Nambu's Nobel Prize,the meson and the mass of visible matter

The electroweak Higgs boson has been discovered in ongoing experiments at the LHC, leading to a mass of this particle of 126 GeV. This Higgs boson mediates the generation of mass for elementary particles, including the mass of elementary (current) quarks. These current‐quark masses leave 98% of the mass of the atom unexplained. This large fraction is mediated by strong interaction, where instead of the Higgs boson the σ meson is the mediating particle. Though already introduced in 1957 by Schwinger, the σ meson has been integrated out in many theories of hadron properties because it had not been observed and was doubted to exist. With the observation of the σ meson in recent experiments on Compton scattering by the nucleon at MAMI (Mainz) it has become timely to review the status of experimental and theoretical researches on this topic.     

Charged multiplicities in Z decays into u, d, and s Quarks

About 4.4 million hadronic decays of Z bosons, recorded by the OPAL detector at LEP at a centre-of-mass energy of around GeV, are used to determine the mean charged particle multiplicities for the three light quark flavours. Events from primary u, d, and s quarks are tagged by selecting characteristic particles which carry a large fraction of the beam energy. The charged particle multiplicities are measured in the hemispheres opposite to these particles. An unfolding procedure is applied to obtain these multiplicities for each primary light quark flavour. This yields where statistical and systematic errors are given. The results for and are almost fully statistically anti-correlated. Within the errors the result is consistent with the flavour independence of the strong interaction for the particle multiplicities in events from the light up, down, and strange quarks. Received: 5 October 2000 / Published online: 15 March 2001     

物质结构在夸克-轻子层次上的动力学规律和研究发展趋势

文章综述了粒子物理中标准模型理论的历史发展、面临挑战以及未来的发展趋势.目前阶段物质结构最小组成单元是夸克和轻子,量子色动力学是描述夸克-胶子之间强相互作用的基本理论,它具有渐近自由和夸克禁闭的特点.量子色动力学和电弱统一理论一起构成粒子物理中标准模型理论.标准模型理论成功同时也面临两大挑战:对称性破缺的本质和夸克禁闭难题,这意味着标准模型理论需要发展和突破.人们期望粒子物理学、天文学和宇宙学交叉发展联手解决物质结构和早期宇宙研究中面临的难题,最终揭示超出标准模型的新物理规律.     

Penetrating flavors

Hadrons made of heavy flavor quarks are expected to have small cross sections and perhaps reduced energy loss in collisions, leading to their being more “penetrating” than ordinary hadrons. Some effects of this in cosmic ray phenomena are considered. If the heavy particle lives long enough it can become the dominant hadron component in the atmosphere. With particles of short lifetime there is a threshold effect in energy where the penetrating hadron travels far enough to become important. Some of the anomalous effects in 10² – 10³ TeV phenomena could be caused via this mechanism by a particle with lifetime ～ 10^?11 s. An ～ 150 cm thick iron absorber would provide a substantial enhancement in the charm/proton ratio in the 10–100 TeV range. If free quarks are produced and have the same cross section as bound quarks, they act as highly penetrating hadrons.     

Searching for quarks: a quantum chemical assisted approach

The evidence for quarks as the basic blocks of matter come only from very expensive experiments, performed in very large particle accelerators. An alternative method of detection is to look for changes in spectroscopic properties that could be influenced by fractionally charged nuclei formed with the ‘wrong’ number of quarks. Although this proposal has already been made by many authors, they were not able to provide feasible and easily interpretable experiments to detect quarks in matter. In this paper, we present the results of configuration interaction (CI) calculations for the transition energies and optical oscillator strengths associated with inner shell electronic spectra of molecular nitrogen made of fractionally charged nuclei. It is shown that these bands can be used as fingerprints characterizing the presence of quarks in matter.     

Event-by-event fluctuation studies in the ALICE experiment

Event-by-event (E-by-E) fluctuations are considered to be one of the possible indications that a phase transition from ordinary hadronic matter to a plasma of quarks and gluons has occurred, as it is expected to happen in ultra-relativistic heavy-ion collisions. In this article, the results of a study concerning the observability of E-by-E fluctuations for the ALICE experiment at the LHC collider at CERN is presented. In particular, an estimate of the E-by-E statistical sensitivity in the measurement of the inverse slope parameter from the transverse momentum spectra of hadrons and of their particle ratios is discussed. The analysis relies on the excellent performance of ALICE in terms of particle identification.     

Center-of-Mass Energy Removal in Relativistic Three-Quark Models of the Proton

A variant of a squared three-body Dirac equation is used to determine center-of-mass energy effects in independent particle motion approximations for three quarks in the nucleon. A scalar linear flux tube potential is used to confine the quarks. The relativistic nearly massless three-quark system, in the rest frame where the total momentum is zero, has a squared energy that is 3/5 the value compared to when the quarks are assumed to move independently. This is smaller than the 2/3 energy ratio determined using the non-relativistic harmonic oscillator model. This analytic model has one parameter, the flux tube constant. Choosing the flux tube constant to reproduce the proton rest energy, results in the analytic wave function well reproducing the proton axial charge and rms charge radius. The proton magnetic moment predicted is 2.235, lower than experiment.     

High-energy hadron-hadron collisions and internal hadron structure

As shown by many authors, central particle emission in pp collisions at centre-of-mass energies ? 20 GeV can be described in terms of independent cluster production. In ref. [1] this process has been related to the quark-gluon picture of nucleon structure. The present paper carries this relation further and links the leading particle spectrum of non-diffractive hadron-hadron collisions to the x distribution of quarks in the hadron. Thus, the flat leading particle spectrum, as observed in non-diffractive pp collisions, is found to be naturally related to the steeply falling x distribution of quarks in the nucleon, as deduced from the structure functions measured in deep inelastic scattering of electrons and neutrinos on nucleons. Our analysis is extended to meson-nucleon collisions and leads to a prediction of the general shape of the quark x distribution in a meson.     

Quark confinement and the short-range component of general affine gauge gravity

Within the framework of a gauge field theory based on the general affine space-time symmetry, we propose a certain purely quadratic gauge field lagrangian. In the large-scale region it yields an Einstein-Cartan-like gravity with Newton's constant generated spontaneously, while in the particle domain it yields a renormalizable theory with a confining potential applying to quarks and not to leptons.     

High-spin states in 22Ne populated in the 14C(12C, α)reaction

The CDF Collaboration reported an excess in the production of two jets in association with a W . We discuss constraints on possible new particle state interpretations of this excess. The fact of no statistically significant deviation from the SM expectation for Z +dijet events in CDF data disfavors the new particle explanation. We show that the nucleon intrinsic strange quarks provide an important contribution to the W boson production in association with a single top quark production. Such W +t single top quark production can contribute to the CDF W +dijet excess, thus the nucleon intrinsic quarks can provide a possible explanation to the CDF excess in W +dijet but not in Z +dijet events.     

Phenomenology of the production,decay, and detection of new hadronic states associated with supersymmetry

Supersymmetric theories involve spinorial partners for the gluons of QCD. If the symmetry breaking is such that they are massless or light, they probably combine with quarks to form families of new, relatively low-lying hadrinic states, which decay into ordinary hadrons and a new, neutrino-like particle. We discuss how present experiments can put limits on their production.     

Meson hyperfine splittings and asymptotic freedom

Meson hyperfine splittings give empirical evidence that the short-ranged part of the potential binding quarks has the behavior expected of single color gluon exchange in an asymptotically free theory. Since the interaction of light confined quarks depends on only one length scale, while that of heavy confined quarks depends on two length scales, it is argued that the spin-dependent interactions are qualitatively different in the cases. Phenomenological evidence suggests that the spin-dependent interactions of light quarks are short-ranged only, while that of heavy quarks are predominantly long-ranged. It is proposed that a measurement of the F¹-F mass-difference will help clarify the nature of a possible long-ranged spin-spin interaction of strange quarks.     

Future of charm physics

Charm particles provide a unique opportunity to study particle–antiparticle mixing induced by virtual down-type quarks. CP violation in charm physics is still a Terra Incognita which remains to be explored. Charm hadrons are also a laboratory to control hadronic uncertainties in weak transitions of heavy quarks. To do this physics program, large data samples registered close to the production threshold or at higher energies are needed.     

ANOMALOUS WEAK CHARGED CURRENTS OF LEPTONS AND QUARKS IN A SUBSTRUCTURE MODEL

We present a general approach to get the anomalous weak charged current of leptons and quarks in a substructure mode1,in which quarks, leptons and W-bosons are composed of preons (fermions and scalar bosons). We have shown that the (V+A) current can be determined by the structure of leptons and quarks and the anomalous weak current can be very small. In particular, it can approach zero, if the wave function of leptons (or quarks) has aspinor structure (I-P/m_f)F.     

Dynamical symmetry breaking as the origin of the pomeranchuk singularity

We consider the viewpoint that Reggeons are built out of Reggeized quarks and that an O(2) symmetry between two kinds of quarks (“heavy” and “light”) is dynamically broken by their interaction. The Goldstone boson thus generated is associated with the Pomeron, and it is argued that it naturally has a smaller slope than the other Reggeons which are ordinary bound states of the quarks.     

Top quark production from black holes at the CERN LHC

LHC is expected to be a top quark factory. If the fundamental Planck scale is near a TeV, then we also expect the top quarks to be produced from black holes via Hawking radiation. In this Letter we calculate the cross sections for top quark production from black holes at the LHC and compare it with the direct top quark cross section via parton fusion processes at next-to-next-to-leading order (NNLO). We find that the top quark production from black holes can be larger or smaller than the pQCD predictions at NNLO depending upon the Planck mass and black hole mass. Hence the observation of very high rates for massive particle production (top quarks, Higgs or supersymmetry) at the LHC may be an useful signature for black hole production.     

Books received

This article is a colloquium-level review of the idea of supersymmetry and why so many physicists expect it to soon be a major discovery in particle physics. Supersymmetry is the hypothesis, for which there is indirect evidence, that the underlying laws of nature are symmetric between matter particles (fermions) such as electrons and quarks, and force particles (bosons) such as photons and gluons.     

A dynamical theory for the off-shell continuation of the πN t-matrix: M. J. Reiner. Physics Department,Virginia Polytechnic Institute and State University,Blacksburg, Virginia 24061 and Department of Physics and Astronomy,University of Rochester,Rochester, New York 14627

First-order gluon radiative corrections to the rate of weak decay of a quark into three quarks are calculated taking full account of all the masses involved. Using dimensional regularization techniques, the infrared divergences inherent to the problem cancel out, and the finite parts in convenient analytic forms which tend to the correct zero-mass limits are obtained. The total correction to the decay rate always exceeds its (negative) zero-mass limit and changes sign as the masses increase. Thus, except for small mass values, it is positive and acts in a direction opposite to that expected when the masses vanish.     

Relativistic many-body theory,quantum chromodynamics and neutron stars/supernova

A systematic account of relativistic many-body theory is presented with particular emphasis on the renormalization of finite temperature and density Green's functions and the thermodynamic potential. This is then applied to Quantum Chromodynamics (QCD), the non-Abelian gauge theory of the strong interaction (quarks and gluons), to demonstrate the applicability of perturbation theory of the strong force at high baryon number densities. For an accepted range of the elementary particle parameters, the quark mass and the quark-gluon structure constant, it is shown that QCD determines the major characteristics of heavy mass neutron stars and predicts two supernova mechanisms: hydrodynamic bounce and hyperonization.     

ON THE RADIATIVE DECAY OF HEAVY VECTOR MESON INTO HIGGS PARTICLE

An estimation of the contribution from the vector meson intermediate state to the width of radiative decay of a heavy vector meson composed of heavy quarks into Higgs particle is given. Under some approximation,it. exhibits a value four times larger than that obtained by using free quark picture. The implication of this result for interpreting ξ(2.2) as Higgs scalar is also discussed.