Report

Why a Linear Collider Now? S. Dawson, BNL October, 2002 Asian, European, and American communities all agree High Energy Linear Collider is next large accelerator WHY??? Where are we going? • US high energy community just completed long range planning process • 20 year roadmap for the future • HEPAP subpanel: We recommend that the highest priority of the U.S. program be a high-energy, high-luminosity, electronpositron linear collider, wherever it is built in the world Linear Collider Basics • Initial design, e+e- at s=500 GeV • Luminosity 1034 cm2/sec 300 fb-1/yr • 80% e- polarization • Energy upgrade to .8-1.2 TeV in future • Physics in 2012 NLC High Power Klystron • The international accelerator community believes that a TeV-scale linear collider can be successfully built JLC Accelerator Test Facility TESLA Superconducting Cavity Preliminary designs for Linear Colliders TESLA NLC ????? • What are the big questions we want to answer? • Why do we think we can predict where we want to go? – What do we know now? – What do we expect to learn from the Tevatron and LHC? – What questions will remain unanswered? What is particle physics? Study of Space, Time, Matter Bagger/Barish report The Big Questions? • What is the origin of mass? • Do protons decay? • Do forces unify at a large scale? • Are there more than four dimensions? • Why are there 4 forces? No unification of couplings in SM Cosmic Connections • What is dark matter? • How are particle physics & cosmology connected? • What is dark energy? • Where did the antimatter go? Planning for the Future Based on Success of last 20 years…. • Model of electroweak physics verified at .1% level • The problem of mass remains • W and Z bosons discovered at CERN in 1983 M W 80 GeV M Z 91 GeV • Masses not zero….or even small Why is Mass a Problem? • Lagrangian for gauge field (spin 1): L=-¼ FF F=A-A • L is invariant under transformation: A (x) A(x)-(x) • Gauge invariance is guiding principle • Mass term for gauge boson ½ m2 AA • Violates gauge invariance • So we understand why photon is massless Simplest possibility for Origin of Mass is Higgs Boson • Higgs mechanism gives gauge invariant masses for W, Z • Requires physical, scalar particle, H, with unknown mass • Observables predicted in terms of: – – – – MZ=91.1875.0021 GeV GF=1.16639(1) x 10-5 GeV-2 =1/137.0359895(61) Mh • Higgs and top quark enter into quantum corrections, Mt2, log(Mh) Precision Measurements sensitive to top quark before it was discovered! Large number of measurements fit electroweak predictions Indirect Indications for Light Higgs Mass • Direct measurements of MW, Mt agree well with indirect measurements • Prefer Higgs in 100200 GeV range • ASSUMES no new physics Where is the Higgs boson? • Higgs couplings of fixed g ffh mf Precision measurements: M h 193 GeV @ 95 % cl v g W W h gM W • Production rates at LEP, Tevatron, LHC fixed in terms of mass • Direct search limit from LEP: M h 114 GeV @ 95 % cl • Higgs contributions to precision measurements calculable G. Mylett, Moriond02 Tantalizingly close….. Direct limit: Mh>114.1 GeV Indirect limit: Mh<193 GeV New Physics is just around the corner! Fits assume Standard Model….if Standard Model incorrect, even more exciting new physics…. Higgs mass and scale of new physics correlated….. 130 < Mh < 170 GeV Sensible theory here Fermilab Tevatron • p p at s=2 TeV • May discover Higgs if very lucky • Requires light Higgs and high luminosity • Physics in 2002-2008 p p Wh , h b b Upgraded Detectors for RunII CDF Enhanced capabilities for b tagging aid Higgs search D0 CERN Large Hadron Collider (LHC) • pp interactions ats =14 TeV • LHC will discover Higgs boson if it exists • Sensitive to Mh from 1001000 GeV • Higgs signal in just a few channels • Physics circa 2008 ATLAS TDR Discovery isn’t enough…. • Is this a Higgs or something else? • Linear Collider can answer critical questions – Does the Higgs generate mass for the W,Z bosons? – Does the Higgs generate mass for fermions? – Does the Higgs generate its own mass? Is it a Higgs? • How do we know what we’ve found? • Measure couplings to fermions & gauge bosons (h bb ) (h ) 3 mb m 2 2 • Measure spin/parity J 0 • Measure self interactions PC V Mh 2 2 h Mh 2v 2 h 3 Mh 8v 2 2 h 4 Coupling Constant Measurements • LHC measures combinations of coupling constants • Typical accuracy, 10-20% • Only some subset of couplings • Assumptions necessary to get couplings L=200 fb-1 Zeppenfeld, hep-ph/0203123 Linear Collider is Higgs Factory! • e+e-Zh produces 40,000 Higgs/year • Clean initial state gives precision Higgs mass measurement Mh2=s-2sEZ+MZ2 • Model independent Higgs branching ratios WWh vertex ZZH vertex Higgs mass measurements LC @ 350 Gev • LC: M h M 120 GeV , 500 fb h 1 50 MeV • LHC: Direct reconstruction of h M h 150 GeV , 300 fb M h 100 MeV 1 Conway, hep-ph/0203206 Precision Measurements of Higgs Couplings • Dots are experimental error • 1-2% measurement • Measure ALL Higgs couplings • Bands are theory error – Larger than experiment – Largest error from mb Battaglia & Desch, hep-ph/0101165 Higgs measurements test model! Standard Model • Couplings to fermions very different in SUSY models • LC can distinguish SM from SUSY up to MA=600 GeV Higgs spin/parity in e+e-Zh Threshold behavior measures spin [20 fb-1 /point] Miller, hep-ph/0102023 • Angular correlations of decay products distinguish scalar/pseudoscalar Measuring Higgs Self Couplings • ghhh, ghhhh completely predicted by Higgs mass • Must measure e+e- Zhh • Small rate (.2 fb for Mh=120 GeV), large background 1000 fb • Large effects in SUSY 1 g hhh 24 % g hhh Lafaye, hep-ph/0002238 Problem with this picture… • Fundamental Higgs is not natural • Quantum corrections to Mh are quadratically divergent Mh22 • So enormous fine-tuning needed to keep Higgs light Mh2\Mh2MW2\Mpl210-32 Solution is Supersymmetry • Quadratic contributions to Higgs mass cancel between scalars and fermions • To make cancellation hold to all orders need symmetry • Bose-Fermi symmetry….supersymmetry Do the forces unify? • Coupling constants change with energy • Coupling constants unify in supersymmetric models Hint for new physics? New particles in SUSY Theory Spin ½ quarks spin 0 squarks Spin ½ leptons spin 0 sleptons Spin 1 gauge bosons spin ½ gauginos Spin 0 Higgs spin ½ Higgsino Experimentalists dream….many particles to search for! What mass scale? Supersymmetry is broken….no scalar with mass of electron • • • • Supersymmetry • Can we find it? • Can we tell what it is? • Masses of new particles depend on mechanism for breaking Supersymmetry • Couplings of new particles predicted in terms of few parameters • Simplest version has 105 new parameters Simplifying Assumption: • Assume masses unify at same scale as couplings • Everything specified in terms of scalar/fermion masses at high scale and 3 parameters • Predictive anzatz….. •LHC/Tevatron will find SUSY • Discovery of many SUSY particles is straightforward • Untangling spectrum is difficult all particles produced together • SUSY mass differences from cascade decays;eg ~ 0 ~ ~ qL 2 q l l 0 ~1 l l q • M0 limits extraction of other masses Catania, CMS Light SUSY consistent with Precision Measurements • SUSY predicts light Higgs M SUSY h 130 GeV • SUSY predicts 5 scalars 0 0 0 h , H , A , H • For MA, SUSY Higgs sector looks like SM • Can we tell them apart? • Higgs BR are different in SUSY Find all the Higgs Bosons Tevatron LHC Carena, hep-ph/9907422 Into the wedge with a LC s>2MH e+e- H+H-, H0A0 observable to MH=460 GeV at s=1 TeV • s<2MH e+e- H+, H+tb L=1000 fb-1, s=500 GeV, 3 signal for MH 250 GeV • LC can step through Energy Thresholds Run-time Scenario for L=1000 fb-1 Year 1 L (fb-1) 10 • • • • • • 2 4 5 6 7 40 150 200 250 250 SUSY masses to .2-.5 GeV from sparticle threshold scans M0/M0 7% (Combine with LHC data) 445 fb-1 at s=450-500 GeV 180 fb-1 at s=320-350 GeV (Optimal for Higgs BRs) Higgs mass and couplings measured, gbbh1.5% Top mass and width measured, Mt150 MeV Battaglia, hep-ph/0201177 How do we know it’s SUSY? • Need to measure masses, couplings • Observe SUSY partners, eg ~ ~ R e , Le • Polarization can help separate states • Discovery is straightforward e e e~ L , R e~ L , R 0 e~ e ~ • e energies measure masses 2 M ~e E CM 2 E e , max E e , min ( E e , max E e , min ) me1 GeV L=50 fb-1 LC Study, hep-ex/0106056 2 SUSY Couplings: g ffX g f~f X~ • Compare rates at NLO: e e qq g ~ ~ e e qqg ~~ e e qq g • Lowest order, g s g~ s • Super-oblique corrections sensitive to higher scales g~ g~ ~ g 16 2 2 ~ m ln m • e e e~ L , R e~ L , R • Masses from endpoints ~e e B~ • Assume ~ B e~ e • Tests coupling to 1% with 20 fb-1 What is the universe made of? • • • • • Stars and galaxies are only 0.1% Neutrinos are ~0.1–10% Electrons and protons are ~5% Dark Matter ~25% Dark Energy ~70% H. Murayama Supersymmetry provides understanding of dark matter? LSP is dark matter Mh=115 GeV M1/2 • Lightest SUSY particle (LSP) could be dark matter candidate! • LSP is weakly interacting, neutral, and stable • LSP in range of LC/LHC • LC can determine LSP mass; check dark matter predictions g-2 M0 (GeV) Drees, hep-ph/0210142 Standard Model Needs Top Quark • Top quark completes 3rd generation – Why are there 3 generations, anyways? • Theory inconsistent without top Top Quark discovery at Fermilab in 1995 Why is Mt(=175 GeV)>>Mb(=5 Gev)?? D0 top event CDF top event Understanding the Top Quark • Why is Mt v ? 2 • Kinematic reconstruction of tt threshold gives pole mass at LC 40 fb 1 M t 200 MeV • Compare LHC 50 fb 2Mt (GeV) Groote , Yakovlov, hep-ph/0012237 QCD effects well understood 1 M t 1 2 GeV NNLO ~20% scale uncertainty Top Yukawa coupling tests models • tth coupling sensitive to strong dynamics • Above tth threshold e+etth • Theoretically clean • s=700 GeV, L=1000 fb-1 g tth • Large scale dependence in tth rate at LHC 6 .5 % g tth Baer, Dawson, Reina, hep-ph/9906419 Juste, Merino, hep-ph/9910301 Reina, Dawson, Orr, Wackeroth Beenacker, hep-ph/0107081 • L=300 fb-1 g tth g tth 16 % Exciting physics ahead • LHC/Tevatron finds Higgs LC makes precision measurements of couplings to determine underlying model • LHC finds evidence for SUSY, measures mass differences LC untangles spectrum, finds sleptons LC makes precision measurements of couplings and masses • etc