Higgs Physics at the Large Hadron Collider Markus Schumacher, Bonn University NRW Phenomenology...
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Transcript of Higgs Physics at the Large Hadron Collider Markus Schumacher, Bonn University NRW Phenomenology...
Higgs Physics at theHiggs Physics at the
Large Hadron ColliderLarge Hadron ColliderMarkus Schumacher, Bonn University
NRW Phenomenology Meeting 2006, Bad Honnef, January 2006
Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006 2
Outline
the Higgs Mechanism and SM Higgs phenomenology at LHC
• discovery of 1 neutral scalar SM like Higgs boson
(determination of mass, spin, CP)
quantum numbers: spin and CP
BRs, total width, couplings
self coupling at SLHC
direct observation of
additional Higgs bosons
determination of Higgs profile:
deviations from SM prediction
- > 1 neutral Higgs boson
- charged Higgs boson
- exotic decays:Hinvisible
Higgs physics program at the LHC
•discrimination: SM or extended Higgs sectors (e.g. MSSM)
Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006 3
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:
The „standard“ solution:
new doublet of complex scalar fields
with appropiately choosen potential V
vacuum spontaneously breaks gauge symmetry
one new particle: the Higgs boson H
= v + H
renormalisibility no precise calculation of observables bad high energy behaviour WLWL scattering violates unitarity at ECM~1.2 TeV
Higgs boson mass unknown: theory: unitarity MH<1TeV
LEP search: MH<114.4 GeV electroweak fit: MH<186 GeV excluded at 95% CL at 95%CL
Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006 4
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 ~ 2 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 !!!
unknown Higgs mass fixes Higgs profile completely
Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006 5
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.
Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006 6
LHC
SPPS
pp collisions at the Large Hadron Collider
start in 2007 at ECM of 14 TeV
first years: low lumi running 10 fb-1/year
later (x10): high lumi running 100 fb-1/year
Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006 7
Complexity of a LHC event
+ ~23 additional pp-interactions per bunch crossing at high lumi
~109 proton-proton collisions / sec
~1600 charged particles in detector per event
hard process
+ ISR,FSR
+ underlying
event
Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006 8
The challenge of reconstruction
low lumi. high lumi.
Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006 9
Production of the SM Higgs Boson at LHC
K = (N)NLO/LO
K ~ 1.2
K ~ 2
K ~ 1.4
K ~ 1.1
~4 to 15% + from PDF (5 to15%)
signal MC at NLO only avaiable for GGF
background: NLO calculations often not avaiable
ATLAS: use K=1 and LO MC for signal and BG
CMS:K-factor for GGF + „guestimated“ K for BG
Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006 10
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
H
WW
l
l
background: mainly QCD driven
signal: often electroweak interaction
photons, leptons, …
q
Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006 11
Considerations for Discovery Channels
sufficient signal rate no sensitivity to H in SM
efficient trigger (,e,, …) no sensitivity for: GGF, WBF: Hbb
H mass reconstructable? yes: H, ZZ, bb, no: HWW
control of background
- signal-to-background ratio - estimate of BG from data possible?
- sometimes: shape from MC needed
excl
ud
ed b
y
LEP
main discovery channels
GGF: H GGF: H ZZ 4l+-
GGF: HWW2(l)
ttH: H bb
VBF: H
VBF: H WW
ATLAS
since
2000
Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006 12
H 2 Photons
signal: two photons background:
- reducible: pp j+x, jj+x,..
photon vs. jet seperation
- irreducible: pp+X
diphoton mass
mass resolution M/M = 0.7%
- uniformity/understanding of ECAL
- dead material: % of unconverted
- pile up: vtx constraint
background estimate from sidebands
no Monte Carlo needed
exp. uncertainty: O(0.1%)
S/BG ~ 1/10
CMS 100fb-1
red./irred. BG: 2 to 1 after final cut
LO NLO: increase of S/B ~ 5060%
(K-factor ~ 2, larger Higgs Pt)
NLO
CMS
Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006 13
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
CMS
CMS
100fb-1
NLO
signal: 4 iso. leptons
1(2) dilepton mass = MZ
irreducible BG:
ZZ 4 leptons
four lepton mass
Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006 14
signal:
- 2 leptons + missing ET
- lepton spin corrleations
- no mass peak transverse mass
H WW l l
ATLAS
M=160GeV
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
normalisation rom sideband
shape from MC
NLO effect on spin corr.
ggWW contribution signal like
Dührssen, prel.
ll
Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006 15
Vector Boson Fusion: ppqqH
signature:2 forward jets with
large rapidity gap only Higgs decay products
in central part of detector
rapidity of tag jets rapidity difference
Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006 16
Vector Boson Fusion: ppqqH
Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006 17
Vector Boson Fusion: challenges
pT>20GeV
forward jet reconstruction
influence of UE and pile up?
so far only for low lumi
ATLAS
central jet veto:
influence of UE and pile up?
so far only for low lumi
efficiency of jet veto at NLO.?
distributions at NLO calculated
but: need NLO MC generator
for signal and BG
Zeppenfeld et al.
Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006 18
Vector Boson Fusion: H tau tau ll 4 (or l had 3 ) signature: tagging jets + 2 high pt leptons + large missing ET
backgrounds: tt,Zjjcentral jet veto
reconstruction of m
mass resolution ~ 10% dominated bei Emiss resolution
He
ATLAS30 fb-1
expected BG uncertainty ~ 5 to 10%
for MH > 125 GeV: flat sideband
for MH < 125 normalisation from Z peak, but shape?
collinear approximation
Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006 19
Idea: jjZandjjZ
look almost the same, esp. in calos
same missing energy
only momenta different
Method: select Z events
randomise momenta
apply „normal“ mass reco.
Vector Boson Fusion, Hestimate of BG shape from data
PTmiss,final (GeV) M (GeV)
promising prel. results from ongoing diploma thesis in BN (M. Schmitz)
Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006 20
Weak Boson Fusion: HWWll (lqq)
HWWeATLAS
10 fb-1
MH=160 GeV
H2 photons
S/BG ~ 1/1
S/BG ~1/10
VBF versus inclusive channel
ATLAS
M=160GeV
30fb-1HWWll
S/BG ~ 4/1
S/BG ~ 2/3
smaller rate larger sig-to-BG ratio smaller K-factor
more challenging for detector understanding
order of significance depends on channel and Higgs mass
CMS
Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006 21
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 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
Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006 22
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
Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006 23
Determination of Higgs boson couplings
couplings in production Hx= const x Hx and decay BR(Hyy) = Hy / tot
Hx x BR ~ HX Hy
tot
prod decay
partial width: Hz ~ gHz2
tasks: - disentangle contribution from production and decay
- determine tot
H WW chosen as reference as best measured for MH>120 GeV
for 30fb-1 worse by factor 1.5 to 2
model independent:
only ratio or partial decay widths
13 signal rates used in global fit
(incl. various syst. uncertainties)
Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006 24
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
Dührssen et al.
lower limit from observable rates:
tot > W+Z+t+g+....
upper limit needs input from theory:
mild assumption: gV<gVSM
rate(VBF,HWW)~V2/tot<(V
2 in SM)/tot
tot< rate/(V2 in SM)
Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006 25
MH2 = 2 =MPlanck
Motivation for Supersymmetry from Higgs Sector
Higgs mass problem in SM: 2
“solves” hierarchy problem: why v=246 GeV << MPl=1019GeV ?
MH2 = (MSM-MSUSY)
2 2
W W+ HH natural value ~ MPl
vs 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 O(5) additional parameters
Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006 26
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 corrections: 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
Mtop=174.3 GeVmain 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?
calculated with
FeynHiggs
Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006 27
Light Higgs Boson h
large area covered by many 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
VBF, H covers hole plane
from either H or h observation
with 30fb-1
Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006 28
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
Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006 29
Higgs Decays to Gauginos
Msleptons=250 GeV
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 +2 leptons )• reduced sensitivity for other channels, consistent interpretation needed
CMS 100fb-1
Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006 30
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 same contribution from GGF
compare expected
measurement of R in MSSM
with prediction from SM
for same value of MH
=|RMSSM-RSM|exp
Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006 31
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 yet uncovered area size and location of „hole“ depends on Mtop and program for calculation
ATLAS preliminary
at Born level: CP symmetry conserved in Higgs sector
complex SUSY parameters mixing between neutral CP eigenstates
no absolute mass limit from LEP
Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006 32
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 see 2nd next talk
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)