# Presentation: 491015

## 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

## 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*

## Is mass due to a Higgs boson?

- 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

- Precision measurements:

- G. Mylett, Moriond02

- LHC

***Higgs Discovery at Tevatron or LHC***

- Tevatron

- ATLAS TDR

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

- Precision masses with recoil technique
- Higgs mass independent of Higgs decay
- Model independent Higgs BRs

## Higgs mass measurements

- LC:
- LHC:
- 	Direct reconstruction of

-              LC @ 350 Gev

- Conway, hep-ph/0203206

## Is it a Higgs?

- How do we verify role in EWSB?
- Measure Yukawa couplings
- Measure spin/parity
- Reconstruct Higgs potential

## Coupling Constant Measurements

- Battaglia & Desch,
- hep-ph/0101165

- LC

- Zeppenfeld, hep-ph/0203123

- LHC

*L=200 fb**-1*

*L=100 fb**-1**, ****s=350 GeV*

## Angular correlations of decay products distinguish scalar/pseudoscalar

- Miller, hep-ph/0102023

- Threshold behavior measures spin

- [20 fb-1 /point]

*Higgs spin/parity in e**+**e**-****Zh*

## 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

- Large effects in SUSY

- Lafaye, hep-ph/0002238

## Light SUSY consistent with Precision Measurements

- 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,

- LHC

*Find all the Higgs Bosons*

- Carena, hep-ph/9907422

- Tevatron

## Into the wedge

-    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

## LHC/Tevatron will find SUSY

- SUSY mass differences from cascade decays;eg
- M0 limits extraction of other masses
- Fit to SUGRA parameters

- Catania, CMS

## LHC:  Fits to SUSY Parameters

- Bachacou, Hinchliffe, Paige, hep-ph/9907518

## LC can step through Energy Thresholds Run-time Scenario for L=1000 fb-1

| Year | 1 | 2 | 4 | 5 | 6 | 7 |
| --- | --- | --- | --- | --- | --- | --- |
| L (fb-1) | 10 | 40 | 150 | 200 | 250 | 250 |

- 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

## How do we know it’s SUSY?

- Need to measure masses, couplings
- Observe SUSY partners, eg
- Polarization can help separate states

- Discovery is straightforward
-  e energies measure masses

- LC Study, hep-ex/0106056

- me1 GeV
- L=50 fb-1

## SUSY Couplings:

- 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

## (e+e-Zh) sensitive to SUSY Parameters

- Dawson, Heinemeyer hep-ph/0203067

- TESLA:
- ZH2-3%,
- L=500 fb-1

## Understanding the Top Quark

- Why is                  ?
- Kinematic reconstruction of  tt threshold gives pole mass at LC
- Compare LHC

- Groote , Yakovlov, hep-ph/0012237

- QCD effects well understood
- NNLO ~20% scale uncertainty

*2M**t **(GeV)*

**

## Top Yukawa coupling tests models

-  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

- Baer, Dawson, Reina, hep-ph/9906419
- Juste, Merino, hep-ph/9910301

- Reina, Dawson, Orr, Wackeroth
- Beenacker, hep-ph/0107081

## 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