Download Higgs physics at the LHC and ILC

Higgs Studies at the LHC
and the ILC
Albert De Roeck CERN
SUSY 2005
18-23 July Durham
The Higgs Mechanism
1964 Higgs, Englert and Brout propose to add
a complex scalar field to the Lagrangian
Expect at least one new scalar particle:
The (Brout-Englert-) Higgs particle
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SM Higgs (LEP)
– MH>114.1 GeV @95% CL
MSSM neutral Higgs bosons (LEP)
– Mh, MA>92.9, 93.3 GeV @95% CL
– MH± >89.6 GeV @95% CL for BR(MH± → τν) =1
– MH± >78.6 GeV @95% CL for any BR
Electroweak fits to all high Q2 measurements give:
– MH=98+52-36 GeV (old top mass)
– MH<186 GeV @ 95% CL (“yesterdays” new top mass)
Tevatron searches  see C. Tully’s talk
Probably the most wanted
particle in HEP
Discover … or prove that it
does not exist
High Energy Frontier in HEP
Next projects on the HEP roadmap
• Large Hadron Collider LHC at CERN: pp @ 14 TeV
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M. Lamont
Tev4LHC meeting
@ CERN (April)
LHC will be closed and set up for beam on 1 July 2007
First beam in machine: August 2007
First collisions expected in November 2007
Followed by a short pilot run
First physics run in 2008 (starting April/May; a few fb-1? )
• Linear Collider (ILC) : e+e- @ 0.5-1 TeV
– Strong world-wide effort to start construction earliest around
2009/2010, if approved and budget established
– Turn on earliest 2015 (in the best of worlds)
– Study groups in Europe, Americas and Asia (World Wide Study)
Quest for the Higgs(*) particle is a major motivation for these new machines
(*) will discuss mostly the Standard Model Higgs in this talk
“Higgs Roadmap”
• Discover the Higgs (in the range 114.4 GeV < MH < 1 TeV)
• Determine its properties/profile
– The mass
– Spin and parity quantum numbers
– How does it decay?
• Measure Yukawa like patterns
• Measure relations between fermion and gauge boson
couplings
• Observe rare decay modes
• Observe unexpected decay modes? (new particles?)
• Measure total width
• Reconstruction of the Higgs potential by determination of
the Higgs self coupling
• Its nature: is it standard, supersymmetric, composite.
BOTH LHC and LC will be crucial in establishing Higgs Dynamics
LHC: pp Collisions at 14 TeV
• ~20 min bias events overlap
at 1034cm-2 s-1
• HZZ Z mm
H 4 muons the cleanest
(“golden”) signature
This (not the H production !!)
repeats every 25 ns…
Reconstructed tracks
with pt > 25 GeV
SM Higgs production
NLO Cross sections
M. Spira et al.
gg fusion
IVB fusion
SM Higgs search channels
Low mass MH ≲ 200 GeV
Production
M. pieri
Inclusive
VBF
WH/ZH
ttH
YES
YES
YES
YES
YES
YES
DECAY
H → γγ
H → bb
YES
H → ττ
H → WW*
YES
H → ZZ*, Z ℓ+ℓ-,
ℓ=e,μ
YES
H → Zγ, Z → ℓ+ℓ-, ℓ=e,μ
very low σ
Intermediate mass
(200 GeV ≲ MH ≲700 GeV)
inclusive H → WW
inclusive H → ZZ
YES
YES
High mass (MH ≳ 700 GeV)
VBF qqH → ZZ → ℓℓνν
VBF qqH → WW → ℓνjj
H → γγ and H → ZZ* → 4ℓ are the only channels
with a very good mass resolution ~1%
Examples
Low MH < 140 GeV/c2
Medium 130<MH<500 GeV/c2
High MH > ~500 GeV/c2
Vector Boson Fusion Channels
Dokshitzer, Khoze, Troyan;
Rainwater, Zeppenfeld et al.
ppqqH +X Higgs and two forward jets (|| ~ 3)
Results
30fb-1
Tag jets to
reduce
background
With these new channels each experiment
can discover the Higgs with 5 with 30 fb-1
Other Channels (Hbb)
S/B=0.03
S/B=0.3
30 fb-1
Not discovery channels but can be used to confirm/measure couplings
Diffractive Higgs Production
b
gap
p
H
gap

p
SM Higgs:
Cross section ~3fb (Khoze et al)
MSSM: s ~ x10 larger (tan)
b -jet 100 fb
Exclusive production:
 Jz=0 suppression of ggbb bkg
 Higgs mass via missing mass
M H2  ( p  p  p' p' ) 2
1fb
Kaidalov et al.,
hep-ph/0307064
M = O(1.0 - 2.0) GeV
 CP structure of the Higgs from angular
distribution of the protons
 Of course, need Roman potsFP420 project
120
Also HWW*
LHC Reach for a Higgs Discovery
Different channels
Total sensitivity
30 fb-1 2-3 years
LHC can cover the whole region of interest with 10 fb-1
Mass and Width Resolution
ATLAS PTDR
5-8%
0.1-1%
MSSM Higgs
h, A, H  gg
H4
H/A  mm
h  bb
H  hh  bb gg
A  Zh  bb 
H/A  tt
m/m (%) 300 fb-1
0.10.4
0.10.4
0.1-1.5
12
1-2
12
1-10
Analysis of indirect widths for
mass range below 200 GeV:
10-20% precision
Branching Ratios and Couplings
Precision on BR
Ratios of couplings
Cannot determine total Higgs cross section
No absolute meas. of partial dec. widths
Dominated by luminosity
uncertainty
Precision 10-40%
With “mild” theoretical
assumptions couplings
Duhrssen et al., hep-ph/0406323
Precision 10-40 (20)%
Assume
(within 5%)
Also measurement of H
Spin and CP-quantum Numbers: H  ZZ4l
Higgs rest
frame
F    1   cos    cos 2

G ( )  L sin 2   T 1  cos 2 

L T
R
L T
 MH>250 GeV: distinguish between S=0,1 and CP even.odd
 MH<250 GeV: only see difference between SM-Higgs and S=0, CP=-1
 , less powerful
ATLAS
100 fb-1
Heavy MSSM Higgs Search
• A/H  tt
• H  t
• A/H  mm
• H  tb
• A/H  bb/ mm in bb H/A
Contours for 5  discovery
MHMAX scenario
New: includes VBF channels
MSSM 5 Higgses: h,H,A,H
At low tan , we may exploit
the sparticle decay modes:
 A, H  20 20  4l + ETmiss
 A, H in cascade decays of sparticles
CP Violating Scenario
M. Schumacher
 CP eigenstates h, A, H mix to
mass eigenstates H1, H2, H3
 maximise effect  CPX scenario
(Carena et al., Phys.Lett B495 155(2000))
arg(At)=arg(Ab)=arg(Mgluino)=900
Small area remains uncovered
Could be covered by MH1 < 70 GeV
(not studied yet)
Significant dependence on the
top mass (now 172.7±2.9 GeV)
Higgs Studies at an e+e- Linear Collider
 L > 1034cm-2s-1  80% electron polarization
 Energy flexibility between √s = 90-500 GeV
 Future: possibility of γγ, e-e-, e+ polarization, Giga –Z
Can detect the
Higgs via the recoil
to the Z
e.g. Desch
Bataglia
LCWS00
 Fully simulated+reconstructed HZ event
 Backgrounds low  Robust signal: if
(eeH+x) 100 times lower, still observable
Observation of the Higgs
independent of decay modes
Higgs Production at an e+e- Linear Collider
Dominant production processes at ILC:
ZH
H
 ~ln(s)
 ~1/s
Example: s=350 GeV
mH = 120 GeV
L= 500 fb-1 (~2-4 years)
~90 K Higgs events produced
Higgs Mass Measurement
Garcia-Abia, et al., hep-ex/0505096
s= 350 GeV 500 fb-1
Beam systematics included
Determine the Higgs mass to
about 40-70 MeV
How much can theory handle/does theory want?
Higgs Branching Ratios
SM Higgs Branching Ratio
Tim Barklow, LCWS04
bb
t t 
gg
cc
W W
gg
M H (GeV)
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Model independent
Absolute branching ratios! Normalized to absolute HZ cross section
Precise measurements: few % to 10%.
Special options to improve further e.g. BR(Hgg) ~ 2% at photon collider
Extraction of Higgs Couplings
Use measured branching ratios to extract Higgs couplings to fermions
and bosons
Global fit to all observables (cross sections and branching ratios)
& take into account correlations
 The precise determination of the effective couplings opens a window
of the sensitivity to the nature of the Higgs Boson
TESLA-TDR values
Rare Higgs Decay Modes
gHmm/gHmm ~15%
for 1 ab-1
Rare Higgs decay modes become accessible eg
 Hbb at higher masses (Yukawa couplings)
 Hmm
 HgZ
Hbb
gHbb/gHbb ~17%
for 1 ab-1
H,A Search at a Photon Collider
J. Gunion et al.
M. Krawczyk et al.
 Extent discovery range to close to kinematic range= 0.8Ecms(e+e-)
 Measurement of / to10-20% with 1 year of data
Invisible Higgs Decays
Invisible Higgs decays –Higgs
decay in undetected particlescan be observed directly in
ZH events
 Observe a peak in the
recoil mass of ZH events
Sum of width
Recoil
Branching ratio can be determined
with good precision:
Better than 5% for large enough
branching ratios
Spin and CP Quantum Numbers
 At threshold: determine J from the  dependence of ZH
 At continuum: use angular distributions to determine CP composition
HZ production
+ also Htt
Top-Higgs Yukawa coupling
• The top-Higgs Yukawa coupling is
very large (gttH ~ 0.7 while gbbH ~
0.02). Precise measurements
important since could could show
largest deviations to new physics
• Needs 0.8-1.0 TeV collider and
large luminosity
• If mH<2mt  e+e- ttH
• If mH>2mt  measure BR(Htt)
LHCLC data: Top Yukawa coupling
Dawson, Desch, Juste, Rainwater, Reina, Schumacher, Wackeroth
Assume a light Higgs < 2mt
Production processes
LC:
e+e-  ttH No precise measurement at 350-500 GeV LC
LHC: gg  ttH measures •BR
(ttbb,ttWW)
depends on g2ttH g2bbH and g2ttH g2WWH
g2bbH and g2WWH can be measured precisely in a
model independent way at the ILC (few %)
LHC alone~ 0.3
(and model
dependent)
ILC
350 GeV 500 fb-1
 can determine g2ttH without any model assumptions
Measuring the Higgs Potential
 Measure the Higgs self-coupling: HH production
Larger precision at higher energies
Eg CLIC: a 3 to 5 TeV LC
MH = 240 GeV
180 GeV
140 GeV
120 GeV
LHC: gHHH (3000 fb-1) for 150<MH<200 GeV
Summary: Higgs at the LHC and LC
~3 years
~1 year
5  discovery
mH > 114.4
Higgs can be discovered over full allowed mass range in 1 year of (good)
LHC operation
 final word about SM Higgs mechanism
• However: it will take time to understand and calibrate ATLAS and CMS
• If Higgs found, mass can be measured to 0.1% up to mH~ 500 GeV
• A LC will provide precision measurements on absolute couplings ~%, quantum
numbers (spin, CP…), rare decays of the Higgs, and the Higgs potential
A LC aims for a full validation of the Higgs Mechanism
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LHC Higgs Summary
• LHC will discover the SM Higgs in the full region up to 1 TeV
or exclude its existence. If no Higgs, other new phenomena
in the WW should be observed around 1 TeV
• The LHC will measure with full luminosity (300 fb-1)
• The Higgs mass with 0.1-1% precision
• The Higgs width, for mH> 200 GeV, with ~5-8% precision
• Cross sections x branching ratios with 6-20% precision
• Ratios of couplings with 10-40% precision
• Absolute couplings only with additional assumptions
• Spin information in the ZZ channel for mH>200 GeV
ILC Higgs Summary
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The Higgs cannot escape the ILC, if within its kinematical range
The Higgs mass can be measured down to 40-70 MeV
Absolute branching ratios can be determined to the % level
Couplings can be determined to the % level
Note new phenomena such as heavy vector bosons or Higgs
triplets give contributions to the Higgs couplings of O(5%)
Rare decay modes can be studied
Invisible decay modes can be detected (to some level also at the
LHC)
Spin and CP quantum numbers can be determined
The Higgs potential can be measured (particulalry with a multiTeV LC)
• LHC+ILC(500) combined data give the best top-yukawa coupling
measurement