We have measured the difference between the pp total cross sections for parallel and antiparallel longitudinal spin states at beam momenta of 1.0, 1,1, 1.30, 1.58, 1.71, 2.1, and 2.25 GeV/c in a transmission counter experiment. These results reveal new structure in the p\^ range of 1.0 to 2.5 GeV/c.Previously we reported measurements of the difference between the pp total cross sections for parallel and antiparallel spin states, Aa^=a tot (r)-a tot «, using a longitudinally polarized beam and target at£ lab = 1.17, 1.47, 1.69, 1.98, 2.47, 2.97, and 6.00 GeV/c. 1 ' 2 A striking energy dependence observed around i>i a b =1.5 GeV/c has been interpreted as evidence for the formation of a diproton resonance with a mass around 2260 MeV, a width of 200 MeV, J P =3", and elasticity of 0.2-0.3. 3 These measurements have given only limited information about the shape of the structure and the underlying background. The purpose of the present experiment was to strengthen the resonance interpretation by measuring Aa L at />M> = 1.0, 1,1, 1.3, 1.58, 1.71, 2.1, and 2.25 GeV/c. The new measurements are in good agreement with the previous ones, give detailed information about the shape of the structure, and also indicate a sharp peak at 1.2 GeV/cThe experiment was performed at the Argonne National Laboratory using a polarized proton beam from the zero-gradient synchrotron (ZGS). The experimental setup was almost the same as the one used for our last measurements. 1 ' 2 ' 4 The incident proton beam, defined by the coincidence of three scintillation counters, was attenuated as it was transmitted through the polarized proton target and finally passed through a transmissioncounter (T-counter) array.The beam position was monitored and centered at the target and the T-counter array. The incident beam intensity was in the range of (0 o 3-3.0) x 10 5 protons/pulse. The magnitude of the beam polarization varied within the range 0.66-0 o 73 o The magnitude of the polarization of the free protons in the target varied within the range 0.66-0.88. The T-counter array consisted of nine circular scintillators positioned concentrically around the beam. The T counters subtended an-gles of 45 to 96 mrad at the center of the target and were used to measure the total-cross-section difference as follows. URf is the fraction of incident particles transmitted through the target which are detected by the T t counter for parallel (+) or antiparallel (-) beam and target polarizations, the total-cross-section difference Aa L (^) for this counter can be calculated by where t { is the equivalent four-momentum transfer subtended by the counter for elastic scattering, A = (N A p F L)~x = 2.80 b is the target constant for free hydrogen, iV A = 6.022 x 10 23 , p F = (0.0731 ±0.0017) g/cm 3 is the free-proton density, L=8.1 cm is the length of the polarized target; and P B and P T are the magnitudes of the beam and target polarization, respectively, Eachitj is measured by the electronic coincidence of counters T { and T i-v ^L^i) represents the total-cross-section...

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