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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 machines
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


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
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
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
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
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
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
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?

the lhc upgrade slhc
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








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
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
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
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
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
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
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
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
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
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
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
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
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
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
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 !!