# Presentation: 158011

## Higgs Production at the Tevatron and the LHC:The Big Picture

- S. Dawson, BNL
- January, 2007

## Question???

- Question: Why is the Higgs so important?
- [6 talks at this meeting!]
- Answer: Discovering (or definitively excluding) the Higgs will fundamentally change our understanding
- It’s a win-win combination
- Single Higgs boson may or may not be Standard Model-like
- There may be many new particles associated with the symmetry breaking
- Higgs sector probes a large variety of new phenomena

## Review of Higgs Couplings

- Higgs couples to fermion mass
- mf = fv/2
- Yukawa  ffh coupling doesn’t vanish for v=0
- Measuring Yukawa coupling doesn’t prove VEV exists!

- h

## Gauge Higgs Couplings

- Higgs couples to gauge boson masses
- WWh coupling vanishes for v=0!  Tests the connection of MW to non-zero VEV

- h

- W

- W

- u

- d

## Standard Model is Incomplete Without Something like a Higgs boson

- Requires physical, scalar particle, h, with unknown mass
-        Mh is ***ONLY*** unknown parameter of EW sector
- 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 masses enter into quantum corrections
-         Mt2, log (Mh)

- Everything is calculable....***testable theory***

## In the Standard Model, the Higgs is light

- Mh < 166 GeV (precision measurements)
- [One sided 95% cl upper limit]
- Mh < 199 GeV if direct search (yellow band) included
- Limits have moved around with top quark quark mass
- [Mt=172.5  2.3 GeV in plot]

- New from ICHEP, 2006

## Quantum Corrections Sensitive to Higgs Mass

- New from ICHEP, 2006

-  Direct observation of W boson and top quark (blue)
-  Inferred values from precision measurements (pink)

## Understanding Higgs Limit

- MW(experiment)=80.392  0.029 GeV*

- Increasing Mh moves MW further from experimental value

- * Average of Tevatron and LEP2 values

## SM isn’t only theory that can fit precision measurements

- Heavy Higgs allowed with large T (T=)
- Straightforward to construct such models

- Peskin and Wells, hep-ph/0101342

## Standard Model is Effective Low Energy Theory

- We don’t know what’s happening at high energy
- Effective theory approach:
- Compute deviations from SM due to new operators and compare with experimental data

- LHC job is to probe physics which generates these operators

## Suppose the LHC finds a Higgs....

- The SM predicts production/decay rates
- We need to understand the uncertainty on these predictions
- Spin/parity
- Is it a scalar or a pseudoscalar?
- Higgs can’t be heavier than  200 GeV in minimal SM
- Minimal SM has no extra scalar particles
- Spectroscopy of new states in non-minimal models crucial

## SM Production Mechanisms at LHC

- Bands show scale dependence

- All important channels calculated to NLO or NNLO
- Relatively small uncertainties from scale dependence

***Production with b’s very small in SM***

## Progress in understanding uncertainties

- Many sources of uncertainties in predictions
- Must have a good handle on them before we can draw inferences about new physics

- Higgs pT spectrum

- NLO rates*

- Belyaev & Reina, hep-ph/025270

- * 30 fb-1 ggh, h WW, 300 fb-1 tth, h WW, Wh, h bb, all others 200 fb-1

## Precision Measurements of Higgs Couplings

- Bands are theory uncertainty
- Largest uncertainty from mb

- Djouadi, hep-ph/0503172

- = 4.88  .07 GeV

## ILC Goal: Precision Measurements of Yukawa Couplings

- Coupling Strength to Higgs Particle

- Particle Mass (GeV)

- Can this sensitivity probe novel phenomena?

- Yukawa Coupling

- New phenomena can cause variations of Yukawa couplings from SM predictions

- Z

## Claim: LHC Can Discover SM Higgs Regardless of Mass

- Tricky if production/branching ratios are highly suppressed
- Can’t directly measure all couplings

## Production can be very different from SM

- Example #1:  Generalized operators
- Dimension 6 operator:
- Expand around vacuum:
- Generate interaction
- For heavy top quark, the SM hGG interaction is well approximated by
- New operator is just arbitrary enhancement or suppression of ggh production rate

- eg. Manohar and Wise, hep-ph/0601212

## Not Hard to Suppress h

- Not Hard to Suppress h

- 2 Higgs doublet model where only 1 couples to fermions (tan =v1/v2)
- Little Higgs,  models with radion/Higgs mixing  also tend to have suppressed h rate

- Phalen, Thomas, Wells, hep-ph/0612219

- SM: h

- 2HD, Mh=140 GeV

##  Higgs Production can be enhanced 

-  For large tan , dominant production mechanism is with b’s
-   bbh can be 10x’s SM Higgs rate in SUSY for large tan 

- LHC

- SUSY Higgs are produced with b’s!

-  Example #2:  MSSM

##  Enhancement in MSSM:

- Can observe heavy MSSM scalar Higgs boson

- Note log scale!

- * Tevatron has significant limits on bh production

## Higgs Production can be suppressed

- Example #3
- Add a single real scalar *S* to the standard model
*S* carries no charge and couples to nothing except the Higgs, through the potential
- Physical particles are linear combination of h, s
- Higgs branching ratios are BRSM  sin2
- If *m**1** > 2 m**2*,  new decay channel:
-           1  2 2    (bb)(bb), (bb)(+-), (+-)(+-)

## Is the Higgs a Scalar?

- Weak boson fusion sensitive to tensor structure of HVV coupling
- Alternative structures from higher dimension operators

- CP even

- SM

- CP odd

- Loop induced

## Need to Measure CP of Higgs

- Azimuthal angle between tagged jets sensitive to c2, c3

- Figy, Hankele, Klamke, Zeppenfeld, hep-ph/0609075

## Conclusion

- Expect the unexpected
- Prejudice is dangerous!
- Theorists can construct models with enhanced or suppressed Higgs production rates and with or without SM-like branching ratios
- We need to measure:
- BR for as many production/decay chains as possible
- Spin/parity
- Spectroscopy