Workshop on the Future of Higgs Physics

May 3-5, 2001
Fermi National Accelerator Laboratory
Batavia, Illinois

A quick review of prospects for Higgs physics at future colliders
(under construction)

Situation after LEP:

In the year 2000, the four LEP experiments collected about 350 pb-1 of data at energies between 200 and 209 GeV, with about 120 pb-1 above 206 GeV. A 2.9 sigma excess of events consistent with a 115 GeV SM Higgs boson was observed in the combined data of the four LEP experiments. Details may be found in the LEP Higgs working group document submitted to the LEP Committee meeting on Nov. 3, 2000. Additional details can be found in Tom Junk's talk at LEP Fest Oct. 10, 2000 (ps, pdf) and P. Igo-Kemenes's talk at LEPC Nov. 3, 2000 (ps, pdf).

The corresponding lower bound on the SM Higgs mass is mH > 113.3 GeV.

LEP results for the MSSM Higgs search can be found in the Note for ICHEP'2000 (Osaka, Japan, July 26 - Aug 2, 2000). See pages 15, 16 and 17 of the note for (preliminary) MSSM Higgs exclusion plots. A slightly more up to date plot for the Max-mh scenario is on slide 22 of Tom Junk's talk at LEP Fest Oct. 10, 2000 (ps, pdf). The mass limits for the light CP even and CP odd Higgs bosons are mh > 89.9 GeV and mA > 90.5 GeV, respectively. Values of tan beta are excluded from 0.52 to 2.25.

Prospects at the Tevatron:

The results from the Higgs working group of the Physics at Run II Workshops are summarized in two figures:


Figure 1 shows the reach of the Standard Model Higgs search at the upgraded Tevatron. Shown are the integrated luminosities delivered per experiment required to exclude the Standard Model Higgs boson at 95% CL, observe it at the 3 sigma level or discover it at the 5 sigma level, as a function of Higgs mass. In the low-mass Higgs region, below 140 GeV, the curves shown are the result of combining the W+Higgs and Z+Higgs channels (where the Higgs decays to b b-bar and the W and Z decay leptonically), using the neural network selection, and the statistical power of both experiments. In the high-mass Higgs region, above 140 GeV, the curves shown are the result of combining various channels in which the Higgs boson decays to WW (where one W may be virtual). The lower edge of the bands is the calculated threshold; the bands extend upward from these nominal thresholds by 30% as an indication of the uncertainties in b-tagging efficiency, background rate, mass resolution, and other effects.


Figure 2 depicts the reach of the Higgs search in the context of the Minimal Supersymmetric extension of the Standard Model (MSSM) at the upgraded Tevatron. The four graphs exhibit experimentally accessible regions of MSSM Higgs parameter space, assuming a total integrated luminosity per experiment, where anticipated data from CDF and D0 are combined. The MSSM parameter space depends on the ratio of vacuum expectation values, tan(beta) and the CP-odd Higgs mass, m_A. There is also sensitivity to the MSSM particle mass spectrum via radiative corrections. The top two graphs assume an average top squark mass of 1 TeV and maximal mixing in the top squark sector (corresponding to the maximum value for the mass of the light CP-even Higgs boson h). The lower two graph corresponds to a particular choice of top squark mixing parameters (mu = -A_t = 1.5 TeV), which leads to the most difficulty for the MSSM Higgs search in the low m_A, large tan(beta) regime.

In each of the two scenarios, the 95% CL exclusion regions and the 5-sigma discovery regions are shown for two different search channels: (i) shaded regions correspond to V+Higgs (where V=W or Z and the associated Higgs boson is one of the two CP-even Higgs scalars of the MSSM---h or H), and (ii) regions in the upper left-hand corner of the graphs bounded by the solid lines correspond to b b-bar Higgs production (where the associated neutral Higgs boson is either h, H or A). Different integrated luminosities are explicitly shown by the color coding. Note that the same colors correspond to different integrated luminosities in the 95% CL and 5-sigma plots. For search channel (ii), the two sets of lines (for a given color) correspond to the CDF and D0 simulations, respectively. The region below the solid black line near the bottom of the plot is excluded by the absence of observed e+e- ---> Z + Higgs events at LEP2.

Further details and a literature survey can be found on the Higgs working group webpage. The final Higgs Working Group Report is available on the Los Alamos archives, hep-ph/0010338 (5.175 MB of gzipped postscript).

A study of p pbar -> t tbar H as a discovery mode for the Higgs boson at the Tevatron is in Phys. Rev. Lett. 86, 1694 (2001)

A Workshop on Monte Carlo generator physics for Run II at the Tevatron will be held at Fermilab from April 18-20, 2001, and will include Higgs physics at the Tevatron as one of the topics.

Prospects at the LHC:

At the LHC the SM Higgs can be discovered throughout its entire mass range:
* ATLAS plots of SM Higgs discovery reach with 30 fb-1 or 100 fb-1.

In the MSSM, one or more MSSM Higgs bosons can be discovered throughout parameter space:
* ATLAS plots of MSSM Higgs discovery regions in the no mixing scenario with 30 fb-1 or 300 fb-1.
* ATLAS plot of MSSM Higgs discovery reach in the max-mh scenario with 300 fb-1.
(Note that the LEP exclusion contours shown in the ATLAS plots were predictions; for the actual exclusion contours from LEP data see the LEP section above.)
* CMS plot of MSSM Higgs discovery regions: see page 14 of the CMS TP Chapter 12 (1M ps.Z).

The ATLAS Detector and Physics Performance TDR is here. Higgs physics is discussed in Chapter 19 (1.4M) [Erratum].

The CMS Technical Proposal is here. Physics performance is in Chapter 12 (1M ps.Z).

- Measurements of ratios of Higgs partial widths can be extracted from combinations of cross sections times branching ratios. [link to come]

Prospects at a Linear Collider:

The Tesla TDR page is here. The Tesla TDR will be officially released at the end of March, during the Tesla Colloquium.

An ongoing study of Linear Collider physics has been in progress at Fermilab. A report is being prepared that summarizes the physics prospects of a 500-1000 GeV e+e- collider, with particular emphasis on Higgs physics.

In October 2000 the 5th International Linear Collider Workshop (LCWS 2000) was held at Fermilab, and included a parallel session on Higgs and SUSY Higgs. Slides are available on the web.

- Higgs mass determination [link to come]

- Higgs branching ratio and cross section measurements [link to come]

- Distinguishing models [link to come]

- 1 or 2 plots?

Prospects at a gamma-gamma collider:

The 2nd International Workshop on High Energy Photon Colliders was held at Fermilab from March 14-17, 2001. Topics included the current status of Higgs physics studies, as well as discussion of a Higgs factory scenario. Slides are available on the workshop website.

The Tesla TDR will contain information on the gamma-gamma option.

- H -> gamma gamma partial width measurement [link to come]

- Reach for heavy MSSM Higgs bosons [link to come]

- Higgs CP properties [link to come]

Prospects at a muon collider:

Under construction.

Other options:

Under construction.
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