International Linear Collider Physics Prospects and Detector Designs
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Transcript of International Linear Collider Physics Prospects and Detector Designs
Seminar, April 2009 Sonja Hillert (Stockholm) p. 1
International Linear Collider
Physics Prospects and Detector Designs
30th April 2009
Sonja Hillert
Stockholm University
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Why a Linear Collider is needed
Hitoshi Murayama, TILC08
To understand galaxies, it helps to observe them at different wavelengths:
To understand physics at a new energy scale, it helps to use complementary colliders
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Complementarity of colliders LEP, SLC & Tevatron: led to understanding of SM at the quantum level
prediction of masses of top quark and Higgs boson
HERA observations of high Q2 events dedicated leptoquark searches at the Tevatron,
which in turn fed back into HERA analyses
Belle discovery of X(3872) dedicated search at CDF & D0: independently confirmed
year 20061996H
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LHC will give access to TeV energy scale: expect ground-breaking discoveries:
• How is electroweak symmetry broken? Higgs? Which one? SM and light SUSY-Higgs accessible
• Does the top-quark play a special role in this? mass ~ scale at which ew symm. is broken
• Why is mW/MPl ~ 10-17? many possible explanations involving New Physics at TeV-scale
• Dark Matter ~ 22% of the Universe: what is it? could be explained by New Physics at TeV-scale
BUT: at LHC, very different New Physics can look alike experimentally:
A complementary accelerator is needed to understand what the SM can’t explain
Physics at the TeraScale
4th generation SUSY technicolor
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The International Linear Collider (ILC) Work towards a high-precision e+e- collider begun 20 years ago
advantages: use full beam energy, tuneable and precisely known; polarised beams
synchrotron radiation prohibitive at > LEP energies Linear Collider
challenges:
• can’t build up energy by circulating beams many times
• to reach required luminosity, need extremely focused bunches, know their position
Stanford Linear Collider (SLC) proof of principle for linear collider concept
until 2004: three independent strands of R&D in the US, Asia and Europe:
• Next Linear Collider (NLC, SLAC) design with X-band acceleration
• Global Linear Collider (GLC, KEK) design with X- or C-band
• TESLA (DESY) design with superconducting RF
August 2004: following consultation ICFA decided for Superconducting RF
Global Design Effort (GDE) to develop common design: International Linear Collider
“warm technology”
“cold technology”
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SLC
FFTB
TESLA
500 nm
50 nm
5 nm
1000 nm
Towards nanometer sized beams
ILC lumi requires beam size 640 nm x 6 nm
for collisions, stability of beam position also
a critical issue
Final Focus Test Beam (FFTB) facility
extension of SLC accelerator (1993)
established beams of 1000 nm x 50 nm
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2004: Decision for Superconducting RF
International Technology Recommendation Panel:
following 6 meetings (RAL, DESY, SLAC, KEK, Caltech, Korea) in report to ICFA emphasised
that both warm and cold technology had considerable strengths;
to proceed further, recommended to ICFA the Superconducting RF technology – reasons:
• less sensitive to ground motion, possibility of inter-bunch feedback (higher beam current?)
• main linac and RF systems of comparatively lower risk
• superconducting XFEL Free Electron Laser will provide prototypes and test many aspects
• industrialization of many components underway
• use of superconducting RF significantly reduces power consumption
Superconducting
RF cavity
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Brian Foster
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ILC baseline machine (2007)
beam energy: initial maximum centre of mass energy 500 GeV, upgradable to 1 TeV
tuneable: physics runs possible between 200 GeV and 500 GeV
low beam energy spread, low beamstrahlung CM-energy of hard process well known
high luminosity: L ~ 2x1034 cm-2s-1 (at least 500 fb-1 over 4 years)
beam polarisation: baseline: e- beam: 80%; possible upgrade: e+ beam polarisation > 50%
beam energy and polarisation must be measurable to 10-3 or better
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The ILC Physics scope
Precision top physics
Understanding electroweak symmetry breaking
• The precision Higgs programme: SM Higgs and beyond SM Higgs
New Physics
• Dark Matter and new particle spectra
• Distinguishing between possible New Physics interpretations
• Determining model parameters
Beyond the TeraScale
• Indirect sensitivity to higher energies through virtual effects
• Extrapolation to the unification scale
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e+e- tt at threshold: top mass measurement
precise measurement of top mass and
couplings needed for
• prediction of electroweak parameters
• indirect determination of Higgs mass
• prediction of dark matter density
• extrapolation of masses, couplings to GUT scale
• understanding of flavour physics
From energy scan of tt-production threshold:
determine top mass with mtop ~ 100 MeV, dominated by theoretical uncertainty
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e+e- tt at threshold: further observables
additional observables
• help disentangle correlations between
parameters (mt, s, t)
• increase New Physics sensitivity
observables are for example
• top momentum distribution
• forward-backward asymmetry
• top polarization
• W decay lepton spectra
peak of top momentum distribution depends strongly on mt,
not very sensitive to s disentangle correlations between mt, s in cross section
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Precision Higgs physics
To fully establish the Higgs mechanism need to measure:
• Higgs mass
• absolute couplings of Higgs to Z, W, t, b, c, , 1 – 5 % precision
• total width
• spin, CP
• top Yukawa coupling (precision at ILC: ~ 5 %)
• self-coupling (~20% precision,
for 120 GeV < mH <140 GeV)
Higgs recoil mass measurement
(decay-mode independent):
• select di-lepton events consistent with Z ee,
• calculate recoil mass as
• find Higgs mass from recoil mass spectrum,
• precision ~ 70 MeV
Z
ILD LoI
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Higgs couplings and spin
mH = 120 GeV
20 fb-1 / point
Higgs spin can be measured from rise of cross section near threshold
in some models same rise for spin 0 and spin 2, but different angular distributions
Precision measurement of Higgs coupling sensitive to number, shape and size
of possible extra spatial dimensions
KEK-REPORT-2003-7V. Barger et al., Phys Rev D49, 79 (1994)
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Higgs branching ratios At ILC absolute measurement of branching ratios possible
most challenging: disentangling hadronic Higgs decays
analysis performed for all ZH events
classify according to number of leptons and vis. energy
for each Z decay channel, fit b-likeness, c-likeness
simultaneous fit of Z qq, ll, distributions
resulting branching ratio precision 1.6 % (bb) to 8.3% (cc)
Kuhl, Desch LC-PHSM-2007-002
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MSSM Higgs sector
Two Higgs doublets needed for electroweak symmetry breaking in MSSM
corresponds to 8 degrees of freedom, 3 of which needed for Higgs mechanism
5 physical Higgs states remaining: h, H: neutral, CP-even; A: neutral, CP-odd; H±
h detectable in entire MSSM parameter space (e+e- hZ, e+e- hA)
heavy Higgses visible up to √s/2 1 TeV ILC covers large part of interesting region
Kiyoura et al.,
hep-ph/0301172
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Higgs parameters at LHC and ILC
Barger, Logan, Shaughnessy, arXiv:0902.0170
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Standard Model: no Dark Matter (DM) candidate clear indication of New Physics
examples of models with candidates: SUSY, extra dimensions, Littlest Higgs
typically dark matter candidates are:
• neutral
• relatively massive
• absolutely stable
LHC should produce DM particles
signature: long decay chains, missing ET
Once observed need to:
• precisely measure the mass of seen candidate
• determine physics of the new model that leads to the WIMP
• from model parameters determine what should be seen in astrophysical experiments
• compare with astrophysical observations
Connections to cosmology: dark matter
Reference Design Report, part II
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Models with DM candidates: two examples MSSM:
for each SM particle have J = ± ½ SUSY particle
with same gauge quantum number & couplings
Higgs sector: h, H, A, H±
for conservation of R parity ( R = (-1) 3(B-L)+2S ):
• sparticles pair-produced
• lightest SUSY-particle (LSP) stable
15-20 free model parameters in constrained MSSM
Models with extra dimensions, e.g.
• “Large” flat extra dimensions: SM fields localised
on one brane, gravitons propagate into extra dim’s
• Randall Sundrum (RS): only 1, curved extra dim.
both cases: compactified dimensions give rise to
Kaluza-Klein tower of excited states for the gravitons
Phys Rev Lett 84, 2080 (2000),
Phys Rev D63, 075004 (2001)
Eur. Phys. J. C46, 43 (2006)
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Precision measurements of new particle spectra To understand possible new particle spectra will measure
• masses
• branching ratios
• cross sections
• angular distributions
Advantages at ILC: tunable energy permits threshold scans; polarised initial beams
important for determining spin
S. Y. Choi et al., hep-ph/0612301
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Large extra dimensions
Energy dependence of cross section sensitive to number of extra dimensions
can be determined from measurement at two centre of mass energies
spin-two nature of exchanged particle tested by azimuthal asymmetry
requires both beams to be polarized (assumed: e-: 80%, e+: 60%)
√s = 500 GeV
500 fb-1
G. W. Wilson, LC-PHSM-2001-010 T. G. Rizzo, JHEP 02, 008 (2003)
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ILC can distinguish between SUSY
reference points much better than LHC
Constrained MSSM Common SUSY reference points studied at ILC and LHC
chosen to be compatible with DM-favoured regions in constrained MSSM with all
experimental and phenomenological constraints imposed
Phys. Lett. B565, 176 (2003)
Phys. Rev. D74, 103521 (2006)
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Possible SUSY spectrum at LHC
Bechtle, Wienemann, Uhlenbrock, Desch (2009)
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The same spectrum as seen with LHC + ILC
Bechtle, Wienemann, Uhlenbrock, Desch (2009)
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Couplings of gauge bosons to fermions
Fermion pair production sensitive to virtual effects
O(106) e+e- ff events allow couplings to be measured with permille accuracy
virtual effects of New Physics parameterised in a model independent way
in terms of contact interactions:
ILC sensitive up to scales ij = 100 TeV
for a new Z’ boson couplings cLl and cR
l can
be determined from asymmetries in Z’
permits distinguishing different models
√s = 500 GeV
1 ab-1
S. Godfrey et al., hep-ph/0511335
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Extrapolation to unification scale direct measurement of s vs energy would improve extrapolation to unification scale
discrepancy between s, weak and em couplings at 1016 GeV
constrains particle content at that energy
hep-ph/0106315
hep-ex/9912051
hep-ph/0403133
Nucl. Phys. Proc. Suppl. 135, 107 (2004)
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Detector requirements
ILC physics and machine conditions challenging for detector systems:
• Physics requires excellent jet energy resolution well beyond current state of the art
requires new detector technologies and reconstruction algorithms
• Higgs studies need charge-track momentum resolution better than at LEP, SLC, LHC
high field magnets and low mass trackers under development
• flavour and quark charge tagging (e.g. Higgs branching ratios, quark asymmetries)
require new generation of vertex detectors
March 2009: three Detector Concept Groups submitted Letters of Intent
Characteristics shared by all detector concepts:
• pixellated vertex detector for high-precision vertex reconstruction and tracking
• sophisticated tracking systems for high tracking efficiency & excellent momentum resolution
• calorimeters inside the magnet coil
• high field solenoids (3.5 – 5 T), building on successful CMS solenoid
• trigger-less readout to maximise physics sensitivity
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Particle Flow For many physics processes need to distinguish di-jets from W- and from Z-decays
To obtain a di-jet mass resolution of order
corresponding to ~ 2.75 separation between W and Z peaks need
Simulations show excellent performance to cos ~ 0.975
√s = 1 TeV
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Dual Readout Calorimetry
Hadron calorimeters generally suffer from
signal non-linearity, non-Gaussian response
main reason: fluctuation in fraction of hadron
energy that is deposited in electromagnetic shower
idea of dual readout calorimetry:
• separately measure scintillation and Cerenkov signal
• from these separate measurements determine the
electromagnetic shower fraction on an
event-by-event basis
• permits correction for fluctuations
technology developed by DREAM collaboration
• extensively studied in beam tests and simulation
• for ILC a combination of BGO crystals in front of a
fibre calorimeter is proposed
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Momentum resolution important for full reconstruction of events
Excellent impact parameter resolution needed for vertexing and flavour tag, goal:
High efficiency over full polar angle coverage (forward region important at ILC)
Precision Tracking
All-silicon tracker (SiD LoI) TPC + silicon tracking (ILD LoI)
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Topological vertexing
Central idea: describe tracks by probability density functions and combine them
to form a vertex function encoding the topological information for a jet
Track probability functions: Gaussian profile in the plane normal to trajectory at
point of closest approach p to 3D-space point r at which function is evaluated:
Vertex function: simplest form:
used to identify vertices and to determine if two vertices are resolved from each other
original ZVTOP algorithm developed by D. Jackson (SLD), NIM A 388 (1997) 247
new C++ implementation with improvements for ILC (LCFIVertex, paper submitted to NIM A)
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Flavour Tagging Neural networks used to distinguish
• b from u, d, s and c jets
• c from u, d, s and b jets
• c from b jets (in some processes only b jet background)
Secondary vertex information best indication of jet-flavour
LCFIVertex
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The ILD concept
676 signatories, 152 institutes, 32 countries
Vertex Detector: long-barrel geometry 3 double-layers OR 5 single-layers, technology tbd
SIT: 2 Si-strip-layers in barrel, FTD: pixel+strip detectors in forward region
TPC: large volume, up to 224 3D space points per track, provides dE/dx-based particle ID
SET, ETD: Si-strip detectors between TPC & ECAL and behind TPC endplate & ECAL
Particle flow calorimetry
ECAL: highly segmented, up to 30
samples in depth, small cell size
HCAL: up to 48 samples in depth,
small cell size; two options
LumiCal, BeamCAL, LHCal:
measure luminosity, monitor beam
Superconducting Coil: 3.5 T
Iron yoke: filter, detector, tail catcher
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Main ILD subdetector optionsMark Thomson
{NB: for detailed simulation in LoI,
similar to what is usual for a TDR,
a “software baseline” was chosen}
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The SiD concept
246 signatories, 77 institutes, 18 countries
Vertex Detector: 5 cylinders, 4 endcaps on each side, technology to be decided
Main tracker: silicon strip detector, 5 barrel layers + 4 endcaps per side, sensors 15x15 cm2,
single sided, 50 m pitch, endcaps: 2 sensors bonded for stereo angle measurement
Particle flow calorimetry: EM calorimeter: dense, highly segmented Si-W
20 layers of 2.5 mm W + 10 layers of 5 mm W (Si: 1.25mm/layer)
HCAL: 4.5 of stainless steel, 40 layers of steel + detector
LumCal, BeamCal: Si-W (LumCal) and
low resistivity Si or diamond (BeamCal)
Superconducting Coil: 5 T; baseline: CMS conductor,
developing advanced conductor (easier to wind)
Flux return: 11 layers of 20 cm iron
absorber for identifier, important for shielding
Polarimeters and energy spectrometers
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The SiD concept
All concepts were asked to provide a cost estimate as part of their LoI
SiD example shows how cost is typically distributed over the different subsystems
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The 4th concept
140 signatories, 33 institutes, 15 countries
Vertex Detector: SiD-design, relying on developments of R&D groups, technology tbd
Cluster timing drift chamber: ultra-low mass, He-based gas,
over 100 three-dimensional 55 m space point per track TPC-like pattern recognition
high-precision dual readout fibre calorimeter plus EM dual readout crystal
calorimeter: for energy measurement of hadrons, jets, electrons, photons,
missing momentum, tagging of ,
extensively tested (e, , , 20 – 300 GeV)
described in 15 papers
dual solenoid: return the flux without
iron, improves identification,
final focus and MDI advantages
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Towards an approved project
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Summary
The ILC is needed to understand the open questions posed by the SM and
by astrophysical observations.
It will go far beyond the LHC in the high precision with which it allows exploration
of new phenomena at energies up to 1 TeV (directly) and up to 100 TeV (indirectly).
ILC R&D both for the accelerator and for the detectors is far advanced
and strongly backed by the Particle Physics community.
It is regularly reviewed internally and externally and an important part of the
Particle Physics roadmap.
Further information:
• ILC Reference Design Report (RDR, 2007): http://www.linearcollider.org/cms/?pid=1000437
• ILC Detector Concept LoIs (2009): http://www.linearcollider.org/cms/?pid=1000472
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Additional Material
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ILC baseline design parameters (at √s = 500 GeV)
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Thomas Teubner
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Constrained MSSM
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The case for polarisation of BOTH beams
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ILC Reference Design Report, Vol. 4: Detectors
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337 ns
2820x
0.2 s
0.95 ms
Beam bunch structure at ILC
Multiple collisions
Data Acquisition
ILC: pulsed operation
Bursts of collisions at 3 MHz for ~1 ms,
followed by 200 ms quiet period
Integrated collision rate 15 kHz moderate
and comparable to LHC event building rate
ILC precision likely to require ~ 10 times as many readout channels than at LHC
DAQ system:
• Dead time free pipeline of 1 ms
• No hardware trigger
• Front-end pipeline readout within 200 ms
• Event selection by software
Front end needs to perform zero suppression and data suppression
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Cluster-timing drift chamber
Data: CluCou;“4th” LoI
record drift times of all individual ionization electrons collected on sense wires
due to passage of ionizing particle through active gaseous medium
particular attention to materials used, especially gas mixture
momentum resolution uncertainty from multiple Coulomb scattering minimized
mechanical design based on KLOE
digitized pulse shape from cosmic
2 cm radius, 30 cm length drift tube
gas: 90% He, 10% isobutane
trigger: plastic scintillator telescope
8-bit, 4GHz sampling oscilloscope
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