Search

We study the near-threshold $J/\psi$ meson photoproduction from protons and nuclei by considering incoherent direct non-resonant (${\gamma}p \to {J/\psi}p$, ${\gamma}n \to {J/\psi}n$) and two-step resonant (${\gamma}p \to P_{ci}^+ \to {J/\psi}p$, ${\gamma}n \to P_{ci}^0 \to {J/\psi}n$, $i=1$, 2, 3, 4; $P_{c1}^{+,0}=P_c^{+,0}(4312)$, $P_{c2}^{+,0}=P_c^{+,0}(4337)$, $P_{c3}^{+,0}=P_c^{+,0}(4440)$, $P_{c4}^{+,0}=P_c^{+,0}(4457)$) charmonium production processes. We calculate the absolute excitation functions, energy and momentum distributions for the non-resonant, resonant and for the combined (non-resonant plus resonant) production of $J/\psi$ mesons on protons as well as, using the nuclear spectral function approach, on carbon and tungsten target nuclei at near-threshold incident photon energies by assuming the spin-parity assignments of the hidden-charm resonances $P_{c}^{+,0}(4312)$, $P_{c}^{+,0}(4337)$, $P_{c}^{+,0}(4440)$ and $P_{c}^{+,0}(4457)$ as $J^P=(1/2)^-$, $J^P=(1/2)^-$, $J^P=(1/2)^-$ and $J^P=(3/2)^-$ within three different realistic scenarios for the branching ratios of their decays to the ${J/\psi}p$ and ${J/\psi}n$ modes (0.25, 0.5 and 1%). We show that will be very hard to measure the $P_{ci}^+$ pentaquark states through the scan of the $J/\psi$ total photoproduction cross section on a proton target in the near-threshold energy region around the resonant photon energies of 9.44, 9.554, 10.04 and 10.12 GeV if these branching ratios $\sim$ 1% and less. We also demonstrate that at these photon beam energies the $J/\psi$ energy and momentum combined distributions considered reveal distinct sensitivity to the above scenarios, respectively, at "low" $J/\psi$ total energies and momenta, which implies that they may be an important tool to provide further evidence for the existence of the pentaquark $P_{ci}^+$ and $P_{ci}^0$ resonances., Comment: 26 pages

We study the $J/\psi$ photoproduction from nuclei in the near-threshold beam energy region of $E_{\gamma}$=5--11 GeV within the nuclear spectral function approach by considering incoherent direct (${\gamma}N \to {J/\psi}N$) and two-step (${\gamma}p \to P^+_c(4312)$, $P^+_c(4312) \to {J/\psi}p$; ${\gamma}p \to P^+_c(4440)$, $P^+_c(4440) \to {J/\psi}p$; ${\gamma}p \to P^+_c(4457)$, $P^+_c(4457) \to {J/\psi}p$) $J/\psi$ production processes. We calculate the absolute excitation functions for the non-resonant and resonant production of $J/\psi$ mesons off $^{12}$C and $^{208}$Pb target nuclei within the different scenarios for in-medium modification of the directly photoproduced $J/\psi$ mesons and for branching ratios of the decays $P^+_c(4312) \to {J/\psi}p$, $P^+_c(4440) \to {J/\psi}p$ and $P^+_c(4457) \to {J/\psi}p$. We show that the non-resonant subthreshold $J/\psi$ production in ${\gamma}A$ reactions reveals some sensitivity to employed in-medium modification scenarios for $J/\psi$ mesons, which is not masked by the resonantly produced $J/\psi$ mesons, only if above branching ratios are less than 5\%. We also demonstrate that if these branching ratios more than 5\% then the presence of the $P^+_c(4312)$, $P^+_c(4440)$ and $P^+_c(4457)$ resonances in $J/\psi$ photoproduction on nuclei produces above threshold additional enhancements in the behavior of the total $J/\psi$ creation cross section on nuclei, which could be also studied in the future JLab experiments at the CEBAF facility to provide both further evidence for their existence and valuable information on their nature., Comment: 14 pages

We study the inclusive near-threshold production of $\eta^\prime$ mesons in $\pi^-$ meson-nucleus reactions on the basis of the first-collision model relying on the nuclear spectral function and including incoherent processes of $\eta^\prime$ production in $\pi^-$ meson--proton collisions. The model accounts for the absorption of initial $\pi^-$ and final $\eta^\prime$ mesons, the binding of intranuclear protons and their Fermi motion, as well as the effect of the scalar $\eta^\prime$--nucleus potential (or the in-medium shift of the $\eta^\prime$ meson mass) on these processes. We calculate the differential and total cross sections for $\eta^\prime$ production off carbon and tungsten nuclei at laboratory angles of 0$^{\circ}$--10$^{\circ}$ and 10$^{\circ}$--45$^{\circ}$ by $\pi^-$ mesons with momentum of 1.7 GeV/c, which is close to the threshold momentum for $\eta^\prime$ creation on a free target proton at rest. We show that the calculated $\eta^\prime$ production cross sections are larger than those, studied earlier in the $\eta^\prime$ photoproduction reactions, by about two orders of magnitude. We also demonstrate that the high absolute values of the present differential and total $\eta^\prime$ production cross sections in the momentum ranges of 0.2--0.3 GeV/c and 0.1--0.6 GeV/c, respectively, possess a high sensitivity to changes in the in-medium shift of the $\eta^\prime$ mass. This offers the possibility of evaluating the above shift at these momenta from the respective data, which could be taken in future experiments at the GSI pion beam facility or at J-PARC., Comment: 12 pages. arXiv admin note: text overlap with arXiv:1806.00303

We study the $J/\psi$ photoproduction from nuclei at near-threshold incident photon energies of 5--11 GeV within the nuclear spectral function approach by considering incoherent direct (${\gamma}N \to {J/\psi}N$) and two-step (${\gamma}p \to P^+_c(4450)$, $P^+_c(4450) \to {J/\psi}p$) photon--nucleon charmonium creation processes. We calculate the absolute and relative excitation functions within the different scenarios for in-medium modification of the directly photoproduced $J/\psi$ mesons. We show that the overall subthreshold $J/\psi$ production in ${\gamma}A$ reactions reveals some sensitivity to adopted in-medium modification scenarios for $J/\psi$ mesons only if branching ratio $Br[P^+_c(4450) \to {J/\psi}p]$ $\sim$ 1% and less. Our studies also demonstrate that the presence of the $P^+_c(4450)$ resonance in $J/\psi$ photoproduction produces above threshold additional enhancements in the behavior of the total $J/\psi$ creation cross section on nuclei, which could be also studied in the future JLab experiments at the upgraded up to 12 GeV CEBAF facility to provide further evidence for its existence., Comment: 13 pages

The production of $\eta^\prime$ mesons in coincidence with forward-going protons has been studied in photon-induced reactions on $^{12}$C and on a liquid hydrogen (LH$_2$) target for incoming photon energies of 1.3-2.6 GeV at the electron accelerator ELSA. The $\eta^\prime$ mesons have been identified via the $\eta^\prime\rightarrow \pi^0 \pi^0\eta \rightarrow 6 \gamma$ decay registered with the CBELSA/TAPS detector system. Coincident protons have been identified in the MiniTAPS BaF$_2$ array at polar angles of $2^{\circ} \le \theta _{p} \le 11^{\circ}$. Under these kinematic constraints the $\eta^\prime$ mesons are produced with relatively low kinetic energy ($\approx$ 150 MeV) since the coincident protons take over most of the momentum of the incident-photon beam. For the C-target this allows the determination of the real part of the $\eta^\prime$-carbon potential at low meson momenta by comparing with collision model calculations of the $\eta^\prime$ kinetic energy distribution and excitation function. Fitting the latter data for $\eta^\prime$ mesons going backwards in the center-of-mass system yields a potential depth of V = $-$(44 $\pm$ 16(stat)$\pm$15(syst)) MeV, consistent with earlier determinations of the potential depth in inclusive measurements for average $\eta^\prime$ momenta of $\approx$ 1.1 GeV/$c$. Within the experimental uncertainties, there is no indication of a momentum dependence of the $\eta^\prime$-carbon potential. The LH$_2$ data, taken as a reference to check the data analysis and the model calculations, provide differential and integral cross sections in good agreement with previous results for $\eta^\prime$ photoproduction off the free proton., Comment: 9 pages, 13 figures. arXiv admin note: text overlap with arXiv:1608.06074

The production of η′ mesons in coincidence with forward-going protons has been studied in photon-induced reactions on 12C and on a liquid hydrogen (LH2) target for incoming photon energies of 1.3-2.6 GeV at the electron accelerator ELSA. The η′ mesons have been identified via the η′→π0π0η→6γ decay registered with the CBELSA/TAPS detector system. Coincident protons have been identified in the MiniTAPS BaF2 array at polar angles of 2∘≤θp≤11∘. Under these kinematic constraints the η′ mesons are produced with relatively low kinetic energy (≈150 MeV) since the coincident protons take over most of the momentum of the incident-photon beam. For the C-target this allows the determination of the real part of the η′-carbon potential at low meson momenta by comparing with collision model calculations of the η′ kinetic energy distribution and excitation function. Fitting the latter data for η′ mesons going backwards in the center-of-mass system yields a potential depth of V=−(44±16(stat)±15(syst)) MeV, consistent with earlier determinations of the potential depth in inclusive measurements for average η′ momenta of ≈1.1 GeV/c. Within the experimental uncertainties, there is no indication of a momentum dependence of the η′-carbon potential. The LH2 data, taken as a reference to check the data analysis and the model calculations, provide differential and integral cross sections in good agreement with previous results for η′ photoproduction off the free proton.

The excitation function and momentum distribution of η′ mesons have been measured in photoproduction off Nb93 in the energy range of 1.2-2.9 GeV. The experiment has been performed with the combined Crystal Barrel and MiniTAPS detector system, using tagged photon beams from the ELSA electron accelerator. Information on the sign and magnitude of the real part of the η′-Nb potential has been extracted from a comparison of the data with model calculations. An attractive potential of -(41±10(stat)±15(syst)) MeV depth at normal nuclear matter density is deduced within model uncertainties. This value is consistent with the potential depth of -(37±10(stat)±10(syst)) MeV obtained in an earlier measurement for a light nucleus (carbon). This relatively shallow η′-nucleus potential will make the search for η′-nucleus bound states more difficult.

We study the photoproduction of $\eta^\prime$ mesons from nuclei near the threshold within the collision model based on the nuclear spectral function. The model takes properly into account both primary photon-nucleon and secondary pion-nucleon $\eta^\prime$ production processes as well as the effect of the nuclear $\eta^\prime$ mean-field potential on these processes. We find that the secondary pion-induced reaction channel ${\pi}N \to {\eta^\prime}N$ plays an insignificant role in the $\eta^\prime$ photoproduction off nuclei. We calculate the transparency ratio for $eta^\prime$ mesons and compare it to the available experimental data. The comparison indicates an inelastic ${\eta^\prime}N$ cross section of the order of 6-10 mb. We show that the existing transparency ratio measurements do not allow one to distinguish between two adopted $\eta^\prime$ in-medium modification scenarios. Our studies also demonstrate that the momentum distribution and excitation function for $\eta^\prime$ production in ${\gamma}A$ reactions reveal some sensitivity to these scenarios, which means that such observables may be an important tool to get a valuable information on the $\eta^\prime$ in-medium properties., Comment: 17 pages

The inclusive production of phi mesons at small angles in proton collisions with C, Cu, Ag, and Au targets has been measured at an incident energy of 2.83 GeV at the ANKE-COSY facility. The phi mesons were registered via the phi -> K^+K^- decay. The momentum dependence of the nuclear transparency ratio, the in-medium phi width, and the differential cross section for phi production have been determined in the momentum region p_phi = 0.6 - 1.6 GeV/c. Comparison with different model calculations suggests a significant broadening of the in-medium phi width for normal nuclear density with evidence for a momentum dependence.

Differential and total cross sections for the pp -> ppK+K- reaction have been measured at a proton beam energy of 2.83 GeV using the COSY-ANKE magnetic spectrometer. Detailed model descriptions fitted to a variety of one-dimensional distributions permit the separation of the pp -> pp phi cross section from that of non-phi production. The differential spectra show that higher partial waves represent the majority of the pp -> pp phi total cross section at an excess energy of 76 MeV, whose energy dependence would then seem to require some s-wave phi-p enhancement near threshold. The non-phi data can be described in terms of the combined effects of two-body final state interactions using the same effective scattering parameters determined from lower energy data., 12 pages, 12 figures, 3 tables

We present a theoretical investigation of $\Lambda(1520)$ attenuation in ${\gamma}A$ reactions near the threshold. It is performed in the framework of a collision model based on the nuclear spectral function. The model accounts for both primary photon-nucleon ${\gamma}N \to K\Lambda(1520)$ and secondary pion-nucleon ${\pi}N \to K\Lambda(1520)$ production processes. We calculate the target mass and momentum dependences of the forward $\Lambda(1520)$ hyperon production from nuclei at photon energy of 2 GeV as well as for two options for its in-medium width. We find that the considered dependences are markedly sensitive to this width. Our studies also demonstrate that the secondary channel ${\pi}N \to K\Lambda(1520)$ plays a substantial role in the intermediate momentum $\Lambda(1520)$ photoproduction on nuclei in the chosen kinematics and, hence, is to be taken into account in the analysis of $\Lambda(1520)$ hyperon photoproduction from nuclei with the aim to get information on its width in the matter., Comment: 16 pages, 7 figures

Within spectator model we study the reaction ${\gamma}d \to K^-{\Theta}^+p \to K^-K^+np$ in the threshold energy region. We present the predictions for the exclusive and inclusive antikaon angular distributions in the laboratory system for this reaction calculated for two possible parity states of the ${\Theta}^+$ resonance at 1.5 and 1.75 GeV beam energies with and without imposing the relevant kinematical cuts on those parts of the sampled phase space where contribution from the main background sources associated with the ${\phi}(1020)$, ${\Lambda}(1520)$ production as well as with the $K^-p$--rescattering in the final state, is expected to be dominant. We show that under chosen kinematics these distributions are sensitive to the ${\Theta}^+$ parity and, therefore, can be used as a filter for the determination of its parity., Comment: 18 pages, 8 figures; will be published in Phys.Atom.Nucl_4_2006

The experimental data on the production of $K^-$-mesons in pp-collisions are analyzed and a method of the unified description of these data in a broad energy range for primary protons is proposed. The $K^-$-mesons production in pA-collisions is considered. The simple formulas for inclusive cross sections of the $K^-$ production in these collisions are given. The results of the calculations by these formulas are compared with the available experimental data., 14 pages, LaTeX, uses ws-art.sty. Figures can be requested from efremov@physics.rice.edu or looked up in the article above

The inclusive $K^+$ mesons production in $\pi^+$--nucleus reactions in the subthreshold energy regime is analyzed with respect to the one--step ($\pi^+n\to K^+\Lambda$) and the two--step ($\pi^+n\to \eta p_1,~ \eta p_2\to K^+\Lambda$) incoherent production processes on the basis of an appropriate folding model, which allows one to take into account the various forms of an internal nucleon momentum distribution as well as on-- and off--shell propagation of the struck target nucleon. Contrary to proton--nucleus reactions primary reaction channel is found to be significant practically at all considered energies. Detailed predictions for the $K^+$ total and invariant differential cross sections from \piC-- and \piPb--collisions at subthreshold energies are provided., Comment: 18 pages, LaTeX, uses ws-art.sty, gzip+uuencoded postscript. Figures are available by request from efremov@physics.rice.edu