Transcript Document 7178429

Physics at
the ILC
Ariane Frey, MPI München
38. Herbstschule Maria Laach
Ariane Frey, MPI München
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Physics at the ILC
Higgs Physics
Beyond the Standard Model:
• Supersymmetry
• Extra Dimensions
• Heavy Z’, Strong EWSB
Precision Physics (top, W, …)
LHC
ILC
Synergy
• top, W
Ariane
Frey,
MPI
München
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Ariane Frey, MPI München
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Success of the Standard Model
• Experimental discovery of
all of its matter constituents
and force carriers
• Simple common approach
to describe all (relevant)
forces: gauge principle
• Self-consistent at the level
of quantum corrections
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However…. many open questions
Origin of mass ?  Higgs
Unification of all forces ?
SUSY ??
SM describes only a tiny fraction of our
universe – what is the dark matter ?
Are quarks and leptons really elementary
particles ? Why q(e) = - q(p) ?
Origin of matter-antimatter asymmetry in the
universe ? (CP violation)
What about Gravity?
Do hidden extra dimensions exist ?
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Terascale Physics
Why is the TeV scale interesting?
1. SM without Higgs violates unitarity (in WLWL WLWL)
at 1.3 TeV! (something must happen!)
2. Evidence for light Higgs
3. What protects the Higgs mass at the TeV scale
4. 2 * Mtop = 350 GeV
5. Dark Matter consistent with
(sub) TeV-scale WIMP (e.g. SUSY-LSP)
6. SUSY: Sparticles < 1 TeV, many models < 200 GeV
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Why an e+e- Collider ?
All of this so far could have been a speech to build the LHC !
p
p
Easier to reach high energies
p = composite particle:
unknown √s of IS partons,
no polarization of IS partons,
parasitic collisions
p = strongly interacting:
huge SM backgrounds,
highly selective trigger needed,
radiation hard detectors needed
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e+
e-
Difficult to reach high energies
(synchrotron radiation)
e = pointlike particle:
known and tunable √s of IS
particles, polarization of IS particles
possible, kinematic contraints can
be used
e = electroweakly interacting
low SM backgrounds,
no trigger needed,
detector design driven by precision
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Hadron vs. Electron Collider
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Why an e+e- Collider ?
Electron positron colliders allow for
1. Discovery of the unexpected
e e  X new (YSM )
2. Precision measurements of new + ‘old’ physics
Prediction of top mass
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e  e   SM
telescopic
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Why an e+e- Collider ?
Electron positron colliders allow for
1. Discovery of the unexpected
e e  X new (YSM )
2. Precision measurements of new + ‘old’ physics
e  e   SM
telescopic
Higher precision can give discoveries:
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Higgs discovery potential at LHC
Higgs production
pb
Higgs decay
fully hadronic final states dominate,
but cannot be extracted from large
QCD background
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Higgs discovery potential at LHC
 “Guaranteed SM-like Higgs
discovery over the full allowed
mass range with 30 fb-1 in one
experiment
 Light Higgs most challenging
 Whole mass range could be
excluded @ 95 % CL after ~ 1
month of running
First measurements of Higgs properties possible:
• Mass: 0.1 – 0.4%
• Production rates: 10-20%
• Ratios of couplings: W/Z, W/t, W/t: 10-20%
• model-independent measurements of absolute
couplings impossible
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Higgs - Task of a Linear Collider
After the discovery of a Higgs boson, the key task of ILC is to
establish the Higgs mechanism in all elements
as being responsible for EW symmetry breaking
Precision Measurements must comprise:
•
•
•
•
•
•
Mass
Total Width
Quantum numbers JPC (Spin 0, CP-even?)
Higgs-Fermion couplings (~ mass ?)
Higgs-Gauge-Boson couplings (W/Z masses)
Higgs self coupling (spontaneous symmetry breaking)
Measurements should be precise enough to distinguish between
different models (e.g. SM/MSSM, effects from extra-dimensions, …)
Aim at model-independence!
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Higgs Production
Dominant production processes at LC:
 ~ 1/s
Higgs-strahlung
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 ~ ln s
WW fusion
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Higgs-strahlung
ee -> HZ
Z -> l l
H -> qq
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Model-independent observation
Anchor of LC Higgs physics:
• select di-lepton events
consistent with Zee/μμ
• calculate recoil mass:
m 2H  (p  p initial )2
model independent,
decay-mode independent
measurement!
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Model-independent observation
efficiency is ~independent of
decay mode:
small differences can be corrected
with MC
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works over the whole range
of possible Higgs masses:
precision on (HZ):
1-3% for mH<200 GeV
3-20% for mH<500 GeV
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Measurement of the Higgs Mass
Model-independent HZ analysis only uses a fraction of the events (Zll)
For a precise mass determination further statistics can be gained if
hadronic Z-decays are used.
For mass measurement, explicit Higgs final states (e.g. Hbb) may be used
Highest sensitivity to Higgs mass comes from purely hadronic events
Kinematic fits improve the mass resolution
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Higgs Mass
M H  120GeV
M H  120GeV
H Z  bbqq
H 0 Z  bbl  l 
0
M H  150GeV
H 0 Z  W W  qq
M H  150GeV
H 0 Z  W W l  l 
500 fb-1 @ s = 350 GeV
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Total Width
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Total Width
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Total Width Precision
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Higgs Quantum Numbers
Is it a Higgs boson ?
Rise of cross section near threshold is sensitive to Higgs Spin
for J=0: rise ~ 
for J>0: rise ~ k ,k>1
(some cases for J=2 are also ~
but can be distinguished from J=0
through angular distributions)
also:
observation of H or H
rule out J=1 and require C = +
mH=120 GeV
20 fb-1/point
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Higgs Branching Ratios
Higgs Branching ratios best to study Higgs Yukawa couplings for a light H
Crucial test: (Hff) ~ mf ?
At ILC measurement of >absolute< BR’s is possible, because of decay-mode
independent gHZZ measurement:
meas
(HZ)xBR(H  X)
BR(H  X) 
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(HZ)meas
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Higgs Branching Ratios
ΔBR/BR
bb
cc
gg
tt
gg
WW
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2.4%
8.3% For 500 fb-1
5.5% MH = 120 GeV
6.0%
23.0%
5.4%
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Higgs Self Coupling
Higgs self-coupling (‘the holy grail’):
V =λv2H2 + λvH3 + 1/4λH4
SM: gHHH = 6λv, fixed by MH
 essential test of the mechanism of
spontaneous symmetry breaking
6 jet final
states !
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Measurement of Higgs self coupling
Tiny cross section
Complicated multi-jet final state
 detector design: energy flow
jet mass
resolution: 60%/√E
Difficult backgrounds
30%/√E
Need highest luminosity
Precision for 1 ab-1 :
  20%

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Higgs Profile
Use precision to check
whether it is the SM
Higgs or signs of new
physics beyong the SM
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Higgs - Global Fits
Interpretation of branching ratio
and
cross section measurements
in global fits (HFITTER)
%-level accuracy – sensitivity beyond SM
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Excellent detector resolution helps !
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SUperSYmmetry
Symmetry between
Fermions  Bosons
(Matter)
(Force carriers)
...now we have doubled the particle spectrum...
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Supersymmetry
... BUT solves several SM problems:
without Supersymmetry
♥
♥
Link to gravity
lightest SUSY particle stable
 Dark matter candidate
♥
♥
♥
Solves fine tuning problems
Predicts light Higgs
with Supersymmetry
Unification of forces
1 TeV
Energy in GeV
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SUSY Higgs Bosons
In MSSM two complex Higgs doublet fields needed
(cancellation of triangle anomalies)
Minimal possibility: two doublets (weak isospin ±1)
 5 physical Higgs bosons:
h,H
neutral, CP-even
A
neutral, CP-odd
H±
charged
Masses at tree-level predicted as function
of mA and tan
but large rad. corrections (top, stop)
mh < 135 GeV
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SUSY Higgs at LHC
To prove the structure of the Higgs sector, the heavier Higgs bosons
have to be observed either directly or through loop-effects.
Direct observation difficult in part of parameter space at LHC
What’s possible at a
Linear Collider?
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SUSY Higgs Bosons
Very clear signal in HA  bbbb
100 – 1000 MeV mass precision due to kinematic fit
drawback: pair production  mass reach ~ s / 2
Example for mH=250 GeV / mA=300 GeV at s = 800 GeV:
√s =800 GeV
mA=300 GeV
mH=250 GeV
Reach extended into
the LHC wedge region
ΔM/M = 0.1-0.5 % with 500 fb-1
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Typical SUSY spectrum
well measurable at LHC
precise spectroscopy at LC
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Supersymmetry
- Task of LC
different SUSY breaking mechanisms yield different spectra:
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SUSY Production at ILC
This will be fun…
cross sections in the
10 – 1000 fb range
o(103 – 105) events
to disentangle this ‘chaos’
the various LC options,
in particular
- tunable s
- tunable beam polarisation
are vital!
200
500
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1000
3000
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Example: Sleptons

L /R
Pair-production
 /Z
Examples:
E-

L /R
E+
Simple two-body kinematics and
beam-constraint allow for mass
measurement of both
slepton and lightest neutralino
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SUSY - Dark Matter
If SUSY LSP responsible for Cold Dark Matter, need accelerators
to show that its properties are consistent with CMB data
- Future precision on h2 ~ 2% (Planck) – match this precision!
- WMAP points to certain difficult regions in parameter space:
small
M  M  M0
1
e.g. smuon pair production at 1TeV
only two very soft muons!
need to fight backgrounds
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LSP – Dark matter candidate
Need to measure LSP mass, composition and couplings !!
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SUSY “cross checks”
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“With a little help from my friends…”
SUSY
cascade
decay at
LHC
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LHC
ILC
Precise
measurement at
ILC
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SUSY Global Fit
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LHC
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ILC
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Extra Dimensions
Completely alternative approach to solve hierarchy problem:
“There is no hierarchy problem”
Suppose the SM fields live in “normal” 3+1 dim. space
Gravity lives in 4 + d dimensions
d extra dimensions are curled to a small volume (radius R)
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Extra Dimensions
Surface~ r2
Density of
field quanta ~ 1 / r2
 Force ~ 1 / r2
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For massless quanta
Coulombforce
Gravity
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Extra Dimensions
cross section for anomalous single
photon production
Exclusion limits (95%CL)
Discovery (5 σ)
500 fb-1 @ 500 GeV,
1000 fb-1 @ 800 GeV
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Extra Dimensions
Range of predictions
for models with XD
Effect on each
particle exactly the
same size !
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Discovery through precision
Precision measurements of SM processes are a
telescope to higher scale physics
Example Higgs




Top quark
Z‘ and similar vector resonances
Alternative EWSB
etc.
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Top quark
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Top quark mass
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Where the top mass comes into play
predictions of EW
parameters:
Light Higgs mass
prediction in SUSY:
Prediction of
DM density
mH/mt ~ 1!
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Top Yukawa Coupling
- need highest energy
- heaviest quark  surprises?
- small cross section
- complicated final state
~g2ttH
- analysis in bb and WW decay
- huge and complicated backgrounds
(ttWW is a 10-fermion final state)
- b-tagging crucial to suppress bkg.
and reduce combinatorial bkg.
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Top Yukawa Coupling
Result:
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Giga Z running
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Improvement in EW parameters
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If no Higgs boson(s) found….
 divergent WL WL  WL WL amplitude in SM at
 4 2
2  o 
 G
F


2
  (1.2TeV )

 SM becomes inconsistent unless a new strong QCD-like interaction sets on
no calculable theory until today in agreement with precision data
Experimental consequences:
triple gauge couplings
deviations in
quartic gauge couplings:
LC (800 GeV): sensitivity to energy scale Λ:
triple gauge couplings: ~ 8 TeV
quartic gauge couplings: ~ 3 TeV
 complete threshold region covered
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New Gauge Bosons (Z’)
Heavy Z’ vector boson motivated by TeV scale remnants of
Grand Unified Theories, string theories etc.
Examples: Z’ in SO10, E6
LHC: M(Z’) up to ~ 5 TeV
ILC: Unlikely to directly produce a Z’ (Tevatron limits approaching 1 TeV)
virtual extension up to 15 TeV measuring its interference with Z, exchange
(PETRA could measure Z properties without producing Z’s)
5
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95%CL
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New Gauge Bosons (Z’)
LHC
ILC
If Z’ mass is known (e.g. from LHC) ILC can measure the
vector and axial-vector couplings an pin down the nature of the Z’
If here, related to origin of neutrino
masses
If here, related to origin of Higgs
If here, Z’ comes from an extra
dimension of space
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Whatever LHC will find,...
…ILC will have a lot to say!
‘What’ depends on LHC findings:
1.
If there is a ‘light’ Higgs (consistent with prec.EW)
 verify the Higgs mechanism is at work in all elements
2.
If there is a ‘heavy’ Higgs (inconsistent with prec.EW)
 verify the Higgs mechanism is at work in all elements
 find out why prec. EW data are inconsistent
3.
1./2. + new states (SUSY, XD, little H, Z’, …)
 precise spectroscopy of the new states
4.
No Higgs, no new states (inconsistent with prec.EW)
 find out why prec. EW data are inconsistent
 look for threshold effects of strong EWSB
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Summary
A linear e+e- collider with 500 -1000 GeV is on our wish list!
Challenging machine and detector requirements, but no major
obstacles.
With ILC data can:
•
•
•
•
•
establish the Higgs mechanism
complete the SUSY spectrum
pin down LSP dark matter
see signs of new physics way beyond the ILC (and LHC)
energy through precision measurements
look for exotic things (extra dimensions, Z’, contact
interactions…)
Best results when combining LHC and ILC
LHC/ILC Study Group
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