Standard Model Higgs Physics at a 4 TeV Upgraded Tevatron

We compute an array of Standard Model Higgs boson (\hsm) signals and backgrounds for a possible upgrade of the Tevatron to E_{\rm cm}=4\tev. Taking \mt\geq 140\gev, and assuming a total accumulated luminosity of L=30\fbi, we find that a Standard Model Higgs boson with \mhsm\lsim 110\gev could almost certainly be detected using the \wpm\hsm\rta l\nu b\anti b mode. A Higgs boson with mass between \sim 120\gev and \sim 140\gev or above \sim 230-250\gev almost certainly would not be seen. A Higgs boson with \mhsm\sim 150\gev or 200\lsim\mhsm\lsim 230-250\gev has a decent chance of being detected in the ZZ\rta 4l mode. There would also be some possibility of discovering the \hsm in the WW\rta l\nu jj mode for 150\lsim\mhsm\lsim 200\gev. Finally, hints of an event excess in the WW\rta ll \nu\nu mode due to the \hsm might emerge for 140\lsim\mhsm\lsim 180\gev. Given the difficult nature of the Higgs boson signals for \mhsm values beyond the reach of LEP-200, and the discontinuous \mhsm range that could potentially be probed, justification of an upgrade of the Tevatron to 4\tev on the basis of its potential for Standard Model Higgs boson discovery would seem inappropriate.Comment: 21 pages; requires phyzzx.tex and tables.tex; full postscript file including embedded figures available via anonymous ftp at ucdhep.ucdavis.edu as [anonymous.gunion]4tev.ps, preprint UCD-94-1

A double parton scattering background to Higgs boson production at the LHC

The experimental capability of recognizing the presence of b quarks in complex hadronic final states has addressed the attention towards final states with b\bar{b} pairs for observing the production of the Higgs boson at the LHC, in the intermediate Higgs mass range.We point out that double parton scattering processes are going to represent a sizeable background to the process.Comment: 9 pages, 2 figure

Associated Production of Higgs and Weak Bosons, with H -> b\bar b, at Hadron Colliders

We consider the search for the Higgs boson at a high-luminosity Fermilab Tevatron, an upgraded Tevatron of energy 3.5 TeV, and the CERN Large Hadron Collider, via $WH/ZH$ production followed by H -> bb~ and leptonic decay of the weak vector bosons. We show that each of these colliders can potentially observe the standard Higgs boson in the intermediate-mass range, 80 GeV <m_H < 120 GeV. This mode complements the search for and the study of the intermediate-mass Higgs boson via H -> \gamma\gamma at the LHC. In addition, it can potentially be used to observe the lightest Higgs scalar of the minimal supersymmetric model in a region of parameter space not accessible to CERN LEP II or the LHC (using h -> \gamma\gamma,ZZ^*).Comment: (changed the analysis of ZH production and the figures for susy), 17 pages + 7 figures, ILL-(TH)-94-8, BNL-6034

Constraints on the Universal Varying Yukawa Couplings: from SM-like to Fermiophobic

Varying the Standard Model (SM) fermion Yukawa couplings universally by a generic positive scale factor ($F_{Yu}$), we study the phenomenological fit to the current available experimental results for the Higgs boson search at hadron colliders. We point out that the Higgs production cross section and its decay branching ratio to $\gamma\gamma$ can be varied oppositely by $F_{Yu}$ to make their product almost invariant. Thus, our scenario and the SM Higgs are indistinguishable in the inclusive $H\to \gamma\gamma$ channel. The current measurements on direct Yukawa coupling strength in the $H\to b\bar{b}/\tau\tau$ channel are not precise enough to fix the scale factor $F_{Yu}$. The most promising is the vector-boson-fusion channel in which the CMS has already observed possible suppression effect on the Yukawa couplings. Further more, the global $\chi^2$ fit of the experimental data can get the optimal value by introducing a suppression factor $F_{Yu}\sim1/2$ on the SM Yukawa couplings.Comment: 16 pages, 12 figures, 5 tables, update analysis is supplemente

QCD and Yukawa corrections to single-top-quark production via q qbar -> t bbar

We calculate the O(alpha_s) and O(alpha_W m_t^2/M_W^2) corrections to the production of a single top quark via the weak process q qbar -> t bbar at the Fermilab Tevatron and the CERN Large Hadron Collider. An accurate calculation of the cross section is necessary in order to extract |V_tb| from experiment.Comment: LaTeX, 13 pages, replaced with version to appear in Phys. Rev.

Radiative Higgs Boson Decays H\to f\bar{f}\gamma Beyond the Standard Model

Neutral Higgs boson radiative decays of the form h_0, H, A \to f\bar{f}\gamma, in the light fermion limit $m_f->0, are calculated in the two Higgs doublet model at one-loop level. Comparisons with the calculation within the standard model are given, which indicates that these two models are distinguishable in the decay mode fermion-antifermion -photon. Our results show that the concerned process may stand as an implement to identify the Higgs belongings in case there is a intermediate mass Higgs detected.Comment: 13 pages in Revtex, version to appear in Phys. Rev.

Window on Higgs Boson: Fourth Generation b′b^\prime Decays Revisited

Direct and indirect searches of the Higgs boson suggest that 113 GeV $\lesssim m_H \lesssim$ 170 GeV is likely. With the LEP era over and the Tevatron Run II search via $p\bar p \to WH+X$ arduous, we revisit a case where $WH$ or $ZH +$ jets could arise via strong $b^\prime\bar b^\prime$ pair production. In contrast to 10 years ago, the tight electroweak constraint on $t^\prime$--$b^\prime$ (hence $t^\prime$--$t$) splitting reduces FCNC $b^\prime\to bZ$, $bH$ rates, making $b^\prime\to cW$ naturally competitive. Such a "cocktail solution" is precisely the mix that could evade the CDF search for $b^\prime\to bZ$, and the $b^\prime$ may well be lurking below the top. In light of the Higgs program, this two-in-one strategy should be pursued.Comment: 4 pages, RevTex, 4 eps figures, One more figure, version to be published in Phys. Rev.

h→μτh\to \mu\tau at Hadron Colliders

We study the observability for a lepton flavor-changing decay of a Higgs boson $h\to \mu\tau$ at hadron colliders. Flavor-changing couplings of a Higgs boson exist at tree level in models with multiple Higgs doublets. The $h\mu\tau$ coupling is particularly motivated by the favorable intepretation of $\nu_\mu-\nu_\tau$ oscillation. We find that at the Tevatron Run II the unique $\mu\tau$ signature could serve as the Higgs discovery channel, surpassing expectations for Higgs boson searches in the SM and in a large parameter region of the MSSM. The sensitivity will be greatly improved at the LHC, beyond the coverage at a muon collider Higgs factory.Comment: Version to appear in PR