Formation and decay of scalar Leptoquarks/Squarks in ep collisions

The cross sections for the formation of scalar resonances, leptoquarks or squarks, in electron/positron-proton collisions at HERA are presented, including next-to-leading order QCD corrections. Depending mildly on the mass of the resonances, the K-factors increase the production cross sections by up to 30% if the target quarks are valence quarks. The QCD corrections to the partial decay widths of leptoquarks/ squarks to leptons and quarks are small. The electron spectrum in the decays is nevertheless softened by perturbative gluon radiation at a level of 2 GeV for a leptoquark/ squark mass of 200 GeV.     

Modular conformal scaling group evidenced in lepton-quark mass

Lepton-quark mass may reflect a correspondence in spacetime structure described by a modular conformal scaling group. Stemming in part from a spacetime line element correspondenceds → (expλ _n)ds in which the eight quantitiesλ ₀,λ ₁, ...,λ ₇ constitute a closed set under a modular addition, the associated formula for lepton-quark mass (yielding values at the 1 GeV scale for the leptons and lighter quarks and at the physical pole for the top) is conjectured to bem=m _fQ²(exp −λ _n), wherem _f=10.245 TeV is the progenitor fermion mass,Q is the charge number of the lepton or quark, and the modular group parameterλ _n is indexed by a fermion principal quantum numbern that depends on three mutually independent projection operators.     

Constraints on the First Generation Scalar Leptoquarks

Inspired by the CMS excess in eejj and evjj channels and possible interpretation using the first generation scalar leptoquarks(SLQs),we consider their contributions to non-standard neutrino interaction and the pion meson Ieptonic decay π→lv.Compared with the relevant experimental data,the constraints on the Brst generation SLQs are obtained.Their corrections to the anomalous magnetic moment a_μ are further calculated and the numerical results show that it is possible to explain the deviation from its standard model prediction.     

Leptoquarks and vector-like strong interactions at the TeV scale

In a vector-like extension of the minimal standard model with mirror fermions leptoquarks can be bound states of fermion-mirror-fermion pairs held together by a new strong interaction at the TeV scale. The small couplings of leptoquarks to light fermion pairs arise due to mixing. The large Q² event excess at HERA and also the high E_T jet excess at Tevatron can potentially be explained.     

Restrictions on the Masses of Scalar Leptoquarks in the Four-Color Model

Physics of Particles and Nuclei Letters - It is shown that, in the framework of four-color symmetry, the restrictions on the masses of scalar leptoquarks are much smaller than those of vector...     

Global lepton-quark neutral current constraint on low scale gravity model

We perform a global analysis of the lepton-quark neutral current data on the low scale gravity model, which arises from the extra dimensions. The global data include HERA neutral current deep-inelastic scattering, Drell-Yan production at the Tevatron, and fermion pair production at LEPII. The Drell-Yan production, due to the large invariant mass data, provides the strongest constraint. Combining all data, the effective Planck scale must be larger than about 1.12 TeV for n=3 and 0.94 TeV for n=4 at 95%CL.     

Multiparton collisions and multiplicity distribution in high-energy collisions

We discuss the multiplicity distribution for the highest accessible energies of pp- and -interactions from the point of view of multiparton collisions. The inelastic cross sections for single, σ₁, and multiple (double and, presumably, triple), σ₂ parton collisions are calculated from the analysis of experimental data on the multiplicity distribution up to Tevatron energies. It is found that σ₁ becomes energy independent while σ₂ increases with for GeV. The observed growth of p with multiplicity is attributed to the increasing role of multiparton collisions for the high-energy -inelastic interactions. σ₂₊₃ reproduces quite well the cross-section for the mini-jet production.     

Entropy in nuclear collisions

Data on the multiplicity of pions produced in nucleon-nucleon interactions and central collisions of identical nuclei are discussed using a statistical approach. It is argued that the suppression of the pion production observed at low energies (p _LAB <15>c per nucleon) is due to entropy transfer to baryons. The enhancement of the entropy production in central S+S collisions at 200 GeV/c per nucleon may be interpreted as manifestation of the increase, by a factor of about 3, of the effective number of degrees of freedom in the early stage of the collision.     

Chemi-ionization in K-I collisions

Accurate partial and integral cross sections for chemi-ionization have been calculated for a two-state model representing collisions between ground state K and I atoms from threshold to 6 eV relative energy using a coupled equations method. In addition, these quantities have been calculated in the Landau-Zener and Stueckelberg approximations. They furnish results for the charge transfer channel which agree with the accurate ones, down to the threshold energy, to within 7%. The integral cross sections for charge neutralization are obtained from the ionization cross sections by microscopic reversibility, and it diverges asE ^?1.     

Bremsstrahlung in nucleon-nucleon collisions

The theory of bremsstrahlung in nucleon-nucleon collisions at non-relativistic energies is reviewed, with special emphasis on the possibility of drawing conclusions concerning the nucleon-nucleon interaction. The basic concepts are introduced in section 2, and illustrated in section 3 for the case of a separable interaction. Soft-photon theorems are discussed in section 4. Section 5 contains some brief comments on the comparison between theory and experiment. The theory needs a number of correction terms, which are discussed in section 6. A generalized Ward identity for bremsstrahlung, which relates the divergence of the contribution from internal lines to off-shell scattering amplitudes is also given.     

高能重离子碰撞中的参与者数和核子-核子碰撞数

采用核-核碰撞的Glauber模型, 给出了高能重离子碰撞中的参与者数和核子-核子碰撞数随碰撞参数的分布方程, 并用其讨论了\{s_NN\}^1/2=200GeV的Au+Au碰撞中的参与者数与核子-核子碰撞数随对心度的变化关系, 所得结果与PHENIX合作组所给出的实验结果符合得很好. 关键词： Glauber 模型 参与者数 核子-核子碰撞数     

Atomic collisions in semiconductors

Abstract

Energetic particle bombardment of semi-conductors (Si and GaAs) is studied by means of Molecular Dynamics simulations using many-body potentials. The simulations show that the diamond lattice structures can lead to the trajectories of particles within the crystal being channelled even at low energies. Some results concerning damage production, low energy implantation profiles and angular distributions of ejected particles are presented.     

Bremsstrahlung in heavy-ion collisions

The bremsstrahlung background emission of γ-rays in equal-mass heavy-ion collisions is calculated. The cross section is found to be about an order of magnitude smaller than preliminary upper limits of ¹²C-¹²C experiments in progress.     

Multiscaling in inelastic collisions

We study relaxation properties of two-body collisions on the mean-field level. We show that this process exhibits multiscaling asymptotic behavior as the underlying distribution is characterized by an infinite set of nontrivial exponents. These nonequilibrium relaxation characteristics are found to be closely related to the steady state properties of the system.     

Hydrogen-antihydrogen collisions

Matter-antimatter interactions are investigated using hydrogen-antihydrogen collisions as an example. Cross sections for elastic scattering and for the antihydrogen loss (either through the rearrangement reaction, resulting in formation of protonium and positronium according to H+&Hmacr;-->p&pmacr;+e(+)e(-), or via annihilation in flight) are calculated for the first time in a fully quantum mechanical approach. Implications for experiments intending to trap and cool antihydrogen are discussed.