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Q2 Dependence of quadrupole strength in the gamma*p --> Delta(+)(1232) --> p pi(0) transition |
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| Authors: | Joo K Smith L C Burkert V D Minehart R Aznauryan I G Elouadrhiri L Stepanyan S Adams G S Amaryan M J Anciant E Anghinolfi M Armstrong D S Asavapibhop B Audit G Auger T Avakian H Barrow S Bagdasaryan H Battaglieri M Beard K Bektasoglu M Bertozzi W Bianchi N Biselli A S Boiarinov S Bonner B E Brooks W K Calarco J R Capitani G P Carman D S Carnahan B Cole P L Coleman A Cords D Corvisiero P Crabb D Crannell H Cummings J De Sanctis E De Vita R Degtyarenko P V Demirchyan R A Denizli H Dennis L C Deppman A Dharmawardane K V Dhuga K S Djalali C Dodge G E Doughty D Dragovitsch P Dugger M Dytman S |
| Affiliation: | University of Virginia, Department of Physics, Charlottesville, Virginia 22903, USA. |
| Abstract: | Models of baryon structure predict a small quadrupole deformation of the nucleon due to residual tensor forces between quarks or distortions from the pion cloud. Sensitivity to quark versus pion degrees of freedom occurs through the Q2 dependence of the magnetic (M1+), electric (E1+), and scalar (S1+) multipoles in the gamma*p-->Delta(+)-->p pi(0) transition. We report new experimental values for the ratios E(1+)/M(1+) and S(1+)/M(1+) over the range Q2 = 0.4-1.8 GeV2, extracted from precision p(e,e(')p)pi(0) data using a truncated multipole expansion. Results are best described by recent unitary models in which the pion cloud plays a dominant role. |
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