Estimates of B-decays into K-resonances and dileptons

Short and long distance contributions to the exclusive B-decays into various K-resonances and dileptons, i.e. $B \to K^i \ell \bar \ell (\ell = e,\mu ,\nu )$ , are examined. The heavy quark effective theory has been used to calculate the hadronic matrix elements. Substantial branching fractions are obtained for the dileptonic B-decays into some higher excited states of K-mesons. The long distance (resonance) contributions to these exclusive rare B-decay modes dominate the short distance contributions mostly by two orders of magnitude. It is pointed out that, excluding the resonance contributions, the P-wave channels are dominant, accounting for about 50% of the inclusiveB→X _s ? ⁺ ? ^? branching fraction.     

Equal-sign dileptons and heavy-quark detection

The production of the t-quark should be associated with a large rate of equal-sign lepton pairs. We estimate the (single and double) angular distributions of events weighted by powers of the leptonic energies, in e⁺e^? → ?⁺?⁺ (?^??^?) … . These quantities provide interesting information on heavy-quark decay and fragmentation in a transparent way.     

Angular distribution of dileptons in hadronic collisions

The polar and azimuthal angular distributions of the lepton pair produced in hadron-hadron collisions are studied. For large Q_T these are calculated from lowest-order QCD diagrams. For low Q_T we present simple expressions which take into account the effect of primordial quark transverse momentum on the angular distributions.     

Chiral symmetry and dileptons in heavy ion collisions

The cross section in terms of three independent radiative gluon correction form factors related to angular dependence and angular asymmetry is calculated as functions of the maximum recorded scaled gluon momentumX _g, with 0X _g 1. The effects of longitudinal and transversal polarization of the initial electron and positron are taken into account. For the same geometry the two independent thrust form factors are obtained as functions of the minimum thrustT _m recorded, with 2/3T _m <1. similarly=" the=" related=" invariant=" mass=" form=" factors=" are=" obtained.=" in=" particular,=" the=" regions=" of=" infrared="> , and of near infrared gluons, , are discussed.     

Radiative and semileptonic B decays involving higher K-resonances in the final states

We study the radiative and semileptonic B decays involving a spin-J resonant $K_{J}^{(*)}$ with parity (?1) ^J for $K_{J}^{*}$ and (?1) ^J+1 for K _J in the final state. Using large energy effective theory (LEET) techniques, we formulate $B\to K_{J}^{(*)}$ transition form factors in the large recoil region in terms of two independent LEET functions $\zeta_{\perp}^{K_{J}^{(*)}}$ and $\zeta_{\parallel}^{K_{J}^{(*)}}$ , the values of which at zero momentum transfer are estimated in the BSW model. According to the QCD counting rules, $\zeta_{\perp,\parallel}^{K_{J}^{(*)}}$ exhibit a dipole dependence in q ². We predict the decay rates for $B\to K_{J}^{(*)}\gamma$ , $B\to K_{J}^{(*)}\ell^{+}\ell^{-}$ and $B\to K_{J}^{(*)}\nu \bar{\nu}$ . The branching fractions for these decays with higher K-resonances in the final state are suppressed due to the smaller phase spaces and the smaller values of $\zeta^{K_{J}^{(*)}}_{\perp,\parallel}$ . Furthermore, if the spin of $K_{J}^{(*)}$ becomes larger, the branching fractions will be further suppressed due to the smaller Clebsch–Gordan coefficients defined by the polarization tensors of the $K_{J}^{(*)}$ . We also calculate the forward–backward asymmetry of the $B\to K_{J}^{(*)}\ell^{+}\ell^{-}$ decay, for which the zero is highly insensitive to the K-resonances in the LEET parametrization.     

Rescattering production of dileptons in nucleus-nucleus collisions

We present a space-time formulation for the rescattering of hard partons produced in primary QCD subcollisions within a nucleus-nucleus collision. As an application we calculate the rescattering rate for dilepton production in 100 GeV/A+100 GeV/A uranium-uranium collisions.     

Quark-lepton contact interactions and high-mass isolated dileptons at LHC

Zeitschrift für Physik C Particles and Fields - Quark-lepton effective contact interactions at large scales can be probed by theshape of the isolated dilepton invariant-mass distribution at...     

Resolution of two charm puzzles: Hadroproduction and neutrino-induced same-sign dileptons

The ambiguities are studied in leading-order QCD calculations of charm hadroproduction and neutrino-induced same-sign dimuons and the popular belief is questioned that these processes constitute a challenge to the standard model.     

Thermal dileptons from quark and hadron phases of an expanding fireball

A fireball model with time evolution based on transport calculations is used to examine the dilepton emission rate of an ultra-relativistic heavy-ion collision. A transition from hadronic matter to a quark-gluon plasma at a critical temperature T _C between 130-170 MeV is assumed. We also consider a possible mixed phase scenario. We include thermal corrections to the hadronic spectra below T _C and use perturbation theory above T _C. The sensitivity of the spectra with respect to the freeze-out temperature, the initial fireball temperature and the critical temperature is investigated. Received: 4 August 2000 / Accepted: 14 November 2000     

The production of soft dileptons in the quark-gluon plasma in resummed perturbation theory

The production rate of soft dileptons in a quarkgluon plasma is calculated for the general case where the intermediate virtual photons have non-zero momenta using Braaten-Pisarski resummed perturbation theory. It is found that the physics is more complicated and the structures are somewhat richer than the special case where the photons produced are stationary in the plasma. These structures are found to be determined, to a large extent, by the dispersion relations of the two propagating modes of the soft quarks. However, the Van Hove singularities present in the zero-momentum case are no longer there. The dependence of the rate on the total momentum of the dilepton pairs is not very strong, unless the photon mass shell is approached. Comparison with the results obtained from the one loop calculation shows that the resummed perturbation theory predicts more dileptons being produced from the plasma when the intermediate virtual photons are near their mass shell.     

Evidence for radial flow of thermal dileptons in high-energy nuclear collisions

The NA60 experiment at the CERN SPS has studied low-mass dimuon production in 158A GeV In-In collisions. An excess of pairs above the known meson decays has been reported before. We now present precision results on the associated transverse momentum spectra. The slope parameter Teff extracted from the spectra rises with dimuon mass up to the rho, followed by a sudden decline above. While the initial rise is consistent with the expectations for radial flow of a hadronic decay source, the decline signals a transition to an emission source with much smaller flow. This may well represent the first direct evidence for thermal radiation of partonic origin in nuclear collisions.     

膨胀的热夸克胶子物质的中等质量双轻子的增强

基于一个描述夸克胶子火柱演化的相对论流体力学模型,研究了夸克相、强子相互作用以及非热过程(DrellYan对、粲强子衰变)的中等质量双轻子的产生.发现由于相边对夸克胶子物质演化的影响和RHIC能量核碰撞产生的夸克胶子物质具有高的初始温度,夸克相对双轻子的贡献显著增强,比那些来自强子相互作用的贡献重要,甚至能与来自非热的贡献比较.表明中等质量双轻子的增强是一个在核碰撞中产生了夸克胶子物质的可能信号. 关键词： 夸克-胶子物质 双轻子增强 相对论流体力学模型     

The effects of interactions between photon and the quark-gluon plasma on production of soft dileptons

We investigate the effects of interactions of the intermediate photons with the quark-gluon plasma on dilepton productions. The singular behaviour at the photon mass shell in the case of free photon is removed by the interactions. Instead, we find double resonance peaks near the photon mass shell due to the transverse and longitudinal modes. The effects of interactions further away fromM ²=0 is negligible and the photons effectively propagate as free particles in the plasma. The result of resummation is the enhancement of dilepton production rate, except in an extremely narrow region around each resonance peak, where its effect is to reduce the peak. The net result is more dilepton pairs come out of the plasma than in the one loop case. Both enhancement and reduction are partly due to Landau damping. Whereas the former is true over most range of the energy-momentum of the photon and is particularly prominent in region close to but not too close to the resonance peaks, the latter is effectively only true at the peaks.