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Diffractive Higgs ProductionPowerPoint Presentation

Diffractive Higgs Production

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Diffractive Higgs Production

- Overview
- Calculating cross-sections
- SM Higgs
- SUSY Higgs
- Tevatron data

Jeff Forshaw

Manchester Meeting Dec 2005

Diffractive Higgs production (exclusive case)

Detect the four-momenta of the protons using detectors situated 420m from the interaction point

Why?

- Excellent mass resolution ~1 GeVLineshape studies
- Spin-parity analyserPossibility to investigate CP structure of Higgs system
- Reduced backgrounds

Challenges

- Theory
- Requires new detectors
- Triggering
- Small signal rates

Calculating the cross-section

- Durham approachperturbative QCDKhoze, Martin, Ryskin, KaidalovMonte Carlo: ExHuME (Monk & Pilkington)
- “Bialas-Landshoff” approachnon-perturbative QCD Saclay group: Peschanski, Boonekamp, Royon, KúcsMonte Carlo: DPECM
- Hybrid approachesBzdak; Petrov & Ryutin

Woefully short on references: see my review on hep-ph/0508274

i.e. colliding gluons must have equal helicity

Start by computing the quark level amplitude…..

becomes…(after integrating over the proton transverse momenta)

Since the suppression factor vanishes faster than any power of the integral is rendered finite.

Sudakov suppression…..

The probability of emitting a gluon off a fusing gluon is logarithmically enhanced:

Summing the large logarithms to all orders gives an exponential for the probability NOT to emit:

We must include this non-emission probability in the amplitude:

A bit more work needed to get the single logarithms right…..

DLLA

LLA

It is crucial to sum to LLA accuracy…

It’s ok to use perturbation theory… right…..

Not much sensitivity to the ambiguity relating to the right…..infra-red behaviour of the gluon distribution functions:

Extrapolation into this regionbut cross-section not sensitive to it.

And finally….gap survival (slightly oversimplified) right…..

Assume that there is a single mechanism which fillsgaps (“an inelastic scatter”) and assume that it isindependent of anything else in the event.

Same b as before: partial cancellation of uncertainty in totalrate.

We need to figure out the “eikonal” factor…. right…..

Combined with the optical theorem this implies that

Hence one can fit the eikonal factor using data.

This model is the basis behind the underlying event generation in PYTHIA andalso the “JIMMY” underlying event model in HERWIG. Both have been testedsuccessfully against data (from HERA and Tevatron). [Sjostrand & Skands;Borozan & Seymour; Odagiri; Butterworth; Field.]

More sophisticated eikonal models: Kaidalov, Khoze, Martin, Ryskin; Gotsman, Levin, Maor et al.

The Bialas-Landshoff inspired approach….. right…..

becomes

Hybrids: Bzdak; Petrov &Ryutin.

But it does not contain Sudakov suppression

Would be flat if right…..

+ right…..

- Is not impossible – due to 0 selection rule
- 11 signal after all cuts (S/B > 1) with 30/fb.
- Hard to trigger at level 1.

- Backgrounds:
- gg: 1% b-quark mistags and 60-120 degree cut => B/S=5%
- b-bar suppressed => B/S = 5%
- J=2 admixture => B/S = 10%
- NLO gqq => 5% (not in ExHuME yet)
- Tail of inclusive production “PP fusion” => negligible?

Full Monte Carlostudy neededusing ExHuME and POMWIG

Standard Model Higgsb quark decay channel

Easy to trigger (require at least one W to decay leptonically)

Small numbers of events but backgrounds under control leptonically)

Don’t need many events to measure the mass and establishcleanly that Higgs is a scalar particle.

Full Monte Carlo of the gg initiated backgrounds to be done, leptonically) first calculations indicate S/B > 1 without anything fancy…

Supersymmetric Higgs leptonically)

- MSSM “intense coupling” scenario
- CPV MSSM “tri-mixing” scenario
- CPV MSSM “CPX light Higgs” scenario
- Benchmark for diffractive production ofnew physics.
- Cross-sections can be much larger than SM
- Some scenarios may be hard to examine withoutdiffraction.
- Complementarity (mass/spin)

Intense coupling region of MSSM leptonically)

Boos, Djouadi, Muhlleitner, Vologdin, Nikitenko

- All three Higgses have similar mass
- tan βlarge
- coupling to b-bar enhanced
- very challenging to study via conventional methods
- ….big diffractive cross-section

Very large cross-sections leptonically) and can detect in theb-quark decay channel

Kaidalov, Khoze, Martin, Ryskin

CPV MSSM “Tri-mixing” leptonically)

- Radiatively induced explicit CP violation mixes CP even and CP odd higgses.
- It is possible for all three Higgs bosons to have similar masses for a charged Higgs mass 140-170 GeV and large tan β > 40.Full coupled channel analysis performed by J. Ellis, J-S. Lee, Pilaftsis

J-S.Lee, Pilaftsis, J. Ellis,Carena, Wagner, Mrenna,Choi, Hagiwara, Drees

CPsuperH

CPV MSSM: CPX scenario leptonically)

- It is possible, with a different choice ofparameters, for the lightest Higgs to bevery light and have avoided detection…

Cox, JF, J-S. Lee, Monk, Pilaftsis leptonically)

Durham Group analysis of backgrounds:all cross-sections in fb

Analysis of background rates reveals that taudecay channel is a possibility.

Also the possibility of using the azimuthaldependence of the tagged protons to form a CP asymmetry:

Total Higgs production cross-section at

LHC (solid) and Tevatron (broken).

Tevatron data leptonically)

Central dijet production can be used totest the theory:

CDF lower bound on exclusive dijets:

Durham group predicts 40 pb.

A “standard candle” at the Tevatron leptonically)

Analysis underway on CDF

CDF has observed a dozen central J/ψ events at a rateconsistent with predictions. But not really perturbative.

Khoze, Martin, Ryskin, Stirling

Summary leptonically)

- Central production of new physics isa possibility for LHC (wide scope).
- It may be the best/only way to examine some physics.
- Theory predictions known to within a factor ~ x 5.
- Good progress on Monte Carlo simulation and study of backgrounds.
- Can learn already from Tevatron data – key measurements in progress.

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