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B. Braun

Bio: B. Braun is an academic researcher from University of Erlangen-Nuremberg. The author has contributed to research in topics: HERMES experiment & Deep inelastic scattering. The author has an hindex of 14, co-authored 21 publications receiving 1148 citations. Previous affiliations of B. Braun include Ludwig Maximilian University of Munich.

Papers
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Journal ArticleDOI
K. Ackerstaff, A. Airapetian1, N. Akopov1, M. Amarian1  +236 moreInstitutions (26)
TL;DR: The HERMES experiment as mentioned in this paper collects data on inclusive and semi-inclusive deep inelastic scattering of polarised positrons from polarised targets of H, D, and 3 He.
Abstract: The HERMES experiment is collecting data on inclusive and semi-inclusive deep inelastic scattering of polarised positrons from polarised targets of H, D, and 3 He. These data give information on the spin structure of the nucleon. This paper describes the forward angle spectrometer built for this purpose. The spectrometer includes numerous tracking chambers (micro-strip gas chambers, drift and proportional chambers) in front of and behind a 1.3 T.m magnetic field, as well as an extensive set of detectors for particle identification (a lead-glass calorimeter, a pre-shower detector, a transition radiation detector, and a threshold Cherenkov detector). Two of the main features of the spectrometer are its good acceptance and identification of both positrons and hadrons, in particular pions. These characteristics, together with the purity of the targets, are allowing HERMES to make unique contributions to the understanding of how the spins of the quarks contribute to the spin of the nucleon.

284 citations

Journal ArticleDOI
K. Ackerstaff, A. Airapetian1, Igor Akushevich, N. Akopov1  +183 moreInstitutions (26)
TL;DR: In this paper, the HERMES experiment at HERA was used for a measurement of the neutron spin structure function g1n(x, Q2) in deep inelastic scattering using 27.5 GeV longitudinally polarized positrons incident on a polarized 3He internal gas target.

222 citations

Journal ArticleDOI
K. Ackerstaff, A. Airapetian, N. Akopov, Igor Akushevich  +254 moreInstitutions (29)
TL;DR: In this article, the first moments of the polarized quark distributions were compared to predictions based on SU(3)f flavor symmetry and to a prediction from lattice QCD.

132 citations

Journal ArticleDOI
A. Airapetian1, N. Akopov, M. Amarian, E. C. Aschenauer  +173 moreInstitutions (1)
TL;DR: In this paper, the longitudinal spin asymmetry of pairs of hadrons with high transverse momentum pT was measured in photoproduction of two hadrons, and the measured asymmetry is A_(||) = -0.28±0.12(stat)± 0.02(syst).
Abstract: We present a measurement of the longitudinal spin asymmetry A|| in photoproduction of pairs of hadrons with high transverse momentum pT. Data were accumulated by the HERMES experiment using a 27.5 GeV polarized positron beam and a polarized hydrogen target internal to the HERA storage ring. For h^+h^- pairs with _(pT)^(h1)>1.5GeV/c and _(pT)^(h2)>1.0GeV/c, the measured asymmetry is A_(||) = -0.28±0.12(stat)±0.02(syst). This negative value is in contrast to the positive asymmetries typically measured in deep inelastic scattering from protons, and is interpreted to arise from a positive gluon polarization.

120 citations

Journal ArticleDOI
TL;DR: A feasibility test of a new method to polarize beams of strongly interacting charged particles circulating in a storage ring is described, and the polarization buildup is clearly demonstrated.
Abstract: A feasibility test of a new method to polarize beams of strongly interacting charged particles circulating in a storage ring is described. The stored particles, here protons, pass through a polarized hydrogen gas target (thickness 6\ifmmode\times\else\texttimes\fi{}${10}^{13}$ H/${\mathrm{cm}}^{2}$) in the ring some ${10}^{10}$ times and become partially polarized because one spin state is attenuated faster than the other. The polarization buildup is clearly demonstrated in the present experiment.

69 citations


Cited by
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Journal ArticleDOI
01 Apr 1988-Nature
TL;DR: In this paper, a sedimentological core and petrographic characterisation of samples from eleven boreholes from the Lower Carboniferous of Bowland Basin (Northwest England) is presented.
Abstract: Deposits of clastic carbonate-dominated (calciclastic) sedimentary slope systems in the rock record have been identified mostly as linearly-consistent carbonate apron deposits, even though most ancient clastic carbonate slope deposits fit the submarine fan systems better. Calciclastic submarine fans are consequently rarely described and are poorly understood. Subsequently, very little is known especially in mud-dominated calciclastic submarine fan systems. Presented in this study are a sedimentological core and petrographic characterisation of samples from eleven boreholes from the Lower Carboniferous of Bowland Basin (Northwest England) that reveals a >250 m thick calciturbidite complex deposited in a calciclastic submarine fan setting. Seven facies are recognised from core and thin section characterisation and are grouped into three carbonate turbidite sequences. They include: 1) Calciturbidites, comprising mostly of highto low-density, wavy-laminated bioclast-rich facies; 2) low-density densite mudstones which are characterised by planar laminated and unlaminated muddominated facies; and 3) Calcidebrites which are muddy or hyper-concentrated debrisflow deposits occurring as poorly-sorted, chaotic, mud-supported floatstones. These

9,929 citations

Journal ArticleDOI
TL;DR: In this article, the science case of an Electron-Ion Collider (EIC), focused on the structure and interactions of gluon-dominated matter, with the intent to articulate it to the broader nuclear science community, is presented.
Abstract: This White Paper presents the science case of an Electron-Ion Collider (EIC), focused on the structure and interactions of gluon-dominated matter, with the intent to articulate it to the broader nuclear science community. It was commissioned by the managements of Brookhaven National Laboratory (BNL) and Thomas Jefferson National Accelerator Facility (JLab) with the objective of presenting a summary of scientific opportunities and goals of the EIC as a follow-up to the 2007 NSAC Long Range plan. This document is a culmination of a community-wide effort in nuclear science following a series of workshops on EIC physics over the past decades and, in particular, the focused ten-week program on “Gluons and quark sea at high energies” at the Institute for Nuclear Theory in Fall 2010. It contains a brief description of a few golden physics measurements along with accelerator and detector concepts required to achieve them. It has been benefited profoundly from inputs by the users’ communities of BNL and JLab. This White Paper offers the promise to propel the QCD science program in the US, established with the CEBAF accelerator at JLab and the RHIC collider at BNL, to the next QCD frontier.

1,022 citations

Journal ArticleDOI
TL;DR: In this article, the properties of generalized parton distributions (GPDs) are discussed, which contain new information on the structure of hadrons and which enter the description of hard exclusive reactions.

615 citations

Journal ArticleDOI
TL;DR: In this paper, the authors review the present understanding of QCD spin physics: the proton spin puzzle and new developments aimed at understanding the transverse structure of the nucleon.
Abstract: This article reviews our present understanding of QCD spin physics: the proton spin puzzle and new developments aimed at understanding the transverse structure of the nucleon. Present experimental investigations of the nucleon's internal spin structure, the theoretical interpretation of the different measurements, and the open questions and challenges for future investigation are discussed.

421 citations

Journal ArticleDOI
Bernhard Mecking1, G. S. Adams2, S. Ahmad3, E. Anciant  +171 moreInstitutions (27)
TL;DR: The CEBAF Large Acceptance Spectrometer (CLAS) as mentioned in this paper is used to study photo-and electro-induced nuclear and hadronic reactions by providing efficient detection of neutral and charged particles over a good fraction of the full solid angle.
Abstract: The CEBAF large acceptance spectrometer (CLAS) is used to study photo- and electro-induced nuclear and hadronic reactions by providing efficient detection of neutral and charged particles over a good fraction of the full solid angle. A collaboration of about 30 institutions has designed, assembled, and commissioned CLAS in Hall B at the Thomas Jefferson National Accelerator Facility. The CLAS detector is based on a novel six-coil toroidal magnet which provides a largely azimuthal field distribution. Trajectory reconstruction using drift chambers results in a momentum resolution of 0.5% at forward angles. Cherenkov counters, time-of-flight scintillators, and electromagnetic calorimeters provide good particle identification. Fast triggering and high data-acquisition rates allow operation at a luminosity of 10 34 nucleon cm −2 s −1 . These capabilities are being used in a broad experimental program to study the structure and interactions of mesons, nucleons, and nuclei using polarized and unpolarized electron and photon beams and targets. This paper is a comprehensive and general description of the design, construction and performance of CLAS.

418 citations