Jefferson Lab Experiments Shed new Light on the Proton

Conference · Thu Sep 15 04:00:00 EDT 2005

OSTI ID:850153

Punjabi, Vina

In experiments 93-027 and 99-007 at Jefferson Lab (JLab) the ratio of the electromagnetic elastic form factors of the proton, G{sub E{sub p}}/G{sub M{sub p}}, was measured with high precision, up to four momentum transfer Q{sup 2} of 3.5 GeV{sup 2} and 5.6 GeV{sup 2}, respectively, with the recoil polarization technique. The data from these two JLab experiments have shown an unexpected and significantly different Q{sup 2}-dependence for the electric and magnetic form factors, starting at about Q{sup 2}=1 GeV{sup 2}, up to the maximum value of 5.6 GeV{sup 2}, revealing a definite difference in spatial distribution of charge and magnetization at short distances. The combined results of the two JLab experiments were surprising as they appeared to contradict the consensus based on Rosenbluth separation results for (G{sub E{sub p}}){sup 2} and G{sub M{sub p}}{sup 2}: the ratio {mu}{sub p}G{sub E{sub p}}/G{sub M{sub p}} obtained with the Rosenbluth method appear to be near 1 up to about 6 GeV{sup 2}. This un-bridgeable difference between cross section and polarization experiments has been reinforced with two recent JLab Rosenbluth experiments; it appears increasingly difficult to explain it away by methodological or systematic errors. We are currently preparing a third experiment at JLab, this time in Hall C, to extend the Q{sup 2}-range to 9 GeV{sup 2}.

• Research Organization: TJNAF (Thomas Jefferson National Accelerator Facility, Newport News, VA)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC05-84ER40150
• OSTI ID: 850153
• Report Number(s): JLAB-PHY-05-397; DOE/ER/40150-3574
• Country of Publication: United States
• Language: English

Related Subjects

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
ACCURACY
CROSS SECTIONS
FORM FACTORS
FOUR MOMENTUM TRANSFER
MAGNETIZATION
NUCLEAR THEORY
POLARIZATION
PROTONS
SPATIAL DISTRIBUTION