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Register a new userAmplitude analysis of gamma n --> pi- p data above 1 GeV
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W. Chen
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We report a new extraction of nucleon resonance couplings using pi- photoproduction cross sections on the neutron. The world database for the process gamma n --> pi- p above 1 GeV has quadrupled with the addition of new differential cross sections from the CEBAF Large Acceptance Spectrometer (CLAS) at Jefferson Lab in Hall B. Differential cross sections from CLAS have been improved with a new final-state interaction determination using a diagramatic technique taking into account the NN and piN final-state interaction amplitudes. Resonance couplings have been extracted and compared to previous determinations. With the addition of these new cross sections, significant changes are seen in the high-energy behavior of the SAID cross sections and amplitudes.
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The production of hidden-bottom pentaquark $P_{b}$ states via $gamma p$ and $pi ^{-}p$ scatterings is studied within an effective Lagrangian approach and the vector-meson-dominance mechnism. For the $P_{b}$ production in the process $gamma prightarrow Upsilon p$, the dipole Pomeron model is employed to calculate the background contribution, and the experimental data can be well described. For the process $pi ^{-}prightarrow Upsilon n$, the Reggeized $t$-channel with $pi $ exchange is considered as the main background for the $P_{b}$ production. Near the threshold, two-peak structure from the states $P_{b (11080)$ and $P_{b}(11125)$ can be observed if energy bin width is chosen as 0.01 GeV, and the same result is obtained in the $pi ^{-}p$ scattering. Moreover, by taking the branching ratio of Br$[{P_{b}rightarrow pi N}]simeq 0.05%$, the numerical result shows that the average value of cross section from the $P_{b}(11080)$ state produced in the $gamma p$ or $pi ^{-}p$ scattering reaches at least 0.1 nb with a bin of 0.1 GeV. Even if we reduce the branching ratio of the $P_{b}$ state into $pi N$ channel by one order, the theoretical average of the cross section from $P_{b}(11080)$ production in $pi ^{-}p$ scattering can reach the order of 0.01 nb with a bin of 0.1 GeV, which means that the signal can still be clearly distinguished from the background. The experimental measurements and studies on the hidden-bottom pentaquark $P_{b}$ state production in the $gamma p $ or $pi ^{-}p$ scattering near-threshold energy region around $Wsimeq 11$ GeV are strongly suggested, which are accessible at COMPASS and JPARC. Particularly, the result of the photoproduction suggests that it is very promising to observe the hidden-bottom pentaquark at proposed EicC facility in China.
Starting from hyperbolic dispersion relations, we derive a system of Roy--Steiner equations for pion Compton scattering that respects analyticity, unitarity, gauge invariance, and crossing symmetry. It thus maintains all symmetries of the underlying quantum field theory. To suppress the dependence of observables on high-energy input, we also consider once- and twice-subtract
The claim that the light quark mass ratio (m_d - m_u)/m_s can be extracted from the decay width ratio Gamma(eta -> pi^0 pi^+ pi^-)/Gamma(eta -> eta pi^+ pi^-) is critically investigated within a U(3) chiral unitary framework. The influence of the recent VES data on the eta -> eta pi^+ pi^- decay is also discussed.
The production of eta mesons in photon- and hadron-induced reactions has been revisited in view of the recent additions of high-precision data to the world data base. Based on an effective Lagrangian approach, we have performed a combined analysis of the free and quasi-free gamma N -> eta N, N N -> N N eta, and pi N -> eta N reactions. Considering spin-1/2 and -3/2 resonances, we found that a set of above-threshold resonances {S_{11}, P_{11}, P_{13}}, with fitted mass values of about M_R=1925, 2130, and 2050 MeV, respectively, and the four-star sub-threshold P_{13}(1720) resonance reproduce best all existing data for the eta production processes in the resonance-energy region considered in this work. All three above-threshold resonances found in the present analysis are essential and indispensable for the good quality of the present fits.
Based on new insights from two recent coupled-channel analyses of $bar{p}p$ annihilation together with $pipi$-scattering data and of $pi^- p$ data, this paper aims at a better understanding of the spin-exotic $pi_1$ resonances in the light meson sector. The Crystal Barrel Collaboration observed the $pi_1$-wave in $bar{p}p$ annihilations in flight for the first time with the coupling to $pi^0eta$ in the reaction $bar{p}p,rightarrow,pi^0pi^0eta$ with a sophisticated coupled-channel approach. Another refined coupled-channel analysis of the P- and D-waves in the $pieta$ and $pieta^prime$ system based on data measured at COMPASS has been performed by the JPAC group. In that study the two spin-exotic signatures listed in the PDG, the $pi_1(1400)$ and $pi_1(1600)$, with a separate coupling to $pieta$ and $pieta^prime$ can be described by a single pole. In this paper, both analyses, the one with the three $bar{p}p$ annihilation channels into $pi^0pi^0eta$, $pi^0etaeta$ and $K^+K^-pi^0$ and 11 different $pipi$-scattering data sets and the one with the P- and D-wave data in the $pieta$ and $pieta^prime$ systems measured at COMPASS, are subjected to a combined coupled channel analysis. By utilizing the K-matrix approach and realizing the analyticity via Chew-Mandelstam functions the $pi_1$ wave can be well described by a single pole for both systems, $pieta$ and $pieta^prime$. The mass and width of the $pi_1$-pole are measured to be $(1561.6 , pm , 3.0 , ^{+6.6}_{-2.6},), mathrm{MeV/c}^2$ and $(388.1 , pm , 5.4 , ^{+0.2}_{-14.1},), mathrm{MeV}$.
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