The Origin of Mass The Origin of Mass - - Exploring the Higgs Sector at the Exploring the Higgs Sector at the Large Hadron Collider with ATLAS Large Hadron Collider with ATLAS Markus Schumacher, Universität Bonn Seminar über Teilchenphysik, Universität Heidelberg, May 2006
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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. Seminar über Teilchenphysik, Universität Heidelberg, May 2006. Outline. Which mass? Why? The mass problem and the SM solution. - PowerPoint PPT Presentation
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The Origin of MassThe Origin of Mass
--
Exploring the Higgs Sector at the Exploring the Higgs Sector at the
Large Hadron Collider with ATLASLarge Hadron Collider with ATLAS
Markus Schumacher, Universität Bonn
Seminar über Teilchenphysik, Universität Heidelberg, May 2006
Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC 2
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 only become public this Friday.
Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC 3
Which mass?
Unknown Form of
Dark Matter
Unknown Formof
Dark Energy60%
40%
20%
80%
100%
0%
neutrinos protons/neutrons in stars, dust,etc.
The nucleon mass
O(%) due to Mu~5 MeV
and Md ~10 MeV
Rest: kinetic energy
of partons +
other QCD effects
Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC 4
Particle masses and their relevance
electron mass: def. length scale of our world, Bohr radius a=1/em me
me = 0 no atomic binding
me = 0.02MeV human giants 45 m, visible light in infrared
me = 105 MeV nucleon capture pen energetically possible only helium, n + different universe
no/small W mass: fusion in stars: p+pD e+ GF~ (MW )-2
short burning time of sun at lower temperature no humans on earth
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
quarks massless or mu=md proton mass > neutron mass proton decay pnepossible modified nucleosynthesis different universe
Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC 5
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 6
Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC 8
Mass generation and Higgs Boson couplings: = v + H
v =247 GeVx
Fermion
gf
MV ~ g v gauge coupling
mf ~ gf v Yukawa coupling
introduced „ad hoc“
x x
W/Z boson
g gauge
interaction with „ether“ v=247 GeV
fermions: gf ~ mf / v
W/Z bosons: gV ~ MV / v = g2 v
interaction with Higgs boson H
fermion
gf
x
W/Z boson
g gauge
Higgs
Higgs v
2
2VVH coupling ~ vev
only existent after EWSB
hint towards background condensate
1 unknown parameter in SM: MH
2
Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC 9
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
Decays of the Higgs boson in the 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.
Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC 10
… mt + … ln(MH)
What is the mass of the Higgs boson ?
MW(Phys) = MW(Born) +
2
WW W
W
WHt
b
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.
MH < 186 GeV (mtop=172.7 GeV)
with 95% CL
Standard Model prefers a light Higgs boson
S. Roth
Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC 11
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 12
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 13
A Toroidal LHC ApparatuS
MC studies with fast simulation of ATLAS detector key performance numbers from full sim.: b/tau/jet/el.// identification, isolation criteria, jet veto, mass resolutions, trigger efficiencies, …
Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC 14
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 15
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 ~7% VBF: K ~ 1.1, ~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
e.g.: gluon gluon fusion
Harlander et al.
Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC 16
Cross sections for background processes
Higgs 150 GeV: S/B <= 10-10
3 level trigger system on
leptons, photons, missing energy
provides reduction by 10 000 000
overwhelming background: mainly QCD driven
signal: often electroweak interaction
photons, leptons, … in final state
no access to fully hadronic events
e.g. GGF, VBF with Hbb
Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC 17
An event at the LHC
+ ~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 > t btw. bunch crossings
„hard“ collision
+ ISR,FSR
+ „underlying
event“
Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC 18
The challenge of event reconstruction
low lumiosity high luminosity
Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC 19
Which channels may provide discovery?
Status 2001discovery channels:
inclusive:
H 2 photons
ZZ 4 leptons
WW ll
exclusive:
ttH, Hbb
VBF, HZZ,WW for large M
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?
Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC 20
H 2 Photons
signature: two high Pt photons
background: irreducible pp +x
reducible pp j, jj, …
exp. issues (mainly for ECAL):
- , jet separation (Eff=80%, Reject. ~ few 1000)
- energy scale, angular resolution
- conversions/dead material
mass resolution M: ~1 to 1.5%
precise background estimate
from sidebands (O(0.1%))
S/BG ~ 1/20
preliminary NLO study:
increase of S/B by 50%
ATLAS 100fb-1
Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC 21
H ZZ(*) 4 leptons
reducible BG:
tt, Zbb 4 leptons
lepton isolation and
veto against b-jets
good mass resolution M ~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%
signal: 4 iso. leptons
1(2) dilepton mass = MZ
irreducible BG:
ZZ 4 leptons
four lepton mass
Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC 22
signal:
- 2 leptons + missing ET
- lepton spin corrleations
- no mass peak transverse mass
H WW l l
ATLAS
M=170GeV
30fb-1
transverse mass BG: WW, WZ, tt
lepton iso., missing E resolution
jet (b-jet) veto against tt
BG estimate in data from ll : 5%
normalisation from sideband
shape from MC
NLO effect on spin corr.
ggWW contribution signal like
Dührssen, prel.
ll
Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC 23
ttH with Hbb
mass resolution M: ~ 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
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
Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC 24
Vektor boson fusion VBF: ppqqH
signature: 2 forward jets
with large rapidity gap only Higgs decays
in central part of dector=-ln tan(/2)
ATLASATLAS
Jet
Jet
Forward tagging jets
Higgs Decay
Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC 25
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 O(5) additional parameters
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