Physics topics at the International Linear Collider

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Physics topics at the International Linear
Collider
Preliminary version Will be replaced by the
final version before the start of the school
R.-D. Heuer (Univ. Hamburg)
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Status of the Standard Model
Verification of triple gauge vertices from ee- ?
WW- cross section
Indirect determination of the top quark
mass Proves high energy reach through virtual
processes
LEP
Towards unification of forces
charged current
neutral current
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Status of the Standard Model
spring 2005
Precision measurements
1990-2005 (LEP,SLD,Tevatron,
NuTeV,) Standard Model tested to permille level
and at the level of Quantum Fluctuations Precis
e and quantitative description of
subatomic physics
However. . .
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. . . key questions open
Standard Model
What is the origin of mass of elementary
particles or why are carriers
of weak force so heavy while the photon is
massless
Higgs mechanism
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. . . key questions open
Cosmic Connections
What is dark matter What is dark energy
What happened to antimatter
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Open key questions
. . . key questions open
Ultimate Unification
Do the forces unify, at what scale Why is
gravity so different Are there new forces
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Open key questions
. . . key questions open
Hidden Dimensions
or Structure of Space -Time
Are there more than four space-time
dimensions What is the quantum theory of
gravity
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The next steps at the energy frontier
There are two distinct and complementary
strategies for gaining new understanding of
matter, space and time at future particle
accelerators HIGH ENERGY direct discovery of
new phenomena i.e. accelerators operating at
the energy scale of the new particle HIGH
PRECISION interference of new physics at high
energies through the precision measurement of
phenomena at lower scales
Both strategies have worked well together ? much
more complete understanding than from either one
alone
prime example LEP / Tevatron
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Experimental limits on the Higgs boson mass
The next steps
We know enough now to predict with great
certainty that fundamental new understanding of
how forces are related, and the way that mass is
given to all particles, will be found with a
Linear Collider operating at an energy of at
least 500 GeV, extendable to around 1000 GeV.
LEP,SLD Tevatron
indirect
direct
MH between 114 and 250 GeV
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Hadron Collider Lepton Collider

• p composite particleunknown ?s of IS
  partons,no polarization of IS partons,parasitic
  collisions
• p strongly interactinghuge SM
  backgrounds,highly selective trigger
  needed,radiation hard detectors needed

• e pointlike particleknown and tunable ?s of
  IS particles,polarization of IS particles
  possible,kinematic contraints can be used
• e electroweakly interactinglow SM
  backgrounds,no trigger needed,detector design
  driven by precision

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A Road Map for the Energy Frontier
Tevatron
HERA
LHC
S-LHC
ILC
CLIC, Muon collider, other technologies
2020
2010
2015
2005
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The ILC Physics Case orRelation of Hadron
Collider and Linear Collider

• 1. Since the ILC will start after the start of
  LHC, it must add significant amount of
  information. This is the case!
• (see e.g. TESLA TDR, Snowmass report, ACFA
  study etc.)
• 2. Neither ILC nor LHC can draw the whole picture
  alone. An ILC will
• add new discoveries and
• precision of ILC will be essential for a better
  understanding of the underlying physics
• 3. There are probably pieces which can only be
  explored by the LHC due to the higher mass reach.
  Joint interpretation of the results will improve
  the overall picture
• 4. Overlapping running of both machines will
  further increase the potential of both machines
  and might be mandatory, depending on the physics
  scenario realized

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The Role of the ILC
Explore new Physics through high precision at
high energy microscopic
telescopic
Study known SM processesto look for tiny
deviationsthrough virtual effects(needs
ultimate precisionof measurements
andtheoretical predictions)
Study the properties ofnew particles(cross
sections,BRs, quantum numbers)

• precision measurements will allow --
  distinction of different physics scenarios --
  extrapolation to higher energies

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Physics at the ILC
Comprehensive and high precision coverage of
energy range from MZ to 1 TeV
Higgs Mechanism Supersymmetry
Strong Electroweak Symmetry Breaking
Precision Measurements at lower
energies
Selected Physics Topics
cross sections few fb to few pb ? e.g.
O(10,000) HZ/yr
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Standard Model
Standard Model (SM) Gauge theory Problem
Gauge invariance only possible for massless gauge
bosons
Introducing mass terms in the SM Lagrangian by
hand violates SU(2)xU(1) gauge symmetry
SM solution introduction of a scalar background
field (Higgs-field) Dynamical generation of
mass terms Analogy Supra conductivity
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The Higgs mechanism
Paradigm All (elementary) particles are
massless ? gauge principle works ? renormalizable
theory (finite cross sections) Permanent
interaction of particles with a scalar Higgs
fieldacts as if the particles had a mass
(effective mass)
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The Higgs mechanism
How to add such a field in a gauge invariant way?
Introduction of SU(2)xU(1) invariantMexican hat
potential Simplest case (SM) complex doublet of
weak iso-spin
This is only the most economic way. Many more
possibilitiesexist, e. g. two doublets (minimal
SUSY), triplets, ... Higgs mechanism requires the
existence of at least onescalar, massive Higgs
boson.
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Tasks at the ILC

• Establishing the Higgs mechanism as being
  responsible forEW symmetry breaking requires
  more than discovering oneor more Higgs bosons
  and measuring its/their mass(es).
• Precision measurements must comprise
• Mass
• Total width
• Quantum numbers JCP (Spin, CP even?)
• Higgs-fermion couplings (? mass?)
• Higgs-gauge-boson couplings (W/Z masses)
• Higgs self-coupling (spontaneous symmetry
  breaking)
• Precision should be sufficient to distinguish
  between
• different models (e. g. SM/MSSM, effects from XD,
  ...)

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Precision physics of Higgs bosons
Dominant production processes at LC
Task at the LC determine properties of the
Higgs-boson establish Higgs mechanism responsible
for the origin of mass
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Precision physics of Higgs bosons
Recoil mass spectrum ee -gt HZ with Z -gt ll-
Ds 3
model independent measurement
Dm 50 MeV
sub-permille precision
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ee -gt HZ Z -gt l l H -gt
qq
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Precision physics of Higgs bosons
ee -gt HZ diff. decay channels
mH 120 GeV
DmH 40 MeV
mH 150 GeV
DmH 70 MeV
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Precision physics of Higgs bosons
Higgs field responsible for particle masses ?
couplings proportional to masses
Precision analysis of Higgs decays
?BR/BR bb 2.4 cc 8.3 gg 5.5 tt 6.0 gg 23.0 W
W 5.4 For 500 fb-1 MH 120 GeV
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Precision Higgs Physics
Determination of absolute coupling values with
high precision
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Reconstruction of the Higgs-potential
gHHH
F(H)?v2H2 ?vH3 1/4?H4 SM gHHH 6?v, fixed
by MH
??/? 10-20 for 1 ab-1
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Precision Higgs Physics Higgs Couplings and New
Physics
Yamashita
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Heavy SUSY-Higgs
Heavy SUSY Higgs bosonsobservation and
mass/BR/width(?) measurements
deep into the LHC wedge
region at 800-1000 GeV LC
HA 5s discovery possible up to Sm
vs 30 GeV
HA? bbbb and HA ? bbtt/ttbb observable
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Precision physics of Higgs bosons
Conclusion
precision measurements at the ILC together with
the results from LHC are crucial to establish
the Higgs mechanism responsible for the origin of
mass and for revealing the character of the Higgs
boson if the electroweak symmetry is broken in
a more complicated way then foreseen in the
Standard Model the LC measurements strongly
constrain the alternative model
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Beyond the Higgs
Why are electroweak scale (102 GeV) and the
Planck scale (1019 GeV) so disparate ? Are
there new particles ? ? supersymmetry
new forces ? ? strong interactions
hidden dimensions ?
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Supersymmetry
Introduction of an additional symmetry to the SM
boson ? fermion symmetry Each SM particle gets a
SUSYpartner whose spin differs by1/2. All other
quantum numbersare equal. But so far no SUSY
particle seen (SUSY symmetry broken)
but SUSY well motivated theory ?
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Solution to hierarchy problem
Motivation 1 It solves the hierarchy problem
The divergence in the Higgs mass corrections is
cancelledexactly for unbroken SUSY. If it is not
broken too strongly (i. e. if the SUSY partners
areat lt 1 TeV), there is no fine tuning
necessary.
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Unification of gauge couplings
Motivation 2 Gauge coupling constants unify
Minimal supersymmetric SM
(Requires light (lt TeV) partnersof EW gauge
bosons)
This is achieved for sin2qWSUSY
0.2335(17) Experiment sin2qWexp 0.2315(2)
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More good reasons ...
Motivation 3 Provides cold dark matter
candidate If lightest SUSY particle is stable, it
is an excellentdark matter candidate Motivation
4 Link to gravity SUSY offers the theoretical
link to incorporate gravity.Most string models
are supersymmetric. Motivation 5 Predicts light
Higgs boson SUSY predicts a light (lt 135 GeV)
Higgs boson as favoredby EW precision data.
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Supersymmetry
? best motivated extension of SM grand
unification connection to gravity light Higgs
sin2TW dark matter candidate . ?
mass spectrum depends on the unknown breaking
scheme ? LC task for SUSY reconstruction of
kinematically accessible sparticle spectrum
i.e. measure sparticle properties (masses,
Xsections, spin-parity) extract
fundamental parameters (mass parameters, mixings,
couplings) at the weak scale
extrapolate to GUT scale using RGEs ?
determine underlying supersymmetric model
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Supersymmetry
Mass spectra depend on choice of models and
parameters...
well measureable at LHC
precise spectroscopy at the Linear Collider
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Production and decay of supersymmetric
particles at ee- colliders
Supersymmetry
charginos
s-muons
Lightest supersymmetric particle stable in most
models candidate for dark
matter
Experimental signature missing energy
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Supersymmetry
Measurement of sparticle masses
ex Charginos threshold scan
ex Sleptons lepton energy spectrum
in continuum
achievable accuracy
dm/m 10-3
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Supersymmetry
Extrapolation to GUT scale
Extrapolation of SUSY parameters from weak to GUT
scale (within mSUGRA) Gauge couplings unify at
high energies, Gaugino masses unify at same
scale Precision provided by LC for slepton,
charginos and neutralinos will allow to test if
masses unify at same scale as forces
Gluino (LHC)
SUSY partners of electroweak bosons and Higgs
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Dark Matter and SUSY
If SUSY LSP responsible for Cold Dark Matter,
need acceleratorsto show that its properties are
consistent with CMB data
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Conclusions
Supersymmetry
The Linear Collider will be a unique tool for
high precision measurements ? model independent
determination of SUSY parameters ? determination
of SUSY breaking mechanism ? extrapolation to
GUT scale possible
but what if
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No Higgs boson(s) found.

• divergent WL WL ? WL WL amplitude in SM at
• SM becomes inconsistent unless a new strong
  QCD-like interaction sets on
• Goldstone bosons (Pions) W states
  (technicolor)
• no calculable theory until today in agreement
  with precision data
• Experimental consequences deviations in
  
• triple gauge couplings
  quartic gauge couplings

LC (800 GeV) sensitivity to energy scale
? triple gauge couplings 8 TeV quartic gauge
couplings 3 TeV ? complete threshold
region covered
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Extra dimensions

• Completely alternative approach to solve
  hierarchy problemThere is no hierarchy
  problem
• Suppose the SM fields live in normal 31 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
classical
GN1/MPl2
ADD-model d new space dimension with radius R,
which only communicates through gravity
rgtgtR
compare 4-dim and 4d ?V(r)
example MD 1 TeV for d 2(3) ? R 1 mm(nm)
potentially macroscopic size! Detectable?
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Extra dimensions
For r lt R, gravity follows Newton's law in 4 d
dimensions
For r gt R, gravity follows effectively Newton's
law in4 dimensions, since the distance in the
extra dimensionsdoes not rise anymore
The Planck mass
only effectively appearsso high at large
distances. The true scale of gravity is
If e. g. R O(100 mm) and d 2, one obtains ?
Gravity might become visible at TeV-scale
colliders!
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Extra dimensions
Extra dimensions provide an explanation for the
hierarchy problem
String theory motivates brane models in which our
world is confined to a membrane embedded in a
higher dimensional space
e.g. large extra dimensions Emission of
gravitons into extra dimensions Experimental
signature single photons
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Hidden dimensions
cross section for anomalous single photon
production
d of extra dimensions
measurement of cross sections at different
energies allows to determine number and scale of
extra dimensions (500 fb-1 at 500 GeV, 1000 fb-1
at 800 GeV)
ee- -gt gG
Energy
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Precision measurementsof SM processes
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Precision electroweak tests
As the heaviest quark, the top-quark could play a
key role in the understanding of flavour
physics..
requires precise determination of its
properties.
Energy scan of top-quark threshold
?Mtop 100 MeV
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Precision electroweak tests
high luminosity running at the Z-pole Giga Z (109
Z/year) 1000 x LEP in 3 months
with e- and e polarisation
?sinTW 0.000013
together with ?MW 7 MeV (threshold
scan) And ?Mtop 100 MeV
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key scientific points at ILC

• Whatever LHC will find, ILC will have a lot to
  say!
• If there is a light Higgs (consistent with
  precision EW data)? verify that Higgs mechanism
  is at work in all elements ? make telescopic
  use of precision data (top, Giga-Z)
• If there is a heavy Higgs (inconsistent with
  prec. EW data)? verify that Higgs mechanism is
  at work in all elements? use precision data
  (top, Giga-Z) to clarify inconsistency
• Higgs new states (SUSY, XD, Z', ...)?
  precise spectroscopy of the new states
  ? extrapolation to high energy
• No Higgs, no new states (inconsistent with prec.
  EW data)? use precision data (top, Giga-Z) to
  clarify inconsistency ? measure effects of
  strong EWSB

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Physics Conclusion
LC with vs 1 TeV and high luminosity allows ?
most stringent test of electroweak Standard
Model ? to establish Higgs mechanism in its
essential elements ? to explore SUSY sector with
high accuracy, model independent ?
extrapolations beyond kinematically accessible
region ? .
World-wide consensus on physics case
http//sbhep1.physics.sunysb.edu/grannis/lc_conse
nsus.html
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International Linear Collider Parameters
global
consensus (Sept. 2003)
(1) baseline machine 200 GeV lt vs lt
500 GeV integrated luminosity 500 fb-1
in 4 years electron polarisation
80 (2) energy upgrade to vs 1 TeV
integrated luminosity 1 ab-1 in 3
years (3) options positron polarisation
of 50 high luminosity running at MZ
and W-pair threshold e-e-, e?, ??
collisions (4) concurrent running with LHC
desired ! Times quoted for
data taking cover only part of program !