Towards a resolution of the proton form factor problem: new electron and positron scattering data.
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. This novel technique allowed us to cover a wide range in virtual photon polarization (ϵ) and momentum transfer (Q(2)) simultaneously, as well as to cancel luminosity-related systematic errors. The cross section ratio increases with decreasing ϵ at Q(2)=1.45  GeV(2). This measurement is consistent with the size of the form factor discrepancy at Q(2)≈1.75  GeV(2) and with hadronic calculations including nucleon and Δ intermediate states, which have been shown to resolve the discrepancy up to 2-3  GeV(2).
Old Dominion University, Norfolk, Virginia 23529, USA.
D
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Adikaram
Florida International University, Miami, Florida 33199, USA.
D
D
Rimal
Old Dominion University, Norfolk, Virginia 23529, USA.
L B
LB
Weinstein
Florida International University, Miami, Florida 33199, USA.
B
B
Raue
Florida International University, Miami, Florida 33199, USA.
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P
Khetarpal
Old Dominion University, Norfolk, Virginia 23529, USA.
R P
RP
Bennett
Argonne National Laboratory, Argonne, Illinois 60439, USA.
J
J
Arrington
Universidad Técnica Federico Santa María, Casilla 110-V Valparaíso, Chile.
W K
WK
Brooks
Old Dominion University, Norfolk, Virginia 23529, USA.
K P
KP
Adhikari
The George Washington University, Washington, DC 20052, USA.
A V
AV
Afanasev
Old Dominion University, Norfolk, Virginia 23529, USA.
M J
MJ
Amaryan
University of Glasgow, Glasgow G12 8QQ, United Kingdom.
M D
MD
Anderson
INFN, Laboratori Nazionali di Frascati, 00044 Frascati, Italy.
S
S
Anefalos Pereira
Thomas Jefferson National Accelerator Facility, Newport News, Virginia 23606, USA.
H
H
Avakian
CEA, Centre de Saclay, Irfu/Service de Physique Nucléaire, 91191 Gif-sur-Yvette, France.
J
J
Ball
INFN, Sezione di Genova, 16146 Genova, Italy.
M
M
Battaglieri
Institute of Theoretical and Experimental Physics, Moscow 117259, Russia.
I
I
Bedlinskiy
Fairfield University, Fairfield, Connecticut 06824, USA.
A S
AS
Biselli
Florida International University, Miami, Florida 33199, USA.
J
J
Bono
Thomas Jefferson National Accelerator Facility, Newport News, Virginia 23606, USA.
S
S
Boiarinov
The George Washington University, Washington, DC 20052, USA.
W J
WJ
Briscoe
Thomas Jefferson National Accelerator Facility, Newport News, Virginia 23606, USA.
V D
VD
Burkert
Thomas Jefferson National Accelerator Facility, Newport News, Virginia 23606, USA.
D S
DS
Carman
Old Dominion University, Norfolk, Virginia 23529, USA.
S
S
Careccia
INFN, Sezione di Genova, 16146 Genova, Italy.
A
A
Celentano
Ohio University, Athens, Ohio 45701, USA.
S
S
Chandavar
Institut de Physique Nucléaire, CNRS/IN2P3 and Université Paris Sud, Orsay, France.
G
G
Charles
INFN, Sezione di Roma Tor Vergata, 00133 Rome, Italy and Universita' di Roma Tor Vergata, 00133 Rome, Italy.
L
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Colaneri
Idaho State University, Pocatello, Idaho 83209, USA.
P L
PL
Cole
INFN, Sezione di Ferrara, 44100 Ferrara, Italy.
M
M
Contalbrigo
Florida State University, Tallahassee, Florida 32306, USA.
V
V
Crede
INFN, Sezione di Roma Tor Vergata, 00133 Rome, Italy and Universita' di Roma Tor Vergata, 00133 Rome, Italy.
A
A
D'Angelo
Yerevan Physics Institute, 375036 Yerevan, Armenia.
N
N
Dashyan
INFN, Sezione di Genova, 16146 Genova, Italy.
R
R
De Vita
INFN, Laboratori Nazionali di Frascati, 00044 Frascati, Italy.
E
E
De Sanctis
Thomas Jefferson National Accelerator Facility, Newport News, Virginia 23606, USA.
A
A
Deur
University of South Carolina, Columbia, South Carolina 29208, USA.
C
C
Djalali
Old Dominion University, Norfolk, Virginia 23529, USA.
G E
GE
Dodge
Argonne National Laboratory, Argonne, Illinois 60439, USA and Institut de Physique Nucléaire, CNRS/IN2P3 and Université Paris Sud, Orsay, France.
R
R
Dupre
Thomas Jefferson National Accelerator Facility, Newport News, Virginia 23606, USA.
H
H
Egiyan
Argonne National Laboratory, Argonne, Illinois 60439, USA and Universidad Técnica Federico Santa María, Casilla 110-V Valparaíso, Chile.
A
A
El Alaoui
Old Dominion University, Norfolk, Virginia 23529, USA and Argonne National Laboratory, Argonne, Illinois 60439, USA.
L
L
El Fassi
Thomas Jefferson National Accelerator Facility, Newport News, Virginia 23606, USA.
L
L
Elouadrhiri
Florida State University, Tallahassee, Florida 32306, USA.
P
P
Eugenio
Skobeltsyn Institute of Nuclear Physics, Lomonosov Moscow State University, 119234 Moscow, Russia and University of South Carolina, Columbia, South Carolina 29208, USA.
G
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Fedotov
INFN, Sezione di Genova, 16146 Genova, Italy and University of Glasgow, Glasgow G12 8QQ, United Kingdom.
S
S
Fegan
INFN, sez. di Torino, 10125 Torino, Italy.
A
A
Filippi
Edinburgh University, Edinburgh EH9 3JZ, United Kingdom.
J A
JA
Fleming
Institut de Physique Nucléaire, CNRS/IN2P3 and Université Paris Sud, Orsay, France.
A
A
Fradi
Institut de Physique Nucléaire, CNRS/IN2P3 and Université Paris Sud, Orsay, France.
B
B
Garillon
University of Richmond, Richmond, Virginia 23173, USA.
G P
GP
Gilfoyle
James Madison University, Harrisonburg, Virginia 22807, USA.
K L
KL
Giovanetti
Thomas Jefferson National Accelerator Facility, Newport News, Virginia 23606, USA.
F X
FX
Girod
Ohio University, Athens, Ohio 45701, USA.
J T
JT
Goetz
University of Connecticut, Storrs, Connecticut 06269, USA.
W
W
Gohn
Skobeltsyn Institute of Nuclear Physics, Lomonosov Moscow State University, 119234 Moscow, Russia.
E
E
Golovatch
University of South Carolina, Columbia, South Carolina 29208, USA.
R W
RW
Gothe
College of William and Mary, Williamsburg, Virginia 23187-8795, USA.
K A
KA
Griffioen
Institut de Physique Nucléaire, CNRS/IN2P3 and Université Paris Sud, Orsay, France.
B
B
Guegan
Institut de Physique Nucléaire, CNRS/IN2P3 and Université Paris Sud, Orsay, France.
M
M
Guidal
Florida International University, Miami, Florida 33199, USA.
L
L
Guo
Argonne National Laboratory, Argonne, Illinois 60439, USA.
K
K
Hafidi
Universidad Técnica Federico Santa María, Casilla 110-V Valparaíso, Chile and Yerevan Physics Institute, 375036 Yerevan, Armenia.
H
H
Hakobyan
Thomas Jefferson National Accelerator Facility, Newport News, Virginia 23606, USA.
C
C
Hanretty
University of Connecticut, Storrs, Connecticut 06269, USA.
N
N
Harrison
Institut de Physique Nucléaire, CNRS/IN2P3 and Université Paris Sud, Orsay, France.
M
M
Hattawy
Ohio University, Athens, Ohio 45701, USA.
K
K
Hicks
University of New Hampshire, Durham, New Hampshire 03824-3568, USA.
M
M
Holtrop
Edinburgh University, Edinburgh EH9 3JZ, United Kingdom.
S M
SM
Hughes
Old Dominion University, Norfolk, Virginia 23529, USA.
C E
CE
Hyde
University of South Carolina, Columbia, South Carolina 29208, USA.
Y
Y
Ilieva
University of Glasgow, Glasgow G12 8QQ, United Kingdom.
D G
DG
Ireland
Skobeltsyn Institute of Nuclear Physics, Lomonosov Moscow State University, 119234 Moscow, Russia.
B S
BS
Ishkhanov
Virginia Tech, Blacksburg, Virginia 24061-0435, USA.
D
D
Jenkins
University of South Carolina, Columbia, South Carolina 29208, USA.
H
H
Jiang
Institut de Physique Nucléaire, CNRS/IN2P3 and Université Paris Sud, Orsay, France.
H S
HS
Jo
University of Connecticut, Storrs, Connecticut 06269, USA.
K
K
Joo
Temple University, Philadelphia, Pennsylvania 19122, USA.
S
S
Joosten
University of Virginia, Charlottesville, Virginia 22901, USA.
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N
Kalantarians
University of Virginia, Charlottesville, Virginia 22901, USA.
D
D
Keller
Idaho State University, Pocatello, Idaho 83209, USA and Norfolk State University, Norfolk, Virginia 23504, USA.
M
M
Khandaker
University of Connecticut, Storrs, Connecticut 06269, USA.
A
A
Kim
Kyungpook National University, Daegu 702-701, Republic of Korea.
W
W
Kim
Old Dominion University, Norfolk, Virginia 23529, USA.
A
A
Klein
Catholic University of America, Washington, D.C. 20064, USA.
F J
FJ
Klein
Old Dominion University, Norfolk, Virginia 23529, USA.
S
S
Koirala
Thomas Jefferson National Accelerator Facility, Newport News, Virginia 23606, USA.
V
V
Kubarovsky
Old Dominion University, Norfolk, Virginia 23529, USA.
S E
SE
Kuhn
University of Glasgow, Glasgow G12 8QQ, United Kingdom.
K
K
Livingston
Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, USA and University of South Carolina, Columbia, South Carolina 29208, USA.
H Y
HY
Lu
University of Glasgow, Glasgow G12 8QQ, United Kingdom.
I J D
IJ
MacGregor
University of Connecticut, Storrs, Connecticut 06269, USA.
N
N
Markov
Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, USA.
P
P
Mattione
Old Dominion University, Norfolk, Virginia 23529, USA.
M
M
Mayer
University of Glasgow, Glasgow G12 8QQ, United Kingdom.
B
B
McKinnon
Thomas Jefferson National Accelerator Facility, Newport News, Virginia 23606, USA.
M D
MD
Mestayer
Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, USA.
C A
CA
Meyer
INFN, Laboratori Nazionali di Frascati, 00044 Frascati, Italy.
M
M
Mirazita
Skobeltsyn Institute of Nuclear Physics, Lomonosov Moscow State University, 119234 Moscow, Russia and Thomas Jefferson National Accelerator Facility, Newport News, Virginia 23606, USA.
V
V
Mokeev
INFN, Laboratori Nazionali di Frascati, 00044 Frascati, Italy.
R A
RA
Montgomery
Argonne National Laboratory, Argonne, Illinois 60439, USA.
C I
CI
Moody
CEA, Centre de Saclay, Irfu/Service de Physique Nucléaire, 91191 Gif-sur-Yvette, France.
H
H
Moutarde
INFN, Sezione di Ferrara, 44100 Ferrara, Italy.
A
A
Movsisyan
Institut de Physique Nucléaire, CNRS/IN2P3 and Université Paris Sud, Orsay, France.
C Munoz
CM
Camacho
Thomas Jefferson National Accelerator Facility, Newport News, Virginia 23606, USA.
P
P
Nadel-Turonski
Institut de Physique Nucléaire, CNRS/IN2P3 and Université Paris Sud, Orsay, France.
S
S
Niccolai
James Madison University, Harrisonburg, Virginia 22807, USA.
G
G
Niculescu
INFN, Sezione di Genova, 16146 Genova, Italy.
M
M
Osipenko
Florida State University, Tallahassee, Florida 32306, USA.
A I
AI
Ostrovidov
Thomas Jefferson National Accelerator Facility, Newport News, Virginia 23606, USA.
K
K
Park
Thomas Jefferson National Accelerator Facility, Newport News, Virginia 23606, USA.
E
E
Pasyuk
Universidad Técnica Federico Santa María, Casilla 110-V Valparaíso, Chile.
C
C
Peña
INFN, Laboratori Nazionali di Frascati, 00044 Frascati, Italy and Institut de Physique Nucléaire, CNRS/IN2P3 and Université Paris Sud, Orsay, France.
S
S
Pisano
Institute of Theoretical and Experimental Physics, Moscow 117259, Russia.
O
O
Pogorelko
California State University, Dominguez Hills, Carson, California 90747, USA.
J W
JW
Price
CEA, Centre de Saclay, Irfu/Service de Physique Nucléaire, 91191 Gif-sur-Yvette, France.
S
S
Procureur
Old Dominion University, Norfolk, Virginia 23529, USA and Christopher Newport University, Newport News, Virginia 23606, USA.
Y
Y
Prok
University of Glasgow, Glasgow G12 8QQ, United Kingdom.
D
D
Protopopescu
University of Connecticut, Storrs, Connecticut 06269, USA.
A J R
AJ
Puckett
INFN, Sezione di Genova, 16146 Genova, Italy.
M
M
Ripani
INFN, Sezione di Roma Tor Vergata, 00133 Rome, Italy and Universita' di Roma Tor Vergata, 00133 Rome, Italy.
A
A
Rizzo
University of Glasgow, Glasgow G12 8QQ, United Kingdom.
G
G
Rosner
INFN, Laboratori Nazionali di Frascati, 00044 Frascati, Italy and Thomas Jefferson National Accelerator Facility, Newport News, Virginia 23606, USA.
P
P
Rossi
Florida State University, Tallahassee, Florida 32306, USA.
P
P
Roy
CEA, Centre de Saclay, Irfu/Service de Physique Nucléaire, 91191 Gif-sur-Yvette, France.
F
F
Sabatié
Norfolk State University, Norfolk, Virginia 23504, USA.
C
C
Salgado
Florida International University, Miami, Florida 33199, USA and The George Washington University, Washington, DC 20052, USA.
D
D
Schott
Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, USA.
R A
RA
Schumacher
University of Connecticut, Storrs, Connecticut 06269, USA.
E
E
Seder
Thomas Jefferson National Accelerator Facility, Newport News, Virginia 23606, USA.
Y G
YG
Sharabian
Yerevan Physics Institute, 375036 Yerevan, Armenia.
A
A
Simonyan
Skobeltsyn Institute of Nuclear Physics, Lomonosov Moscow State University, 119234 Moscow, Russia and University of South Carolina, Columbia, South Carolina 29208, USA.
I
I
Skorodumina
Thomas Jefferson National Accelerator Facility, Newport News, Virginia 23606, USA.
E S
ES
Smith
Edinburgh University, Edinburgh EH9 3JZ, United Kingdom and University of Glasgow, Glasgow G12 8QQ, United Kingdom.
G D
GD
Smith
Catholic University of America, Washington, D.C. 20064, USA.
D I
DI
Sober
University of Glasgow, Glasgow G12 8QQ, United Kingdom.
D
D
Sokhan
Temple University, Philadelphia, Pennsylvania 19122, USA.
N
N
Sparveris
Thomas Jefferson National Accelerator Facility, Newport News, Virginia 23606, USA.
S
S
Stepanyan
Rensselaer Polytechnic Institute, Troy, New York 12180, USA.
P
P
Stoler
University of South Carolina, Columbia, South Carolina 29208, USA.
S
S
Strauch
Universidad Técnica Federico Santa María, Casilla 110-V Valparaíso, Chile.
V
V
Sytnik
Università di Genova, 16146 Genova, Italy.
M
M
Taiuti
University of South Carolina, Columbia, South Carolina 29208, USA.
Ye
Y
Tian
University of South Carolina, Columbia, South Carolina 29208, USA.
A
A
Trivedi
University of Connecticut, Storrs, Connecticut 06269, USA and Thomas Jefferson National Accelerator Facility, Newport News, Virginia 23606, USA.
M
M
Ungaro
Yerevan Physics Institute, 375036 Yerevan, Armenia.
H
H
Voskanyan
LPSC, Université Grenoble-Alpes, CNRS/IN2P3, Grenoble, France.
E
E
Voutier
Catholic University of America, Washington, D.C. 20064, USA.
N K
NK
Walford
Edinburgh University, Edinburgh EH9 3JZ, United Kingdom.
D P
DP
Watts
Thomas Jefferson National Accelerator Facility, Newport News, Virginia 23606, USA.
X
X
Wei
Canisius College, Buffalo, New York 14208, USA.
M H
MH
Wood
The George Washington University, Washington, DC 20052, USA and University of South Carolina, Columbia, South Carolina 29208, USA.
N
N
Zachariou
University of New Hampshire, Durham, New Hampshire 03824-3568, USA and Edinburgh University, Edinburgh EH9 3JZ, United Kingdom.
L
L
Zana
Thomas Jefferson National Accelerator Facility, Newport News, Virginia 23606, USA.
J
J
Zhang
Old Dominion University, Norfolk, Virginia 23529, USA and Thomas Jefferson National Accelerator Facility, Newport News, Virginia 23606, USA and University of Virginia, Charlottesville, Virginia 22901, USA.
Z W
ZW
Zhao
INFN, Sezione di Roma Tor Vergata, 00133 Rome, Italy and Universita' di Roma Tor Vergata, 00133 Rome, Italy.
I
I
Zonta