D Müller

Publications (28)6.45 Total impact

• Article: The Energy Spectra and Relative Abundances of Electrons and Positrons in the Galactic Cosmic Radiation

  W. Barwick, J. Beatty, R. Bower, J. Chaput, S. Coutu, Nolfo, A. DuVernois, D. Ellithorpe, D. Ficenec, J. Knapp, M. Lowder, S. McKee, D. Müller, A. Musser, L. Nutter, E. Schneider, P. Swordy, G. Tarlé, D. Tomasch, and E. Torbet
  [show abstract] [hide abstract]
  ABSTRACT: Observations of cosmic-ray electrons and positrons have been made with a new balloon-borne detector, the High-Energy Antimatter Telescope (HEAT), which was first flown in 1994 May from Fort Sumner, New Mexico. We describe the instrumental approach and the data analysis procedures, and we present results from this flight. The measurement has provided a new determination of the individual energy spectra of electrons and positrons from 5 GeV to about 50 GeV and of the combined "all-electron" intensity (e+ + e-) up to ~100 GeV. The single power-law spectral indices for electrons and positrons are α = 3.09 ± 0.08 and 3.3 ± 0.2, respectively. We find that a contribution from primary sources to the positron intensity in this energy region, if it exists, must be quite small.
  The Astrophysical Journal 01/2009; 498(2):779. · 6.02 Impact Factor
• Source

  Available from: arxiv.org

  Article: Theory of deeply virtual Compton scattering on the nucleon

  A. V. Belitsky, D Müller, A. Kirchner
  [show abstract] [hide abstract]
  ABSTRACT: We compute the cross section for leptoproduction of the real photon off the nucleon, which is sensitive to the deeply virtual Compton scattering amplitude with power accuracy. Our considerations go beyond the leading twist and involve the complete analysis in the twist-three approximation. We discuss consequences of the target and lepton beam polarizations for accessing the generalized parton distributions from experimental measurements of the azimuthal angular dependence of the final state photon or nucleon. We introduce several sets of asymmetries, defined as Fourier moments with respect to the azimuthal angle, which allow for a clear separation of the twist-two and -three sectors. Relying on a simple ansatz for the generalized parton distributions, we give quantitative estimates for azimuthal and spin asymmetries, discuss the uncertainties of these predictions brought in by radiative corrections, and compare them with experimental data as well as other theoretical expectations. Furthermore, we derive a general parametrization of the DVCS amplitudes in the region of small Bjorken variable. Comment: 76 pages, LaTeX, 16 figures, 3 tables, minor corrections
  12/2001;
• Source

  Available from: ArXiv

  Article: Twist-three analysis of photon electroproduction off the pion

  A. V. Belitsky, D. Müller, A. Kirchner, A. Schäfer
  [show abstract] [hide abstract]
  ABSTRACT: We study twist-three effects in spin, charge, and azimuthal asymmetries in deeply virtual Compton scattering on a spin-zero target. Contributions which are power suppressed in 1/Q generate a new azimuthal angle dependence of the cross section that is not present in the leading twist results. On the other hand, the leading twist terms are not modified by the twist-three contributions. They may get corrected at the twist-four level, however. In the Wandzura-Wilczek approximation these new terms in the Fourier expansion with respect to the azimuthal angle are entirely determined by the twist-two generalized parton distributions. We also discuss more general issues such as the general form of the angular dependence of the differential cross section, the validity of factorization at the twist-three level, and the relation of generalized parton distributions to spectral functions.
  Phys. Rev. D. 11/2001; 64(11).
• Source

  Available from: arxiv.org

  Article: Spin effects in deeply virtual Compton scattering

  A. V. Belitsky, A. Kirchner, D Müller
  [show abstract] [hide abstract]
  ABSTRACT: We consider the azimuthal angle dependence in the cross section of the hard leptoproduction of a photon on a nucleon target. We show that this dependence allows to define observables that isolate the twist-two and twist-three sectors in the deeply virtual Compton scattering amplitude. All twist-two and twist-three Compton form factors can be extracted from measurements of the charge odd part of the polarized cross section and give access to all generalized parton distributions.
  07/2001;
• Source

  Available from: arxiv.org

  Article: Hard exclusive meson production at next-to-leading order

  A. V. Belitsky, D Müller
  [show abstract] [hide abstract]
  ABSTRACT: We evaluate perturbative next-to-leading order corrections to the hard exclusive leptoproduction of pi+ mesons on a transversely polarized proton target. A model dependent study shows that these corrections can be large. We analyze the scale dependence and explore the Brodsky-Lepage-Mackenzie scale setting procedure. Although the predictions for the cross section suffer from theoretical uncertainties, the transverse nucleon single spin asymmetry turns out to be a rather stable observable since higher order effects approximately cancel there. Comment: 14 pages, LaTeX, 3 figures
  05/2001;
• Source

  Available from: arxiv.org

  Article: Twist-three observables in deeply virtual Compton scattering on the nucleon

  A. V. Belitsky, A. Kirchner, D Müller, A. Schäfer
  [show abstract] [hide abstract]
  ABSTRACT: We study twist-three effects in deeply virtual Compton scattering on an unpolarized spin-1/2 target. A careful definition of observables as Fourier moments w.r.t. the azimuthal angle allows for a clear separation of twist-two and -three effects. Although the latter are power suppressed, they give leading contributions to the twist-three asymmetries and do not affect the twist-two observables. Comment: 10 pages, LaTeX
  03/2001;
• Source

  Available from: arxiv.org

  Article: Off-forward gluonometry

  A. V. Belitsky, D Müller
  [show abstract] [hide abstract]
  ABSTRACT: We explore the deeply virtual Compton scattering process at NLO with the emphasis on the measurement of the tensor gluon skewed distributions. We recalculate the one-loop coefficient function and give two-loop results for anomalous dimensions and exclusive evolution kernels required for studying the logarithmic scaling violation. We evaluate weighted cross sections which give direct access to these functions on experiment. Comment: 11 pages, LaTeX, 3 figures
  05/2000;
• Source

  Available from: arxiv.org

  Article: Leading twist asymmetries in deeply virtual Compton scattering

  A. V. Belitsky, D Müller, L. Niedermeier, A. Schäfer
  [show abstract] [hide abstract]
  ABSTRACT: We calculate spin, charge, and azimuthal asymmetries in deeply virtual Compton scattering at leading twist-two level. The measurement of these asymmetries gives an access to the imaginary and real part of all deeply virtual Compton scattering amplitudes. We note that a consistent description of this process requires taking into account twist-three contributions and give then a model dependent estimate of these asymmetries. Comment: 21 pages, LaTeX, 4 figures, typos in Eqs. 18, 41 and 49 corrected, references updated
  04/2000;
• Source

  Available from: arxiv.org

  Article: Radiactiv corrections to deeply virtual compton scattering

  A. V. Belitsky, D. Müller, L. Niedermeier, A. Schäfer
  [show abstract] [hide abstract]
  ABSTRACT: We discuss possibilities of measurement of deeply virtual Compton scattering amplitudes via different asymmetries in order to access the underlying skewed parton distributions. Perturbative one-loop coefficient functions and two-loop evolution kernels, calculated recently by a tentative use of residual conformal symmetry of QCD, are used for a model dependent numerical estimation of scattering amplitudes.
  Czechoslovak Journal of Physics 12/1999; 50:123-130. · 0.42 Impact Factor
• Source

  Available from: ArXiv

  Article: Radiative corrections to deeply virtual Compton scattering

  A. V. Belitsky, D Müller, L. Niedermeier, A. Schäfer
  [show abstract] [hide abstract]
  ABSTRACT: We discuss possibilities of measurement of deeply virtual Compton scattering amplitudes via different asymmetries in order to access the underlying skewed parton distributions. Perturbative one-loop coefficient functions and two-loop evolution kernels, calculated recently by a tentative use of residual conformal symmetry of QCD, are used for a model dependent numerical estimation of scattering amplitudes. Comment: 9 pages LaTeX, 3 figures, czjphyse.cls required Talk given by D. M\"uller at Inter. Workshop ``PRAHA-Spin99'', Prague, Sept. 6-11, 1999
  10/1999;
• Source

  Available from: arxiv.org

  Article: Deeply virtual Compton scattering in next-to-leading order

  A. V. Belitsky, D Müller, L. Niedermeier, A. Schäfer
  [show abstract] [hide abstract]
  ABSTRACT: We study the amplitude of deeply virtual Compton scattering in next-to-leading order of perturbation theory including the two-loop evolution effects for different sets of skewed parton distributions (SPDs). It turns out that in the minimal subtraction scheme the relative radiative corrections are of order 20-50%. We analyze the dependence of our predictions on the choice of SPD, that will allow to discriminate between possible models of SPDs from future high precision experimental data, and discuss shortly theoretical uncertainties induced by the radiative corrections. Comment: 10 pages, LaTeX, 3 figures
  08/1999;
• Source

  Available from: arxiv.org

  Article: Exclusive evolution kernels in two-loop order: parity even sector

  A. V. Belitsky, D Müller
  [show abstract] [hide abstract]
  ABSTRACT: We complete the construction of the non-forward evolution kernels in next-to-leading order responsible for the scale dependence of e.g. parity even singlet distribution amplitudes. Our formalism is designed to avoid any explicit two-loop calculations employing instead conformal and supersymmetric constraints as well as known splitting functions. Comment: 10 pages, LaTeX
  06/1999;
• Source

  Available from: ArXiv

  Article: $\cN = 1$ supersymmetric constraints for evolution kernels

  A. V. Belitsky, D Müller
  [show abstract] [hide abstract]
  ABSTRACT: We provide a complete set of supersymmetric constraints for the anomalous dimensions of the conformal twist-two operators to all orders of perturbation theory. Employing them we derive new relations between the exclusive evolution kernels and apply them in QCD in order to get definite predictions at leading order and beyond. Comment: LaTeX, npb.sty required, 4 pages, Talk given at the 7th International Workshop on Deep Inelastic Scattring and QCD, DESY-Zeuthen, April 19-23, 1999
  05/1999;
• Source

  Available from: arxiv.org

  Article: Evolution of non-forward parton distributions in next-to-leading order: singlet sector

  A. V. Belitsky, D Müller, L. Niedermeier, A. Schäfer
  [show abstract] [hide abstract]
  ABSTRACT: We present a general method for the solution of the renormalization group equations for the non-forward parton distributions on the two-loop level in the flavour singlet channel based on an orthogonal polynomial reconstruction. Using this formalism we study the effects of the evolution on recently proposed model distribution functions. Comment: 19 pages, LaTeX, 3 figures; factor of momentum fraction in front of forward gluon density, lost in numerical modeling of input gluon SPD from double distribution, is recovered: evolution curves in Figs. 2 and 3 are rescaled accordingly
  10/1998;
• Article: Performance of the HEAT spectrometer for cosmic ray electrons and positrons

  Dietrich Müller, S.W Barwick, J.J Beatty, C.R Bower, C Chaput, S Coutu, G de Nolfo, D Ellithorpe, D Ficenec, D.M Lowder, S McKee, D Müller, J.A Musser, S.L Nutter, E Schneider, S.P Swordy, K.K Tang, G Tarlé, A.D Tomasch, E Torbet
  [show abstract] [hide abstract]
  ABSTRACT: A new detector system for observations of cosmic ray electrons and positrons has been flown on a high altitude balloon in May 1994. The instrumentation includes a superconducting magnet and a drift tube hodoscope for the measurement of particle rigidities, and a combination of transition radiation detectors, shower counters and a time-of-flight system for particle identification and energy measurement. We will discuss the performance of the individual components and demonstrate that a reliable identification of the rare positron component has been achieved up to 50 GeV.
  Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment.
• Article: Predictions from conformal algebra for the deeply virtual Compton scattering

  A.V. Belitsky, D. Müller
  [show abstract] [hide abstract]
  ABSTRACT: Basing on the constraint equalities which arise from the algebra of the collinear conformal group and the conformal operator product expansion, we predict the solutions of the leading order evolution equations for the non-forward distributions, including transversity, in terms of the conformal moments; next-to-leading order flavour singlet coefficient functions for the polarized and unpolarized deeply virtual Compton scattering; as well as the contribution from renormalon chains to the eigenfunctions of the exclusive non-singlet evolution kernel.
  Physics Letters B.
• Source

  Available from: arxiv.org

  Article: Leading logarithmic evolution of the off-forward distributions

  A.V Belitsky, B Geyer, D Müller, A Schäfer
  [show abstract] [hide abstract]
  ABSTRACT: We have found the analytical solution of the LO-evolution equation for off-forward distributions which arise in the processes of deeply virtual Compton scattering or exclusive production of mesons. We present the predictions for their evolution with an input distribution taken from recent bag model calculations.
  Physics Letters B.
• Article: Two-loop effects in the evolution of non-forward distributions

  A.V. Belitsky, D. Müller, L. Niedermeier, A. Schäfer
  [show abstract] [hide abstract]
  ABSTRACT: We study the effects of next-to-leading order corrections on the evolution of the twist-two non-forward parton distribution functions in the flavour non-singlet sector. It is found that the deviation from leading order evolution is small for all values of the parton momentum fraction variable for moderately large values of the scale parameter.
  Physics Letters B.
• Article: Evolution of non-forward parton distributions in next-to-leading order: singlet sector

  A.V. Belitsky, D. Müller, L. Niedermeier, A. Schäfer
  [show abstract] [hide abstract]
  ABSTRACT: We present a general method for the solution of the renormalization group equations for the non-forward parton distributions on the two-loop level in the flavour singlet channel based on an orthogonal polynomial reconstruction. Using this formalism we study the effects of the evolution on recently proposed model distribution functions.
  Nuclear Physics B.
• Article: Theory of deeply virtual Compton scattering on the nucleon

  A.V. Belitsky, D. Müller, A. Kirchner
  [show abstract] [hide abstract]
  ABSTRACT: We compute the cross section for leptoproduction of the real photon off the nucleon, which is sensitive to the deeply virtual Compton scattering amplitude with power accuracy. Our considerations go beyond the leading twist and involve the complete analysis in the twist-three approximation. We discuss consequences of the target and lepton beam polarizations for accessing the generalized parton distributions from experimental measurements of the azimuthal angular dependence of the final state photon or nucleon. We introduce several sets of asymmetries, defined as Fourier moments with respect to the azimuthal angle, which allow for a clear separation of the twist-two and -three sectors. Relying on a simple ansatz for the generalized parton distributions, we give quantitative estimates for azimuthal and spin asymmetries, discuss the uncertainties of these predictions brought in by radiative corrections, and compare them with experimental data as well as other theoretical expectations. Furthermore, we derive a general parametrization of the DVCS amplitudes in the region of small Bjorken variable.
  Nuclear Physics B.