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Register a new userTwo-Pion Production in Proton-Proton Collisions -- Experimental Total Cross Sections and their Isospin Decomposition
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The two-pion production in pp-collisions has been investigated at CELSIUS in exclusive measurements from threshold up to $T_p$ = 1.36 GeV. Total and differential cross sections have been obtained for the channels $pnpi^+pi^0$, $pppi^+pi^-$, $pppi^0pi^0$ and also $nnpi^+pi^+$. For intermediate incident energies $T_p >$ 1 GeV, i.e. in the region which is beyond the Roper excitation but at the onset of $DeltaDelta$ excitation, the total $pppi^0pi^0$ cross section falls behind theoretical predictions by as much as an order of magnitude near 1.2 GeV, whereas the $nnpi^+pi^+$ cross section is a factor of five larger than predicted. An isospin decompostion of the total cross sections exhibits a s-channel-like energy dependence in the region of the Roper excitation as well as a significant contribution of an isospin 3/2 resonance other than the $Delta(1232)$. As possible candidates the $Delta(1600)$ and the $Delta(1700)$ are discussed.
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The two-pion production reaction $vec{p}pto pppi^+pi^-$ was measured with a polarized proton beam at $T_p approx$ 750 and 800 MeV using the short version of the COSY-TOF spectrometer. The implementation of a delayed pulse technique for Quirl and central calorimeter provided positive $pi^+$ identification in addition to the standard particle identification, energy determination as well as time-of-flight and angle measurements. Thus all four-momenta of the emerging particles could be determined with 1-4 overconstraints. Total and differential cross sections as well as angular distributions of the vector analyzing power have been obtained. They are compared to previous data and theoretical calculations. In contrast to predictions we find significant analyzing power values up to $A_y$ = 0.3.
The reaction $ ppto ppbf omega$ was investigated with the TOF spectrometer, which is an external experiment at the accelerator COSY (Forschungszentrum Julich, Germany). Total as well as differential cross sections were determined at an excess energy of $93 MeV$ ($p_{beam}=2950 MeV/c$). Using the total cross section of $(9.0pm 0.7 pm1.1) mu b$ for the reaction $ ppto ppomega$ determined here and existing data for the reaction $ppto ppbf phi$, the ratio $mathcal{R}_{phi/omega}=sigma_phi/sigma_omega$ turns out to be significantly larger than expected by the Okubo-Zweig-Iizuka (OZI) rule. The uncertainty of this ratio is considerably smaller than in previous determinations. The differential distributions show that the $omega$ production is still dominated by S-wave production at this excess energy, however higher partial waves clearly contribute. A comparison of the measured angular distributions for $omega$ production to published distributions for $phi$ production at $83 MeV$ shows that the data are consistent with an identical production mechanism for both vector mesons.
Values of the proton analysing power in the $pdto{}^{3}textrm{He},pi^0/^{3}textrm{H},pi^+$ reactions at 350-360~MeV per nucleon were obtained by using a polarised proton beam incident on a deuterium cluster-jet target and with a polarised deuteron beam incident on a target cell filled with polarised hydrogen. These results have a much larger angular coverage than existing data. First measurements are also presented of the deuteron vector analysing power and the deuteron-proton spin correlations. Data were also obtained on the deuteron-proton spin correlation and proton analysing power at small angles at 600~MeV per nucleon, though the angular coverage at this energy was much more restricted even when using a deuteron beam. By combining the extrapolated values of the spin correlations to the forward or backward directions with published measurements of the deuteron tensor analysing powers, the relative phases between the two non-vanishing amplitudes were evaluated.
To settle the question whether the growth with energy is universal for different hadronic total cross-sections, we present results from theoretical models for pion-proton, proton-proton and proton-antiproton total cross-sections. We show that present and planned experiments at LHC can differentiate between different models, all of which are consistent with presently available (lower energy) data. This study is also relevant for the analysis of those very high energy cosmic ray data which require reliable pion-proton total cross-sections as seeds. A preliminary study of the total pion-pion cross-sections is also made.
We report results on the total and elastic cross sections in proton-proton collisions at $sqrt{s}=200$ GeV obtained with the Roman Pot setup of the STAR experiment at the Relativistic Heavy Ion Collider (RHIC). The elastic differential cross section was measured in the squared four-momentum transfer range $0.045 leq -t leq 0.135$ GeV$^2$. The value of the exponential slope parameter $B$ of the elastic differential cross section $dsigma/dt sim e^{-Bt}$ in the measured $-t$ range was found to be $B = 14.32 pm 0.09 (stat.)^{scriptstyle +0.13}_{scriptstyle -0.28} (syst.)$ GeV$^{-2}$. The total cross section $sigma_{tot}$, obtained from extrapolation of the $dsigma/dt$ to the optical point at $-t = 0$, is $sigma_{tot} = 54.67 pm 0.21 (stat.) ^{scriptstyle +1.28}_{scriptstyle -1.38} (syst.)$ mb. We also present the values of the elastic cross section $sigma_{el} = 10.85 pm 0.03 (stat.) ^{scriptstyle +0.49}_{scriptstyle -0.41}(syst.)$ mb, the elastic cross section integrated within the STAR $t$-range $sigma^{det}_{el} = 4.05 pm 0.01 (stat.) ^{scriptstyle+0.18}_{scriptstyle -0.17}(syst.)$ mb, and the inelastic cross section $sigma_{inel} = 43.82 pm 0.21 (stat.) ^{scriptstyle +1.37}_{scriptstyle -1.44} (syst.)$ mb. The results are compared with the world data.
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