First data are presented for the polarized-target asymmetry in the reaction π+p→π+pγ at an incident pion energy of 298 MeV. The geometry was chosen to maximize the sensitivity to the radiation of the magnetic dipole moment μΔ of the Δ++(1232 MeV). A fit of the asymmetry in the cross section d5σ/dΩπ dΩγ dk as a function of the photon energy k to predictions from a recent isobar-model calculation with μΔ as the only free parameter yields μΔ=1.64(±0.19expΔ,±0.14 theor)μp. Though this value agrees with bag-model corrections to the SU(6) prediction μΔ=2μp, further clarifications on the model dependence of the result are needed, in particular since the isobar model fails to describe both the cross section and the asymmetry at the highest photon energies.
No description provided.
No description provided.
A fresh analysis is reported of high statistics Crystal Barrel data on p p → 3π 0 , ηηπ 0 , ηπ 0 π 0 and ηη ′ π 0 at rest. This analysis is made fully consistent with CERN-Munich data on π + π − → π + π − up to a mass of 1900 MeV, with GAMS data on π + π − → π 0 π 0 , and with BNL and ANL data on π + π − → K K , which are fitted simultaneously. There is evidence for an I = 0, J PC = 2 ++ resonance with weak (≤ 7%) coupling to ππ, strong coupling to both ϱϱ and ωω and pole position 1534 - i90 MeV. This resonance agrees qualitatively with GAMS and VES data on ππ → ωω, previously interpreted in terms of a resonance at 1590–1640 MeV. New masses and widths for (A) ƒ 0 (1370) and (B) ƒ 0 (1500) , fitted to all eight data sets, are M A = 1300 ± 15 Mev, Γ A = 230 ± 15 MeV, M B = 1500 ± 8 MeV, Γ B = 132 ± 15 MeV. Branching ratios to ππ and ηη are given, and differ significantly from earlier determinations because of a new procedure.
A fraction of the initial P-state annihilation into F2(1270) cannot be ruled out. Therefore, the ratio magnitudes include the contribution due to this channel. MESON0 denotes A2(1630) state, not present in RPP.
Differential cross sections for π ± p→ π ± p have been measured at P π between 378 and 687 MeV / c at 9 angles in the range −0.8⩽cos θ c.m. ⩽0.6. Scattered pions and recoil protons were detected in coincidence using scintillation counter hodoscopes. For almost all of the data the statistical and normalization uncertainties are each less than 2%. Our measurements are compared with existing data and the results of recent partial wave analyses.
No description provided.
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No description provided.
Measurements of the midrapidity transverse energy distribution, $d\Et/d\eta$, are presented for $p$$+$$p$, $d$$+$Au, and Au$+$Au collisions at $\sqrt{s_{_{NN}}}=200$ GeV and additionally for Au$+$Au collisions at $\sqrt{s_{_{NN}}}=62.4$ and 130 GeV. The $d\Et/d\eta$ distributions are first compared with the number of nucleon participants $N_{\rm part}$, number of binary collisions $N_{\rm coll}$, and number of constituent-quark participants $N_{qp}$ calculated from a Glauber model based on the nuclear geometry. For Au$+$Au, $\mean{d\Et/d\eta}/N_{\rm part}$ increases with $N_{\rm part}$, while $\mean{d\Et/d\eta}/N_{qp}$ is approximately constant for all three energies. This indicates that the two component ansatz, $dE_{T}/d\eta \propto (1-x) N_{\rm part}/2 + x N_{\rm coll}$, which has been used to represent $E_T$ distributions, is simply a proxy for $N_{qp}$, and that the $N_{\rm coll}$ term does not represent a hard-scattering component in $E_T$ distributions. The $dE_{T}/d\eta$ distributions of Au$+$Au and $d$$+$Au are then calculated from the measured $p$$+$$p$ $E_T$ distribution using two models that both reproduce the Au$+$Au data. However, while the number-of-constituent-quark-participant model agrees well with the $d$$+$Au data, the additive-quark model does not.
Et EMC distributions for sqrt(sNN) = 62.4 GeV Au+Au collisions shown in 5% wide centrality bins.
Et EMC distributions for sqrt(sNN) = 62.4 GeV Au+Au collisions shown in 5% wide centrality bins.
Et EMC distributions for sqrt(sNN) = 62.4 GeV Au+Au collisions shown in 5% wide centrality bins.
Results are presented from data recorded in 2009 by the PHENIX experiment at the Relativistic Heavy Ion Collider for the double-longitudinal spin asymmetry, $A_{LL}$, for $\pi^0$ and $\eta$ production in $\sqrt{s} = 200$ GeV polarized $p$$+$$p$ collisions. Comparison of the $\pi^0$ results with different theory expectations based on fits of other published data showed a preference for small positive values of gluon polarization, $\Delta G$, in the proton in the probed Bjorken $x$ range. The effect of adding the new 2009 \pz data to a recent global analysis of polarized scattering data is also shown, resulting in a best fit value $\Delta G^{[0.05,0.2]}_{\mbox{DSSV}} = 0.06^{+0.11}_{-0.15}$ in the range $0.05<x<0.2$, with the uncertainty at $\Delta \chi^2 = 9$ when considering only statistical experimental uncertainties. Shifting the PHENIX data points by their systematic uncertainty leads to a variation of the best-fit value of $\Delta G^{[0.05,0.2]}_{\mbox{DSSV}}$ between $0.02$ and $0.12$, demonstrating the need for full treatment of the experimental systematic uncertainties in future global analyses.
PI0 ASYM(LL) measurements from 2005.
PI0 ASYM(LL) measurements from 2006.
PI0 ASYM(LL) measurements from 2009.
We present results for the charged-particle multiplicity distribution at mid-rapidity in Au - Au collisions at sqrt(s_NN)=130 GeV measured with the PHENIX detector at RHIC. For the 5% most central collisions we find $dN_{ch}/d\eta_{|\eta=0} = 622 \pm 1 (stat) \pm 41 (syst)$. The results, analyzed as a function of centrality, show a steady rise of the particle density per participating nucleon with centrality.
130 GeV is sqrt(S) per nucleon-nucleon collision. N(C=N_NUCLEONS) and N(C=N_COLLISONS) are the number of participating nucleons and binary collisions. The statistical errors are negligible and only systematic errors are quoted. COL(NAME=CENTRALITY) is centrality.
This paper presents a large solid angle measurement of the positive pion absorption cross section on 4He and its decomposition into partial channels. The total absorption cross sections at incident pion kinetic energies of Tπ+=70, 118, 162, and 239 MeV are 35±5, 52±4, 51±5, and 27±2 mb, respectively. These values are lower than those reported in some previous experiments. At all pion energies a large fraction of the absorption cross section is due to multinucleon channels.
Data with (C=PRC) are taken from PR C56, 1872.
The first spin-transfer experiment performed for the πd→→p→p reaction is described. Three spin-transfer parameters for this π-absorption process were determined, KLSa, KSSa, and KNNa, which correspond to the π-production parameters, KSLp, KSSp, and KNNp, of the time-reversed p→p→d→π process. Each observable was measured at a single angle for a number of energies spanning the Δ resonance of this system. The results are compared with the predictions of published partial wave amplitude fits which are primarily based on existing data for the time-reversed pp→dπ reaction, and also with the predictions of two current theories. The failure of these theories to describe the fundamental features of the data clearly demonstrates the need for further theoretical work in this area.
No description provided.
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Results from a 4π solid angle measurement of the reactions 3He(π+,ppp) and 4He(π+,ppp)n at incident pion energies of Tπ+=70, 118, 162, 239, and 330 MeV are presented. For 3He the total absorption cross sections and their decomposition into two-proton and three-proton components are evaluated; for 4He the three-proton absorption cross sections are given. The differential distributions of the three-proton multinucleon absorption mode of both nuclei are analyzed and compared to each other by making use of a complete set of variables. The data are investigated for signatures of initial and final state interactions: it is found that more than half of the three-proton yield cannot be accounted for by cascade mechanisms. The remaining strength shows dependence on the incident pion angular momentum, but also structures that are not explained by simple semiclassical models.
Absorption cross section. Total errors are presented.
First and second errors are due to fits and normalization uncertainties, respectively.
First and second errors are due to fits and normalization uncertainties, respectively.
Differential and total cross sections for π+ absorption on Li6 leading to the pp+4Heg.s final state are presented at incident pion energies of 100 and 165 MeV. The narrow width of the pp angular correlation is observed and reported.
No description provided.
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