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


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


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

igg

s m

ass

lim

it,

95%

CL


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


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”


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


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


Brian Foster


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


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


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


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


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


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)


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


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


Higgs parameters at LHC and ILC

Barger, Logan, Shaughnessy, arXiv:0902.0170


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


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)


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


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)


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)


Possible SUSY spectrum at LHC

Bechtle, Wienemann, Uhlenbrock, Desch (2009)


The same spectrum as seen with LHC + ILC

Bechtle, Wienemann, Uhlenbrock, Desch (2009)


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


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)


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


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


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


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)


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)


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


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


Main ILD subdetector optionsMark Thomson

{NB: for detailed simulation in LoI,

similar to what is usual for a TDR,

a “software baseline” was chosen}


The SiD concept


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


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


The 4th concept


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


Towards an approved project


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


Additional Material


ILC baseline design parameters (at √s = 500 GeV)


Thomas Teubner


Constrained MSSM


The case for polarisation of BOTH beams



ILC Reference Design Report, Vol. 4: Detectors


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


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


Documents

International Linear Collider Physics Prospects and Detector Designs