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1.
A parameter-free, nonperturbative calculation of the ΔNγ electromagnetic transition amplitudes GM*(q2), GE*(q2), and the resonant multipole ratio REM(q2)≡E1+3/2(q2)/M1+3/2(q2) is performed in terms of the well-known nucleon isovector Sachs form factor GMV. Our methods are fully relativistic with conservation of the electromagnetic current guaranteed. We find that GM*(q2) decreases more rapidly than the nucleon dipole form factor when −q21 GeV2/c2 and that REM(q2) remains small even for very high four-momentum transfer implying that the perturbative QCD prediction REM(q2)→1 is purely asymptotic and is valid only for extremely high |q2|.  相似文献   

2.
We show that the HERA data for the inclusive structure function F2(x,Q2) for x10−2 and 0.045Q245 GeV2 can be well described within the color dipole picture, with a simple analytic expression for the dipole–proton scattering amplitude, which is an approximate solution to the non-linear evolution equations in QCD. For dipole sizes less than the inverse saturation momentum 1/Qs(x), the scattering amplitude is the solution to the BFKL equation in the vicinity of the saturation line. It exhibits geometric scaling and scaling violations by the diffusion term. For dipole sizes larger than 1/Qs(x), the scattering amplitude saturates to one. The fit involves three parameters: the proton radius R, the value x0 of x at which the saturation scale Qs equals 1 GeV, and the logarithmic derivative of the saturation momentum λ. The value of λ extracted from the fit turns out to be consistent with a recent calculation using the next-to-leading order BFKL formalism.  相似文献   

3.
Nucleon–nucleon scattering observables are considered in the context of the large Nc limit of QCD for initial states with moderately high momenta (pNc). The scattering is studied in the framework of the time-dependent mean-field approximation. We focus on the dependence of those observables on the spin and isospin of the initial state which may be computed using time-dependent mean-field theory. We show that, up to corrections, all such observables must be invariant under simultaneous spin and isospin flips (i.e., rotations through π/2 in both spin and isospin) acting on either particle. All observables of this class obtained from spin unpolarized measurements must be isospin independent up to 1/Nc corrections. Moreover, it can be shown that the leading correction is of relative order 1/Nc2 rather than 1/Nc.  相似文献   

4.
S. A. Kulagin 《Nuclear Physics A》1998,640(3-4):435-456
We study nuclear effects in the structure function F3 which describes the parity violating part of the charged-current neuitrino nucleon deep inelastic scattering. Starting from a covariant approach we derive a factorized expression for the nuclear structure function in terms of the nuclear spectral function and off-shell nucleon structure functions valid for arbitrary momentum transfer Q and in the limit of weak nuclear binding, i.e. when a nucleus can be treated as a non-relativistic system. We develop a systematic expansion of nuclear structure functions in terms of a Q−2 series caused by nuclear effects (“nuclear twist” series). Basing ourselves on this expansion we calculate nuclear corrections to the Gross-Llewellyn-Smith sum rule as well as to higher moments of F3. We show that corrections to the GLS sum rule due to nuclear effects cancel out in the Bjorken limit and calculate the corresponding Q−2 correction. Special attention is paid to the discussion of the off-shell effects in the structure functions. A sizable impact of these effects both on the Q2 and x dependence of nuclear structure functions is found.  相似文献   

5.
Using analyticity of the virtual Compton scattering amplitude in Q2 sum rules are derived relating meson-nucleon total cross-sections with certain integrals over the large Q2 and x0 part of nucleon structure functions. Of preliminary quantitative analysis of the sum rules for both singlet and non-singlet amplitudes is presented. For the singlet amplitude the sum rules relate, in particular, the rise of sea-quark distributions implied by perturbative QCD and the increase of total meson-proton cross sections with energy. Quantitatively, however, nonunitary leading log Q2 results for the former give a too rapid increase of the latter.  相似文献   

6.
We have measured the deuteron A(Q2) structure function in the momentum transfer region between 1 and 18 fm−2. The accuracy of the data ranges from 2 to 6%. These measurements allow a sensitive test of theoretical predictions. We find that meson-exchange currents and relativistic corrections significantly improve the agreement between experiment and theory. We investigate the sensitivity of A(Q2) to the nucleon-nucleon interaction and to the neutron electric form factor GEn(Q2). Our analysis shows that GEn(Q2) can be extracted from these data with a significantly improved accuracy. The model dependence of this analysis is discussed.  相似文献   

7.
Recent measurements from the HERMES and SMC Collaborations show a remarkably large azimuthal single-spin asymmetries AUL and AUT of the proton in semi-inclusive pion leptoproduction γ*(q)p→πX. We show that final-state interactions from gluon exchange between the outgoing quark and the target spectator system lead to single-spin asymmetries in deep inelastic lepton–proton scattering at leading twist in perturbative QCD; i.e., the rescattering corrections are not power-law suppressed at large photon virtuality Q2 at fixed xbj. The existence of such single-spin asymmetries requires a phase difference between two amplitudes coupling the proton target with Jzp=±1/2 to the same final-state, the same amplitudes which are necessary to produce a nonzero proton anomalous magnetic moment. We show that the exchange of gauge particles between the outgoing quark and the proton spectators produces a Coulomb-like complex phase which depends on the angular momentum Lz of the proton's constituents and is thus distinct for different proton spin amplitudes. The single-spin asymmetry which arises from such final-state interactions does not factorize into a product of distribution function and fragmentation function, and it is not related to the transversity distribution δq(x,Q) which correlates transversely polarized quarks with the spin of the transversely polarized target nucleon.  相似文献   

8.
We derive a unitarity relationship between the spin structure function gLT(x,Q2)=g1(x,Q2)+g2(x,Q2), the LT interference diffractive structure function and the spin-flip coupling of the pomeron to nucleons. Our diffractive mechanism gives rise to a dramatic small-x rise , where δg is an exponent of small-x rise of the unpolarized gluon density in the proton at a moderate hard scale for light flavour contribution and large hard scale for heavy flavour contribution. It invalidates the Burkhardt–Cottingham sum rule. The found small-x rise of diffraction driven gLT(x,Q2) is steeper than given by the Wandzura–Wilczek relation under conventional assumptions on small-x behaviour of g1(x,Q2).  相似文献   

9.
《Physics letters. [Part B]》1999,470(1-4):39-44
In order to test modern theories of two-nucleon bound and scattering states, we have measured the spin polarization of ejectile protons in the electrodisintegration reaction . Compared with spin-averaged observations, these observables offer the potential of enhanced sensitivity to details of the reaction process. The experiment was carried out in quasielastic kinematics (qμqμ=−2mpω=−0.38 GeV2/c2). Protons were detected at two angles corresponding to neutron recoil momenta pr of 0 and 100 MeV/c. Full nonrelativistic calculations of the polarization transfer components sl and st, including leading order relativistic contributions, describe our measurements well, but calculations of the induced polarization sn at pr=100 MeV/c underpredict the experimental result.  相似文献   

10.
The order (Q2) correction to the particle multiplicity ratio in gluon and quark jets is calculated in QCD. Through (Q2) we find
, with r = <n>gluon jet/<n>quark jet. This ratio is independent of the opening angle chosen to define the jets.  相似文献   

11.
The complete set of Wolfenstein parameters, the polarization, the asymmetry of scattering and the unpolarized double-differential cross section are presented for inclusive quasielastic proton scattering from 12C at a central momentum transfer of q = 1.9 fm−1 and incident energies of 290 and 420 MeV. The spin observables D0, Dx, Dy and Dz as well as the longitudinal-to-transverse ratio of spin-flip probabilities are extracted from the data. Across the quasielastic continuum, the experimental data is compared to the variations expected from a single-scattering Fermi-gas approximation using the free NN amplitudes. Medium effects are evident in the pronounced quenching of the polarization parameter relative to the free value.  相似文献   

12.
Sum rules involving the spin structure of the nucleon like those due to Bjorken, Ellis and Jaffe and the one due to Gerasimov, Drell and Hearn offer the opportunity to study the structure of strong interactions. At long distance scales in the confinement regime the Gerasimov-Drell-Hearn (GDH) Sum Rule connects static properties of the nucleon like the anomalous magnetic moment κ and the nucleon mass m, with the spin dependent absorption of real photons with total cross sections 0gs3/2 and σ1/2:
Here 3/2 and 1/2 identify relative spin orientation of the photon and the nucleon parallel or anti-parallel respectively in the nucleon rest frame; denotes the fine-structure constant and ν the energy of the photon. Hence the full spin-dependent excitation spectrum of the nucleon is related to its static properties. The sum rule has not been investigated experimentally until recently. For the first time this fundamental sum rule is verified by the GDH-Collaboration with circularly polarized real photons and longitudinally polarized nucleons at the two accelerators and . The investigation of the response of the proton as well as of the neutron allows to perform an isospin decomposition. Data from the resonance region up to the onset of the Regge regime are shown. The “sum” on the left hand side of the GDH Sum Rule can be generalized to the case of virtual photons. This allows to establish a Q2 dependency and to study the transition to the perturbative regime of QCD. This is the subject of several experiments e.g. at for the resonance region and of the experiment at for higher Q2. Moreover, this paper covers the status of theory concerning the GDH Sum Rule, the different experimental approaches and the results for the absorption of real and virtual photons will be reviewed.  相似文献   

13.
Intensities have been measured for individual transitions in the Q and R branches of the ν1 band of NH3 using a difference-frequency laser spectrometer. The data yield an integrated band strength of S0v=219.36±1.03 cm-2/MPa at 297 K, corresponding to a transition moment of μv = 8.535(20) × 10-32 C·m, and a Herman-Wallis correction factor, (1 + jm)2, where j = 0.0209(20). The intensities of a few lines for K 7 were noticeably perturbed by a perpendicular Coriolis interaction with 2ν4 (E, L = 2), so were excluded from the fit. A small sample of ν3 band lines occurring in the ν1 band scans also yields a rough estimate of the ν3 band intensity with evident irregular perturbations.  相似文献   

14.
We exhibit and discuss the QCD prediction for the transverse momentum distribution of W bosons, Z bosons and high-mass virtual photons produced in high-energy hadron-hadron collisions. Recent work has shown that this prediction is consistent with the structure of leading twist initial state interactions.

The expression we present is expected to give results correct up to order sN(Q) for any QT when the boson mass Q is very large (> 108 GeV!), given only input from perturbative calculations at order sN+2 and deeply inelastic scattering structure functions. We specify the required N = 0 coefficients, employing the order s2 results of Kodaira and Trentadue and of Davies and Stirling. We then show how the expression should be modified to deal with current energy scales. We also discuss the connection between low-QT and high-QT formulae.  相似文献   


15.
Measurements for the elastic and inelastic scattering of 500 MeV protons from 40Ca and 208Pb at small momentum transfers are reported. The induced proton polarization P and the spin rotation parameter Q were measured for the elastic scattering. The spin rotation parameters DSS, DSL, DLL, dLS and the induced polarization P were measured for transitions to the 3(3.37 MeV) and 5(4.48 MeV) states in 40Ca and the 3(2.61 MeV) state in 208Pb. Comparisons of the data with the theoretical calculations were carried out in the framework of nonrelativistic and relativistic approaches. We extracted the spin-up and spin-down channels for the elastic scattering cross sections and found that predictions of the relativistic and nonrelativistic approaches agree well with the spin-up channel data and differ considerably in the spin-down channel.  相似文献   

16.
17.
We study the nonresonant three-body decays of B+D(*)−sK+π+ and BdDs(*)−K0π+. We find that these decays can provide the information on the time-like form factors of D(*)sK. We also explicitly investigate BdDs(*)−K*+ decays by discriminating the nonresonant contributions with the unknown D(*)s wave functions being fixed by the measured mode of BdDsK+.  相似文献   

18.
伊天成  丁悦然  任杰  王艺敏  尤文龙 《物理学报》2018,67(14):140303-140303
研究了具有Dzyaloshinskii-Moriya(DM)相互作用的一维横场XY自旋链的量子相变和量子相干性.采用约旦-维格纳变换严格求解了哈密顿量,并描绘了体系的关联函数和相图,相图包含反铁磁相、顺磁相和螺旋相.利用相对熵和Jensen-Shannon熵讨论了XY模型的量子相干性.研究发现,相对熵与Jensen-Shannon熵所表现的行为都可以很好地表征该模型的量子相变.非螺旋相中量子相干性不依赖DM相互作用,而在螺旋相DM相互作用对量子相干性有显著影响.此外,指出了在带有DM相互作用的这一类反射对称破缺体系中关联函数计算的常见问题.  相似文献   

19.
Kedong Wang 《中国物理 B》2021,30(12):123401-123401
We report elastic cross sections for low-energy electron scattering with formamide-(H2O)n complexes (n=1, 2) in the energy region of 0.01-8 eV. The scattering calculations are performed using the R-matrix method in the static-exchange (SE) approximation. We consider three structures of formamide-H2O and six structures of formamide-(H2O)2 in the present work. Our purpose is to investigate effects of water molecules hydrogen-bonding to formamide. We focus on the influence of microsolvation on the π* and σ* resonances of formamide. The scattering result for complexes shows that the position of π* resonance appears at lower or higher energies in the cluster than in the isolated formamide depending on the complex structure and the water role in the hydrogen bonding. We explain this behavior according to the net charge of the solute. It is found that the microsolvation environment has a substantial effect on the width of π* resonance. Our results indicate that surrounding water molecules may affect the lifetime of the resonances, and hence the process is driven by the anion state, such as the dissociative electron attachment.  相似文献   

20.
张华  陈少平  龙洋  樊文浩  王文先  孟庆森 《物理学报》2015,64(24):247302-247302
德拜弛豫理论表明, 在频率为2.45 GHz的外加交变电磁场的作用下, 微波对极性分子的极化过程约为10-10 s, 因此利用微波固相反应可以在短时低温条件下制备出纳米粉体材料. 本文以MgH2代替Mg粉, 利用微波固相反应在低温下制备了Mg2Si0.4Sn0.6-yBiy (0 ≤y ≤q 0.03)固溶体, 并结合单带抛物线计算模型对其热电传输机理进行了分析. 研究结果表明: 利用该工艺可以有效抑制Mg的挥发和MgO 的生成, 在400 ℃保温15 min内即可完成MgH2与Si粉和Sn粉的固相反应, 获得片层间距为100 nm的超细化学计量比产物; 杂质Bi的引入可以有效增加载流子浓度, 并引起晶格畸变, 在晶格畸变和样品特有的纳米片层结构的协同作用下, 声子得到有效散射, 样品具有最低的热导率1.36 W·m-1·K-1. 较低的有效掺杂率和复杂的能带结构具有降低能带态密度有效质量和减小载流子弛豫时间的双刃效应, 使得本征激发提前, 在600 K样品取得最大ZT值为0.66.  相似文献   

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