Second-order contributions to the structure functions in deep inelastic scattering: (II) Comparison with experiment for the non-singlet contributions to e, μ-nucleon scattering

Quantum chromodynamics predictions for the non-singlet structure functions of ep and μp inclusive scattering are tested against experiment. Target mass corrections and leading and next-to-leading terms α_c are taken into account. The fits to experimental data are very good; they improve systematically when including second-order corrections. The preferred value for the invariant parameter Λ entering α_c is Λ=0.20 ± 0.06 GeV, when second-order and target mass corrections are taken into account.     

QCD corrections to single top quark production in electron-photon interactions

Single top quark production in electron-photon interactions provides a clean environment for the measurement of the Cabibbo-Kobayashi-Maskawa matrix element V_tb. Aiming at an experimental precision at the percent level the knowledge of radiative corrections is important. In this paper we present results for the radiative corrections in quantum chromodynamics.Received: 7 April 2003, Published online: 1 August 2003     

Structure functions at HERA

HERA provides the key facility for the measurement of proton structure functions. Formalism and methods are outlined for the measurement and interpretation of inclusive structure functions, including the use of polarised e ^± beams. The measurement of charm, beauty and photon structure functions is discussed, together with special runs at low proton energy for measurement of the longitudinal structure function. Finally, the functions accessed using polarised beams on polarised targets are indicated.     

Fragmentation of heavy quarks in polarized quarkonium in the effective heavy quark theory

Fragmentation of abantiquark into polarized B_c ^* mesons has been studied within the framework of the effective theory of heavy quarks. The functions ofb fragmentation into longitudinally polarized and transversely polarizedb S-wave states have been calculated with precise account for corrections of the first order in 1/m_b. The results are shown to agree with the corresponding calculations in quantum chromodynamics. Samara State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, p. 97–104, July, 1996.     

Photon structure functions in quantum chromodynamics: (II). Feynman diagram method

We compute the strong interaction corrections to the polarized photon structure functions using perturbative chromodynamics. The results agree with those of our previous calculations with the operator product expansion method.     

Quantum chromodynamics predictions in renormalization scheme invariant perturbation theory

It has recently been shown that any physical quantity ℛ, in perturbation theory, can be obtained as a function of only the renormalization scheme (rs) invariants,ρ ₀,ρ ₁,ρ ₂, … Physical predictions, to any given order, are renormalization scheme independent in this approach. Quantum chromodynamics (qcd) predictions to second order, within thisrs-invariant perturbation theory, are given here for several processes. These lead to some novel relations between experimentally measurable quantities, which do not involve the unknownqcd scale parameter Λ. They can therefore be directly confronted with experiments and this has been done wherever possible. It is suggested that these relations can be used to probe the neglected higher order corrections.     

Polarisation effects in Mössbauer absorption by powder samples in external magnetic fields

The polarisation dependence of the absorption cross section must generally be taken into account in calculating Mössbauer absorption spectra of powder samples if they are partly polarised by an external magnetic field. The dependence of the intensity of the absorption lines on the aboorber thickness with an external field ofH _a=50 kG is shown in the case of the paramagnetic specimen Fe(ClO₄)₂·6H₂O. The calculation procedure is described and the results are compared with the usual thickness corrections neglecting polarisation effects.     

IR-renormalon contributions to the structure functions g 3 and g 5

We calculate the leading 1/N _f perturbative contributions to the polarized nonsinglet structure functions g ₃ and g ₅ to all orders in α_s. The contributions from the first renormalon pole are determined. It is a measure for the ambiguity of the perturbative calculation and is hypothetically assumed to dominate the power corrections. The corrections Δg ₃ and Δg ₅ are given as functions of the Bjorken variable x and turn out to be negligible. The anomalous dimensions of the leading twist operators are obtained in the next-to-leading order. Received: 10 June 1998 / Revised version: 25 September 1998     

Gottfried sum rule from maximum entropy method quark distributions with DGLAP evolution and with DGLAP evolution with GLR-MQ-ZRS corrections

A new method to test the valence quark distribution of nucleons obtained from the maximum entropy method using the Gottfried sum rule by performing the DGLAP equations with GLR-MQ-ZRS corrections and the original leading-order/next-to-leading-order(LO/NLO) DGLAP equations is outlined. The test relies on knowledge of the unpolarized electron–proton structure function F_2~(ep) and the electron–neutron structure function F_2~(en) and the assumption that Bjorken scaling is satisfied. In this work, the original Gottfried summation value obtained by the integrals of the structure function at different Q~2 is in accordance with the theoretical value of 1/3 under the premise of light-quark flavor symmetry of the nucleon sea, whether it results from dynamical evolution equations or from global quantum chromodynamics fits of PDFs. Finally, we present the summation value of the LO/NLO DGLAP global fits of PDFs under the premise of light-quark flavor asymmetry of the nucleon sea. According to analysis of the original Gottfried summation value with two evolution equations at different Q~2, we find that the valence quark distributions of nucleons obtained by using the maximum entropy method are effective and reliable.     

Polarised neutron study on Ni rich NiCr alloys

Magnetic structure amplitudes in Ni_1-xCr_x alloys (x = 0.023 and 0.034) are measured using the polarised neutron diffraction technique. The structure amplitudes are analysed using the projection operator formalism. In this framework a new approach for defining local site moment, diffuse moment and asphericity in the site moment are discussed. A detailed multiband Coherent Potential Approximation (CPA) calculation for ferromagnetic $\text{Ni}$Cr alloys using the Hubbard Hamiltonian with realistic parameters is discussed. The results of these calculations are compared with the existing bulk measurements like magnetisation and transport properties. The evolution of site moment and its asphericity with impurity concentration are obtained and compared with the present polarised neutron results.     

Circularly polarised attosecond pulses: generation and applications

ABSTRACT

Molecular high-order harmonic generation(MHOHG) is simulated for H⁺₂ in the nonlinear nonperturbative regime of laser-molecule interactions with ultrashort intense circularly polarised laser pulses. It is shown that combinations of co-rotating or counter-rotating pulses produce laser-induced Coriolis forces with electron-parent ion recollisions, thus enhancing circularly polarised MHOHG, the source of circularly polarised attosecond pulses. Such pulses can be used to induce electron attosecond currents for the generation of attosecond magnetic field pulses, new tools for molecular attomagnetism.     

Study of Amorphous Ferrimagnet Fe0.66Er0.19B0.15 by Means of Monochromatic Circularly Polarised Source

Properties of amorphous alloy Fe_0.66Er_0.19B_0.15 are reported. A reorientation of the Fe and Er magnetic moments during sample cooling through the compensation point in a large magnetic field is found by means of monochromatic circularly polarised radiation. This revised version was published online in August 2006 with corrections to the Cover Date.     

Polarised Drell-Yan measurements at COMPASS-II

The spin structure of the nucleon and its Parton Distribution Functions (PDFs) are important topics studied by the COMPASS experiment at CERN. So far, the transverse momentum dependent PDFs (TMD PDFs) of the proton and deuteron have been studied in Semi-Inclusive Deep Inelastic Scattering (SIDIS). The Drell-Yan (DY) process is a complementary way to access the TMD PDFs, using a transversely polarised target. Studying the angular distributions of dimuons from the DY events produced in the collisions of a π^? beam with 190 GeV/c momentum off a transversely polarised proton target (NH₃) we are able to extract the azimuthal spin asymmetries, which are generated by 4 out of the 8 TMD PDFs needed to describe the nucleon structure at leading order QCD. The expected sign change in Sivers and Boer-Mulders functions when accessed from DY and SIDIS will be checked [1]. The opportunity to study, in the same experiment, the TMD PDFs from both SIDIS and DY processes is unique at COMPASS. The COMPASS II Proposal [2] was approved by CERN including one year for polarised DY measurements; the beginning of the DY data taking is scheduled for 2014. The feasibility of the measurement was proven by several beam tests performed so far.     

QCD at finite temperature

Quantum chromodynamics is studied at finite temperatures and densities using the temperature Green functions method. For the Green functions the renormalized Schwinger-Dyson equations are obtained and their qualitative properties are discussed. The equality of the renormalization constants for the equations obtained at T, μ ≠ 0 with those for quantum field theory is pointed out. General properties of the gluon polarization tensor are investigated at T, μ ≠ 0. The temperature Green functions are calculated within the one-loop approximation using both relativistic and axial gauges. The fulfilment of the Slavnov-Taylor identities is verified. The asymptotic behaviour of the polarization tensor at T, μ ≠ 0 is established and the excitation spectrum of quark-gluon plasma is found. Both Fermi and Bose excitations are considered and the gauge invariance of the spectra is demonstrated. The renormalization group extension of the dispersion laws into the regions of high temperatures and densities is presented. The exact representation of the thermodynamical potential in QCD is found in terms of the temperature Green functions. For the quark-gluon plasma the thermodynamical potential is calculated with the g³-term taken into account. The equation of state of the hot quark-gluon plasma is found and its properties are discussed. The complete evolutional diagram of the hadronic matter is outlined. The phase curve asymptotics, which put bounds on the quark-gluon plasma domain, are found for the two limiting cases (μ = 0, T → T₀; T = 0, μ → μ₀). The phase transition of the hot quark-gluon plasma placed in external Abelian field is studied. The instability of such plasma has been found and the program of its stabilization is indicated. The infrared behaviour of the non-Abelian gauge theory is studied for finite temperatures when power divergencies are essential. The propagator of transverse gluons is shown to be singular for momenta |p| ˜ g²T and this cannot be avoided by summing the simplest bubble chains. The infrared asymptotic behaviour of the tree-gluon vertex is found and the results obtained are checked using the Slavnov-Taylor identities. The Green functions asymptotics found indicate either an instability of the quark-gluon plasma in the infrared momentum domain or the inconsistency of the perturbational methods. A non-perturbative approach to the infrared problem in QCD is developed within the axial gauge. The closed equations for the structure functions that determine the gluon polarization tensor are obtained by using the Slavnov-Taylor identities to found approximately the three-gluon vertex. It is shown that the solution of the equations obtained by iterations does not remove the infrared singularity from the temperature Green functions. The nonperturbative solution of such equations is discussed.     

Semileptonic decays of heavy quarks in quantum chromodynamics

We investigate the semileptonic decays of heavy quarks in the leading non-trivial order in quantum chromodynamics. Effects of gluon corrections and the initial quark Fermi motion on the semileptonic rates and decay distributions are calculated. The resulting lepton energy spectrum for the charm semileptonic decay is compared with data to extract the mass of the charm quark. This is combined with the semileptonic branching ratio to predict the charm-quark lifetime. We find the lepton energy spectrum very stable with respect to gluon corrections. Expected spectra from the semileptonic decays of bottom and top quarks are presented. We also study the semileptonic decay process Q → q?v_? + G, involving the emission of a single hard non-collinear gluon. This process should be observable with a branching ratio of a few percent in the decays of top (and heavier) quarks.     

Curvature corrections and Kac–Moody compatibility conditions

We study possible restrictions on the structure of curvature corrections to gravitational theories in the context of their corresponding Kac–Moody algebras, following the initial work on E ₁₀ in Damour and Nicolai [Class Quant Grav 22:2849 (2005)]. We first emphasize that the leading quantum corrections of M-theory can be naturally interpreted in terms of (non-gravity) fundamental weights of E ₁₀. We then heuristically explore the extent to which this remark can be generalized to all over-extended algebras by determining which curvature corrections are compatible with their weight structure, and by comparing these curvature terms with known results on the quantum corrections for the corresponding gravitational theories.     

Neutrino and antineutrino charged-current inclusive scattering in iron in the energy range 20<E v <300 GeV

Inclusive charged-current interactions of high-energy neutrinos and antineutrinos have been studied with high statistics in a counter experiment at the CERN Super Proton Synchrotron. The energy dependence of the total cross-sections, the longitudinal structure function, and the nucleon structure functionsF ₂,xF ₃, and \(\bar q^{\bar v} \) are determined from these data. The analysis of theQ ²-dependence of the structure functions is used to test quantum chromodynamics, to determine the scale parameter Λ and the gluon distribution in the nucleon.     

Diquark correlations in the proton

The colour-magnetic interaction of quantum chromodynamics with a smearing function found from the fit to the - splitting is strong enough to support a bound state of a singletqq pair. We examine the possibility that this interaction leads to short-range quark-quark correlations in light baryons there-by providing the dynamical mechanism for a quark-diquark picture of the proton. In particular, we show that the correlation function of a singlet diquark in the proton is strongly enhanced at the origin (compared to that for the triplet diquark) with the correlation radiusr ₀, a typical cut-off radius in the spin interaction. The Fourier transform of the correlation function, which is related to the dependence on the momentum transfer of the structure functions in inclusive electron-proton scattering, may provide quite fundamental information on the diquark structure of the proton.     

On the 1-Loop Renormalization of the Electroweak Standard Model and its Application to Leptonic Processes

A renormalization scheme for the electroweak standard model is presented in which the electric charge and the masses of the gauge bosons, Higgs particle and fermions are used as physical parameters. The photon is treated such that quantum electrodynamics is contained as a simple substructure. Field renormalization respecting the gauge symmetry gives finite propagators and vertex functions. The Ward identities between the Green functions of the unphysical sector allow a renormalization that maintains the simple pole structure of the propagators in the t'Hooft-Feynman gauge. We give a complete list of self energies and all renormalization constants also in the unphysical Higgs and ghost sector. Explicit results are given for the renormalized self energies, vertex functions and boxes that enter the evaluation of 1-loop radiative corrections to fermionic processes. We calculate the 1-loop radiative corrections to purely leptonic reactions like μ decay, vμ_μe scattering and μ pair production in e⁺e⁻annihilation. A test of the standard model is performed by comparing these low energy data with the results of the PP collider experiments for the W and Z boson masses.