Day2: Physics at TESLA

Transcription

1 Day2: Physics at TESLA Origin of Electroweak Symmetry Breaking as one great Motivation for a Linear Collider The TESLA project Higgs Precision Physics at TESLA Leaving the Standard Model Behind Precision tests Summary Klaus Desch, Physics at e+e- Colliders, DESY Summer Student Lecture 08/2002 Page 61

2 Electro-Weak Symmetry Breaking Quantum Field Theory with massive Quanta fails at high Energies: Cross section: σ s Violates unitarity at s ~1. 2TeV (if forces remain weak) if nothing happens, something must happen The SM solution: (rescue of the beautiful gauge principle) Introduction of a new scalar field with non-zero field strength In the vacuum: the Higgs Field. Klaus Desch, Physics at e+e- Colliders, DESY Summer Student Lecture 08/2002 Page 62

3 Klaus Desch, Physics at e+e- Colliders, DESY Summer Student Lecture 08/2002 Page 63 The Higgs Mechanism The Higgs Mechanism v g M where M q = Paradigm: All (elementary) particles are massless (per se) gauge principle works renormalizable theory (finite cross sections) permanent interaction with the Higgs field acts as if particles had a mass (effective mass) 2 q 1 gv q 1 gv 2 q 1

4 Where is the Higgs Boson? Theory: Upper bound: perturbativity (λ<1) Lower bound: vacuum stability Models: minimal SUSY: m<135 GeV GUT s : m<180 GeV Experiment: Precision measurements (LEP,SLC,Tevatron) are sensitive to virtual corrections: m<200 GeV (95% CL) The Higgs Boson is probably light! Klaus Desch, Physics at e+e- Colliders, DESY Summer Student Lecture 08/2002 Page 64

5 Higgs Search at Tevatron Maybe Klaus Desch, Physics at e+e- Colliders, DESY Summer Student Lecture 08/2002 Page 65

6 Production processes: Higgs Search at the LHC For m=120 GeV: σ ~ 25 pb LHC = Higgs factory? 2.5 million Higgs/year Klaus Desch, Physics at e+e- Colliders, DESY Summer Student Lecture 08/2002 Page 66

7 Higgs Search at the LHC Gigantic backgrounds! gg H bb is hopeless! look for rare but well measureable final states Klaus Desch, Physics at e+e- Colliders, DESY Summer Student Lecture 08/2002 Page 67

8 Higgs Search at the LHC (m<150 GeV) Loop induced decay: Backgrounds: γγ production 2pb/GeV need σ(m)/m ~ 1% -3 0 γ + jet, jet-jet production (reducibel) need 10 γ/π suppression Klaus Desch, Physics at e+e- Colliders, DESY Summer Student Lecture 08/2002 Page 68

9 Higgs Search at the LHC: m> 150 GeV ATLAS clear 4-lepton signature, almost background free Up to m<600 GeV: Standalone discovery 1 with 30 fb Above: ZZ llνν and WW lνqq needed Klaus Desch, Physics at e+e- Colliders, DESY Summer Student Lecture 08/2002 Page 69

10 Discovery potential: Higgs Search at the LHC Single channels: Combined channel + expts: With 10 fb : 5σ discovery in the whole mass range! Klaus Desch, Physics at e+e- Colliders, DESY Summer Student Lecture 08/2002 Page 70

11 Higgs at the LHC after discovery: Measurements? In the SM, all properties of the Higgs boson are predicted, once its mass is known crucial test of EW symmetry breaking Absolute measurements are difficult at hadron machines, due to uncertainties in production cross sections (QCD,structure functions) and background modelling Some first measurements can be done: Mass: % Total Width: 10-20%, model dependent Production rates: 10-20% Ratios of couplings: W/Z, W/t, W/τ: 10-20% To really establish the Higgs mechanism, higher precision and less model depence is needed: Linear Collider! Klaus Desch, Physics at e+e- Colliders, DESY Summer Student Lecture 08/2002 Page 71

12 The TESLA Project Superconducting + - e e linear collider Phase 1: 500 GeV Phase 2: GeV Luminosity: 3-5x10 cm s fb / year Polarized beams Running options: γγ, eγ, e - e -,Giga-Z Integrated X-Ray Free Electron Laser Klaus Desch, Physics at e+e- Colliders, DESY Summer Student Lecture 08/2002 Page 72

13 Beamstrahlung Klaus Desch, Physics at e+e- Colliders, DESY Summer Student Lecture 08/2002 Page 73

14 Beamstrahlung Klaus Desch, Physics at e+e- Colliders, DESY Summer Student Lecture 08/2002 Page 74

15 A Detector for TESLA Detector optimized for precision physics Design driven by Higgs physics in many cases: -Vertex detector (b/c separation) -Momentum resolution 0 + ( Z ) -Energy flow: jet reconstruction Broad R&D program Currently starting Klaus Desch, Physics at e+e- Colliders, DESY Summer Student Lecture 08/2002 Page 75

16 Calorimetry Klaus Desch, Physics at e+e- Colliders, DESY Summer Student Lecture 08/2002 Page 76

17 Calorimetry Klaus Desch, Physics at e+e- Colliders, DESY Summer Student Lecture 08/2002 Page 77

18 Mask Klaus Desch, Physics at e+e- Colliders, DESY Summer Student Lecture 08/2002 Page 78

19 Physics Program at TESLA Highlights: Origin of Elctroweak symmetry breaking: precision Higgs physics Breakdown of the Standard Model Supersymmetry Extra Space Dimensions New Gauge Bosons Flavour physics: top quark (SM?) Precision measurements Klaus Desch, Physics at e+e- Colliders, DESY Summer Student Lecture 08/2002 Page 79

20 Precision Higgs Physics at a Linear Collider After the discovery of a Higgs boson, the key task is to establish the Higgs mechanism in all elements as responsible for EW symmetry breaking Electron-Positron Linear Colliders (NLC,JLC,TESLA) with -1 energies up to 1 TeV and high ( fb /year) are 1. Technologically within reach 2. The ideal tool for precision Higgs physics Precision Measurements should comprise: Mass Total Width PC Quantum numbers J (Spin 0?) Higgs-Fermion couplings (~ mass?) Higgs-Gauge-Boson couplings (W/Z masses) Higgs self coupling (spontaneous symmetry breaking) Measurements should be precise enough to distinguish between different models (e.g. SM/MSSM, extra dimensional effects, ) Klaus Desch, Physics at e+e- Colliders, DESY Summer Student Lecture 08/2002 Page 80

21 The Higgs Boson Profile at TESLA decay-mode independent Higgs tag: select di-lepton events consistent with Z ll calculate recoil mass σ ~ 3% model independent measurement! Mass measurement: m ~ 50 MeV Klaus Desch, Physics at e+e- Colliders, DESY Summer Student Lecture 08/2002 Page 81

22 The Higgs Boson Profile at TESLA Key issue: momentum resolution: Lep -like resolution Goal with TESLA TPC+Si Klaus Desch, Physics at e+e- Colliders, DESY Summer Student Lecture 08/2002 Page 82

23 WW-fusion process: The Higgs Boson Profile at TESLA large cross section at large s model independent handle on total width, when combined with BR(H WW): Γ tot ΓWW = BR(H WW) Γtot 5% Klaus Desch, Physics at e+e- Colliders, DESY Summer Student Lecture 08/2002 Page 83

24 The Higgs Boson Profile at TESLA Higgs field responsible for particle masses Couplings must be proportional to the particle masses Decisive Test: precision analysis of the Higgs branching ratios: Decay Precision -1 for 500 fb, m=120 GeV Klaus Desch, Physics at e+e- Colliders, DESY Summer Student Lecture 08/2002 Page 84

25 The Higgs Boson Profile at TESLA Separation of H bb and H cc Needs high resolution vertex dector: First layer at 1.5 cm from interaction point! Klaus Desch, Physics at e+e- Colliders, DESY Summer Student Lecture 08/2002 Page 85

26 The Higgs Boson Profile at TESLA b- and c-tagging efficiencies: Klaus Desch, Physics at e+e- Colliders, DESY Summer Student Lecture 08/2002 Page 86

27 The Higgs Boson Profile at TESLA Higgs Quantum Numbers: Is it really a Higgs? Spin from threshold scan: CP quantum numbers from: -Angular distribution of H and Z -Transverse polarisation correlations in H ττ fb /point Klaus Desch, Physics at e+e- Colliders, DESY Summer Student Lecture 08/2002 Page 87

28 The Higgs Boson Profile at TESLA Top quark Yukawa coupling: -need highest energy -heaviest quark surprises? -small cross section -complicated final state achievable precision: Klaus Desch, Physics at e+e- Colliders, DESY Summer Student Lecture 08/2002 Page 88

29 The Higgs Boson Profile at TESLA Global fit of Higgs couplings (HFITTER): Measurements precise enough to obatain sensitivity beyond cms energy! Klaus Desch, Physics at e+e- Colliders, DESY Summer Student Lecture 08/2002 Page 89

30 The Higgs Boson Profile at TESLA Higgs self-coupling ( the holy grail ): Close connection to the shape of the Higgs potential essential test of the mechanism of spontaneous symmetry breaking Tiny cross section Complicated multi-jet final state detector design: energy flow LEP TESLA Need highest luminosity Precision for 1 ab -1: λ λ 20% Klaus Desch, Physics at e+e- Colliders, DESY Summer Student Lecture 08/2002 Page 90

31 No Higgs Boson? divergent W LW L W LW L amplitude new strong interaction at spontaneously broken chiral symmetry Goldstone bosons ( Pions ) = W states ( technicolor ) L no calculable theory until today in agreement with precision data Experimental consequences: deviations in triple and quartic gauge couplings: Klaus Desch, Physics at e+e- Colliders, DESY Summer Student Lecture 08/2002 Page 91

32 Triple Gauge Couplings TGC s are a universal precision test for new physics Sensitivity to new physics scale Λ: At 500 GeV, 500 fb -1 Klaus Desch, Physics at e+e- Colliders, DESY Summer Student Lecture 08/2002 Page 92

33 Quartic Gauge Couplings - complicated final state - need to separate WW 4q and ZZ 4q energy flow! Sensitivity to new physics scale Λ: complete threshold region of new strong interaction covered Klaus Desch, Physics at e+e- Colliders, DESY Summer Student Lecture 08/2002 Page 93

34 Physics beyond the Standard Model SM cannot be the ultimate theory! Why??? Hierarchy problem Gravity Many free parameters Cold dark matter Baryon asymmetry Connection between quarks and leptons? Q(proton) = Q(positron) Connection between the families: flavour physics Klaus Desch, Physics at e+e- Colliders, DESY Summer Student Lecture 08/2002 Page 94

35 The Hierarchy problem In Nature, there are two largely different mass scales: 1. The electroweak scale: v = 246 GeV 2. The Planck scale: M Planck 19 =10 GeV The particle masses (especially the Higgs mass) recieve large scale dependent corrections, e.g. δm Λ 2 2 Λ is the scale up to which The SM should be valid 2 2 If δ M M Planck it is hard to believe that the correction 2 Gets compensated by a bare mass which is also 2 Planck To yield a physical Higgs mass o(v ) Something should protect the Higgs mass! o(m ) Klaus Desch, Physics at e+e- Colliders, DESY Summer Student Lecture 08/2002 Page 95

36 Supersymmetry is one of the most attractive extensions to the SM! Simple Idea: Symmetry between Bosons and Fermions each SM particle has a SUSY partner with same Quantum numbers and Spin differing by ½. But where are the SUSY Partners? Must be heavy SUSY must be broken! Why is it so attractive, then? Klaus Desch, Physics at e+e- Colliders, DESY Summer Student Lecture 08/2002 Page 96

37 Why is SUSY so attractive? 1. It solves the Hierarchy problem: The divergency in the Higgs mass corrections if cancelled exactly For unbroken SUSY. If it is not broken too heavily (i.e. if the SUSY partners are at <~ 1 TeV), there is no fine tuning necessary. Klaus Desch, Physics at e+e- Colliders, DESY Summer Student Lecture 08/2002 Page 97

38 Why is SUSY so attractive? 2. It shows a path to Grand unification: Minimal SUSY prediction: This is achieved for Experiment: 2 SUSY sin θ W = (17) 2 exp. sin θ W = (2) Klaus Desch, Physics at e+e- Colliders, DESY Summer Student Lecture 08/2002 Page 98

39 Why is SUSY so attractive? 3. Cold Dark Matter: The lightest SUSY partner particle might well be stable and An excellent candidate for the observed cold dark matter 4. Link to Gravity: SUSY offers the theoretical link to incorporate gravity. Most string models are supersymmetric. 5. Light Higgs Boson: SUSY predicts a light (< 135 GeV) Higgs boson as favoured by Electro-weak precision data from LEP and Tevatron. Klaus Desch, Physics at e+e- Colliders, DESY Summer Student Lecture 08/2002 Page 99

40 The Supersymmetric particle spectrum Klaus Desch, Physics at e+e- Colliders, DESY Summer Student Lecture 08/2002 Page 100

41 SUSY precision measurements at TESLA + - Typical production in ee collisions: pair production, e.g.: Detector signature: 2 Muons + miss.energy Muon energies: box spectrum Endpoints contain information about masses of Smuon and Neutralino Reachable precision o(100 MeV) Klaus Desch, Physics at e+e- Colliders, DESY Summer Student Lecture 08/2002 Page 101

42 SUSY precision measurements at TESLA Alternative: mass from threshold scan ee χ χ χ χ Reachable precision < 100 MeV Disentangle different states, in case There are many SUSY particles Klaus Desch, Physics at e+e- Colliders, DESY Summer Student Lecture 08/2002 Page 102

43 SUSY precision measurements at TESLA Beam Polarisation allows SUSY parameter determination. Example: Neutralino-sector depends on 4 parameters: tan β, µ, M, M M can be obtained from polarisation dependence of cross section and FB-Asymmetry Klaus Desch, Physics at e+e- Colliders, DESY Summer Student Lecture 08/2002 Page 103

44 But maybe more demanding signatures In some SUSY scenarios ( GMSB ) the Neutralino is not stable: χ 0 γg 1 non-pointing photon signature demanding for calorimetry! Klaus Desch, Physics at e+e- Colliders, DESY Summer Student Lecture 08/2002 Page 104

45 Extrpolation to very high scales SUSY parameters run with energy (like SM coupling constants) Running described by Renormaisation Group Equations (RGE s) Precise measurement of SUSY parameters at low (i.e. TESLA) allows to extrapolate to very high (e.g. GUT) scales and test the high energy behaviour of SUSY Test of Grand Unification becomes possible Information about the mechanism which breaks SUSY can be obtained msugra GMSB Klaus Desch, Physics at e+e- Colliders, DESY Summer Student Lecture 08/2002 Page 105

46 Extra Space Dimensions? Completely alternative approach to solve the hierarchy problem: There is no hierarchy problem Suppose, the SM fields live in normal 3+1D space Gravity lives in 4 + δ Dimensions δ extra Dimensions are curled to a small volume (radius R): Klaus Desch, Physics at e+e- Colliders, DESY Summer Student Lecture 08/2002 Page 106

47 Extra Space Dimensions? For r < R, gravity follows Newtons law in 4+δ dimensions: G () S1 r δ+ V r = For r > R, gravity follows effectively Newton s law in 4 dimensions, since the distance in the extra dimensions does not rise anymore: V( r) = G = G with G G N = δ Rr r R 2 M = c/ G S N S δ The Planck-Mass only effectively appears Planck N so high at large distances. The true scale of gravity is M = c/ G = cr / G 2 δ S S N If e.g. R ~ o(100 µm) and δ=2 one obtains! M S = o(1 TeV) Gravity might become visible in TeV-scale colliders as TESLA!! Klaus Desch, Physics at e+e- Colliders, DESY Summer Student Lecture 08/2002 Page 107

48 Extra Space Dimensions? Effects from real graviton emission: measures the number of extra dimensions! Klaus Desch, Physics at e+e- Colliders, DESY Summer Student Lecture 08/2002 Page 108

49 Extra Space Dimensions? Effects from virtual graviton exchange: can prove Spin-2 exchange! Klaus Desch, Physics at e+e- Colliders, DESY Summer Student Lecture 08/2002 Page 109

50 New Gauge Bosons If there is a GUT, the GUT gauge group (e.g. SU(5)) might be broken in steps e.g. new U(1) at the TeV scale new Z boson. TESLA has reach up >10 TeV through interference of Z with Z and γ. Klaus Desch, Physics at e+e- Colliders, DESY Summer Student Lecture 08/2002 Page 110

51 New Gauge Bosons If LHC observes at Z, TESLA can measure its couplings and pin down the model Klaus Desch, Physics at e+e- Colliders, DESY Summer Student Lecture 08/2002 Page 111

52 Top Quark precision physics Threshold scan of e e + tt m(top) ~ 100 MeV Γ(top)/Γ(top) ~ 5% study top production and decay angular distributions Klaus Desch, Physics at e+e- Colliders, DESY Summer Student Lecture 08/2002 Page 112

53 Return to the Z0: Giga-Z Operate TELSA at the Z-Pole and WW-threshold 1 Billion Z0 s in a few months (100xLEP) 2 sin θ W = (factor 10 better than LEP) = 6MeV M W Klaus Desch, Physics at e+e- Colliders, DESY Summer Student Lecture 08/2002 Page 113

54 Summary TESLA physics is fascinating Higgs Mechanism can be established in all essential details Precision SUSY measurements reconstruct fundamental theory Precision is the key sensitivity far beyond collider energy World-wide consenus that a Linear Collider should be the next major step in HEP This will be YOUR machine! Klaus Desch, Physics at e+e- Colliders, DESY Summer Student Lecture 08/2002 Page 114