Fluctuations and correlations of soft gluons at the nonperturbative stage of evolution of QCD jets

At the nonperturbative stage of jet evolution, fluctuations of soft gluons are less than those for coherent states under specific conditions. This fact suggests that there can arise squeezed gluon states. The angular and rapidity dependences of the gluon correlation function are investigated at this stage of jet evolution. It is shown that these new states of soft gluons can display sub-Poissonian or super-Poissonian statistics corresponding to, respectively, antibunching and bunching of gluons, by analogy with squeezed photon states.     

All-order results for soft and collinear gluons

Some general features and some recent developments concerning the resummation of long-distance singularities in QCD and in more general non-Abelian gauge theories are reviewed. The field-theoretical tools of the trade are emphasized, with the focus mostly on the exponentiation of infra-red and collinear divergences in amplitudes, which underlies the resummation of large logarithms in the corresponding cross-sections. Some recent results concerning the conformal limit, notably the case of N = 4 superymmetric Yang-Mills theory are also described.      

Constituent gluons and a new mechanism for radiative weak decays of hyperons

An effective quark-gluon-photon operator is considered as the mechanism for radiative weak decays of hyperons. The coefficient function is unsuppressed by GIM cancellations, suggesting a significant decay rate, and a substantial amount of parity violation (large decay asymmetry) is expected. Attempted model calculations confirm this last feature but fail to provide an adequate absolute decay rate.     

Hybrids: Mixed states of quarks and gluons

We calculate the spectrum of the four ground state hybrid $\text{(}\text{q}\text{qg}\text{)}$ nonets, J^PC = (0, 1, 2)^?+, 1^??, using the MIT bag model to first order in cavity perturbation theory. Quark and gluon self-energies are included by a fit to the s-wave mesons and baryons and to the glueball candidate i(1440). We find a large gluon self-energy which substantially increases our predictions of the glueball and hybrid masses. We discuss the phenomenology of hybrids, including a suggestion that the A₃ (1670) and a second peak at 1850 MeV in the fπ channel may be mixtures of the isovector $\text{q}\text{q}$ d-wave state with the $\text{q}\text{qg}$ s-wave.     

Jet calculus: A simple algorithm for resolving QCD jets

It is argued that, in the leading logarithm approximation (LLA) of asymptotically free quantum chromodynamics (QCD), a simple algorithm (jet calculus) can be justified for computing a large number of quantities related to the longitudinal and transverse structure of quark and gluon jets.We formulate the rules of jet calculus in two variables, x and y which are related to longitudinal (energy) and transverse momentum respectively. Throughout the paper, quark and gluon jets are contrasted. After reviewing what has been done on longitudinal spectra, we turn to the transverse structure of jets down to relative transverse momenta of the order of a few GeV (independently of the total energy). The relation of our work to that of Dokshitzer, D'Yakonov and Troyan is elucidated. We also study jets generated by (almost) real photons and compare both with standard “final” parton jets.We also discuss calorimeter measured quantities, compare our results with those of other authors and propose a new and easy way for measuring QCD-predictable anomalous dimensions.We finally give a Lagrangian formulation of jet calculus, as a non-local theory in 1 + 1 dimensions to be solved in the tree approximation.     

Quarks and gluons in a model with induced geometry

It is shown that the QCD-Lagrangian describing interacting gluons and uncharged quarks can be consistently introduced in a classical field model involving induced geometry. A discussion of quark confinement is given.     

Contribution of gluons and coloured Higgs bosons to e+-e− annihilation into three jets

Three-jet thrust and angular distributions in e⁺e^? annihilation are calculated in the integer-charge quark model. The complete contributions of gluons and Higgs scalars are presented. Deviations from QCD results are in general less than or comparable to the experimental errors, except for m_g ? 2 GeV and m_H ? 30 GeV.     

Finding the reconstructions of semiconductor surfaces via a genetic algorithm

In this article we show that the reconstructions of semiconductor surfaces can be determined using a genetic procedure. Coupled with highly optimized interatomic potentials, the present approach represents an efficient tool for finding and sorting good structural candidates for further electronic structure calculations and comparison with scanning tunneling microscope (STM) images. We illustrate the method for the case of Si(1 0 5), and build a database of structures that includes the previously found low-energy models, as well as a number of novel configurations.     

Colour gluons and scaling in a unified gauge model

Deep inelastic weak and electromagnetic processes are considered within the parton framework taking the partons to be integrally charged quarks and coloured gluons. Despite the participation of the spin-one gluons in these processes, scaling is shown to be maintained by treating the problem in a unified gauge model based on the groupSU (3)_colour⊗SU _L (2)⊗U(1). This is a consequence of the vector-dominance type of couplings between the gluons and the weak or electromagnetic vector bosons which are induced by the spontaneous breakdown of gauge symmetry. As a further consequence it is found that in the asymptotic region far above the gluon masses the colour octet parts of the weak and electromagnetic currents of the quarks are damped so that, in particular, the integrally charged quarks behave as fractionally charged quarks in this region.     

Double logs of perturbative QCD for parton jets and soft hadron spectra

The influence of coherence in a soft parton bremsstrahlung on hadron spectra in jets is discussed. We present a simple functional method for calculation of different inclusive parton distributions in the “plateau” region. Inclusive parton cross sections, spectra, multiplicities, energy and angular correlations, etc. are derived in the Double Logarithmic approximation.     

Universility of hadron jets in soft and hard particle interactions at high energies

Hadron jet production is studied in softπ ^? p and cumulativeπ ^? C interactions at a 40 GeV/c momentum. The collective characteristics of jets and the form of the quark and diquark fragmentation into charted poins and neutral strange particles are analyzed. The results obtained are compared to analogous data fore ⁺ e ^? andv(≈v)p interactions. The hadron jet properties are also studied by means of relativistic invariant variables—the squared relative 4-velocities \(b_{ik} = - \left( {\frac{{P_i }}{{m_i }} - \frac{{P_k }}{{m_k }}} \right)^2 \) . The results obtained show that quark (diquark) fragmentation proceeds in a similar manner in soft hadron-hadron collisions, cumulative interactions on light nuclei,e ⁺ e ^? annihilation and deep inelasticv(≈v)p scattering. In the relativistically invariant variables the fragmentation function is similar for the hadronization of quarks and diquarks and it does not matter whether they are knocked out of usual hadrons or multiquark systems.     

A new jet algorithm based on the k-means clustering for the reconstruction of heavy states from jets

A jet algorithm based on the k-means clustering procedure is proposed which can be used for the invariant-mass reconstruction of heavy states decaying to hadronic jets. The proposed algorithm was tested by reconstructing e⁺e^-→tt̄→6 jets and e⁺e^-→W⁺W^-→4 jets processes at using a Monte Carlo simulation. It was shown that the algorithm has a reconstruction efficiency similar to traditional jet-finding algorithms, and leads to 25% and 40% improvement of the top-quark and W mass resolution, respectively, compared to the k_T (Durham) algorithm. In addition, it is expected that the peak positions measured with the new algorithm have smaller systematical uncertainty.     

Decay of PSI and upsilon into a lepton pair and gluons

We calculate the decay of a heavy vector quarkonium state into a lepton pair and two gluon jets, in lowest order QCD. We present branching ratios, and the lepton pair spectrum as a function of its invariant mass, and of the missing mass recoiling against it.     

Quasi-radial wall jets as a new concept in boundary layer flow control

This work aims to introduce a novel concept of wall jets wherein the flow is radially injected into a medium through a sector of a cylinder, called quasi-radial (QR) wall jets. The results revealed that fluid dynamics of the QR wall jet flow differs from that of conventional wall jets. Indeed, lateral and normal propagations of a conventional three-dimensional wall jet are via shear stresses. While, lateral propagation of a QR wall jet is due to mean lateral component of the velocity field. Moreover, discharged Arrays of conventional three-dimensional wall jets in quiescent air lead to formation of a combined wall jet at large distant from the nozzles, while QR wall jet immediately spread in lateral direction, meet each other and merge together very quickly in a short distance downstream of the jet nozzles. Furthermore, in discharging the conventional jets into an external flow, there is no strong interaction between them as they are moving parallel. While, in QR wall jets the lateral components of the velocity field strongly interact with boundary layer of the external flow and create strong helical vortices acting as vortex generators.     

On the confinement of quarks and vector gluons in a superconducting phase

Within a simple model of a self-interacting quark field an attempt is described to introduce diquarks a priori by spontaneous breaking of gauge invariance much in the same way as electron pairs are incorporated by the nonrelativistic BCS theory of superconductivity. This is done because baryons can be regarded as a quark-diquark system. It is shown that quarks with a mass smaller than the invariant mass gap will find it energetically unfavourable to enter a superconducting region. By referring to the Boson transformation method it is argued that bag, respectively, vortex type solutions exist. The quark-quark pairing in the groundstate induces a spontaneous breaking of Lorentz isotropy which, by the Goldstone theorem, leads to automatically confined (abelian) vector gluons of zero mass in the skin region of the hadron. A large anomalous spin-spin coupling among the valence quarks, as required by the π-? mass difference, is likely to be present. It is pointed out that the skin region of mesons and baryons may have a different structure. Solutions where the quark moves freely inside a confined region correspond to the possibility of having a space dependent mass gap.     

一种新的自动聚焦算法的研究

聚焦评价函数和极点搜索策略是自动聚焦的重要模块,直接影响聚焦的效果.为同时满足自动聚焦速度和精度上的要求,提出了一种新的自动聚焦算法.该算法综合了快速改进的灰度差分法和高精度小波变换法的优点,根据各阶段聚焦评价函数的梯度选择合适的评价函数和镜头移动步长,并且实现了从大步长快速粗扫到小步长精确细调的过渡.实验表明,与传统...     

Electric and magnetic screenings of gluons in a model with a dimension-2 gluon condensate

Electric and magnetic screenings of thermal gluons are studied using the background expansion method in a gluodynamic model with a gauge invariant dimension-2 gluon condensate at zero momentum. At low temperature, the electric and magnetic gluons are degenerate. With the increase of temperature, it is found that the electric and magnetic gluons start to split at a certain temperature T₀ . The electric screening mass changes rapidly with temperature when T >T₀ , and the Polyakov loop expectation value rises sharply around T₀ from zero in the vacuum to a value around 0.8 at a high temperature. This suggests that the color electric deconfinement phase transition is driven by electric gluons. It is also observed that the magnetic screening mass remains almost the same as its vacuum value, which manifests that the magnetic gluons remain confined. Both the screening masses and the Polyakov loop results are qualitatively in agreement with the Lattice calculations.