A Measurement of the Strange Quark Contributions to the Electromagnetic Form Factors of the Nucleon PDF Download

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Languages : en
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G0 is a parity violating electron scattering program at the Thomas Jefferson National Accelerator Facility, and its forward angle measurement is reported in this thesis. In this experiment, parity violating asymmetries of elastic electron-proton scattering were measured over a range of four-momentum transfer from 0.12 to 1.0 (GeV/c)2. From the asymmetries, linear combinations of the strange electric and magnetic form factors of the nucleon, G$s\atop{E}$ + [eta]G$s\atop{M}$, are extracted over the same kinematic range. These results, combined with existing data from other experiments, indicate that both G$s\atop{E}$ and [eta]G$s\atop{M}$ are non-zero and dependent on the four-momentum transfer, with imply non-trivial strange quark contributions to the low energy electromagnetic properties of the nucleon.

Author: Mathew O. Muether
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Languages : en
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The G0 collaboration has measured parity-violating asymmetries in elastic electron-proton and quasi-elastic electron-deuteron scattering at Q^2 = 0.22, 0.63 GeV^2. These asymmetries are sensitive to strange quark contributions to electric and magnetic properties of the nucleon, as well as to the axial current of the nucleon. The measurements were made using the polarized beam at Jefferson Laboratory by detecting electrons scattered at ~110 degrees from liquid targets. Together with previous results from the G0 forward angle measurement, the form factors which characterize the strange electric, strange magnetic and axial contributions were found to be G^{s}_{E}(0.221 GeV^2)= -0.0142305 +/- 0.035562 +/- 0.0181952 +/-0.0176497 G^{s}_{M}(0.221 GeV^2)=0.0833777 +/- 0.18337 +/- 0.0854892 +/- 0.0780912 G^{e}_{A}(0.221 GeV^2)=-0.501236 +/- 0.317127 +/- 0.193005 +/- 0.0878386 G^{s}_{E}(0.628 GeV^2)=0.110227 +/-0.0488068 +/- 0.0296044 +/- 0.0236998 G^{s}_{M}(0.628 GeV^2)=-0.12354 +/- 0.10953 +/- 0.0614285 +/- 0.0316972 G^{e}_{A}(0.628 GeV^2)=-0.197329 +/- 0.425414 +/- 0.256755 +/- 0.0948741 with statistical, point-to-point systematic and global systematic uncertainties given respectively. These results indicate small (

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The G0 backward angle experiment, completed in Hall C of the Thomas Jefferson National Accelerator Facility (TJNAF), measured parity-violating asymmetries in elastic electron-proton and quasielastic electron-deuteron scattering at Q2 = 0.22 and 0.63 (GeV/c)2. The asymmetries are sensitive to strange quark contributions to currents in the nucleon and the nucleon axial-vector current. The results indicate strange quark contributions of lte 10% of the charge and magnetic nucleon form factors at these four-momentum transfers. This was also the first measurement of the anapole moment effects in the axial-vector current at these four-momentum transfers.

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We review a recent theoretical determination of the strange quark content of the electromagnetic form factors of the nucleon. These are compared with a global analysis of current experimental measurements in parity-violating electron scattering.

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The goal of the G0 experiment is to determine the contribution of the strange quarks in the quark-antiquark sea to the structure of the nucleon. To this end, the experiment measured parityviolating asymmetries from elastic electron-proton scattering from 0.12 ≤ Q2 ≤ 1.0 (GeV/c)2 at Thomas Jefferson National Accelerator Facility. These asymmetries come from the interference of the electromagnetic and neutral weak interactions, and are sensitive to the strange quark contributions in the proton. The results from the forward-angle measurement, the linear combination of the strange electric and magnetic form factors GsE +[eta]GsM, suggest possible non-zero, Q2 dependent, strange quark contributions and provide new information to understand the magnitude of the contributions. This dissertation presents the analysis and results of the forward-angle measurement. In addition, the G0 experiment measured the beam-normal single-spin asymmetry in the elastic scattering of transversely polarized 3 GeV electrons from unpolarized protons at Q2 = 0.15, 0.25 (GeV/c)2 as part of the forward-angle measurement. The transverse asymmetry provides a direct probe of the imaginary component of the two-photon exchange amplitude, the complete description of which is important in the interpretation of data from precision electron-scattering experiments. The results of the measurement indicate that calculations using solely the elastic nucleon intermediate state are insufficient and generally agree with calculations that include significant inelastic hadronic intermediate state contributions. This dissertation presents the analysis and results of this measurement.

Author: Phiala Elisabeth Shanahan
Publisher: Springer
ISBN: 3319314386
Category : Science
Languages : en
Pages : 224

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This thesis discusses two key topics: strangeness and charge symmetry violation (CSV) in the nucleon. It also provides a pedagogical introduction to chiral effective field theory tailored to the high-precision era of lattice quantum chromodynamics (QCD). Because the nucleon has zero net strangeness, strange observables give tremendous insight into the nature of the vacuum; they can only arise through quantum fluctuations in which strange–antistrange quark pairs are generated. As a result, the precise values of these quantities within QCD are important in physics arenas as diverse as precision tests of QCD, searches for physics beyond the Standard Model, and the interpretation of dark matter direct-detection experiments. Similarly, the precise knowledge of CSV observables has, with increasing experimental precision, become essential to the interpretation of many searches for physics beyond the Standard Model. In this thesis, the numerical lattice gauge theory approach to QCD is combined with the chiral perturbation theory formalism to determine strange and CSV quantities in a diverse range of observables including the octet baryon masses, sigma terms, electromagnetic form factors, and parton distribution functions. This thesis builds a comprehensive and coherent picture of the current status of understanding of strangeness and charge symmetry violation in the nucleon.

Author: Julie Roche
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Languages : en
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The possible role of the strange quarks in the spin structure of the nucleon has spawned a great deal of interest in the study of the contribution of strange quarks to the electromagnetic (EM) structure of the nucleon. Weak neutral form factors arising from the Z{sup 0} coupling of the electron to the proton, in addition to the usual electromagnetic form factors, give access to G{sub E}{sup s} and G{sub M}{sup s}: contributions of the strange quarks to the nucleon EM form factors. Various collaborations (SAMPLE at Bates, HAPPEX and G0 at Jefferson Lab, PVA4 at MAMI) have performed parity-violating electron scattering experiments in order to measure the strange quark form factors. In these high luminosity experiments, longitudinally-polarized electron beams are scattered off unpolarized targets of protons or deuterons; the resulting asymmetry in cross sections measured between the two beam helicity states is a simple function of G{sub E}{sup s} and G{sub M}{sup s}. Measurements at different angles and/or on different targets are necessary to separate the electric and magnetic strange quark form factors. The G0 collaboration has built a dedicated large acceptance apparatus which allows measurements of the asymmetry both at forward and backward angles off LH2 and LD2. As a result, the collaboration will be able to separately extract G{sub E}{sup s} and G{sub M}{sup s} over a range of four momentum transfer Q{sup 2} from 0.3 to 0.8 (GeV/c){sup 2} when the entire experimental program in Hall C at Jefferson Lab is completed. The first phase of the experiment (forward angle configuration) which is sensitive to linear combinations of the two strange quark form factors over the whole range of Q{sup 2}, was completed in May 2004; progress on the analysis set will be reported.

Author: Dean Darnell
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Category : Lattice theory
Languages : en
Pages : 122

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The strangeness contribution to the electric and magnetic properties of the nucleon has been under investigation experimentally for many years. Lattice Quantum Chromodynamics (LQCD) gives theoretical predictions of these measurements by implementing the continuum gauge theory on a discrete, mathematical Euclidean space-time lattice which provides a cutoff removing the ultra-violet divergences. In this dissertation we will discuss effective methods using LQCD that will lead to a better determination of the strangeness contribution to the nucleon properties. Strangeness calculations are demanding technically and computationally. Sophisticated techniques are required to carry them to completion. In this thesis, new theoretical and computational methods for this calculation such as twisted mass fermions, perturbative subtraction, and General Minimal Residual (GMRES) techniques which have proven useful in the determination of these form factors will be investigated. Numerical results of the scalar form factor using these techniques are presented. These results give validation to these methods in future calculations of the strange quark contribution to the electric and magnetic form factors.

Author: Serge Kox
Publisher: Springer Science & Business Media
ISBN: 3540263454
Category : Science
Languages : en
Pages : 198

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Almost 50 years after the proposal of Lee and Young in 1956 to test the hypothesis of parity violation in weak interactions and the subsequent experimental verification of parity violation by C. S. Wu, parity violation has today become a useful property of weak interactions. This is due to the fact that the focus nowadays has changed: parity violation in weak interactions is no more a topic of investigation but is used as a tool in many different fields ranging from nuclear physics to the search for the hidden extra dimensions requested by string theory. For our first workshop which took place June 5-8, 2002, at the Institut fiir Ke- physik of the Johannes Gutenberg-Universitat Mainz, we concentrated on the in vestigation of the strangeness contribution in the nucleon. This book contains the refereed and selected papers of the second workshop "From Parity Violation to Hadron Structure and more (Part II)", which took place June 8-11, in the Labo- toire de Physique Subatomique et de Cosmologie, in Grenoble. These papers appear in EPJAdirect, the electronic-only part of EPJA, and they are accessible without restrictions. They will also appear in printed form and can be ordered through Springer. The excellent presentations show the dramatic and steady progress in the accuracy of measured parity violating asymmetries over the last few years.

Author: Antonio Dobado
Publisher: Springer Science & Business Media
ISBN: 3540725164
Category : Science
Languages : en
Pages : 615

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The QNP series of international conferences on Quarks and Nuclear Physics is by now a well established and highly respected forum where the most recent developments in the field are discussed and communicated. QNP 2006 is the forth edition of this biennial meeting. Selected and refereed original contributions of QNP 2006 have been published in The European Physical Journal A - Hadrons and Nuclei (EPJ A), while the present proceedings book, in addition to reprinting the articles published in EPJ A, further includes all other contributions selected and accepted by the organizing committee for publication and archiving.