physics and detectors at the ilc...ilc 2x1034 5 1312 2 0.6 0.006 slc 2x1030 120 1 4 1.5 0.5 lep2...

Physics and Detectors at the ILC Mark Thomson

University of Cambridge

Overview

Mark Thomson 2 RHUL, October, 2013

Motivation for an e+e- collider The ILC Physics at the ILC ILC Detector Concepts Calorimetry at the ILC Particle Flow Detector R&D What next? Conclusions

This talk:


The LHC

The LHC and a LC provide a complimentary approach to studying the physics of EWSB and beyond

Open the door to new physics – already one major discovery Will push the energy frontier with p-p collisions at ~14 TeV

• qq, qg and gg collisions in the energy range ~0.5-5 TeV

The ILC

A different approach: very high precision as opposed to very high energy

Electron-positron collisions in the energy range 0.1-1 TeV Very clean final states + high resolution detectors: very precise measurements (as at LEP) give detailed understanding of new physics + tight constraints on theory (as at LEP)

The complementarity of the LHC and ILC very well studied: e.g. “Physics Interplay of the LHC and ILC”, G. Weiglein et al., Phys. Rept. 426 (2006) 47-358

Motivation for an e+e- collider


e+ e– ≡ precision Electron-positron colliders provide clean environment for precision physics

The LHC The ILC

At electron-positron the final state corresponds to the underlying physics interaction, e.g. above see and and nothing else…


Why linear? Circular colliders have a big advantage – circulating beams In a linear collider get e+e– to full energy in “one shot” Hence, most previous e+e– colliders were circular machines However in a circular collider have to “fight” synchrotron radiation

• accelerating electrons lose energy

co

st

Circular machine :

Linear machine :

Energy

Circular Collider

Linear Collider

Breakpoint approximately √s = 200 GeV (LEP 2) To get above this energy need a linear collider… the ILC


Why now?


…the Higgs is out there the Higgs is now standard textbook* physics

The ILC is THE machine to study the Higgs The ILC in Japan is now a very realistic possibility high level discussions ongoing…

*apologies for the gratuitous plug


The Machine


Centre-of-mass energy adjustable from 200-500 GeV • upgradeable to 1 TeV (i.e. make it longer)

Integrated luminosity of 500 fb-1 in first 4 years operation • require high luminosity: ~2x1034 cm-2s-1

Electron polarization of >80 % at interaction point (see later)

ILC TDR (2012)

The ILC

The ILC is much more than the “linear bit”…

Mark Thomson RHUL, October, 2013 10

Basic accelerating structure The main accelerating structures are the two 11km long LINACs

Longitudinal Electric Field (standing wave)

Positron Bunch

• LINACs built out of 9-cell super- conducting RF cavities operating at 1.3 GHz • Accelerating gradient of >30 MV/m • Basic idea - electrons and positrons accelerated in RF standing waves in the cavities


Beam and Luminosity To achieve high luminosity is challenging:

To reach the ILC goal of L = 2x1034cm-2s-1 small beam spot at the interaction point !

L [cm-2s-1] frep[Hz] nb Ne [1010] sx [mm] sy [mm]

ILC 2x1034 5 1312 2 0.6 0.006

SLC 2x1030 120 1 4 1.5 0.5

LEP2 5x1031 10000 8 30 240 4

Small beam spot complex beam delivery/final focus

574 nm

6 nm !!!

The ILC is a challenging machine…


TDR published in June 2013 - based on many years of work

Challenging, but doable…

Cavities produced in industry routinely approaching required gradients

European XFEL being constructed at DESY…

Commissioned with beam in 2015… …ultimate systems test for the ILC


The ILC is doable

Physics case?


Physics at the ILC

• Time Structure: 5 Bunch-trains per second

e+e-gqq ~100/hr e+e-gW+W- ~1000/hr e+e-gtt ~50/hr e+e-gHX ~10/hr

Baseline design of the ILC now fixed as of TDR

Very clean physics environment: low event rates, modest backgrounds, long time between collisions

554 ns 0.2 s

0.73 ms

Bunch Train

Bunch Spacing 1312 bunches/train

• “Backgrounds” low

• Modest physics event rates

e+e-gqq ~0.1/Train, e+e-gggghadrons ~200/Train

~500 hits/BX in Vertex det. ~5 tracks/BX in TPC

Re-discover Higgs in a day


Energy Staging The ILC is naturally stageable … just add more Linac

Stage 1: 250 GeV

Precision Higgs physics

Stage 2: 500 GeV

Precision Higgs and top physics

Stage 1: 1 TeV

Precision Higgs physics (rare processes) + BSM

>100000 cleanly IDed top-pairs

Here focus on Higgs physics…

ILC Stage 1: 250 GeV


250 fb-1 at a centre-of-mass energy of 250 GeV

~75000 Higgs decays precision branching ratio measurements

Higgs-strahlung @ 250 GeV


Measure Higgs production cross section independent of Higgs decay mode Sensitive to invisible/exotic Higgs decay modes ! Absolute measurement of HZ coupling

e.g. 250 fb-1 at √s = 250 GeV

Model independent analysis Select Higgs based on observed di-lepton system alone Independent of Higgs decay Analysis:

Find Z:

Plot:


Invisible Higgs Decays Absolute coupling measurement is unique to a lepton collider, other unique measurements…

What if Higgs decays invisibly? For example: Neutral light stable SUSY states Dark sector gauge bosons “dark photons”

Precise measurement not possible at the LHC

Easy at the ILC: look for Z recoiling against a neutral state Clean environment clean signature Identify invisible Higgs decays from qq recoil mass*

Z

050

100

150

200

0

50

100

150

200

*plot is for 350 GeV, but idea is the same

Higgs branching ratios


Given absolute measurement of s(HZ) production cross section Event counts in exclusive final states give BRs (model independent!)

Nature has been kind, there is a lot to measure…

Note: Measure s(HZ) × BR BR measurements

ultimately limited by Ds(HZ) precision

Clean ILC environment allows b-tagging and charm tagging +…


@ 250 GeV

Process e+e-→ ZH

Int Lumi. [fb-1] 250

Ds(HZ)/s(HZ) 2.6 %

Decay Mode D(s x BR)/s x BR H→ bb 1.2 %

H→ cc 8.3 %

H→ gg 7.0 %

H→ WW* 6.4 %

H→ tt 4.2 %

H→ ZZ* 18 %

H→ gg 34 %

ILC @ 250 GeV

~ 1.3 % model indep. measurement of gHZZ

< 10 % model indep. measurements of s x BR

Ultimately want MI measurements of couplings… or equivalently partial decay widths


Higgs Couplings At 250 GeV measure:

Total HZ cross section (recoil mass)

+exclusive cross sections

Total Higgs width best determined from fusion process

e.g.

and

everything else follows….

ILC Stage 2: 500 GeV


500 fb-1 at a centre-of-mass energy of 500 GeV

~125000 Higgs decays precision coupling measurements


@ 250 GeV @ 500 GeV

Process e+e-→ ZH e+e-→ ZH e+e-→ nnH

Int Lumi. [fb-1] 250 500

Ds(HZ)/s(HZ) 2.6 % 3.0 % -

Decay Mode D(s x BR)/s x BR H→ bb 1.2 % 1.8 % 0.7 %

H→ cc 8.3 % 13 % 6.2 %

H→ gg 7.0 % 11 % 4.1 %

H→ WW* 6.4 % 9.2 % 2.4 %

H→ tt 4.2 % 5.4 % 9.0 %

H→ ZZ* 18 % 25 % 8.2 %

H→ gg 34 % 34 % 23 %

ILC @ 500 GeV

~5 % BR measurements ~2.5 % coupling determinations

ILC at 1 TeV

Mark Thomson 24

01000

2000

3000

-210

1 210

410

√s = 1 TeV

Int Lumi [fb] 1000

Cross section [fb] 425

N(Hnn) Events 425000

In the ultimate 1 TeV stage of ILC… Fusion cross section becomes large Large numbers of events Precise BR measurements

RHUL, October, 2013

+ Rarer processes give access to top Yukawa coupling Higgs self-coupling

Hard at HL-LHC


Coupling 250 GeV +500 GeV +1 TeV

HZZ 1.3 % 1.0 % 1.0 %

HWW 4.8 % 1.1 % 1.1 %

Hbb 5.3 % 1.6 % 1.3 %

Hcc 6.8 % 2.8 % 1.8 %

Hgg 6.4 % 2.3 % 1.6 %

Htt 5.7 % 2.3 % 1.6 %

Hmm - 91 % 16 %

Htt - 14 % 3.1 %

HHH - 83 % 21 %

GH 12 % 4.9 % 4.5 %

Putting it all together Expected precisions for ILC programme

Evaluated using full G4 simulations/full reconstruction Measurement precisions then combined in global fit

ILC gives O(1%) model independent Coupling determinations

250 GeV 250 fb-1

500 GeV 500 fb-1

1 TeV 1000 fb-1


c.f. HL-LHC Summary from Snowmass Energy Frontier report

can only really compare model-dependent fits…

General picture Impressive prospects for HL-LHC ! But ILC precisions mostly factor 5-10 smaller than HL-LHC + ILC has several unique measurements + model indep.


Why does this matter? What level of deviations from SM Higgs properties might be expected?

depends on assumptions No new physics (beyond 125 GeV Higgs) seen at LHC deviations not usually large

General conclusion Likely to need ~1 % precision to see few sigma effects ! The ILC can deliver this

e.g. R.S. Gupta, H.Rzehak, J.D. Wells, arXiv: 1206.3560v1

maximum deviations

Composite Higgs:

SUSY:


The Higgs boson is a totally new type of “matter”

scientifically imperative to study its properties in detail this alone is a compelling argument to build the ILC…


not just Higgs… Clean environment at ILC: ideal for precision top studies

e.g. top mass from fully-hadronic events √s = 500 GeV

Use:

• b-tagging • Invariant masses • Kinematic fits mW

b-tag

mt

mW

mt

b-tag

TOP

100 fb-1 with 500 fb-1 at √s = 500 GeV • stat. error < 50 MeV • limited by theory

Threshold scan at √s ~ 350 GeV • stat. error < 100 MeV • more closely related to pole mass • theory better under control

+ BSM

Mark Thomson

If TeV-scale SUSY is not discovered at the LHC: doesn’t mean it is not there could just be hiding in one of the dark corners where the LHC is blind the ILC closes many of these loopholes !

RHUL, October, 2013 30

SUSY


The clean ILC environment allows precise physics measurements. These measurements will compliment the high energy reach of the LHC/HL-LHC in pinning down the nature of TeV scale physics

BUT

Precision physics at the ILC places stringent requirements on the performance of the ILC detector(s)

…have only scratched the surface of ILC physics…

ILC Detector Concepts


Mark Thomson



There are arguments for having two complementary ILC detectors: Scientific redundancy – confirmation Complementarity in physics performance Competition Efficiency and reliability Broaden scientific opportunity

But a linear collider is … linear Baseline “solution” is push-pull: 1 interaction point – 2 detectors

Physics Driven Requirements

Mark Thomson

momentum: (1/10 x LEP) e.g. Smuon endpoint, Higgs recoil mass

hermetic: e.g. missing energy signatures in SUSY

impact parameter: (1/3 x SLD) e.g. c/b-tagging, Higgs BR

jet energy: (1/3 x LEP/ZEUS) e.g. W/Z di-jet mass separation, SUSY


Mark Thomson



Both concepts “validated” by IDAG (independent expert review) Detailed GEANT4 studies show ILD/SiD meet ILC detector goals Fairly conventional technology – although many technical challenges

Represent plausible/high-performance designs for an ILC detector

SiD: Silicon Detector “Small” : tracker radius 1.2m B-field : 5 T Tracker : Silicon Calorimetry : high granularity particle flow ECAL + HCAL inside large solenoid

ILD: International Large Detector

“Large” : tracker radius 1.8m B-field : 3.5 T Tracker : TPC Calorimetry : high granularity particle flow ECAL + HCAL inside large solenoid


Ultra low-mass vertex detector with ~20 μm pixels

Tracking: TPC+silicon (ILD) all-silicon (SiD)

Fine grained calorimeters for PFA

Strong SC solenoid 4 T or 5 T

Instrumented return yoke for muon ID

Complex forward region with final beam focusing

6.5 m

ILC Detectors in a Nutshell


Vertex detector

Inner radius: as close to beam pipe as possible for impact parameter resolution 15-30 mm Layer thickness: as thin as possible to minimize multiple scattering

Main design considerations:

T. Maruyama

B=5 T

ILD and SiD assume Silicon pixel based vertex detectors (5 or 6 layers)

Constraints:

Inner radius limited by pair background depends on machine + detector B-field Layer thickness depends on technology Some time-stamping capability required


Challenging ongoing

R&D project

e.g. Vertex + forward tracking layout of ILD

~20×20 μm pixel size 0.2% X0 material per layer - very thin !

Very thin materials/sensors Low-power design, power pulsing, air cooling

Radiation level <1011 neq cm-2 year-1 - 104 lower than LHC

Vertex detector


The two options considered:

Large number of samples

ILD: Time Projection Chamber

Few very well measured points

SiD: Silicon tracker (5 layers)

Tracking at the ILC


TPC + silicon tracker in 4 Tesla field

TPC with MPGD readout (GEMs or MicroMegas)

1.2

m

Si tracker in 5 Tesla field

chip on sensor

Tracking at ILC 1

.65

m


Performance of tracking/vertex systems validated in full MC studies

Efficie

ncy

00.2

0.4

0.6

0.8

1

Purity

0

0.2

0.4

0.6

0.8 1

b

c

c (b-b

kg)

q q

®a) Z

= 9

1 G

eV

s = 2

50 G

eV

s

Flavour tagging (ILD) Momentum resolution (SiD)

Tracking Performance goals can be met: – provided material budget kept under control

Calorimetry at the ILC



Calorimetry at the ILC What motivates calorimetry requirements at a future LC ?

depends on physics measurements NOT driven by single particle resolution Jet energy resolution much more important Likely to be primarily interested in di-jet mass resolution

For a narrow resonance (Higgs), want best possible di-jet mass res.

+ strong desire to separate W/Z hadronic decays

j1

j2 j3

j4

e–

e+ W/Z

W/Z q2

q3

q4

q1

e.g.


Calorimetry at the ILC Perfect 2 % 3 % 6 % LEP-like

Jet E res. W/Z sep perfect 3.1 s

2% 2.9 s 3% 2.6 s 4% 2.3 s 5% 2.0 s 10% 1.1 s

Defined as effective Gaussian equivalent Mass resolution

3 – 4 % jet energy resolution give decent W/Z separation 2.6 – 2.3 s for W/Z separation, not much to gain beyond this as limited by W/Z widths

sets a reasonable choice for Lepton Collider jet energy minimal goal ~3.5 %



ILC Goal: ~3.5 % jet energy res. for 50 – 250 GeV jets

Can not be achieved with conventional calorimetry !

High Granularity Particle Flow Dual Readout

Unproven, not clear if viable for a collider detector



Traditional calorimetric approach: Measure all components of jet energy in ECAL/HCAL ! ~70 % of energy measured in HCAL: Intrinsically poor HCAL resolution limits jet energy resolution

In a typical jet : 60 % of jet energy in charged hadrons 30 % in photons (mainly from ) 10 % in neutral hadrons (mainly and )

EJET = EECAL + EHCAL

n

p+

g


Calorimetry at the ILC Particle flow approach:

Try and measure energies of individual particles Reduce dependence on intrinsically poor HCAL resolution

EJET = ETRACK + Eg + En

Idealised Particle Flow Calorimetry paradigm: charged particles measured in tracker (essentially perfectly) Photons in ECAL Neutral hadrons (and ONLY neutral hadrons) in HCAL Only 10 % of jet energy from HCAL

EJET = EECAL + EHCAL

n

p+

g improved jet energy resolution


Calorimetry at the ILC Hardware: need to be able to resolve energy deposits from different particles

• Requires highly granular detectors

Software: need to be able to identify energy deposits from each individual particle • Requires sophisticated reconstruction software

Particle Flow Calorimetry = HARDWARE + SOFTWARE

Calo hits Particles


Particle flow reconstruction In practice, what one means by particle flow reconstruction depends on the detector

CMS

ILD Concept for the ILC

Our dreams..

Reality i)

ii)

Apply particle flow techniques to an existing detector

Design the detector for particle flow

Soon to become reality?

Particle Flow Calorimetry

ECAL Considerations

Material X0/cm rM/cm lI/cm lI/X0

Fe 1.76 1.69 16.8 9.5

Cu 1.43 1.52 15.1 10.6

W 0.35 0.93 9.6 27.4

Pb 0.56 1.00 17.1 30.5

HCAL

ECAL

Want to minimise transverse spread of EM showers Require small Molière radius High transverse granularity ~Molière radius

Want to longitudinally separate EM and Hadronic showers

Require large ratio of lI/X0 Longitudinal segmentation to cleanly ID EM showers

Favoured option : Tungsten absorber • Need ‘thin’ sensitive material to

maintain small Molière radius

EC

AL

H

CA

L


HCAL Considerations Want to resolve structure in hadronic showers

Require longitudinal and transverse segmentation

Want to fully contain hadronic showers

Require small lI

HCAL will be large, so absorber cost & structural properties will be important

Material X0/cm rM/cm lI/cm lI/X0

Fe 1.76 1.69 16.8 9.5

Cu 1.43 1.52 15.1 10.6

W 0.35 0.93 9.6 27.4

Pb 0.56 1.00 17.1 30.5

Technological options under study, e.g. by CALICE collaboration:

CAlorimetry for the LInear Collider Experiment

?

EC

AL

H

CA

L


Particle Flow Reconstruction

PFlow Reconstruction

Particle Flow Algorithms (PFA)

High granularity calorimeters – very different to previous detectors

“Tracking calorimeter” – requires a new approach to ECAL/HCAL reconstruction

g

granularity

g

PFlow Algorithm

e.g. Need to separate tracks (charged hadrons) from photons

hardware software


PandoraPFA

Typical topology of a simulated 250 GeV jet in ILD

High granularity particle flow calorimetry lives or dies on the quality of the reconstruction of particles Requires high-performance software, both in terms of:

algorithmic sophistication CPU/memory usage – these are complex events with many hits

Almost all LC studies based on Pandora C++ software development kit Provides highly sophisticated PFlow reconstruction for LC-style detectors

+ flexibility for much more…

PandoraPFA


PandoraPFA Algorithms ConeClustering

Algorithm

Topological Association Algorithms

Track-Cluster Association Algorithms

Reclustering Algorithms

Fragment Removal

Algorithms

PFO Construction Algorithms

Looping tracks

Cone associations

Back-scattered

tracks

Neutral hadron Charged hadron Photon

9 GeV

6 GeV

3 GeV

Layers in close contact

9 GeV

6 GeV

3 GeV

Fraction of energy in cone

Projected track position

Cluster first layer position

12 GeV 32 GeV

18 GeV

30 GeV Track

38 GeV

M. T

ho

mson, N

IM 6

11

(2

00

9)

24

-40


Particle Flow Objects

Particle flow objects (PFOs) built from tracks and clusters:

List of reconstructed particles with energies and particle ID

Build jets… Study physics performance

Assess performance of a Particle Flow detector using simulation…

Typical 250GeV Jet in ILD:

3GeV e+

2GeV e-

photons

Charged hadrons

Neutral hadron

After all that:


Performance

EJET sE/Ej

45 GeV 3.7 %

100 GeV 2.8 %

180 GeV 2.9 %

250 GeV 2.9 %

rms90

Benchmark performance using G4 simulation of ILD detector: Z’ decays at rest to light quarks

Factor 2-3 better than traditional calorimetry !

GOAL MET !


Goal: jet energy resolution:

W/Z Separation

125 GeV Z 250 GeV Z 500 GeV Z 1 TeV Z

On-shell W/Z decay topology depends on energy:

LEP ILC CLIC

Note: Particle multiplicity does not change

Boost means higher particle density

For boosted jets – no sub-jet finding, just sum the 4-momenta of the PFOs !

More confusion !


W/Z Separation Studied di-jet/mono-jet masses in ILD concept

ILC-like energies

CLIC-like energies

Clear separation of W/Z di-jet mass peaks

W and Z still resolved from monojet invariant mass

Impressive demonstration of power of Particle Flow at a Linear Collider



From Design to Reality

if time allows…


Detector R&D

ILC Detector concepts backed-up by strong programme of detector R&D

CALICE: High-granularity Calorimetry LCTPC: TPC design FCAL: Forward calorimetry PLUME and others: VTX detector …

No time for detailed overview – take CALICE as example

CALICE Activities CALICE = “Umbrella R&D collaboration for LC calorimetry”

studies encompass a number of technological options

Absorber

Active

CALO

Readout


e.g. Si-ECAL prototype Technological Si-ECAL prototype:

Real-scale detector integration model Large Si sensors with small 5×5 mm2 PADs System with 1200 cells in DESY test beam in 2012

Full-scale mechanical structure Test beam characterisation of technology


e.g. Digital HCAL

W-DHCAL π- at 210 GeV (SPS)

54 glass RPC chambers, 1m2 each PAD size 1×1 cm2

Digital readout (1 threshold) Fully integrated electronics Total: 500000 readout channels

Detailed 3D images of hadronic showers

Test beam campaigns: Demonstrate technology

Provide high quality physics data test GEANT4 models Many CALICE publications



Where Now?


| The next steps Japan has announced an interest in hosting the ILC

the site has been selected

Far from a “done deal”… but Japan is serious discussions at ministerial level discussions with potential partners (Europe, US)


What does this mean for the UK ?

The ILC could be the next major HEP project If the ILC happens, the UK has to be there

Despite the fact funding is tight UK HEP community has to reengage with the ILC Even if initially at a low level

Planning modest proposal to STFC early 2014 Main aim is to regain a foothold Watch this space…


} Conclusions The Higgs boson is something completely new in nature

fundamental scalar field !?

Studying its properties in detail is essential for the field

a portal to BSM physics?

The ILC is ready to meet the challenge

Now in the hands of the politicians…


Spares


~1000 events

Exact physics programme depends on what is out there…

e+e– collisions at √s = 0.2-1.0 TeV provide rich environment

ILC offers Flexibility in running, e.g. new particle thresholds

Can accumulate large samples of cleanly identified/well-measured events

ILC Physics = Precision Studies:

Higgs sector (EWSB)

SUSY particle spectrum (if exists)

SM particles (e.g. W-boson, top)

and much more...

Take Higgs sector as an example of the power of the ILC…

ILC Physics Potential

physics and detectors at the ilc...ilc 2x1034 5 1312 2 0.6 0.006 slc 2x1030 120 1 4 1.5 0.5 lep2...

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