Download 200 GeV

The Electron-Positron Linear Collider
Probing the Secrets of the Universe
R.-D. Heuer (Univ. Hamburg)
Colloquium Brookhaven, May 25, 2003
History of the Universe
LHC, LC
RHIC,HERA
● Particle Physics today
● The case for the Linear Collider
● Status of the TESLA project
● The LC as a global project
What have we learned the last 50 years
or
Status of the Standard Model
The physical world is
composed of
Quarks and Leptons
interacting via
force carriers
(Gauge Bosons)
Last entries:
top-quark
1995
tau-neutrino 2000
Standard Model
Precision measurements
1990-2000
(LEP,SLD,Tevatron,
NuTeV,…)
Standard Model tested
to permille level
Precise and quantitative
description of subatomic
physics
Top quark mass
LEP indirect
Test of the SM at the Level of
Quantum Fluctuations
Indirect determination of the
top mass
possible due to
• precision measurements
• known higher order
electroweak corrections
(
Mt 2
M
) , ln( h )
MW
MW
Proves high energy reach through virtual processes
Higgs boson mass
LEP indirect
Test of the SM at the Level of
Quantum Fluctuations
Indirect determination of the
Higgs mass
possible due to
• precision measurements
• known higher order
electroweak corrections
Mt 2
Mh
(
) , ln(
)
MW
MW
Electroweak Unification
HERA ep collider
Weak and electromagnetic
Interactions:
Similar magnitude
beyond ~ 100 GeV
Open questions
Standard Model
• What is the origin of mass
Open questions
Ultimate Unification
• Do the forces unify, at what scale
• Why is gravity so different
• Are there new forces
•
•
•
Open questions
Hidden Dimensions
• Are there more than four space-time dimensions
• What is the quantum theory of gravity
•
•
•
Open questions
Cosmic Connections
• What is dark matter
• What is dark energy
• What happened to antimatter
•
•
•
Particle Physics and Cosmology
Particle Physics and Cosmology
both point to New Physics at the TeV scale
Electroweak unification
Dark Matter
Dark Energy
Inflation
Neutrino Masses
CP Violation
The next steps
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
ex: top quark , prediction of Higgs boson mass range (LEP/Tevatron)
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.
Experimental
limits on the
Higgs boson mass
indirect
direct
MH between 114 and ~200 GeV
The power of e+e- Colliders
Electron-Positron Linear Collider offers
● well defined initial state
collision energy √s well defined
collision energy √s tuneable
precise knowledge of quantum numbers
polarisation of e- and e+ possible
e+
e-
LEP(OPAL)
● Clean environment
collision of point-like particles
→ low backgrounds
● precise knowledge of cross sections
● Additional options: e-e- , eγ , γγ collisions
qqmm
Machine for
Discoveries and Precision Measurements
Physics Potential of a Linear Collider (highlights)
√s: 91…500…~1000 GeV
• Higgs bosons
• Supersymmetry
• Structure of space-time
• Precision tests of
electroweak interactions
top
W
Z
Precision physics of Higgs-Bosons
Discovery and first measurements at the LHC (perhaps at Tevatron?)
The Higgs boson is a new form of matter
a fundamental scalar
a new force coupling to mass
Therefore, need to establish Higgs mechanism as the mechanism
responsible for
giving mass to elementary particles
breaking of the electroweak symmetry
Task of the Linear Collider:
Precision measurements to determine
mass(es)
quantum numbers (spin zero)
couplings (proportional to masses of bosons, quarks, leptons)
self-coupling (→ reconstruction of Higgs potential)
Precision physics of Higgs bosons
Dominant production processes at LC:
Precision physics of Higgs bosons
Recoil mass spectrum
ee -> HZ with Z -> l+l-
Ds ~ 3%
model independent
measurement
Dm ~ 50 MeV
sub-permille
precision
Precision physics of Higgs bosons
mH =
ee -> HZ
diff. decay channels
120 GeV
DmH =
mH =
40 MeV
150 GeV
DmH =
70 MeV
Precision physics of Higgs bosons
mH=240
GeV
e e   ZH 
 
qqqq
ΔmH = 400 MeV (0.2%)
Δ σ (HZ) = 4%
Results available
for
MH up to 320 GeV
Reconstructed Higgs Mass (GeV)
Precision physics of Higgs bosons
Determination of quantum numbers
Spin from threshold
measurement
CP-quantum numbers
from
H,Z angular distributions
or
polarisation analysis
of Higgs decays to taus
Precision physics of Higgs bosons
Higgs field responsible for particle masses
→ couplings proportional to masses
Precision analysis
of Higgs decays
ΔBR/BR
bb
cc
gg
tt
gg
WW
2.4%
8.3%
5.5%
6.0%
23.0%
5.4%
For 500 fb-1
MH = 120 GeV
Precision physics of Higgs bosons
High precision allows
sensitivity to new effects
e.g.
additional heavy Higgs bosons
Standard Model Higgs
vs
MSSM Higgs
Reconstruction of the
Higgs-potential
gHHH
Φ(H)=λv2H2 + λvH3 + 1/4λH4
SM: gHHH = 6λv, fixed by MH
D  20%

(1 ab-1)
Precision physics of Higgs bosons
Conclusion
The precision measurements at the Linear Collider
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
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 ?
Supersymmetry
● unifies matter with forces
for each particle a
supersymmetric partner
(sparticle) of opposite
statistics is introduced
● allows to unify strong
and
electroweak forces
● provides a link
to string theories
Supersymmetry
● Predicts
• light Higgs boson ( + additional heavier Higgs bosons)
• spectrum of sparticles (→doubling number of particles)
● Contains
• many new parameters connected to SUSY breaking
● High precision measurements of
• masses
• couplings
• quantum numbers
needed to
• extract fundamental parameters (few)
• determine the way Supersymmetry is broken
i.e the underlying supersymmetric model
Supersymmetry
Mass spectra depend on choice
of models and parameters...
well measureable at LHC
precise spectroscopy
at the Linear Collider
Supersymmetry
charginos
Production and decay of
supersymmetric particles
at e+e- colliders
s-muons
Lightest supersymmetric particle stable in most models
candidate for dark matter
Experimental signature: missing energy
Supersymmetry
Sleptons
Production and decay of
smuons:
320 GeV, 160 fb-1
Mass errors (MeV):
smuon
Χ1 0
end points:
300
100
threshold:
90
50
3‰
1‰
Energy spectrum of muons
Supersymmetry
Charginos
Produced in pairs
Easy detection through
their decays
350 GeV
160 fb-1
Dm ~ 50 MeV
Cross section rises as
Shape of X-section -> spin
Supersymmetry
MSSM: one additional Higgs doublet
Di-jet inv mass (500 fb-1, E = 800 GeV)
→ h0,H0,A0,H+,H-
Mass peak (50 fb-1, E = 800 GeV)
HA: 5σ discovery possible up to Σm = √s – 30 GeV
Supersymmetry
Gluino (LHC)
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
SUSY partners of
electroweak bosons and Higgs
Supersymmetry
Conclusions
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 ……
No Higgs boson(s) found….
WLWL scattering:
Standard Model mathematically
inconsistent unless new
physics at about 1.3 TeV
Experimental consequence: New strong interaction measurable in
triple and quartic gauge boson couplings
Sensitivity at a TeV Linear Collider: ~ 8 TeV (TGC)
~ 3 TeV (QGC)
Hidden dimensions
In how many dimensions do
we live?
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
Hidden dimensions
cross section for anomalous single
photon production
d = # of extra dimensions
e+e- -> gG
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)
Energy
Hidden dimensions
Effects from virtual graviton exchange:
can prove Spin-2 exchange!
Hidden dimensions
Randall-Sundrum Model
Direct observation…
cross-section
for
e+e-→μ+μ-
including
exchange of
a KK-tower
of gravitons
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….
σ (pb)
Energy scan of top-quark threshold
ΔMtop ≈ 100 MeV
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
ΔsinΘW = 0.000013
together with
ΔMW = 7 MeV
(threshold scan)
And
ΔMtop = 100 MeV
Summary: key scientific points
The Linear Collider Report of the Worldwide Physics and Detector Study Group:
We know enough now to predict with very high confidence that the
Linear Collider, operating at energies up to 500 GeV, will be needed
to understand how forces are related and the way mass is given to all
particles.
We are confident that the new physics that we expect beyond the
standard model will be illuminated by measurements at both the LHC
and the LC, through an intimate interplay of results from the two
accelerators.
The physics investigations envisioned at the LC are very broad and
fundamental, and will require a leading edge program of research for
many years.
General layout of a Linear Collider
For E > 200
GeV need to
build linear
colliders
Proof of
principle:
SLC
The challenges:
Luminosity:
high charge density (1010), > 10,000 bunches/s
very small vertical emittance (damping rings, linac)
tiny beam size (5x500 nm) (final focus)
Energy:
high accelerating gradient (> 25 MV/m, 500 - 1000 GeV)
To meet these challenges:
A lot of R&D on LC’s world-wide
different technologies: NLC/JLC…..TESLA……CLIC
The TESLA
Linear Collider
superconducting Nb cavities
Decisions of the German Ministry for Education and
Research concerning the TESLA Linear Collider
5 February 2003
● Today no German site for the TESLA linear collider will be put forward.
● This decision is connected to plans to operate this project within a
world-wide collaboration
● DESY will continue its research work on TESLA in the existing
international framework, to facilitate and assure German participation
in a future global project
● DESY will remain a world-wide leading centre of particle physics.
● The decision to not propose a site today is not meant as a
reduction of the importance of particle physics in Germany
Essence:
The statement by the German government
• is positive on a linear collider in general,
• approves continued R&D on TESLA,
• encourages the German participation in a
global project,
• but leaves the site selection open for the
time being.
The TESLA
Linear Collider
Routine production of cavities
exceeding 25 MV/m
(TESLA goal for 500 GeV)
New surface treatment,
gradients of
> 40 MV/m (single cells)
-> clear energy upgrade
TESLA
The path to higher energies….
High power
test of
electropolished
nine-cell
cavity
April 2003: 38 MV/m
Next steps
or
How to arrive at a LC as a Global Project
International LC Steering Group:
1. unite first behind one project with all its aspects,
including the technology choice, and then
2. approach all possible governments in parallel in order to
trigger the decision process and site selection.
Next steps 1. Technology Recommendation
Aim at joint selection of one technology in spring 2004
How:
• Gather a committee of wise persons, who use criteria to be
developed by the ILCSG, to recommend a technology choice to the
ILCSC.
• The regional steering committees will each nominate 4 persons
from which the ILCSG will choose three from each list for a total of 9
wise persons.
First discussion of the make-up of the committee in August.
Next steps 2. Global Linear Collider Center
The ILCSG agrees that it would be highly desirable to form a
precursor to the Global Linear Collider Center:
Core group to begin making an international design, based
on accumulated work to date, but reexamined in a
completely international context.
In parallel to the work of the design group:
preparation of political decision, definition of organisational
structure, site analysis
Aim at approval of LC around 2006/2007
Conclusion
We have a convincing scientific case and a world consensus on the
importance of a Linear Collider and on its timing w.r.t. the LHC
LC and LHC offer complementary view of Nature at energy frontier
We have the technology/ies for the LC at hand
We are developing detector technologies to do the physics at the LC
We have a great dynamics in the international coordination
and are gaining political attention
We have an exciting and promising future for discoveries and for
understanding the universe and its origin
Let’s make it happen