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Final state interactions are an important component of any neutrino-nucleus Monte Carlo program. GENIE has 2 FSI programs which serve different purposes. Each has fair-good agreement with a wide range of hadron-nucleus data. Recent improvements and planned advancements are described.
Final State Interactions effects are discussed in the context of Monte Carlo simulations of neutrino-nucleus interactions. A role of Formation Time is explained and several models describing this effect are compared. Various observables which are sensitive to FSI effects are reviewed including pion-nucleus interaction and hadron yields in backward hemisphere. NuWro Monte Carlo neutrino event generator is described and its ability to understand neutral current $\pi^0$ production data in $\sim 1$ GeV neutrino flux experiments is demonstrated.
In the factorized picture of semi-inclusive deep inelastic scattering the naive time reversal-odd parton distributions exist by virtue of the gauge link which is intrinsic to their definition. The link structure describes initial/final-state interactions of the active parton due to soft gluon exchanges with the target remnant. Though these interactions are non-perturbative, calculations of final-state interaction have been performed in a perturbative one-gluon approximation. Here, we include higher-order contributions by applying non-perturbative eikonal methods to calculate the Boer-Mulders function of the pion. Using this framework we explore under what conditions the Boer Mulders function can be described in terms of factorization of final state interactions and a spatial distortion.
Semi-inclusive deep inelastic scattering off the deuteron with production of a slow nucleon in recoil kinematics is studied in the virtual nucleon approximation, in which the final-state interaction (FSI) is calculated within generalized eikonal approximation. The cross section is derived in a factorized approach, with a factor describing the virtual photon interaction with the off-shell nucleon and a distorted spectral function accounting for the final-state interactions. One of the main goals of the study is to understand how much the general features of the diffractive high-energy soft rescattering accounts for the observed features of FSI in deep inelastic scattering (DIS). Comparison with the Jefferson Lab data shows good agreement in the covered range of kinematics. Most importantly, our calculation correctly reproduces the rise of the FSI in the forward direction of the slow nucleon production angle. By fitting our calculation to the data we extracted the W and Q{sup 2} dependencies of the total cross section and slope factor of the interaction of DIS products, X, off the spectator nucleon. This analysis shows the XN-scattering cross section rising with W and decreasing with an increase of Q{sup 2}. Finally, our analysis points at a largely suppressed off-shell part of the rescattering amplitude.
Final state interactions (FSI) are an important part of all neutrino event generators because modern detectors are made of nuclei to maximize count rate. The incident neutrino will interact with one (or two) nucleons but the final state can be quite different because the hadrons will have further interactions in the residual nucleus. This has historically been one of the major differences between event generators. GENIE will now have 2 FSI codes which allow interesting comparisons for the first time.
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The incoherent pion photoproduction reaction {gamma}d {yields} {pi}{sup -}pp is considered theoretically in a wide energy region E{sub th}{<=}E{sub {gamma}}{<=}2700 MeV. The model applied contains the impulse approximation as well as the NN and {pi}N final-state-interaction (FSI) amplitudes. The aim of the paper is to study a reliable way for getting the information on elementary {gamma}n {yields} {pi}{sup -}p reaction cross sections beyond the impulse approximation for {gamma}d {yields} {pi}{sup -}pp. For the elementary {gamma}N {yields} {pi}N, N N {yields} N N, and {pi}N {yields} {pi}N amplitudes, the results of The George Washington University (GW) Data Analysis Center (DAC) are used. There are no additional theoretical constraints. The calculated cross sections d{sigma} /d{Omega}({gamma}d {yields} {pi}{sup -}pp) are compared with existing data. The procedure used to extract information on the differential cross section d{sigma} /d{Omega}({gamma}n {yields} {pi}{sup -}p) on the neutron from the deuteron data using the FSI correction factor R is discussed. The calculations for R versus {pi}{sup -}p center-of-mass (CM) angle {theta}{sub 1} of the outgoing pion are performed at different photon-beam energies with kinematic cuts for a ''quasifree'' process {gamma}n {yields} {pi}{sup -}p. The results show a sizable FSI effect R{ne}1 from the S-wave part of pp-FSI at small angles close to {theta}{sub 1}{approx}0: this region narrows as the photon energy increases. At larger angles, the effect is small (|R - 1|<<1) and agrees with estimations of FSI in the Glauber approach.
We show that particle species dependence of enhanced hadron production at intermediate transverse momentum (p{sub T}) for d+Au collisions at RHIC can be understood in terms of the hadronization from string fragmentation and the subsequent hadronic rescatterings in the final state. A multiphase transport model (AMPT) with two different hadronization mechanisms, string fragmentation or parton coalescence, is used in our study. When the hadrons are formed from string fragmentation, the subsequent hadronic rescatterings will result in particle mass dependence of the nuclear modification factor R{sub CP}, which is consistent with the present experimental data. On the other hand, in the framework of parton coalescence, the mass dependence disappears and the strangeness plays an important role in hadron production.
Theoretical studies suggest that experimental observables for hyperon production reactions can place stringent constraints on the free parameters of hyperon-nucleon potentials, which are critical for the understanding of hypernuclear matter and neutron stars. Here we present preliminary experimental results for the polarization observables S, Py, Ox, Oz, Cx, and Cz for final-state interactions (FSI) in exclusive L photoproduction off the deuteron. The observables were obtained from data collected during the E06-103 (g13) experiment with the CEBAF Large Acceptance Spectrometer (CLAS) in Hall B at Jefferson Lab. The g13 experiment ran with unpolarized deuteron target and circularly- and linearly-polarized photon beams with energies between 0.5 GeV and 2.5 GeV and collected about 51010 events with multiple charged particles in the final state. To select the reaction of interest, the K+ and the L decay products, a proton and a negative pion, were detected in the CLAS. The missing-mass technique was used to identify exclusive hyperon photoproduction events. Final-state interaction events were selected by requesting that the reconstructed neutron has a momentum larger than 200 MeV/c. The large statistics of E06-103 provided statistically meaningful FSI event samples, which allow for the extraction of one- and two-fold differential single- and double-polarization observables. Here we present preliminary results for a set of six observables for photon energies between 0.9 GeV and 2.3 GeV and for several kinematic variables in the Ln center-of-mass frame. Our results are the very first estimates of polarization observables for FSI in hyperon photoproduction and will be used to constrain the free parameters of hyperon-nucleon potentials.
Precise knowledge of neutrino-nucleus interactions is increasingly important as neutrino oscillation measurements transition into the systematics-limited era. In addition to modifying the initial interaction, the nuclear medium can scatter and absorb the interaction by-products through final state interactions, changing the types and kinematic distributions of particles seen by the detector. Recent neutrino pion production data from MiniBooNE is inconsistent with the final state interaction strength predicted by models and theoretical calculations, and some models fit best to the MiniBooNE data only after removing final state interactions entirely. This thesis presents a measurement of dσ/dT π and dσ/dθ π for muon-neutrino charged current charged pion production in the MINER A scintillator tracker. MINER A is a neutrino-nucleus scattering experiment installed in the few-GeV NuMI beam line at Fermilab. The analysis is limited to neutrino energies between 1.5-10 GeV. Dependence on invariant hadronic mass W is studied through two versions of the analysis that impose the limits W < 1.4 GeV and W < 1.8 GeV. The lower limit on W increases compatibility with the MiniBooNE pion data. The shapes of the differential cross sections, which depend strongly on the nature of final state interactions, are compared to Monte Carlo and theoretical predictions. It is shown that the measurements presented in this thesis favor models that contain final state interactions. Additionally, a variety of neutrino-nucleus interaction models are shown to successfully reproduce the thesis measurements, while simultaneously failing to describe the shape of the MiniBooNE data.
We explore the role of final-state interactions (FSI) in inclusive deep-inelastic scattering from the deuteron. Relating the inclusive cross section to the deuteron forward virtual Compton scattering amplitude, a general formula for the FSI contribution is derived in the generalized eikonal approximation, utilizing the diffractive nature of the effective hadron-nucleon interaction. The calculation uses a factorized model with a basis of three resonances with mass W~<2 GeV and a continuum contribution for larger W as the relevant set of effective hadron states entering the final-state interaction amplitude. The results show sizeable on-shell FSI contributions for Bjorken x ~> 0.6 and Q 2 < 10 GeV 2 increasing in magnitude for lower Q 2 , but vanishing in the high-Q 2 limit due to phase space constraints. The off-shell rescattering contributes at x ~> 0.8 and is taken as an uncertainty on the on-shell result.
The non-vanishing of naive T-odd parton distributions function can be explained by the existence of the gauge link which emerges from the factorized description of the deep inelastic scattering cross section into perturbatively calculable and non-perturbative factors. This path ordered exponential describes initial / final-state interactions of the active parton due to soft gluon exchanges with the target remnants. Although these interactions are non-perturbative, studies of final state interactions have been approximated by perturbative one-gluon exchange in Abelian models. We include higher-order gluonic contributions from the gauge link by applying non-perturbative eikonal methods, incorporating color degrees of freedom in a calculation of the Sivers function. In this context we study the effects of color by considering the FSIs with with Abelian and non-Abelian gluon interactions. We confirm the large N{sub c} QCD scaling behavior of Sivers functions and further uncover the deviations for finite N{sub c}. Within this framework of FSIs we perform a quantitative check of approximate relations between T-odd TMDs and GPD which goes beyond the discussion of overall signs.
Jefferson Lab experiment E91-016 studied kaon electroproduction on hydrogen, deuterium and helium targets at a beam energy of 3.245 GeV and four-momentum transfer, Q 2 , ranging from 0.34 to 0.5 GeV 2 . Among a variety of other topics, part of this study was the investigation of the threshold region for signatures of final-state interaction between the electroproduced Λ-hyperon and spectator neutron. Compared to a purely quasi-free description, an excess yield was observed in the threshold region. This is compared to the predictions from three different hyperon-nucleon potentials. Though the data exhibit some sensitivity to the tested hyperon-nucleon potentials, further studies would require a more dedicated measurement with better resolution in the threshold region.
We consider the scattering of high energy leptons off bound atomic electrons focusing primarily on final state interactions between the outgoing energetic electron, and the heavy residual charged “debris” in the final state. These effects are inherently absent from calculations for a free electron at rest. Coulomb exchanges are enhanced by the large number of electrons in the atomic debris, and are unsuppressed by nonrelativistic velocities in the debris. We find that these exchanges can be resummed using operator methods, and cancel at the level of the cross section until at least 𝑂(𝛼 3 ). Furthermore, we argue that both final and initial state Coulomb exchanges (enhanced by the number of electrons in the atom) do not affect the cross section until at least 𝑂(𝛼 3 ). Transverse photon couplings to nonrelativistic electrons are proportional to their small velocities, and rotational invariance suppresses their contribution to 𝑂(𝛼 3 ). Our results are relevant for precision experiments involving neutrinos, electrons, positrons, and muons scattering off of atomic electrons in a fixed target.
Coincidence cross section measurements to determine p - p and p - t final state interactions in He-3/d, tp/p reaction
In this research the exclusive decay of B{sup 0} → J/ψπ{sup 0} is calculated by QCD factorization (QCDF) method and final-state interaction (FSI). First, the B{sup 0} → J/ψπ{sup 0} decay is calculated via QCDF method. The result that is found by using the QCDF method is less than the experimental result. So FSI is considered to solve the B{sup 0} → J/ψπ{sup 0} decay. For this decay, the D{sup +}D{sup −}* and D{sup 0}<##> } } D }¯<!-- ?? --> } 0 ∗<!-- ??? --> $ /bar D^{0*} $ D-bar {sup 0∗} </##> via the exchange of D{sup −}, D{sup −}* and <##> } } D }¯<!-- ?? --> 0 $ /bar D^0 $ D-bar {sup 0} </##>, <##> } } D }¯<!-- ?? --> } 0 ∗<!-- ??? --> $ /bar D^{0*} $ D-bar {sup 0∗} </##> mesons are chosen for the intermediate states. The above intermediate states are calculated by using the QCDF method. The experimental branching ratio of B{sup 0} → J/ψπ{sup 0} decay is (1.76 ± 0.16) × 10{sup −5} and our results calculated by QCDF and FSI are (0.56 ± 0.11) × 10{sup −5} and (1.3 ± 0.09) × 10{sup −5}, respectively.
A scattering formalism is developed in a multiple scattering model to describe inclusive momentum distributions for high-energy projectiles. The effects of final state interactions on response functions and momentum distributions are investigated. Calculations for high-energy protons that include shell model response functions are compared with experiments.