Recent update on the world wide lc project
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Recent update on the world-wide LC Project. François Richard LAL/Orsay. 9th Franco-Italian meeting on B physics at LAPP, Annecy February 18-19 2013. Introduction.

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Recent update on the world-wide LC Project

François Richard LAL/Orsay

9th Franco-Italian meeting on B physics

at LAPP, AnnecyFebruary 18-19 2013

F. Richard LAL


  • There exist a technically well established scenario to build right away a LC (and its detectors) reaching up to ECM=1 TeV

  • There are solid physics arguments to believe that such a machine can achieve major physics resultsi.e. provide a decisive test of the SM

  • The main unknown, in the present international context, is whether our developed nations are willing to commit the large resources needed to build globally such a machine

F. Richard

Process to build a world-wide LC

  • At the end of LEP2 it was felt that the next project should not only go well beyond LEP energy but also allow for X100 luminosity and beam polarization

  • 500 GeV was considered as the minimal energy range to cover the light Higgs (ttH, ZHH) and the top program (couplings and mass measurement)

  • Accordingly a consensus (OECD meeting of Minister of science) emerged in 2004 to state that the next large collider after LHC should be an e+e- collider which should be a WORLD WIDE machine (TESLA, mainly led by Germany could not fly)

F. Richard

The Present Situation

  • Japan/Asia logically becomes the next contender given that CERN is over-booked with LHC commitments

  • It should be stressed that the commitment of Japan, very cautious as usual, has recently gained momentum with strong support from politicians (including the new prime minister) and industry

  • Two sites are being officially studied

  • The discovery at CERN of a ‘H-like’ candidate has considerably boosted the process

  • A window of opportunity for HEP that our community is ready to exploit

F. Richard

Erice and ILC (draft version)

  • Gobalisation is emphasized

  • There is a strong scientific case for an electron-positron collider, complementary to the LHC, that can study the properties of the Higgs boson and other particles with unprecedented precision and whose energy can be upgraded. The Technical Design Report of the International Linear Collider(ILC) has been completed, with large European participation. The initiative from the Japanese particle physics community to host the ILC in Japan is most welcome, and European groups are eager to participate

  • Europe looks forward to a proposal from Japan to discuss a possible participation.

F. Richard




F. Richard

The WW effort on ILC

F. Richard

Physics aspects

  • What could be our future?

  • The present picture can be tentatively summarized by saying that we can imagine 3 types of scenarios:

  • 1 The present standard theory valid up to the Planck scale (DM, Baryogenesis, EW phase transition ?)

  • 1 cannot be known a priori and only very precise measurements allow to ‘close’ the model (GigaZ, superB)

  • 2 A SUSY scenario emerging at a TeV scale

  • 2 is difficult to cover completely with LHC given the possibility of light SUSY particles ~degenerate with the LSP while ILC offers cleaner techniques to deal with this

F. Richard


  • 3 A composite scenario with its various avatars (Technicolor, extra dimensions, little Higgs…)

  • 3 usually predicts new heavy bosons and quarks but without the guarantee that they could be observed at LHC

  • We should therefore be prepared for a scenario where the new signals are not directly accessible to LHC in which case only precision measurements are left to indirectly predict the new phenomena as was the case in the past (W/Z masses, existence of 2nd and 3d generations, c mass, top mass, Higgs mass)

F. Richard

Size of deviations

  • After LHC results most scenarios predict small deviations (<10%) and it will not be easy for LHC to indirectly demonstrate (>5 sd) the existence of phenomena beyond the SM and, moreover, to find a full set of EW observables to pin down the new theory to guide our choice of the next colliders 

  • This mission is clearly given to e+e- colliders (and b factories) which, in many instances, can extend the domain of vision to energy scales reaching beyond 10 TeV

  • I will illustrate this with Higgs and top precision measurements

F. Richard

Higgs at ILC

  • 250 GeV

    gHZZ 1% s>>b

    CP (small admixture)

    Spin 0 or 2 ?

    Brinv <1%

    BR(ccbar) 7%

  • ≥ 500 GeV

    G(WW)+BR(WW) ->GT 6%

    crucial to extract width in a model independent way ttHdgt/gt~5%H->2H dl/l~10-20% ongoing analysis (7 sd significance)

F. Richard

Why so precise ?

F. Richard

ILC500 vs LHC 3000 fb-1

M. Klute et al.

F. Richard

Top mass

G. Degrassi et al arXiv:1205.6497

dMt<100 MeVdGt=22 MeV

F. Richard

Top couplings

  • stt+ AFBt+Leptonhelicity slope with Pe-,e+=±0.8,∓0.3provide 6 observable from which g/Z form factors are extracted separately

  • (g-2)t can be measured (~as/p) to 10%

  • CPV form factors are also accessible

  • These measurements allow to test extra dimensions up to 50TeV

F. Richard

What can we expect in the next years ?

  • TDR for the 500 GeV machine : done with costing shown this month in Vancouver (ICFA meeting)

  • Global organization ILC+CLICwith one project leader under ICFA: done (L. Evans)

  • A worldwide political agreement, G20 type, is needed: the hidden sector that we cannot control

  • First step will be the Japanese expression of interest but, in my view, this can only happen with positive signs from the 2 other regions

  • It is essential that the community becomes aware of this aspect which conditions the future of our field

F. Richard

Time scale

  • Given the time scale, we need to launch the ILC right now to be in phase with the next ‘energy frontier’ machine

  • To understand this last point, imagine that after ‘freezing’ the LC project (and therefore wasting the present effort, discouraging the Japanese offer and dispersing the community of physicist & engineers), we get stuck at LHC without any clear message indicating the parameters of the next machine…

F. Richard


  • The proposed detectors, ILD & SiD, have required a formidable R&D effort again only conceivable as a world-wide organisation

  • Typically ~CMS type but with much more ambitious performances made possible with the ‘friendly’ environment of ILC: e.g. a TPC detector becomes possible, thin Si detectors <20%X0 in from ECAL, very thin µvertex detectors close by (<2cm) to the interaction point etc…

  • 2 of them scientifically highly desirable and efforts with machine experts have resulted in a realistic push pull set up

  • ~same detectors for CLIC with special features

F. Richard

Some features

sE/E = 0.3/ÖE

sE/E = 0.6/ÖE

  • Multijet topologies like ttttH and ZHH demand high performance detectors far beyond LEP2:

  • Full coverage for tracking (including tagging) , calorimetry, µ/e identification

  • Resolution on jets ~3% e.g. for W/Z separation

  • PFLOW method requiring high granularity of calorimetry and large BR² (B in SiD R in ILD)

  • Excellent momentum resolution for recoil mass in Z->µµ(ee)+H

  • Sophisticated b/c tagging capabilities (b charge determination for AFBt and AFBb)

  • Luminosity and polarization at the 0.1% level

  • All of these features are necessary and optimized at variance between SiD and ILD

F. Richard

Construction aspects

  • Cost drivers are mainly the magnet (+return yoke) and calorimetry

  • CMS allows a safe extrapolation of the magnet while realistic calorimetry prototypes are being developed

  • Typical cost is ~500 M$/detector including MY (will be delivered soon) but not the R&D part

  • ~10% of the cost of the machine but of strategical importance: Some experts even think that the time of construction will be conditioned by our ability to construct the detectors

  • When ? The answer given at Krakow is: before 2030

F. Richard


  • The worldwide community has been preparing for a LC since many years and is ready for a timely decision

  • The impact of the ‘H-like’ candidate discovery should be used to trigger this decision

  • Japan is expressing strong interest to build ILC in a worldwide framework (Japan cannot do it alone)

  • The future of our field would be strongly reinforced if this happens and therefore we should do our best to make it happen

F. Richard


F. Richard

ILD overview

Return Yoke

Beam line






Forward components

(QD0 magnet – FCals)





F. Richard

ILC 500 GeV (RDR 2006)

Components 4.15 B

CF 2.47 B


RDR Costs

Total Value Cost

$4.65B Shared


$1.67B Host


17 106manhours

(in-house labor)

Impact parameter resolution






Jet energy resolution

Jet Energy Resolution s/Ejet (%)

ALEPH measured

CDF measured

ATLAS simulation

H1 measured



ILC goal



Jet Energy (GeV)

Invisible width

F. Richard

ILC250/500 vs LHC 3000 fb-1

M. Klute et al.

F. Richard


F. Richard


F. Richard

Composite Higgs

G. Giudice et al hep-ph/0703164

F. Richard

Discrimination between models

P. Doublet, PhD-Thesis

F. Richard

Another observable

  • In the rest system of the top quark the lepton angular distribution is given by:

    where alep=1 l=1 for tR and -1 for tL (NB: helicities)

  • The angle qhel is measured in the rest frame of the top quark with the z axis defined by the direction of motion of the top quark in the laboratory

  • It is easy to reconstruct qhelat a LC

  • Can be done with b jets (ab=-0.4) which are sensitive to tbW anomalous couplings

F. Richard

The top mass

  • For many years LC studies have shown that a threshold scan can provide a top mass with <100 MeVaccuracy (including theory)

  • LC can also measure very precisely mt and Gt (~20 MeV) as a fit to an invariant mass distribution but theorists cannot relate easily this measurement to a well defined quantity to deduce the EW parameter

  • LHC will suffer from this problem and it is proposed to use other observables (xsection, gluon radiation)

    -> Not clear that an error <1 GeV can be reached when one includes theory uncertainties

F. Richard

What is needed ?

  • The evolution of l in the Higgs potential towards the high energy scale is controlled by mt and as

  • As noted by several authors with mh=126 GeV l tends to come very close to the stability limit (0) at high energy which may have some interesting cosmological consequences

  • mH=126 GeV was ‘predicted’ assuming SM+gravity valid up to arbitrary energies also implying l(Planck)=0arXiv:0912.0208 M. Shaposnikov & C. Wetterich

  • To assess such ideas one will ultimately need an unambiguous (QCD) and precise (<200 MeV) determination of mtwhich seems to require a LC

F. Richard

F2A form factor

  • One has:

  • One can construct CPV observables with optimized sensitivity (W.Bernreuther et al hep-ph/9511256 & 9602273)

  • Example:

  • Where where one uses the direction of the anti-top and of the positron coming from the top. One then defines a CP image of this observable O- (replace the first vector by –kt the second by –le- and draw the difference O+ - O-. The quality of the estimator depends on the dispersion of this distribution.

F. Richard

TOTAL 1650

F. Richard


F. Richard

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