QCD corrections,virtual heavy quark effects and electroweak precision measurements

QCD corrections to virtual heavy quark effects on electroweak parameters are calculated, which may effect planned precision measurements at SLC and LEP. The influence of toponium and T_b resonances is incorporated as well as the proper threshold behaviour of the imaginary part of the vacuum polarization function. The shift of the W-boson mass from these corrections and their influence on the polarization assymetry are calculated and compared to the envisaged experimental precision.     

Radiative corrections with two Higgs doublets at LEP/SLC and HERA

Formulae for the radiative corrections toe ⁺ e ^?→f \(\bar f\) andep→eX,v _e X′ are given for two Higgs doublets inSU(2)×U(1). The magnitude of deviations from the minimal model is discussed for theM _W ?M _Z mass correlation, thee ⁺ e ^? forward-backward and polarization asymmetries and σ(e ⁺ e ^? → hadrons) at LEP/SLC, and for σ(NC)/σ(CC), charge and polarization asymmetries in deep inelasticep scattering at HERA. Precision experiments can restrict the mass splitting between neutral and charged Higgs bosons to ?100 GeV. In the supersymmetric Higgs model the additional corrections remain unobservably small.     

Uncertainties in τ polarization measurement at SLC/LEP and QED/electroweak radiative corrections

We discuss the τ polarization measurement at SLC/LEP energies as a data point in the precision tests of the Glashow-Salam-Weinberg model. Theoretical and experimental uncertainties of this measurement are examined and it is concluded that apart from left-right asymmetry measurement, and for typical values of the parameters of the Standard Model, the τ polarization offers the best probe of the couplings of leptons to the Z⁰. In particular, the dependence of the τ polarization on the top and Higgs masses is discussed. The interplay of QED initial state bremsstrahlung and other classes of radiative corrections is also discussed.     

Model independent constraints on a heavy neutral vector boson from present and future LEP and SLC data

We review the information that is already provided and will be soon provided on the parameters of a new neutral boson of general nature from LEP and SLC experiments. We develop a strategy that associates the general independent lepton and quarkZ couplings to precisely defined experiments. For the specific case of particular popular models (E ₆, left-right symmetry, compositeZ) that we have analyzed, we predict, in case of negative searches, bounds of typical order one percent for theZ mixing angle and one TeV for theZ mass, at the end of the various experimental phases.Unité associée au CNRS n^oURA 768, PM/90-18     

Analysis of t-b-W and t-t-Z couplings from CLEO and LEP/SLC data

We update the constraints on anomalous dimension four t-b-W and t-t-Z couplings by using CLEO b→sγ and LEP/SLC precision Z-pole data. It is found that the data imposes very stringent bounds on them. Moreover, the 2σ pull from SM predictions of A_LR(hadrons), A_b and A_FB(b) have little chance of being explained by the strongly constrained anomalous couplings.     

Plastic scintillation detectors for precision Time-of-Flight measurements of relativistic heavy ions

Plastic scintillation detectors for Time-of-Flight(TOF) measurements are almost essential for event-byevent identification of relativistic rare isotopes. In this work, a pair of plastic scintillation detectors of dimensions50×50×3~t mm~3and 80×100×3~t mm~3have been set up at the External Target Facility(ETF), Institute of Modern Physics(IMP). Their time, energy and position responses are measured with the~(18)O primary beam at 400 Me V/nucleon. After off-line corrections for walk effect and position, the time resolutions of the two detectors are determined to be 27 ps(σ) and 36 ps(σ), respectively. Both detectors have nearly the same energy resolution of3.1%(σ) and position resolution of about 3.4 mm(σ). The detectors have been used successfully in nuclear reaction cross section measurements, and will be be employed for upgrading the RIBLL2 beam line at IMP as well as for the high energy branch at HIAF.     

Dynamical effects on the way to fusion of very heavy nuclei

The central collision of ⁴⁰Ar and ²⁰⁸Pb is studied considering the ellipsoidal deformations and isovector dipole mode of motion in the approaching phase. The collective energy dissipation is suggested to originate from the Fermi surface deformation which is treated as a kinematically independent mode of motion within the canonical Lagrange-Rayleigh dynamics. The possible extensions of the approach are discussed. The potential energy surface, calculated using the generalized (folded) surface potential, is studied. The saddle point in the potential energy surface lying at the border of strongly deformed compact configurations is located. The potential energy at this point is about 10MeV smaller than that of the ions touching each other in the spherical shape. The examination of trajectories followed by the system in its evolution shows that the inertia forces strongly hinder the motion of ions along the potential energy valley. The collective energy dissipated during the approach is found to be smaller than the difference in the potential energies at saddle point and at the touching configuration of unpolarized ions.     

On the precision of calculations of initial state radiation in the LEP Z line-shape fits

Calculation of initial state radiation (ISR) in the fitting program MIZA and in the Standard Model program BHM is improved within the analysis of the Z line-shape measurements at LEP. The uncertainty on the determination of the Z line-shape parameters coming from the precision of ISR calculations is 2×10⁻⁴ on σ₀ and 0.1 MeV on m_Z and Γ_Z.     

Photoproduction of top quarks in peripheral heavy ion collisions

In relativistic heavy ion collisions, top quarks can be produced by photon-gluon fusion when a photon from the Weizs?cker-Williams virtual photon field of one nucleus interacts with a gluon in the other nucleus. Photoproduction with heavy ions at the Large Hadron Collider (LHC) will be the first accessible non-hadronic top production channel. We calculate the photoproduction cross sections, pair mass and top quark rapidity distributions in peripheral lead-lead and oxygen-oxygen collisions. The cross sections are sensitive to the top quark charge and the large- gluon distribution in the nucleus. We find a cross section of 15 pb in oxygen-oxygen collisions, leading to 210 pairs in a one month ( s) LHC run. In pA collisions, the rate is higher, 1100 pairs per month for pO. A comparison of the AA and pA data might allow for a study of gluon shadowing at high Q . Received: 18 May 2001 / Revised version: 13 June 2001 / Published online: 24 August 2001     

原子核质量精密测量的研究进展

原子核质量的精密测量是原子核物理学的重要课题之一,它对探索奇特原子核的结构和性质、重元素核合成之谜等均具有重大意义.文章简要介绍了原子核质量高精度测量的两个主要设备——储存环和潘宁阱,并回顾了近年来原子核质量精密测量在核结构、元素核合成、新同核异能素等领域中的研究亮点,探讨原子核质量测量的发展趋势.