Physics Options Overview
for the ILC
A.De Roeck
CERN
SLAC, MDI meeting, January 2005
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Physics Case for New High Energy Machines
Understand the mechanism Electroweak Symmetry Breaking
 What is the origin of mass of the fundamental particles?
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 !
- no unification of the forces at high energy
S
Most popular extensions these days
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…
S
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The ILC
• ILC world wide consensus for a baseline linear collider with a centre
of mass energy up to 500 GeV and a luminosity above 1034cm-2s-1
• However the ILC will be much more
– Its required flexibility/tunability in CMS energy,
and additional options will greatly enhance its physics
potential for precision EWSB studies, or
disentangling the new physics
– The baseline & options have been
outlined in the document parameters
for the linear collider
 Special studies and/or R&D for these options is required (and ongoing)
 We do not know for sure what path Nature has chosen, hence the priority an
importance these options will become clear with the data of the LHC and
first data of the ILC.
 The implications of these options on machine, MDI and detectors should
be taken into account –where possible - from the start.
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ILC Parameters & options
Several years of intense physics studies have led to:
• Baseline ILC

– Minimum energy of 500 GeV, with int. luminosity of 500 fb-1 in the first 4 years
– Scan energies between from LEP2 till new energy range: 200-500 GeV with a
luminosity ~ s. Switch over should be quick (max 10% of data taking time)
– Beam energy stability should be to less than 0.1%.
– Electron beam polarization with at least 80%
– Two interaction regions should be planned for
– Should allow for calibration running at the Z (s = 90 GeV)
– Upgrade: Energy upgrade up to ~ 1 TeV with high luminosity should be planned
• Options beyond the baseline: enhance the physics reach
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Running as an e-e- collider
Running as a e or  collider
Polarization of the positron beam
Running at Z0 with a luminosity of several 1033cm-2s-1 (GigaZ)
Running at WW mass threshold with a luminosity of a few times 1033cm-2s-1
(not in the document) Extendability to multi-TeV??
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Interaction Regions
 baseline recommendation for the ILC parameters
for two interaction regions
(KEK)
November 04
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Interaction regions
• How symmetric should these interaction regions be (for physics)?
• High versus low energy IR?
• Simultaneous or staged running?
As an experimentalist on LEP, HERA, LHC I believe that
– Both experiments will want to measure e+e- collisions at the
maximum ILC energy
– Both experiments will want to have data as soon as they are ready
(even before)
• Simultaneous like running will be preferred if not a technically
nightmare and if the efficiency to collect good data is acceptable,
especially at the start. (Moenig/Stahl: worry about polarization?)
So I would not give up on that option (yet).
• Ideally: experiments have a specialization. Eg. one may include gammagamma in its baseline design, or may optimize detector more for Z runs
May help to decide on which experiment goes to what IR
• Cost of 2nd interaction region? (~10%?)
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e-e- collisions
Advantages of e-e-:
 Large polarization for both beams: eL,eR
Large polarization of the e- beam
Work with fundamental fields of
particles with well defined handiness
 Exotic quantum numbers (H--)
 Larger sensitivity in some processes
 Some very clean processes
No s-channel, lower luminosity
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e-e- option
Minkowski
Higgs production
Mass reconstructed
from tagged electrons
needs good forward
detector coverage
down to a few degrees
Supersymmetry
Heusch
Thomas
measurement
of CP violating
phases
Note: before detector simulation, IR, beamstrahlung, selectron width…
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e-e-option
Non-Commutative QED
Hewett, Petriollo, Rizzo
Sensitivity to contact
interactions
Barklow
…Majorana neutrinos
Heusch Minkowski
…for equal luminosities
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e-e- option
Parameters (Snowmass 2001)
Study for TESLA (S. Schreiber)
Luminosity 5-(10)•1033 cm-2 s-1
L e-e- = 1/6 –(1/3) L e+eStability ~OK with intra-train feedback system
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e-e- option
No ‘major’ changes
required in IP
or accelerator but
need to include
 spent beam
 kicker magnets?
 feedback system
 second e-source
…
Clem Heusch’s dream:
Future control room at the ILC??
S. Schreiber
e-e- is the option
which should be
easy to realize
Has to be revisited
during the MDI
discussions to keep
on the roadmap
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The photon collider option
 and
e option
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Gamma-gamma and e-gamma
Compton backscattering on laser photons
 Peaked but smeared energy spectrum
 Highly polarised photon beams
However: needs extra effort
Is it worthwile?
Jeju LCWS02 panel discusion:  Yes!
Examples of advantages
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Higher cross sections for charg. particles
Different JPC state than in e+eHiggs s-channel produced!
Higher mass reach in some scenarios
Pure QED interaction (in e+e- also Z exchange)
Higher polarization of initial state (>80%/beam)
CP analysis opportunities (linear  polarization…)
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Parameters for the TESLA design
V. Telnov
Since in  collisions
the electron beams do not
meet (and self-destroy)
one can reach higher
geometrical luminosities
by focusing stronger and
have a smaller emittance
(round beams) than in
e+e-/e-e- optics
Only the high energy part is of
interest for the luminosity!
Both beams are e-
z=W/2Ebeam
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Higgs
Golden Processes
for a
Photon Collider
Added value to
an e+e- collider
Boos et al.,
hep-ph/0103090
ADR (ECFA/DESY)
hep-ph/0311138
SUSY
EDs,…
Trilin.
coupl.
Top
QCD
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Example: Higgs
The precise measurement of the
2-photon width of the Higgs is
very important.
It is affected by all charged
particles that can occur in the loop
Very sensitive to new physics
Krawczyk et al., Moenig et al.
QCD bb in  suppression: V. Khoze,…
New physics effects are few % to 10%
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Example: MSSM Higgses H,A
Minimal Supersymmetric SM: 5 Higgses: h,H (CP even), A (CP odd) and H
Krawczyk et al
Photon collider only option to close
the wedge for masses up to ~800GeV
PC: Measurement of / to
10-20% (1 year running)
e+e- collider: H,A produced in pairs, hence MA reach is see/2
 collider: s-channel production, hence MA reach is 0.8•see
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SUSY example
Extended reach for sleptons
Watanabe et al.
e+e-: reach is s/2
e:
reach is 0.8s - M(LSP)
Can extend the mass range by
100-200 GeV if LSP is light
M(LSP) = 100 GeV
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The Photon Collider Option
Summary letter sent to the ISCLC in July 04, after LCWS04
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•
•
•
•
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Special requirements for a Photon Collider at the ILC
Crossing angle between the beams should be O(25-30mrad), for the removal of
the disrupted beams, (angle > disruption + Rquad/L ~0.01+6/400 ~ 0.025)
Product of horizontal and vertical emittance should be as small as possible to
allow for high  luminosity
Final focus: as small as possible spot size at IR (reduce horizontal  function by
order of magnitude compared to e+e-)
Beam dump: cannot deflect photon beam  narrow photon beam in a straight line
from the IR
Modified detector in the region  < 100 mrad, including the vacuum pipe and
vertex detector
Space needed for laser beam lines and housing
Proposal of the PC study contact persons and workgroup convenors
 Design the 2nd IR optimized for a PC, but keep full compatibility of the
FFS to allow to run also in e+e- mode (horizontal  function).
 Detector to be designed to operate in both modes, with easy transition
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Interaction region
K. Moenig et al.
Mask and laser optical paths designs
Study of beam related background:
e+e- pairs, overlap events, neutrons
 # of hits in the layers of pixel detector
 Incoherent pair production: essentially
the same as for e+e Coherent pair production: High! but ok,
similar to e+e- (Moenig,Sekaric)
 same vertex detector as for e+e Neutrons? Under study (V. Telnov)
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Optical
cavity
to store
laser
pulses
(TESLA)
G. Klemz
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Beam Dump Design
V. Telnov
See talk
tomorrow
Angular divergences of disrupted beams
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PC R&D
• Photon collider IP introduces new challenges
– Laser & Optics
– Stability/control in IR (1nm), cavity length control, alignment, feedback…
– Extraction line, beam dumps…
 Opportunities also for university projects/contributions
• Important to involve laser expert community (LLNL, others)
– Some collaboration established but need intensifying
– Hardware e.g. (reduced size) cavity or focus region needs to be tested
– Suitable lasers (prototypes) need to be tested
• Some related activities
– LLNL plan to work on cavities to generate sufficient laser power for
making a positron source via Compton scattering; Gain experience with
high power issues, critical for PC lasers
– Orsay: build a laser resonator for a polarimeter, as part of EuroTeV
World wide organized R&D for this option is needed
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Polarized Positrons
• Polarization of the electron beam in base-line program
– Techniques have been already succesfully (SLC)
– Allows to reduce background/enhance signal for s-channel processes
– Allows e.g. for LR measurements in s-channel processes, single spin
asymmetries, measurements of couplings…
• Polarization of the positron beam
– Techniques in R&D phase (helical undulator, Compton scattering)
– Increases the effective polarization
– Reduce the uncertainty of the polarization
• By error propagation (factor 3-4)
eg. for Pe-=80% and Pe+=-60%  Peff=95% Peff/Peff~1/3P/P
• By using the Blondel scheme
See K. Moeing talk
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Polarized Positrons: Physics Topic Examples
• High precision analysis in the SM
– Triple gauge couplings in e+e-Z
– Anomalous couplings in e+e- W+W– Transversely polarized beams in e+e- W+W-, graviton effects
– GigaZ (see later)
– Sensitivity to CP violation the SM
• Revealing the structure of SUSY
– Quantum numbers in e+e-  selectron pairs
– Stop mixing angle in e+e-  stop pairs
– Study of the chiral structure of the Gaugino/Higgsino sector
–  polarization (large tan case)
– CP phase determination in stau sector
– Identification of extended susy scenarios
• Enhancing reach for extra dimensions in e.g. e+e-G, etc, etc..
Report from the POWER group being released soon
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Polarized Positrons: Examples
Test if the sparticles have the same chiral quantum numbers as their SM partners
G. Moortgat-pick
Disentangle
from
with
polarized e+
U. Nauenberg et al

Discovery:
Look for kinematic
edges in inclusive
muon distribution
! WW background !
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Polarized Positrons: Examples
ADD eeG cross section
Z’ couplings from e+e-ff
Background
no polarization
e+ polarization
e+ and e- polar
G. Wilson
Casalbuoni et al.
ADD effects in e+e-ff
e+e-cc
e+e-bb
Transverse
polarization
PT=0.8 P’T=0.6
T. Rizzo
cos
cos
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Polarization and MDI
• Polarimeters for longitudinal (and transverse) polarized beams
• Polarimeters before and after the IR?
– Polarimeter after the IR only possible with crossing angle (?)
– Depolarization effects: so far expected to be in control for
0.5-1 TeV but is large for e.g. for CLIC
– Redundancy is not a luxury for precision measurements so if
we can have data to check, so much the better. But what can
we really learn from this measurement?
– Use also other physics processes to check, see talk of Klaus
• Precision of the polarimeters 0.5-0.25% adequate for everything?
– High statistics channels (Z’, TGCs) require O(0.1)%
– GigaZ requires 10-4, needs polarized e+ (Blondel Method)
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GigaZ option
Luminosity ~ 51033cm-2s-1 at Z pole 109Zs in less than a year
 100 x more statistics than LEP (1000x SLC for polarized studies)
• Measure
to a precision of O(10-5) from left-right asymmetries
• Z-lineshape: improve Z-width with a factor two, cross section ratios by a
factor three ( factor two on  and a factor 3 on s)
• Zbb couplings improved by factor 5-10 wrt. LEP
• B-physics: Factor 10 improvement in Electro-weak b-quark physics
possible, CP violation effects, rare B-decays (maybe need 1010 Zs)
Imposes stringent requirement on the control of the beam energy and
beam energy spread, polarization, luminosity precision, detector (b-tagging)…
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Measurement of sin2
•
•
•
Stat. error with 109 Zs: ALR/ALR=4.10-5 (Pe-=80%,Pe+=0%)
Error from the polarization ALR/ALR= P/P
With positon polarization (Pe-=80%,Pe+=60%)
– Gain a factor 3-4 with error propagation
– Apply Blondel scheme
 Need to understand polarization differences between the
two helicity states to the level of 10-4. Need to take into
account correlations between the polarizations of the two
beams. Track time dependencies of the polarization.
 Beam energy ALR/ s = 2 10-2/GeV from Z
interference need to know s ~ 1 MeV relative to the
MZ (spectrometer with 10-5 relative precision)
 Beamstrahlung: need to be controlled to a few %
Challenging requirements!!
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Z-scan observables
• If relative beam energy measurement of 10-5 can be reached then
/=0.410-3 (compared to 0.910-3 at LEP)
• Assume the selection efficiency for leptons to be improved by a
factor 3 w.r.t. LEP detectors  improve the leptonic to the
hadronic cross section ratio Rlep/Rlep=0.310-3 (1.210-3 at LEP)
• With luminosity measurement improvements w.r.t LEP: improve
the hadronic pole cross section 0
 Beam energy spread should be kept below 0.1% and understood
to the level of a few% for the 0 and  measurements
 In principle both are in reach of the Bhabha acolinearity
measurement.
Improvements on line shape
related quantities
Z properties affected by new physics: e.g. Z’ like objects in hep-ph/0303107
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WW factory
Revisiting the W mass
G. Wilson
 Threshold scan: a six point scan with
100 fb-1 (1 year)
• Efficiencies and purities as at LEP
• Beam polarization used to measure the
background/enhance the signal
– Need P/P < 0.25%
– If polarized positrons are available,
can use the Blondel scheme
• Beam energy needs to be controlled to
510-5 between mZ and 2mW
• Can reach a precision of 6 MeV on MW
(compare: 15 MeV at the LHC)
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Multi-TeV collider
• CLIC two beam acceleration presently thought to be only feasible way to
multi-TeV region
 CTF3 under construction/operation at CERN
• MDI related issues to keep in mind if one plans for a facility that
should be upgradable to a multi-TeV collider in future
– crossing angle needed of ~20 mrad (multi-bunch kink stability; see tomorrow)
– Present desing: Long collimator syst. (2 km on each side) and final focus (0.5 km)
– Energy collimators most important.
Fast kicker solution not applicable. Maybe rotating collimators …
– Gentle bending to reduce SR & beam spot growth construct the linacs already
under an angle of ~ 20 mrad
– Internal geometry differences of the collimation system and final focus, allow
for enough space in the tunnels (O(m))
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Multi-TeV physics: Examples
New Z’ resonance
Heavy Higgs
MH=900 GeV
s=5
s=3
ADD Extra Dimensions
CLIC physics study
CERN-2004-005 & hep-ph/0412251
Supersymmetric particles:
# of higgses, sleptons
gauginos, squarks
detected for benchmark
scenarios (hep-ph/0306219)
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Importace of the Options: Eg. SUSY
Supersymmetry: Study of benchmark point (SPS1a or B)
From the document
LHC/ILC complementarity
hep-ph/0410364
To fully exploit the ILC potential and measure the new sparticle masses we
need: e+e- up to 1 TeV, e-e-, polarized positrons (60% assumed here), and
a PC to measure the heavy Higgses.. (H,A)…
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Summary
• Additional options to the ILC will certainly increase the physics
reach of the ILC. All have their merits
Today we do not know which one of these will have the highest
impact on the physics program
• The options have consequences for the MDI
With the WG4 recommendation it looks natural to suggest to study
in detail the IR with large crossing angle (15-20) mrad is kept
compatible for a PC option (or even multi-TeV) from the start
What would we loose if the crossing has to be 25 mrad?
– Affects small angle tagging efficiency of electrons from
backgrounds SUSY: eg. reduced efficiency for stau’s in stau-
degenerate mass scenarios (CDM studies). Perhaps affordable?
– Some luminosity reduction
– Are there additional technical risks?
• Should include all options & their requirements in the MDI studies
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