Colour intransparency and the cross sections for colour-singlet and colour-octet hadrons in the Low-Nussinov model

The dependence of cross sections on the colour state of the colliding hadrons is investigated within the Low-Nussinov model of two-gluon exchange. The total cross sections for colour-octet hadrons are practically constant as functions of the hadronic radii, while they tend to zero when the radii of the colour-singlet hadrons approach zero. The slope parameter of the differential clastic cross sections for small momentum transfers is rather insensitive to the colour structure of the colliding hadrons. The integrated colour exchange cross section is calculated.     

Bremsstrahlung produced by colliding particles in an external electric field

We have used the nonrelativistic dipole Born approximation to study bremsstrahlung from two colliding charged particles in a uniform electric field. We have calculated the differential cross sections for photon emission as the system transitions into various states of internal motion. We find the cross sections exhibit spatial anisotropy due to the uniform electric field, and that oscillations can arise that are probably due to interference effects between the colliding particles.Khabarovskii State Pedagogical University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 46–50, July, 1994.     

He与HD、HT、DT碰撞的转动激发研究

采用Tang-Toennies势模型,通过坐标变换,得到了氦原子与氢的非对称同位素替代分子体系在质心坐标系中的势能函数.在此基础上,计算了上述体系的低能碰撞转动激发截面.文中最后讨论了氦原子与氢的非对称同位素替代体系碰撞的微分截面的变化规律     

Using dileptons to probe the color glass condensate

The rapidity and transverse momentum dependence of the nuclear modification ratio for dilepton production at RHIC and LHC is presented, calculated in the color glass condensate (CGC) framework. The transverse momentum ratio is compared for two distinct dilepton mass values and a suppression of the Cronin peak is verified even for large mass. The nuclear modification ratio suppression in the dilepton rapidity spectra, as obtained experimentally for hadrons at RHIC, is verified for LHC energies at large transverse momentum, although not present at RHIC energies. The ratio between LHC and RHIC nuclear modification ratios is evaluated in the CGC, showing the large saturation effects at LHC compared with the RHIC results. These results consolidate the dilepton as a most suitable observable to investigate the QCD high density approaches.     

Ionization of heavy ions in collisions with neutral atoms at relativistic energies

Ionization processes of heavy ions colliding with atoms and ions at relativistic energies are considered. Formulaes for calculating ionization cross sections in the Born approximation using momentum-transfer representation without regard to magnetic interactions are given as well as those in dipole and impulse approximations. Using the LOSS-R [25] and HERION codes, calculations of relativistic cross sections are performed for H-like multiply changed ions with the nuclear charge Z ≈ 80?90, colliding with neutral atoms and for multiply changed uranium ions colliding with protons and carbon atoms. The results of calculations are compared with available experimental data and calculations performed by other authors.     

On the relaxation-time approximation for the two-body dissipation in HI collisions

In several previous publications the author has treated two-body collisions between the nucléons (the two-body dissipation) encountered in heavy-ion collisions by a relaxation-time approximation. This approximation is here tested against the calculations of Danielewicz in which he studied the dynamics of two slabs of nuclear matter (two Fermi spheres in momentum space) colliding with the NN interactions parameterized to fit NN cross sections. The relaxation-time approximation is found to be in good agreement especially with quantum-dynamical calculations.     

中等能量入射的质子,α粒子与氦原子碰撞的电荷转移

将最近引入的渐近两态原子轨道展开方法用来研究双电子碰撞体系H⁺+He和He²⁺+He的电荷转移过程．结果表明,由该方法得到的电子俘获截面在中高能区与满足边界条件的一级波恩近似（即B1B近似）和实验结果符合得很好,并且在中低能区,比B1B方法有很大改善,然后指出了由一级微扰理论所得结果在中低能区与实验结果不符的原因． 关键词：     

Open charm contribution to dilepton spectra produced in nuclear collisions at SPS energies

Measurements of open charm hadro-production from CERN and Fermilab experiments are reviewed, with particular emphasis on the absolute cross sections and on their A and √s dependences. Differentialp _T andx _F cross sections calculated with thePythia event generator are found to be in reasonable agreement with recent data. The calculations are scaled to nucleus-nucleus collisions and the expected lepton pair yield is deduced. The charm contribution to the low mass dilepton continuum observed by the CERES experiment is found to be negligible. In particular, it is shown that the observed low mass dilepton excess in S-Au collisions cannot be explained by charm enhancement.     

Radiative quenching and excitation of metastable states upon differential scattering of atoms: II. The He(1<Superscript>1</Superscript><Emphasis Type="Italic">S</Emphasis>–2<Superscript>1</Superscript><Emphasis Type="Italic">S</Emphasis>)-Ne molecule

The differential cross sections of radiative-collisional quenching (absorption) of a metastable state of a colliding atom are calculated for the first time. As a particular example, the reaction of quenching (excitation) of the metastable state He(2¹S) in collisions with Ne atoms in the ground state is considered. The calculations are performed for the thermal collisional energy E = 10^?3 au for a wide range of radiation frequencies, including both wings and the center of the line of a forbidden atomic transition, and are based on the uniform quasi-classical approximation, which generalizes the Franck-Condon approximation to the case of an exponential dependence of the transition dipole moment on the internuclear distance, as well as to the case of nonintersecting terms. The calculated differential cross sections have an oscillating structure, which, for the blue wing of the forbidden spectral line, is interpreted as Stückelberg oscillations. At a radiation frequency close to the frequency of the forbidden atomic transition, a sharp maximum in the differential cross section—the giant glory effect—is observed in the range of small scattering angles. This effect is shown to occur as a result of superimposition of the rainbowlike feature of the differential cross section on the glory feature.     

Parametrization of the shape of hadron-production spectra in high-energy particle interactions

The transverse-momentum dependence of inclusive differential cross sections measured in various collider experiments for processes involving the production of long-lived charged hadrons was approximated by the sum of an exponential and a power-law function. The dependence of the parameters appearing in these functions on the colliding-particle energy and type was studied, and relationships between these parameters were established. A number of new regularities in the behavior of charged-particle spectra were discovered.     

Interactions of heavy stable hadronising particles

In this article, we study the interactions of stable, hadronising new states, arising in certain extensions of the standard model. A simple model, originally intended for stable gluino hadrons, is developed to describe the nuclear interactions of hadrons containing any new colour triplet or octet stable parton. Hadron mass spectra, nuclear scattering cross sections and interaction processes are discussed. Furthermore, an implementation of the interactions of heavy hadrons in GEANT 3 is presented, signatures are studied, and a few remarks about possible detection with the ATLAS experiment are given.Received: 2 April 2004, Published online: 6 August 2004     

A clear-cut test of low mass dilepton production mechanism in hadronic collisions

It is pointed out that the dependence of the mean number of low mass dileptons per event on the multiplicity of charged hadrons can disentangle various mechanisms contributing to the low mass dilepton production. Specific predictions are presented for the contribution due to annihilations of quarks and antiquarks created during the collision.     

Scattering of ultrarelativistic deuterons by nuclei

Theoretical study of the interaction of ultrarelativistic hadrons with one another and with nuclei is stimulated by a number of experiments on the scattering of these particles with energies of ten billion electronvolt and more. It is difficult to explain the data obtained in such experiments because of the absence of a consistent relativistic quantum theory of hadrons. However, the existing experiments on the interaction of hadrons with hadrons and nuclei at high and superhigh energies can be well described phenomenologically in the framework of the diffraction approximation [1, 2], which was also used successfully earlier but at much lower, nonrelativistic energies [3, 4]. In the present paper, we derive a general formula for Hyugens's principle for monochromatic vector waves describing particles with spin 1 (for example, deuterons); this is used to obtain formulas for the cross sections of elastic and inelastic (accompanied by the emission of photons without disintegration of the particles) scattering of ultrarelativistic deuterons by nuclei with allowance for the spin and structure of the deuteron and the target nucleus; some special cases are also considered. The internal structure of the colliding nuclei, and also the possibility of excitation and disintegration of the target nuclei are taken into account by means of a generalization of the diffraction method to the case of the collision of any two nuclei, consideration being given to the interaction between each nucleon of the incident nucleus and all the nucleons of the target nucleus. In particular, this generalizes the results of [3–6] (in which diffraction scattering of elementary charged particles with spins 0, 1/2, and 1 with emission of photons was studied) to the case of composite incident particles with spin.Translated from Izvestiya Vysshikh Uchbenykh Zavedenii, Fizika, No. 9, pp. 3–8, September, 1980.     

Simple estimates for Fermi jets

The phenomenon of Fermi jets is investigated in the approximation of two colliding potential wells filled with degenerate Fermi gases of nucleons. A model is formulated which largely bypasses the explicit treatment of the relative motion of the nuclei, assumed to be governed by the window friction mechanism. Formulae for the velocity distributions and differential cross sections for neutrons and protons jetting through either target or projectile are derived. The numerical results are investigated systematically over a wide range of nuclear reactions. It is shown that the net linear momentum carried away by Fermi jets accounts for only a rather minor fraction of the observed missing momentum in typical heavy-ion fusion reactions.     

Precision Calculations for the T-Odd Quark Pair Production at the CLIC e+e- Linear Collider

We perform the precision calculations for the e⁺e^-→q_q_(q_q_=u_u_, c_c_, d_d_,s_s_) processes up to the QCD next-to-leading order (NLO) including full weak decays for the final T-odd mirror quarks in the littlest Higgs model with T-parity (LHT) at the Compact Linear Collider (CLIC). We show the dependence of the leading order (LO) and NLO QCD corrected cross sections on the colliding energy √s, and provide the LO and QCD NLO kinematic distributions of final particles. The results show that the LO cross section can be enhanced by the NLO QCD correction and the K-factor increases obviously when the threshold of the on-shell q_q_-pair production approaches the colliding energy √s. The K-factor value varies in the range of 1.04 ～ 1.41 in our chosen parameter space. We find that a simple approximation of multiplying the LO kinematic distribution with the integrated K-factor is not appropriate for precision study of the e⁺e^-→q_q_(q_q_=u_u_, c_c_, d_d_,s_s_) processes, since the NLO QCD corrections are phase space dependent. It is necessary to calculate the differential cross sections including full NLO QCD corrections to get reliable results.     

Ionization of heavy ions in relativistic collisions with neutral atoms

The problem of ionization of ions in ion-ion and ion-neutral relativistic collisions is considered. Formulas for ionization cross sections are derived in the Born approximation in terms of the momentum transfer without allowance for magnetic interactions. Using these formulas implemented in the LOSS-R code, the ionization cross sections are calculated for the K shells of neutral atoms colliding with protons and also for 1s and 2p electrons of multiply charged heavy ions (nuclear charge Z = 80−90) colliding with bare nuclei and neutral atoms. The calculation results are compared with experimental data and calculations of other authors.     

Soft multihadron production from partonic structure and fragmentation functions

We describe a two-chain model for soft multiparticle production in hadronic collisions. The model is formulated in a parton framework and is consistent with the dual topological scheme for the Pomeron. The sole inputs are valence quark structure functions in the colliding hadrons and parton fragmentation functions, both of which are known from “hard” processes. Our model, which contains no adjustable parameters, reproduces the shape, the energy dependence, and the normalization of inclusive spectra both in the central region and in the fragmentation region. The model provides a natural explanation for the ratio of πp topp cross sections.     

Neutrino production of charm

Cross Sections for the production of charm and bottom in neutrino (antineutrino) reactions are calculated in asymptotically free Quantum Chromodynamics. Total and differential cross sections are given for Cabibbo suppressed valence and Cabibbo favoured strange quark ocean production. The next order Quantum Chromodynamic correction to the charm production cross section is calculated. Arguments and estimates for the distribution of final state charmed hadrons are considered.