H. Breuer

Publications (118)240.81 Total impact

• Article: First Measurement of the Neutral Current Excitation of the Delta Resonance on a Proton Target

  Collaboration, D. Androic, D. S. Armstrong, J. Arvieux, S. L. Bailey, D. H. Beck, E. J. Beise, J. Benesch, F. Benmokhtar, L. Bimbot, [......], M. Stutzman, R. Suleiman, V. Tadevosyan, W. T. H. van Oers, M. Versteegen, E. Voutier, W. Vulcan, S. P. Wells, S. E. Williamson, S. A. Wood
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  ABSTRACT: The parity-violating asymmetry arising from inelastic electron-nucleon scattering at backward angle (~95 degrees) near the Delta(1232) resonance has been measured using a hydrogen target. From this asymmetry, we extracted the axial transition form factor G^A_{N\Delta}, a function of the axial Adler form factors C^A_i. Though G^A_{N\Delta} has been previously studied using charged current reactions, this is the first measurement of the weak neutral current excitation of the Delta using a proton target. For Q^2 = 0.34 (GeV/c)^2 and W = 1.18 GeV, the asymmetry was measured to be -33.4 \pm (5.3)_{stat} \pm (5.1)_{sys} ppm. The value of G^A_{N\Delta} determined from the hydrogen asymmetry was -0.05 \pm (0.35)_{stat} \pm (0.34)_{sys} \pm (0.06)_{theory}. These findings agree within errors with theoretical predictions for both the total asymmetry and the form factor. In addition to the hydrogen measurement, the asymmetry was measured at the same kinematics using a deuterium target. The asymmetry for deuterium was determined to be -43.6 \pm (14.6)_{stat} \pm (6.2)_{sys} ppm.
  12/2012;
• Article: Virtual Compton scattering and the generalized polarizabilities of the proton at Q2=0.92 and 1.76 GeV2

  H. Fonvieille, G. Laveissière, N. Degrande, S. Jaminion, C. Jutier, L. Todor, R. Di Salvo, L. Van Hoorebeke, L. C. Alexa, B. D. Anderson, [......], E. Voutier, J. W. Watson, L. B. Weinstein, K. Wijesooriya, R. Wilson, B. B. Wojtsekhowski, D. G. Zainea, W-M. Zhang, J. Zhao, Z.-L. Zhou
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  ABSTRACT: Virtual Compton scattering (VCS) on the proton has been studied at the Jefferson Laboratory using the exclusive photon electroproduction reaction ep→epγ. This paper gives a detailed account of the analysis which has led to the determination of the structure functions PLL−PTT/ε and PLT and the electric and magnetic generalized polarizabilities (GPs) αE(Q2) and βM(Q2) at values of the four-momentum transfer squared Q2=0.92 and 1.76 GeV2. These data, together with the results of VCS experiments at lower momenta, help building a coherent picture of the electric and magnetic GPs of the proton over the full measured Q2 range and point to their nontrivial behavior.
  Phys. Rev. C. 07/2012; 86(1).
• Article: Virtual Compton Scattering and the Generalized Polarizabilities of the Proton at Q^2=0.92 and 1.76 GeV^2

  H. Fonvieille, G. Laveissiere, N. Degrande, S. Jaminion, C. Jutier, L. Todor, R. Di Salvo, L. Van Hoorebeke, L. C. Alexa, B. D. Anderson, [......], E. Voutier, J. W. Watson, L. B. Weinstein, K. Wijesooriya, R. Wilson, B. B. Wojtsekhowski, D. G. Zainea, W. -M. Zhang, J. Zhao, Z. -L. Zhou
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  ABSTRACT: Virtual Compton Scattering (VCS) on the proton has been studied at Jefferson Lab using the exclusive photon electroproduction reaction (e p --> e p gamma). This paper gives a detailed account of the analysis which has led to the determination of the structure functions P_LL-P_TT/epsilon and P_LT, and the electric and magnetic generalized polarizabilities (GPs) alpha_E(Q^2) and beta_M(Q^2) at values of the four-momentum transfer squared Q^2= 0.92 and 1.76 GeV^2. These data, together with the results of VCS experiments at lower momenta, help building a coherent picture of the electric and magnetic GPs of the proton over the full measured Q^2-range, and point to their non-trivial behavior.
  05/2012;
• Source

  Available from: Elizabeth Beise

  Article: Measurement of the parity-violating asymmetry in inclusive electroproduction of π- near the Δ0 resonance.

  D Androić, D S Armstrong, J Arvieux, S L Bailey, D H Beck, E J Beise, J Benesch, F Benmokhtar, L Bimbot, J Birchall, [......], M Stutzman, R Suleiman, V Tadevosyan, W T H van Oers, M Versteegen, E Voutier, W Vulcan, S P Wells, S E Williamson, S A Wood
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  ABSTRACT: The parity-violating (PV) asymmetry of inclusive π- production in electron scattering from a liquid deuterium target was measured at backward angles. The measurement was conducted as a part of the G0 experiment, at a beam energy of 360 MeV. The physics process dominating pion production for these kinematics is quasifree photoproduction off the neutron via the Δ0 resonance. In the context of heavy-baryon chiral perturbation theory, this asymmetry is related to a low-energy constant d(Δ)- that characterizes the parity-violating γNΔ coupling. Zhu et al. calculated d(Δ)- in a model benchmarked by the large asymmetries seen in hyperon weak radiative decays, and predicted potentially large asymmetries for this process, ranging from A(γ)-=-5.2 to +5.2  ppm. The measurement performed in this work leads to A(γ)-=-0.36±1.06±0.37±0.03  ppm (where sources of statistical, systematic and theoretical uncertainties are included), which would disfavor enchancements considered by Zhu et al. proportional to V(ud)/V(us). The measurement is part of a program of inelastic scattering measurements that were conducted by the G0 experiment, seeking to determine the N-Δ axial transition form factors using PV electron scattering.
  Physical Review Letters 03/2012; 108(12):122002. · 7.37 Impact Factor
• Article: Transverse beam spin asymmetries at backward angles in elastic electron-proton and quasielastic electron-deuteron scattering.

  D Androić, D S Armstrong, J Arvieux, S L Bailey, D H Beck, E J Beise, J Benesch, F Benmokhtar, L Bimbot, J Birchall, [......], V Tadevosyan, W T H van Oers, M Versteegen, E Voutier, W Vulcan, S P Wells, S E Williamson, S A Wood, B Pasquini, M Vanderhaeghen
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  ABSTRACT: We have measured the beam-normal single-spin asymmetries in elastic scattering of transversely polarized electrons from the proton, and performed the first measurement in quasielastic scattering on the deuteron, at backward angles (lab scattering angle of 108°) for Q² = 0.22 GeV²/c² and 0.63 GeV²/c² at beam energies of 362 and 687 MeV, respectively. The asymmetry arises due to the imaginary part of the interference of the two-photon exchange amplitude with that of single-photon exchange. Results for the proton are consistent with a model calculation which includes inelastic intermediate hadronic (πN) states. An estimate of the beam-normal single-spin asymmetry for the scattering from the neutron is made using a quasistatic deuterium approximation, and is also in agreement with theory.
  Physical Review Letters 07/2011; 107(2):022501. · 7.37 Impact Factor
• Source

  Available from: Barbara Pasquini

  Article: Transverse Beam Spin Asymmetries at Backward Angles in Elastic Electron-Proton and Quasi-elastic Electron-Deuteron Scattering

  The Collaboration, D. Androić, D. S. Armstrong, J. Arvieux, S L Bailey, D. H. Beck, E. J. Beise, J. Benesch, F. Benmokhtar, L. Bimbot, [......], V. Tadevosyan, W T H Van Oers, M. Versteegen, E. Voutier, W. Vulcan, S.P. Wells, S. E. Williamson, S. A. Wood, B. Pasquini, M. Vanderhaeghen
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  ABSTRACT: We have measured the beam-normal single-spin asymmetries in elastic scattering of transversely polarized electrons from the proton, and performed the first measurement in quasi-elastic scattering on the deuteron, at backward angles (lab scattering angle of 108 degrees) for Q2 = 0.22 GeV^2/c^2 and 0.63 GeV^2/c^2 at beam energies of 362 MeV and 687 MeV, respectively. The asymmetry arises due to the imaginary part of the interference of the two-photon exchange amplitude with that of single photon exchange. Results for the proton are consistent with a model calculation which includes inelastic intermediate hadronic (piN) states. An estimate of the beam-normal single-spin asymmetry for the scattering from the neutron is made using a quasi-static deuterium approximation, and is also in agreement with theory.
  03/2011;
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  Available from: John Robert Arrington

  Article: Semi-inclusive charged-pion electroproduction off protons and deuterons: Cross sections, ratios, and access to the quark-parton model at low energies

  R. Asaturyan, R. Ent, H. Mkrtchyan, T. Navasardyan, V. Tadevosyan, G. S. Adams, A. Ahmidouch, T. Angelescu, J. Arrington, A. Asaturyan, [......], A. Villano, W. F. Vulcan, M. Wang, G. Warren, F. R. Wesselmann, B. Wojtsekhowski, S. A. Wood, C. Xu, L. Yuan, X. Zheng
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  ABSTRACT: A large set of cross sections for semi-inclusive electroproduction of charged pions (π±) from both proton and deuteron targets was measured. The data are in the deep-inelastic scattering region with invariant mass squared W2>4 GeV2 (up to ≈7 GeV2) and range in four-momentum transfer squared 2<Q2<4 (GeV/c)2, and cover a range in the Bjorken scaling variable 0.2<x<0.6. The fractional energy of the pions spans a range 0.3<z<1, with small transverse momenta with respect to the virtual-photon direction, Pt2<0.2 (GeV/c)2. The invariant mass that goes undetected, Mx or W′, is in the nucleon resonance region, W′<2 GeV. The new data conclusively show the onset of quark-hadron duality in this process, and the relation of this phenomenon to the high-energy factorization ansatz of electron-quark scattering and subsequent quark→pion production mechanisms. The x, z, and Pt2 dependences of several ratios (the ratios of favored-unfavored fragmentation functions, charged pion ratios, deuteron-hydrogen and aluminum-deuteron ratios for π+ and π−) have been studied. The ratios are found to be in good agreement with expectations based upon a high-energy quark-parton model description. We find the azimuthal dependences to be small, as compared to exclusive pion electroproduction, and consistent with theoretical expectations based on tree-level factorization in terms of transverse-momentum-dependent parton distribution and fragmentation functions. In the context of a simple model, the initial transverse momenta of d quarks are found to be slightly smaller than for u quarks, while the transverse momentum width of the favored fragmentation function is about the same as for the unfavored one, and both fragmentation widths are larger than the quark widths.
  Phys. Rev. C. 03/2011; 85(1).
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  Available from: R. Frascaria

  Article: The G0 Experiment: Apparatus for Parity-Violating Electron Scattering Measurements at Forward and Backward Angles

  Collaboration, D. Androic, D. S. Armstrong, J. Arvieux, R. Asaturyan, T. D. Averett, S L Bailey, G. Batigne, D. H. Beck, E. J. Beise, [......], E. Voutier, W. F. Vulcan, S.P. Wells, G. Warren, S. E. Williamson, R. J. Woo, S. A. Wood, C Yan, J Yun, V. Zeps
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  ABSTRACT: In the G0 experiment, performed at Jefferson Lab, the parity-violating elastic scattering of electrons from protons and quasi-elastic scattering from deuterons is measured in order to determine the neutral weak currents of the nucleon. Asymmetries as small as 1 part per million in the scattering of a polarized electron beam are determined using a dedicated apparatus. It consists of specialized beam-monitoring and control systems, a cryogenic hydrogen (or deuterium) target, and a superconducting, toroidal magnetic spectrometer equipped with plastic scintillation and aerogel Cerenkov detectors, as well as fast readout electronics for the measurement of individual events. The overall design and performance of this experimental system is discussed.
  03/2011;
• Source

  Available from: John Robert Arrington

  Article: Measurements of the electric form factor of the neutron up to Q2=3.4 GeV2 using the reaction 3He(e,e'n)pp.

  S Riordan, S Abrahamyan, B Craver, A Kelleher, A Kolarkar, J Miller, G D Cates, N Liyanage, B Wojtsekhowski, A Acha, [......], G M Urciuoli, B Vlahovic, H Voskanyan, K Wang, F R Wesselmann, J R Vignote, S A Wood, J Wright, H Yao, X Zhu
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  ABSTRACT: The electric form factor of the neutron was determined from studies of the reaction 3He(e,e'n)pp in quasielastic kinematics in Hall A at Jefferson Lab. Longitudinally polarized electrons were scattered off a polarized target in which the nuclear polarization was oriented perpendicular to the momentum transfer. The scattered electrons were detected in a magnetic spectrometer in coincidence with neutrons that were registered in a large-solid-angle detector. More than doubling the Q2 range over which it is known, we find G(E)(n)=0.0236±0.0017(stat)±0.0026(syst), 0.0208±0.0024±0.0019, and 0.0147±0.0020±0.0014 for Q(2)=1.72, 2.48, and 3.41 GeV2, respectively.
  Physical Review Letters 12/2010; 105(26):262302. · 7.37 Impact Factor
• Source

  Available from: Guy Ron

  Article: Measurements of the Electric Form Factor of the Neutron up to Q2=3.4 GeV2 using the Reaction He3(e,e'n)pp

  S. Riordan, S. Abrahamyan, B Craver, A Kelleher, A Kolarkar, J Miller, G D Cates, N Liyanage, B Wojtsekhowski, A. Acha, [......], G. M. Urciuoli, B. Vlahovic, H. Voskanyan, K Wang, F. R. Wesselmann, J. R. Vignote, S. A. Wood, J Wright, H Yao, X Zhu
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  ABSTRACT: The electric form factor of the neutron was determined from studies of the reaction He3(e,e'n)pp in quasi-elastic kinematics in Hall A at Jefferson Lab. Longitudinally polarized electrons were scattered off a polarized target in which the nuclear polarization was oriented perpendicular to the momentum transfer. The scattered electrons were detected in a magnetic spectrometer in coincidence with neutrons that were registered in a large-solid-angle detector. More than doubling the Q2-range over which it is known, we find GEn = 0.0225 +/- 0.0017 (stat) +/- 0.0024 (syst), 0.0200 +/- 0.0023 +/- 0.0018, and 0.0142 +/- 0.0019 +/- 0.0013 for Q2 = 1.72, 2.48, and 3.41 GeV2, respectively.
  08/2010;
• Source

  Available from: Elizabeth Beise

  Article: Strange quark contributions to parity-violating asymmetries in the backward angle G0 electron scattering experiment.

  D Androić, D S Armstrong, J Arvieux, S L Bailey, D H Beck, E J Beise, J Benesch, F Benmokhtar, L Bimbot, J Birchall, [......], M Stutzman, R Suleiman, V Tadevosyan, W T H van Oers, M Versteegen, E Voutier, W Vulcan, S P Wells, S E Williamson, S A Wood
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  ABSTRACT: We have measured parity-violating asymmetries in elastic electron-proton and quasielastic electron-deuteron scattering at Q2=0.22 and 0.63 GeV2. They are sensitive to strange quark contributions to currents in the nucleon and the nucleon axial-vector current. The results indicate strange quark contributions of approximately < 10% of the charge and magnetic nucleon form factors at these four-momentum transfers. We also present the first measurement of anapole moment effects in the axial-vector current at these four-momentum transfers.
  Physical Review Letters 01/2010; 104(1):012001. · 7.37 Impact Factor
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  Available from: L. Lagamba

  Article: Cross sections and Rosenbluth separations in 1H(e, e'K+)Lambda up to Q2=2.35 GeV2

  M. Coman, P. Markowitz, K. A. Aniol, K Baker, W. U. Boeglin, H. Breuer, P. Bydzovsky, A. Camsonne, J. Cha, C C Chang, [......], G. M. Urciuoli, A. Uzzle, A Vacheret, K Wang, K. Wijesooriya, B Wojtsekhowski, S. Wood, I. Yaron, X Zheng, L Zhu
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  ABSTRACT: The kaon electroproduction reaction 1H(e,e'K+)Lambda was studied as a function of the virtual-photon four-momentum, Q2, total energy, W, and momentum transfer, t, for different values of the virtual- photon polarization parameter. Data were taken at electron beam energies ranging from 3.40 to 5.75 GeV. The center of mass cross section was determined for 21 kinematics corresponding to Q2 of 1.90 and 2.35 GeV2 and the longitudinal, sigmaL, and transverse, sigmaT, cross sections were separated using the Rosenbluth technique at fixed W and t. The separated cross sections reveal a flat energy dependence at forward kaon angles not satisfactorily described by existing electroproduction models. Influence of the kaon pole on the cross sections was investigated by adopting an off-shell form factor in the Regge model which better describes the observed energy dependence of sigmaT and sigmaL. Comment: 5 pages, 4 figures. Submitted to Physical Review C, Rapid Communications
  11/2009;
• Article: High-resolution spectroscopy of Lambda16N by electroproduction.

  F Cusanno, G M Urciuoli, A Acha, P Ambrozewicz, K A Aniol, P Baturin, P Y Bertin, H Benaoum, K I Blomqvist, W U Boeglin, [......], R Subedi, V A Sulkosky, T Suzuki, H Ueno, P E Ulmer, P Veneroni, E Voutier, B B Wojtsekhowski, X Zheng, C Zorn
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  ABSTRACT: An experimental study of the (16)O(e,e'K(+))(Lambda)(16)N reaction has been performed at Jefferson Lab. A thin film of falling water was used as a target. This permitted a simultaneous measurement of the p(e,e'K(+))Lambda, Sigma(0) exclusive reactions and a precise calibration of the energy scale. A ground-state binding energy of 13.76+/-0.16 MeV was obtained for (Lambda)(16)N with better precision than previous measurements on the mirror hypernucleus (Lambda)(16)O. Precise energies have been determined for peaks arising from a Lambda in s and p orbits coupled to the p(1/2) and p(3/2) hole states of the (15)N core nucleus.
  Physical Review Letters 11/2009; 103(20):202501. · 7.37 Impact Factor
• Article: Applications of quark-hadron duality in the F2 structure function

  S. P. Malace, G. S. Adams, A. Ahmidouch, T. Angelescu, J. Arrington, R. Asaturyan, O. K. Baker, N. Benmouna, H. P. Blok, W. U. Boeglin, [......], M. Ungaro, A. Uzzle, S. Vidakovic, A. N. Villano, W. F. Vulcan, F. R. Wesselmann, B. Wojtsekhowski, S. A. Wood, L. Yuan, X. Zheng
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  ABSTRACT: Inclusive electron-proton and electron-deuteron inelastic cross sections have been measured at Jefferson Lab (JLab) in the resonance region, at large Bjorken x, up to 0.92, and four-momentum transfer squared Q2 up to 7.5 GeV2 in the experiment E00-116. These measurements are used to extend to larger x and Q2 precision, quantitative, studies of the phenomenon of quark-hadron duality. Our analysis confirms, both globally and locally, the apparent “violation” of quark-hadron duality previously observed at a Q2 of 3.5 GeV2 when resonance data are compared to structure function data created from CTEQ6M and MRST2004 parton distribution functions (PDFs). More importantly, our new data show that this discrepancy saturates by Q2~4 GeV2, becoming Q2 independent. This suggests only small violations of Q2 evolution by contributions from the higher-twist terms in the resonance region that is confirmed by our comparisons to ALEKHIN and ALLM97. We conclude that the unconstrained strength of the CTEQ6M and MRST2004 PDFs at large x is the major source of the disagreement between data and these parametrizations in the kinematic regime we study and that, in view of quark-hadron duality, properly averaged resonance region data could be used in global quantum chromodynamics fits to reduce PDF uncertainties at large x.
  Phys. Rev. C. 09/2009; 80(3).
• Source

  Available from: John Robert Arrington

  Article: Neutral Pion Electroproduction in the Resonance Region at High $Q^2$

  A. N. Villano, P Stoler, P. E. Bosted, S. H. Connell, M. M. Dalton, M K Jones, V Kubarovsky, G. S. Adams, A. Ahmidouch, J. Arrington, [......], V. Tvaskis, M Ungaro, A. Uzzle, S. Vidakovic, F. R. Wesselmann, B Wojtsekhowski, S. A. Wood, L Yuan, X Zheng, H Zhu
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  ABSTRACT: The process $ep \to e^{\prime}p^{\prime}\pi^0$ has been measured at $Q^2$ = 6.4 and 7.7 GeV/c$^2$)$^2$ in Jefferson Lab's Hall C. Unpolarized differential cross sections are reported in the virtual photon-proton center of mass frame considering the process $\gamma^{\ast}p \to p^{\prime}\pi^0$. Various details relating to the background subtractions, radiative corrections and systematic errors are discussed. The usefulness of the data with regard to the measurement of the electromagnetic properties of the well known $\Delta(1232)$ resonance is covered in detail. Specifically considered are the electromagnetic and scalar-magnetic ratios $R_{EM}$ and $R_{SM}$ along with the magnetic transition form factor $G_M^{\ast}$. It is found that the rapid fall off of the $\Delta(1232)$ contribution continues into this region of momentum transfer and that other resonances Comment: 41 pages including numerical cross section tables, updates include new phenomenological fit for multipole extraction in addition to simplified previous method, These fits are seen in figures 24,26 and 27 and the values are reported in Table VIII
  06/2009;
• Article: Virtual Compton scattering and neutral pion electroproduction in the resonance region up to the deep inelastic region at backward angles

  G. Laveissière, N. Degrande, S. Jaminion, C. Jutier, L. Todor, R. Di Salvo, L. Van Hoorebeke, L. C. Alexa, B. D. Anderson, K. A. Aniol, [......], E. Voutier, J. W. Watson, L. B. Weinstein, K. Wijesooriya, R. Wilson, B. B. Wojtsekhowski, D. G. Zainea, W.-M. Zhang, J. Zhao, Z.-L. Zhou
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  ABSTRACT: We have made the first measurements of the virtual Compton scattering (VCS) process via the H(e, e'p)γ exclusive reaction in the nucleon resonance region, at backward angles. Results are presented for the W-dependence at fixed Q2=1 GeV2 and for the Q2 dependence at fixed W near 1.5 GeV. The VCS data show resonant structures in the first and second resonance regions. The observed Q2 dependence is smooth. The measured ratio of H(e, e'p)γ to H(e, e'p)π0 cross sections emphasizes the different sensitivity of these two reactions to the various nucleon resonances. Finally, when compared to real Compton scattering (RCS) at high energy and large angles, our VCS data at the highest W (1.8-1.9 GeV) show a striking Q2 independence, which may suggest a transition to a perturbative scattering mechanism at the quark level.
  Phys. Rev. C. 01/2009; 79(1).
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  Available from: L. Lagamba

  Article: High Resolution Spectroscopy of 16N_Lambda by Electroproduction

  F. Cusanno, G. M. Urciuoli, A. Acha, P Ambrozewicz, K. A. Aniol, P. Baturin, P Y Bertin, H Benaoum, K. I. Blomqvist, W. U. Boeglin, [......], R. Subedi, V. A. Sulkosky, T Suzuki, H Ueno, P E Ulmer, P Veneroni, E. Voutier, B. B. Wojtsekhowski, X. Zeng, C. Zorn
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  ABSTRACT: An experimental study of the 16O(e,e'K^+)16N_Lambda reaction has been performed at Jefferson Lab. A thin film of falling water was used as a target. This permitted a simultaneous measurement of the p(e,e'K^+)Lambda,Sigma_0 exclusive reactions and a precise calibration of the energy scale. A ground-state binding energy of 13.76 +/- 0.16 MeV was obtained for 16N_Lambda with better precision than previous measurements on the mirror hypernucleus 16O_Lambda. Precise energies have been determined for peaks arising from a Lambda in s and p orbits coupled to the p_{1/2} and p_{3/2} hole states of the 15N core nucleus. Comment: 5 pages, 3 figures, 2 tables
  10/2008;
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  Available from: John Robert Arrington

  Article: Charged pion form factor between $Q^2$=0.60 and 2.45 GeV$^2$. I. Measurements of the cross section for the ${^1}$H($e,e'\pi^+$)$n$ reaction

  H.P. Blok, T. Horn, G. M. Huber, E. J. Beise, D. Gaskell, D. J. Mack, V. Tadevosyan, J Volmer, D. Abbott, K. Aniol, [......], D. Van Westrum, S. Vidakovic, W. Vulcan, G. Warren, S. A. Wood, C Xu, C Yan, W. -X. Zhao, X Zheng, B. Zihlmann
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  ABSTRACT: Cross sections for the reaction ${^1}$H($e,e'\pi^+$)$n$ were measured in Hall C at Thomas Jefferson National Accelerator Facility (JLab) using the CEBAF high-intensity, continous electron beam in order to determine the charged pion form factor. Data were taken for central four-momentum transfers ranging from $Q^2$=0.60 to 2.45 GeV$^2$ at an invariant mass of the virtual photon-nucleon system of $W$=1.95 and 2.22 GeV. The measured cross sections were separated into the four structure functions $\sigma_L$, $\sigma_T$, $\sigma_{LT}$, and $\sigma_{TT}$. The various parts of the experimental setup and the analysis steps are described in detail, including the calibrations and systematic studies, which were needed to obtain high precision results. The different types of systematic uncertainties are also discussed. The results for the separated cross sections as a function of the Mandelstam variable $t$ at the different values of $Q^2$ are presented. Some global features of the data are discussed, and the data are compared with the results of some model calculations for the reaction ${^1}$H($e,e'\pi^+$)$n$.
  10/2008;
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  Available from: John Robert Arrington

  Article: Charged pion form factor between Q2=0.60 and 2.45 GeV2. II. Determination of, and results for, the pion form factor

  G. M. Huber, H. P. Blok, T. Horn, E. J. Beise, D. Gaskell, D. J. Mack, V. Tadevosyan, J. Volmer, D. Abbott, K. Aniol, [......], D. Van Westrum, S. Vidakovic, W. Vulcan, G. Warren, S. A. Wood, C. Xu, C. Yan, W.-X. Zhao, X. Zheng, B. Zihlmann
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  ABSTRACT: The charged pion form factor, Fπ(Q2), is an important quantity that can be used to advance our knowledge of hadronic structure. However, the extraction of Fπ from data requires a model of the 1H(e,e'π+)n reaction and thus is inherently model dependent. Therefore, a detailed description of the extraction of the charged pion form factor from electroproduction data obtained recently at Jefferson Lab is presented, with particular focus given to the dominant uncertainties in this procedure. Results for Fπ are presented for Q2=0.60-2.45 GeV2. Above Q2=1.5 GeV2, the Fπ values are systematically below the monopole parametrization that describes the low Q2 data used to determine the pion charge radius. The pion form factor can be calculated in a wide variety of theoretical approaches, and the experimental results are compared to a number of calculations. This comparison is helpful in understanding the role of soft versus hard contributions to hadronic structure in the intermediate Q2 regime.
  Phys. Rev. C. 10/2008; 78(4).
• Article: Charged pion form factor between Q2=0.60 and 2.45 GeV2. I. Measurements of the cross section for the 1H(e,e'π+)n reaction

  H. P. Blok, T. Horn, G. M. Huber, E. J. Beise, D. Gaskell, D. J. Mack, V. Tadevosyan, J. Volmer, D. Abbott, K. Aniol, [......], D. Van Westrum, S. Vidakovic, W. Vulcan, G. Warren, S. A. Wood, C. Xu, C. Yan, W.-X. Zhao, X. Zheng, B. Zihlmann
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  ABSTRACT: Cross sections for the reaction 1H(e,e'π+)n were measured in Hall C at Thomas Jefferson National Accelerator Facility (JLab) using the high-intensity Continuous Electron Beam Accelerator Facility (CEBAF) to determine the charged pion form factor. Data were taken for central four-momentum transfers ranging from Q2=0.60 to 2.45 GeV2 at an invariant mass of the virtual photon-nucleon system of W=1.95 and 2.22 GeV. The measured cross sections were separated into the four structure functions σL,σT,σLT, and σTT. The various parts of the experimental setup and the analysis steps are described in detail, including the calibrations and systematic studies, which were needed to obtain high-precision results. The different types of systematic uncertainties are also discussed. The results for the separated cross sections as a function of the Mandelstam variable t at the different values of Q2 are presented. Some global features of the data are discussed, and the data are compared with the results of some model calculations for the reaction 1H(e,e'π+)n.
  Phys. Rev. C. 10/2008; 78(4).