A new measurement of the elastic scattering of 250-GeV/e negative pions by electrons provides form-factor results from 0.0368&q~& 0.0940 (Gev/c)2. These measurements determine the mean square pion radius to be (r~~) = 0.439 + 0.030 fm' or (r~~) 'I~= 0.663 + 0.023 fm. Comparisons are made with previous elastic-scattering experiments as well as with results obtained from electroproduction experiments, e e annihilation experiments, and phenomenological analyses.
We report preliminary results of elastic e-d scattering at large momentum transfer performed at the Stanford Linear Accelerator Center with use of two high-re solution spectrometers in coincidence. Our results are in sharp disagreement with the mesonexchange calculations, they are in rough agreement with the nonrelativistic potential models, and they are in agreement with the predictions of the quark dimensional-scaling model which pictures the deuteron as a bound state of six quarks at large momentum transfer.
We have performed an experiment in a 100-GeV/c negatively charged-pion beam at the Fermi National Accelerator Laboratory to measure the form factor of the pion by elastically scattering pions from the atomic electrons in a liquidhydrogen target. The square of the pion form factor as a function of the square of the four-momentum transfer, q 2 , is defined to be the tr-e elastic (el) differential scattering cross section after radiation correction, divided by that predicted for a point (pt) pion;(da/dqX^ida/drtplFrtf)?In the second line the point-pion cross section is written in terms of the fine-structure constant ot and F w (q 2 ) has been expanded in powers of q 2 . In our experiment the maximum recoil energy of the electron was 84 GeV corresponding to q max 2 = 0.086 (GeV/c) 2 .In this Letter we present data University Report No. OITS-73, 1977 (unpublished). 7 Glennys R. Farrar and Darrel R. Jackson, Phys. Rev. Lett. 35, 1416Lett. 35, (1975.on the pion form factor in the range 0.03 ^ q 2 <0.07 (GeV/c) 2 . 3The charged pion is a particularly simple sysr-tern compared to the proton. Its isovector character implies that it couples almost exclusively to the p meson. In the timelike domain the pion o-form factor has been well measured experimentally. 1 Measurements of the pion form factor at i spacelike momentum transfers, coupled with analyticity, provide a useful test of the vectordominance model. Furthermore, the size of the pion can be extracted directly from these spacelike measurements. I 2The first direct measurement 2 of the pion form 0 • factor by n-e elastic scattering obtained (r n 2 ) = 0 o 61±0.15 F 2 . Our experiment provides an imis proved measurement through refinement of the 01 techniques employed in the earlier experiment [n and by exploiting the higher-momentum-transfer "he values available at Fermilab. The apparatus is shown in Fig. 1. The princii pal features of the experiment are as follows:We have measured the electromagnetic form factor of the charged pion by direct scattering of 100-GeV/c 7r" from stationary electrons in a liquid-hydrogen target at Fermilab. The deviations from the pointlike pion-scattering cross section may be characterized by a root-mean-square charge radius for the pion of (r^2) 1^2 = 0 e 56± 0,04 F.
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