A. Schaefer - University Regensburg

A. Schaefer
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Name
A. Schaefer
Affiliation
University Regensburg
City
Regensburg
Country
Germany

Pubs By Year

Pub Categories

 
High Energy Physics - Phenomenology (15)
 
High Energy Physics - Lattice (13)
 
Astrophysics of Galaxies (10)
 
High Energy Physics - Experiment (9)
 
Mathematics - Combinatorics (6)
 
Nuclear Theory (5)
 
High Energy Physics - Theory (3)
 
Instrumentation and Methods for Astrophysics (3)
 
Nonlinear Sciences - Chaotic Dynamics (1)
 
Physics - Statistical Mechanics (1)
 
Mathematics - Group Theory (1)
 
Quantitative Biology - Quantitative Methods (1)
 
Nuclear Experiment (1)

Publications Authored By A. Schaefer

Particle tracking is a powerful biophysical tool that requires conversion of large video files into position time series, i.e. traces of the species of interest for data analysis. Read More

Recent cosmological hydrodynamical simulations suggest that integral field spectroscopy can connect the high-order stellar kinematic moments h3 (~skewness) and h4 (~kurtosis) in galaxies to their cosmological assembly history. Here, we assess these results by measuring the stellar kinematics on a sample of 315 galaxies, without a morphological selection, using 2D integral field data from the SAMI Galaxy Survey. A proxy for the spin parameter ($\lambda_{R_e}$) and ellipticity ($\epsilon_e$) are used to separate fast and slow rotators; there exists a good correspondence to regular and non-regular rotators, respectively, as also seen in earlier studies. Read More

We use data from the Sydney-AAO Multi-Object Integral Field Spectrograph (SAMI) Galaxy Survey and the Galaxy And Mass Assembly (GAMA) survey to investigate the spatially-resolved signatures of the environmental quenching of star formation in galaxies. Using dust-corrected measurements of the distribution of H$\alpha$ emission we measure the radial profiles of star formation in a sample of 201 star-forming galaxies covering three orders of magnitude in stellar mass (M$_{*}$; $10^{8.1}$-$10^{10. Read More

Hector will be the new massively-multiplexed integral field spectroscopy (IFS) instrument for the Anglo-Australian Telescope (AAT) in Australia and the next main dark-time instrument for the observatory. Based on the success of the SAMI instrument, which is undertaking a 3400-galaxy survey, the integral field unit (IFU) imaging fibre bundle (hexabundle) technology under-pinning SAMI is being improved to a new innovative design for Hector. The distribution of hexabundle angular sizes is matched to the galaxy survey properties in order to image 90% of galaxies out to 2 effective radii. Read More

We present LZIFU (LaZy-IFU), an IDL toolkit for fitting multiple emission lines simultaneously in integral field spectroscopy (IFS) data. LZIFU is useful for the investigation of the dynamical, physical and chemical properties of gas in galaxies. LZIFU has already been applied to many world-class IFS instruments and large IFS surveys, including the Wide Field Spectrograph, the new Multi Unit Spectroscopic Explorer (MUSE), the Calar Alto Legacy Integral Field Area (CALIFA) survey, the Sydney-Australian-astronomical-observatory Multi-object Integral-field spectrograph (SAMI) Galaxy Survey. Read More

In this paper we investigate the existence of singular endomorphisms of the cuboidal Hamming graph $H(n_1,... Read More

In this paper we determine all singular endomorphisms of the Hamming graph and other related graphs. The Hamming graph has vertices $\mathbb{Z}^{m}_n$ where two vertices are adjacent, if their Hamming distance is $1$. We show that its singular endomorphisms are uniform (each kernel has the same size) and that they are induced by Latin hypercubes (which essentially determines the number of singular endomorphisms). Read More

We study triples of labeled dice in which the relation "is a better die than" is non-transitive. Focusing on such triples with an additional symmetry we call "balance," we prove that such triples of $n$-sided dice exist for all $n \geq 3$. We then examine the sums of the labels of such dice, and use these results to construct an $O(n^2)$ algorithm for verifying whether or not a triple of $n$-sided dice is balanced and non-transitive. Read More

This paper analyses the construction of the kernel graph of a non-synchronizing transformation semigroup and introduces the inverse synchronization problem. Given a transformation semigroup $S\leq T_n$, we construct the kernel graph $\text{Gr}(S)$ by saying $v$ and $w$ are adjacent, if there is no $f\in S$ with $vf=wf$. The kernel graph is trivial or complete if the semigroup is a synchronizing semigroup or a permutation group, respectively. Read More

A signed graph is a graph where the edges are assigned labels of either "$+$" or "$-$". The sign of a cycle in the graph is the product of the signs of its edges. We equip each signed complete graph with a vector whose entries are the number of negative $k$-cycles for $k\in\{3,\dots,n\}$. Read More

In the low redshift Universe (z<0.3), our view of galaxy evolution is primarily based on fibre optic spectroscopy surveys. Elaborate methods have been developed to address aperture effects when fixed aperture sizes only probe the inner regions for galaxies of ever decreasing redshift or increasing physical size. Read More

Finite 't Hooft coupling corrections to multiple physical observables in strongly coupled $N=4$ supersymmetric Yang-Mills plasma are examined, in an attempt to assess the stability of the expansion in inverse powers of the 't Hooft coupling $\lambda$. Observables considered include thermodynamic quantities, transport coefficients, and quasinormal mode frequencies. Although large $\lambda$ expansions for quasinormal mode frequencies are notably less well behaved than the expansions of other quantities, we find that a partial resummation of higher order corrections can significantly reduce the sensitivity of the results to the value of $\lambda$. Read More

We give a new proof of the theorem of Boesch-Tindell and Farzad-Mahdian-Mahmoodian-Saberi-Sadri that a directed graph extends to a strongly connected digraph on the same vertex set if and only if it has no complete directed cut. Our proof bounds the number of edges needed for such an extension; we give examples to demonstrate sharpness. We apply the characterization to a problem on non-transitive dice. Read More

We have observed two kinematically offset active galactic nuclei (AGN), whose ionised gas is at a different line-of-sight velocity to their host galaxies, with the SAMI integral field spectrograph (IFS). One of the galaxies shows gas kinematics very different to the stellar kinematics, indicating a recent merger or accretion event. We demonstrate that the star formation associated with this event was triggered within the last 100 Myr. Read More

Let $\Omega$ be a set of cardinality $n$, $G$ a permutation group on $\Omega$, and $f:\Omega\to\Omega$ a map which is not a permutation. We say that $G$ \emph{synchronizes} $f$ if the transformation semigroup $\langle G,f\rangle$ contains a constant map, and that $G$ is a \emph{synchronizing group} if $G$ synchronizes \emph{every} non-permutation. A synchronizing group is necessarily primitive, but there are primitive groups that are not synchronizing. Read More

The SAMI Galaxy Survey will observe 3400 galaxies with the Sydney-AAO Multi-object Integral-field spectrograph (SAMI) on the Anglo-Australian Telescope (AAT) in a 3-year survey which began in 2013. We present the throughput of the SAMI system, the science basis and specifications for the target selection, the survey observation plan and the combined properties of the selected galaxies. The survey includes four volume limited galaxy samples based on cuts in a proxy for stellar mass, along with low-stellar mass dwarf galaxies all selected from the Galaxy And Mass Assembly (GAMA) survey. Read More

We present the Early Data Release of the Sydney-AAO Multi-object Integral field spectrograph (SAMI) Galaxy Survey. The SAMI Galaxy Survey is an ongoing integral field spectroscopic survey of ~3400 low-redshift (z<0.12) galaxies, covering galaxies in the field and in groups within the Galaxy And Mass Assembly (GAMA) survey regions, and a sample of galaxies in clusters. Read More

We present a methodology for the regularisation and combination of sparse sampled and irregularly gridded observations from fibre-optic multi-object integral-field spectroscopy. The approach minimises interpolation and retains image resolution on combining sub-pixel dithered data. We discuss the methodology in the context of the Sydney-AAO Multi-object Integral-field spectrograph (SAMI) Galaxy Survey underway at the Anglo-Australian Telescope. Read More

Optical positions from the SuperCOSMOS Sky Survey have been compared in detail with accurate radio positions that define the second realisation of the International Celestial Reference Frame (ICRF2). The comparison was limited to the IIIaJ plates from the UK/AAO and Oschin (Palomar) Schmidt telescopes. A total of 1373 ICRF2 sources was used, with the sample restricted to stellar objects brighter than $B_J=20$ and Galactic latitudes $|b|>10^{\circ}$. Read More

We utilize H1 and ZEUS data for exclusive electroproduction of photons, $\rho^0$- and $\phi$-mesons to access generalized parton distributions at small momentum fraction. To do so, we employ state-of-the art techniques, based on next-to-leading order perturbation theory, flexible model parametrization, and Bayesian inference. We provide a partonic interpretation of our analysis, where emphasize is given to the transverse distribution of sea quarks and gluons. Read More

We analyze the time-like processes gamma gamma -> B Bbar and p p-bar -> gamma M at large Mandelstam variables within the handbag approach for which the process amplitudes factorize in hard partonic subprocesses and annihilation form factor. The latter represent moments of baryon-antibaryon generalized parton distributions. Symmetry relations restrict the number of independent annihilation form factors for the ground state baryons drastically. Read More

Based on the collinear factorization approach, we present a comprehensive perturbative next-to-leading (NLO) analysis of deeply virtual meson production (DVMP). Our representation in conformal Mellin space can serve as basis for a global fitting procedure to access generalized parton distributions from experimental measurements of DVMP and deeply virtual Compton scattering (DVCS). We introduce a rather general formalism for the evaluation of conformal moments that can be developed further beyond the considered order. Read More

We study the thermalization process in classical Yang-Mills (CYM) field theory starting from noisy glasma-like initial conditions by investigating the initial-value sensitivity of trajectories. Kunihiro et al. linked entropy generation to the Kolmogorov-Sinai entropy, which gives the entropy production rate in classical chaotic systems, calculated numerically for CYM fields starting from purely random initial field configurations. Read More

We study the influence of strong external magnetic fields on gluonic and fermionic observables in the QCD vacuum at zero and nonzero temperatures, via lattice simulations with N_f=1+1+1 staggered quarks of physical masses. The gluonic action density is found to undergo magnetic catalysis at low temperatures and inverse magnetic catalysis near and above the transition temperature, similar to the quark condensate. Moreover, the gluonic action develops an anisotropy: the chromo-magnetic field parallel to the external field is enhanced, while the chromo-electric field in this direction is suppressed. Read More

We present a study of baryon ground states and low lying excitations of non-strange and strange baryons. The results are based on seven gauge field ensembles with two dynamical light Chirally Improved (CI) quarks corresponding to pion masses between 255 and 596 MeV and a strange valence quark with mass fixed by the Omega baryon. The lattice spacing varies between 0. Read More

Within the collinear twist-3 framework, we analyze the double-spin asymmetry in collisions between longitudinally polarized nucleons and transversely polarized nucleons with focus on hadron and jet production. As was the case in direct photon production, the double-spin dependent cross section for hadron and jet production has the advantage of involving a complete set of collinear twist-3 functions. In addition, we outline further benefits of this observable for a potential future measurement at RHIC, which includes insight on the gluon helicity distribution as well as information on the Efremov-Teryaev-Qiu-Sterman function T_F(x,x) that plays a crucial role in single-spin asymmetries. Read More

The response of the QCD vacuum to a constant external (electro)magnetic field is studied through the tensor polarization of the chiral condensate and the magnetic susceptibility at zero and at finite temperature. We determine these quantities using lattice configurations generated with the tree-level Symanzik improved gauge action and N_f=1+1+1 flavors of stout smeared staggered quarks with physical masses. We carry out the renormalization of the observables under study and perform the continuum limit both at T>0 and at T=0, using different lattice spacings. Read More

Transverse single-spin asymmetries in inclusive deep inelastic lepton-nucleon scattering can be generated through multiphoton exchange between the leptonic and the hadronic part of the process. Here we consider the two-photon exchange, and mainly focus on the transverse target spin asymmetry. In particular, we investigate the case where two photons couple to different quarks. Read More

We present results for the spectrum of light and strange mesons on configurations with two flavors of mass-degenerate Chirally Improved sea quarks. The calculations are performed on seven ensembles of lattice size 16^3x32 at three different gauge couplings and with pion masses ranging from 250 to 600 MeV. To reliably extract excited states, we use the variational method with an interpolator basis containing both gaussian and derivative quark sources. Read More

The excited isovector meson spectrum is explored using two chirally improved dynamical quarks. Seven ensembles, with pion masses down to \approx 250 MeV are discussed and used for extrapolations to the physical point. Strange mesons are investigated using partially quenched s-quarks. Read More

2011Jun
Authors: The HERMES Collaboration, A. Airapetian, N. Akopov, Z. Akopov, E. C. Aschenauer, W. Augustyniak, R. Avakian, A. Avetissian, E. Avetisyan, S. Belostotski, N. Bianchi, H. P. Blok, A. Borissov, J. Bowles, I. Brodski, V. Bryzgalov, J. Burns, M. Capiluppi, G. P. Capitani, E. Cisbani, G. Ciullo, M. Contalbrigo, P. F. Dalpiaz, W. Deconinck, R. De Leo, L. De Nardo, E. De Sanctis, P. Di Nezza, M. Dueren, M. Ehrenfried, G. Elbakian, F. Ellinghaus, R. Fabbri, A. Fantoni, L. Felawka, S. Frullani, D. Gabbert, G. Gapienko, V. Gapienko, F. Garibaldi, G. Gavrilov, V. Gharibyan, F. Giordano, S. Gliske, M. Golembiovskaya, M. Hartig, D. Hasch, M. Hoek, Y. Holler, I. Hristova, Y. Imazu, A. Ivanilov, H. E. Jackson, H. S. Jo, S. Joosten, R. Kaiser, G. Karyan, T. Keri, E. Kinney, A. Kisselev, V. Korotkov, V. Kozlov, P. Kravchenko, V. G. Krivokhijine, L. Lagamba, L. Lapikas, I. Lehmann, P. Lenisa, A. Lopez Ruiz, W. Lorenzon, X. -G. Lu, X. -R. Lu, B. -Q. Ma, D. Mahon, N. C. R. Makins, S. I. Manaenkov, L. Manfre, Y. Mao, B. Marianski A. Martinez de la Ossa, H. Marukyan, C. A. Miller, Y. Miyachi, A. Movsisyan, M. Murray, A. Mussgiller, E. Nappi, Y. Naryshkin, A. Nass, M. Negodaev, W. -D. Nowak, L. L. Pappalardo, R. Perez-Benito, M. Raithel, P. E. Reimer, A. R. Reolon, C. Riedl, K. Rith, G. Rosner, A. Rostomyan, J. Rubin, D. Ryckbosch, Y. Salomatin, A. Schaefer, G. Schnell, K. P. Schueler, B. Seitz, T. -A. Shibata, V. Shutov, M. Stancari, M. Statera, E. Steffens, J. J. M. Steijger, F. Stinzing, S. Taroian, A. Terkulov, R. Truty, A. Trzcinski, M. Tytgat, Y. Van Haarlem, C. Van Hulse, D. Veretennikov, V. Vikhrov, I. Vilardi, S. Wang, S. Yaschenko, Z. Ye, S. Yen, V. Zagrebelnyy, D. Zeiler, B. Zihlmann, P. Zupranski

Double-spin asymmetries in exclusive electroproduction of real photons from a transversely polarized hydrogen target are measured with respect to the product of target polarization with beam helicity and beam charge, and with respect to the product of target polarization with beam helicity alone. The asymmetries arise from the deeply virtual Compton scattering process and its interference with the Bethe--Heitler process. They are related to the real part of the same combination of Compton form factors as that determining the previously published transverse target single-spin asymmetries through the imaginary part. Read More

We discuss modeling of generalized parton distributions (GPDs), their access from present experiments, and the phenomenological potential of an electron-ion collider. In particular, we present a comparison of phenomenological models of GPD H, extracted from hard exclusive meson and photon production. Specific emphasis is given to the utilization of evolution effects at moderate x_Bj in a future high-luminosity experiment within a larger Q^2 lever arm. Read More

2011Mar
Authors: The HERMES Collaboration, A. Airapetian, N. Akopov, Z. Akopov, E. C. Aschenauer, W. Augustyniak, R. Avakian, A. Avetissian, E. Avetisyan, S. Belostotski, N. Bianchi, H. P. Blok, A. Borissov, J. Bowles, V. Bryzgalov, J. Burns, M. Capiluppi, G. P. Capitani, E. Cisbani, G. Ciullo, M. Contalbrigo, P. F. Dalpiaz, W. Deconinck, R. De Leo, L. De Nardo, E. De Sanctis, M. Diefenthaler, P. Di Nezza, M. Dueren, M. Ehrenfried, G. Elbakian, F. Ellinghaus, R. Fabbri, A. Fantoni, L. Felawka, S. Frullani, D. Gabbert, G. Gapienko, V. Gapienko, F. Garibaldi, G. Gavrilov, V. Gharibyan, F. Giordano, S. Gliske, M. Golembiovskaya, C. Hadjidakis, M. Hartig, D. Hasch, G. Hill, A. Hillenbrand, M. Hoek, Y. Holler, I. Hristova, Y. Imazu, A. Ivanilov, H. E. Jackson, H. S. Jo, S. Joosten, R. Kaiser, G. Karyan, T. Keri, E. Kinney, A. Kisselev, V. Korotkov, V. Kozlov, P. Kravchenko, V. G. Krivokhijine, L. Lagamba, R. Lamb, L. Lapikas, I. Lehmann, P. Lenisa, L. A. Linden-Levy, A. Lopez Ruiz, W. Lorenzon, X. -G. Lu, X. -R. Lu, B. -Q. Ma, D. Mahon, N. C. R. Makins, S. I. Manaenkov, L. Manfre, Y. Mao, B. Marianski, A. Martinez de la Ossa, H. Marukyan, C. A. Miller, Y. Miyachi, A. Movsisyan, V. Muccifora, M. Murray, A. Mussgiller, E. Nappi, Y. Naryshkin, A. Nass, M. Negodaev, W. -D. Nowak, L. L. Pappalardo, R. Perez-Benito, N. Pickert, M. Raithel, P. E. Reimer, A. R. Reolon, C. Riedl, K. Rith, G. Rosner, A. Rostomyan, J. Rubin, D. Ryckbosch, Y. Salomatin, F. Sanftl, A. Schaefer, G. Schnell, K. P. Schueler, B. Seitz, T. -A. Shibata, V. Shutov, M. Stancari, M. Statera, E. Steffens, J. J. M. Steijger, H. Stenzel, J. Stewart, F. Stinzing, S. Taroian, A. Trzcinski, M. Tytgat, A. Vandenbroucke, Y. Van Haarlem, C. Van Hulse, D. Veretennikov, V. Vikhrov, I. Vilardi, C. Vogel, S. Wang, S. Yaschenko, H. Ye, Z. Ye, S. Yen, W. Yu, D. Zeiler, B. Zihlmann, P. Zupranski

Results of inclusive measurements of inelastic electron and positron scattering from unpolarized protons and deuterons at the HERMES experiment are presented. The structure functions $F_2^p$ and $F_2^d$ are determined using a parameterization of existing data for the longitudinal-to-transverse virtual-photon absorption cross-section ratio. The HERMES results provide data in the ranges $0. Read More

2010Dec
Authors: The HERMES Collaboration, A. Airapetian, N. Akopov, Z. Akopov, E. C. Aschenauer, W. Augustyniak, R. Avakian, A. Avetissian, E. Avetisyan, S. Belostotski, N. Bianchi, H. P. Blok, A. Borissov, J. Bowles, V. Bryzgalov, J. Burns, M. Capiluppi, G. P. Capitani, E. Cisbani, G. Ciullo, M. Contalbrigo, P. F. Dalpiaz, W. Deconinck, R. De Leo, L. De Nardo, E. De Sanctis, M. Diefenthaler, P. Di Nezza, M. Dueren, M. Ehrenfried, G. Elbakian, F. Ellinghaus, R. Fabbri, A. Fantoni, L. Felawka, S. Frullani, D. Gabbert, G. Gapienko, V. Gapienko, F. Garibaldi, G. Gavrilov, V. Gharibyan, F. Giordano, S. Gliske, M. Golembiovskaya, C. Hadjidakis, M. Hartig, D. Hasch, G. Hill, A. Hillenbrand, M. Hoek, Y. Holler, I. Hristova, Y. Imazu, A. Ivanilov, H. E. Jackson, H. S. Jo, S. Joosten, R. Kaiser, G. Karyan, T. Keri, E. Kinney, A. Kisselev, N. Kobayashi, V. Korotkov, V. Kozlov, P. Kravchenko, V. G. Krivokhijine, L. Lagamba, R. Lamb, L. Lapikas, I. Lehmann, P. Lenisa, L. A. Linden-Levy, A. Lopez Ruiz, W. Lorenzon, X. -G. Lu, X. -R. Lu, B. -Q. Ma, D. Mahon, N. C. R. Makins, S. I. Manaenkov, L. Manfre, Y. Mao, B. Marianski, A. Martinez de la Ossa, H. Marukyan, C. A. Miller, Y. Miyachi, A. Movsisyan, V. Muccifora, M. Murray, A. Mussgiller, E. Nappi, Y. Naryshkin, A. Nass, M. Negodaev, W. -D. Nowak, L. L. Pappalardo, R. Perez-Benito, N. Pickert, P. E. Reimer, A. R. Reolon, C. Riedl, K. Rith, G. Rosner, A. Rostomyan, J. Rubin, D. Ryckbosch, Y. Salomatin, F. Sanftl, A. Schaefer, G. Schnell, K. P. Schueler, B. Seitz, T. -A. Shibata, V. Shutov, M. Stancari, M. Statera, E. Steffens, J. J. M. Steijger, F. Stinzing, S. Taroian, A. Terkulov, A. Trzcinski, M. Tytgat, A. Vandenbroucke, Y. Van Haarlem, C. Van Hulse, D. Veretennikov, V. Vikhrov, I. Vilardi, S. Wang, S. Yaschenko, S. Yen, W. Yu, B. Zihlmann, P. Zupranski

Exclusive rho^0-meson electroproduction is studied in the HERMES experiment, using a 27.6 GeV longitudinally polarized electron/positron beam and unpolarized hydrogen and deuterium targets in the kinematic region 0.5 GeV^2 < Q^2 < 7. Read More

2010Aug
Authors: The HERMES Collaboration, A. Airapetian, N. Akopov, Z. Akopov, E. C. Aschenauer, W. Augustyniak, R. Avakian, A. Avetissian, E. Avetisyan, S. Belostotski, N. Bianchi, H. P. Blok, A. Borissov, J. Bowles, I. Brodski, V. Bryzgalov, J. Burns, M. Capiluppi, G. P. Capitani, E. Cisbani, G. Ciullo, M. Contalbrigo, P. F. Dalpiaz, W. Deconinck, R. De Leo, L. De Nardo, E. De Sanctis, M. Diefenthaler, P. Di Nezza, M. Dueren, M. Ehrenfried, G. Elbakian, F. Ellinghaus, A. Fantoni, L. Felawka, S. Frullani, D. Gabbert, G. Gapienko, V. Gapienko, F. Garibaldi, G. Gavrilov, V. Gharibyan, F. Giordano, S. Gliske, M. Golembiovskaya, C. Hadjidakis, M. Hartig, D. Hasch, G. Hill, A. Hillenbrand, M. Hoek, Y. Holler, I. Hristova, Y. Imazu, A. Ivanilov, H. E. Jackson, A. Jgoun, H. S. Jo, S. Joosten, R. Kaiser, G. Karyan, T. Keri, E. Kinney, A. Kisselev, N. Kobayashi, V. Korotkov, V. Kozlov, B. Krauss, P. Kravchenko, V. G. Krivokhijine, L. Lagamba, R. Lamb, L. Lapikas, I. Lehmann, P. Lenisa, L. A. Linden-Levy, A. Lopez Ruiz, W. Lorenzon, X. -G. Lu, X. -R. Lu, B. -Q. Ma, D. Mahon, N. C. R. Makins, S. I. Manaenkov, L. Manfre, Y. Mao, B. Marianski, A. Martinez de la Ossa, H. Marukyan, C. A. Miller, A. Movsisyan, V. Muccifora, M. Murray, D. Mueller, A. Mussgiller, E. Nappi, Y. Naryshkin, A. Nass, M. Negodaev, W. -D. Nowak, L. L. Pappalardo, R. Perez-Benito, N. Pickert, M. Raithel, P. E. Reimer, A. R. Reolon, C. Riedl, K. Rith, G. Rosner, A. Rostomyan, J. Rubin, D. Ryckbosch, Y. Salomatin, F. Sanftl, A. Schaefer, G. Schnell, K. P. Schueler, B. Seitz, T. -A. Shibata, V. Shutov, M. Stancari, M. Statera, E. Steffens, J. J. M. Steijger, H. Stenzel, J. Stewart, F. Stinzing, S. Taroian, A. Terkulov, A. Trzcinski, M. Tytgat, A. Vandenbroucke, P. B. Van der Nat, Y. Van Haarlem, C. Van Hulse, D. Veretennikov, V. Vikhrov, I. Vilardi, C. Vogel, S. Wang, S. Yaschenko, Z. Ye, S. Yen, W. Yu, D. Zeiler, B. Zihlmann, P. Zupranski

Azimuthal asymmetries in exclusive electroproduction of a real photon from a longitudinally polarized deuterium target are measured with respect to target polarization alone and with respect to target polarization combined with beam helicity and/or beam charge. The asymmetries appear in the distribution of the real photons in the azimuthal angle $\phi$ around the virtual photon direction, relative to the lepton scattering plane. The asymmetries arise from the deeply virtual Compton scattering process and its interference with the Bethe-Heitler process. Read More

2010Jun
Authors: HERMES collaboration, A. Airapetian, N. Akopov, Z. Akopov, E. C. Aschenauer, W. Augustyniak, R. Avakian, A. Avetissian, E. Avetisyan, A. Bacchetta, S. Belostotski, N. Bianchi, H. P. Blok, A. Borissov, J. Bowles, I. Brodski, V. Bryzgalov, J. Burns, M. Capiluppi, G. P. Capitani, E. Cisbani, G. Ciullo, M. Contalbrigo, P. F. Dalpiaz, W. Deconinck, R. De Leo, L. De Nardo, E. De Sanctis, M. Diefenthaler, P. Di Nezza, M. Dueren, M. Ehrenfried, G. Elbakian, F. Ellinghaus, U. Elschenbroich, R. Fabbri, A. Fantoni, L. Felawka, S. Frullani, D. Gabbert, G. Gapienko, V. Gapienko, F. Garibaldi, V. Gharibyan, F. Giordano, S. Gliske, M. Golembiovskaya, C. Hadjidakis, M. Hartig, D. Hasch, G. Hill, A. Hillenbrand, M. Hoek, Y. Holler, I. Hristova, Y. Imazu, A. Ivanilov, A. Izotov, H. E. Jackson, H. S. Jo, S. Joosten, R. Kaiser, G. Karyan, T. Keri, E. Kinney, A. Kisselev, N. Kobayashi, V. Korotkov, V. Kozlov, P. Kravchenko, L. Lagamba, R. Lamb, L. Lapikas, I. Lehmann, P. Lenisa, L. A. Linden-Levy, A. Lopez Ruiz, W. Lorenzon, X. -G. Lu, X. -R. Lu, B. -Q. Ma, D. Mahon, N. C. R. Makins, S. I. Manaenkov, L. Manfre, Y. Mao, B. Marianski, A. Martinez de la Ossa, H. Marukyan, C. A. Miller, Y. Miyachi, A. Movsisyan, M. Murray, A. Mussgiller, E. Nappi, Y. Naryshkin, A. Nass, M. Negodaev, W. -D. Nowak, L. L. Pappalardo, R. Perez-Benito, N. Pickert, M. Raithel, P. E. Reimer, A. R. Reolon, C. Riedl, K. Rith, G. Rosner, A. Rostomyan, J. Rubin, D. Ryckbosch, Y. Salomatin, F. Sanftl, A. Schaefer, G. Schnell, B. Seitz, T. -A. Shibata, V. Shutov, M. Stancari, M. Statera, E. Steffens, J. J. M. Steijger, H. Stenzel, J. Stewart, F. Stinzing, S. Taroian, A. Terkulov, A. Trzcinski, M. Tytgat, P. B. van der Nat, Y. Van Haarlem, C. Van Hulse, D. Veretennikov, V. Vikhrov, I. Vilardi, C. Vogel, S. Wang, S. Yaschenko, H. Ye, Z. Ye, S. Yen, W. Yu, D. Zeiler, B. Zihlmann, P. Zupranski

Single-spin asymmetries for pions and charged kaons are measured in semi-inclusive deep-inelastic scattering of positrons and electrons off a transversely nuclear-polarized hydrogen target. The dependence of the cross section on the azimuthal angles of the target polarization (phi_S)and the produced hadron (phi) is found to have a substantial sin(phi+phi_S) modulation for the production of pi+, pi- and K+. This Fourier component can be interpreted in terms of non-zero transversity distribution functions and non-zero favored and disfavored Collins fragmentation functions with opposite sign. Read More

2010Apr
Authors: The HERMES Collaboration, A. Airapetian, N. Akopov, Z. Akopov, E. C. Aschenauer, W. Augustyniak, R. Avakian, A. Avetissian, E. Avetisyan, B. Ball, S. Belostotski, N. Bianchi, H. P. Blok, H. Boettcher, A. Borissov, J. Bowles, I. Brodski, V. Bryzgalov, J. Burns, M. Capiluppi, G. P. Capitani, E. Cisbani, G. Ciullo, M. Contalbrigo, P. F. Dalpiaz, W. Deconinck, R. De Leo, L. De Nardo, E. De Sanctis, M. Diefenthaler, P. Di Nezza, M. Dueren, M. Ehrenfried, G. Elbakian, F. Ellinghaus, R. Fabbri, A. Fantoni, L. Felawka, S. Frullani, D. Gabbert, G. Gapienko, V. Gapienko, F. Garibaldi, G. Gavrilov, V. Gharibyan, F. Giordano, S. Gliske, M. Golembiovskaya, C. Hadjidakis, M. Hartig, D. Hasch, G. Hill, A. Hillenbrand, M. Hoek, Y. Holler, I. Hristova, Y. Imazu, A. Ivanilov, A. Izotov, H. E. Jackson, H. S. Jo, S. Joosten, R. Kaiser, G. Karyan, T. Keri, E. Kinney, A. Kisselev, N. Kobayashi, V. Korotkov, V. Kozlov, P. Kravchenko, V. G. Krivokhijne, L. Lagamba, R. Lamb, L. Lapikas, I. Lehmann, P. Lenisa, L. A. Linden-Levy, A. Lopez~Ruiz, W. Lorenzon, X. -G. Lu, X. -R. Lu, B. -Q. Ma, D. Mahon, N. C. R. Makins, S. I. Manaenkov, L. Manfre, Y. Mao, B. Marianski, A. Martinez de la Ossa, H. Marukyan, C. A. Miller, Y. Miyachi, A. Movsisyan, V. Muccifora, M. Murray, A. Mussgiller, E. Nappi, Y. Naryshkin, A. Nass, M. Negodaev, W. -D. Nowak, L. L. Pappalardo, R. Perez-Benito, N. Pickert, M. Raithel, P. E. Reimer, A. R. Reolon, C. Riedl, K. Rith, G. Rosner, A. Rostomyan, J. Rubin, D. Ryckbosch, Y. Salomatin, F. Sanftl, A. Schaefer, G. Schnell, K. P. Schueler, B. Seitz, T. -A. Shibata, V. Shutov, M. Stancari, M. Statera, E. Steffens, J. J. M. Steijger, H. Stenzel, J. Stewart, F. Stinzing, S. Taroian, A. Terkulov, A. Trzcinski, M. Tytgat, A. Vandenbroucke, P. B. van der Nat, Y. Van Haarlem, C. Van Hulse, D. Veretennikov, V. Vikhrov, I. Vilardi, C. Vogel, S. Wang, S. Yaschenko, H. Ye, Z. Ye, S. Yen, W. Yu, D. Zeiler, B. Zihlmann, P. Zupranski

Polarisation asymmetries are measured for the hard exclusive leptoproduction of real photons from a longitudinally polarised hydrogen target. These asymmetries arise from the deeply virtual Compton scattering and Bethe-Heitler processes. From the data are extracted two asymmetries in the azimuthal distribution of produced real photons about the direction of the exchanged virtual photon: A_UL with respect to the target polarisation and A_LL with respect to the product of the beam and target polarisations. Read More

2009Nov
Affiliations: 1QCDSF Collaboration, 2QCDSF Collaboration, 3QCDSF Collaboration

We present results on the scalar strangeness and charm contents of the nucleon and of the disconnected contributions to the nucleon spin. These are obtained on two flavour non-perturbatively improved Sheikholeslami-Wilson configurations at a pseudoscalar mass of 290 MeV. We quote f_{T_s} = m_s/m_N< = 0. Read More

Many Lattice QCD observables of phenomenological interest include so-called all-to-all propagators. The computation of these requires prohibitively large computational resources, unless they are estimated stochastically. This is usually done. Read More

We investigate hadrons and direct photon production in pp and pA collisions at the energies of RHIC and LHC within the color-dipole approach employing various saturation models. We show that greatest sensitivity to saturation effects is reached at very forward rapidities for pp collisions at LHC (\sqrt{s}=14 TeV). The ratio of direct-photon to pion production can be about 20-10 (at \eta=7-8). Read More

Results on semileptonic decay matrix elements of heavy-light mesons and charmonium spectrum and decay constant using a fine quenched lattice are presented. Read More

Tunneling between different topological sectors with dynamical chiral fermions is difficult because of a poor mass scaling of the pseudo-fermion estimate of the determinant. For small fermion masses it is virtually impossible using standard methods. However, by projecting out the small Wilson eigenvectors from the overlap operator, and treating the correction determinant exactly, we can significantly increase the rate of topological sector tunneling and reduce substantially the auto-correlation time. Read More

We evaluate IBM's Enhanced Cell Broadband Engine (BE) as a possible building block of a new generation of lattice QCD machines. The Enhanced Cell BE will provide full support of double-precision floating-point arithmetics, including IEEE-compliant rounding. We have developed a performance model and applied it to relevant lattice QCD kernels. Read More

We present two improvements to our previous dynamical overlap HMC algorithm. We introduce a new method of differentiating the eigenvectors of the Kernel operator, which removes an instability in the fermionic force. Secondly, by simulating part of the fermion determinant exactly, without pseudo-fermions, we are able to increase the rate of topological tunnelling by a factor of more than ten, reducing the auto-correlation. Read More

Quark-quark double scattering in eA DIS and its contribution to quark and anti-quark fragmentation functions are investigated with the generalized factorization of the relevant twist-four processes in pQCD. It is shown that the resulting modifications to quark and anti-quark fragmentation functions are different. While the numerical size of these effects cannot be determined from pQCD, the structure of our result leads to a number of qualitative predictions for the relative size of the effect for different hadrons. Read More

We study hard exclusive electroproduction of two pions in the QCD factorization approach at next-to-leading order (NLO) in the strong coupling. The pion pair can be produced both in an isovector and in an isoscalar state. The angular distribution of the produced pion pairs allows one to project out a component that depends on the interference of the isovector and isoscalar channels. Read More

We analyze the overlap of color-octet meson operators with the $\Upsilon$ and the $\eta_b$ and their excited states, especially the first radial excitations. Our analysis is based on NRQCD and includes all terms up to order $v^4$. We use a variety of source and sink operators as a basis for the variational method, which enables us to clearly separate the mass eigenstates and hence to extract the desired amplitudes. Read More

We present the non-forward quark matrix elements of operators with one and two covariant derivatives needed for the renormalisation of the first and second moments of generalised parton distributions in one-loop lattice perturbation theory using clover fermions. For some representations of the hypercubic group commonly used in simulations we define the sets of possible mixing operators and compute the one-loop mixing matrices of renormalisation factors. Tadpole improvement is applied to the results and some numerical examples are presented. Read More