1. Physics @ CLIC Albert De Roeck CERN and University of Antwerp
and the IPPP Durham

2. Linear e+e- Colliders
Since end of 2001 there seems to be a worldwide consensus
(ECFA/HEPAP/Snowmass 2001…)
The machine which will complement and extend the LHC
best, and is closest to be realized is a Linear e+e- Collider
with a collision energy of at least 500 GeV
PROJECTS:
 TeV Colliders (cms energy up to 1 TeV)  Technology ~ready
August’04 ITRP: NLC/GLC/TESLA ILC superconducting cavities
 Multi-TeV Collider (cms energies in multi-TeV range)  R&D
CLIC (CERN + collaborators)  Two Beam Acceleration

3. 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

4. LC: Few More Examples ‘WMAP’ 7 % LHC ~15 % ‘Planck’ ~2 % LC ~3 %
Understanding SUSY
High accuracy of sparticle mass measurements
relevant for reconstruction of SUSY breaking
mechanism
 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
‘WMAP’
7 %
LHC
~15 %
‘Planck’
~2 % LC
~3 %
F. Richard/SPS1a

11. CTF2: CLIC Test Facility 2
Demonstrated that 2 beam acceleration works
Reached up to 190 MV/m for short pulses (16ns)

16. Building CLIC at CERN? It is possible!
Geological analyses show that there is a contineous stretch of 40 km parallel to the
Jura and the lake,
with good geological
conditions.
Reminder

17. Cross Sections at CLIC

18. Experimental Issues: Backgrounds
CLIC 3 TeV e+e- collider with a luminosity ~ 1035cm-2s-1 (1 ab-1/year)
To reach this high luminosity: CLIC
has to operate in a regime of high
beamstrahlung
Expect large backgrounds
# of photons/beam particle
 e+e- pair production
   events
 Muon backgrounds
Neutrons
Synchrotron radiation
Expect distorted lumi spectrum
Report 
Old Values

19. Experimental issues: Luminosity Spectrum
Luminosity spectrum not as
sharply peaked as e.g. at LEP
or TESLA/NLC

20. e+e- Pair Production Coherent pair production
 number/BX
 energy/BX TeV
Disappear in the beampipe
Can backscatter on machine elements
Need to protect detector with mask
Incoherent pair production:
 number/BX
 energy/BX TeV
Can be suppressed by strong magnetic
field in of the detector
hits/mm2/bunch train
4T field
30mm O(1) hit/mm2/bunch train 

21.  Background Neutral and charged energy as function of cos per bx
  hadrons: 4 interactions/bx with WHAD>5 GeV
Neutral and charged energy
as function of cos per bx
Particles
accepted
within
 > 120mrad
For studies: take 20 bx and overlay events

22. Muon Background Muon pairs produced in electromagnetic interactions
upstream of the IP e.g beam halo
scraping on the collimators
GEANT3 simulation, taking into
account the full CLIC beam
delivery system
# of muons expected in the
detector ~ few thousand/bunch
train ( bunches/ ns)
 OK for (silicon like) tracker
 Calorimeter?
~20 muons
per bx
1 shower
>100 GeV/5 bx

23. Studies include background, spectra,…
Physics generators (COMPHEP
PYTHIA6,… )
+ CLIC lumi spectrum (CALYPSO)
+   hadrons background
e.g. overlay 20 bunch crossings
(+ e+e- pair background files…)
Detector simulation (2004)
 SIMDET (fast simulation)
 GEANT3 based program
Studies of the benchmark processes include backgrounds,
effects of lumi spectrum etc.

24. Detector:Active (small) group at CERN now: backgrounds, calorimetry,
Time stamping, forward region…  Weekly meetings…

25. Example B-tagging Define Area of Interest by
B-Decay length is long!
Define Area of Interest by
 0.04 rad cone around the jet axis
Count hit multiplicity (or pulse
height) in Vertex Track layers
Tag heavy hadron decay by step
in detected multiplicity
 Can reach 50% eff./~80% purity

26. Calorimetry Importance of good energy resolution (e.g via energy flow)
Interesting developments in TeV-class LC working groups
e.g. compact 3D EM calorimeters, or “digital” hadronic calorimeters
Detailed simulation studies of key processes required
R&D accordingly afterwards/Join ILC detector efforts

27. General Physics Context
New physics expected in TeV energy range
Higgs, supersymmetry, extra dimensions, …?
LHC will indicate what physics, and at which energy scale
Two scenarios:
New physics at a low energy scale
But perhaps more particles/phenomena at higher energies (e.g., supersymmetry)
New physics threshold at higher energy scale
In many scenarios, e.g., SUSY, LHC will soon tell us the threshold

28. Example: Resonance Production
Resonance scans, e.g. a Z’
1 ab-1 M/M ~ 10-4 & / =
Degenerate resonances
e.g. D-BESS model
Can measure M down to 13 GeV
Smeared lumi spectrum allows
still for precision measurements

29. Physics Case: A light Higgs
Low mass Higgs:
Higgses/
 Large cross sections
 Large CLIC luminosity
 Large events statistics
 Keep large statistics also
for highest Higgs masses
 O(500 K) Higgses/year
Allows to study the decay
modes with BRs ~ 10-4 such
as H and Hbb (>180 GeV)
Eg: determine gH to ~4%

30. Physics case: Higgs potential
Reconstruct shape of the Higgs potential to complete the study of the Higgs
profile and to obtain a direct proof of the EW symmetry breaking mechanism
 Measure the triple (quartic) couplings
process

31. Physics case: the Higgs Potential
Reconstruct shape of the Higgs potential to complete the study of the Higgs
profile and to obtain a direct proof of the EW symmetry breaking mechanism
Can measure the Higgs potential for Higgs even for masses up to 300 GeV
with precision up to 5-10% (using polarization/weighting)

32. Physics case: Heavy Higgs (MSSM)
LHC: Plot for 5  discovery
3 TeV CLIC
 H, A
detectable
up to ~ 1.2 TeV

33. Physics case: SUSY measurements
 LC/LHC complementarity
Precision measurements at ILC/CLIC
Eg GeV smuon mass to O(1%)
Will a TeV collider be enough?
Benchmark Scenarios: CMSSM
Allowed by present data constraints
ADR,F., Gianotti,JE,F. Moortgat, K. Olive, L. Pape
hep-ph/

34. Susy Mass Measurements
Momentum resolution (G3)
Mass measurements
to O(1%)
Momentum resolution
pt/pt2 ~ 10-4 GeV-1
adequate for this
measurement

35. ILC Sparticle Detection Full Model samples
J. Ellis et al.
Full
Model
samples
← Second lightest visible sparticle
Detectable
@ LHC
ILC
Provide
Dark Matter
Dark Matter
Detectable
Directly
Lightest visible sparticle →
JE + Olive + Santoso + Spanos

36. Sensitivity to 2 1+2 leptons
Case study: 2
Sensitivity (5) for LHC and LC
Mass measurement precision
m2= 540 GeV, m1=290 GeV
~1.5% precision
on 2 mass

37. Physics Case: Extra Dimensions
Universal extra dimensions:
 Measure all (pair produced) new
particles and see the higher level
excitations
RS KK resonances…
Scan the different states

38. Precision Measurements
E.g.: Contact interactions:
Sensitivity to scales up to
TeV

39. Indicative Physics Reach
Ellis, Gianotti, ADR
hep-ex/ few updates
Units are TeV (except WLWL reach)
Ldt correspond to 1 year of running at nominal luminosity for 1 experiment
PROCESS LHC SLHC DLHC VLHC VLHC ILC CLIC
14 TeV TeV TeV TeV TeV TeV TeV
100 fb fb fb fb fb fb fb-1
Squarks
WLWL       
Z’ † †
Extra-dim (=2) † † q*
compositeness
TGC ()
† indirect reach
(from precision measurements)
Approximate mass reach machines:
s = 14 TeV, L=1034 (LHC) : up to  TeV
s = 14 TeV, L=1035 (SLHC) : up to  8 TeV
s = 28 TeV, L= : up to  10 TeV
Extend this table

40. Summary: Physics at CLIC
Experimental conditions at CLIC are more challenging than at LEP, or ILC
Physics studies for CLIC have included the effects of the detector, and backgrounds e.g e+e- pairs and  events.
Benchmark studies show that CLIC
will allow for precision measurements in the TeV range
CLIC has a very large physics potential, reach beyond that of the LHC.
Ongoing now: Detector studies and R&D
Tracking with good time stamping, - -
improved calorimetry, pflow, mask area,…

41. Summary: Scenarios with early LHC data…
New physics shows up at the LHC  CLIC will
Complete the particle spectra, with a very high reach
Measure accurately parameters of the model (LC quality)
Only a light Higgs at the LHC  CLIC will
Measure its properties very accurately, like ILC and more..
Extend the LHC direct search reach for non-colored particles
Extend the indirect search reach to a scale of 500 (1000?) TeV via precision measurements
No signs of new physics or a Higgs at the LHC  CLIC can
Study WW scattering in the 1-2 TeV range in detail

42. Backup