Mass spectra of higher states of quarkonia and decays for scalar-vector confining interaction

Recently, we have studied a flavour-independent potential for quark-antiquark systems of equal and unequal masses in which the confining interaction is scalar-vector admixture with dominant scalar interaction and the spin-dependent part of the potential has been obtained from the non-relativistic reduction of the Bethe-Salpeter kernel. This potential was found to explain the heavy-quark data well. In the present work we have obtained further affirmative tests of the model by calculating the mass spectra of higher levels as well as the confining contribution of the spin-orbit forces forL1 states of quarkonia. We have considered the annihilation processes and radiative transitions too. The former include leptonic decay, two-photon decay, two-gluon annihilation, three-photon decay and three-gluon annihilations.     

Can the Higgs be seen in rapidity gap events at the Tevatron or the LHC?

Double diffractive Higgs production at pp (or ) colliders continues to attract attention as a potential signal in the search for the boson. We present improved perturbative QCD estimates of the event rates for both the exclusive and inclusive double diffractive Higgs processes, paying particular attention to the survival probability of the rapidity gaps. We find that the major uncertainty is in the prediction for the survival probability associated with soft rescattering. We show that an analogous process, the double diffractive production of a pair of jets with large values of , has an event rate which makes it accessible at the Tevatron. Observation of this process can therefore be used as a luminosity monitor for two-gluon exchange processes, such as the production of a Higgs boson with rapidity gaps on either side. Received: 8 February 2000 / Published online: 14 April 2000     

Timelike and spacelike QCD characteristics of the e^+e^- annihilation process

We consider the Adler D-function, which is defined in the spacelike region, and the annihilation ratio smeared, according to the Poggio, Quinn, and Weinberg method, which is determined for timelike argument. We show that the method of the nonperturbative a-expansion allows one to describe these Euclidean and Minkowskian characteristics of the process of annihilation down to the lowest energy scales. Received: 23 November 1999 / Published online: 6 March 2000     

Temperature Dependence of Two- and Three-Gluon Condensates in the Instanton Vacuum

The two-gluon and three-gluon condensates at finite temperature are calculated in the framework of the grand partition function for a weak-interacting instanton medium of a disordered phase. The interference parts of both chromomagnetic and chromoelectric two-gluon condensates are found to be small but still significant for a quantitative determination of the value of the condensates at very low temperature, and negligible at the temperature above 1.5Λ_MS, with respect to their non-interference ones. The interference parts of the threegluon condensates are found to be quite small even at very low temperature. With the QCD scale parameter fixed by the value of the Lorentz invariant two-gluon condensate at zero temperature, the value of the three-gluon condensate at zero temperature is found to be coincident with the phenomenological estimate. The values of the gluon condensates decrease when temperature increases, and are negligible when the temperature goes beyond 2.5Λ_MS in the case of the SU_C(3) pure gauge theory.     

Hadroproduction of heavy quark flavors in QCD

Within the framework of perturbative QCD, we investigate the hadroproduction of charmed particles via two-gluon as well as quark-pair annihilation. The total production cross section is found to be sensitive to the choice of the scale parameter Q² and in general not free from non-perturbative effects. Charmed-particle production in the high-p_T region is also studied.     

Gluon jet-like structure in the upsilon decay

The properties of hadronic jets in e⁺ e^– annihilation in quantum chromodynamics have been studied. Motivated by the observation of the hadronic jets (arising from quark jets), the partial cross sections from the two-gluon jet-like events are calculated perturbatively. Estimates for the jet angular radius and its energy dependence are discussed.The author would like to thank Dr. Mubarak Ahmad for his guidance and encouragement.     

The generalised vector dominance/colour-dipole picture of deep-inelastic scattering at low x

We give a detailed account of the recently formulated generalised vector dominance/colour-dipole picture (GVD/CDP) of deep-inelastic scattering at low , including photoproduction. The approach, based on transitions, propagation and diffractive scattering via the generic structure of the two-gluon exchange, provides a unique and quantitatively successful theory for the total cross section, , at low x. The GVD/CDP is shown to imply the empirical low-x scaling law, with , that was established by a model-independent analysis of the experimental data. Received: 16 February 2001 / Published online: 3 May 2001     

Four pion final states with tagged photons at electron positron colliders

A Monte Carlo generator has been constructed to simulate the reaction , where the photon is assumed to be observed in the detector. Only initial state radiation is considered. Additional collinear photon radiation has been incorporated with the technique of structure functions. Predictions are presented for CMS energies of 1 GeV, 3 GeV and 10 GeV, corresponding to the energies of DANE, BEBC and of B-meson factories. The event rates are sufficiently high to allow for a precise measurement of in the region of Q between approximately 1 GeV and 2.5 GeV. For the construction of the program we employ isospin relations between the amplitudes governing decays into four pions and electron positron annihilation into four pions. Estimates of the kinematic breaking of these isospin relations as a consequence of the – mass difference are given. Received: 29 August 2000 / Revised version: 17 November 2000 / Published online: 21 December 2000     

Vector meson photoproduction at high-<Emphasis Type="Italic">t</Emphasis> and comparison to HERA data

We explore QCD calculations for the process where V is a vector meson, in the region and . We compare our calculations for the , and mesons with data from the ZEUS Collaboration at HERA and demonstrate that the BFKL approach is consistent with the data even for light mesons, whereas the two-gluon exchange approach is inadequate. We also predict the differential cross-sections for the and for which no data are currently available. Received: 23 May 2002 / Published online: 9 December 2002     

Transverse spin effects in diffractive hadron leptoproduction

We consider double spin asymmetries for longitudinally polarized leptons and transversely polarized protons in diffractive vector meson and production at high energies within the two-gluon model. The connection of the two-gluon approach with skewed gluon distributions is discussed. The asymmetry predicted for meson production is quite small. The asymmetry for production contains two independent terms which are large and can be used to obtain information on the polarized skewed gluon distributions in the proton. Received: 19 February 2002 / Revised version: 19 March 2002 / Published online: 22 May 2002     

Dilepton production from ρ-mesons in a quark-gluon plasma

Assuming that ρ-mesons exist in a quark-gluon plasma at temperatures close to the QCD phase transition, we calculate the dilepton production rate from q-ˉq annihilation via a ρ-meson state using Vector Meson Dominance. The result is compared to the rates from direct q-ˉq annihilation and from π⁺-π⁻ annihilation. Furthermore we discuss the suppression of low mass dileptons if the quarks assume an effective mass in the quark-gluon plasma. Received: 8 September 1999 / Revised version: 22 October 1999     

Nonperturbative corrections of quark and gluon condensates to QCD inspired quark potentials

We adopt the Lorentz gauge to derive the non-local two-gluon vacuum expectation value (VEV) with translational invariance. By means of the obtained non-local two-gluon VEV, the leading nonperturbative QCD corrections to one gluon exchange quark-quark, quark-antiquark and pair-excitation potentials are given by employing non-vanishing vacuum condensates of quarks and gluons to modify the free gluon propagator. The linear, cubic and Yukawa-type terms in quark-quark potential appear automatically. In the pair-excitation potential with , the linear, square and cubic terms arise from the nonzero quark and gluon condensates. Received: 22 June 1998 / Revised version: 10 August 1998 / Published online: 29 October 1998     

Spin dependence of deep inelastic diffraction

Using a perturbative model for diffractive interactions, we derive an expression for the polarized diffractive structure function in the high energy limit. This structure function is given by the interference of diffractive amplitudes with polarized and unpolarized exchanges. For the polarized exchange we consider both two-gluon and quark-antiquark amplitudes. The polarized diffractive amplitude receives sizable contributions from non-strongly ordered regions in phase space, resulting in a double logarithmic enhancement at small x. The resummation of these double logarithmic terms is outlined. We also discuss the transition from our perturbative expression to the nonperturbative region. A first numerical estimate indicates that the perturbative contribution to the spin asymmetry is substantially larger than the nonperturbative one. Received: 7 July 1999 / Published online: 14 October 1999     

Cosmic rays through the Higgs portal

We consider electroweak singlet dark matter with a mass comparable to the Higgs mass. The singlet is assumed to couple to standard matter through a perturbative coupling to the Higgs particle. The annihilation of a singlet in the mass range m_Sm_h is dominated by proximity to the W, Z and Higgs peaks in the annihilation cross section. We find that the continuous photon spectrum from annihilation of perturbatively coupled singlets in the galactic halo can reach a level of several per mil of the EGRET diffuse γ ray flux.     

Collisional quenching of ¯pHe+ metastable states

Collisions of metastable ¯pHe⁺ with He atoms are considered by multichannel semiclassical theory. Strong dependence of Stark transitions on both the energy-level splitting inl and collision velocity results in the separation of metastable states into two groups: long-lived and short-lived with respect to collisional quenching. An essential enhancement of delayed annihilation would be expected in a very rarefied target (p 1 Torr).     

Positron annihilation study on nanometer cavities in porous silicon

Measurements were carried out on the positron lifetime and the Doppler broadening of its annihilation radiation in porous silicon. A very long lifetime of a few tens of nanoseconds was found. TheS parameter increased upon annealing in vacuum at 350 °C. It is pointed out that positron/positronium spectroscopy is very useful for the study of physical and chemical properties of porous silicon.     

Charmonium production from secondary collisions at LHC energy

We consider the charmonium production in the thermalized hadronic medium created in ultrarelativistic heavy ion collisions at LHC energy. The calculations for secondary and production by annihilation are performed within a kinetic model taking into account the space-time evolution of a longitudinally and transversely expanding medium. We show that secondary charmonium production appears almost entirely during the mixed phase, and that it is very sensitive to the charmonium dissociation cross section with co-moving hadrons. Within the most likely scenario for the dissociation cross section of the mesons their regeneration in the hadronic medium will be negligible. The secondary production of mesons however, due to their large cross section above the threshold, can substantially exceed the primary yield. Received: 3 January 2000 / Published online: 6 July 2000     

The use of QCD in hadronic cascades between heavy quark-antiquark bound states

We argue that a perturbative calculation of the spectra and rates of hadronic transitions between heavy quark-antiquark bound states makes sense within QCD provided suitable spin-parity projections are performed. Applications are made to various kinds of cascades. We obtain the correct ψ′ → J/ψππ mass spectrum. The cascades involving the emission of at least three gluons appear very strongly suppressed as compared to those allowing two-gluon emission. Application to the ? family is made.     

SU(3) analysis of annihilation contributions and CP violating relations in B\to P P decays

Several methods proposed to measure the angle in the KM unitarity triangle assumed that the tree contribution to is purely due to annihilation contributions and is negligibly small. This assumption has to be tested in order to have a correct interpretation of the experimental data. In this paper we show that using SU(3) symmetry, the smallness of the tree contribution can be tested in a dynamic model-independent way. We also derive several relations between CP violating rate differences for decays without assuming the smallness of the annihilation contributions. These relations provide important tests for the standard model of CP violation. Received: 5 January 1999 / Revised version: 4 March 1999 / Published online: 18 June 1999     

B→ηlν decays and the flavor-singlet form factors

We study semileptonic decays B→η^(′)lν, taking into account the flavor-singlet contribution (F^singlet₊) to the B→η^(′) form factors, which arises from the two-gluon emission in a decaying B meson. It has been recently pointed out that, in addition to large weak annihilation effects, the unknown value of F^singlet₊ prevents accurate theoretical estimates in the analysis of B→η′K decays in QCD factorization. We present a certain method to determine F^singlet₊ with a reasonable accuracy, using B→η^(′)lν and B→πlν decays. We also investigate the possible effect of F^singlet₊ on the estimated branching ratios (BRs) for B→η^(′)lν and find that the BR for B→η′lν is particularly sensitive to the effect of F^singlet₊.