Future colliders why do we need them and which one do we need
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Future Colliders Why do we need them? And which one do we need?. Albert De Roeck CERN. VLHC. Future Machines. Introduction Restrict to machines at the high energy frontier …as a warm–up for the round table discussion Future Hadron Machines LHC SLHC VLHC Future Lepton Machines

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Future Colliders Why do we need them?And which one do we need?

Albert De Roeck



Future Machines

  • Introduction

    • Restrict to machines at the high energy frontier

      …as a warm–up for the round table discussion

  • Future Hadron Machines

    • LHC

    • SLHC

    • VLHC

  • Future Lepton Machines

    • TeV e+e- LC Hot topic these days!

    • Multi-TeV e+e+ LC

  • Others (neutrino factories, muon colliders)

    • Skip due lack of time…Apologies!



Physics case for new High Energy Machines

Understand the mechanism Electroweak Symmetry Breaking

Discover physics beyond the Standard Model

Reminder: The Standard Model

- tells us how but not why (contains 19 parameters!)

3 flavour families? Mass spectra? Hierarchy?

- needs fine tuning of parameters to level of 10-30 !

- has no connection with gravity

- no unification of the forces at high energy

If a Higgs field exists:

- Supersymmetry

- Extra space dimensions

If there is no Higgs below ~ 700 GeV

- Strong electroweak symmetry breaking around 1 TeV

Other ideas: more gauge bosons/quark & lepton substructure,

Little Higgs models…

See R. Barbieri

Most popular extensions these days

The Next Collider: LHC

Dipoles arriving at CERN…

…and in a few years

Production of components well on track

Some problems with the QRL/Cryogenics,

but delay should be recovered

Plan still for first collisions in 2007

Commissioning will take time (~months)

 Luminosities at start will be low and then

gradually move to 0.5-2.1033cm2 s-1

The CMS & ATLAS Experiments

  • Major Challenge

  • Event pile up ~23 evts/bx @ high lumi

  • ~100 000 000 readout channels

  • Size of 1 event

  • 1 000 000 bytes

  • Trigger selection

  • Total Event Rate 40 MHz 100 Hz

  • Radiation, stability, calibration…

CMS: ~2350 people/~159 institutes

  • Construction of the experiments

    progressing well (some problems;

    but being tackled)

  •  Commissioning:in situ calibrations

  • allignements, synchronization etc.

  •  On schedule to be ready for

  • physics by 2007.

  • Maybe with some reduced acceptance

Physics Landscape by 2010?

  • Hence the future begins in 2007 (2008)

    • Unless advanced by results from low energy experiments (g-2…), Tevatron, EGRET…

  • LHC should have told us, say, by 2010 (with ~30 fb-1)

    • Whether a light (or heavy) Higgs exist ..unveil the EWSB mechanism

    • Whether the world is or could be (low energy) supersymmetric

    • Whether we can produce dark matter in the lab

    • Whether there are more space time dimensions, micro-black holes…

    • Whether it is all different than what we thought

    • Whether there is nothing strikingly new found in its reach…unlikely!

  • Theory

  •  Either at least one Higgs exisits with mass below 1 TeV, or new

  • phenomena (strong EWSB?) set on in the TeV region

  • New physics prefers the TeV scale (Hierarchy problem, fine

    tunning) but not fully guaranteed

What do we know about the Higgs?

Probability for

mH combining

direct and indirect


LHC: SM Higgs with 10 fb-1

~1 good year of data taking

  •  Light Higgs preferred by EW data

  •  Light Higgs needed for SUSY (<135 GeV)

  • Caution … some recent developments

  •  Higgs + higher dimensional operators

  • ( Higgs could be heavy)

  •  Higgsless models in Extra Dimensions scenarios

  • EW fit criticism…

     A light Higgs is not guaranteed

114.4 < Mhiggs < 237 GeV

LHC: low scale SUSY discovery

  • If low scale SUSY: then large

    production of squarks/gluinos at the LHC

  • LSP responsible for dark matter?

    Comparison with WMAP to within 15%

Discovery reach

300 fb-1: 2.5-3 TeV

30 fb-1: 2 TeV already

Upgrades of the LHC

J. Strait exercise:

Not an “official” LHC plot

Possible lumi scenario

If startup is as smooth as assumed here:

Around 2013: simple continuation becomes less exciting

Time for an upgrade?

95% CL14 TeV 300 fb-114 TeV 3000 fb-128 TeV 300 fb-128 TeV 3000 fb-1

 (TeV) 40 60 60  85

The LHC upgrade: SLHC

Time to think of upgrading the machine if wanted in ~10 years

Two options presently discussed/studied

  • Higher luminosity ~1035cm-2 s-1 (SLHC)

    • Needs changes in machine and particularly in the detectors

    •  Start change to SLHC mode some time 2013-2016?

    •  Collect ~3000 fb-1/experiment in 3-4 years data taking.

  • Higher energy?

    • LHC can reach s = 15 TeV with present magnets (9T field)

    • s of 28 (25) TeV needs ~17 (15) T magnets  R&D needed!

LHC project report 626


Extended search reach for both upgrades: Example Contact Interaction Scale









Some Examples with Increased Luminosity

MSSM Heavy Higgs reach

If no Higgs,expect strong VLVL scattering

(resonant or non-resonant)

Maybe difficult for LHC (eg. perhaps only

3-5 effect for WW scattering with 100 fb-1)

3000 fb-1/5

3000fb-1/95% CL

Heavy Higgs observable region

increased by ~100 GeV.

LHC Upgrades

The LHC luminosity upgrade to 1035 cm-2s-1

  •  Extend the LHC discovery mass range by 25-30% (SUSY,Z’,,EDs)

  •  Higgs self-coupling (20-30%)

  •  Rear decays: H, Z, top decays…

  • Improved Higgs coupling ratios,…

  • In general: SLHC looks like giving a good physics return for modest cost.

  •  Get the maximum out of the (by then) existing machine

  •  Will extend the LHC mass range by factor 1.5

  •  Is generally more powerful than a luminosity upgrade

  •  Needs a new machine, magnet& machine R&D, and will not be cheap

 It will be a challenge for the experiments!

 Needs detector R&D starting now

Tracking, electronics, trigger,endcaps,…

 CMS and ATLAS started working groups

 Aim: be ready around 2013

An LHC energy upgrade to s ~ 28 TeV

VLHC: Very Large Hadron Collider


Tunnel of 233 km (E.G could be somewhere near FNAL)

Stage 1: 40 TeV collider with “cheap” 2T field magnets L=1034cm-2 s-1

Stage 2: 200 TeV collider with superconducting magnets. L=2.1034cm-2 s-1

Magnet & Vacuum R&D required (and ongoing)

Detectors with good tracking up to 10 TeV (increase B,L), calorimeter

coverage || up to 6-7, good linearity up to 10 TeV, harsh forward radiation

Why a VLHC?

  • Probe directly the region 10-100 TeV

  • Unlike for the TeV scale, no clear preference today for specifc energy-scale in the multi-10 TeV region.

  • However indirect evidence for New Physics at 10-100 TeV could emerge from LHC and first LC  compelling arguments for a direct exploration of this range.

  • eg. if MH ~ 115 GeV

     New physics at  < 105-106 GeV

     A VLHC can probe directly a large

    part of this range


Effective potential


Unstable EW vacuum

The importance and role of such a machine can be appreciated better after

LHC(/LC) data will be fully understood  revisite during the next decade

Linear Colliders



33 km





TESLA/NLC/GLC: 90 GeV 1 TeV with 35-70 MV/m

CERN: CLIC Two-Beam acceleration scheme to reach >3TeV with 150 MV/m

Machine Parameters

Table from ILC-TRC (2003)


  • International LC scope document

  •  500 GeV upgradeable to ~1 TeV,  500 fb-1 in 4 years

  •  2 interaction regions,  80% electron polarization

  •  Energy flexibility between √s = 90-500 GeV

  • Future: possibility of γγ, e-e-, e+ polarization, Giga –Z

     TeV e+e- Linear Collider

Warm/Cold Technologies



CLIC beam structure

similar to the warm


Choice has impact

on detector R&D/choice

(e.g. time stamping…)

We can built at most one collider: which technology to choose?

 International Technology Recommendation Panel (ITRP) to make a

recommendation on the technology choice

 Next ITRP meeting: Korea 11-13 August (Tomorrow)

??Perhaps a decision announced at ICHEP04 in Beijing??

LC is Moving Forward Strongly!

Study groups of ACFA, ECFA, HEPAP The next large accelerator-based project of particle physics should be a linear collider

US DOE Office of Science Future Facilities Plan:LC is first priority mid-term new facility for all US Office of Science

Major Funding Agencies Regular meetings concerning LC

ICFA (February 2004) reaffirms its conviction that the highest priority for a new machine for particle physics is a linear electron-positron collider with an initial energy of 500 GeV, extendible up to about 1 TeV, with asignificant period of concurrent running with the LHC

LCWS04 Paris(April 2004) publication of the document “understanding

matter, space and time” by 2600 physicists, in support of a linear collider

EUROTEV selected by EC 9 MEuro for R&D for a LC

Very sizable community wants a e+e- Linear Collider

A LC is a Precision Instrument

  • Clean e+e- (polarized intial state, controllable s for hard scattering

  • Detailed study of the properties of Higgs particles

    mass to 0.03%, couplings to 1-3%, spin & CP structure, total width (6%) factor 2-5 better than LHC/measure couplings in model indep. way

  • Precision measurements of SUSY particles properties, i.e. slepton masses to better than 1%, if within reach

  • Precision measurements a la LEP (TGC’s, Top and W mass)

  • Large indirect sensitivity to new phenomena (eg WLWL scattering)

LC will very likely play important role to disentangle the underlying new theory

LC: Few More Examples

Understanding SUSY

High accuracy of sparticle mass measurements

relevant for reconstruction of SUSY breaking


Dark Matter

LC will accurately measure m and couplings,

i.e. Higgsino/Wino/Bino content

 Essential input to cosmology & searches

LC will make a prediction of DMh²~ 3% (SPS1a)

A mismatch with WMAP/Planck would reveal

extra sources of DM (Axions, heavy objects)

 Quantum level consistency: MH(direct)= MH(indirect)?

sin2W~10-5 (GigaZ), MW ~ 6 MeV

(+theory progress)

 MH (indirect) ~ 5%

1/M GeV-1

Gaugino mass parameters

G. Blair et al

F. Richard/SPS1a

What if no new particles in LC range?

Precision measurements of the top quark, e.g top mass!

Compare mW and sin2eff experimental accuracy with

theoretical prediction  theoretical consistency!

Top mass uncertainty is a limiting factor

Mtop=175 GeV

100 fb-1 per point

~ similar to theoretical HO uncertainties, 5x better than exp. precision

Precision indirect measurements (TGCs, Z’, strong EWSB...)

e.g Compares indirect (LC) Z’ searches with direct LHC

Note: some indirect searches also possible at the LHC

e.g. ZKK indirect sensitivity up to 15-20 TeV for SLHC

LC has large reach for indirect measurements

LHC/LC Complementarity


  •  The complementarity of the LHC and LC results has been studied

  • by a working group and has produced a huge document

  • (>450 pages, G. Weiglein principal editor, finishing stage…)

  • Working group contains members from LHC and LC community + theorists

  • Most meetings at CERN (one in the US)

Conclusion: lot to gain for analysis of BOTH machines if there is a

substantial overlap in running time.

Example: at LHC masses of the measured particles are strongly

correlated with the mass of the lightest neutralino




Largely improve

LHC mass

measurements when

LC 10 value is used



LSP 1

LC Time Scales

R. Heuer LCWS04

ILCSC Road Map

2004 technology recommendation(confirmed by ITRP)

Establish Global Design Initiative / Effort (GDI/E)

2005 CDR for Collider (incl. first cost estimate)

2007 TDR for Collider

2008 site selection

2009/2010 construction could start (if budget approved)

First collisions in 2015?

LC the first real “global machine” in HEP?

CLIC: a Multi-TeV Linear Collider

 Two beam acceleration presently only

feasible way to reach multi-TeV region

 Principle demonstrated with CTF2

CLIC: aim for 3 TeV (5 TeV) LC

  •  CERN: accelerate CLIC R&D support to

  • evaluate the technology by 2009/2010 with

  • extra external contributions

    • CLIC collaboration.

  • FAQs:

  • CLIC technology O(5-6) years behind TeV class LCs

  • CLIC can operate from 90 GeV 3 (5) TeV .

    Physics case for CLIC documented in a new CERN yellow report CERN-2004-005 (June)

CLIC: Examples of the Large Reach

Eur.Phys. J C33 273 (2004)

E.g.: Contact interactions:

Sensitivity to scales up to

100-400 TeV (1 year of data)

E.g. Supersymmetry

# sparticles that can be detected

Expect higher precision at LC vs LHC

Summary: Indicative Physics Reach

Ellis, Gianotti, ADR

hep-ex/0112004+ few updates

Units are TeV (except WLWL reach)

Ldt correspond to 1 year of running at nominal luminosity for 1 experiment


  • 14 TeV14 TeV 28 TeV 40 TeV 200 TeV 0.8 TeV 5 TeV

  • 100 fb-11000 fb-1 100 fb-1 100 fb-1100 fb-1 500 fb-1 1000 fb-1

  • Squarks 2.534 5200.4 2.5

  • WLWL24 4.5 7 18 6 30

  • Z’ 56811 358†30†

  • Extra-dim (=2) 91215 25 655-8.5† 30-55†

  • q* 6.57.5 9.5 13 750.8 5

  • compositeness 3040 40 50100 100 400

    TGC () 0.00140.0006 0.0008 0.0003 0.0004 0.00008

† indirect reach

(from precision measurements)

Don’t forget: (much) better precision at an e+e- machine


  • LHC will be the next high energy collider

    • It will unveil the EWSB mechanism

    • It will probe the TeV scale for new physics

  • SHLC (luminosity upgrade) will give good return for a modest investment

  • VLHC is still for the far future

  • A LC will be the next proposed machine/it will complement LHC perfectly

    • A LC collider is a precision instrument

    • LC community has built up large momentum

    • TESLA and NLC/GLC technologies essentially ready choice?

    • Construction could start around 2009/2010  collisions in 2015?

    • CLIC (3 TeV) aims to demonstrate feasibility of the technology by 2009/2010

  • Is 500 (1000) GeV the optimal energy reach for the machine? Will certainly be addressed in the light of the LHC data by 2009/2010

In any case: exciting times ahead !!

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