排序方式: 共有28条查询结果,搜索用时 625 毫秒
11.
Horn T Aniol K Arrington J Barrett B Beise EJ Blok HP Boeglin W Brash EJ Breuer H Chang CC Christy ME Ent R Gaskell D Gibson E Holt RJ Huber GM Jin S Jones MK Keppel CE Kim W King PM Kovaltchouk V Liu J Lolos GJ Mack DJ Margaziotis DJ 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 PG Sarty A Smith GR Tadevosyan V Tang LG Tvaskis V Vidakovic S Volmer J Vulcan W Warren G Wood SA Xu C 《Physical review letters》2006,97(19):192001
The 1H(e,e'pi+)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 (F(pi)) was extracted from the data by comparing the separated longitudinal pion electroproduction cross section to a Regge model prediction in which F(pi) 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. 相似文献
12.
Aniol KA Armstrong DS Averett T Benaoum H Bertin PY Burtin E Cahoon J Cates GD Chang CC Chao YC Chen JP Choi S Chudakov E Craver B Cusanno F Decowski P Deepa D Ferdi C Feuerbach RJ Finn JM Frullani S Fuoti K Garibaldi F Gilman R Glamazdin A Gorbenko V Grames JM Hansknecht J Higinbotham DW Holmes R Holmstrom T Humensky TB Ibrahim H de Jager CW Jiang X Kaufman LJ Kelleher A Kolarkar A Kowalski S Kumar KS Lambert D LaViolette P LeRose J Lhuillier D Liyanage N Margaziotis DJ Mazouz M McCormick K 《Physical review letters》2006,96(2):022003
We have measured the parity-violating electroweak asymmetry in the elastic scattering of polarized electrons from 4He at an average scattering angle = 5.7 degrees and a four-momentum transfer Q2 = 0.091 GeV2 . From these data, for the first time, the strange electric form factor of the nucleon G(E)s can be isolated. The measured asymmetry of A(PV) = (6.72 +/- 0.84(stat) +/- 0.21(syst) x 10(-6) yields a value of G(E)s = -0.038 +/- 0.042(stat) +/- 0.010(syst), consistent with zero. 相似文献
13.
Wijesooriya K Afanasev A Amarian M Aniol K Becher S Benslama K Bimbot L Bosted P Brash E Calarco J Chai Z Chang CC Chang T Chen JP Choi S Chudakov E Churchwell S Crovelli D Dieterich S Dumalski S Dutta D Epstein M Fissum K Fox B Frullani S Gao H Gao J Garibaldi F Gayou O Gilman R Glamazdin S Glashausser C Gomez J Gorbenko V Hansen O Holt RJ Hovdebo J Huber GM de Jager CW Jiang X Jones C Jones MK Kelly J Kinney E Kooijman E Kumbartzki G Kuss M LeRose J Liang M Lindgren R Liyanage N Malov S 《Physical review letters》2001,86(14):2975-2979
We present measurements of the recoil proton polarization for the d(gamma-->,p-->)n reaction at straight theta(c.m.) = 90 degrees for photon energies up to 2.4 GeV. These are the first data in this reaction for polarization transfer with circularly polarized photons. The induced polarization p(y) vanishes above 1 GeV, contrary to meson-baryon model expectations, in which resonances lead to large polarizations. However, the polarization transfer Cx does not vanish above 1 GeV, inconsistent with hadron helicity conservation. Thus, we show that the scaling behavior observed in the d(gamma,p)n cross sections is not a result of perturbative QCD. These data should provide important tests of new nonperturbative calculations in the intermediate energy regime. 相似文献
14.
Boeglin WU Coman L Ambrozewicz P Aniol K Arrington J Batigne G Bosted P Camsonne A Chang G Chen JP Choi S Deur A Epstein M Finn JM Frullani S Furget C Garibaldi F Gayou O Gilman R Hansen O Hayes D Higinbotham DW Hinton W Hyde C Ibrahim H de Jager CW Jiang X Jones MK Kaufman LJ Klein A Kox S Kramer L Kumbartzki G Laget JM LeRose J Lindgren R Margaziotis DJ Markowitz P McCormick K Meziani Z Michaels R Milbrath B Mitchell J Monaghan P Moteabbed M Moussiegt P Nasseripour R Paschke K Perdrisat C 《Physical review letters》2011,107(26):262501
The (2)H(e,e'p)n cross section at a momentum transfer of 3.5 (GeV/c)(2) was measured over a kinematical range that made it possible to study this reaction for a set of fixed missing momenta as a function of the neutron recoil angle θ(nq) and to extract missing momentum distributions for fixed values of θ(nq) up to 0.55 GeV/c. In the region of 35°≤θ(nq)≤45° recent calculations, which predict that final-state interactions are small, agree reasonably well with the experimental data. Therefore, these experimental reduced cross sections provide direct access to the high momentum component of the deuteron momentum distribution in exclusive deuteron electrodisintegration. 相似文献
15.
Kozlov A Sarty AJ Aniol KA Bartsch P Baumann D Bertozzi W Bohinc K Böhm R Chen JP Dale D Dennis L Derber S Ding M Distler MO Dragovitsch P Ewald I Fissum KG Friedrich J Friedrich JM Geiges R Gilad S Jennewein P Kahrau M Kohl M Krygier KW Liesenfeld A Margaziotis DJ Merkel H Merle P Müller U Neuhausen R Pospischil T Potokar M Riccardi G Roché R Rosner G Rowntree D Schmieden H Sirca S Templon JA Thompson MN Wagner A Walcher T Weis M Zhao J Zhou ZL Golak J Glöckle W Witała H;A Collaboration 《Physical review letters》2004,93(13):132301
New, high-precision measurements of the 3He(e,e(')p) reaction using the A1 Collaboration spectrometers at the Mainz microtron MAMI are presented. These were performed in antiparallel kinematics at energy transfers below the quasielastic peak, and at a central momentum transfer of 685 MeV/c. Cross sections and distorted momentum distributions were extracted and compared to theoretical predictions and existing data. The longitudinal and transverse behavior of the cross section was also studied. Sizable differences in the cross-section behavior from theoretical predictions based on the plane wave impulse approximation were observed in both the two- and three-body breakup channels. Full Faddeev-type calculations account for some of the observed excess cross-section, but significant differences remain. 相似文献
16.
Acha A Aniol KA Armstrong DS Arrington J Averett T Bailey SL Barber J Beck A Benaoum H Benesch J Bertin PY Bosted P Butaru F Burtin E Cates GD Chao YC Chen JP Chudakov E Cisbani E Craver B Cusanno F De Leo R Decowski P Deur A Feuerbach RJ Finn JM Frullani S Fuchs SA Fuoti K Gilman R Glesener LE Grimm K Grames JM Hansen JO Hansknecht J Higinbotham DW Holmes R Holmstrom T Ibrahim H de Jager CW Jiang X Katich J Kaufman LJ Kelleher A King PM Kolarkar A Kowalski S Kuchina E Kumar KS Lagamba L 《Physical review letters》2007,98(3):032301
We report new measurements of the parity-violating asymmetry A(PV) in elastic scattering of 3 GeV electrons off hydrogen and 4He targets with approximately 6.0 degrees . The 4He result is A(PV)=(+6.40+/-0.23(stat)+/-0.12(syst))x10(-6). The hydrogen result is A(PV)=(-1.58+/-0.12(stat)+/-0.04(syst))x10(-6). These results significantly improve constraints on the electric and magnetic strange form factors G(E)(s) and G(M)(s). We extract G(E)(s)=0.002+/-0.014+/-0.007 at
=0.077 GeV2, and G(E)(s)+0.09G(M)(s)=0.007+/-0.011+/-0.006 at=0.109 GeV2, providing new limits on the role of strange quarks in the nucleon charge and magnetization distributions. 相似文献
17.
Kramer K Armstrong DS Averett TD Bertozzi W Binet S Butuceanu C Camsonne A Cates GD Chen JP Choi S Chudakov E Cusanno F Deur A Djawotho P Dutta D Finn JM Gao H Garibaldi F Gayou O Gilman R Glamazdin A Gorbenko V Griffioen KA Hansen JO Higinbotham DW Hinton W Horn T de Jager CW Jiang X Korsch W LeRose J Lhuillier D Liyanage N Margaziotis DJ McCormick K Meziani ZE Michaels R Milbrath B Moffit B Nanda S Perdrisat CF Pomatsalyuk R Punjabi V Reitz B Roche J Roché R Roedelbronn M Savvinov N Secrest J 《Physical review letters》2005,95(14):142002
We present the first measurement of the Q2 dependence of the neutron spin structure function g2(n) at five kinematic points covering 0.57 (GeV/c)2 < or = Q2 < or = 1.34 (GeV/c)2 at x approximately = 0.2. Though the naive quark-parton model predicts g2 = 0, nonzero values occur in more realistic models of the nucleon which include quark-gluon correlations, finite quark masses, or orbital angular momentum. When scattering from a noninteracting quark, g2(n) can be predicted using next-to-leading order fits to world data for g1(n). Deviations from this prediction provide an opportunity to examine QCD dynamics in nucleon structure. Our results show a positive deviation from this prediction at lower Q2, indicating that contributions such as quark-gluon interactions may be important. Precision data obtained for g1(n) are consistent with next-to-leading order fits to world data. 相似文献
18.
Qattan IA Arrington J Segel RE Zheng X Aniol K Baker OK Beams R Brash EJ Calarco J Camsonne A Chen JP Christy ME Dutta D Ent R Frullani S Gaskell D Gayou O Gilman R Glashausser C Hafidi K Hansen JO Higinbotham DW Hinton W Holt RJ Huber GM Ibrahim H Jisonna L Jones MK Keppel CE Kinney E Kumbartzki GJ Lung A Margaziotis DJ McCormick K Meekins D Michaels R Monaghan P Moussiegt P Pentchev L Perdrisat C Punjabi V Ransome R Reinhold J Reitz B Saha A Sarty A Schulte EC Slifer K Solvignon P Sulkosky V 《Physical review letters》2005,94(14):142301
We report the results of a new Rosenbluth measurement of the proton electromagnetic form factors at Q2 values of 2.64, 3.20, and 4.10 GeV2. Cross sections were determined by detecting the recoiling proton, in contrast to previous measurements which detected the scattered electron. Cross sections were determined to 3%, with relative uncertainties below 1%. The ratio mu(p)G(E)/G(M) was determined to 4%-8% and showed mu(p)G(E)/G(M) approximately 1. These results are consistent with, and much more precise than, previous Rosenbluth extractions. They are inconsistent with recent polarization transfer measurements of similar precision, implying a systematic difference between the techniques. 相似文献
19.
Malace SP Paolone M Strauch S Albayrak I Arrington J Berman BL Brash EJ Briscoe B Camsonne A Chen JP Christy ME Chudakov E Cisbani E Craver B Cusanno F Ent R Garibaldi F Gilman R Glamazdin O Glister J Higinbotham DW Hyde-Wright CE Ilieva Y de Jager CW Jiang X Jones MK Keppel CE Khrosinkova E Kuchina E Kumbartzki G Lee B Lindgren R Margaziotis DJ Meekins D Michaels R Park K Pentchev L Perdrisat CF Piasetzky E Punjabi VA Puckett AJ Qian X Qiang Y Ransome RD Saha A Sarty AJ Schulte E Solvignon P 《Physical review letters》2011,106(5):052501
We measured with unprecedented precision the induced polarization P(y) in (4)He(e,e'p)(3)H at Q(2)=0.8 and 1.3 (GeV/c)(2). The induced polarization is indicative of reaction-mechanism effects beyond the impulse approximation. Our results are in agreement with a relativistic distorted-wave impulse approximation calculation but are overestimated by a calculation with strong charge-exchange effects. Our data are used to constrain the strength of the spin-independent charge-exchange term in the latter calculation. 相似文献
20.
Danagoulian A Mamyan VH Roedelbronn M Aniol KA Annand JR Bertin PY Bimbot L Bosted P Calarco JR Camsonne A Chang CC Chang TH Chen JP Choi S Chudakov E Degtyarenko P de Jager CW Deur A Dutta D Egiyan K Gao H Garibaldi F Gayou O Gilman R Glamazdin A Glashausser C Gomez J Hamilton DJ Hansen JO Hayes D Higinbotham DW Hinton W Horn T Howell C Hunyady T Hyde CE Jiang X Jones MK Khandaker M Ketikyan A Kubarovsky V Kramer K Kumbartzki G Laveissière G Lerose J Lindgren RA Margaziotis DJ Markowitz P 《Physical review letters》2007,98(15):152001
Cross-section values for Compton scattering on the proton were measured at 25 kinematic settings over the range s=5-11 and -t=2-7 GeV2 with a statistical accuracy of a few percent. The scaling power for the s dependence of the cross section at fixed center-of-mass angle was found to be 8.0+/-0.2, strongly inconsistent with the prediction of perturbative QCD. The observed cross-section values are in fair agreement with the calculations using the handbag mechanism, in which the external photons couple to a single quark. 相似文献