Mary Katherin Gaillard

A phenomenological profile of the Higgs boson

A discussion is given of the production, decay and observability of the scalar Higgs boson H expected in gauge theories of the weak and electromagnetic interactions such as the Weinberg-Salam model. After reviewing previous experimental limits on the mass of the Higgs boson, we give a speculative cosmological argument for a small mass. If its mass is similar to that of the pion, the Higgs boson may be visible in the reactions π−p → Hn or γp → Hp near threshold. If its mass is ≲300 MeV, the Higgs boson may be present in the decays of kaons with a branching ratio O(10−7), or in the decays of one of the new particles: 3.7 → 3.1 + H with a branching ratio O(10−4). If its mass is ⩽4 GeV, the Higgs boson may be visible in the reaction pp → H + X, H → μ+μ−. If the Higgs boson has a mass ⩽2mμ, the decays H → e+e− and H → γγ dominate, and the lifetime is O(6 × 10−4 to 2 × 10−12) seconds. As thresholds for heavier particles (pions, strange particles, new particles) are crossed, decays into them become dominant, and the lifetime decreases rapidly to O(10−20) sec for a Higgs boson of mass 10 GeV. Decay branching ratios in principle enable the quark masses to be determined.

Aspects of the Flipped Unification of Strong, Weak and Electromagnetic Interactions

We study issues arising in attempts to unify strong and other elementary particle interactions. The proton lifetime is estimated in theories with second-order baryon number violation, and found to be O(103–104) longer than naive dimensional counting suggested. The renormalization of quark and lepton masses below the grand unification mass is considered in some detail. Application is made to the SU(5) model of Georgi and Glashow, and we find strange and bottom quark masses: ms ≈ 0.4–0.5 GeV, mb ≈ 4.8–5.6 GeV . Inputs are the values of the strong interactions coupling constant favoured by electroproduction and charmonium analyses, and the observed muon and heavy lepton (τ) masses. These estimates are substantially increased if there are more than six flavours of quark. Symmetry breaking in the SU(5) model is studied, including radiative corrections to the effective Higgs potential.

THE PRICE OF NATURAL FLAVOUR CONSERVATION IN NEUTRAL WEAK INTERACTIONS

Abstract The natural conservation of flavours to O( G F 2 ) in neutral weak interactions severely constrains choices of gauge groups as well as their fermion representations. In the absence of exactly conserved quantum numbers other than charge, and of | ΔQ | ⩾ 2 charged currents, essentially the only weak and electromagnetic gauge groups whose neutral interactions naturally conserve all flavours are SU(2) L ⊗ U(1) and SU(2) L ⊗ [U(1)] 2 . The plausible extensions of these gauge groups to grand unified models including the strong interactions are based on SU(5) and SO(10) respectively. Making the SU(5) model completely natural, including in the Higgs sector, gives the prediction m d /m e ⋍ m s /m μ ⋍ m b /m τ ⋍ 2605 where τ is the probable new heavy lepton and b is the conjectured third flavour of charge −1 3 quark . The SO(10) model contains a potential SU(2) L ⊗ SU(2) R ⊗ U(1) weak and electromagnetic gauge group, and has a complicated Higgs structure which does not naturally conserve quark flavours.

Search for gluons in e+e− annihilation

Abstract We study the deviations to be expected at high energies from the recently observed two-jet structure of hadronic final states in e + e − annihilation. Motivated by the approximate validity of the naive parton model and by asymptotic freedom, we suggest that hard gluon bremsstrahlung may be the dominant source of hadrons with large momenta transverse to the main jet axes. This process should give rise to three-jet final states. These may be observable at the highest SPEAR or DORIS energies, and should be important at the higher PETRA or PEP energies.

Left-handed currents and CP violation

An analysis is presented of a model for CP violation due to Kobayashi and Maskawa, which has six quarks and purely left-handed currents. The model can reproduce approximately results of the Glashow, Iliopoulos and Maiani four-quark model in CP conserving processes. It gives a close approximation to superweak predictions for CP violation in common K decays, whatever the masses of the fifth and sixth quarks. In principle there are substantial deviations from superweak predictions in rare K decays, but these seem difficult to observe in practice. There are also deviations from superweak results for CP violation in charmed particle decays. The neutron electric dipole moment is very sensitive to the masses of the b and t quarks, lying in a range containing the superweak prediction.

The phenomenology of the next left-handed quarks

The observation of ϒ(9.5) suggests that the -onium of at least one new quark has been discovered. We discuss the production and decays of the lowest-lying vector states. Recent observations have no indications of right-handed currents in antineutrino-nucleon scattering. We discuss the properties of new states made of t (charge = 23) or b (charge = −13) quarks in a model with just left-handed currents. Particular attention is paid to decay modes, production by neutrinos or antineutrinos, the analogues of K0 − K0 mixing, and CP violation.

On the weak decays of high-mass hadrons

Abstract Several arguments for the dominance of certain types of non-leptonic weak decays of strange particles are examined for their applicability to high-mass hadrons. Arguments based on asymptotic freedom, duality, current algebra and PCAC, and coloured fermion quarks are all found to be weaker than for strange decays. Specific calculations in the Glashow-Iliopoulos-Maiani charm scheme yield total semi-leptonic decay rates of 20% or more. Estimates of branching ratios for two-body decays of charmed mesons are given, and remarks are made about charmed baryon decays.

Baryon number generation in grand unified theories

Abstract Grand unified models of elementary particle interactions suggest that there was an early epoch during the Big Bang while the temperature was slightly less than the Planck temperature, during which no known interactions were in thermal equilibrium. This epoch was probably followed by a brief period during which baryon number violating forces were in equilibrium and could have annihilated any previously existing net baryon number. As these forces dropped out of equilibrium, a CP violating component could have generated the observed baryon to entropy ratio of O(10 −9 ).

Is the Mass of the Higgs Boson About 10-GeV?

Abstract Grand unified models of strong, weak and electromagnetic interactions improve the motivation for weak symmetry breaking by radiative corrections, which would imply that mH ∼ 10 GeV for sin2 θW ∼ 0.20. We make a systematic study of the phenomenology of a Higgs boson in this mass range, and find that it may be observable in ϒ decays and pp collisions, as well as in toponium decays.

Mass corrections to scaling in deep inelastic processes

Abstract We study subasymptotic hadron target and quark-parton mass corrections to scaling in deep inelastic scattering, ignoring interactions. The results can be summarized using a modified scaling variable common to parton, light-cone and short-distance operator product expansion formalisms, but with model-dependent spectral conditions. The analysis is expected to break down near the kinematic boundaries because of the bound state nature of hadrons. Related effects probably also dominate mass corrections due to very light quarks, but the analysis should be applicable to the production of new heavy quarks in neutrino production. Experimental deviations from scaling in deep inelastic electroproduction do not seem to be describable in terms of mass corrections alone, suggesting that interaction effects may be important at large momentum transfers as suggested by the renormalization group.