q\bar q pair creation in a flux tube with confinement

We calculate the effect of radial confinement on the Schwinger pair production rate by solving the Dirac equation in a flux-tube cylinder containing a constant chromoelectric field in the longitudinal direction. We show how the Dirac equation separates into radial and longitudinal equations for a mass term which has an arbitrary radial dependence and introduce radial confinement by having a finite mass inside the cylinder and an infinitely large mass outside. The resulting boundary conditions are equivalent to the MIT boundary condition. The equations are solved analytically for a constant quark mass inside the flux-tube, which acts like a waveguide. The discretization of the transverse wave vector which has a continuous spectrum in the non-confined case leads to a large suppression of the Schwinger pair-production rate for small radii. The minimal radius where pairs are created decreases with increasing field strength. The suppression turns out to be larger for heavier quarks than for light quarks.     

QCD radiative corrections to the decayW \to q\bar q\gamma

The complete order α _s QCD corrections to the rate and the Dalitz plot for \(W \to q\bar q\gamma \) are presented. We discuss how these corrections modify the factorization property of the lowest order decay rate.     

Complete mass spectra ofq\bar q andQ\bar q mesons with improved Bethe-Salpeter dynamics of confinementmesons with improved Bethe-Salpeter dynamics of confinement

The Bethe-Salpeter (bs) dynamics of harmonic confinement developed byanm and collaborators over the last three years and already applied with considerable experimental success to various hadron spectra and coupling structures has been significantly improved through (i) a more exact treatment of a certain momentum-dependent operator \(\hat Q_q \) appearing in thebs equation, using the techniques of SO (2, 1) Lie algebra, and (ii) a sharpened definition of theqcd Coulomb term, so as to yield unambiguous values for different flavour sectors. The resulting mass spectra of light \((q\bar q)\) meson towers and semi-heavy \((Q\bar q)\) quarkonia which are most sensitive to the improved treatment of \(\hat Q_q \) , reveal excellent agreement with experiment, one in which only slight changes in the reduced spring constant \((\tilde \omega )\) and quark masses (m _q ) over the earlier parametrizations are involved. These changes are however found to have a negligible effect on the (already good) numerical values of the other predictions (electroweak and pionic couplings) depending on the \(q\bar q\) andqqq wave functions. A critical assessment of the strong and weak points of this method is madevis-a-vis other related approaches.     

Dynamics of confinement and chiral symmetry breaking in the heavy-light q\bar Q system

At large N _c , the gauge-invariant Green's function of the heavy-light $q\bar Q$ system satisfies a nonlinear nonlocal equation, which is studied in detail. Chiral-symmetry breaking reveals itself through the appearance of scalar confinement at large distances. Equations for partial waves are written explicitly with perturbative Coulomb interaction taken into account, and the structure of the interaction kernel is studied semiclassically.     

Understanding the scalar mesonq\bar q nonet

It is shown that one can fit the available data on thea _o(980),f _o(1300) andK _o ^* (1430) mesons as a distorted 0⁺⁺ nonet using very few (5–6) parameters and an improved version of the unitarized quark model. This includes all light two-pseudoscalar thresholds, constraints from Adler zeroes, flavour symmetric couplings, unitarity and physically acceptable analyticity. The parameters include a bare or mass, an over-all coupling constant, a cutoff and a strange quark mass of 100 MeV, which is in accord with expectations from the quark model. It is found that in particular for thea ₀(980) andf ₀(980) the component, in the wave function is large, i.e., for a large fraction of the time the state is transformed into a virtual pair. This component, together with a similar component of for thea ₀(980), and , and components for thef ₀(980), causes the substantial shift to a lower mass than what is naively expected from the component alone. Mass, width and mixing parameters, including sheet and pole positions, of the four resonances are given, with a detailed pedagogical discussion of their meaning.     

Evidence for non-q \bar q mesons

The non-Abelian nature of QCD suggests that particles that have a gluon constituent, such as glueballs or hybrids, should exist. In addition,q q states are also predicted. This paper describes a search for these non-q q mesons performed by experiment WA 76 using the CERN Omega Spectrometer and discusses three candidates which have been observed.Invited talk at HEXAM 89, Bechyn Castle, Czechoslovakia, June 25–30, 1989.     

A method to compare quark and gluon jets in $$e^ + e^ - \to q\bar qg$$ hadronisation

The conserved charges of non-abelian gauge theories are systematically investigated in the framework of the manifestly-covariant canonical formalism. An internal-symmetry superalgebra consisting of 4n+5 generators is found in the Landaugauge case of the Yang-Mills theory, wheren denotes the dimension of the gauge group. Likewise, a superalgebra consisting of 4×6+5 generators is found in the internal-Lorentz (local-Lorentz) part of the vierbein formalism of quantum gravity. It is pointed out that there is a complete parallelism between both superalgebras.     

Systematic shifts in jet energy scale from the process W \to q\bar q in CMS detector

The absolute scale of jet energy set in a CMS experiment using the W mass constraint in $t\bar t$ events with $W \to q\bar q$ decay is studied. The main effects leading to systematic shifts in the jet-energy scale are identified. Estimations of these shifts are given.     

A study of the high-energy reaction\bar PP \to \bar PP

The high-energy behavior of the reaction atP _L =8 GeV/c andP _L =16 GeV/c is studied in the context of O(3,1) symmetry. In view of the many exchanged particles, approximate equivalence relations ins-channel amplitudes are used which cut down the unknown parameters to a manageable set of adjustable constants. Our analysis has essentially explained the characteristic features of this reaction, which are (i) the ending of the forward peak at |t| 0.6 (GeV/c)²; (ii) developing of a shoulder at larger |t|'s; and (iii) decreasing of the differential cross section at the shoulder for 16 GeV/c at a slower rate than 8 GeV/c.On leave of absence from Department of Physics, University of Azarabadgan, Tabriz, Iran.     

Partial wave analysis of $\bar pp \to \bar \Lambda \Lambda$

A partial wave analysis of PS185 data for is presented. A ³ S ₁ cusp is identified in the inverse process at threshold, using detailed balance to deduce cross sections from . Partial wave amplitudes for ³ P ₀, ³ F ₃, ³ D ₃ and ³ G ₃ exhibit a behaviour very similar to resonances observed in Crystal Barrel data. With this identification, the data then provide evidence for a new I = 0, J ^PC = 1^- resonance with mass MeV, MeV, coupling to both ³ S ₁ and ³ D ₁.Received: 4 June 2004, Published online: 9 July 2004     

(Q\bar{q}) \to \ell \widetilde{v} _\ell decay constant in the covariant simultaneous approach

In the framework of the covariant simultaneous approach in quantum field theory, an expression is obtained for the decay constant of the decay bound state of quark and antiquark of different masses into a lepton pair.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 101–103, February, 1992.     

Proton spectrum from\bar pd \to 5\pi p at rest and the elementary\bar pnannihilation

We calculate the shape of the proton spectator distribution in \(\bar pd \to 5\pi p\) at low proton momenta. The sensitivity to atomicS- andP-state orbits and to the size of elementarys- andp-wave annihilation is discussed. Implications for the elementary annihilation amplitude \(\bar pn \to 5\pi \) subthreshold are presented.     

Z \to b\bar b andZ \to c\bar c as tests of the Standard Modelas tests of the Standard Model

We consider the decays $Z \to b\bar b$ and $Z \to c\bar c$ as tests of the Standard Model (SM). We find thatR _b =0.2141 andR _c =0.1719. Comparing with recent experimental measurements, we find thatR _b ^exp is too high by 3.9σ andR _c ^exp is too low by 2.4σ.     

\bar v_e + d \to \bar v_e + n + pat reactor energies

The deuteron disintegration process \(\bar v_e + d \to \bar v_e + n + p\) is calculated at reactor energies using the antineutrino spectra given by various authors. Numerical results are presented and compared with the experimental and other theoretical results.     

q$$ \bar q $$ pair production in non-Abelian gauge fields

We calculate the q pair production probability in the colour-flux tube model by considering the effect of non-Abelian interactions in the theory. Non-Abelian interactions in the colour field are time-dependent and hence should oscillate with a characteristic frequency ω ₀, which depends on the amplitude of the field strength. Using the WKB approximation in complex time, we calculated the pair production probability. When the strength of the field is comparable to the quark masses, the corresponding pair creation probability is maximum, and for the static field ω ₀ → 0, we recovered the well-known Schwinger result.      

The process\pi ^0 \to \lambda _\gamma \bar \lambda _\gamma as an alternative to\pi ^0 \to v\bar v

The process \(\pi ^0 \to \lambda _\gamma \bar \lambda _\gamma \) is investigated as an alternative to \(\pi ^0 \to v\bar v\) . It is shown that the experimental bound on the branching fraction for missing energy (in the form of \(\lambda _\gamma \bar \lambda _\gamma \) and/or \(v\bar v\) ) may be understood in terms of \(\pi ^0 \to \lambda _\gamma \bar \lambda _\gamma \) for the kinematically allowed photino mass, if the squark mass is >8 GeV.     

Quark masses in a BCS-like approach usingQ\bar Q potentials

Using a BCS like equation we have computed constituent quark masses as a function of a parameterC. This parameter is a measure of the effective strength of the interaction for off-the-mass-shell, localised \(q\bar q\) pairs and is given byC=R/E, whereE is the energy required to separate the pair to a distanceR. Several phenomenological flavour independent \(q\bar q\) potentials and correlation functions yield results similar in nature. Predictions for distribution functions of intrinsic sea quarks have been made.