# Presentation: 083309

## Associated Higgs Boson Production with Heavy QuarksS. DawsonVictoria, July, 2004

- Motivation (discovery, precision studies)
-                               (LHC)
-                             (Tevatron, Run II)
- With emphasis on:
- Theoretical predictions
- Relevance to Higgs Boson studies
- With L. Riena, C. Jackson, L. Orr, D. Wackeroth

## Old:
Mt=1745.1 GeV
MH=96+60-38 GeV
MH< 219 (95% cl)
New:
Mt=1784.3 GeV
MH=117+67-45 GeV
MH < 251 (95% cl)

- Mt=1745.1 GeV
- MH=96+60-38 GeV
- MH< 219 (95% cl)
- New:
- Mt=1784.3 GeV
- MH=117+67-45 GeV
- MH < 251 (95% cl)

*NEW*

***Best fit not in region excluded from direct searches***

- Strong case for a light scalar Higgs boson, both SM and MSSM

## Once we find the Higgs, we need to measure its couplings

- Coupling constants measured quite precisely at LHC

- Battaglia & Desch, hep-ph/0101165

- Linear Collider is the place!

- e+e- LC at s=350 GeV
-  L=500 fb-1, MH=120 GeV

- Duhrssen, Heinemeyer, Logan, Rainwater, Weiglein, Zeppenfeld  hep-ph/0406323

- LC measures couplings to a few %

##  ttH is important for LHC Discovery

## General Framework

-                   important for discovery at the LHC
-  Only         production can measure directly the top Yukawa Coupling (Yt):

- -

- Yt2

##    Need for NLO calculationTree level cross sections have very strong  dependence

- NLO O(s3) corrections by 2 groups: Beenakker, Dittmaier, Kramer, Plumper, Spira; Dawson, Reina, Orr, Wackeroth

## LHC, NLO cross section:

- Theoretical uncertainty reduced to about 15%

- Dawson, Jackson, Reina, Orr ,Wackeroth, hep-ph/0305087; Beenacker et al, hep-ph/0211352, hep-ph/0107081

## Tevatron, NLO cross section

- Note reduced  dependence of NLO result

- Rate too small to be observed at Tevatron

- Reina, Dawson, Wackeroth, hep-ph/0109066;  Reina, Dawson, hep-ph/0107101; Beenacker et al, hep-ph/0211352, hep-ph/0107081

## What about bbH?

- In SM, bbH couplings suppressed by
-             (mb/v)2.0004
- SUSY models have more Higgs bosons
-              h0, H0, A0, H
- At tree level, couplings depend only on
-              tan ,  MA

- Can be huge enhancement!

## Production of SUSY Higgs Bosons

-  For large tan , dominant production mechanism is with b’s
-   bbh can be10x’s SM Higgs rate in SUSY for large tan 

- Spira

- LHC

- SUSY Higgs are produced with b’s!

## What is the dominant process?

***Answer depends on whether you tag outgoing b’s***

##               at NLO

- Almost identical calculation to tth calculation
- Dominant contribution at both Tevatron and LHC is gg initial state
- Virtual + real corrections computed numerically using phase space slicing
-  b quark mass included everywhere
- Differences:  closed loops with top quarks,  numerical problems from large log(mb/MH)

## Strong dependence on ptb cuts:

- Dawson, Jackson, Reina, Wackeroth, hep-ph/-311067; Dittmaier, Kramer, Spira, hep-ph/0309204

##  Enhancement in MSSM

- Can observe heavy MSSM scalar Higgs boson

- Note log scale!

## Large Residual Scheme Dependence

- Large remaining scale/scheme dependence between OS and
-             at NLO

-  Effect  10-20%

- Not obvious what “best” scheme is

## Inclusive and semi-inclusive bbH  production

- Two approaches:
- Fixed flavor approach
- Fixed order matrix element calculation based on   the processes ggbbH, qq bbH
- Variable flavor number scheme:
- Use b quark PDF to sum to all orders large logarithms  slog(MH2/mb2) which arise due to gluon splitting g bb to collinear b’s

## bH production at NLO

- Larger rate than 2-b tag process
- Extra b tag and Higgs transverse momentum improve detection efficiency from 0-b tag process (bbH)
- Variable flavor number scheme, dominant process is bg bH
- Fixed flavor number scheme, dominant process is gg bbH

*** ******D0 search: tag 3 b’s***

## Exclusive cross section for                : 1 b tag

- Compare *variable flavor number scheme* with *fixed flavor number scheme* for PDFs

- No closed top loop in gb curves

- Campbell et al, hep-ph/0405302

## Inclusive Cross Section for bbH:  0 b tags

- Harlander & Kilgore, hep-ph/0304035

- Campbell et al, hep-ph/0405302

##  bbH in MSSM

- 5 discovery region

- Dawson, Dicus, Kao, Malhotra, hep-ph/0402172

## State of the art predictions for Higgs production

- Bands represent factorization/renormalization scale uncertainty

- Dawson, Jackson, Reina, Wackeroth

## QCD &EW Corrections to e+e- tth Production

- Cancellation of QCD & EW corrections at high s

- Belanger et al, hep-ph/0301040
- Denner, Dittmaier, Roth, Weber, hep-ph/0309274

## Conclusion

-  ttH, bbH interesting production modes at Tevatron and LHC
- Top Yukawa coupling:  the LHC can play a crucial role and complement a s=500 GeV LC
- Enhanced bbh:  possible signal of New Physics at the Tevatron and LHC
- Crucial to have NLO QCD corrections: theoretical uncertainty greatly reduced