Physics
Permanent URI for this communityhttp://hdl.handle.net/1903/2269
Browse
19 results
Search Results
Item Strange-Quark Contributions to Parity-Violating Asymmetries in the Forward G0 Electron-Proton Scattering Experiment(American Physical Society, 2005-08-26) Armstrong, D.S.; Arvieux, J.; Asaturyan, R.; Averett, T.; Bailey, S.L.; Batigne, G.; Beck, D.H.; Beise, E.J.; Benesch, J.; Bimbot, L.; Birchall, J.; Korsch, W.; Kox, S.; Kuhn, J.; Lachniet, J.; Lee, L.; Lenoble, J.; Liatard, E.; Liu, J.; Loupias, B.; G0 Collaboration; Lung, A.; MacLachlan, G.A.; Marchand, D.; Martin, J.W.; McFarlane, K.W.; McKee, D.W.; McKeown, R.D.; Merchez, F.; Mkrtchyan, H.; Moffit, B.; Morlet, M.; Nakagawa, I.; Nakahara, K.; Nakos, M.; Neveling, R.; Niccolai, S.; Ong, S.; Page, S.; Papavassiliou, V.; Pate, S.F.; Phillips, S.K.; Pitt, M.L.; Poelker, M.; Porcelli, T.A.; Quemener, G.; Quinn, B.; Ramsay, W.D.; Rauf, A.W.; Real, J.-S.; Roche, J.; Roos, P.; Rutledge, G.A.; Secrest, J.; Simicevic, N.; Smith, G.R.; Spayde, D.T.; Stepanyan, S.; Stutzman, M.; Sulkosky, V.; Tadevosyan, V.; Tieulent, R.; van de Wiele, J.; van Oers, W.; Voutier, E.; G0 Collaboration; Vulcan, W.; Warren, G.; Wells, S.P.; Williamson, S.E.; Wood, S.A.; Yan, C.; Yun, J.; Zeps, V.; Biselli, A.; Bosted, P.; Boukobza, E.; Breuer, H.; Carlini, R.; Carr, R.; Chant, N.; Chao, Y.-C.; Chattopadhyay, S.; Clark, R.; Covrig, S.; Cowley, A.; Dale, D.; Davis, C.; Falk, W.; Finn, J.M.; Forest, T.; Franklin, G.; Furget, C.; Gaskell, D.; Grames, J.; Griffioen, K.A.; Grimm, K.; Guillon, B.; Guler, H.; Hannelius, L.; Hasty, R.; Hawthorne Allen, A.; Horn, T.; Johnston, K.; Jones, M.; Kammel, P.; Kazimi, R.; King, P.M.; Kolarkar, A.; Korkmaz, E.We have measured parity-violating asymmetries in elastic electron-proton scattering over the range of momentum transfers 0.12≤Q2≤1.0 GeV2. These asymmetries, arising from interference of the electromagnetic and neutral weak interactions, are sensitive to strange-quark contributions to the currents of the proton. The measurements were made at Jefferson Laboratory using a toroidal spectrometer to detect the recoiling protons from a liquid hydrogen target. The results indicate nonzero, Q2 dependent, strange-quark contributions and provide new information beyond that obtained in previous experiments.Item Longitudinal Electroproduction of Charged Pions from 1H, 2H, and 3He(American Physical Society, 2001-11-12) Gaskell, D.; Ahmidouch, A.; Ambrozewicz, P.; Anklin, H.; Arrington, J.; Assamagan, K.; Avery, S.; Bailey, K.; Baker, O.K.; Beedoe, S.; Beise, B.; Breuer, H.; Brown, D.S.; Carlini, R.; Cha, J.; Chant, N.; Cowley, A.; Danagoulian, S.; DeSchepper, D.; Dunne, J.; Dutta, D.; Ent, R.; Gan, L.; Gasparian, A.; Geesaman, D.F.; Gilman, R.; Glashausser, C.; Gueye, P.; Harvey, M.; Hashimoto, O.; Hinton, W.; Hofman, G.; Jackson, C.; Jackson, H.E.; Keppel, C.; Kinney, E.; Koltenuk, D.; Kyle, G.; Lung, A.; Mack, D.; McKee, D.; Mitchell, J.; Mkrtchyan, H.; Mueller, B.; Niculescu, G.; Niculescu, I.; O'Neill, T.G.; Papavassiliou, V.; Potterveld, D.; Reinhold, J.; Roos, P.; Sawafta, R.; Segel, R.; Stepanyan, S.; Tadevosyan, V.; Takahashi, T.; Tang, L.; Terburg, B.; van Westrum, D.; Volmer, J.; Welch, T.P.; Wood, S.; Yuan, L.; Zeidman, B.; Zihlmann, B.Separated longitudinal and transverse cross sections for charged pion electroproduction from 1H, 2H, and 3He were measured at Q2 = 0.4(GeV/c)2 for two values of the invariant mass, W = 1.15GeV and W = 1.60GeV, in a search for a mass dependence which would signal the effect of nuclear pions. This is the first such study that includes recoil momenta significantly above the Fermi surface. The longitudinal cross section, if dominated by the pion-pole process, should be sensitive to nuclear pion currents. Comparisons of the longitudinal cross section target ratios to a quasifree calculation reveal a significant suppression in 3He at W = 1.60GeV. The W = 1.15GeV results are consistent with simple estimates of the effect of nuclear pion currents, but are also consistent with pure quasifree production.Item Measurement of Tensor Polarization in Elastic Electron-Deuteron Scattering at Large Momentum Transfer(American Physical Society, 2000-05-29) Abbott, D.; Ahmidouch, A.; Anklin, H.; Arvieux, J.; Ball, J.; Beedoe, S.; Beise, E.J.; Bimbot, L.; Boeglin, W.; Breuer, H.; Brindza, P.; Carlini, R.; Chant, N.S.; Danagoulian, S.; Dow, K.; Ducret, J.-E.; Dunne, J.; Ewell, L.; Eyraud, L.; Furget, C.; Garcon, M.; Gilman, R.; Glashausser, C.; Gueye, P.; Gustafsson, K.; Hafidi, K.; Honegger, A.; Jourdan, J.; Kox, S.; Kumbartzki, G.; Lu, L.; Mack, D.; Markowitz, P.; McIntyre, J.; Meekins, D.; Merchez, F.; Mitchell, J.; Mohring, R.; Mtingwa, S.; Mrktchyan, H.; Pitz, D.; Qin, L.; Ransome, R.D.; Real, J.-S.; Roos, P.G.; Rutt, P.; Sawafta, R.; Stepanyan, S.; Tieulent, R.; Tomasi-Gustafsson, E.; Turchinetz, W.; Vansyoc, K.; Volmer, J.; Voutier, E.; Vulcan, W.; Williamson, C.; Wood, S.A.; Yan, C.; Zhao, J.; Zhao, W.; Lung, A.; Jefferson Lab t20 CollaborationTensor polarization observables ( t20, t21, and t22) have been measured in elastic electron-deuteron scattering for six values of momentum transfer between 0.66 and 1.7(GeV/c)2. The experiment was performed at the Jefferson Laboratory in Hall C using the electron High Momentum Spectrometer, a specially designed deuteron magnetic channel and the recoil deuteron polarimeter POLDER. The new data determine to much larger Q2 the deuteron charge form factors GC and GQ. They are in good agreement with relativistic calculations and disagree with perturbative QCD predictions.Item Parity Violation in Elastic Electron-Proton Scattering and the Proton's Strange Magnetic Form Factor(American Physical Society, 2000-02-07) Spayde, D.T.; Averett, T.; Barkhuff, D.; Beck, D.H.; Beise, E.J.; Benson, C.; Breuer, H.; Carr, R.; Covrig, S.; DelCorso, J.; Dodson, G.; Dow, K.; Eppstein, C.; Farkhondeh, M.; Filippone, B.W.; Frazier, P.; Hasty, R.; Ito, T.M.; Jones, C.E.; Korsch, W.; Kowalski, S.; Lee, P.; Maneva, E.; McCarty, K.; McKeown, R.D.; Mikell, J.; Mueller, B.; Naik, P.; Pitt, M.; Ritter, J.; Savu, V.; Sullivan, M.; Tieulent, R.; Tsentalovich, E.; Wells, S.P.; Yang, B.; Zwart, T.; SAMPLE CollaborationWe report a new measurement of the parity-violating asymmetry in elastic electron scattering from the proton at backward scattering angles. This asymmetry is sensitive to the strange magnetic form factor of the proton as well as electroweak axial radiative corrections. The new measurement of A = -4.92±0.61±0.73ppm provides a significant constraint on these quantities. The implications for the strange magnetic form factor are discussed in the context of theoretical estimates for the axial corrections.Item Transverse Beam Spin Asymmetries in Forward-Angle Elastic Electron-Proton Scattering(American Physical Society, 2007-07-31) Armstrong, D.S.; Arvieux, J.; Asaturyan, R.; Averett, T.; Bailey, S.L.; Batigne, G.; Beck, D.H.; Beise, E.J.; Benesch, J.; Bimbot, L.; Birchall, J.; Roche, J.; Roos, P.; Rutledge, G.A.; Secrest, J.; Simicevic, N.; Smith, G.R.; Spayde, D.T.; Stepanyan, S.; Stutzman, M.; Sulkosky, V.; Tadevosyan, V.; Tieulent, R.; Van de Wiele, J.; van Oers, W.T.H.; Voutier, E.; Vulcan, W.; Warren, G.; Wells, S.P.; Williamson, S.E.; Wood, S.A.; Yan, C.; Yun, J.; Zeps, V.; G0 Collaboration; Biselli, A.; Bosted, P.; Boukobza, E.; Breuer, H.; Carlini, R.; Carr, R.; Chant, N.; Chao, Y.-C.; Chattopadhyay, S.; Clark, R.; Covrig, S.; Cowley, A.; Dale, D.; Davis, C.; Falk, W.; Finn, J.M.; Forest, T.; Franklin, G.; Furget, C.; Gaskell, D.; Grames, J.; Griffioen, K.A.; Grimm, K.; Guillon, B.; Guler, H.; Hannelius, L.; Hasty, R.; Hawthorne Allen, A.; Horn, T.; Johnston, K.; Jones, M.; Kammel, P.; Kazimi, R.; King, P.M.; Kolarkar, A.; Korkmaz, E.; Korsch, W.; Kox, S.; Kuhn, J.; Lachniet, J.; Lee, L.; Lenoble, J.; Liatard, E.; Liu, J.; Loupias, B.; Lung, A.; Marchand, D.; Martin, J.W.; McFarlane, K.W.; McKee, D.W.; McKeown, R.D.; Merchez, F.; Mkrtchyan, H.; Moffit, B.; Morlet, M.; Nakagawa, I.; Nakahara, K.; Neveling, R.; Ong, S.; Page, S.; Papavassiliou, V.; Pate, S.F.; Phillips, S.K.; Pitt, M.L.; Poelker, M.; Porcelli, T.A.; Quéméner, G.; Quinn, B.; Ramsay, W.D.; Rauf, A.W.; Real, J.-S.We have measured the beam-normal single-spin asymmetry in elastic scattering of transversely polarized 3 GeV electrons from unpolarized protons at Q2=0.15, 0.25 (GeV/c)2. The results are inconsistent with calculations solely using the elastic nucleon intermediate state and generally agree with calculations with significant inelastic hadronic intermediate state contributions. An provides a direct probe of the imaginary component of the 2γ exchange amplitude, the complete description of which is important in the interpretation of data from precision electron-scattering experiments.Item Determination of the Pion Charge Form Factor at Q2=1.60 and 2.45 (GeV/c)2(American Physical Society, 2006-11-10) Horn, D.T.; Aniol, K.; Arrington, J.; Barret, B.; Beise, E.J.; Blok, H.P.; Boeglin, W.; Brash, E.J.; Breuer, H.; Chang, C.C.; Christy, M.E.; Ent, R.; Gaskell, D.; Gibson, E.; Holt, R.J.; Huber, G.M.; Jin, S.; Jones, M.K.; Keppel, C.E.; Kim, W.; King, P.M.; Kovaltchouk, V.; Liu, J.; Lolos, G.J.; Mack, D.J.; Margaziotis, D.J.; Markowitz, P.; Matsumura, A.; Meekins, D.; Miyoshi, T.; Mkrtchyan, H.; Niculescu, I.; Okayasu, Y.; Pentchev, L.; Perdrisat, C.; Potterveld, D.; Punjabi, V.; Reimer, P.; Reinhold, J.; Roche, J.; Roos, P.G.; Sarty, A.; Smith, G.R.; Tadevosyan, V.; Tang, L.G.; Tvaskis, V.; Vidakovic, S.; Volmer, J.; Vulcan, W.; Warren, G.; Wood, S.A.; Xu, C.; X. Zheng, X.; Jefferson Lab F_{π} CollaborationThe 1H(e,e′π+)n cross section was measured at four-momentum transfers of Q2=1.60 and 2.45 GeV2 at an invariant mass of the photon nucleon system of W=2.22 GeV. The charged pion form factor (Fπ) was extracted from the data by comparing the separated longitudinal pion electroproduction cross section to a Regge model prediction in which Fπ is a free parameter. The results indicate that the pion form factor deviates from the charge-radius constrained monopole form at these values of Q2 by one sigma, but is still far from its perturbative quantum chromodynamics prediction.Item Recoil Polarization for Δ Excitation in Pion Electroproduction(American Physical Society, 2005-09-02) Kelly, J.J.; Roche, R.E.; Chai, Z.; Jones, M.K.; Gayou, O.; Sarty, A.J.; Frullani, S.; Aniol, K.; Beise, E.J.; Benmokhtar, F.; Bertozzi, W.; Boeglin, W.U.; Botto, T.; Brash, E.J.; Breuer, H.; Brown, E.; Burtin, E.; Calarco, J.R.; Cavata, C.; Chang, C.C.; Chant, N.S.; Chen, J.-P.; Coman, M.; Crovelli, D.; De Leo, R.; Dieterich, S.; Escoffier, S.; Fissum, K.G.; Garde, V.; Garibaldi, F.; Georgakopoulus, S.; Gilad, S.; Gilman, R.; Glashausser, C.; Hansen, J.-O.; Higinbotham, D.W.; Hotta, A.; Huber, G.M.; Ibrahim, H.; Iodice, M.; de Jager, C.W.; Jiang, X.; Klimenko, A.; Kozlov, A.; Kumbartzki, G.; Kuss, M.; Lagamba, L.; Laveissiere, G.; LeRose, J.J.; Lindgren, R.A.; Liyanage, N.; Lolos, G.J.; Lourie, R.W.; Margaziotis, D.J.; Marie, F.; Markowitz, P.; McAleer, S.; Meekins, D.; Michaels, R.; Milbrath, B.D.; Mitchell, J.; Nappa, J.; Neyret, D.; Perdrisat, C.F.; Potokar, M.; Punjabi, V.A.; Pussieux, T.; Ransome, R.D.; Roos, P.G.; Rvachev, M.; Saha, A.; Sirca, S.; Suleiman, R.; Strauch, S.; Templon, J.A.; Todor, L.; Ulmer, P.E.; Urciuoli, G.M.; Weinstein, L.B.; Wijesooriya, K.; Wojtsekhowski, B.; Zheng, X.; Zhu, L.; Jefferson Laboratory E91011 and Hall A CollaborationsWe measured angular distributions of recoil-polarization response functions for neutral pion electroproduction for W=1.23 GeV at Q2=1.0 (GeV/c)2, obtaining 14 separated response functions plus 2 Rosenbluth combinations; of these, 12 have been observed for the first time. Dynamical models do not describe quantities governed by imaginary parts of interference products well, indicating the need for adjusting magnitudes and phases for nonresonant amplitudes. We performed a nearly model-independent multipole analysis and obtained values for Re (S1+/M1+)=-(6.84±0.15)% and Re (E1+/M1+)=-(2.91±0.19)% that are distinctly different from those from the traditional Legendre analysis based upon M1+ dominance and ℓπ≤1 truncation.Item Charged pion form factor between Q2=0.60 and 2.45 GeV2. II. Determination of, and results for, the pion form factor(2008-10) Huber, G.M.; Blok, H.P.; Horn, T.; Beise, E.J.; Gaskell, D.; Mack, D.J.; Tadevosyan, V.; Volmer, J.; Abbott, D.; Aniol, K.; Anklin, H.; Armstrong, C.; Arrington, J.; Assamagan, K.; Avery, S.; Baker, O.K.; Barrett, B.; Bochna, C.; Boeglin, W.; Brash, E.J.; Breuer, H.; Chang, C.C.; Chant, N.; Christy, M.E.; Dunne, J.; Eden, T.; Ent, R.; Fenker, H.; Gibson, E.F.; Gilman, R.; Gustafsson, K.; Hinton, W.; Holt, J.; Jackson, H.; Jin, S.; Jones, M.K.; Keppel, C.E.; Kim, P.H.; Kim, W.; King, P.M.; Klein, A.; Koltenuk, D.; Kovaltchouk, V.; Liang, M.; Liu, J.; Lolos, G.J.; Lung, A.; Margaziotis, D.J.; Markowitz, P.; Matsumura, A.; McKee, D.; Meekins, D.; Mitchell, J.; Miyoshi, T.; Mkrtchyan, H.; Mueller, B.; Niculescu, G.; Niculescu, I.; Okayasu, Y.; Pentchev, L.; Perdrisat, C.; Pitz, D.; Potterveld, D.; Punjabi, V.; Qin, L.M.; Reimer, P.E.; Reinhold, J.; Roche, J.; Roos, P.G.; Sarty, A.; Shin, I.K.; Smith, G.R.; Stepanyan, S.; Tang, L.G.; Tvaskis, V.; van der Meer, R.L.J.; Vansyoc, K.; VanWestrum, D.; Vidakovic, S.; Vulcan, W.; Warren, G.; Wood, S.A.; Xu, C.; Yan, C.; Zhao, W.-X.; Zheng, X.; Zihlmann, B.; The Jefferson Lab Fπ CollaborationThe 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.Item Recoil polarization measurements for neutral pion electroproduction at Q2=1(GeV/c)2 near the Δ resonance(2007-02) Kelly, J.J.; Gayou, O.; Roche, R.E.; Chai, Z.; Jones, M.K.; Sarty, A.J.; Frullani, S.; Aniol, K.; Beise, E.J.; Benmokhtar, F.; Bertozzi, W.; Boeglin, W.U.; Botto, T.; Brash, E.J.; Breuer, H.; Brown, E.; Burtin, E.; Calarco, J.R.; Cavata, C.; Chang, C.C.; Chant, N.S.; Chen, J.-P.; Coman, M.; Crovelli, D.; De Leo, R.; Dieterich, S.; Escoffier, S.; Fissum, K.G.; Garde, V.; Garibaldi, F.; Georgakopoulos, S.; Gilad, S.; Gilman, R.; Glashausser, C.; Hansen, J.-O.; Higinbotham, D.W.; Hotta, A.; Huber, G.M.; Ibrahim, H.; Iodice, M.; de Jager, C.W.; Jiang, X.; Kimenko, A.; Kozlov, A.; Kumbartzki, G.; Kuss, M.; Lagamba, L.; Laveissiere, G.; LeRose, J.J.; Lindgren, R.A.; Liyange, N.; Lolos, G.J.; Lourie, R.W.; Margaziotis, D.J.; Marie, F.; Markowitz, P.; McAleer, S.; Meekins, D.; Michaels, R.; Milbrath, B.D.; Mitchell, J.; Nappa, J.; Neyret, D.; Perdrisat, C.F.; Potokar, M.; Punjabi, V.A.; Pussieux, T.; Ransome, R.D.; Roos, P.G.; Rvachev, M.; Saha, A.; Sirca, S.; Suleiman, R.; Strauch, S.; Templon, J.A.; Todor, L.; Ulmer, P.E.; Urciuoli, G.M.; Weinstein, L.B.; Wijsooriya, K.; Wojtsekhowski, B.; Zheng, X.; Zhu, L.; Jefferson Laboratory E91011 and Hall A CollaborationsWe measured angular distributions of differential cross section, beam analyzing power, and recoil polarization for neutral pion electroproduction at Q2=1.0 (GeV/c)2 in 10 bins of 1.17⩽W⩽1.35 GeV across the Δ resonance. A total of 16 independent response functions were extracted, of which 12 were observed for the first time. Comparisons with recent model calculations show that response functions governed by real parts of interference products are determined relatively well near the physical mass, W=MΔ≈1.232 GeV, but the variation among models is large for response functions governed by imaginary parts, and for both types of response functions, the variation increases rapidly with W>MΔ. We performed a multipole analysis that adjusts suitable subsets of ℓπ⩽2 amplitudes with higher partial waves constrained by baseline models. This analysis provides both real and imaginary parts. The fitted multipole amplitudes are nearly model independent—there is very little sensitivity to the choice of baseline model or truncation scheme. By contrast, truncation errors in the traditional Legendre analysis of N→Δ quadrupole ratios are not negligible. Parabolic fits to the W dependence around MΔ for the multiple analysis gives values for Re(S1+/M1+)=(-6.61±0.18)% and Re(E1+/M1+)=(-2.87±0.19)% for the pπ0 channel at W=1.232 GeV and Q2=1.0 (GeV/c)2 that are distinctly larger than those from the Legendre analysis of the same data. Similarly, the multipole analysis gives Re(S0+/M1+)=(+7.1±0.8)% at W=1.232 GeV, consistent with recent models, while the traditional Legendre analysis gives the opposite sign because its truncation errors are quite severe.Item Quasielastic (e,e′p) reaction on 12C,56Fe, and 197Au(2003-12) Dutta, D.; van Westrum, D.; Abbott, D.; Ahmidouch, A.; Amatuni, A.; Armstrong, C.; Arrington, J.; Assamagan, K.A.; Bailey, K.; Baker, O.K.; Barrow, S.; Beard, K.; Beatty, D.; Beedoe, S.; Beise, E.; Belz, E.; Bochna, C.; Bosted, P.E.; Breuer, H.; Bruins, E.E.W.; Carlini, R.; Cha, J.; Chant, N.; Cothran, C.; Cummings, W.J.; Danagoulian, S.; Day, D.; DeSchepper, D.; Ducret, J.-E.; Duncan, F.; Dunne, J.; Eden, T.; Ent, R.; Fortune, H.T.; Frolov, V.; Geesaman, D.F.; Gao, H.; Gilman, R.; Gueye, P.; Hansen, J.O.; Hinton, W.; Holt, R.J.; Jackson, C.; Jackson, H.E.; Jones, C.; Kaufman, S.; Kelly, J.J.; Keppel, C.; Khandaker, M.; Kim, W.; Kinney, A.; Klein, A.; Koltenuk, D.; Kramer, L.; Lorenzon, W.; Lung, A.; McFarlane, K.; Mack, D.J.; Madey, R.; Markowitz, P.; Martin, J.; Mateos, A.; Meekins, D.; Miller, M.A.; Milner, R.; Mitchell, J.; Mohring, R.; Mkrtchyan, H.; Nathan, A.M.; Niculescu, G.; Niculescu, I.; O'Neill, T.G.; Potterveld, D.; Price, J.W.; Reinhold, J.; Salgado, C.; Schiffer, J.P.; Segel, R.E.; Stoler, P.; Suleiman, R.; Tadevosyan, V.; Tang, L.; Terburg, B.; Welch, T.P.; Williamson, C.; Wood, S.; Yan, C.; Yang, J.-C.; Yu, J.; Zeidman, B.; Zhao, W.; Zihlmann, B.We report the results from a systematic study of the quasielastic (e,e′p) reaction on 12C, 56Fe, and 197Au performed at Jefferson Lab. We have measured nuclear transparency and extracted spectral functions (corrected for radiation) over a Q2 range of 0.64–3.25 (GeV∕c)2 for all three nuclei. In addition, we have extracted separated longitudinal and transverse spectral functions at Q2 of 0.64 and 1.8 (GeV∕c)2 for these three nuclei (except for 197Au at the higher Q2). The spectral functions are compared to a number of theoretical calculations. The measured spectral functions differ in detail but not in overall shape from most of the theoretical models. In all three targets the measured spectral functions show considerable excess transverse strength at Q2=0.64 (GeV∕c)2, which is much reduced at 1.8 (GeV∕c)2.