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Why a Linear Collider Now?

Explore the pivotal role of Linear Colliders (LC) and Large Hadron Collider (LHC) in uncovering particle mysteries like Higgs boson and SUSY through precision measurements and couplings. Understand the significance of energy upgrades and collaborative efforts in advancing particle physics research.

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Why a Linear Collider Now?

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  1. Why a Linear Collider Now? S. Dawson, BNL October, 2002 • The Physics case • Why we need both the LC and the LHC • Examples: EWSB, SUSY, top quark

  2. LC is Next • European, Asian, American communities all agree: LC is next step • Initial design, • Luminosity • 80% e- polarization • Physics arguments for 1 TeV energy scale Energy upgrade a must! Combination of LHC/LC physics probes EWSB

  3. Is mass due to a Higgs boson? Precision measurements: • Higgs couplings of SM fixed • Production rates at LEP, Tevatron, LHC fixed in terms of mass • Direct search limit from LEP: • Higgs contributions to precision measurements calculable G. Mylett, Moriond02

  4. Higgs Discovery at Tevatron or LHC LHC Tevatron ATLAS TDR

  5. Well determined initial state Precision masses with recoil technique Higgs mass independent of Higgs decay Model independent Higgs BRs

  6. LC: LHC: Direct reconstruction of LC @ 350 Gev Higgs mass measurements Conway, hep-ph/0203206

  7. How do we verify role in EWSB? Measure Yukawa couplings Measure spin/parity Reconstruct Higgs potential Is it a Higgs?

  8. Coupling Constant Measurements LC LHC L=100 fb-1, s=350 GeV L=200 fb-1 Battaglia & Desch, hep-ph/0101165 Zeppenfeld, hep-ph/0203123

  9. Angular correlations of decay products distinguish scalar/pseudoscalar Threshold behavior measures spin Higgs spin/parity in e+e-Zh [20 fb-1 /point] Miller, hep-ph/0102023

  10. ghhh, ghhhh completely predicted by Higgs mass Must measure e+e- Zhh Small rate (.2 fb for Mh=120 GeV), large background Large effects in SUSY Measuring Higgs Self Couplings Lafaye, hep-ph/0002238

  11. SUSY predicts light Higgs For MA, SUSY Higgs sector looks like SM Can we tell them apart? Higgs BR are different in SUSY Find all SUSY Higgs, Light SUSY consistent with Precision Measurements

  12. Find all the Higgs Bosons Tevatron LHC Carena, hep-ph/9907422

  13. 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 Moretti, hep-ph/0209210 Into the wedge

  14. SUSY mass differences from cascade decays;eg M0 limits extraction of other masses Fit to SUGRA parameters LHC/Tevatron will find SUSY Catania, CMS

  15. LHC: Fits to SUSY Parameters Bachacou, Hinchliffe, Paige, hep-ph/9907518

  16. LC can step through Energy Thresholds Run-time Scenario for L=1000 fb-1 • SUSY masses to .2-.5 GeV from sparticle threshold scans • M0/M0 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, gbbh1.5% • Top mass and width measured, Mt150 GeV Battaglia, hep-ph/0201177

  17. Need to measure masses, couplings Observe SUSY partners, eg Polarization can help separate states Discovery is straightforward e energies measure masses How do we know it’s SUSY? me1 GeV L=50 fb-1 LC Study, hep-ex/0106056

  18. Compare rates at NLO: Lowest order, Super-oblique corrections sensitive to higher scales Masses from endpoints Assume Tests coupling to 1% with 20 fb-1 SUSY Couplings:

  19. (e+e-Zh) sensitive to SUSY Parameters TESLA: ZH2-3%, L=500 fb-1 Dawson, Heinemeyer hep-ph/0203067

  20. Understanding the Top Quark • Why is ? • Kinematic reconstruction of tt threshold gives pole mass at LC • Compare LHC  2Mt (GeV) Groote , Yakovlov, hep-ph/0012237 QCD effects well understood NNLO ~20% scale uncertainty

  21. tth coupling sensitive to strong dynamics Above tth threshold e+etth Theoretically clean s=700 GeV, L=1000 fb-1 Large scale dependence in tth rate at LHC L=300 fb-1 Top Yukawa coupling tests models Baer, Dawson, Reina, hep-ph/9906419 Juste, Merino, hep-ph/9910301 Reina, Dawson, Orr, Wackeroth Beenacker, hep-ph/0107081

  22. 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

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