J. Arrington - The Jefferson Lab Fpi Collaboration

J. Arrington
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J. Arrington
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The Jefferson Lab Fpi Collaboration
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Nuclear Experiment (47)
 
Nuclear Theory (18)
 
High Energy Physics - Phenomenology (13)
 
High Energy Physics - Experiment (10)
 
Physics - Instrumentation and Detectors (3)
 
Physics - Atomic Physics (3)

Publications Authored By J. Arrington

The spatial distribution of charge and magnetization within the nucleon (proton and neutron) is encoded in the elastic electromagnetic form factors $G_E^{(p,n)}$ and $G_M^{(p,n)}$. These form factors have been precisely measured utilizing elastic electron scattering, and the combination of proton and neutron form factors allows for the separation of the up- and down-quark contributions to the nucleon form factors. We expand on our original analyses and extract the up- and down-quark contributions to the nucleon electromagnetic form factors from worldwide data with an emphasis on precise new data covering the low-momentum region, which is sensitive to the large-scale structure of the nucleon. Read More

The charge and magnetic form factors, FC and FM, of 3He have been extracted in the kinematic range 25 fm-2 < Q2 < 61 fm-2 from elastic electron scattering by detecting 3He recoil nuclei and electrons in coincidence with the High Resolution Spectrometers of the Hall A Facility at Jefferson Lab. The measurements are indicative of a second diffraction minimum for the magnetic form factor, which was predicted in the Q2 range of this experiment, and of a continuing diffractive structure for the charge form factor. The data are in qualitative agreement with theoretical calculations based on realistic interactions and accurate methods to solve the three-body nuclear problem. Read More

We propose to measure the photo-production cross section of $J/{\psi}$ near threshold, in search of the recently observed LHCb hidden-charm resonances $P_c$(4380) and $P_c$(4450) consistent with 'pentaquarks'. The observation of these resonances in photo-production will provide strong evidence of the true resonance nature of the LHCb states, distinguishing them from kinematic enhancements. A bremsstrahlung photon beam produced with an 11 GeV electron beam at CEBAF covers the energy range of $J/{\psi}$ production from the threshold photo-production energy of 8. Read More

Structure functions, as measured in lepton-nucleon scattering, have proven to be very useful in studying the quark dynamics within the nucleon. However, it is experimentally difficult to separately determine the longitudinal and transverse structure functions, and consequently there are substantially less data available for the longitudinal structure function in particular. Here we present separated structure functions for hydrogen and deuterium at low four--momentum transfer squared, Q^2< 1 GeV^2, and compare these with parton distribution parameterizations and a k_T factorization approach. Read More

2016Mar
Authors: D. Rimal, D. Adikaram, B. A. Raue, L. B. Weinstein, J. Arrington, W. K. Brooks, M. Ungaro, K. P. Adhikari, Z. Akbar, S. Anefalos Pereira, R. A. Badui, J. Ball, N. A. Baltzell, M. Battaglieri, V. Batourine, I. Bedlinskiy, R. P. Bennett, A. S. Biselli, S. Boiarinov, W. J. Briscoe, S. Bültmann, D. S. Carman, A. Celentano, T. Chetry, G. Ciullo, L. Clark, L. Colaneri, P. L. Cole, N. Compton, M. Contalbrigo, O. Cortes, V. Crede, A. D'Angelo, N. Dashyan, R. De Vita, A. Deur, C. Djalali, R. Dupre, H. Egiyan, A. El Alaoui, L. El Fassi, P. Eugenio, G. Fedotov, R. Fersch, A. Filippi, J. A. Fleming, T. A. Forest, A. Fradi, N. Gevorgyan, Y. Ghandilyan, G. P. Gilfoyle, K. L. Giovanetti, F. X. Girod, C. Gleason, W. Gohn, E. Golovatch, R. W. Gothe, K. A. Griffioen, L. Guo, K. Hafidi, C. Hanretty, N. Harrison, M. Hattawy, D. Heddle, K. Hicks, M. Holtrop, S. M. Hughes, Y. Ilieva, D. G. Ireland, B. S. Ishkhanov, E. L. Isupov, D. Jenkins, H. Jiang, S. Joosten, D. Keller, P. Khetarpal, G. Khachatryan, M. Khandaker, W. Kim, A. Klein, F. J. Klein, V. Kubarovsky, S. E. Kuhn, S. V. Kuleshov, L. Lanza, P. Lenisa, K. Livingston, H. Y. Lu, I . J . D. MacGregor, N. Markov, B. McKinnon, M. D. Mestayer, M. Mirazita, V. Mokeev, A Movsisyan, E. Munevar, C. Munoz Camacho, P. Nadel-Turonski, A. Ni, S. Niccolai, G. Niculescu, I. Niculescu, M. Osipenko, A. I. Ostrovidov, M. Paolone, R. Paremuzyan, K. Park, E. Pasyuk, W. Phelps, S. Pisano, O. Pogorelko, J. W. Price, Y. Prok, D. Protopopescu, A. J. R. Puckett, A. Rizzo, G. Rosner, P. Rossi, P. Roy, F. Sabatié, C. Salgado, R. A. Schumacher, E. Seder, Y. G. Sharabian, Iu. Skorodumina, G. D. Smith, D. Sokhan, N. Sparveris, Ivana Stankovic, S. Stepanyan, S. Strauch, V. Sytnik, M. Taiuti, B. Torayev, H. Voskanyan, E. Voutier, N. K. Walford, D. P. Watts, X. Wei, M. H. Wood, N. Zachariou, L. Zana, J. Zhang, Z. W. Zhao, I. Zonta

[Background] The electromagnetic form factors of the proton measured by unpolarized and polarized electron scattering experiments show a significant disagreement that grows with the squared four momentum transfer ($Q^{2}$). Calculations have shown that the two measurements can be largely reconciled by accounting for the contributions of two-photon exchange (TPE). TPE effects are not typically included in the standard set of radiative corrections since theoretical calculations of the TPE effects are highly model dependent, and, until recently, no direct evidence of significant TPE effects has been observed. Read More

In a recent paper, Hagelstein and Pascalutsa examine the error associated with an expansion of proton structure corrections to the Lamb shift in terms of moments of the charge distribution. They propose a small modification to a conventional parameterization of the proton's charge form factor and show that this can resolve the proton radius puzzle. However, while the size of the "bump" they add to the form factor is small, it is large compared to the total proton structure effects in the initial parameterization, yielding a final form factor that is unphysical. Read More

2015Nov
Affiliations: 1Jefferson Lab Hall A Collaboration, 2Jefferson Lab Hall A Collaboration, 3Jefferson Lab Hall A Collaboration, 4Jefferson Lab Hall A Collaboration, 5Jefferson Lab Hall A Collaboration, 6Jefferson Lab Hall A Collaboration, 7Jefferson Lab Hall A Collaboration, 8Jefferson Lab Hall A Collaboration, 9Jefferson Lab Hall A Collaboration, 10Jefferson Lab Hall A Collaboration, 11Jefferson Lab Hall A Collaboration, 12Jefferson Lab Hall A Collaboration, 13Jefferson Lab Hall A Collaboration, 14Jefferson Lab Hall A Collaboration, 15Jefferson Lab Hall A Collaboration, 16Jefferson Lab Hall A Collaboration, 17Jefferson Lab Hall A Collaboration, 18Jefferson Lab Hall A Collaboration, 19Jefferson Lab Hall A Collaboration, 20Jefferson Lab Hall A Collaboration, 21Jefferson Lab Hall A Collaboration, 22Jefferson Lab Hall A Collaboration, 23Jefferson Lab Hall A Collaboration

Report of the experimental activities in Hall A at Thomas Jefferson National Accelerator Facility during 2013. Read More

The past decade has provided a much clearer picture of the structure of high-momentum components in nucleons, associated with hard, short-distance interactions between pairs of nucleons. Recent Jefferson Lab data on light nuclei suggest a connection between these so-called 'short-range correlations' and the modification of the quark structure of nucleons in the nuclear environment. In light of this discovery that the detailed nuclear structure is important in describing the nuclear quark distributions, we examine the potential impact of the isospin-dependent structure of nuclei to see at what level this might yield flavor-dependent effects in nuclear quark distributions. Read More

We have determined the structure function ratio $R^d_{\rm EMC}=F_2^d/(F_2^n+F_2^p)$ from recently published $F_2^n/F_2^d$ data taken by the BONuS experiment using CLAS at Jefferson Lab. This ratio deviates from unity, with a slope $dR_{\rm EMC}^{d}/dx= -0.10\pm 0. Read More

A detailed examination of issues associated with proton radius extractions from elastic electron-proton scattering experiments is presented. Sources of systematic uncertainty and model dependence in the extractions are discussed, with an emphasis on how these may impact the proton charge and magnetic radii. A comparison of recent Mainz data to previous world data is presented, highlighting the difference in treatment of systematic uncertainties as well as tension between different data sets. Read More

In light of the proton radius puzzle, the discrepancy between measurements of the proton charge radius from muonic hydrogen and those from electronic hydrogen and electron-proton scattering measurements, we reexamine the charge radius extractions from electron scattering measurements. We provide a recommended value for the proton RMS charge radius, $r_E = 0.879 \pm 0. Read More

We perform a new analysis of electron-proton scattering data to determine the proton electric and magnetic radii, enforcing model-independent constraints from form factor analyticity. A wide-ranging study of possible systematic effects is performed. An improved analysis is developed that rebins data taken at identical kinematic settings, and avoids a scaling assumption of systematic errors with statistical errors. Read More

The spatial distribution of charge and magnetization within the proton is encoded in the elastic form factors. These have been precisely measured in elastic electron scattering, and the combination of proton and neutron form factors allows for the separation of the up- and down-quark contributions. In this work, we extract the proton and neutron form factors from world's data with an emphasis on precise new data covering the low-momentum region, which is sensitive to the large-scale structure of the nucleon. Read More

Using data from the recent BONuS experiment at Jefferson Lab, which utilized a novel spectator tagging technique to extract the inclusive electron-free neutron scattering cross section, we obtain the first direct observation of quark-hadron duality in the neutron F_2 structure function. The data are used to reconstruct the lowest few (N=2, 4 and 6) moments of F_2 in the three prominent nucleon resonance regions, as well as the moments integrated over the entire resonance region. Comparison with moments computed from global parametrizations of parton distribution functions suggest that quark--hadron duality holds locally for the neutron in the second and third resonance regions down to Q^2 ~ 1 GeV^2, with violations possibly up to 20% observed in the first resonance region. Read More

Background: Measurements of forward exclusive meson production at different squared four-momenta of the exchanged virtual photon, $Q^2$, and at different four-momentum transfer, t, can be used to probe QCD's transition from meson-nucleon degrees of freedom at long distances to quark-gluon degrees of freedom at short scales. Ratios of separated response functions in $\pi^-$ and $\pi^+$ electroproduction are particularly informative. The ratio for transverse photons may allow this transition to be more easily observed, while the ratio for longitudinal photons provides a crucial verification of the assumed pole dominance, needed for reliable extraction of the pion form factor from electroproduction data. Read More

2014Nov
Authors: O. Hen, M. Sargsian, L. B. Weinstein, E. Piasetzky, H. Hakobyan, D. W. Higinbotham, M. Braverman, W. K. Brooks, S. Gilad, K. P. Adhikari, J. Arrington, G. Asryan, H. Avakian, J. Ball, N. A. Baltzell, M. Battaglieri, A. Beck, S. May-Tal Beck, I. Bedlinskiy, W. Bertozzi, A. Biselli, V. D. Burkert, T. Cao, D. S. Carman, A. Celentano, S. Chandavar, L. Colaneri, P. L. Cole, V. Crede, A. DAngelo, R. De Vita, A. Deur, C. Djalali, D. Doughty, M. Dugger, R. Dupre, H. Egiyan, A. El Alaoui, L. El Fassi, L. Elouadrhiri, G. Fedotov, S. Fegan, T. Forest, B. Garillon, M. Garcon, N. Gevorgyan, Y. Ghandilyan, G. P. Gilfoyle, F. X. Girod, J. T. Goetz, R. W. Gothe, K. A. Griffioen, M. Guidal, L. Guo, K. Hafidi, C. Hanretty, M. Hattawy, K. Hicks, M. Holtrop, C. E. Hyde, Y. Ilieva, D. G. Ireland, B. I. Ishkanov, E. L. Isupov, H. Jiang, H. S. Jo, K. Joo, D. Keller, M. Khandaker, A. Kim, W. Kim, F. J. Klein, S. Koirala, I. Korover, S. E. Kuhn, V. Kubarovsky, P. Lenisa, W. I. Levine, K. Livingston, M. Lowry, H. Y. Lu, I. J. D. MacGregor, N. Markov, M. Mayer, B. McKinnon, T. Mineeva, V. Mokeev, A. Movsisyan, C. Munoz Camacho, B. Mustapha, P. Nadel-Turonski, S. Niccolai, G. Niculescu, I. Niculescu, M. Osipenko, L. L. Pappalardo, R. Paremuzyan, K. Park, E. Pasyuk, W. Phelps, S. Pisano, O. Pogorelko, J. W. Price, S. Procureur, Y. Prok, D. Protopopescu, A. J. R. Puckett, D. Rimal, M. Ripani, B. G. Ritchie, A. Rizzo, G. Rosner, P. Rossi, P. Roy, F. Sabatie, D. Schott, R. A. Schumacher, Y. G. Sharabian, G. D. Smith, R. Shneor, D. Sokhan, S. S. Stepanyan, S. Stepanyan, P. Stoler, S. Strauch, V. Sytnik, M. Taiuti, S. Tkachenko, M. Ungaro, A. V. Vlassov, E. Voutier, D. Watts, N. K. Walford, X. Wei, M. H. Wood, S. A. Wood, N. Zachariou, L. Zana, Z. W. Zhao, X. Zheng, I. Zonta

The atomic nucleus is composed of two different kinds of fermions, protons and neutrons. If the protons and neutrons did not interact, the Pauli exclusion principle would force the majority fermions (usually neutrons) to have a higher average momentum. Our high-energy electron scattering measurements using 12C, 27Al, 56Fe and 208Pb targets show that, even in heavy neutron-rich nuclei, short-range interactions between the fermions form correlated high-momentum neutron-proton pairs. Read More

The ratio of the elastic $e^+ p$ to $e^- p$ scattering cross sections has been measured precisely, allowing the determination of the two-photon exchange contribution to these processes. This neglected contribution is believed to be the cause of the discrepancy between the Rosenbluth and polarization transfer methods of measuring the proton electromagnetic form factors. The experiment was performed at the VEPP-3 storage ring at beam energies of 1. Read More

2014Nov
Authors: D. Adikaram, D. Rimal, L. B. Weinstein, B. Raue, P. Khetarpal, R. P. Bennett, J. Arrington, W. K. Brooks, K. P. Adhikari, A. V. Afanasev, M. J. Amaryan, M. D. Anderson, J. Ball, M. Battaglieri, I. Bedlinskiy, A. S. Biselli, J. Bono, S. Boiarinov, W. J. Briscoe, V. D. Burkert, D. S. Carman, A. Celentano, S. Chandavar, G. Charles, L. Colaneri, P. L. Cole, M. Contalbrigo, A. D'Angelo, N. Dashyan, R. De Vita, E. De Sanctis, A. Deur, C. Djalali, G. E. Dodge, R. Dupre, H. Egiyan, A. El Alaoui, L. El Fassi, P. Eugenio, G. Fedotov, S. Fegan, A. Filippi, J. A. Fleming, A. Fradi, G. P. Gilfoyle, K. L. Giovanetti, F. X. Girod, J. T. Goetz, W. Gohn, E. Golovatch, R. W. Gothe, K. A. Griffioen, M. Guidal, L. Guo, K. Hafidi, H. Hakobyan, N. Harrison, M. Hattawy, K. Hicks, M. Holtrop, S. M. Hughes, C. E. Hyde, Y. Ilieva, D. G. Ireland, B. S. Ishkhanov, D. Jenkins, H. Jiang, K. Joo, S. Joosten, M. Khandaker, W. Kim, A. Klein, F. J. Klein, S. Koirala, V. Kubarovsky, S. E. Kuhn, H. Y. Lu, I . J . D. MacGregor, N. Markov, M. Mayer, B. McKinnon, M. D. Mestayer, C. A. Meyer, M. Mirazita, V. Mokeev, R. A. Montgomery, C. I. Moody, H. Moutarde, A Movsisyan, C. Munoz Camacho, P. Nadel-Turonski, S. Niccolai, G. Niculescu, M. Osipenko, A. I. Ostrovidov, K. Park, E. Pasyuk, S. Pisano, O. Pogorelko, S. Procureur, Y. Prok, D. Protopopescu, A. J. R. Puckett, M. Ripani, A. Rizzo, G. Rosner, P. Rossi, F. Sabatié, D. Schott, R. A. Schumacher, Y. G. Sharabian, A. Simonyan, I. Skorodumina, E. S. Smith, G. D. Smith, D. I. Sober, N. Sparveris, S. Stepanyan, S. Strauch, V. Sytnik, M. Taiuti, Ye Tian, A. Trivedi, M. Ungaro, H. Voskanyan, E. Voutier, N. K. Walford, D. P. Watts, X. Wei, M. H. Wood, N. Zachariou, L. Zana, J. Zhang, Z. W. Zhao, I. Zonta, The CLAS Collaboration

There is a significant discrepancy between the values of the proton electric form factor, $G_E^p$, extracted using unpolarized and polarized electron scattering. Calculations predict that small two-photon exchange (TPE) contributions can significantly affect the extraction of $G_E^p$ from the unpolarized electron-proton cross sections. We determined the TPE contribution by measuring the ratio of positron-proton to electron-proton elastic scattering cross sections using a simultaneous, tertiary electron-positron beam incident on a liquid hydrogen target and detecting the scattered particles in the Jefferson Lab CLAS detector. Read More

2014Nov
Authors: MOLLER Collaboration, J. Benesch, P. Brindza, R. D. Carlini, J-P. Chen, E. Chudakov, S. Covrig, M. M. Dalton, A. Deur, D. Gaskell, A. Gavalya, J. Gomez, D. W. Higinbotham, C. Keppel, D. Meekins, R. Michaels, B. Moffit, Y. Roblin, R. Suleiman, R. Wines, B. Wojtsekhowski, G. Cates, D. Crabb, D. Day, K. Gnanvo, D. Keller, N. Liyanage, V. V. Nelyubin, H. Nguyen, B. Norum, K. Paschke, V. Sulkosky, J. Zhang, X. Zheng, J. Birchall, P. Blunden, M. T. W. Gericke, W. R. Falk, L. Lee, J. Mammei, S. A. Page, W. T. H. van Oers, K. Dehmelt, A. Deshpande, N. Feege, T. K. Hemmick, K. S. Kumar, T. Kutz, R. Miskimen, M. J. Ramsey-Musolf, S. Riordan, N. Hirlinger Saylor, J. Bessuille, E. Ihloff, J. Kelsey, S. Kowalski, R. Silwal, G. De Cataldo, R. De Leo, D. Di Bari, L. Lagamba, E. NappiV. Bellini, F. Mammoliti, F. Noto, M. L. Sperduto, C. M. Sutera, P. Cole, T. A. Forest, M. Khandekar, D. McNulty, K. Aulenbacher, S. Baunack, F. Maas, V. Tioukine, R. Gilman, K. Myers, R. Ransome, A. Tadepalli, R. Beniniwattha, R. Holmes, P. Souder, D. S. Armstrong, T. D. Averett, W. Deconinck, W. Duvall, A. Lee, M. L. Pitt, J. A. Dunne, D. Dutta, L. El Fassi, F. De Persio, F. Meddi, G. M. Urciuoli, E. Cisbani, C. Fanelli, F. Garibaldi, K. Johnston, N. Simicevic, S. Wells, P. M. King, J. Roche, J. Arrington, P. E. Reimer, G. Franklin, B. Quinn, A. Ahmidouch, S. Danagoulian, O. Glamazdin, R. Pomatsalyuk, R. Mammei, J. W. Martin, T. Holmstrom, J. Erler, Yu. G. Kolomensky, J. Napolitano, K. A. Aniol, W. D. Ramsay, E. Korkmaz, D. T. Spayde, F. Benmokhtar, A. Del Dotto, R. Perrino, S. Barkanova, A. Aleksejevs, J. Singh

The physics case and an experimental overview of the MOLLER (Measurement Of a Lepton Lepton Electroweak Reaction) experiment at the 12 GeV upgraded Jefferson Lab are presented. A highlight of the Fundamental Symmetries subfield of the 2007 NSAC Long Range Plan was the SLAC E158 measurement of the parity-violating asymmetry $A_{PV}$ in polarized electron-electron (M{\o}ller) scattering. The proposed MOLLER experiment will improve on this result by a factor of five, yielding the most precise measurement of the weak mixing angle at low or high energy anticipated over the next decade. Read More

The parity-violating asymmetries between a longitudinally-polarized electron beam and an unpolarized deuterium target have been measured recently. The measurement covered two kinematic points in the deep inelastic scattering region and five in the nucleon resonance region. We provide here details of the experimental setup, data analysis, and results on all asymmetry measurements including parity-violating electron asymmetries and those of inclusive pion production and beam-normal asymmetries. Read More

E12-14-009: We propose to extract the ratio of the electric form factor (G_E) of 3He and 3H from the measured ratio of the elastic-scattering cross sections at E_beam = 1.1 GeV. Measurements at low Q^2 ( < 0. Read More

2014Apr
Affiliations: 1The Jefferson Lab Fpi Collaboration, 2The Jefferson Lab Fpi Collaboration, 3The Jefferson Lab Fpi Collaboration, 4The Jefferson Lab Fpi Collaboration, 5The Jefferson Lab Fpi Collaboration, 6The Jefferson Lab Fpi Collaboration, 7The Jefferson Lab Fpi Collaboration, 8The Jefferson Lab Fpi Collaboration, 9The Jefferson Lab Fpi Collaboration, 10The Jefferson Lab Fpi Collaboration, 11The Jefferson Lab Fpi Collaboration, 12The Jefferson Lab Fpi Collaboration, 13The Jefferson Lab Fpi Collaboration, 14The Jefferson Lab Fpi Collaboration, 15The Jefferson Lab Fpi Collaboration, 16The Jefferson Lab Fpi Collaboration, 17The Jefferson Lab Fpi Collaboration, 18The Jefferson Lab Fpi Collaboration, 19The Jefferson Lab Fpi Collaboration, 20The Jefferson Lab Fpi Collaboration, 21The Jefferson Lab Fpi Collaboration, 22The Jefferson Lab Fpi Collaboration, 23The Jefferson Lab Fpi Collaboration, 24The Jefferson Lab Fpi Collaboration, 25The Jefferson Lab Fpi Collaboration, 26The Jefferson Lab Fpi Collaboration, 27The Jefferson Lab Fpi Collaboration, 28The Jefferson Lab Fpi Collaboration, 29The Jefferson Lab Fpi Collaboration, 30The Jefferson Lab Fpi Collaboration, 31The Jefferson Lab Fpi Collaboration, 32The Jefferson Lab Fpi Collaboration, 33The Jefferson Lab Fpi Collaboration, 34The Jefferson Lab Fpi Collaboration, 35The Jefferson Lab Fpi Collaboration, 36The Jefferson Lab Fpi Collaboration, 37The Jefferson Lab Fpi Collaboration, 38The Jefferson Lab Fpi Collaboration, 39The Jefferson Lab Fpi Collaboration, 40The Jefferson Lab Fpi Collaboration, 41The Jefferson Lab Fpi Collaboration, 42The Jefferson Lab Fpi Collaboration, 43The Jefferson Lab Fpi Collaboration, 44The Jefferson Lab Fpi Collaboration, 45The Jefferson Lab Fpi Collaboration, 46The Jefferson Lab Fpi Collaboration, 47The Jefferson Lab Fpi Collaboration, 48The Jefferson Lab Fpi Collaboration, 49The Jefferson Lab Fpi Collaboration, 50The Jefferson Lab Fpi Collaboration, 51The Jefferson Lab Fpi Collaboration, 52The Jefferson Lab Fpi Collaboration, 53The Jefferson Lab Fpi Collaboration, 54The Jefferson Lab Fpi Collaboration, 55The Jefferson Lab Fpi Collaboration, 56The Jefferson Lab Fpi Collaboration, 57The Jefferson Lab Fpi Collaboration, 58The Jefferson Lab Fpi Collaboration, 59The Jefferson Lab Fpi Collaboration, 60The Jefferson Lab Fpi Collaboration, 61The Jefferson Lab Fpi Collaboration, 62The Jefferson Lab Fpi Collaboration, 63The Jefferson Lab Fpi Collaboration, 64The Jefferson Lab Fpi Collaboration, 65The Jefferson Lab Fpi Collaboration, 66The Jefferson Lab Fpi Collaboration, 67The Jefferson Lab Fpi Collaboration, 68The Jefferson Lab Fpi Collaboration, 69The Jefferson Lab Fpi Collaboration, 70The Jefferson Lab Fpi Collaboration, 71The Jefferson Lab Fpi Collaboration, 72The Jefferson Lab Fpi Collaboration, 73The Jefferson Lab Fpi Collaboration, 74The Jefferson Lab Fpi Collaboration, 75The Jefferson Lab Fpi Collaboration, 76The Jefferson Lab Fpi Collaboration, 77The Jefferson Lab Fpi Collaboration, 78The Jefferson Lab Fpi Collaboration, 79The Jefferson Lab Fpi Collaboration, 80The Jefferson Lab Fpi Collaboration, 81The Jefferson Lab Fpi Collaboration, 82The Jefferson Lab Fpi Collaboration, 83The Jefferson Lab Fpi Collaboration, 84The Jefferson Lab Fpi Collaboration, 85The Jefferson Lab Fpi Collaboration, 86The Jefferson Lab Fpi Collaboration, 87The Jefferson Lab Fpi Collaboration, 88The Jefferson Lab Fpi Collaboration

The study of exclusive $\pi^{\pm}$ electroproduction on the nucleon, including separation of the various structure functions, is of interest for a number of reasons. The ratio $R_L=\sigma_L^{\pi^-}/\sigma_L^{\pi^+}$ is sensitive to isoscalar contamination to the dominant isovector pion exchange amplitude, which is the basis for the determination of the charged pion form factor from electroproduction data. A change in the value of $R_T=\sigma_T^{\pi^-}/\sigma_T^{\pi^+}$ from unity at small $-t$, to 1/4 at large $-t$, would suggest a transition from coupling to a (virtual) pion to coupling to individual quarks. Read More

2014Feb
Authors: S. Tkachenko1, N. Baillie2, S. E. Kuhn3, J. Zhang4, J. Arrington5, P. Bosted6, S. Bültmann7, M. E. Christy8, D. Dutta9, R. Ent10, H. Fenker11, K. A. Griffioen12, M. Ispiryan13, N. Kalantarians14, C. E. Keppel15, W. Melnitchouk16, V. Tvaskis17, K. P. Adhikari18, M. Aghasyan19, M. J. Amaryan20, S. Anefalos Pereira21, H. Avakian22, J. Ball23, N. A. Baltzell24, M. Battaglieri25, I. Bedlinskiy26, A. S. Biselli27, W. J. Briscoe28, W. K. Brooks29, V. D. Burkert30, D. S. Carman31, A. Celentano32, S. Chandavar33, G. Charles34, P. L. Cole35, M. Contalbrigo36, O. Cortes37, V. Crede38, A. D'Angelo39, N. Dashyan40, R. De Vita41, E. De Sanctis42, A. Deur43, C. Djalali44, G. E. Dodge45, D. Doughty46, R. Dupre47, H. Egiyan48, A. El Alaoui49, L. El Fassi50, L. Elouadrhiri51, P. Eugenio52, G. Fedotov53, J. A. Fleming54, B. Garillon55, N. Gevorgyan56, Y. Ghandilyan57, G. P. Gilfoyle58, K. L. Giovanetti59, F. X. Girod60, J. T. Goetz61, E. Golovatch62, R. W. Gothe63, M. Guidal64, L. Guo65, K. Hafidi66, H. Hakobyan67, C. Hanretty68, N. Harrison69, M. Hattawy70, K. Hicks71, D. Ho72, M. Holtrop73, C . E. Hyde74, Y. Ilieva75, D. G. Ireland76, B. S. Ishkhanov77, H. S. Jo78, D. Keller79, M. Khandaker80, A. Kim81, W. Kim82, P. M. King83, A. Klein84, F. J. Klein85, S. Koirala86, V. Kubarovsky87, S. V. Kuleshov88, P. Lenisa89, S. Lewis90, K. Livingston91, H. Lu92, M. MacCormick93, I. J. D. MacGregor94, N. Markov95, M. Mayer96, B. McKinnon97, T. Mineeva98, M. Mirazita99, V. Mokeev100, R. A. Montgomery101, H. Moutarde102, C. Munoz Camacho103, P. Nadel-Turonski104, S. Niccolai105, G. Niculescu106, I. Niculescu107, M. Osipenko108, L. L. Pappalardo109, R. Paremuzyan110, K. Park111, E. Pasyuk112, J. J. Phillips113, S. Pisano114, O. Pogorelko115, S. Pozdniakov116, J. W. Price117, S. Procureur118, D. Protopopescu119, A. J . R. Puckett120, D. Rimal121, M. Ripani122, A. Rizzo123, G. Rosner124, P. Rossi125, P. Roy126, F. Sabatié127, D. Schott128, R. A. Schumacher129, E. Seder130, I. Senderovich131, Y. G. Sharabian132, A. Simonyan133, G. D. Smith134, D. I. Sober135, D. Sokhan136, S. Stepanyan137, S. S. Stepanyan138, S. Strauch139, W. Tang140, M. Ungaro141, A. V. Vlassov142, H. Voskanyan143, E. Voutier144, N. K. Walford145, D. Watts146, X. Wei147, L. B. Weinstein148, M. H. Wood149, L. Zana150, I. Zonta151
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Much less is known about neutron structure than that of the proton due to the absence of free neutron targets. Neutron information is usually extracted from data on nuclear targets such as deuterium, requiring corrections for nuclear binding and nucleon off-shell effects. These corrections are model dependent and have significant uncertainties, especially for large values of the Bjorken scaling variable x. Read More

2014Jan

We studied simultaneously the 4He(e,e'p), 4He(e,e'pp), and 4He(e,e'pn) reactions at Q^2=2 [GeV/c]2 and x_B>1, for a (e,e'p) missing-momentum range of 400 to 830 MeV/c. The knocked-out proton was detected in coincidence with a proton or neutron recoiling almost back to back to the missing momentum, leaving the residual A=2 system at low excitation energy. These data were used to identify two-nucleon short-range correlated pairs and to deduce their isospin structure as a function of missing momentum in a region where the nucleon-nucleon force is expected to change from predominantly tensor to repulsive. Read More

The charge form factor of $^$4He has been extracted in the range 29 fm$^{-2}$ $\le Q^2 \le 77$ fm$^{-2}$ from elastic electron scattering, detecting $^4$He nuclei and electrons in coincidence with the High Resolution Spectrometers of the Hall A Facility of Jefferson Lab. The results are in qualitative agreement with realistic meson-nucleon theoretical calculations. The data have uncovered a second diffraction minimum, which was predicted in the $Q^2$ range of this experiment, and rule out conclusively long-standing predictions of dimensional scaling of high-energy amplitudes using quark counting. Read More

Recent measurements of the neutron's electric to magnetic form factors ratio, R_n= \mu_n G_E^n/G_M^n, up to 3.4 (GeV/c)^2 combined with existing R_p= \mu_p G_E^p/G_M^p measurements in the same Q^2 range allowed, for the first time, a separation of the up- and down-quark contributions to the form factors at high Q^2, as presented by Cates, et al. Our analysis expands on the original work by including additional form factor data, applying two-photon exchange (TPE) corrections, and accounting for the uncertainties associated with all of the form factor measurements Read More

2013Jun
Authors: M. Moteabbed, M. Niroula, B. A. Raue, L. B. Weinstein, D. Adikaram, J. Arrington, W. K. Brooks, J. Lachniet, Dipak Rimal, M. Ungaro, K. P. Adhikari, M. Aghasyan, M. J. Amaryan, S. Anefalos Pereira, H. Avakian, J. Ball, N. A. Baltzell, M. Battaglieri, V. Batourine, I. Bedlinskiy, R. P. Bennett, A. S. Biselli, J. Bono, S. Boiarinov, W. J. Briscoe, V. D. Burkert, D. S. Carman, A. Celentano, S. Chandavar, P. L. Cole, P. Collins, M. Contalbrigo, O. Cortes, V. Crede, A. D'Angelo, N. Dashyan, R. De Vita, E. De Sanctis, A. Deur, C. Djalali, D. Doughty, R. Dupre, H. Egiyan, L. El Fassi, P. Eugenio, G. Fedotov, S. Fegan, R. Fersch, J. A. Fleming, N. Gevorgyan, G. P. Gilfoyle, K. L. Giovanetti, F. X. Girod, J. T. Goetz, W. Gohn, E. Golovatch, R. W. Gothe, K. A. Griffioen, M. Guidal, N. Guler, L. Guo, K. Hafidi, H. Hakobyan, C. Hanretty, N. Harrison, D. Heddle, K. Hicks, D. Ho, M. Holtrop, C. E. Hyde, Y. Ilieva, D. G. Ireland, B. S. Ishkhanov, E. L. Isupov, H. S. Jo, K. Joo, D. Keller, M. Khandaker, A. Kim, F. J. Klein, S. Koirala, A. Kubarovsky, V. Kubarovsky, S. E. Kuhn, S. V. Kuleshov, S. Lewis, H. Y. Lu, M. MacCormick, I . J . D. MacGregor, D. Martinez, M. Mayer, B. McKinnon, T. Mineeva, M. Mirazita, V. Mokeev, R. A. Montgomery, K. Moriya, H. Moutarde, E. Munevar, C. Munoz Camacho, P. Nadel-Turonski, R. Nasseripour, S. Niccolai, G. Niculescu, I. Niculescu, M. Osipenko, A. I. Ostrovidov, L. L. Pappalardo, R. Paremuzyan, K. Park, S. Park, E. Phelps, J. J. Phillips, S. Pisano, O. Pogorelko, S. Pozdniakov, J. W. Price, S. Procureur, D. Protopopescu, A. J. R. Puckett, M. Ripani, G. Rosner, P. Rossi, F. Sabatié, M. S. Saini, C. Salgado, D. Schott, R. A. Schumacher, E. Seder, H. Seraydaryan, Y. G. Sharabian, E. S. Smith, G. D. Smith, D. I. Sober, D. Sokhan, S. Stepanyan, S. Strauch, W. Tang, C. E. Taylor, Ye Tian, S. Tkachenko, H. Voskanyan, E. Voutier, N. K. Walford, M. H. Wood, N. Zachariou, L. Zana, J. Zhang, Z. W. Zhao, I. Zonta

The discrepancy between proton electromagnetic form factors extracted using unpolarized and polarized scattering data is believed to be a consequence of two-photon exchange (TPE) effects. However, the calculations of TPE corrections have significant model dependence, and there is limited direct experimental evidence for such corrections. We present the results of a new experimental technique for making direct $e^\pm p$ comparisons, which has the potential to make precise measurements over a broad range in $Q^2$ and scattering angles. Read More

We report on parity-violating asymmetries in the nucleon resonance region measured using $5 - 6$ GeV longitudinally polarized electrons scattering off an unpolarized deuterium target. These results are the first parity-violating asymmetry data in the resonance region beyond the $\Delta(1232)$, and provide a verification of quark-hadron duality in the nucleon electroweak $\gamma Z$ interference structure functions at the (10-15)% level. The results are of particular interest to models relevant for calculating the $\gamma Z$ box-diagram corrections to elastic parity-violating electron scattering measurements. Read More

The Proton Radius Puzzle is the inconsistency between the proton radius determined from muonic hydrogen and the proton radius determined from atomic hydrogen level transitions and ep elastic scattering. No generally accepted resolution to the Puzzle has been found. Possible solutions generally fall into one of three categories: the two radii are different due to novel beyond-standard-model physics, the two radii are different due to novel aspects of nucleon structure, and the two radii are the same, but there are underestimated uncertainties or other issues in the ep experiments. Read More

The five-fold differential cross section for the 12C(e,e'p)11B reaction was determined over a missing momentum range of 200-400 MeV/c, in a kinematics regime with Bjorken x > 1 and Q2 = 2.0 (GeV/c)2. A comparison of the results and theoretical models and previous lower missing momentum data is shown. Read More

Multi-photon exchange contributions are important in extracting the proton charge radius from elastic electron--proton scattering. So far, only diagrams associated with the exchange of a second photon have been evaluated. At the very low $Q^2$ values relevant to the radius extraction, higher order contributions may become important. Read More

Background: The spatial distribution of charge and magnetization in the proton and neutron are encoded in the nucleon electromagnetic form factors. The form factors are all approximated by a simple dipole function, normalized to the charge or magnetic moment of the nucleon. The differences between the proton and neutron form factors and the deviation of GEn from zero are sensitive to the difference between up- and down-quark contributions to the form factors. Read More

2012Aug
Authors: The HAPPEX, PREX Collaborations, :, S. Abrahamyan, A. Acha, A. Afanasev, Z. Ahmed, H. Albataineh, K. Aniol, D. S. Armstrong, W. Armstrong, J. Arrington, T. Averett, B. Babineau, S. L. Bailey, J. Barber, A. Barbieri, A. Beck, V. Bellini, R. Beminiwattha, H. Benaoum, J. Benesch, F. Benmokhtar, P. Bertin, T. Bielarski, W. Boeglin, P. Bosted, F. Butaru, E. Burtin, J. Cahoon, A. Camsonne, M. Canan, P. Carter, C. C. Chang, G. D. Cates, Y. C. Chao, C. Chen, J. P. Chen, Seonho Choi, E. Chudakov, E. Cisbani, B. Craver, F. Cusanno, M. M. Dalton, R. De Leo, K. de Jager, W. Deconinck, P. Decowski, D. Deepa, X. Deng, A. Deur, D. Dutta, A. Etile, C. Ferdi, R. J. Feuerbach, J. M. Finn, D. Flay, G. B. Franklin, M. Friend, S. Frullani, E. Fuchey, S. A. Fuchs, K. Fuoti, F. Garibaldi, E. Gasser, R. Gilman, A. Giusa, A. Glamazdin, L. E. Glesener, J. Gomez, M. Gorchtein, J. Grames, K. Grimm, C. Gu, O. Hansen, J. Hansknecht, O. Hen, D. W. Higinbotham, R. S. Holmes, T. Holmstrom, C. J. Horowitz, J. Hoskins, J. Huang, T. B. Humensky, C. E. Hyde, H. Ibrahim, F. Itard, C. M. Jen, E. Jensen, X. Jiang, G. Jin, S. Johnston, J. Katich, L. J. Kaufman, A. Kelleher, K. Kliakhandler, P. M. King, A. Kolarkar, S. Kowalski, E. Kuchina, K. S. Kumar, L. Lagamba, D. Lambert, P. LaViolette, J. Leacock, J. Leckey IV, J. H. Lee, J. J. LeRose, D. Lhuillier, R. Lindgren, N. Liyanage, N. Lubinsky, J. Mammei, F. Mammoliti, D. J. Margaziotis, P. Markowitz, M. Mazouz, K. McCormick, A. McCreary, D. McNulty, D. G. Meekins, L. Mercado, Z. E. Meziani, R. W. Michaels, M. Mihovilovic, B. Moffit, P. Monaghan, N. Muangma, C. Munoz-Camacho, S. Nanda, V. Nelyubin, D. Neyret, Nuruzzaman, Y. Oh, K. Otis, A. Palmer, D. Parno, K. D. Paschke, S. K. Phillips, M. Poelker, R. Pomatsalyuk, M. Posik, M. Potokar, K. Prok, A. J. R. Puckett, X. Qian, Y. Qiang, B. Quinn, A. Rakhman, P. E. Reimer, B. Reitz, S. Riordan, J. Roche, P. Rogan, G. Ron, G. Russo, K. Saenboonruang, A. Saha, B. Sawatzky, A. Shahinyan, R. Silwal, J. Singh, S. Sirca, K. Slifer, R. Snyder, P. Solvignon, P. A. Souder, M. L. Sperduto, R. Subedi, M. L. Stutzman, R. Suleiman, V. Sulkosky, C. M. Sutera, W. A. Tobias, W. Troth, G. M. Urciuoli, P. Ulmer, A. Vacheret, E. Voutier, B. Waidyawansa, D. Wang, K. Wang, J. Wexler, A. Whitbeck, R. Wilson, B. Wojtsekhowski, X. Yan, H. Yao, Y. Ye, Z. Ye, V. Yim, L. Zana, X. Zhan, J. Zhang, Y. Zhang, X. Zheng, V. Ziskin, P. Zhu

We have measured the beam-normal single-spin asymmetry $A_n$ in the elastic scattering of 1-3 GeV transversely polarized electrons from $^1$H and for the first time from $^4$He, $^{12}$C, and $^{208}$Pb. For $^1$H, $^4$He and $^{12}$C, the measurements are in agreement with calculations that relate $A_n$ to the imaginary part of the two-photon exchange amplitude including inelastic intermediate states. Surprisingly, the $^{208}$Pb result is significantly smaller than the corresponding prediction using the same formalism. Read More

Improved measurements of the proton's structure are now possible thanks to significant technical advances that allow us to probe the proton with polarized photons. These measurements have shown that the proton is not as simple as previously believed: quark orbital angular momentum and relativistic effects play an important role and the spatial distribution of charge and magnetization do not simply mimic the spatial distribution of the quarks. Even more recently, the large scale structure and size of the proton have been examined more carefully, and a significant discrepancy has been observed between the charge radius of the proton as measured in the Lamb shift of muonic hydrogen and measurements using the electron-proton interaction. Read More

Background: The density of the nucleus has been important in explaining the nuclear dependence of the quark distributions, also known as the EMC effect, as well as the presence of highmomentum nucleons arising from short-range correlations (SRCs). Recent measurements of both of these effects on light nuclei have shown a clear deviation from simple density-dependent models. Purpose: A better understanding of the nuclear quark distributions and short-range correlations requires a careful examination of the experimental data on these effects to constrain models that attempt to describe these phenomena. Read More

The electromagnetic calorimeters of the various magnetic spectrometers in Hall C at Jefferson Lab are presented. For the existing HMS and SOS spectrometers design considerations, relevant construction information, and comparisons of simulated and experimental results are included. The energy resolution of the HMS and SOS calorimeters is better than $\sigma/E \sim 6%/\sqrt E $, and pion/electron ($\pi/e$) separation of about 100:1 has been achieved in energy range 1 -- 5 GeV. Read More

2012Jan
Authors: L. El Fassi, L. Zana, K. Hafidi, M. Holtrop, B. Mustapha, W. K. Brooks, H. Hakobyan, X. Zheng, K. P. Adhikari, D. Adikaram, M. Aghasyan, M. J. Amaryan, M. Anghinolfi, J. Arrington, H. Avakian, H. Baghdasaryan, M. Battaglieri, V. Batourine, I. Bedlinskiy, A. S. Biselli, C. Bookwalter, D. Branford, W. J. Briscoe, S. Bultmann, V. D. Burkert, D. S. Carman, A. Celentano, S. Chandavar, P. L. Cole, M. Contalbrigo, V. Crede, A. D'Angelo, A. Daniel, N. Dashyan, R. De Vita, E. De Sanctis, A. Deur, B. Dey, R. Dickson, C. Djalali, G. E. Dodge, D. Doughty, R. Dupre, H. Egiyan, A. El Alaoui, L. Elouadrhiri, P. Eugenio, G. Fedotov, S. Fegan, M. Y. Gabrielyan, M. Garcon, N. Gevorgyan, G. P. Gilfoyle, K. L. Giovanetti, F. X. Girod, J. T. Goetz, W. Gohn, E. Golovatch, R. W. Gothe, K. A. Griffioen, M. Guidal, L. Guo, C. Hanretty, D. Heddle, K. Hicks, R. J. Holt, C. E. Hyde, Y. Ilieva, D. G. Ireland, B. S. Ishkhanov, E. L. Isupov, S. S. Jawalkar, D. Keller, M. Khandaker, P. Khetarpal, A. Kim, W. Kim, A. Klein, F. J. Klein, V. Kubarovsky, S. E. Kuhn, S. V. Kuleshov, V. Kuznetsov, J. M. Laget, H. Y. Lu, I. J. D. MacGregor, Y. Mao, N. Markov, M. Mayer, J. McAndrew, B. McKinnon, C. A. Meyer, T. Mineeva, M. Mirazita, V. Mokeev, B. Moreno, H. Moutarde, E. Munevar, P. Nadel-Turonski, A. Ni, S. Niccolai, G. Niculescu, I. Niculescu, M. Osipenko, A. I. Ostrovidov, L. Pappalardo, R. Paremuzyan, K. Park, S. Park, E. Pasyuk, S. Anefalos Pereira, E. Phelps, S. Pisano, S. Pozdniakov, J. W. Price, S. Procureur, D. Protopopescu, B. A. Raue, P. E. Reimer, G. Ricco, D. Rimal, M. Ripani, B. G. Ritchie, G. Rosner, P. Rossi, F. Sabatie, M. S. Saini, C. Salgado, D. Schott, R. A. Schumacher, H. Seraydaryan, Y. G. Sharabian, E. S. Smith, G. D. Smith, D. I. Sober, D. Sokhan, S. S. Stepanyan, S. Stepanyan, P. Stoler, S. Strauch, M. Taiuti, W. Tang, C. E. Taylor, D. J. Tedeschi, S. Tkachenko, M. Ungaro, B . Vernarsky, M. F. Vineyard, H. Voskanyan, E. Voutier, D. Watts, L. B. Weinstein, D. P. Weygand, M. H. Wood, N. Zachariou, B. Zhao, Z. W. Zhao

We have measured the nuclear transparency of the incoherent diffractive $A(e,e'\rho^0)$ process in $^{12}$C and $^{56}$Fe targets relative to $^2$H using a 5 GeV electron beam. The nuclear transparency, the ratio of the produced $\rho^0$'s on a nucleus relative to deuterium, which is sensitive to $\rho A$ interaction, was studied as function of the coherence length ($l_c$), a lifetime of the hadronic fluctuation of the virtual photon, and the four-momentum transfer squared ($Q^2$). While the transparency for both $^{12}$C and $^{56}$Fe showed no $l_c$ dependence, a significant $Q^2$ dependence was measured, which is consistent with calculations that included the color transparency effects. Read More

We report on the status of the Novosibirsk experiment on a precision measurement of the ratio $R$ of the elastic $e^+ p$ and $e^- p$ scattering cross sections. Such measurements determine the two-photon exchange effect in elastic electron-proton scattering. The experiment is conducted at the VEPP-3 storage ring using a hydrogen internal gas target. Read More

We present a detailed analysis of the uncertainty in the neutron F2n structure function extracted from inclusive deuteron and proton deep-inelastic scattering data. The analysis includes experimental uncertainties as well as uncertainties associated with the deuteron wave function, nuclear smearing, and nucleon off-shell corrections. Consistently accounting for the Q^2 dependence of the data and calculations, and restricting the nuclear corrections to microscopic models of the deuteron, we find significantly smaller uncertainty in the extracted F2n/F2p ratio than in previous analyses. Read More

2011Oct
Authors: N. Baillie, S. Tkachenko, J. Zhang, P. Bosted, S. Bultmann, M. E. Christy, H. Fenker, K. A. Griffioen, C. E. Keppel, S. E. Kuhn, W. Melnitchouk, V. Tvaskis, K. P. Adhikari, D. Adikaram, M. Aghasyan, M. J. Amaryan, M. Anghinolfini, J. Arrington, H. Avakian, H. Baghdasaryan, M. Battaglieri, A. S. Biselli, 5 D. Branford, W. J. Briscoe, W. K. Brooks, V. D. Burkert, D. S. Carman, A. Celentano, S. Chandavar, G. Charles, P. L. Cole, M. Contalbrigo, V. Crede, A. D'Angelo, A. Daniel, N. Dashyan, R. De Vita, E. De Sanctis, A. Deur, B. Dey, C. Djalali, G. Dodge, J. Domingo, D. Doughty, R. Dupre, D. Dutta, R. Ent, H. Egiyan, A. El Alaoui, L. El Fassi, L. Elouadrhiri, P. Eugenio, G. Fedotov, S. Fegan, A. Fradi, M. Y. Gabrielyan, N. Gevorgyan, G. P. Gilfoyle, K. L. Giovanetti, F. X. Girod, W. Gohn, E. Golovatch, R. W. Gothe, L. Graham, B. Guegan, M. Guidal, N. Guler, L. Guo, K. Hafidi, D. Heddle, K. Hicks, M. Holtrop, E. Hungerford, C. E. Hyde, Y. Ilieva, D. G. Ireland, M. Ispiryan, E. L. Isupov, S. S. Jawalkar, H. S. Jo, N. Kalantarians, M. Khandaker, P. Khetarpal, A. Kim, W. Kim, P. M. King, A. Klein, F. J. Klein, A. Klimenko, V. Kubarovsky, S. V. Kuleshov, N. D. Kvaltine, K. Livingston, H. Y. Lu, I . J . D. MacGregor, Y. Mao, N. Markov, B. McKinnon, T. Mineeva, B. Morrison, H. Moutarde, E. Munevar, P. Nadel-Turonski, A. Ni, S. Niccolai, I. Niculescu, G. Niculescu, M. Osipenko, A. I. Ostrovidov, L. Pappalardo, K. Park, S. Park, E. Pasyuk, S. Anefalos Pereira, S. Pisano, S. Pozdniakov, J. W. Price, S. Procureur, Y. Prok, D. Protopopescu, B. A. Raue, G. Ricco, D. Rimal, M. Ripani, G. Rosner, P. Rossi, F. Sabatie, M. S. Saini, C. Salgado, D. Schott, R. A. Schumacher, E. Seder, Y. G. Sharabian, D. I. Sober, D. Sokhan, S. Stepanyan, S. S. Stepanyan, P. Stoler, S. Strauch, M. Taiuti, W. Tang, M. Ungaro, M. F. Vineyard, E. Voutier, D. P. Watts, L. B. Weinstein, D. P. Weygand, M. H. Wood, L. Zana, B. Zhao

We report on the first measurement of the F2 structure function of the neutron from semi-inclusive scattering of electrons from deuterium, with low-momentum protons detected in the backward hemisphere. Restricting the momentum of the spectator protons to < 100 MeV and their angles to < 100 degrees relative to the momentum transfer allows an interpretation of the process in terms of scattering from nearly on-shell neutrons. The F2n data collected cover the nucleon resonance and deep-inelastic regions over a wide range of Bjorken x for 0. Read More

We present new data for the polarization observables of the final state proton in the $^{1}H(\vec{\gamma},\vec{p})\pi^{0}$ reaction. These data can be used to test predictions based on hadron helicity conservation (HHC) and perturbative QCD (pQCD). These data have both small statistical and systematic uncertainties, and were obtained with beam energies between 1. Read More

We extract the two-photon exchange (TPE) contributions to electron--proton elastic scattering using two parametrizations and compare the results to different phenomenological extractions and direct calculations of the TPE effects. We find that many of the extractions give similar results, and highlight the common assumptions and the impact of not including such assumptions. We provide a simple parametrization of the TPE contribution to the unpolarized cross section, along with an estimate of the fit uncertainties and the uncertainties associated with the assumptions made in the extraction. Read More

In a recent Letter, Bernauer, et al. present fits to the proton electromagnetic form factors, GEp(Q^2) and GMp(Q^2), along with extracted proton charge and magnetization radii based on large set of new, high statistical precision (<0.2%) cross section measurements. Read More

The parity-violating cross-section asymmetry in the elastic scattering of polarized electrons from unpolarized protons has been measured at a four-momentum transfer squared Q2 = 0.624 GeV and beam energy E =3.48 GeV to be A_PV = -23. Read More

We review the role of two-photon exchange (TPE) in electron-hadron scattering, focusing in particular on hadronic frameworks suitable for describing the low and moderate Q^2 region relevant to most experimental studies. We discuss the effects of TPE on the extraction of nucleon form factors and their role in the resolution of the proton electric to magnetic form factor ratio puzzle. The implications of TPE on various other observables, including neutron form factors, electroproduction of resonances and pions, and nuclear form factors, are summarized. Read More

One of the primary goals of nuclear physics is providing a complete description of the structure of atomic nuclei. While mean-field calculations provide detailed information on the nuclear shell structure for a wide range of nuclei, they do not capture the complete structure of nuclei, in particular the impact of small, dense structures in nuclei. The strong, short-range component of the nucleon-nucleon potential yields hard interactions between nucleons which are close together, generating a high-momentum tail to the nucleon momentum distribution, with momenta well in excess of the Fermi momentum. Read More

We present an updated extraction of the proton electromagnetic form factor ratio, mu_p G_E/G_M, at low Q^2. The form factors are sensitive to the spatial distribution of the proton, and precise measurements can be used to constrain models of the proton. An improved selection of the elastic events and reduced background contributions yielded a small systematic reduction in the ratio mu_p G_E/G_M compared to the original analysis. Read More