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Electron- Linear

Jan Timmermans DESY-FLC (and NIKHEF)

Summer Student Lecture 25.07.2011 Schedule

§ Introduction § Global Context § Case § ILC Accelerator Design § CLIC Principle § ILC Detectors § Outlook

Thanks to Karsten Buesser for using part of his 2009 slides, who in turn thanked P. Wienemann, N. Walker, T. Behnke, B. Foster, J.P. Delahaye and others for letting him stealing some of their plots and slides

J. Timmermans -Positron Linear Collider 2 Introduction

J. Timmermans Electron-Positron Linear Collider 3 The of

§ Extremely successful description of the § 12 matter particles § 4 force mediators

§ 1 missing piece: Higgs

§ No significant deviation found in many precision under hypothesis being relatively light

J. Timmermans Electron-Positron Linear Collider 4 The Higgs-Boson

§ Where is the Higgs-Boson? § Direct searches done at LEP, still ongoing at and now also at LHC § Indirect searches point to low Higgs

J. Timmermans Electron-Positron Linear Collider 5 Does SUSY exist?

§ relates and § It must be a broken symmetry – otherwise we would have found SUSY particles § New particle spectrum § Neutral SUSY particles are strong candidate for dark matter!

J. Timmermans Electron-Positron Linear Collider 6 and Electron

p p e+ e-

§ Proton (anti-) proton : § Electron positron colliders: § range higher (limited by § Energy range limited (by RF bending power) power) § Composite particles, different initial § Point-like particles, exactly state constituents and in defined initial state quantum each collision numbers and energies § Hadronic final states difficult § Hadronic final states easy § Discovery machines § Precision machines § Excellent for some precision § Discovery potential measurements

J. Timmermans Electron-Positron Linear Collider 7 Protons vs

pp è H + X e+e- è HZ

J. Timmermans Electron-Positron Linear Collider 8 ILC Requirements

§ The e+e- cross section drops ~1/s

§ The key parameters for a com- petitive e+e- are § energy reach § Luminosity

(LEP2 had integrated luminosity of -1 ~ 700 pb /expt; ZHH peak luminosity ~1032 cm-2s-1 ) Reminder:

Nint = σ ∫Ldt 1 pico- = 10-36 cm2

J. Timmermans Electron-Positron Linear Collider 9 ILC baseline parameters

• CMS energy (max.): 500 GeV • Luminosity (peak): 2 x 1034 cm-2s-1 ∫Ldt = 500 fb-1 (4 yrs) • e- polarisation: ≥ 80% • One IR with 14 mrad beam crossing angle Upgrade: • Energy up to 1 TeV • ∫Ldt = 1 ab-1 (3-4 yrs) 10 Cost Scalings for Storage Rings

§ Cost for RF: 4 €RF ~ E /r

§ Linear costs (tunnelling, beam line, etc.):

€lin ~ r § Total cost: 2 €tot = €RF+ €lin ~ E 2 ropt ~ E For details check: B. Richter, NIM 136 (1976) pp. 47-60

J. Timmermans Electron-Positron Linear Collider 11 Scaling LEP

€€LC~LC~ E E

§ The next high-energy e +e- collider will have to be linear:

§ €LC~ E

J. Timmermans Electron-Positron Linear Collider 12 The Global Context

J. Timmermans Electron-Positron Linear Collider 13 Linear Collider Developments

§ International Linear Collider ILC § superconducting acceleration § 31.5 MeV/m, 1.3 GHz § advanced design (c.f. XFEL) § 500 GeV (→ 1TeV) § Luminosity: 2 x 1034 cm-2 s-1 § is at hand

§ CLIC § normalconducting acceleration § 100 MeV/m, 12 GHz § two-beam acceleration principle § up to several TeV § still in fundamental R&D phase

J. Timmermans Electron-Positron Linear Collider 14 Timeline

§ Physics will decide the way forward! § LHC will tell us which energy reach will be needed CLIC LHC Results Feasibility Study ILC Timeline

§ Years around 2012 will be the decision years on how to proceed: § ILC, CLIC, LHC-Upgrades, something completely different?

J. Timmermans Electron-Positron Linear Collider 15 ILC Reference Design Report (2007)

Download it at www.linearcollider.org

2011: CLIC Conceptual Design Report

J. Timmermans Electron-Positron Linear Collider 16 Physics Case

J. Timmermans Electron-Positron Linear Collider 17 Physics Case § There are other lectures which deal with the physics of electron-positron collisions § Introduction to particle physics – C. Sander § Introduction to physics – P. Bechtle (HEP- Lectures) § Physics at e+e- colliders - G. Moortgat-Pick (HEP-Lectures)

§ I will just give one example and will leave the rest to the specialised lectures

J. Timmermans Electron-Positron Linear Collider 18 Higgs Physics

19 Establishing the Higgs-Mechanism

§ Measuring the couplings of the Higgs to massive particles § Check coupling-mass relation § The smoking gun!

J. Timmermans Electron-Positron Linear Collider 20 • Any questions sofar? – Introduction – Global context – Physics case

21 ILC Accelerator Design

J. Timmermans Electron-Positron Linear Collider 22 The Future is Linear

€LC~ E

J. Timmermans Electron-Positron Linear Collider 23 The Luminosity Issue

The Luminosity (cm-2 s-1) for a collider with Gaussian beams is given by:

2 nb N frep L = H D 4! " x" y

nb = bunches / train N = particles per bunch frep = repetition frequency 4πσx σy = beam cross-section at IP HD = beam-beam enhancement factor

J. Timmermans Electron-Positron Linear Collider 24 The Luminosity Issue: RF Power

Introducing the Beam Power: nb NfrepEcm = Pbeams =! P RF "beam RF yields

E n Nf N ( cm b rep ) !RF PRF N L = H D L = H D 4! " x" y Ecm 4" # x# y Ecm

J. Timmermans Electron-Positron Linear Collider 25 RF Power

Some numbers: !RF PRF N L = H D Ecm = 500 GeV 4" # # E N = 1010 x y cm nb = 100 2 nb N frep frep = 100 Hz L = H D 4! " x" y àPbeams = 8 MW Adding efficiencies Wall plug à RF à beam yields AC power needs > 100 MW just to accelerate beams and maintain luminosity!

J. Timmermans Electron-Positron Linear Collider 26 Storage Ring vs Linear Collider

§ LEP f 44 kHz 2 rep nb N frep § ILC frep few-100 Hz (power limited) L = H D 4! " x" y § Factor ~ 400 in L already lost! § Recover by pushing hard on the beam spot sizes at collision: LEP: 130 x 6 µm2 ILC: 500 x 5 nm2 y Needed to achieve L~ O(1034 cm-2 s-1)!

ILC x

J. Timmermans Electron-Positron Linear Collider 27 Beamstrahlung

§ Strong mutual focusing of beams gives rise to significant luminosity γ enhancement (H ≈2): Pinch effect e- d e γ § e± pass through intense field of + opposite beam, radiate hard γ photons: Beamstrahlung

y 3 2 ere # Ecm $ N ! BS % 0.86 2 & ' 2 2m0c ( " z ) (" x +" y )

2 n N f ILC b rep } x L = H D 4! " x" y Choose flat beams!

J. Timmermans Electron-Positron Linear Collider 28 Luminosity Scaling Law

§ Choose flat beam (σy << σx): N ! " # z BS ! x Ecm

! P # N $ 1 L RF RF § Luminosity law: % & ' Ecm ( " x ) " y

# P ! BS" z § yields: RF RF L $ 3/ 2 Ecm " y

J. Timmermans Electron-Positron Linear Collider 29 How to Maximise Luminosity

#RF PRF ! BS" z L $ 3/ 2 Ecm " y

§ high RF beam-power conversion efficiency ηRF

§ high RF power PRF

§ small vertical beam size σy

§ large bunch length σz

§ could go to higher beamstrahlung δBS, if willing to live with consequences

J. Timmermans Electron-Positron Linear Collider 30 ILC Baseline Design

J. Timmermans Electron-Positron Linear Collider 31 ILC Bunch Structure

§ Superconducting RF has small dissipation losses in cavity walls → long pulses with large bunch spacing possible

Reduced by factor 2 in SB2009

J. Timmermansr Electron-Positron Linear Collider 32 ILC Technical Systems

J. Timmermans Electron-Positron Linear Collider 33 Sources

§ Requirements: § Produce long bunch trains of high charge bunches § ~3000 bunches per train § 5 trains per second § With small emittances § And polarisation: § mandatory for electrons § nice to have for

J. Timmermans Electron-Positron Linear Collider 34 Electron Source

§ driven photo injector based

on SLC design ! = 840 nm ns oto ph er § Circular polarised photons on GaAs las → longitudinal polarised electrons 20 mm GaAs electrons cathode § very high vacuum requirements (< -11 10 mbar) to protect cathode from 120 kV impurities and ion backdrift § 140-160 keV electron kinetic energy at exit § 1ns bunch length at 3 MHz § Peak current: 4.5-5 nC/ns (needed at IP 1.6-3.2 nC), space charge limited

J. Timmermans Electron-Positron Linear Collider 35 Positron Source

§ Production of e± pairs by ~30 MeV undulator photons hitting a thin (0.4 X0) target § Thin target reduces multiple scattering, hence better emittance § Needs >150 GeV electrons in undulator!

250GeV e t!o IP

e+e- pairs N S N S N S N S N S from e- linac ~30MeV photons S N S N S N S N S N undulator (~100m)

0.4X target

J. Timmermans Electron-Positron Linear Collider 36 Positron Source Design

§ Using a helical undulator allows the production of polarised positrons! § Positron source links electron and positron linac § Keep-alive positron source planned

J. Timmermans Electron-Positron Linear Collider 37 Damping Rings

J. Timmermans Electron-Positron Linear Collider 38 Damping Rings

§ RF system in damping rings accelerates beam particles in longitudinal direction § Interplay between radiation and RF reduces transverse emittance! § Typical damping are of order 100 ms § Linac RD pulse length is 1ms! § Whole bunch train (300 km @ 300ns) needs to be stored in a damping ring O(10km)! § Bunch train needs to be compressed in damping ring

J. Timmermans Electron-Positron Linear Collider 39 ILC Damping Ring Design

• Damping by SR from bending would be too large O(400ms) • Include damping wigglers in the beam to reduce damping time to ~25 ms

J. Timmermans Electron-Positron Linear Collider 40 Main Linac

J. Timmermans Electron-Positron Linear Collider 41 ILC’s Workhorse - SCRF

Parameter� Value� C.M. Energy� 500 GeV� Peak luminosity� 2x1034 cm-2s-1� Beam Rep. rate� 5 Hz� Pulse time duration� 1 ms� Average beam 9 mA �(in current � pulse)� Av. field 31.5 MV/ gradient� m� # 9-cell cavity� 14,560� # cryomodule� 1,680� # RF units� 560� B. Foster - DESY - 06/10 Global Design Effort 42 How does a work?

§ DC Beam at (<500 kV, < 500 A) is emitted from the gun § A low-power signal at the design frequency excites the input cavity § Particles are accelerated or decelerated in the input cavity, depending on phase/arrival time § Velocity modulation becomes time modulation in the long drift tube (beam is bunched at drive frequency) § Bunched beam excites output cavity at design frequency (beam loading) § Spent beam is stopped in the collector.

J. Timmermans Electron-Positron Linear Collider 43 ILC

§ 10 MW multibeam klystron

J. Timmermans Electron-Positron Linear Collider 44 ILC Cavities

§ Acceleration gradient goal: § 35 MV/m in 9-cell cavities with production yield >80% § 50 MV/m have been reached with single cavities § Mass production reliability is the key problem

2010 ILC target

2nd pass

J. Timmermans Electron-Positron Linear Collider 45 Tunnel Configuration

§ Two tunnel solution: § Three RF/cable penetrations every rf unit § Safety crossovers every 500 m § 34 kV power distribution § 72.5 km tunnels § 13 major shafts > 9 meter diameter § 443 K cu. m. underground excavation: caverns, alcoves, halls § Or is one tunnel better (XFEL-like)?

J. Timmermans Electron-Positron Linear Collider 46 From RDR -> SB2009

RDR SB2009 • Single Tunnel for main linac

• Move positron source to end of linac

• Reduce number of bunches factor of two (lower power)

• Reduce size of damping rings (3.2km)

• Integrate central region

• Single stage bunch compressor

B. Foster - DESY - 06/10 Global Design Effort 47 Beam Delivery System

J. Timmermans Electron-Positron Linear Collider 48 Beam Delivery System Tasks

§ The main tasks of the Beam Delivery System are:

§ Collimation: remove the beam halo to reduce background § Beam diagnostics (up- and downstream of the IP) § Final Focus System: squeeze the beams to nanometre sizes to provide luminosity at the IP § Beam dumps: dispose spent beams after the collision

J. Timmermans Electron-Positron Linear Collider 49 Final Focus

final doublet (FD) IP

f1 f2 f2 f1 * f2 (=L )

*! Use telescope optics to de-magnify beam by factor m = f1/f2= f1/L Need typically m = 300

* putting L = 2m → f1 = 600m In real life much more complicated: correction for large chromatic and geometric aberrations needed " principle design challenge

J. Timmermans Electron-Positron Linear Collider 50 Crossing Angle

§ ILC beams collide with 14 mrad crossing angle § Facilitates extraction of spent beam § Requires crab crossing

J. Timmermans Electron-Positron Linear Collider 51 IP Region

J. Timmermans Electron-Positron Linear Collider 52 Detectors and Push/Pull

§ Integrated luminosity at linear colliders scales not with the number of interaction regions

§ ILC has just one interaction beam line (cost issue) but should have two detectors

§ Try to find a solution where two detectors share one interaction region à Push/Pull System

J. Timmermans Electron-Positron Linear Collider 53 Sample Sites

§ Three deep sites under study: § Americas: Fermilab § Asia: Japan § Europe: CERN

§ Two shallow sites: § DESY § Dubna

§ Sample sites are studied for technical reasons. § Real site choice will be a political decision!

J. Timmermans Electron-Positron Linear Collider 54 • Any further questions (on ILC)? – Luminosity – Baseline design; bunch structure – Sources – Damping rings – Main linac, cavities – Beam delivery

55 CLIC Technology

J. Timmermans Electron-Positron Linear Collider 56 What if we need to go way beyond 1 TeV?

§ LHC will tell us the region of the interesting physics ahead § All seems to hint to the <1TeV region § But what if the interesting area is the multi-TeV region?

§ A Linear Collider with multi-TeV energy reach will be needed then!

§ The CLIC technology opens the path to the multi-TeV regime.

J. Timmermans Electron-Positron Linear Collider 57 The Luminosity Challenge

§ Remember:

#RF PRF ! BS" z L $ 3/ 2 Ecm " y

§ Challenge: Luminosity of 1034 cm-2s-1 at 3-5 TeV!

§ Need high RF power PRF

§ Need high RF efficiency ηRF § Need very small bunch sizes at the IP § Challenge: Energy of 3-5 TeV on reasonable length (50km) § Acceleration gradients ~100 MV/m § Impossible with superconducting cavities (limit around 40-50 MV/m) § Normalconducting copper cavities needed § lower RF efficiencies, more RF power needed!

J. Timmermans Electron-Positron Linear Collider 58 Two-beam Acceleration

§ Use low-energy high-current electron drive-beam as klystron replacement: Two Beam Scheme:

Drive Beam supplies RF power • 12 GHz bunch structure • low energy (2.4 GeV - 240 MeV) • high current (100A) Main beam for physics • high energy (9 GeV – 1.5 TeV) • current 1.2 A

J. Timmermans Electron-Positron Linear Collider 59 Copper Acceleration Cavities

J. Timmermans Electron-Positron Linear Collider 60 Beam Spot Sizes

J. Timmermans Electron-Positron Linear Collider 61 ILC/CLIC parameters -,+-&85&?&*4@&8AB&>((&C4@

Center-of-mass energy ILC 500 GeV CLIC 500 GeV CLIC 3 TeV Total (Peak 1%) luminosity [·1034] 2(1.5) 2.3 (1.4) 5.9 (2.0) Repetition rate (Hz) 5 50 Loaded accel. gradient MV/m 32 80 100 Main linac RF frequency GHz 1.3 12 Bunch charge [·109] 2.420 6.8 3.7 Bunch separation (ns) 370 0.5 Beam pulse duration (ns) 950!s 177 156 Beam power/beam (MWatts) 4.9 14 Hor./vert. IP beam size (nm) 600 / 6 200 / 2.3 40 / 1.0 Hadronic events/crossing at IP 0.12 0.2 2.7 Incoherent pairs at IP 1 ·105 1.7·105 3·105 BDS length (km) (2 x) 2.25 1.87 2.75 Total site length km 31 13 48 Total power consumption MW 230 130 415 !"#$$%&'!(&')*!+,!-"./!!012!!34!-"./5

http://www.cern.ch/lcd Lucie Linssen,*+,-()&./#012/"&&3$454#&672%8554#& 13/11/2009 62 !"#$%&'(() > 62 9-:;<= CLIC Test Facility CTF3

§ Show CLIC feasibility by 2010

J. Timmermansr Electron-Positron Linear Collider 63 ILC Detectors

J. Timmermans Electron-Positron Linear Collider 64 Generic Detector

J. Timmermansr Electron-Positron Linear Collider 65 Basic detector design concept (and compared to LEP detector) • Performance goal (common to all det. concepts)

3/ 2 – Vertex Detector: δ (IP) ≤ 5⊕10 / psin θ [µm] (ILC 5x better than LEP)

2 −5 -1 – Tracking: δpt / pt ≤ 5×10 [GeV ] (ILC: 10x better) (CMS: 1.5 10-4) – Jet energy res.: δE / E ≤ 0.3/ E [E in GeV] (ILC: 2x better) è Detector optimized for Particle Flow Algorithm (PFA)

66 The Particle Flow Concept

§ Idea: use the sub-detector with the best resolution for the energy ! § Charged particles: tracking system (~65% of jet energy) § Photons: ECAL (~25%) § Neutral : HCAL (~10%)

§ Avoid double counting! § Trace every single particle through the detector

§ Ejet = Echarged + Ephotons + Eneutral hadr. 2 2 2 § σ (Ejet)= σ (Echarged) + σ (Ephotons )+ 2 2 σ (Eneutral hadr.)+σ confusion

J. Timmermans Electron-Positron Linear Collider 67 Detector

§ High magnetic field needed for precision in measurement: § 3.5 - 4 T

§ Field homogeneity is crucial for TPC operation

§ Coil is a major cost driver for the experiments!

§ CMS coil (4T) is the model

J. Timmermans Electron-Positron Linear Collider 68 Validated ILC concepts

CLIC detector concepts will be based on SiD and ILD. Modified to meet CLIC requirements

http://www.cern.ch/lcd Lucie Linssen, 13/11/2009 69 Imaging Detector

§ e+e- → ZH

J. Timmermans Electron-Positron Linear Collider 70 Conclusion

J. Timmermans Electron-Positron Linear Collider 71 Conclusion

§ The LHC will need to be complemented by an electron-positron collider for precision measurements § LHC results will tell the parameter needs § ILC is the far most advanced collider design § CLIC could be a high- energy option § on a much longer timescale though... § Machine and experiments demand high-tech solutions on yet untested scales J. Timmermans Electron-Positron Linear Collider 72 Backup detector slides

73 Vertex Detector

§ Requirements: § excellent point resolution <4μm § small pixel sizes: 20 x 20 μm2 § ~109 channels

§ low material budget: ~0.1% X0 § fast read-out to minimise pile-up § immune against EMI effects

§ Flavour tagging is crucial § b-tagging easier than c-tagging

§ Many under study

J. Timmermans Electron-Positron Linear Collider 74 Tracking Options: Pixelated or Gaseous?

J. Timmermans Electron-Positron Linear Collider 75 Tracking System Option: Time Projection Chamber

§ Genuine 3d trajectory measurement § Spacepoint resolution ~100μm § Minimal amount of material in front of calorimeters § Rather slow: 150 bunch crossings per picture

J. Timmermans Electron-Positron Linear Collider 76 Tracking System Option: Tracker

§ Axial strips, no z information § rφ resolution: < 7μm 2 -5 -1 § pt resolution: Δpt/pt < 2 x 10 GeV

J. Timmermans Electron-Positron Linear Collider 77 ILD Detector Concept

J. Timmermans Electron-Positron Linear Collider 78