Polarization in π−p elastic scattering, with emphasis in the region around the secondary dip and also θc.m.=90°, has been measured at 2.93 and 3.25 GeV/c. We observe an interesting sign change in this angular region.
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We have measured the spin-spin correlation parameter CLL=(L, L;0, 0) in p−p elastic scattering around θc.m.=90° from plab=1.0 to 3.0 GeV/c. We observe a rapid energy dependence in CLL and describe our interpretation of the results.
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Toward the goal of experimentally determining the p-p elastic-scattering amplitudes at 6 GeV/c, we have measured a number of triple- and double-spin correlation parameters over the ‖t‖ range between 0.2 and 1.0 (GeV/c)2. These new data permit the first nucleon-nucleon amplitude determination in the multi-GeV energy range. Polarized beams from the Argonne Zero Gradient Synchrotron and polarized targets were utilized. The polarization of the recoil proton was measured with a carbon polarimeter. A total of 14 different spin observables were measured (five spin transfer, four depolarization, and five triple-spin correlation parameters). These have been combined with earlier results, resulting in a data set of typically 30 measurements of 20 different spin observables for each of six ‖t‖ values between 0.2 and 1.0 (GeV/c)2. A solution for the amplitudes has been found at each ‖t‖, and comparisons are presented with several different models. The spin-nonflip helicity amplitudes are found to be much larger than the spin-flip amplitudes.
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We have made the first measurement of the spin-spin correlation parameter CSS in pp elastic scattering at 6 GeV/c over the |t| range from 0.05 to 1.5 (GeV/c)2. The measured CSS data points are all negative, and their absolute values increase with |t|. The results are compared with some existing attempts to describe the pp scattering process.
NUMERICAL VALUES OBTAINED FROM AUTHORS. MAGNETIC FIELD ALIGNMENT AND APERTURE EFFECTS MEAN THAT QUANTITY ACTUALLY MEASURED IS 0.98 CSS + 0.02 CNN - 0.12 CSL. SEE LATER NUMBERS IN THE RECORD OF I. P. AUER ET AL., PL 70B, 475 (1977).
Toward the goal of experimentally determining pp elastic scattering amplitudes at 6 GeV/c, we have measured a linear combination of triple-spin correlation parameters and also a linear combination of spintransfer parameters over the |t| range between 0.2 and 1.0 (GeV/c)2. A horizontally polarized beam (S direction) was obtained by precessing the spin of the polarized beam from the Argonne Zero Gradient Synchrotron using a superconducting solenoid. The target protons were polarized vertically (N direction) and the polarization of the recoil protons was measured with a carbon polarimeter. The results are consistent with the amplitude corresponding to π exchange being almost real and positive.
KSS = (S00S) AND HSNS = (SN0S) MEASURED HERE CONTAIN SMALL ADMIXTURES OF THE OTHER SPIN-TRANSFER AND TRIPLE-SPIN CORRELATION PARAMETERS RESPECTIVELY DUE TO THE POLARIZED TARGET MAGNETIC FIELD - SEE TEXT. MEAN VALUE OF HSNS OVER THIS T-RANGE IS 0.098 +- 0.085. PARITY CONSERVATION REQUIRES THE VANISHING OF THE PARAMETERS KSN, HSNN, (000S) AND DNS, WHILE (000N) MUST AGREE WITH THE SINGLE SCATTERING POLARIZATION PARAMETER (0N00).
A new measurement of the elastic scattering of 250-GeV/c negative pions by electrons provides form-factor results from 0.0368
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We have measured the difference between the pp total cross-sections for parallel and anti-parallel longitudinal spin states at beam momenta of 3 and 6 GeV/ c . These results, combined with our previous measurements, at lower momenta, are useful in clarifying a striking structure appearing at around 1.5 GeV/ c . We have also measured for the first time, the spin-spin correlation parameter C LL ( t ) in pp elastic scattering at 6 GeV/ c . We observe evidence for an exchange with A 1 -like quantum-numbers.
NOTE: HIGHER -T DATA ARE BEING ANALYSED. PUBLISHED GRAPH HAS LARGER ERRORS.
THESE NUMBERS APPEAR TO UPDATE THOSE REPORTED IN I. P. AUER ET AL., PRL 37, 1727 (76). NOTE: DATA MAY HAVE SMALLER ERROR BARS IN THE FINAL ANALYSIS.
NOTE: MORE DATA ARE BEING ANALYSED. SINCE THE POLARIZED TARGET MAGNETIC FIELD WAS TILTED AT 18 DEG AWAY FROM THE BEAM DIRECTION, THE MEASURED CSL CONTAINS AN ADMIXTURE OF CSS. THE CSL VALUES QUOTED HERE HAVE BEEN CORRECTED FOR THIS EFFECT USING THE EXPERIMENTAL VALUES OF CSS.
None
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The STAR Collaboration reports on the photoproduction of $\pi^+\pi^-$ pairs in gold-gold collisions at a center-of-mass energy of 200 GeV/nucleon-pair. These pion pairs are produced when a nearly-real photon emitted by one ion scatters from the other ion. We fit the $\pi^+\pi^-$ invariant mass spectrum with a combination of $\rho$ and $\omega$ resonances and a direct $\pi^+\pi^-$ continuum. This is the first observation of the $\omega$ in ultra-peripheral collisions, and the first measurement of $\rho-\omega$ interference at energies where photoproduction is dominated by Pomeron exchange. The $\omega$ amplitude is consistent with the measured $\gamma p\rightarrow \omega p$ cross section, a classical Glauber calculation and the $\omega\rightarrow\pi^+\pi^-$ branching ratio. The $\omega$ phase angle is similar to that observed at much lower energies, showing that the $\rho-\omega$ phase difference does not depend significantly on photon energy. The $\rho^0$ differential cross section $d\sigma/dt$ exhibits a clear diffraction pattern, compatible with scattering from a gold nucleus, with 2 minima visible. The positions of the diffractive minima agree better with the predictions of a quantum Glauber calculation that does not include nuclear shadowing than with a calculation that does include shadowing.
The $\pi^+\pi^-$ invariant-mass distribution for all selected $\pi\pi$ candidates with $p_T~<~100~\textrm{MeV}/c$.
The ratio $|B/A|$ of amplitudes of nonresonant $\pi^+\pi^-$ and $\rho^0$ mesons in the present STAR analysis.
The ratio $|B/A|$ of amplitudes of nonresonant $\pi^+\pi^-$ and $\rho^0$ mesons in the previous STAR analysis, Phys. Rev. C 77 034910 (2008).
Results of a high-statistics study of elastic scattering and meson resonances produced by π−p interactions at 8 GeV/c are presented. Large statistics and small systematic errors permit examination of the complete kinematic region. Total differential cross sections are given for ρ0,−, f0, g0,−, Δ±, Δ0, and N* resonances. Spin-density matrix elements and Legendre-polynomial moments are given for ρ, f, and Δ resonances. The results for ρ0 and f0 resonances are compared with the predictions of a Regge-pole-exchange model. Properties of the above resonances are compared and discussed. In particular, we present evidence that the ρ0 and f0 production mechanisms are similar. The similarity of the g0 t distribution to that of the ρ0 and f0 suggests a common production mechanism for all three resonances.
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SLOPE REFERS TO EXPONENTIAL FIT IN U.
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