鞘场加速机理中质子束的特性与其初始尺寸的关系

为了研究激光鞘场中质子层的尺寸对质子束特性的影响,本文应用中国工程物理研究院 激光聚变研究中心的二维Particle-In-Cell (2D-PIC)数值模拟程序Flips2D进行了相关数值模拟研究. 研究了质子束总能量随时间的变化,得出了加速持续过程与激光脉冲持续时间的关系; 研究了质子层的宽度对加速后质子束发散角和能谱的影响;研究了质子层的厚与加速后质子束 发散角和能谱的关系;得出了质子层的初始尺寸对加速后质子特性的影响规律.     

Forward Proton Scattering in Association with Muon Pair Production via the Photon Fusion Mechanism at the LHC

JETP Letters - Dilepton production in proton–proton collision through γγ-fusion with one proton scattered elastically while the second produces a hadron jet is considered....     

Monopole Excitation of the Nucleon in a Relativistic Three-Quark Model

The densities and form factors of the proton andthe Roper monopole excitedstate resonance are calculatedusing a relativistic three-quark model. Small currentquark masses are used with the three-body Dirac equation solved in hypercentralapproximation. A QCD-based three-body potential,proportional to a minimum string length between thethree quarks, is used for confinement. The calculatedelectric form factor for the proton reproduces closelya dipole fit to the data. The proton density is morecompact than is the Roper resonance density. The centraldensity of the proton is about five times that for the Roper resonance. The hyperradial nodein the Roper resonance composite three-quark wavefunction shows up as a node in the transition densitybetween the proton and the Roper resonance. This node also causes the calculated transition formfactor to be larger than either the proton or Roperresonance form factors, all evaluated at the same valueof momentum transfer. The Roper resonance form factor is smaller than the proton form factor, asexpected, indicative of the Roper resonance being a morediffuse system than the proton.     

Effect of the momentum dependence of nuclear symmetry potential on the transverse and elliptic flows

In the framework of the isospin-dependent Boltzmann-Uehling-Uhlenbeck transport model, the effect of the momentum dependence of nuclear symmetry potential on nuclear transverse and elliptic flows in the neutron-rich reaction ¹³²Sn+¹²⁴Sn at a beam energy of 400MeV/nucleon is studied. We find that the momentum dependence of nuclear symmetry potential affects the rapidity distribution of the free neutron to proton ratio, the neutron and the proton transverse flows as a function of rapidity. The momentum dependence of nuclear symmetry potential affects the neutron-proton differential transverse flow more evidently than the difference of neutron and proton transverse flows as well as the difference of proton and neutron elliptic flows. It is thus better to probe the symmetry energy by using the difference of neutron and proton flows since the momentum dependence of nuclear symmetry potential is still an open question. And it is better to probe the momentum dependence of nuclear symmetry potential by using the neutron-proton differential transverse flow the rapidity distribution of the free neutron to proton ratio.     

On the strong and weak effects in the s-wave monopole-fermion interactions

Neglecting the masses of light fermions at small distances and corrections due to higher angular momentum excitations and heavy fermions, we show that strong and weak effects do not forbid the monopole catalysis of proton decay. We develop a simple bag-like model of a proton with a monopole sitting at its center and estimate the proton lifetime. We show that the monopole catalysis is not allowed in a variant of the SU(5) grand unified theory, so this process is not characteristic to all GUTs.     

A study of the thermal contact between the nuclear Zeeman system and the electron dipole-dipole interaction system

In order to explain proton spin-lattice relaxation measurements in a deuterated copper Tutton salt [1], we performed a theoretical investigation of the thermal contact between the proton Zeeman system (PZS) and the electron dipole-dipole interaction system (EDDS). The basic process that maintains the contact between these two spin systems is a three-spin process in which one proton spin and two electron spins make a simultaneous transition. We calculated the transition probability of this three-spin process. It was proved that neither electron spin-lattice relaxation nor cross-relaxation are a bottle-neck in the proton spin-lattice relaxation, so the observed relaxation time values are completely determined by this three-spin process. Hence, the contact time between the PZS and the EDDS can be derived directly from the measurements.     

放射性核束引起反应中轻带电粒子发射的同位旋效应

研究了69MeV/u³⁶Ar轰击Be靶的碎裂产物与Si靶反应引起的前角区轻带电粒子的发射产额与原子核同位旋、原子核序数的关系.发现前角区轻带电粒子发射产额对于丰质子核的结构非常敏感,与同位旋存在一种指数关系.因此可以把前角区轻带电粒子发射产额作为探测丰质子核结构的一种手段,也是一种新的验证一个核是否具有质子晕结构的实验证据.     

Binuclear atom as the bound state of a proton and a heavy atom

The existence of a bound state of a proton and a heavy atom is predicted. The atom is described by the Thomas-Fermi method. The electrons screen the field of the proton, which suppresses the repulsive force between the proton and the atomic nucleus. On the other hand, the force of attraction between the proton and the electrons is directed along the electron density gradient (i.e., towards the nucleus). It is concluded that for Z = 80, the two forces are balanced at a distance from the nucleus of about 0.6 of the Bohr radius. It is found that the potential energy minimum of the proton with a depth of several tens of electronvolts lies in the range of negative energies (attraction). It is proposed that such a system be referred to as a binuclear atom. It is emphasized that, in contrast to molecules, in which binding with the hydrogen atom is ensured by a rearrangement of the states of the outer-shell (valence) electrons, a binuclear atom is formed as a result of the collective response of the system of inner electrons to the proton potential.     

Electron capture in the collision of a proton with a hydrogen atom

Electron capture in the collision of a proton with a hydrogen atom is investigated. The probability of electron capture is calculated from first principles by the direct solving of the three-dimensional nonstationary Schr?dinger equation. The dependence of the probability of electron capture by a proton on the proton??s velocity and impact parameter is obtained and analyzed thanks to highly efficient computations with the use of graphic processing units.     

Proton Radiography for the Diagnostics of a Dense Plasma

The possibility of using high-energy proton radiography for dense plasma diagnostics is discussed. The designed telescopic ion optical system for a proton radiography installation with a 1 GeV beam is presented. The schematic diagram of the proton microscope is given. It is shown that the estimate of spatial resolution for the installation obtained with consideration of chromatic aberrations of magnetic quadrupole lenses is limited from below.     

Flavor symmetry,EMC results and the spin content of the proton

The analysis of the EMC result on the quark contribution to the spin of the proton has caused considerable confusion and is unnecessarily complicated because of the completely unjustified and incorrect use of SU(3) flavor symmetry to provide input on the proton wave function from hyperon decays. There is no reliable method for obtaining information on the proton spin structure from data on the couplings of currents to hyperons. Interesting peculiar results obtained without use of SU(3) and hyperon data show the crucial point to be the apparent contradiction between the contribution of valence u quarks to the proton spin observed in the axial vector contribution to nucleon beta decay and the failure of this contribution to appear in the conventional quark-parton interpretation of the EMC results. When input from hyperon data is not used this paradox can be resolved without requiring the quark contribution to the proton spin to be near zero, but it can be large only if it is due to the strange quarks, with the nonstrange quark contribution opposite to the spin of the proton.     

Viewing the proton through "color" filters

While the form factors and parton distributions provide separately the shape of the proton in coordinate and momentum spaces, a more powerful imaging of the proton structure can be obtained through phase-space distributions. Here we introduce the Wigner-type quark and gluon distributions which depict a full-3D proton at every fixed light-cone momentum, like what is seen through momentum ("color") filters. After appropriate phase-space reductions, the Wigner distributions are related to the generalized parton distributions (GPDs) and transverse-momentum dependent parton distributions, which are measurable in high-energy experiments. The new interpretation of GPDs provides a classical way to visualize the orbital motion of the quarks, which is known to be the key to the spin and magnetic moment of the proton.     

Different Methods for the Two-Nucleon T-Matrix in the Operator Form

We compare three methods to calculate the nucleon–nucleon t-matrix based on the three-dimensional formulation of Golak et al. (Phys Rev C 81:034006, 2010). In the first place we solve a system of complex linear inhomogeneous equations directly for the t-matrix. Our second method is based on iterations and a variant of the Lanczos algorithm. In the third case we obtain the t-matrix in two steps, solving a system of real linear equations for the k-matrix expansion coefficients and then solving an on-shell equation, which connects the scalar coefficients of the k- and t-matrices. A very good agreement among the three methods is demonstrated for selected nucleon–nucleon scattering observables using a chiral next-to-next-to-leading-order neutron–proton potential. We also apply our three-dimensional framework to the demanding problem of proton–proton scattering, using a corresponding version of the nucleon–nucleon potential and supplementing it with the (screened) Coulomb force, taken also in the three-dimensional form. We show converged results for two different screening functions and find a very good agreement with other methods dealing with proton–proton scattering.     

Determining the inelastic proton–proton cross section at the large hadron collider using minimum bias events

In this paper a new method is described for determining the non-diffractive part of the inelastic proton–proton cross section, at the LHC centre of mass energy of 14 TeV. The method is based on counting the number of inelastic proton–proton interactions in the collision regions. According to a preliminary investigation, this measurement will be best suited for the initial low luminosity phase of the LHC. Knowledge of the proton–proton luminosity is likely to dominate the measurement uncertainty. PACS 13.85.Hd     

Study of the mechanisms of cumulative-proton production in neutrino-nucleus interactions

The mechanisms of cumulative proton production are studied on the basis of data from the SCAT propane-freon bubble chamber exposed to a wideband neutrino beam at the Serpukhov accelerator. Kinematic correlations between the cumulative proton and muon, as well as pair correlations of the final protons, are analyzed. The former correlations are predicted by the two-nucleon correlation mechanism (TCM), whereas the latter are caused by the mechanism of secondary pion absorption (SPA) in the nucleus. It is shown that the TCM contribution to the cumulative proton production is most significant in the peripheral interactions (about 50%). The SPA contribution accounts for about a quarter of the inclusive cross section of cumulative proton production.     

A DFT investigation into the structure and energetics for nonadiabatic proton transfer in the benzophenone/N,N‐dimethylaniline contact radical ion pair

For the past 60 years, the standard model for the interpretation of the mechanism for proton transfer has been based upon transition‐state theory, which posits that the transition state is found in the proton transfer coordinate involving the breaking and making of bonds. However, the observed dynamics of proton transfer within the triplet contact radical ion pair, derived from a variety of substituted benzophenones complexed with N,N‐dimethylaniline, cannot be accounted for within the standard model for proton transfer. Instead, the kinetic behavior is in accord with nonadiabatic proton transfer theory that has the transition state in the solvent coordinate. Evidence for the importance of the solvent coordinate comes from the existence of an inverted region; as the driving force for reaction increases, the rate of proton transfer decreases. This kinetic behavior is not found in the standard model. The present paper employs density function theory to examine the question as to whether the inverted region can be attributed to the transition state being in the solvent coordinate or whether the inverted region is an artifact produced by changes in the structure of the triplet contact radical ion pair with the placement of substituents upon the p,p′ positions of benzophenone. It is concluded that the inverted region is not an artifact of substituent effects upon structure. These results support the conclusion that the transition state for proton transfer resides in the solvent coordinate and challenges the validity of the standard model for interpreting the mechanism of proton transfer. Copyright © 2014 John Wiley & Sons, Ltd.     

Theoretical study on the mechanism for the excited-state double proton transfer process of an asymmetric Schiff base ligand

Excited-state double proton transfer (ESDPT) in the 1-[(2-hydroxy-3-methoxy-benzylidene)-hydrazonomethyl]-naphthalen-2-ol (HYDRAVH₂) ligand was studied by the density functional theory and time-dependent density functional theory method. The analysis of frontier molecular orbitals, infrared spectra, and non-covalent interactions have cross-validated that the asymmetric structure has an influence on the proton transfer, which makes the proton transfer ability of the two hydrogen protons different. The potential energy surfaces in both S₀ and S₁ states were scanned with varying O-H bond lengths. The results of potential energy surface analysis adequately proved that the HYDRAVH₂ can undergo the ESDPT process in the S₁ state and the double proton transfer process is a stepwise proton transfer mechanism. Our work can pave the way towards the design and synthesis of new molecules.     

Possible method for measuring the proton form factors in processes with and without proton spin flip

The ratio of the squares of the electric and magnetic proton form factors is shown to be proportional to the ratio of the cross sections for the elastic scattering of an unpolarized electron on a partially polarized proton with and without proton spin flip. The initial proton at rest should be polarized along the direction of the motion of the final proton. Similar results are valid for both radiative ep scattering and the photoproduction of pairs on a proton in the Bethe-Heitler kinematics. When the initial proton is fully polarized in the direction of the motion of the final proton, the cross section for the ep → ep process, as well as for the ep → epγ and γp → $ e\bar ep $ e\bar ep processes, without (with) proton spin flip is expressed only in terms of the square of the electric (magnetic) proton form factor. Such an experiment on the measurement of the cross sections without and with proton spin flip would make it possible to acquire new independent data on the behavior of G _E ²(Q ²) and G _M ²(Q ²), which are necessary for resolving the contradictions appearing after the experiment of the JLab collaboration on the measurement of the proton form factors with the method of polarization transfer from the initial electron to the final proton.     

Measurement of the proton spin polarizabilities at MAMI

The spin polarizabilities of the nucleon are fundamental structure constants which describe the response of the nucleon spin to an incident polarized photon. The most model-independent way to measure the nucleon spin polarizabilities is the Compton scattering with polarization degrees of freedom. Three Compton scattering asymmetries on the proton were measured in the Δ(1232) region using a polarized incident photon beam and a polarized (or unpolarized) proton target at the Mainz Microtron (MAMI). These asymmetries are sensitive to values of the spin polarizabilities. Fits to asymmetry data were performed using a dispersion model calculation, and a separation of all four proton spin-polarizabilities in the multipole basis was achieved. The values of the proton spin polarizabilities are presented.