Final State Interaction Effects Research Articles

Traces of the hidden-charm S=−1 pentaquark in the Λb→J/ΨηΛ decay

The hidden charm pentaquark state Pc (4450), observed recently by the LHCb collaboration in the Λb →J/ψK − p decay, may be of molecular nature, as advocated by some unitary approaches that also predict pentaquark partners in the strangeness S=−1 sector. In this work we argue that a hidden-charm strange pentaquark could also be seen in the decay of theΛb , but through the J/ψη Λ decay mode, by studying the invariant mass spectrum of J/ψ Λ pairs.In our model we assume a standard weak decay topology, then incorporate the hadronization process and final state interaction effects, and we find that the J/ψη Λ final state is populated with the strength similar to that of the J/ψK− p . We have studied the dependence of our results on reasonable changes in the parameters of the models as well as on the unknown properties of the speculated hidden charm strange pentaquark. We have observed that, while there appear changes in the position of the peak and in the shapes of the distributions, a resonance signal in the J/ψ Λ invariant mass spectrum is clearly seen in all the cases. This gives us confidence that such an experimental study could result into a successful proof of the existence of this new state.

Femtoscopy of identified particles in Pb–Pb collisions with ALICE at the LHC

Femtoscopy provides information on system size and its dynamics due to the effects of quantum statistics and final-state interactions. The results of femtoscopic correlations of different identified particles measured by ALICE in Pb–Pb collisions at sNN=2.76 TeV are presented. Hydrodynamic models predict a decrease of the radii with increasing pair transverse mass (mT) due to radial flow. Correlation measurements of heavy particles extend the range over which the transverse mass dependence of the source radii can be studied and thus can serve as a tool to learn about the dynamics of the deconfined medium. In particular, the measured three-dimensional radii of kaons are compared with a model where the hydrodynamic phase is succeeded by a hadronic rescattering phase and a purely hydrodynamical calculation. The latter predicts an approximate mT scaling of source radii obtained from pion and kaon correlations. This mT scaling appears to be broken in the data. The breaking of scaling is well reproduced by the full hydro-kinetic model calculations, thereby indicating the importance of the rescattering phase at LHC energies. The emission duration and the decoupling time of the system are also estimated for kaons and pions.

Analysis of the $B_{s}\rightarrow \bar{D}^{0} \phi$ decay

In this paper we analyzed the $ B_{s}\rightarrow \bar{D}^{0} \phi$ decay within different frameworks. At first we consider the naive factorization (NF) and the QCD factorization (QCDF) approach, where the final states are a pseudoscalar meson and vector meson; then we consider the final state interaction (FSI) effect, where the intermediate state is $ D_{s}^{\ast-}K^{+}$ to improve the branching ration. In QCDF we considered the nonfactorizable corrections, such as vertex correction and hard spectator interactions. First observation of the $ B_{s} \rightarrow \bar{D}^{0} \phi$ decay is reported using pp collision data, corresponding to an integrated luminosity of 1.0 fb-1, collected by the LHCb experiment at a center-of-mass energy of 7TeV. Our results in the naive factorization approach is $ 8.73^{+0.01}_{-0.01} \times 10^{-7}$ and in QCDF approach is $ 4.03^{+0.01}_{-0.02} \times 10^{-6}$ and the improved branching ratio is $ 1.84^{+0.18}_{-0.17} \times 10^{-5}$ , when we consider the final state interaction effect in energy scale $ \mu = m_{b}$ . It is near the experimental value, which is $ 2.3\times 10^{-5}$ .

Photoproduction of $\eta$ $\pi$ pairs off nucleons and deuterons

Quasi-free photoproduction of $\pi\eta$-pairs has been investigated from threshold up to incident photon energies of 1.4 GeV, respectively up to photon-nucleon invariant masses up to 1.9 GeV. Total cross sections, angular distributions, invariant-mass distributions of the $\pi\eta$ and meson-nucleon pairs, and beam-helicity asymmetries have been measured for the reactions $\gamma p\rightarrow p\pi^0\eta$, $\gamma n\rightarrow n\pi^0\eta$, $\gamma p\rightarrow n\pi^+\eta$, and $\gamma n\rightarrow p\pi^-\eta$ from nucleons bound inside the deuteron. For the $\gamma p$ initial state data for free protons have also been analyzed. Finally, the total cross sections for quasi-free production of $\pi^0\eta$ pairs from nucleons bound in $^3$He nuclei have been investigated in view of final state interaction (FSI) effects. The experiments were performed at the tagged photon beam facility of the Mainz MAMI accelerator using an almost $4\pi$ covering electromagnetic calorimeter composed of the Crystal Ball and TAPS detectors. The shapes of all differential cross section data and the asymmetries are very similar for protons and neutrons and agree with the conjecture that the reactions are dominated by the sequential $\Delta^{\star}3/2^-\rightarrow\eta\Delta(1232)\rightarrow\pi\eta N$ decay chain, mainly with $\Delta(1700)3/2^-$ and $\Delta(1940)3/2^-$. The ratios of the magnitude of the total cross sections also agree with this assumption. However, the absolute magnitudes of the cross sections are reduced by FSI effects with respect to free proton data.

A hidden-charm $$\varvec{S=-1}$$ S = - 1 pentaquark from the decay of $$\varvec{\varLambda _b}$$ Λ b into $$\varvec{J/\psi \, \eta \varLambda }$$ J / ψ η Λ states

The hidden charm pentaquark state $P_c(4450)$ observed recently by the LHCb collaboration may be of molecular nature, as advocated by some unitary approaches that also predict pentaquark partners in the strangeness $S=-1$ sector. In this work we argue that a hidden-charm strange pentaquark could be seen from the decay of the $\Lambda_b$, just as in the case of the non-strange $P_c(4450)$, but looking into the $J/\psi \eta \Lambda$ decay mode and forming the invariant mass spectrum of $J/\psi\Lambda$ pairs. In the model presented here, which assumes a standard weak decay topology and incorporates the hadronization process and final state interaction effects, we find the $J/\psi \eta \Lambda$ final states to be populated with similar strength as the $J/\psi K^- p$ states employed for the observation of the non-strange pentaquark. This makes the $\Lambda_ b \to J/\psi \eta \Lambda$ decay to be an interesting process to observe a possible strange partner of the $P_c(4450)$ . We study the dependence of the $J/\psi \Lambda$ mass spectra on various model ingredients and on the unknown properties of the strange pentaquark.

Impact of the $$\gamma _{\nu }$$NN* Electrocoupling Parameters at High Photon Virtualities and Preliminary Cross Sections off the Neutron

Meson-photoproduction measurements and their reaction-amplitude analyses can establish more sensitively, and in some cases in an almost model-independent way, nucleon excitations and non-resonant reaction amplitudes. However, to investigate the strong interaction from already explored—where meson-cloud degrees of freedom contribute substantially to the baryon structure—to still unexplored distance scales—where quark degrees of freedom dominate and the transition from dressed to current quarks occurs—we depend on experiments that allow us to measure observables that are probing this evolving non-perturbative QCD regime over its full range. Elastic and transition form factors are uniquely suited to trace this evolution by measuring elastic electron scattering and exclusive single-meson and double-pion electroproduction cross sections off the nucleon. These exclusive measurements will be extended to higher momentum transfers with the energy-upgraded CEBAF beam at JLab to study the quark degrees of freedom, where their strong interaction is responsible for the ground and excited nucleon state formations. After establishing unprecedented high-precision data, the imminent next challenge is a high-quality analysis to extract these relevant electrocoupling parameters for various resonances that can then be compared to state-of-the-art models and QCD-based calculations. The vast majority of the available exclusive electroproduction cross sections are off the proton. Hence flavor-dependent analyses of excited light-quark baryons are lacking experimental data off the neutron. The goal is to close this gap by providing exclusive \({\gamma }_{\nu }(n) \rightarrow p^{+} {\pi }^{-}\) reaction cross section off deuterium and to establish a kinematical final-state-interaction (FSI) correction factor (R) map that can be determined from the data set itself. The “e1e” Jefferson Lab CLAS data set, that is analyzed, includes both a hydrogen and deuterium target run period, which allows a combined analysis of the pion electroproduction off the free proton, the bound proton, and the bound neutron under the same experimental conditions. Hence it will provide the experimentally best possible information on the off-shell and FSI effects in deuterium, which must be considered in order to extract the information off the neutron. The cross section analysis of this data set, that is currently underway, will considerably improve our knowledge of the \(Q^{2}\) evolution of resonance states off bound protons and neutrons. Recent results presented here and in these proceedings are demonstrating the status and continuous progress of data analyses and their theoretical descriptions, as well as highlighting the experimental and theoretical outlook of what shall and may be achieved in the new era of the 12-GeV upgraded transition form factor program.

Analysis of the Bs → K∓∗K± decay

In this paper, we analyzed the process of [Formula: see text] decay within QCD factorization (QCDF) and final state interaction (FSI) effects. At first, the [Formula: see text] decay is calculated via QCDF approach. The result that is found by using the QCDF method is less than the experimental result. Then we considered FSI effect as a sizable correction where there are the intermediate state [Formula: see text] mesons via the exchange of [Formula: see text]. The experi mental branching ratio of [Formula: see text] decay is [Formula: see text], and our results by QCDF and FSI are [Formula: see text] and [Formula: see text], respectively.

Phenomenological analysis of near-threshold periodic modulations of the proton timelike form factor

We have recently highlighted the presence of a periodically oscillating 10 \% modulation in the BABAR data on the proton timelike form factors, in the reaction $e^++e^-$ $\rightarrow$ $\bar{p}+p$. Here we deepen our previous data analysis, and confirm that in the case of several standard parametrizations it is possible to write the form factor in the form $F_0$ $+$ $F_{osc}$, where $F_0$ is a parametrization expressing the long-range trend of the form factor (for $q^2$ ranging from the $\bar{p}p$ threshold to 36 GeV$^2$), and $F_{osc}$ is a function of the form $\exp(-Bp)\cos(Cp)$, where $p$ is the relative momentum of the final $\bar{p}p$ pair. Error bars allow for a clean identification of the main features of this modulation for $q^2$ $<$ 10 GeV$^2$. Assuming this oscillatory modulation to be an effect of final state interactions between the forming proton and the antiproton, we propose a phenomenological model based on a double-layer imaginary optical potential. This potential is flux-absorbing when the distance between the proton and antiproton centers of mass is $\gtrsim$ 1.7-1.8 fm and flux-generating when it is $\lesssim$ 1.7-1.8 fm. The main features of the oscillations may be reproduced with some freedom in the potential parameters, but the transition between the two layers must be sudden (0-0.2 fm) to get the correct oscillation period. The flux-absorbing part of the $\bar{p}p$ interaction is due to the annihilation of $\bar{p}p$ pairs into multi-meson states. We interpret the flux-creating part of the potential as due to the creation of a $1/q$-ranged state when the virtual photon decays into a set of current quarks and antiquarks, including heavy ones, that may exist for a short time. The decay of these large mass states leads to an intermediate stage regeneration of the $\bar{p}p$ channel.

Final-state interactions in two-nucleon knockout reactions

Background: Exclusive two-nucleon knockout after electroexcitation of nuclei ($A(e,e'NN)$ in brief) is considered to be a primary source of information about short-range correlations (SRC) in nuclei. For a proper interpretation of the data, final-state interactions (FSI) need to be theoretically controlled. Purpose: Our goal is to quantify the role of FSI effects in exclusive $A(e,e'pN)$ reactions for four target nuclei representative for the whole mass region. Our focus is on processes that are SRC driven. We investigate the role of FSI for two characteristic detector setups corresponding with a "small" and "large" coverage of the available phase space. Results: The transparency $T^{pN}_{A}$, defined as the ratio of exclusive $(e,e'pN)$ cross sections on nuclei to those on "free" nucleon pairs, drops from $ 0.2-0.3 $ for $^{12}$C to $0.04-0.07$ for $^{208}$Pb. For all considered kinematics, the mass dependence of the $T^{pN}_{A}$ can be captured by the power law $T^{pN}_{A} \propto A^{- \lambda}$ with $ 0.4 \lesssim \lambda \lesssim 0.5 $. Apart from an overall reduction factor, we find that FSI only modestly affects the distinct features of SRC-driven $A(e,e'pN)$ which are dictated by the c.m. distribution of close-proximity pairs. Conclusion: The SCX mechanisms represent a relatively small (order of a few percent) contribution of SRC-driven $A(e,e'pN)$ processes. The mass dependence of FSI effects in exclusive $A(e,e'pN)$ can be captured in a robust power law and is in agreement with the predictions obtained in a toy model.

Effect of final state interaction in 3He (π−, π+) 3n reaction

The calculation of the doubly differential cross section was performed using sequential single charge exchange mechanism for the double charge exchange reaction 3He (π−, π+) 3n. The effect of the final state interaction between two active neutrons was investigated using Malfliet Tjon potential. Our results were compared with experimental results at intermediate energy range for the values 120, 180, 210 and 240 MeV. In this study, pion production was used to interpret the low energy peak that was observed on the forward angles at the incident energies of 210 and 240 MeV.

Effects of Final State Interactions in Pure Annihilation Decay of B+ → D+K0*

The decay of the B + meson to the D + and K 0* mesons is a pure annihilation decay. For this reason, in the framework of the quantum chromodynamics factorization (QCDF) approach, this decay has a small amplitude and a small branching ratio. In this research we find that, before the D + and K 0* mesons are produced in the final states, pair mesons such as D s +* and D s +ρ0 are produced. The intermediate-state mesons via the exchange of K 0(K 0*) and D +(D +*) go to the D + and K 0* final state mesons. However we calculate the B + → D + K 0* decay in two different frameworks. The first framework is the QCDF method and the second one is final state interaction (FSI). The experimental branching ratio of B + → D + K 0* decay is less than 3 × 10–6, and our results obtained by the QCDF method and FSI are (0.35 ± 0.04) × 10–6 and (2.94 ± 0.10) × 10–6, respectively.

Exclusive π−Electroproduction off the Neutron in Deuterium in the Resonance Region

The goal of our research is to provide the exclusive γ*(n) → p+π− reaction cross section from deuterium data using the correction factor that account for the final state re-scattering that can be determined from the data set itself. The “e1e” Jefferson Lab CLAS data set that we analyze includes both a hydrogen and deuterium target run period, which allows a combined analysis of pion electroproduction off the free proton, the bound proton, and the bound neutron under the same experimental conditions. Hence it will provide the experimentally best possible information about the off-shell and final state interaction effects in deuterium, which must be considered in order to extract the neutron information. This data set will provide results with a kinematic coverage for the hadronic invariant mass W up to 1.7 GeV and in the momentum transfer Q2 range of 0.4 − 1.0 GeV/c2. The cross section analysis of this data set is currently underway, which will considerably improve our knowledge of the Q2 evolution of π−p electroproduction cross sections off bound neutron needed for the extraction of excited neutron state electrocouplings for the first time.

Bose-Einstein correlations of charged and neutral kaons in pp and Pb—Pb collisions at the LHC with the ALICE experiment

Due to the effects of quantum statistics and final state interactions, momentum correlations of two or more particles at small relative velocities, i.e. at small relative momenta in their center-of-mass system, are sensitive to the space-time characteristics of the production processes at the level of fm (10-15 m). Kaons are the perfect tool to study Bose-Einstein correlations due to the fact that they are less influenced by resonance decays and therefore probe more effectively directly produced particles. In conjunction with femtoscopic measurements of pions and protons, they can also reveal properties of collective dynamics in heavy-ion collisions. We report on the results of Bose-Einstein correlations of charged and neutral kaons in pp collisions at√s = 7 TeV and in Pb-Pb collisions at √sNN = 2.76 TeV by the ALICE experiment at the LHC. The results are compared with existing data from Bose-Einstein correlations of identical pions at LHC energies, and of kaons in pp collisions. A comparison of experimental data with theoretical expectations is also carried out.

Analysis of B0 → Ds−∗K+ decay

In this paper, we analyzed the decay [Formula: see text] within QCD factorization (QCDF) and final state interaction (FSI) methods. At first, we consider the QCDF approach, where the final states are a pseudoscalar meson and vector meson. Then, we consider the FSI method where the intermediate states are [Formula: see text] and [Formula: see text] via the exchange of [Formula: see text], [Formula: see text], [Formula: see text] and [Formula: see text] to improve the branching ratio. The above intermediate states are calculated by using the QCDF method. In the FSI effects, the results of our calculations depend on [Formula: see text] as the phenomenological parameter. The experimental branching ratio of this decay is [Formula: see text]. Our results in QCDF approach is [Formula: see text], and with [Formula: see text], the improved branching ratio is [Formula: see text].

Chiral nonet mixing inπKscattering

The underlying mixing of quark components of scalar mesons is probed in $\ensuremath{\pi}K$ scattering within a generalized linear sigma model that contains two scalar meson nonets and two pseudoscalar meson nonets (a quark-antiquark and a four-quark). In the leading order of this model, all free parameters have been previously fixed using the mass spectra and several low-energy parameters known from experiment and consistent predictions have been made. As in other predictions of the model, in the present work the isospins $I=1/2$, $3/2$ and $J=0$ projection of the $\ensuremath{\pi}K$ scattering amplitude (as well as phase shifts) are computed and compared with experiment. In the $I=1/2$ channel, it is shown that within the uncertainties of the model parameters a good agreement with experimental data up to an energy of about 1 GeV is obtained, whereas in the $I=3/2$ channel there is a better agreement with experiment which extends to about 1.4 GeV. The effect of final state interactions of $\ensuremath{\pi}K$ in the $I=1/2$ channel is approximated by the K-matrix method and the poles of the unitarized scattering amplitude are found. It is shown that the model predicts a light and broad kappa resonance with a mass and decay width of 670--770 MeV and 640--750 MeV consistent with other prior works. Moreover, the scattering lengths in the $I=1/2$, $3/2$ are also computed and shown to qualitatively agree with experiment. The overall predictions presented here further support previous findings that the scalar mesons below and above 1 GeV have substantial underlying mixings and that those below 1 GeV have dominant four-quark substructures while those above 1 GeV are closer to conventional $P$-wave quark-antiquark states.

Final state interaction effect in the pure annihilation B→ϕϕ decay

We analyzed the process of [Formula: see text] decay in quantum chromodynamics factorization (QCDF) and final state interaction (FSI). In QCDF for this decay we have only the annihilation graph and we expected small branching ratio. Then we considered FSI effect as a sizable correction where the intermediate states are [Formula: see text], K+ K–, and [Formula: see text] mesons. To consider the amplitudes of these intermediate states, the QCDF approach was used. The experimental branching ratio of [Formula: see text] is less than 2 × 10–7 and our results are 0.04 × 10–7 and 1.54 × 10–7 from QCDF and FSI, respectively.

Photoproduction of $ \pi^{0}$ -pairs off protons and off neutrons

Total cross sections, angular distributions, and invariant-mass distributions have been measured for the photoproduction of pairs off free protons and off nucleons bound in the deuteron. The experiments were performed at the MAMI accelerator facility in Mainz using the Glasgow photon tagging spectrometer and the Crystal Ball/TAPS detector. The accelerator delivered electron beams of 1508 and 1557MeV, which produced bremsstrahlung in thin radiator foils. The tagged photon beam covered energies up to 1400MeV. The data from the free proton target are in good agreement with previous measurements and were only used to test the analysis procedures. The results for differential cross sections (angular distributions and invariant-mass distributions) for free and quasi-free protons are almost identical in shape, but differ in absolute magnitude up to 15%. Thus, moderate final-state interaction effects are present. The data for quasi-free neutrons are similar to the proton data in the second resonance region (final-state invariant masses up to MeV), where both reactions are dominated by the decay. At higher energies, angular and invariant-mass distributions are different. A simple analysis of the shapes of the invariant-mass distributions in the third resonance region is consistent with strong contributions of an decay for the proton, while the reaction is dominated by a sequential decay via a intermediate state for the neutron. The data are compared to predictions from the Two-Pion-MAID model and the Bonn-Gatchina coupled-channel analysis.

Double pion photoproduction off Ca-40

The pbotoproduction of pi(0)pi(0) and pi(0)pi(+/-) pairs off Ca-40 has been investigated with the TAPS detector using the Glasgow photon tagging spectrometer at the Mainz MAMI accelerator. Data have been taken for incident photon energies in the energy range from 200-820MeV. Total cross-sections have been extracted from threshold up to the maximum photon energy and invariant-mass distributions of the pion pairs have been obtained for incident photon energies between 400-500 MeV and 500 550 MeV. The double pi(0) invari ant- mass distributions show some relative enhancement with respect to the mixed charge channel at small invariant masses. The effects are smaller than previously observed for lead nuclei and the distributions do not significantly deviate from carbon data. The data are in good agreement with the results of recent calculations in the framework of the BUU model, with careful treatment of final-state interaction effects but without an explicit in-medium modification of scalar, iso-scalar pion pairs. This means that for Ca most of the experimentally observed effect can be explained by final-state interactions. Only at low incident photon energies there is still a small low mass enhancement of the double pi(0) data over the BUU results.

Final state interactions at the threshold of Higgs boson pair production

We study the effect of final state interactions at the threshold of Higgs boson pair production in the Glashow–Weinberg–Salam model. We consider three major processes of the pair production in the model: lepton pair annihilation, ZZ fusion, and WW fusion. We find that the corrections caused by the effect for these processes are markedly different. According to our results, the effect can cause non-negligible corrections to the cross sections for lepton pair annihilation and small corrections for ZZ fusion, and this effect is negligible for WW fusion.

Nonleptonic decays of charmed mesons into two pseudoscalars

We examine the role of resonant coupled channel final state interactions (FSI), as well as weak annihilation and exchange contributions in explaining all the two body hadronic $D\rightarrow PP$ decay modes data. In the un-unitarized amplitudes we include modified Wilson coefficients with non-factorizable corrections as parameters. For the hadronic form factors, the z-series expansion method is used to get the $q^2$ dependence. The FSI effects are incorporated via a phenomenological approach with widths of resonances to various channels taken from observations where available, and others as additional parameters to be determined from fits of all the theoretical rates to the measured ones. Our results for the rather hard to explain $D^0\rightarrow K^+K^-, \pi^+\pi^- $ are in agreement with measured values. We demonstrate that both weak exchange as well as FSI effects are required to get the correct branching ratio for the $D^ \rightarrow K^0\bar{K^0}$ mode. Using our unitarized amplitudes we evaluate the strong phase difference between the amplitudes for $D^0\rightarrow K^-\pi^+$ and $D^0\rightarrow K^+\pi^-$ and find it to be in complete agreement with the recent BES III result.