# Presentation: 465992

## 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

- What have we learned the last 50 yearsorStatus of the Standard Model

## Standard Model

- Precision measurements
-          1990-2000
- (LEP,SLD,Tevatron,
-   NuTeV,...)
- Standard Model tested
- to permille level
- Precise and quantitative
- description of subatomic
- physics

## 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

- Proves high energy reach through virtual processes

- Top quark mass
- LEP indirect

## Higgs boson mass 

- 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

## 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

- 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

- 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

*M**H** between 114 and **~**200 GeV*

## The power of e+e- Colliders

- ● well defined initial state
-      collision energy √s well defined
-      collision energy √s tuneable
-      precise knowledge of quantum numbers
-      polarisation of e- and e+ possible
- ● Clean environment
-      collision of point-like particles
-                     → low backgrounds
- ● precise knowledge of cross sections
- ● Additional options: e-e- , eγ , γγ collisions

- Machine for
-                     Discoveries and Precision Measurements

- The power of e+e- Colliders

- q q 

- LEP(OPAL)

- e+

- e-

## Physics Potential of a Linear Collider (highlights) 

- Physics Potential of a Linear Collider (highlights)

- • Higgs bosons
- • Supersymmetry
- • Structure of space-time
- • Precision tests of
-   electroweak interactions
-        top
-        W
-         Z

- √s:  91...500...~1000 GeV

## 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

- model independent
- measurement

- Recoil mass spectrum
- ee -> HZ   with  Z -> l+l-

-  ~ 3%

- m ~ 50 MeV

- sub-permille
- precision

## Precision physics of Higgs bosons

- mH =    40 MeV

- mH =    120 GeV

- ee -> HZ
- diff. decay channels

- mH =    150 GeV

- mH =    70 MeV

## Precision physics of Higgs bosons

- Reconstructed Higgs Mass (GeV)

- mH=240 GeV

- ΔmH = 400 MeV  (0.2%)
- Δ σ (HZ) = 4%

- Results available
- for
- MH up to 320 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	2.4%
- cc	8.3%
- gg	5.5%
- tt	6.0%
- gg	23.0%
- WW	5.4%
- For 500 fb-1
- MH = 120 GeV

## Standard Model Higgs vsMSSM Higgs

- Standard Model Higgs vsMSSM Higgs

- Precision physics of Higgs bosons

- High precision allows
- sensitivity to new effects
- e.g.
- additional heavy Higgs bosons

## Reconstruction of the  Higgs-potential

- Φ(H)=λv2H2 + λvH3 + 1/4λH4
- SM: gHHH = 6λv, fixed by MH

- gHHH

- (1 ab-1)

## Precision physics of Higgs bosons    

- 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

- Conclusion

## 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

- well measureable at LHC

- precise spectroscopy
- at the Linear Collider

## Supersymmetry

- Production and decay of
- supersymmetric particles
- at e+e- colliders

- charginos                                    s-muons

- Lightest supersymmetric particle stable in most models
-                   candidate for dark matter

- Experimental signature: missing energy

## Supersymmetry

- Production and decay of smuons:
- 320 GeV, 160 fb-1
- Mass errors (MeV):
- 	        smuon      Χ10
- end points:      300        100
- threshold:         90         50

-    Sleptons

-   3 ‰       1 ‰

## Supersymmetry

- Produced in pairs

- 350 GeV
- 160 fb-1

- m ~ 50 MeV

- Easy detection through their decays

-   Charginos

## Supersymmetry

- Di-jet inv mass (500 fb-1, E = 800 GeV)

- Mass peak (50 fb-1, E = 800 GeV)

- MSSM:   one additional Higgs doublet
-                →  h0,H0,A0,H+,H-

- HA:   5σ discovery possible up to Σm = √s – 30 GeV

## Supersymmetry

- 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

- Extrapolation to GUT scale

## 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

- String theory motivates brane models in which our world is confined
- to a membrane embedded in a higher dimensional space

- Extra dimensions provide an explanation for the hierarchy problem

- e.g. large extra dimensions:
- Emission of gravitons
- into extra dimensions
- Experimental signature
-       single photons

- In how many _dimensions_ do we live?

## Hidden 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)

- cross section for anomalous single photon production

- Energy

-  = # of extra dimensions

- e+e- -> G

## Hidden dimensions

- Effects from virtual graviton exchange:

- can prove Spin-2 exchange!

## Hidden dimensions

- Randall-Sundrum Model

- cross-section
- for
- e+e-→μ+μ-
- including
- exchange of
- a KK-tower
- of gravitons

- Direct observation...

## Precision electroweak tests

- σ (pb)

- Energy scan of top-quark threshold

- As the heaviest quark, the top-quark could play a key role in
- the understanding of flavour physics.....

- ...requires precise determination
-     of its properties....

-   ΔMtop  ≈ 100 MeV

## Precision electroweak tests

- together with
- ΔMW = 7 MeV
- (threshold scan)
- And
- ΔMtop =  100 MeV

- 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

##  Summary:  key scientific points  

*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.*

-  Summary:  key scientific points

- The Linear Collider Report of the Worldwide Physics and Detector Study Group:

## General layout of a Linear Collider

- 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

- For E > 200 GeV need to build linear colliders
- Proof of principle:
- SLC

## The TESLALinear Collider

- The TESLALinear 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:

-   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.

- Essence:

## 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

- The TESLALinear Collider

## TESLA

**April 2003: ****38 MV/m**

**High power**
**test of**
**electropolished**
**nine-cell**
**cavity**

- The path to higher energies....

## Next steps  or  

-      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  or
-                    How to arrive at a LC as a Global Project

*I**nternational **LC** **S**teering **G**roup:*

## Next steps  1. Technology Recommendation

-   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.

- Aim at joint selection of one technology in spring 2004

## 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                        **