of Higgs boson couplings
  • coupling in production sHx= const x GHxand decay BR(Hyy)= 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 g v g v sm
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,HWW)/(GV2 in SM)

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

slide33

The Higgs sector of the MSSM

  • 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
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, Htt covers whole plane

via observation of h or H

with 30fb-1

  • VBF dominates observation
  • small area from bbh,hmm

for small Mh

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

overall discovery potential 300 fb 1
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/Att 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
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
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
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, H1bb

final state: 4b 2j l n same as ttH, Hbb

  • revised studies for H2/3H1H1 also interesting

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

conclusions
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
Higgs Physics is golden (J.Lykken 2000)

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

the new welt meister formel
The new „Weltmeisterformel“ ???

54 x 74 – 1990 = ???

  • Thanks for your attention!

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