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Transcript of Higgs Physics at the Large Hadron Collider Markus Schumacher, Bonn University NRW Phenomenology...
![Page 1: Higgs Physics at the Large Hadron Collider Markus Schumacher, Bonn University NRW Phenomenology Meeting 2006, Bad Honnef, January 2006.](https://reader033.fdocuments.us/reader033/viewer/2022061305/551460a7550346494e8b58ed/html5/thumbnails/1.jpg)
Higgs Physics at theHiggs Physics at the
Large Hadron ColliderLarge Hadron ColliderMarkus Schumacher, Bonn University
NRW Phenomenology Meeting 2006, Bad Honnef, January 2006
![Page 2: Higgs Physics at the Large Hadron Collider Markus Schumacher, Bonn University NRW Phenomenology Meeting 2006, Bad Honnef, January 2006.](https://reader033.fdocuments.us/reader033/viewer/2022061305/551460a7550346494e8b58ed/html5/thumbnails/2.jpg)
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)
![Page 3: Higgs Physics at the Large Hadron Collider Markus Schumacher, Bonn University NRW Phenomenology Meeting 2006, Bad Honnef, January 2006.](https://reader033.fdocuments.us/reader033/viewer/2022061305/551460a7550346494e8b58ed/html5/thumbnails/3.jpg)
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
![Page 4: Higgs Physics at the Large Hadron Collider Markus Schumacher, Bonn University NRW Phenomenology Meeting 2006, Bad Honnef, January 2006.](https://reader033.fdocuments.us/reader033/viewer/2022061305/551460a7550346494e8b58ed/html5/thumbnails/4.jpg)
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
![Page 5: Higgs Physics at the Large Hadron Collider Markus Schumacher, Bonn University NRW Phenomenology Meeting 2006, Bad Honnef, January 2006.](https://reader033.fdocuments.us/reader033/viewer/2022061305/551460a7550346494e8b58ed/html5/thumbnails/5.jpg)
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.
![Page 6: Higgs Physics at the Large Hadron Collider Markus Schumacher, Bonn University NRW Phenomenology Meeting 2006, Bad Honnef, January 2006.](https://reader033.fdocuments.us/reader033/viewer/2022061305/551460a7550346494e8b58ed/html5/thumbnails/6.jpg)
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
![Page 7: Higgs Physics at the Large Hadron Collider Markus Schumacher, Bonn University NRW Phenomenology Meeting 2006, Bad Honnef, January 2006.](https://reader033.fdocuments.us/reader033/viewer/2022061305/551460a7550346494e8b58ed/html5/thumbnails/7.jpg)
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
![Page 8: Higgs Physics at the Large Hadron Collider Markus Schumacher, Bonn University NRW Phenomenology Meeting 2006, Bad Honnef, January 2006.](https://reader033.fdocuments.us/reader033/viewer/2022061305/551460a7550346494e8b58ed/html5/thumbnails/8.jpg)
Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006 8
The challenge of reconstruction
low lumi. high lumi.
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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
![Page 10: Higgs Physics at the Large Hadron Collider Markus Schumacher, Bonn University NRW Phenomenology Meeting 2006, Bad Honnef, January 2006.](https://reader033.fdocuments.us/reader033/viewer/2022061305/551460a7550346494e8b58ed/html5/thumbnails/10.jpg)
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
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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
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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
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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
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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
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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
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Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006 16
Vector Boson Fusion: ppqqH
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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.
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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
![Page 19: Higgs Physics at the Large Hadron Collider Markus Schumacher, Bonn University NRW Phenomenology Meeting 2006, Bad Honnef, January 2006.](https://reader033.fdocuments.us/reader033/viewer/2022061305/551460a7550346494e8b58ed/html5/thumbnails/19.jpg)
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)
![Page 20: Higgs Physics at the Large Hadron Collider Markus Schumacher, Bonn University NRW Phenomenology Meeting 2006, Bad Honnef, January 2006.](https://reader033.fdocuments.us/reader033/viewer/2022061305/551460a7550346494e8b58ed/html5/thumbnails/20.jpg)
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
![Page 21: Higgs Physics at the Large Hadron Collider Markus Schumacher, Bonn University NRW Phenomenology Meeting 2006, Bad Honnef, January 2006.](https://reader033.fdocuments.us/reader033/viewer/2022061305/551460a7550346494e8b58ed/html5/thumbnails/21.jpg)
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
![Page 22: Higgs Physics at the Large Hadron Collider Markus Schumacher, Bonn University NRW Phenomenology Meeting 2006, Bad Honnef, January 2006.](https://reader033.fdocuments.us/reader033/viewer/2022061305/551460a7550346494e8b58ed/html5/thumbnails/22.jpg)
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
![Page 23: Higgs Physics at the Large Hadron Collider Markus Schumacher, Bonn University NRW Phenomenology Meeting 2006, Bad Honnef, January 2006.](https://reader033.fdocuments.us/reader033/viewer/2022061305/551460a7550346494e8b58ed/html5/thumbnails/23.jpg)
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)
![Page 24: Higgs Physics at the Large Hadron Collider Markus Schumacher, Bonn University NRW Phenomenology Meeting 2006, Bad Honnef, January 2006.](https://reader033.fdocuments.us/reader033/viewer/2022061305/551460a7550346494e8b58ed/html5/thumbnails/24.jpg)
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)
![Page 25: Higgs Physics at the Large Hadron Collider Markus Schumacher, Bonn University NRW Phenomenology Meeting 2006, Bad Honnef, January 2006.](https://reader033.fdocuments.us/reader033/viewer/2022061305/551460a7550346494e8b58ed/html5/thumbnails/25.jpg)
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
![Page 26: Higgs Physics at the Large Hadron Collider Markus Schumacher, Bonn University NRW Phenomenology Meeting 2006, Bad Honnef, January 2006.](https://reader033.fdocuments.us/reader033/viewer/2022061305/551460a7550346494e8b58ed/html5/thumbnails/26.jpg)
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
![Page 27: Higgs Physics at the Large Hadron Collider Markus Schumacher, Bonn University NRW Phenomenology Meeting 2006, Bad Honnef, January 2006.](https://reader033.fdocuments.us/reader033/viewer/2022061305/551460a7550346494e8b58ed/html5/thumbnails/27.jpg)
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
![Page 28: Higgs Physics at the Large Hadron Collider Markus Schumacher, Bonn University NRW Phenomenology Meeting 2006, Bad Honnef, January 2006.](https://reader033.fdocuments.us/reader033/viewer/2022061305/551460a7550346494e8b58ed/html5/thumbnails/28.jpg)
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
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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
![Page 30: Higgs Physics at the Large Hadron Collider Markus Schumacher, Bonn University NRW Phenomenology Meeting 2006, Bad Honnef, January 2006.](https://reader033.fdocuments.us/reader033/viewer/2022061305/551460a7550346494e8b58ed/html5/thumbnails/30.jpg)
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
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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
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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)