Diffractive Higgs Production

1. Diffractive Higgs Production • Overview • Calculating cross-sections • SM Higgs • SUSY Higgs • Tevatron data Jeff Forshaw Manchester Meeting Dec 2005

2. Diffractive Higgs production (exclusive case) Detect the four-momenta of the protons using detectors situated 420m from the interaction point

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

4. Challenges • Theory • Requires new detectors • Triggering • Small signal rates

5. 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

6. Scalar Higgs i.e. colliding gluons must have equal helicity Start by computing the quark level amplitude…..

7. Pseudo-scalar Higgs:

8. Need to replace the quarks by protons…..

9. Hence….. becomes…(after integrating over the proton transverse momenta)

10. 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:

11. A bit more work needed to get the single logarithms right….. DLLA LLA It is crucial to sum to LLA accuracy…

13. It’s ok to use perturbation theory…

15. Not much sensitivity to the ambiguity relating to theinfra-red behaviour of the gluon distribution functions: Extrapolation into this regionbut cross-section not sensitive to it.

16. Factor ~2 uncertainty from choice of gluon

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

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

19. The Bialas-Landshoff inspired approach….. becomes Hybrids: Bzdak; Petrov &Ryutin. But it does not contain Sudakov suppression

22. Would be flat if

23. + • 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 Higgs b quark decay channel

24. Perhaps more interesting is the WW decay…

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

26. Small numbers of events but backgrounds under control Don’t need many events to measure the mass and establishcleanly that Higgs is a scalar particle.

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

28. Supersymmetric Higgs • 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)

29. Intense coupling region of MSSM 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

30. Very large cross-sectionsand can detect in theb-quark decay channel Kaidalov, Khoze, Martin, Ryskin

31. CPV MSSM “Tri-mixing” • 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

32. J. Ellis, J-S. Lee, A. Pilaftsis Note that cross-sectionsare much bigger than SM case

34. CPV MSSM: CPX scenario • It is possible, with a different choice ofparameters, for the lightest Higgs to bevery light and have avoided detection…

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

36. Tevatron data Central dijet production can be used totest the theory: CDF lower bound on exclusive dijets: Durham group predicts 40 pb.

37. Preliminary result [Uncorrected CDF data] Cox & Pilkington

38. A “standard candle” at the Tevatron 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

39. Summary • 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.