Measurement of two-photon exchange effect by comparing elastic e±p cross sections

被引：47

作者：

Rimal, D. ^{[1
,45
]}

Adikaram, D. ^{[2
]}

Raue, B. A. ^{[1
]}

Weinstein, L. B. ^{[2
]}

Arrington, J. ^{[3
]}

Brooks, W. K. ^{[4
]}

Ungaro, M. ^{[5
,6
]}

Adhikari, K. P. ^{[2
,30
]}

Afanasev, A. V. ^{[17
]}

Akbar, Z. ^{[15
]}

Pereira, S. Anefalos ^{[20
]}

Badui, R. A. ^{[1
]}

Ball, J. ^{[11
]}

Baltzell, N. A. ^{[3
,5
]}

Battaglieri, M. ^{[21
]}

Batourine, V. ^{[5
]}

Bedlinskiy, I. ^{[26
]}

Biselli, A. S. ^{[14
]}

Boiarinov, S. ^{[5
]}

Briscoe, W. J. ^{[17
]}

Bultmann, S. ^{[2
]}

Burkert, V. D. ^{[5
]}

Carman, D. S. ^{[5
]}

Celentano, A. ^{[21
]}

Chetry, T. ^{[33
]}

Ciullo, G. ^{[19
]}

Clark, L. ^{[40
]}

Colaneri, L. ^{[22
,35
]}

Cole, P. L. ^{[5
,18
]}

Compton, N. ^{[33
]}

Contalbrigo, M. ^{[19
]}

Cortes, O. ^{[18
]}

Crede, V. ^{[15
]}

D'Angelo, A. ^{[22
,35
]}

Dashyan, N. ^{[44
]}

De Vita, R. ^{[21
]}

Deur, A. ^{[5
]}

Djalali, C. ^{[37
]}

Dupre, R. ^{[3
,24
,25
]}

Egiyan, H. ^{[5
]}

El Alaoui, A. ^{[4
]}

El Fassi, L. ^{[3
,30
]}

Eugenio, P. ^{[15
]}

Fanchini, E.

Fedotov, G. ^{[36
,37
]}

Fersch, R. ^{[12
]}

Filippi, A. ^{[23
]}

Fleming, J. A. ^{[39
]}

Forest, T. A. ^{[18
]}

Fradi, A. ^{[24
,25
]}

机构：

[1] Florida Int Univ, Miami, FL 33199 USA

[2] Old Dominion Univ, Norfolk, VA 23529 USA

[3] Argonne Natl Lab, Argonne, IL 60439 USA

[4] Univ Tecn Federico Santa Maria, Casilla 110-V, Valparaiso, Chile

[5] Thomas Jefferson Natl Accelerator Facil, Newport News, VA 23606 USA

[6] Rensselaer Polytech Inst, Troy, NY 12180 USA

[7] Calif State Univ Dominguez Hills, Carson, CA 90747 USA

[8] Canisius Coll, Buffalo, NY 14208 USA

[9] Carnegie Mellon Univ, Pittsburgh, PA 15213 USA

[10] Catholic Univ Amer, Washington, DC 20064 USA

[11] Ctr Saclay, CEA, Irfu, Serv Phys Nucl, F-91191 Gif Sur Yvette, France

[12] Christopher Newport Univ, Newport News, VA 23606 USA

[13] Univ Connecticut, Storrs, CT 06269 USA

[14] Fairfield Univ, Fairfield, CT 06824 USA

[15] Florida State Univ, Tallahassee, FL 32306 USA

[16] Univ Genoa, I-16146 Genoa, Italy

[17] George Washington Univ, Washington, DC 20052 USA

[18] Idaho State Univ, Pocatello, ID 83209 USA

[19] INFN, Sez Ferrara, I-44100 Ferrara, Italy

[20] INFN, Lab Nazl Frascati, I-00044 Frascati, Italy

[21] INFN, Sez Genova, I-16146 Genoa, Italy

[22] INFN, Sez Roma Tor Vergata, I-00133 Rome, Italy

[23] INFN, Sez Torino, I-10125 Turin, Italy

[24] Inst Phys Nucl, CNRS, IN2P3, Orsay, France

[25] Univ Paris Sud, Orsay, France

[26] Inst Theoret & Expt Phys, Moscow 117259, Russia

[27] James Madison Univ, Harrisonburg, VA 22807 USA

[28] Kyungpook Natl Univ, Daegu 702701, South Korea

[29] Univ Grenoble Alpes, CNRS, IN2P3, LPSC, Grenoble, France

[30] Mississippi State Univ, Mississippi State, MS 39762 USA

[31] Univ New Hampshire, Durham, NH 03824 USA

[32] Norfolk State Univ, Norfolk, VA 23504 USA

[33] Ohio Univ, Athens, OH 45701 USA

[34] Univ Richmond, Richmond, VA 23221 USA

[35] Univ Roma Tor Vergata, I-00133 Rome, Italy

[36] Lomonosov Moscow State Univ, Skobeltsyn Inst Nucl Phys, Moscow 119234, Russia

[37] Univ South Carolina, Columbia, SC 29208 USA

[38] Temple Univ, Philadelphia, PA 19122 USA

[39] Univ Edinburgh, Edinburgh EH9 3JZ, Midlothian, Scotland

[40] Univ Glasgow, Glasgow G12 8QQ, Lanark, Scotland

[41] Virginia Tech, Blacksburg, VA 22901 USA

[42] Univ Virginia, Charlottesville, VA 22901 USA

[43] Coll William & Mary, Williamsburg, VA 23187 USA

[44] Yerevan Phys Inst, Yerevan 375036, Armenia

[45] Univ Florida, Gainesville, FL 32611 USA

[46] Univ Kentucky, Lexington, KY 40506 USA

来源：

PHYSICAL REVIEW C | 2017年 / 95卷 / 06期

基金：

美国国家科学基金会; 英国科学技术设施理事会; 美国能源部; 新加坡国家研究基金会;

关键词：

ELECTRON-PROTON SCATTERING; FORM-FACTORS; POSITRON-PROTON; RADIATIVE-CORRECTIONS; 4-MOMENTUM TRANSFERS; CLAS; HYDROGEN; RATIO; BEAM;

D O I：

10.1103/PhysRevC.95.065201

中图分类号：

O57 [原子核物理学、高能物理学];

学科分类号：

070202 ;

摘要：

Background: The electromagnetic form factors of the proton measured by unpolarized and polarized electron scattering experiments showa 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. Purpose: We measured the ratio of positron-proton to electron-proton elastic-scattering cross sections in order to determine the TPE contribution to elastic electron-proton scattering and thereby resolve the proton electric form factor discrepancy. Methods: We produced a mixed simultaneous electron-positron beam in Jefferson Lab's Hall B by passing the 5.6-GeV primary electron beam through a radiator to produce a bremsstrahlung photon beam and then passing the photon beam through a convertor to produce electron-positron pairs. The mixed electron-positron (lepton) beam with useful energies from approximately 0.85 to 3.5 GeV then struck a 30-cm-long liquid hydrogen (LH2) target located within the CEBAF Large Acceptance Spectrometer (CLAS). By detecting both the scattered leptons and the recoiling protons, we identified and reconstructed elastic scattering events and determined the incident lepton energy. A detailed description of the experiment is presented. Results: We present previously unpublished results for the quantity R-2 gamma, the TPE correction to the elastic-scattering cross section, at Q(2) approximate to 0.85 and 1.45 GeV2 over a large range of virtual photon polarization epsilon. Conclusions: Our results, along with recently published results from VEPP-3, demonstrate a nonzero contribution from TPE effects and are in excellent agreement with the calculations that include TPE effects and largely reconcile the form-factor discrepancy up to Q(2) approximate to 2 GeV2. These data are consistent with an increase in R-2 gamma. with decreasing e at Q(2) approximate to 0.85 and 1.45 GeV2. There are indications of a slight increase in R-2 gamma with Q(2).

引用

页数：20

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