Heavy Quark Pair Production Research Articles

Production and propagation of heavy-quark pairs in nuclei

We study the phenomenology of nuclear charmonium and bottomonium production by high-energy protons incident on nuclear targets. We combine concepts of color (singlet) trans-parency with the proposition that colored states can propagate in the medium over a limited space-time range (color opacity). It is shown that color transparency alone is incapable of explaining the significant depletion of quarkonium production rates in nuclei. We suggest that, under quite modest assumptions, the propagation of color-octet quark-antiquark pairs in intermediate states can provide a successful description of the observed A-dependence.

Heavy quark symmetry and pair production of heavy mesons. A perturbative QCD estimate

Physical and mathematical arguments are given which suggest that heavy quark symmetry makes clear predictions for production of pairs of heavy mesons in e ++ e − annihilation. A perturbative QCD calculation is done which explicitly demonstrates this result in the heavy quark limit. However these calculations also suggest very large 1 M corrections for realistic quark masses.

On the associate production of a neutral intermediate-mass Higgs boson with a single top quark at the LHC and SSC

The typical behaviour of the semiweak single top quark production mechanism in hadron-hadron collisions in comparison with heavy quark pair production suggests that boson-gluon fusion may lead to important associated Higgs cross-sections. This is of particular interest for the interval in which the Higgs mass is close to the mass of the Z 0 and well below 2 M Z 0 . In this region experimentally significant signals are expected to be small, while complicated to extract due to large backgrounds. In two recent papers, studies have been presented in which contradicting results have been reported on the magnitude of Higgs production in association with a single top quark. We present an independent analysis and trace the origin of the discrepancies.

Heavy quark production by double pomeron exchange

Using the two-gluon exchange model of the pomeron, the double pomeron exchange contribution to production of heavy quark ( c c, b b, and t t ) pairs in the central region of rapidity is calculated. The predicted cross-section for b b pairs turns out to be about 0.2 μb at the CERN collider rising to about 1 μb at LHC. The tt̄ production at the LHC is expected at the level of about 0.1 nb.

Heavy quark multiplicities in gluon jets

In view of recent theoretical developments we reanalyse the production of heavy quark pairs inside gluon jets, and compare the new results with the prediction of the HERWIG shower Monte Carlo program.

Phenomenological implications of an electroweak theory without Higgs

An alternative to the standard electroweak gauge theory is considered which does not involve the physical Higgs particle, but contains heavy vector boson resonances manifesting the strong gauge boson self-interactions. We investigate phenomenological implications of such a theory and demonstrate that processes including heavy quarks (in particular heavy quark pair production and asymmetry in e +e − annihilation) constitute a good testing ground for experimentally discriminating this theory from the SM at energies available at present or within the near future.

Search for the fourth generation: Present and future prospects

A survey is given of searches for fourth generation fermions at e + e − and p p colliders. The most stringent current constraints are obtained from neutrino counting, determinations of the Γ Z / Γ W ratio and searches at p p colliders for W → Lν L and heavy quark pair production. Techniques for future searches are discussed.

Radiative Corrections toe+e-Reactions in Electroweak Theory

Radiative corrections necessary for high energy e^+^e- colliding beam experiments are reviewed. They are considered in an on-shell renormalization scheme of the standard SU(2) × U(1) theory. Comparisons of the adopted scheme with other various schemes are given. The corrections are obtained by both calculating one-loop virtual corrections in the full electroweak theory and by taking into account realistic experimental cuts on the hard photon emission cross section. The reviewed processes are the lepton pair production, i.e., µ^+µ^−-, τ^+ τ^−- and e^+e^−-pair production, yy production, the neutrino counting reaction, the hadron production, i.e., light- and heavy-quark pair production and the hadron production through narrow resonance. Higher order QED corrections are also applied to the Z^0 line shape and the narrow resonance production.

Heavy flavours in high-energy e+e- annihilation

This paper reviews the quantum flavour dynamic properties of the heavy leptons and quarks and, for the purpose of this paper, the heavy flavours are taken to be the tau lepton and the c and b quarks. The production of tau + tau - and the electroweak properties of the tau are first discussed and then the tau charged current decay properties are considered and compared with those of the mu . The role of tau decays in the understanding of QCD is also considered. The production of heavy quark pairs is considered in the framework of the Standard Model and the weak neutral current charges of the quarks are presented from a global analysis of all existing data. The weak decays of c and b are discussed and the measurements of lifetimes and leptonic widths considered as input parameters to the eventual determination of the KM matrix elements. Finally, the fragmentation of c and b quarks is discussed and the various measurements presented.

Heavy flavor production at high energyep colliders

The total production rates for heavy quark pairs due to gauge boson fusion processes at high energyep colliders are evaluated. At HERA,b\(\bar t\) production dominates overt\(\bar t\) production form t ≧60 GeV and is observable up tom t ≃80(90)GeV where the number of expectedb\(\bar t\) events is about 15(10) for ∝L=200pb−1. Including the contributions fromep→WX→btX the total number of expectedbt events amounts to about 50 events form t ≃80GeV. The influence of thresholds for heavy quark pair production is also studied for the relevant structure functionsF i (x,Q2) and shown to contribute to the measured scaling violations. All these effects are sensitive to the heavy quark massesand to the shape of the gluon distribution which can thus be tested experimentally by analyzing heavy quark pair signals.

Hadron production near threshold in photon-photon collisions.

A dual picture between perturbative QCD and resonance production is exploited to describe non-diffractive meson pair production near threshold in 77 annihilation. Submitted to Physical Review Letters * Work supported in part by the Department of Energy, contract DE-AC03-76SF00515. In quantum chromodynamics, hadron production in 77 annihilation is initiated by the coupling of the incident photons to either one or two quark pairs. At high momentum transfer, both inclusive and exclusive reactions can be computed in terms of underlying elementary quark and gluon scattering subprocesses.’ A large body of data from PEP and PETRA gives good support to the validity of this perturbative QCD description. At low momentum transfer, the processes which convert the quarks into hadrons are generally nonperturbative, coherent, complex, and thus, at this point, not calculable. There are, however, exceptional low momentum processes where perturbative QCD predictions should be reliable even at threshold energies if Coulombic rescattering corrections are properly taken into account; e.g., those rare 77 annihilation processes in which only hadrons containing heavy quarks are produced. As an example, we illustrate the leading order minimally-connected QCD diagrams for heavy meson pair, production in Fig. 1. Since the exchanged gluon momenta and the effective renormalization scale are of order of the heavy quark mass a perturbative QCD analysis can be justified. Unfortunately, the predicted rate is small, and tests of this basic feature of QCD appear remote. Nevertheless, we shall argue here, that given the validity of a dual picture between the perturbative amplitudes and suitably-averaged resonant contributions, one can obtain reasonable estimates of relatively light meson pair production 77 cross sections even near threshold. Let us recall the situation for heavy quark-pair production in e+eannihilation. In this case the cross section is well under control in QCD not only at high energies but also near threshold where only a minimal number of hadrons

Are there heavy quarks of mass 23 GeV?

An excess of events with an isolated muon and low thrust observed by the MARK-J collaboration at the highest PETRA energy s ≅ 46.7 GeV , is found to be consistent with the near threshold production of heavy quarks of charge − 1 3 . A natural candidate is a fourth-generation “down” quark or, possibly, a member of a 27 representation of E 6. Signatures of such heavy quark pair production at the CERN p p collider are investigated and it is concluded that the present data have a chance to confirm the signal.

On the QCD 2 → 3 contributions to the hadroproduction of heavy quarks

The use of tree level QCD 2 → 3 cross sections for heavy quark production are examined in detail; they are known to give significant contributions to cc̄ and bb̄ production at hadron colliders. Results are presented for the 2 → 3 contributions which can be reliably calculated from QCD, namely (A) the production of three isolated high p T jets, (B) heavy flavour excitation where only one of the heavy quarks has large p T and, (C) collinear heavy quark pair production where the pair form a single high p T jet. There are no appreciable 2 → 3 contributions for t-quark production.

Massive Lepton Pair Production in High Energy Hadron-Hadron Scattering

Massive lepton pair production in high energy hadronic collisions is studied in the framework of perturbative QCD. As for the origin of lepton pairs, the Drell-Yan process and the heavy quark pair production followed by the decay into leptons are taken into account. A model is proposed to reproduce existing experimental data. In the same model, predictions are presented for the massive lepton pair continuum spectrum at future accelerator energies. The effect of scaling violation, form of gluon distribution and Z0 boson are discussed in detail. In the region where , the cross section of lepton pair producion by heavy quark pair is found to dominate over that by the Drell-Yan mechanism. This result indicates a possibility for observing a clean signal of gluon-gluon hard collisions in future high energy accelerators.

Momentum distributions for [formula omitted] photoproduction

The contributions to heavy quark pair production from the subprocesses γg → QQ̄g and γq → QQ̄q have been calculated using perturbative quantum chromodynamics. The results have been used to obtain predictions for the longitudinal and transverse momentum distributions for Jψ photoproduction. The comparison with data from a recent muon scattering experiment is encouraging.

Comparison of trimuon production mechanisms

We compare the predictions of six models for neutrino (and antineutrino) production of trimuon events. In particular, results are given for models based on heavy-charged-lepton decays, heavy-neutral- lepton decays together with heavy-quark decays, diffractive production and decay of heavy-quark pairs, heavy-quark cascade decays, the decays of Higgs mesons, and the radiative production of muon pairs. Our comparison should help to unravel the sources of the trimuon events detected at Fermilab and CERN. We also examine the probability of explaining the so-called superevents in which the muons are extremely energetic.

Trimuons from charm

We have calculated charm pair production in νμN collisions using quantum chromodynamics (QCD). The resulting trimuon rate turns out to be small at present energies: σ(3μ)σ(1μ)≲10−6 at Eν = 200 GeV for αs = 0.2. (However, this process may be measurable at the high energies attainable with colliding beam ep machines.) We emphasize the general importance of looking for inclusive JΨ or the bound states of heavier flavors in deep inelastic reactions, as a signal for the pair production of heavy quarks.