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The recent search for non $q bar{q}$ mesons in $pi^{-}p$ interactions at Brookhaven National Laboratory is summarized. Many final states such as $eta pi$, $eta pi^{-}$, $a_{0} pi$, $f_{1} pi$, $a_{2} pi$, $b_{1} pi$, which are favored decay modes of exotics, are under investigation.
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The use of nuclear transparency effect of pi^{-}-mesons in proton, and deuteron induced interactions with carbon nuclei at 4.2A GeV/c, to get information about the properties of nuclear matter, is presented in this work. Half angle (theta_{1/2}) technique is used to extract information on nuclear transparency effect. The theta_{1/2} divides the multiplicity of charged particles into two equal parts depending on their polar angle in the lab. frame in pp interactions. Particles with angle smaller than (incone particles) and greater than (outcone particles) theta_{1/2} are considered separate. The average values of multiplicity, momentum and transverse momentum of the pi^{-}-mesons are analyzed as a function of a number of identified protons in an event. We observed evidences in the data which could be considered as transparency effect. For quantitative analysis, the results are compared with cascade model. The observed effects are categorized into leading effect transparency and medium effect transparency. The transparency in the latter case could be the reason of collective interactions of grouped nucleons with the incident particles.
We have performed the most comprehensive resonance-model fit of $pi^-pi^-pi^+$ states using the results of our previously published partial-wave analysis (PWA) of a large data set of diffractive-dissociation events from the reaction $pi^- + p to pi^-pi^-pi^+ + p_text{recoil}$ with a 190 GeV/$c$ pion beam. The PWA results, which were obtained in 100 bins of three-pion mass, $0.5 < m_{3pi} < 2.5$ GeV/$c^2$, and simultaneously in 11 bins of the reduced four-momentum transfer squared, $0.1 < t < 1.0$ $($GeV$/c)^2$, are subjected to a resonance-model fit using Breit-Wigner amplitudes to simultaneously describe a subset of 14 selected waves using 11 isovector light-meson states with $J^{PC} = 0^{-+}$, $1^{++}$, $2^{++}$, $2^{-+}$, $4^{++}$, and spin-exotic $1^{-+}$ quantum numbers. The model contains the well-known resonances $pi(1800)$, $a_1(1260)$, $a_2(1320)$, $pi_2(1670)$, $pi_2(1880)$, and $a_4(2040)$. In addition, it includes the disputed $pi_1(1600)$, the excited states $a_1(1640)$, $a_2(1700)$, and $pi_2(2005)$, as well as the resonancelike $a_1(1420)$. We measure the resonance parameters mass and width of these objects by combining the information from the PWA results obtained in the 11 $t$ bins. We extract the relative branching fractions of the $rho(770) pi$ and $f_2(1270) pi$ decays of $a_2(1320)$ and $a_4(2040)$, where the former one is measured for the first time. In a novel approach, we extract the $t$ dependence of the intensity of the resonances and of their phases. The $t$ dependence of the intensities of most resonances differs distinctly from the $t$ dependence of the nonresonant components. For the first time, we determine the $t$ dependence of the phases of the production amplitudes and confirm that the production mechanism of the Pomeron exchange is common to all resonances.
We have studied the reaction K+ p -> K+ n pi+ using an 11 GeV/c K+ beam and the Large Acceptance Superconducting Solenoid (LASS) multiparticle spectrometer facility at SLAC. We put limits on the production of narrow theta+ baryons in this reaction.
First results are presented from BNL experiment E910 on pion production and stopping in proton-Be, Cu, and Au collisions at a beam momentum of 18 GeV/c. We characterize the centrality of the collisions using the measured number of grey tracks, Ngrey,and a derived quantity, nu, the number of inelastic nucleon-nucleon scatterings suffered by the projectile during the collision. We find that for the three targets the average backward rapidity shift of the leading proton follows a common trend versus nu with the projectile losing, on average, 2 units of rapidity in the first 2-3 scatterings. The average rapidity shift increases more slowly with subsequent scatterings reaching a maximum of 2.5 units. The pi- multiplicity measured within the E910 acceptance saturates with increasing nu in p-Au collisions while the pi- multiplicity in p-Be collisions increases faster with nu than expected from the wounded-nucleon model. Comparisons of our data with the RQMD cascade model suggest that in very central p-Au collisions most of the pions are produced near zero rapidity in the lab.
Precise knowledge of hadron production rates in the generation of neutrino beams is necessary for accelerator-based neutrino experiments to achieve their physics goals. NA61/SHINE, a large-acceptance hadron spectrometer, has recorded hadron+nucleus interactions relevant to ongoing and future long-baseline neutrino experiments at Fermi National Accelerator Laboratory. This paper presents three analyses of interactions of 60 GeV/$c$ $pi^+$ with thin, fixed carbon and beryllium targets. Integrated production and inelastic cross sections were measured for both of these reactions. In an analysis of strange, neutral hadron production, differential production multiplicities of $K^0_{S}$, $Lambda$ and anti-$Lambda$ were measured. Lastly, in an analysis of charged hadron production, differential production multiplicities of $pi^+$, $pi^-$, $K^+$, $K^-$ and protons were measured. These measurements will enable long-baseline neutrino experiments to better constrain predictions of their neutrino flux in order to achieve better precision on their neutrino cross section and oscillation measurements.
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