# Presentation: 099889

## Why is it interesting?
What’s new?
QCD effects
SUSY effects
Experimental studies
How do the LC and LHC stack up?

- What’s new?
- QCD effects
- SUSY effects
- Experimental studies
- How do the LC and LHC stack up?

-  ***tth Associated Production:  An Update***

- S. Dawson,  LC Meeting, Arlington, Texas, January, 2003

- With L. Reina, D. Wackeroth, L. Orr

##  gtth is largest Higgs Yukawa coupling
If new physics exists in Higgs sector, maybe this is first place it’s seen
SUSY models, gtth coupling suppressed for small MA
Little Higgs models, 
         gtth(mt/v)[1+(v/f)]
            f10 TeV

- If new physics exists in Higgs sector, maybe this is first place it’s seen
- SUSY models, gtth coupling suppressed for small MA
- Little Higgs models,
-          gtth(mt/v)[1+(v/f)]
-             f10 TeV

***Why is it interesting?***

## NLO QCD calculation in e+e- complete
Rather large scale dependence 15-20%

K 1.4-2.4 for s=500 GeV

- Rather large scale dependence 15-20%
- K 1.4-2.4 for s=500 GeV

***Is a deviation from the SM prediction***
*** ******new physics or QCD?***

- Dawson & Reina, hep-ph/0101079, hep-ph/9808443;
- Dittmaier et al, hep-ph/9808433

## New couplings; resonance effects
Shaded regions have NLO > .75 fb

- Shaded regions have NLO > .75 fb

- SUSY QCD loops (squarks and gluinos) decrease 

- Large Effects in SUSY

-  e+e-ttH

-  e+e- tth

- Dawson & Reina, hep-ph/0011290

- S. Zhu, hep-ph/0212273

-  tan 

- (fb)

- NLO SUSY

- LO SUSY

- At=1 TeV, MS=400 GeV, =-100 GeV, MA=300 GeV, mg=200 GeV

## Most of region where 
    e+e- tth large in SUSY models excluded by LEP limits....

-     e+e- tth large in SUSY models excluded by LEP limits....

- Unfortunately......

- MA (GeV)

-  tan 

- Sopczak, hep-ph/0112082

## Optimal energy is s=800 GeV
Large luminosity required
           (L=1000 fb-1)
hW+W- channel, plus hbb channel gives 
            gtth/gtth7.5-15%
      120 < Mh < 175 GeV

- Large luminosity required
-            (L=1000 fb-1)
- hW+W- channel, plus hbb channel gives
-             gtth/gtth7.5-15%
-       120 < Mh < 175 GeV

***Experimental Studies in e******+******e******-****** Colliders***

- A. Gay, www.desy.de/~desch/higgs/stmalo/gay.ps

-  Juste and  Merino, hep-ph/9910301

- What about s=500 GeV?

- Semi-leptonic channel,
- gtth/gtth33%

- Baer, Dawson, Reina, hep-ph/9906419
- Juste, Chicago LC Workshop, 1/02

**Notes:**
H->bb, sigma=1-2 fb  bkgd:  qqbar: 1600 fb, WW: 4300 fb....

H->WW smaller bkgds

## Complete NLO calculation
Dominant contribution from gg initial state at LHC
State of the art: pentagon diagrams with 3 mass scales
Real corrections evaluated with both 1 and 2 cutoff phase space slicing technique

- Dominant contribution from gg initial state at LHC
- State of the art: pentagon diagrams with 3 mass scales
- Real corrections evaluated with both 1 and 2 cutoff phase space slicing technique

- Still 15-20 % uncertainty from  dependence at NLO (much smaller than LO calculation)

***pp************tth at NLO QCD at the LHC***Dawson, Orr, Reina, Wackeroth, hep-ph/0211438Beenakker et al, hep-ph/0107081

## NLO corrections give K1.2-1.4

- Shape of distributions largely unaffected by NLO corrections

- pptth at NLO QCD at LHC

- Dawson, Orr, Reina Wackeroth,
- hep-ph/0211438

- Beenakker et al, hep-ph/0211352

## tth is discovery mode for Mh < 130 GeV

-  tth is important channel at LHC

- gtth/gtth16%

- Signal

- Bkgd

- pptth; hbb

- LHC top study, hep-ph/0003033

## Theory for both e+e- and hadronic collisions complete to NLO QCD; need EW & SUSY corrections
NLO  QCD results show reduced scale dependence
 Precision on gtth/gtth in e+e- at s=500 GeV 
     much poorer than at LHC
		Argument for higher energy e+e- 

- NLO  QCD results show reduced scale dependence
-  Precision on gtth/gtth in e+e- at s=500 GeV
-      much poorer than at LHC
- 		Argument for higher energy e+e-

- Conclusions on tth Production