Search

Recently, the LHCb Collaboration reported pronounced structures in the invariant mass spectrum of $J/\ensuremath{\psi}$ pairs produced in proton-proton collisions at the Large Hadron Collider. In this Letter, we argue that the data can be very well described within two variants of a coupled-channel approach employing $T$ matrices consistent with unitarity: (i) with just two channels, $J/\ensuremath{\psi}J/\ensuremath{\psi}$ and $\ensuremath{\psi}(2S)J/\ensuremath{\psi}$, as long as energy-dependent interactions in these channels are allowed, or (ii) with three channels $J/\ensuremath{\psi}J/\ensuremath{\psi}$, $\ensuremath{\psi}(2S)J/\ensuremath{\psi}$, and $\ensuremath{\psi}(3770)J/\ensuremath{\psi}$ with just constant contact interactions. Both formulations hint at the existence of a near-threshold state in the $J/\ensuremath{\psi}J/\ensuremath{\psi}$ system with the quantum numbers ${J}^{PC}={0}^{++}$ or ${2}^{++}$, which we refer to as $X(6200)$. We suggest experimental tests to check the existence of this state and discuss what additional channels need to be studied experimentally to allow for distinctive tests between the two mechanisms proposed. If the molecular nature of $X(6200)$, as hinted by the three-channel approach, is confirmed, many other double-quarkonium states should exist driven by the same binding mechanism. In particular, there should be an ${\ensuremath{\eta}}_{c}{\ensuremath{\eta}}_{c}$ molecule with a similar binding energy.

The dipion transitions $\mathrm{\ensuremath{\Upsilon}}(10860)\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}\mathrm{\ensuremath{\Upsilon}}(nS)$ ($n=1$, 2, 3) are studied in the framework of a unitary and analytic coupled-channel formalism previously developed for analyzing experimental data on the bottomoniumlike states ${Z}_{b}(10610)$ and ${Z}_{b}(10650)$ [Phys. Rev. D 98, 074023 (2018)] and predicting the properties of their spin partners [Phys. Rev. D 99, 094013 (2019)]. In this work we use a relatively simple but realistic version of this approach, where the scattering and production amplitudes are constructed employing only short-ranged interactions between the open- and hidden-flavor channels consistent with the constraints from heavy quark spin symmetry, for an extended analysis of the experimental line shapes. In particular, the transitions from the $\mathrm{\ensuremath{\Upsilon}}(10860)$ to the final states $\ensuremath{\pi}\ensuremath{\pi}{h}_{b}(mP)$ ($m=1$, 2) and $\ensuremath{\pi}{B}^{(*)}{\overline{B}}^{*}$ already studied before, are now augmented by the $\mathrm{\ensuremath{\Upsilon}}(10860)\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}\mathrm{\ensuremath{\Upsilon}}(nS)$ final states ($n=1$, 2, 3). This is achieved by employing dispersion theory to account for the final state interaction of the $\ensuremath{\pi}\ensuremath{\pi}$ subsystem including its coupling to the $K\overline{K}$ channel. Fits to the two-dimensional Dalitz plots for the ${\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}\mathrm{\ensuremath{\Upsilon}}$ final states were performed. Two real subtraction constants are adjusted to achieve the best description of the Dalitz plot for each $\mathrm{\ensuremath{\Upsilon}}(nS)$ ($n=1$, 2, 3) while all the parameters related to the properties of the ${Z}_{b}\mathrm{s}$ are kept fixed from the previous study. A good overall description of the data for all $\mathrm{\ensuremath{\Upsilon}}(10860)\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}\mathrm{\ensuremath{\Upsilon}}(nS)$ channels achieved in this work provides additional strong support for the molecular interpretation of the ${Z}_{b}$ states.

We present a comprehensive analysis of the deuteron charge and quadrupole form factors based on the latest two-nucleon potentials and charge density operators derived in chiral effective field theory. The single- and two-nucleon contributions to the charge density are expressed in terms of the proton and neutron form factors, for which the most up-to-date empirical parametrizations are employed. By adjusting the fifth-order short-range terms in the two-nucleon charge density operator to reproduce the world data on the momentum-transfer dependence of the deuteron charge and quadrupole form factors, we predict the values of the structure radius and the quadrupole moment of the deuteron: $r_{\rm str}=1.9729\substack{+0.0015\\ -0.0012}\ \text{fm},\ Q_d=0.2854\substack{+0.0038\\ -0.0017}\ \text{fm}^2. $ A comprehensive and systematic analysis of various sources of uncertainty in our predictions is performed. Following the strategy advocated in our recent publication Phys. Rev. Lett. 124, 082501 (2020), we employ the extracted structure radius together with the accurate atomic data for the deuteron-proton mean-square charge radii difference to update the determination of the neutron charge radius, for which we find: $r_n^2=-0.105\substack{+0.005\\ -0.006} \, \text{fm}^2$. Given the observed rapid convergence of the deuteron form factors in the momentum-transfer range of $Q \simeq 1-2.5$ fm$^{-1}$, we argue that this intermediate-energy domain is particularly sensitive to the details of the nucleon form factors and can be used to test different parametrizations., Comment: 39 pages, 9 figures

Three hidden-charm pentaquark ${P}_{c}$ states, ${P}_{c}(4312)$, ${P}_{c}(4440)$, and ${P}_{c}(4457)$ were revealed in the ${\mathrm{\ensuremath{\Lambda}}}_{b}^{0}\ensuremath{\rightarrow}J/\ensuremath{\psi}p{K}^{\ensuremath{-}}$ process measured by LHCb using both run I and run II data. Their nature is under lively discussion, and their quantum numbers have not been determined. We analyze the $J/\ensuremath{\psi}p$ invariant mass distributions under the assumption that the crossed-channel effects provide a smooth background. For the first time, such an analysis is performed employing a coupled-channel formalism with the scattering potential involving both one-pion exchange as well as short-range operators constrained by heavy quark spin symmetry. We find that the data can be well described in the hadronic molecular picture, which predicts seven ${\mathrm{\ensuremath{\Sigma}}}_{c}^{(*)}{\overline{D}}^{(*)}$ molecular states in two spin multiplets, such that the ${P}_{c}(4312)$ is mainly a ${\mathrm{\ensuremath{\Sigma}}}_{c}\overline{D}$ bound state with ${J}^{P}=1/{2}^{\ensuremath{-}}$, while ${P}_{c}(4440)$ and ${P}_{c}(4457)$ are ${\mathrm{\ensuremath{\Sigma}}}_{c}{\overline{D}}^{*}$ bound states with quantum numbers $3/{2}^{\ensuremath{-}}$ and $1/{2}^{\ensuremath{-}}$, respectively. We also show that there is evidence for a narrow ${\mathrm{\ensuremath{\Sigma}}}_{c}^{*}\overline{D}$ bound state in the data which we call ${P}_{c}(4380)$, different from the broad one reported by LHCb in 2015. With this state included, all predicted ${\mathrm{\ensuremath{\Sigma}}}_{c}\overline{D}$, ${\mathrm{\ensuremath{\Sigma}}}_{c}^{*}\overline{D}$, and ${\mathrm{\ensuremath{\Sigma}}}_{c}{\overline{D}}^{*}$ hadronic molecules are seen in the data, while the missing three ${\mathrm{\ensuremath{\Sigma}}}_{c}^{*}{\overline{D}}^{*}$ states are expected to be found in future runs of the LHC or in photoproduction experiments.

In a recent paper [Phys. Rev. D 98, 074023 (2018)], the most up-to-date experimental data for all measured production and decay channels of the bottomoniumlike states ${Z}_{b}(10610)$ and ${Z}_{b}(10650)$ were analyzed in a field-theoretical coupled-channel approach which respects analyticity and unitarity and incorporates both the pion exchange and a short-ranged potential nonperturbatively. All parameters of the interaction were fixed directly from data, and pole positions for both ${Z}_{b}$ states were determined. In this work we employ the same approach to predict in a parameter-free way the pole positions and the line shapes in the elastic and inelastic channels of the (still to be discovered) spin partners of the ${Z}_{b}$ states. They are conventionally referred to as ${W}_{bJ}$'s with the quantum numbers ${J}^{PC}={J}^{++}$ ($J=0$, 1, 2). It is demonstrated that the results of our most advanced pionful fit, which gives the best ${\ensuremath{\chi}}^{2}/\mathrm{d}.\mathrm{o}.\mathrm{f}.$ for the data in the ${Z}_{b}$ channels, are consistent with all ${W}_{bJ}$ states being above-threshold resonances which manifest themselves as well-pronounced hump structures in the line shapes. On the contrary, in the pionless approach, all ${W}_{bJ}$'s are virtual states which can be seen as enhanced threshold cusps in the inelastic line shapes. Since the two above scenarios provide different imprints on the observables, the role of the one-pion exchange in the ${B}^{(*)}{\overline{B}}^{(*)}$ systems can be inferred from the once available experimental data directly.

The most recent experimental data for all measured production and decay channels of the bottomoniumlike states ${Z}_{b}(10610)$ and ${Z}_{b}(10650)$ are analyzed simultaneously using solutions of the Lippmann-Schwinger equations which respect constraints from unitarity and analyticity. The interaction potential in the open-bottom channels ${B}^{(*)}{\overline{B}}^{*}+\mathrm{c}.\mathrm{c}.$ contains short-range interactions as well as a one-pion exchange. It is found that the long-range interaction does not affect the line shapes as long as only $S$ waves are considered. Meanwhile, the line shapes can be visibly modified once $D$ waves, mediated by the strong tensor forces from the pion exchange potentials, are included. However, in the fit they get balanced largely by a momentum dependent contact term that appears to be needed also to render the results for the line shapes independent of the cutoff. The resulting line shapes are found to be insensitive to various higher-order interactions included to verify stability of the results. Both ${Z}_{b}$ states are found to be described by the poles located on the unphysical Riemann sheets in the vicinity of the corresponding thresholds. In particular, the ${Z}_{b}(10610)$ state is associated with a virtual state residing just below the $B{\overline{B}}^{*}/\overline{B}{B}^{*}$ threshold while the ${Z}_{b}(10650)$ state most likely is a shallow state located just above the ${B}^{*}{\overline{B}}^{*}$ threshold.

In a recent paper Phys.Rev.Lett. 111, 042002 (2013) (arXiv:1304.0846), the charmonium state X(3872) is studied in the framework of an effective field theory. In that work it is claimed that (i) the one-pion exchange (OPE) alone provides sufficient binding to produce the X as a shallow bound state at the $D^0\bar{D}^{*0}$ threshold, (ii) short-range dynamics (described by a contact interaction) provides only moderate corrections to the OPE, and (iii) the X-pole disappears as the pion mass is increased slightly and therefore the X should not be seen on the lattice, away from the pion physical mass point, if it were a molecular state. In this paper we demonstrate that the results of Phys.Rev.Lett. 111, 042002 (2013) (arXiv:1304.0846) suffer from technical as well as conceptual problems and therefore do not support the conclusions drawn by the authors.

A calculation of the pion-production operator up to next-to-next-to-leading order for s-wave pions is performed within chiral effective field theory. In the previous study [Phys. Rev. C 85, 054001 (2012)] we discussed the contribution of the pion-nucleon loops at the same order. Here we extend that study to include explicit Delta degrees of freedom and the 1/m_N^2 corrections to the pion-production amplitude. Using the power counting scheme where the Delta-nucleon mass difference is of the order of the characteristic momentum scale in the production process, we calculate all tree-level and loop diagrams involving Delta up to next-to-next-to-leading order. The long-range part of the Delta loop contributions is found to be of similar size to that from the pion-nucleon loops which supports the counting scheme. The net effect of pion-nucleon and Delta loops is expected to play a crucial role in understanding of the neutral pion production data.

The transverse spin correlations ${A}_{x,x}$ and ${A}_{y,y}$ have been measured in the $\stackrel{P\vec}{d}\stackrel{P\vec}{p}\ensuremath{\rightarrow}{p}_{\text{spec}}{{pp}}_{s}{\ensuremath{\pi}}^{\ensuremath{-}}$ reaction at COSY-ANKE at 353 MeV per nucleon. Here ${{pp}}_{s}$ denotes a proton-proton pair with low excitation energy, which is dominantly in the ${}^{1}{S}_{0}$ state. By measuring three protons in the final state it was possible to extract events where there was a spectator proton ${p}_{\text{spec}}$ so that the reaction could be interpreted in terms of quasifree $\stackrel{P\vec}{n}\phantom{\rule{0.16em}{0ex}}\stackrel{P\vec}{p}\ensuremath{\rightarrow}{{pp}}_{s}{\ensuremath{\pi}}^{\ensuremath{-}}$. The proton and neutron analyzing powers in this reaction were also deduced from this data set by averaging over the polarizations of the deuteron beam and hydrogen target, respectively. The values of ${A}_{y}$ were shown to be consistent with a refined analysis of our earlier results obtained with a polarized proton incident on a deuterium target. Taking these data in combination with our previous measurements of the differential cross sections and analyzing powers in the $\stackrel{P\vec}{p}p\ensuremath{\rightarrow}{{pp}}_{s\phantom{\rule{0.16em}{0ex}}}{\ensuremath{\pi}}^{0}$ reaction, a more robust partial wave decomposition was achieved. Three different acceptable solutions were found, and the only way of resolving this ambiguity without further theoretical input would be through a measurement of the mixed spin-correlation parameter ${A}_{x,z}$.

We report on an exclusive and kinematically complete high-statistics measurement of the basic double-pionic fusion reaction pn -> d pi(0)pi(0) over the full energy region of the ABC effect, a pronounced low-mass enhancement in the pi pi-invariant mass spectrum. The measurements, which cover also the transition region to the conventional t- channel Delta Delta process, were performed with the upgraded WASA detector setup at COSY. The data reveal the Abashian-Booth-Crowe effect to be uniquely correlated with a Lorentzian energy dependence in the integral cross section. The observables are consistent with a narrow resonance with m = 2.37 GeV, Gamma approximate to 70 MeV and I(J(P)) = 0(3(+)) in both pn and Delta Delta systems. Necessary further tests of the resonance interpretation are discussed.

We investigate p-wave pion production in nucleon-nucleon collisions up to next-to-next-to-leading order in chiral effective field theory. In particular, we show that it is possible to describe simultaneously the p-wave amplitudes in the $pn\to pp\pi^-$, $pp\to pn\pi^+$, $pp\to d\pi^+$ channels by adjusting a single low-energy constant accompanying the short-range operator which is available at this order. This study provides a non-trivial test of the applicability of chiral effective field theory to reactions of the type $NN\to NN\pi$., Comment: 29 pages, revised version published in PRC

We discuss the theoretical and experimental situations for charge symmetry violation (CSV) effects in the elastic scattering of pi+ and pi- on deuterium (D) and 3He/3H. Accurate comparison of data for both types of targets provides evidence for the presence of CSV effects. While there are indications of a CSV effect in deuterium, it is much more pronounced in the case of 3He/3H. We provide a description of the CSV effect on the deuteron in terms of single- and double- scattering amplitudes. The Delta-mass splitting is taken into account. Theoretical predictions are compared with existing experimental data for pi-d scattering; a future article will speak to the pi-three nucleon case., 16 pages of RevTeX, 7 postscript figures