Heavy Quark Physics Research Articles

Non-Abelian Dipole Radiation and the Heavy Quark Expansion

Dipole radiation in QCD is derived to the second order in $\alpha_s$. A power-like evolution of the spin-singlet heavy quark operators is obtained to the same accuracy. In particular, ${\cal O}(\alpha_s^2)$ relation between a short-distance low-scale running heavy quark mass and the $\barMS$ mass is given. We discuss the properties of the effective QCD coupling $\aw(E)$ which governs the dipole radiation. This coupling is advantageous for heavy quark physics.

Parton-hadron duality in QCD sum rules: Quantum-mechanical examples

Motivated by recent work on three-point QCD sum rules in heavy quark physics, we use simple quantum mechanical models to study the basic issue of duality in three-point sum rules. We show that while in all of these models the duality in two-point sum rules works fine, the duality in three-point sum rules may be 100% violated, leading to completely unreliable predictions for the matrix elements in question. The implications for three-point QCD sum rules are discussed. A new estimate for the parameter ${\mathrm{\ensuremath{\lambda}}}_{1}$ of HQET is given.

Theoretical issues in heavy quark physics on the lattice: Computation of power corrections to hard scattering and decay processes

I review the problem of evaluating power (“higher twist”) corrections to hard scattering and decay processes. The appearance and cancellation of renormalons and power divergences is discussed. The loss of precision associated with this cancellation, and the need to perform the matching to higher orders of perturbation theory than are currently available are explained. The ideas are illustrated by a toy model, as well as three physical examples, the evaluation of the mass of the b -quark, its kinetic energy inside beauty hadrons and the gluon condensate.

Non-pertubative improvement of composite operators with Wilson fermions

We propose a method to improve lattice operators composed of Wilson fermions which allows the removal of all corrections of O ( a ), including those proportional to the quark mass, leaving only errors of O ( a 2 ). The method exploits the fact that chiral symmetry is restored at short distances. By imposing this requirement on correlation functions of improved lattice operators at short distances, the coefficients which appear in these operators can be determined. The method is an extension of the improvement program of the Alpha collaboration, which, up to now, has only been applicable in the chiral limit. The extension to quarks with non-zero masses is particularly important for applications in heavy quark physics.

Operator Product Expansion, Heavy Quarks, QCD Duality and Its Violations

The quark(gluon)–hadron duality constitutes a basis for the theoretical treatment of a wide range of inclusive processes — from hadronic τ decays and Re+e- to semileptonic and nonleptonic decay rates of heavy flavor hadrons. A theoretical analysis of these processes is carried out by using the operator product expansion in the Euclidean domain, with subsequent analytic continuation to the Minkowski domain. We formulate the notion of the quark(gluon)–hadron duality in quantitative terms, then classify various contributions leading to violations of duality. A prominent role in the violations of duality seems to belong to the so-called exponential terms which, conceptually, may represent the (truncated) tail of the power series. A qualitative model, relying on an instanton background field, is developed, allowing one to get an estimate of the exponential terms. We then discuss a number of applications, mostly from heavy quark physics.

Heavy quark results at DØ

Recent results on heavy quark physics from the DØ experiment at the Fermilab Tevatron Collider are reported. Topics included are top quark production and mass determination, bottom production and correlations, and charmonium production.

Calculation of power corrections to hadronic event shapes

We compute power corrections to hadronic event shapes in e + e − annihilation, assuming an infrared regular behaviour of the effective coupling α S. With the integral of α S over the infrared region as the only non-perturbative parameter, also measured in heavy quark physics, we can account for the empirical features of 1 Q corrections to the mean values of various event shapes.

A lattice study of spin and flavour symmetry in heavy quark physics

We present a first test of heavy quark spin-flavour symmetries in matrix elements for semi-leptonic decays B → D ∗λ ν and B → Dλ ν . We show that O(1/ m Q ) corrections are small at masses around the charm for form factors protected by Luke's Theorem, but are of order 30–40 % for h v and h v / h A 1 .

Effects of automated transfer coalescing on production physics

Diverse lattice gauge applications coded using the Canopy paradigm (augmented by transfer coalescing techniques) have been making effective use of the 50 Gflop ACPMAPS system at Fermilab for heavy-quark physics. These investigations have uncovered neccessities and limitations beyond the unusual CPU-Memory-Communications triad. Mass storage bandwith and system robustness requirements are discussed in light of this experience.

Heavy quarks and nuclei

In this talk I discuss some aspects of heavy (mainly charmed) quark physics that can be studied with low-energy antiproton beams and nuclear targets. The list of reviewed topics includes charmonium production off nuclei, exotic ( cq cq ) four-quark states, charmed nuclei and multiple strangeness production. Suggestions for the future experiments are outlined.

Heavy quark physics at HERA

A brief overview of the anticipated heavy quark physics at HERA is given. The topics discussed include heavy quark photo- and leptoproduction cross sections at HERA calculated in the context of perturbative QCD, various mechanisms of J/ ϕ-leptoproduction and their rates, determination of the gluon density of the proton using open and bound charmed hadrons, and rare D 0-meson decays. Some selected aspects of B-Physics at HERA are also discussed.

Improved nonrelativistic QCD for heavy-quark physics.

We construct an improved version of nonrelativistic QCD for use in lattice simulations of heavy quark physics, with the goal of reducing systematic errors from all sources to below 10\%. We develop power counting rules to assess the importance of the various operators in the action and compute all leading order corrections required by relativity and finite lattice spacing. We discuss radiative corrections to tree level coupling constants, presenting a procedure that effectively resums the largest such corrections to all orders in perturbation theory. Finally, we comment on the size of nonperturbative contributions to the coupling constants.

CP asymmetry in top-quark radiative decays.

We analyze the $\mathrm{CP}$ asymmetry in the top-quark radiative decay $t\ensuremath{\rightarrow}q\ensuremath{\gamma}$, where $q=c, u \mathrm{and} \ensuremath{\gamma}$ is an on-shell photon, due to the one-loop penguin diagram in the three-generation standard model. This penguin-dominated $\mathrm{CP}$ asymmetry is a new phenomenon of heavy-quark physics, and corresponds to the onset in the amplitude of the physical thresholds $t\ensuremath{\rightarrow}\mathrm{real}{\mathrm{Wl}}$, where $l=b, s, d$ is a quark in the loop. A $\mathrm{CP}$ asymmetry in a radiative decay to an on-shell photon in the light-quark sector (e.g. $B$-meson decays) cannot be generated by the one-loop penguin. The origin of this asymmetry is thus formally of some interest, although the phenomenological application turns out to be rather limited, due to extremely small branching ratios for $t\ensuremath{\rightarrow}q\ensuremath{\gamma}$, at least to one-loop order (however, our calculations raise an interesting possibility with respect to the role of QCD corrections to this asymmetry). This calculation should also serve as a useful benchmark for the study of possible $\mathrm{CP}$ asymmetries in the top-quark sector, in the context of new physics.

New heavy-quark physics in the strongly Yukawa-coupled standard model.

We show that for strong enough Yukawa coupling the electroweak standard-model quark finds it energetically advantageous to transform itself into a bound state in a Skyrme background. This picture implies a maximum mass for the quark and predicts the existence of an excited spin-(3/2 quark. Moreover, two-quark, color-antitriplet, and three-quark, color-singlet, bound states, which can be very deeply bound, are shown to occur. The spectrum is studied in the semiclassical approximation. On including the one-loop Casimir effect in the exponential background approximation one loses the present picture for the single-quark case. The leading decays of the excited states are estimated, which should provide clear experimental signatures of this scheme. For the quarkonium, surprisingly, the attractive potential is found to be dominated by QCD around the Bohr radius.

Sum Rule Approach to Heavy Quark Spectroscopy

The physics of heavy quarks is surveyed with particular attention paid to the structure of charmonium states.(AIP)

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.

A possible practical application of heavy quark physics

A POSSIBLE method for storing very large amounts of useable energy within small volumes is described here. Our proposal is based on the existence of two new, virtually stable, forms of matter that annihilate each other with enormous energy release, but neither of which annihilates ordinary matter (and can thus be stored easily). The existence of these new forms of matter is suggested1,2 by the phenomenology of heavy quarks and also by a large class of widely discussed unified field theories.