Jet-like distributions from the weak decay of heavy quarks

We consider the production and weak decay of a pair of heavy quarks (mesons) ine ⁺ e ^? experiments and study their effect on the various jet distributions. The relative magnitudes of the two-quark-jet and three-quark-jet final states, in the decay of a heavy quark are estimated in the framework of an SU(2) _L ×U(1) model. We find that the three quark configuration dominates over the two quark configuration. For the quark jets resulting from the weak decay of the heavy quarks, we calculate the jet distributions in Sphericity, Spherocity and Thrust for the process \(e^ + e^ - \to Q\bar Q \to 6\) quarks. These distributions are compared with the corresponding quantities from the non-perturbative process \(e^ + e^ - \to q\bar q\) and the QCD process \(e^ + e^ - \to q\bar qg\) . We find that the weak decay of heavy quarks is the dominant mechanism for jet broadening ine ⁺ e ^? experiments, in the intermediate energy region relevant for PETRA and PEP.     

On the semileptonic decay distributions from the next heavy quark

Motivated by the discovery of λ(9.4), we study the semileptonic decay correlations of the next heavy quark, and their consequences for thee ⁺ e ^? colliding beam and neutrino experiments. A detailed comparison is made with the corresponding correlations from the production and decay of charm and heavy leptons, τ^±. Some tests of the \({\rm B}^0 - \bar {\rm B}^0 \) mixing ( \(B = b\bar q\) withbaQ=?1/3 heavy quark) are suggested fore ⁺ e ^? colliding beam experiments.     

Heavy quark correlations ine + e − annihilations

In heavy quark jets the quark mass acts as a regulator of collinear singularities, making the quark momentum an infra-red safe variable in perturbative QCD. This allows a direct comparison of measured heavy hadron momentum spectra with perturbative calculations. We exploit the factorisation of heavy quark fragmentation to derive QCD predictions for momentum correlations between heavy hadrons produced ine ⁺ e ^? annihilations. We study the practical feasibility and model sensitivity of our approach using Monte Carlo simulations. Higher order perturbative corrections and contributions from non-perturbative effects are found to be at the level of 10%.     

Exclusive heavy-meson production and the Z width

We calculate in lowest order QCD perturbation theory the production from Z⁰ decay and e⁺e^? annihilation of two mesons, each containing a heavy quark. With reasonable assumptions about the vertex functions that couple mesons to quarks, we find that the rates for these final states are strongly enhanced. Present-day knowledge even allows these rates to be so large that the Z⁰ may be too wide to be detected in $\text{p}\text{p}$ collisions, with disastrous consequences also for event rates at e⁺e^? colliders.     

Three-jet distributions ine + e − annihilation: Electromagnetic and weak production

Hard gluon bremsstrahlung off quarks ine ⁺ e ^? annihilation is expected to produce three-jet events. The angular distributions of the jets are calculated for electromagnetic and weak production in the high energy region (Z resonance decay included). Numerical estimates are presented for the vectoraxialvector interference terms within the Weinberg-Salam theory. We discuss (i) angular correlations between jets, (ii) semiinclusive pion distributions and (iii) we comment on angular asymmetries of leptons originating from heavy quark decays.     

Perturbative QCD and the exclusive decay of heavy quarkonium into a photon and two mesons

We consider the radiative decays of the ³S₁ ground state Q$\text{Q}$ into a real photon and two light pseudoscalar or vector mesons. For sufficiently large mass of the heavy quark Q, the decay, e.g. ? → γππ, can be calculated in perturbative QCD, provided that the photon does not carry away a predominant fraction of the available energy. We present differential and integrated Dalitz plot distributions and, for quarkonium states produced with transverse polarization in e⁺e^? annihilation, angular distributions of the orientation of the decay triangle relative to the beam direction.     

The source of trimuon events in neutrino scattering

A comprehensive study indicates that equally likely sources for trimuon events neutrino scattering are (a) charged heavy lepton production (with decay to three muons) and (b) simultaneous production of a neutral lepton (with decay to two muons) and a heavy quark (with decay to one muon). The sequential decay of a heavy quark to two muons is less likely. An intriguing model yielding simultaneous M⁰ and b quark production is proposed.     

An approach to the study of heavy quarks ine + e − collisions

The production ofb- andt-quarks ine ⁺ e ^? collisions may be appropriately investigated from the observation of like-sign dileptons. We estimate the branching ratios and the average lepton energies in semileptonic decays of heavy particles, taking into account both cascade decays and the mass-mixing of neutral mesons. They are found to be relatively large. Then, we consider the angular distribution and correlations for events wheighted by powers of the lepton energies. These quantities (moments) have a transparent decomposition, where each factor corresponds to a dynamical step in the production of dileptons. Our computations suggest that the study of like-sign dileptons along these lines would provide interesting information on the heavy quark fragmentation and decay.     

Jets and the physics of new heavy quarks

We have developed methods that can be used to isolate a clean sample of events with pair-produced heavy quarks in e⁺e^? collisions. We show that most of the fundamental properties of a given heavy quark, as they would appear in pair production or in weak decays, can be deduced from a careful examination of this purified sample.     

Charged Higgs bosons and decays of heavy flavored mesons

We explore the possibility that charged Higgs bosons exist. The role of e⁺e^? experiments carried out above heavy quark thresholds is stressed. Striking experimental signatures are predicted.     

Observations on K-production in e+e− collisions

We examine recent K-production data in e⁺e^? collisions in the framework of a heavy quark bound state model for the new resonances. If the rise in R is due to the production of new particles which are bound states of a heavy quark and an ordinary quark, we deduce that approximately half of the time the weak decays of these particles will contain a K-meson. Theoretical consequences of this fact are discussed. We also use the K-production rate at the ψ and ψ' resonances to calculate the branching ratio of these states to ?π and K¹$\text{K}$. The number obtained for the ψ, where it is measured, is in satisfactory agreement with experiment.     

Instantons - how significant numerically at short distances?

It is attempted to calculate the instanton effects in the hadronic cross section of e⁺e^? annihilation, the magnetic form factor of quark, and the potential of heavy quark-antiquark by expanding the quark-instanton interaction in the dilute gas limit.     

Semi-leptonic decays of charmed mesons produced in γN collisions

We report here on a study of the characteristics of the semileptonic decay spectra from a pair of charmed hadrons produced via photoproduction. The inclusive production of charmed hadrons is phenomenologically parametrized as e^?aze^?bp_t2. Their decays are described by (i) decay of free charm quark in GIM, (ii) K¹ dominant mode, $\text{D}\text{→}\text{K}{}^1\text{l}\text{ν}$, and (iii) pure leptonic decays. We deduce that 〈M_eμ²〉 = 0.18 M_D² for free quark decay and 〈M_eμ²〉 = ?0.35 +-0.24 M_D² for K¹ dominant decay. For the specific purpose of the photoproduction experiment at FNAL whicc is currently searching for μe events, we incorporate the incident photon spectrum, and the decay distributions with and without the experimental acceptance criteria are presented.     

Parity violating effects in Σ→Λγ and Σ→Λe t>+ e − decays

Parity violating effects in Σ→Λγ are calculated in non relativistic quark model usingW, Z and gluon exchanges. These effects are found to give dominant contribution to the parity violating effects in Σ→Λe ⁺⁺ e ^? decay as compared to the neutral current effects.     

Higgs radiation off top quarks in high-energye + e − colliders

Higgs particles can be radiated off heavy top quarks which will be produced copiously in high energye ⁺ e ^? colliders. This process can be used to measure the Higgs-top quark coupling. We present the cross section for the production of Higgs bosons in the Standard Model. In addition we have studied the production of neutral and charged Higgs particles in association with heavy fermions in the Minimal Supersymmetric Standard Model.     

Scaling in soft hadroproduction by positive projectiles in the range of 32–147 GeV/c

The total hadron multiplicity and the multiplicity in the three-jet events ine ⁺ e ^?-annihilation are considered. The formula for the total multiplicity (with account for the heavy quark contribution) agrees well with experiment. The value of the multiplicity for three-jet events is predicted.     

Leading logarithms of heavy quark masses in processes with light and heavy quarks

The matrix elements of operators containing both heavy quark (Q) and light quark (q) fields can contain large logarithms of the type ln(m_Q²/μ²), where μ is a typical QCD mass scale and m_Q is the heavy quark mass. We outline a method for summing leading logarithms of this type. We apply it to the decay constant f_M of a low lying pseudoscalar meson M with Q̄q flavor quantum numbers and predict the ratios of decay constants for mesons with different heavy flavors. We also apply it to a matrix element of a four-quark operator which is relevant for B⁰−B̄⁰ mixing.