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Register a new userOdd and Even Partial Waves of $etapi^-$ and $etapi^-$ in $pi^-ptoeta^{(prime)}pi^-p$ at $191,textrm{GeV}/c$
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Exclusive production of $etapi^-$ and $etapi^-$ has been studied with a $191,textrm{GeV}/c$ $pi^-$ beam impinging on a hydrogen target at COMPASS (CERN). Partial-wave analyses reveal different odd/even angular momentum ($L$) characteristics in the inspected invariant mass range up to $3,textrm{GeV}/c^2$. A striking similarity between the two systems is observed for the $L=2,4,6$ intensities (scaled by kinematical factors) and the relative phases. The known resonances $a_2(1320)$ and $a_4(2040)$ are in line with this similarity. In contrast, a strong enhancement of $etapi^-$ over $etapi^-$ is found for the $L=1,3,5$ waves, which carry non-$qbar q$ quantum numbers. The $L=1$ intensity peaks at $1.7,textrm{GeV}/c^2$ in $etapi^-$ and at $1.4,textrm{GeV}/c^2$ in $etapi^-$, the corresponding phase motions with respect to $L=2$ are different.
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The production of $eta^{(prime)}pi$ pairs constitutes one of the golden channels to search for hybrid exotics, with explicit gluonic degrees of freedom. Understanding the dynamics and backgrounds associated to $eta^{(prime)}pi$ production above the resonance region is required to impose additional constraints to the resonance extraction. We consider the reaction $pi^-pto eta^{(prime)} pi^- ,p$ measured by COMPASS. We show that the data in $2.4 < m_{eta^{(prime)}pi} < 3.0$ GeV can be described by amplitudes based on double-Regge exchanges. The angular distribution of the meson pairs, in particular in the $eta pi$ channel, can be attributed to flavor singlet exchanges, suggesting the presence of a large gluon content that couples strongly to the produced mesons.
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.
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.
Using $448.0 times 10^6$~$psi(3686)$ events collected with the BESIII detector, an amplitude analysis is performed for $psi(3686)togammachi_{c1}$, $chi_{c1}toetapi^+pi^-$ decays. The most dominant two-body structure observed is $a_0(980)^{pm}pi^{mp}$; $a_0(980)^{pm}toetapi^{pm}$. The $a_0(980)$ line shape is modeled using a dispersion relation, and a significant non-zero $a_0(980)$ coupling to the $eta^{prime}pi$ channel is measured. We observe $chi_{c1}to a_2(1700)pi$ production for the first time, with a significance larger than 17$sigma$. The production of mesons with exotic quantum numbers, $J^{PC}=1^{-+}$, is investigated, and upper limits for the branching fractions $chi_{c1}to pi_1(1400)^{pm}pi^{mp}$, $chi_{c1}to pi_1(1600)^{pm}pi^{mp}$, and $chi_{c1}topi_1(2015)^{pm}pi^{mp}$, with subsequent $pi_1(X)^{pm} to etapi^{pm}$ decay, are determined.
The COMPASS collaboration has collected the currently largest data set on diffractively produced $pi^-pi^-pi^+$ final states using a negative pion beam of 190 GeV/c momentum impinging on a stationary proton target. This data set allows for a systematic partial-wave analysis in 100 bins of three-pion mass, $0.5 < m_{3pi} < 2.5$ GeV/c$^2$ , and in 11 bins of the reduced four-momentum transfer squared, $0.1 < t < 1.0$ (GeV/c)$^2$ . This two-dimensional analysis offers sensitivity to genuine one-step resonance production, i.e. the production of a state followed by its decay, as well as to more complex dynamical effects in nonresonant $3pi$ production. In this paper, we present detailed studies on selected $3pi$ partial waves with $J^{PC} = 0^{-+}$, $1^{++}$, $2^{-+}$, $2^{++}$, and $4^{++}$. In these waves, we observe the well-known ground-state mesons as well as a new narrow axial-vector meson $a_1(1420)$ decaying into $f_0(980) pi$. In addition, we present the results of a novel method to extract the amplitude of the $pi^-pi^+$ subsystem with $I^{G}J^{PC} = 0^+ 0^{++}$ in various partial waves from the $pi^-pi^-pi^+$ data. Evidence is found for correlation of the $f_0(980)$ and $f_0(1500)$ appearing as intermediate $pi^- pi^+$ isobars in the decay of the known $pi(1800)$ and $pi_2(1880)$.
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