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 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84 GeV corresponding to q max 2 = 0.086 (GeV/c) 2 .In this Letter we present data University Report No. OITS-73, 1977 (unpublished). 7 Glennys R. Farrar and Darrel R. Jackson, Phys.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.
The reaction T-9 + qn has been observed through the decay mode 7 -t 27 a t T,-=592, 653, 704, 875, 975, 1117, and 1300 MeV. The detection apparatus was a cubic array of six steel-plate optical spark chambers that completely surrounded a liquid-hydrogen target. We identified events attributed to the decay of an 7 by the large c.m. opening angle between the two showers generated in the steel plates by the decay photons. We have calculated the total cross section for 7 production, which is proportional to the number of events under the large-angle peak in the opening-angle distribution. The total cross section rises steeply from threshold to a maximum of about 2.4 mb a t 650 MeV, and then falls gradually to about 0.66 mb a t 1300 MeV. The differential cross section was obtained by taking the coefficients of a Legendre-polynomial fit to the angular distribution of bisectors of selected two-shower events, and converting them to the coefficients of the 7 c.m. angular distribution. The differential cross section is found to be isotropic a t 592 MeV, to require terms through Pe(cos0,) between 655 and 975 MeV, and to have a forward peak fitted by terms through P~(CO&,) a t 1117 MeV and through P.%(CO&~) a t 1300 MeV. I t is suggested that production a t threshold is predominantly through an S state, with some PI and Da waves entering by 655 MeV.We suggest that all the absorption in the Sli T N state can be explained by the 7 production.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.