Physics and Detectors at the ILC. Mark Thomson University of Cambridge

Transcription

1 Physics and Detectors at the ILC University of Cambridge

2 Overview This talk: 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 2

3 Motivation for an e+e- collider The LHC and a LC provide a complimentary approach to studying the physics of EWSB and beyond The LHC 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 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)

4 + 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 4

5 Why linear? Circular machine : cost 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 Circular Collider Linear machine : Breakpoint approximately s = 200 GeV (LEP 2) To get above this energy need a linear collider the ILC Linear Collider Energy 5

6 Why now? 6

7 the Higgs is out there the Higgs is now standard textbook* physics *apologies for the gratuitous plug The ILC is THE machine to study the Higgs The ILC in Japan is now a very realistic possibility high level discussions ongoing 7

8 The Machine 8

9 The ILC Centre-of-mass energy adjustable from GeV upgradeable to 1 TeV (i.e. make it longer) Integrated luminosity of 500 fb-1 in first 4 years operation ILC require high luminosity: ~2x10 cm s Electron polarization of >80 % at interaction point (see later) TDR (2012) The ILC is much more than the linear bit 9

10 Basic accelerating structure The main accelerating structures are the two 11km long LINACs LINACs built out of 9-cell superconducting 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 Longitudinal Electric Field (standing wave) Positron Bunch 10

11 Beam and Luminosity To achieve high luminosity is challenging: To reach the ILC goal of L = 2x1034cm-2s-1 the interaction point! small beam spot at L [cm-2s-1] frep[hz] nb Ne [1010] sx [mm] sy [mm] ILC 2x SLC 2x LEP2 5x Small beam spot complex beam delivery/final focus 6 nm!!! 574 nm The ILC is a challenging machine 11

12 Challenging, but doable TDR published in June based on many years of work 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 12

13 The ILC is doable Physics case? 13

14 Physics at the ILC Baseline design of the ILC now fixed as of TDR Time Structure: 5 Bunch-trains per second Bunch Train 0.2 s 554 ns 1312 bunches/train Bunch Spacing 0.73 ms Modest physics event rates e+e-gqq ~100/hr e+e-gtt ~50/hr Backgrounds low e+e-gw+w- ~1000/hr e+e-ghx ~10/hr e+e-gqq ~0.1/Train, Re-discover Higgs in a day e+e-gggghadrons ~200/Train ~500 hits/bx in Vertex det. ~5 tracks/bx in TPC Very clean physics environment: low event rates, modest backgrounds, long time between collisions 14

15 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: > cleanly IDed top-pairs 1 TeV Precision Higgs physics (rare processes) + BSM Here focus on Higgs physics 15

16 ILC Stage 1: 250 GeV 250 fb-1 at a centre-of-mass energy of 250 GeV ~75000 Higgs decays precision branching ratio measurements 16

17 250 GeV Model independent analysis Select Higgs based on observed di-lepton system alone Independent of Higgs decay Analysis: Find Z: Plot: 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 17

18 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 *plot is for 350 GeV, but idea is the same 18

19 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 + 19

20 GeV Process Int Lumi. [fb-1] Ds(HZ)/s(HZ) Decay Mode e+e- ZH % D(s x BR)/s x BR H bb 1.2 % H cc 8.3 % H gg 7.0 % H WW* H tt 6.4 % H ZZ* 18 % H gg ~ 1.3 % model indep. measurement of ghzz < 10 % model indep. measurements of s x BR 4.2 % 34 % Ultimately want MI measurements of couplings or equivalently partial decay widths 20

21 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. 21

22 ILC Stage 2: 500 GeV 500 fb-1 at a centre-of-mass energy of 500 GeV ~ Higgs decays precision coupling measurements 22

23 GeV Process Int Lumi. [fb-1] 500 GeV e+e- ZH e+e- nnh e+e- ZH % 3.0 % - H bb 1.2 % 1.8 % 0.7 % H cc 8.3 % 13 % 6.2 % H gg 7.0 % 11 % 4.1 % H WW* H tt 6.4 % 9.2 % 2.4 % 4.2 % 5.4 % 9.0 % H ZZ* 18 % 25 % 8.2 % 34 % 34 % 23 % Decay Mode H gg D(s x BR)/s x BR ~5 % BR measurements ~2.5 % coupling determinations 23

24 ILC at 1 TeV In the ultimate 1 TeV stage of ILC Fusion cross section becomes large Large numbers of events Precise BR measurements 1000 s = 1 TeV 1000 Cross section [fb] N(Hnn) Events 2000 Int Lumi [fb] + Rarer processes give access to top Yukawa coupling Higgs self-coupling Hard at HL-LHC 24

25 Putting it all together Expected precisions for ILC programme Evaluated using full G4 simulations/full reconstruction Measurement precisions then combined in global fit Coupling 250 GeV +500 GeV +1 TeV HZZ 1.3 % 1.0 % HWW 4.8 % Hbb 250 GeV 250 fb % 500 GeV 500 fb % 1.1 % 1 TeV 1000 fb % 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 % 12 % 4.9 % 4.5 % GH ILC gives O(1%) model independent Coupling determinations 25

26 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. 26

27 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 e.g. R.S. Gupta, H.Rzehak, J.D. Wells, arxiv: v1 maximum deviations Composite Higgs: SUSY: General conclusion Likely to need ~1 % precision to see few sigma effects! The ILC can deliver this 27

28 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 28

29 not just Higgs TOP Clean environment at ILC: ideal for precision top studies e.g. top mass from fully-hadronic events s = 500 GeV b-tag b-tag mt mt mw 100 fb-1 Use: b-tagging Invariant masses Kinematic fits mw 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 29

30 + BSM SUSY 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! 30

31 have only scratched the surface of ILC physics 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) 31

32 ILC Detector Concepts 32

33 ILC Detector Concept s 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 33

34 Physics Driven Requirements momentum: (1/10 x LEP) e.g. Smuon endpoint, Higgs recoil mass jet energy: (1/3 x LEP/ZEUS) e.g. W/Z di-jet mass separation, SUSY impact parameter: (1/3 x SLD) e.g. c/b-tagging, Higgs BR hermetic: e.g. missing energy signatures in SUSY 34

35 ILC Detector Concepts 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 SiD: Silicon Detector Small : tracker radius 1.2m B-field :5T Tracker : Silicon Calorimetry : high granularity particle flow ECAL + HCAL inside large solenoid 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 35

36 ILC Detectors in a Nutshell Complex forward region with final beam focusing Instrumented return yoke for muon ID Strong SC solenoid 4 T or 5 T Fine grained calorimeters for PFA 6.5 m Tracking: TPC+silicon (ILD) all-silicon (SiD) Ultra low-mass vertex detector with ~20 μm pixels 36

37 Vertex detector ILD and SiD assume Silicon pixel based vertex detectors (5 or 6 layers) Main design considerations: Inner radius: as close to beam pipe as possible for impact parameter resolution mm Layer thickness: as thin as possible to minimize multiple scattering Constraints: Inner radius limited by pair background depends on machine + detector B-field Layer thickness depends on technology Some time-stamping capability required T. Maruyama B=5 T 37

38 Vertex detector 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 lower than LHC Challenging ongoing R&D project 38

39 Tracking at the ILC The two options considered: ILD: Time Projection Chamber Large number of samples SiD: Silicon tracker (5 layers) Few very well measured points 39

40 Tracking at ILC Si tracker in 5 Tesla field 1.2 m 1.65 m TPC + silicon tracker in 4 Tesla field chip on sensor TPC with MPGD readout (GEMs or MicroMegas) 40

41 Performance of tracking/vertex systems validated in full MC studies Flavour tagging (ILD) Purity Momentum resolution (SiD) a) Z qq s = 91 GeV 0.4 c 0.8 c (b-bkg) 0.6 s = 250 GeV 0.2 b 1 Efficiency Tracking Performance goals can be met: provided material budget kept under control 41

42 Calorimetry at the ILC 42

43 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 e.g. e+ W/Z e W/Z q1 j4 j1 q2 q3 q4 j2 j3 43

44 Calorimetry at the ILC Perfect Jet E res. perfect 2% 3% 4% 5% 10% 2% 3% 6% LEP-like W/Z sep 3.1 s 2.9 s 2.6 s 2.3 s 2.0 s 1.1 s Defined as effective Gaussian equivalent Mass resolution 3 4 % jet energy resolution give decent W/Z separation s sets a reasonable choice for Lepton Collider jet energy minimal goal ~3.5 % for W/Z separation, not much to gain beyond this as limited by W/Z widths 44

45 Calorimetry at the ILC ILC Goal: ~3.5 % jet energy res. for GeV jets Can not be achieved with conventional calorimetry! High Granularity Particle Flow Dual Readout Unproven, not clear if viable for a collider detector 45

46 Calorimetry at the ILC In a typical jet : 60 % of jet energy in charged hadrons 30 % in photons (mainly from ) 10 % in neutral hadrons (mainly and ) Traditional calorimetric approach: Measure all components of jet energy in ECAL/HCAL! ~70 % of energy measured in HCAL: Intrinsically 䇾poor䇿 HCAL resolution limits jet energy resolution p+ g n EJET = EECAL + EHCAL 46

47 Calorimetry at the ILC Particle flow approach: Try and measure energies of individual particles Reduce dependence on intrinsically 䇾poor䇿 HCAL resolution 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 improved jet energy resolution p+ g n EJET = ETRACK + Eg + En EJET = EECAL + EHCAL 47

48 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 Calo hits Particles Particle Flow Calorimetry = HARDWARE + SOFTWARE 48

49 Particle Flow Calorimetry Particle flow reconstruction In practice, what one means by particle flow reconstruction depends on the detector i) Reality CMS Apply particle flow techniques to an existing detector ii) Soon to become reality? Our dreams.. ILD Concept for the ILC Design the detector for particle flow 49

50 ECAL Considerations Want to minimise transverse spread of EM showers Require small Molière radius High transverse granularity ~Molière radius HCAL Want to longitudinally separate EM and Hadronic showers Require large ratio of li/x0 Longitudinal segmentation to cleanly ID EM showers rm/cm li/cm li/x0 Fe Cu W Pb HCAL X0/cm ECAL Material ECAL Favoured option : Tungsten absorber Need thin sensitive material to maintain small Molière radius 50

51 HCAL Considerations 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 Cu W Pb ECAL HCAL Want to resolve structure in hadronic showers Require longitudinal and transverse segmentation? Technological options under study, e.g. by CALICE collaboration: CAlorimetry for the LInear Collider Experiment 51

52 Particle Flow Reconstruction

53 PFlow Reconstruction High granularity calorimeters very different to previous detectors Tracking calorimeter requires a new approach to ECAL/HCAL reconstruction Particle Flow Algorithms (PFA) e.g. Need to separate 䇾tracks䇿 (charged hadrons) from photons hardware software granularity PFlow Algorithm g g 53

54 PandoraPFA 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 PandoraPFA Almost all LC studies based on Pandora C++ software development kit Provides highly sophisticated PFlow reconstruction for LC-style detectors + flexibility for much more Typical topology of a simulated 250 GeV jet in ILD 54

55 PandoraPFA Algorithms M. Thomson, NIM 611 (2009) ConeClustering Algorithm Topological Association Algorithms Cluster first layer position Projected track position Track-Cluster Association Algorithms Reclustering Algorithms 3 GeV 3 GeV 6 GeV 9 GeV Layers in close contact Cone associations Backscattered tracks Looping tracks 38 GeV 18 GeV 12 GeV 32 GeV 30 GeV Track Fragment Removal Algorithms 6 GeV 9 GeV Fraction of energy in cone PFO Construction Algorithms Neutral hadron Photon Charged hadron 55

56 Particle Flow Objects Typical 250GeV Jet in ILD: After all that: Particle flow objects (PFOs) built from tracks and clusters: photons 3GeV e+ 2GeV e- List of reconstructed particles with energies and particle ID Build jets Study physics performance Charged hadrons Neutral hadron Assess performance of a Particle Flow detector using simulation 56

57 Performance Goal: jet energy resolution: Benchmark performance using G4 simulation of ILD detector: Z decays at rest to light quarks rms90 EJET se/ej 45 GeV 3.7 % 100 GeV 2.8 % 180 GeV 2.9 % 250 GeV 2.9 % GOAL MET! Factor 2-3 better than traditional calorimetry! 57

58 W/Z Separation On-shell W/Z decay topology depends on energy: LEP ILC CLIC Note: Particle multiplicity does not change More confusion! Boost means higher particle density For boosted jets no sub-jet finding, just sum the 4-momenta of the PFOs! 125 GeV Z 250 GeV Z 500 GeV Z 1 TeV Z 58

59 W/Z Separation Studied di-jet/mono-jet masses in ILD concept ILC-like energies Clear separation of W/Z di-jet mass peaks CLIC-like energies W and Z still resolved from monojet invariant mass Impressive demonstration of power of Particle Flow at a Linear Collider 59

60 From Design to Reality if time allows 60

61 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 61

62 CALICE Activities CALICE = Umbrella R&D collaboration for LC calorimetry studies encompass a number of technological options CALO Absorber Readout Active 62

63 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 63

64 e.g. Digital HCAL 54 glass RPC chambers, 1m2 each PAD size 1 1 cm2 Digital readout (1 threshold) Fully integrated electronics Total: readout channels Detailed 3D images of hadronic showers Test beam campaigns: Demonstrate technology Provide high quality physics data test GEANT4 models Many CALICE publications W-DHCAL π- at 210 GeV (SPS) 64

65 Where Now? 65

66 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) 66

67 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 67

68 } 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 68

69 Spares 69

70 ILC Physics Potential e+e collisions at s = TeV provide rich environment Exact physics programme depends on what is out there ILC offers Flexibility in running, e.g. new particle thresholds Can accumulate large samples of cleanly identified/well-measured events ~1000 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 70