Pion emission in 2H, 12C, 27Al, gamma pi+ reactions at threshold
P. Golubev, V. Avdeichikov, K. G. Fissum, B. Jakobsson, I. A. Pshenichnov, W. J. Briscoe, G. V. O'Rielly, J. Annand, K. Hansen, L. Isaksson, H. Jaederstrom, M. … 展开作者
P. Golubev, V. Avdeichikov, K. G. Fissum, B. Jakobsson, I. A. Pshenichnov, W. J. Briscoe, G. V. O'Rielly, J. Annand, K. Hansen, L. Isaksson, H. Jaederstrom, M. Karlsson, M. Lundin, B. Schroeder, L. Westerberg
The first data from MAX-lab in Lund, Sweden on pion production in photonuclear reactions at threshold energies, is presented. The decrease of the total yield of pi+ in gamma + 12C, 27Al reactions below 200 MeV as well as differential, dsigma/dOmega, cross sections follow essentially predictions from an intranuclear cascade model with an attractive potential for pion-nucleus interaction in its simplest form. Double differential, d2sigma/dOmegadT, cross sections at 176 MeV show, however, deviations from the model, which call for refinements of nuclear and Coulomb potentials and possibly also for coherent pion production mechanisms.
We propose to measure the two--photon capture mode of pionic hydrogen using the RMC pair spectrometer at the TRIUMF cyclotron. Currently, only an experimental upper limit of B.R.<= 5.5E-4 is available for the two-gamma capture mode. Our new data will critically test the theoretical calculations and the intriguing predicted dominance of the pi pi --> gamma gamma annihilation graph. More speculatively, since crossing symmetry relates pi pi --> gamma gamma to gamma pi --> gamma pi, this threshold reaction may be a novel probe of the pion's electric polarizability. We show results of our 1997 engi…
Recently, we have performed the experiment on studying the pion electroproduction at photon point on the internal polarized deuterium target at the VEPP-3 storage ring. For the more complete treatment of the reaction d(e,pp)X we investigate the reaction channel with an additional neutral pion production as background to the leading reaction of the single negative pion production. To study this background process we considered the nucleon pole mechanism and the two-body mechanism. In the latter mechanism a Delta(1232) and the pion are produced in one nucleon then the pion is absorbed by other n…
For the very first time, the correlation femtoscopy method is applied to a kinematically complete measurement of meson production in the collisions of hadrons. The shape of the two-proton correlation function derived for the pp -> ppeta reaction differs from that for the pp -> pp(pions) and both do not show a peak structure opposite to results determined for inclusive measurements of heavy ion collisions.
The pion production reaction $π^+ \to π^+π^{\pm}$ on $^{45}Sc$ was studied at incident pion energies of $T_{π^{+}}$ = 240, 260, 280, 300, and 320 MeV. The experiment was performed using the $M11$ pion-channel at TRIUMF, and multiparticle events, ($π^+,π^+π^{\pm}$) and ($π^+,π^+π^{\pm}p$), were detected with the CHAOS spectrometer. Results are reported in the form of both differential and total cross sections, and are compared to theoretical predictions and the reaction phase space. The present investigation of the T-dependence of the $π^+ A \to π^+π^{\pm} A'$ reaction complements earlier exami…
Differences in the photoproduction of mesons on the free proton and on nuclei are expected to reveal changes in the properties of hadrons. Inclusive studies of nuclear photoabsorption have provided evidence of medium modifications. However, the results have not been explained in a model independent way. A deeper understanding of the situation is anticipated from a detailed experimental study of meson photoproduction from nuclei in exclusive reactions. In the energy regime above the Delta(1232) resonance, the dominant double pion production channels are of particular interest. Double pion photo…
Results are presented of an analysis of proton and charged pion azimuthal distributions measured with respect to the reaction plane in Au + Au collisions at a beam momentum of about 11 AGeV/c. The azimuthal anisotropy is studied as a function of particle rapidity and transverse momentum for different centralities of the collisions. The triple differential (in rapidity, transverse momentum, and azimuthal angle) distributions are reconstructed. A comparison of the results with a previous analysis of charged particle and transverse energy flow as well as with model predictions is presented.
We develop an event mixing technique with a missing mass consistency (MMC) cut and a pion energy (PE) cut for the measurement of two-pion Bose-Einstein correlations (BEC) in reactions with only two identical pions produced in the final state. A multi mixing mode that allows one event to be mixed with multiple other events is proposed for the purpose of improving the statistics of mixed samples, and compared with the single mixing mode which requires one original event can be mixed only once. Numerical tests using the γp -> π^0 π^0 p events are used to testify its ability to measure two-pion co…
Differential cross sections of neutral pions emitted in 181Ta + 197Au collisions at a beam energy of 39.5A MeV have been measured with the photon spectrometer TAPS. The kinetic energy and transverse momentum spectra of neutral pions cannot be properly described in the framework of the thermal model, nor when the reabsorption of pions is accounted for in a phenomenological model. However, high energy and high momentum tails of the pion spectra can be well fitted through thermal distributions with unexpectedly soft temperature parameters below 10 MeV.
It has been observed that the yield of neutral pions at high transverse momentum (pT $>$ 5 GeV/c) region is strongly suppressed in central Au+Au collisions at Relativistic Heavy Ion Collider (RHIC), compared to the one expected in p+p collisions. This suppression may be due to an energy loss of hard scattered partons in the medium (jet quenching), that results in a decrease of the yield at a given pT. The magnitude of the suppression would depend on the path length of scattering partons in the medium, and therefore is associated with azimuthal angle from reaction plane in non-central collision…
The double differential cross sections for $^{nat}$In($^{28}$Si, $π^{\pm}$) reactions are measured at 400, 600, and 800 MeV/nucleon. Both $π^+$ and $π^-$ are found to be emitted isotropically from a single moving source. The $π^- / π^+$ yield ratio is determined as a function of the charged pion energy between 25 and 100 MeV. The experimental results significantly differ from the prediction of the standard transport model calculation using the code PHITS. This discrepancy suggests that more theoretical works are required to deduce firm information on the nuclear symmetry energy from the $π^- /…
A systematic experimental study of inclusive pion double charge exchange in 4He has been undertaken. The reaction 4He(pi+,pi-)4p was observed at incident energies 120, 150, 180, 240 and 270 MeV; the 4He(pi-,pi+)4n reaction was observed at incident energies 180 and 240 MeV. At each incident energy, the doubly differential cross section was measured at three to five outgoing pion laboratory angles between 25 deg and 130 deg. At each angle, cross sections were measured over the range of outgoing pion energies from 10 MeV up to the kinematic limit for the reaction in which the final state consists…
Measured values of the differential cross section for pion-nucleon charge exchange are presented at momenta 148, 174, 188, 212, 238, 271, 298, and 323 MeV/c, a region dominated by the Delta resonance. Complete angular distributions were obtained using the Crystal Ball detector at the Alternating Gradient Synchrotron (AGS) at Brookhaven National Laboratory (BNL). Statistical uncertainties of the differential cross sections are typically 2-6%, exceptions being the results at the lowest momentum and at the most forward measurements of the five lowest momenta. We estimate the systematic uncertaint…
The increase at low energy of the S-factor for the 16O(p,gamma)17F* reaction claimed by Morlock et al. to be a new observation is well documented and explained in the literature.
For the very first time, the correlation femtoscopy method is applied to a kinematically complete measurement of meson production in the collisions of hadrons. A two-proton correlation function was derived from the data for the pp -> ppX reaction, measured near the threshold of eta meson production. A technique developed for the purpose of this analysis permitted to establish the correlation function separately for the production of the pp+eta and of the pp+pions systems. The shape of the two-proton correlation function for the ppeta differs from that for the pp(pions) and both do not show a p…
The most important systematical errors in determination of level density and radiative strength functions for deformed nuclei have been estimated from the gamma-ray spectra in nuclear reactions like the stripping or pickup reactions.
Results on transverse mass spectra of neutral pions measured at central rapidity are presented for impact parameter selected 158$\cdot A$ GeV Pb + Pb, and Pb + Nb collisions. The distributions cover the range $0.5 \mathrm{GeV}/c^{2} \le m_{T} - m_{0} \le 4 \mathrm{GeV}/c^{2}$. The change of the spectral shape with centrality is studied in detail. In going from peripheral to medium central collisions there is a nuclear enhancement increasing with transverse mass similar to the well known Cronin effect, while for very central collisions this enhancement appears to be weaker than expected.
The cross sections of 70Ge(n,2n)69Ge, 72Ge(n,2n)71Ge, 76Ge(n,gamma)77(g+0.21m)Ge, 76Ge(n,2n)75Ge nuclear reactions were measured at the energy of neutrons 13.96(6) MeV by activation method with gamma-ray and X-ray spectra studies.
Photoactivation measurements on 144Sm have been performed with bremsstrahlung endpoint energies from 10.0 to 15.5 MeV at the bremsstrahlung facility of the superconducting electron accelerator ELBE of Forschungszentrum Dresden-Rossendorf. The measured activation yield for the 144Sm(gamma,n) reaction is compared with the calculated yield using cross sections from previous photoneutron experiments. The activation yields measured for all disintegration channels 144Sm(gamma,n), (gamma,p) and (gamma,alpha) are compared to the yield calculated by using Hauser-Feshbach statistical models. A new param…
The quantum properties are important to study nuclear structure. The energy, spin, parity, transition order are usually interesting to research. In this experiment, 59Ni is activated by thermal neutron on 3rd horizontal channel of Dalat nuclear Reactor.
(Shorten version of the PRC abstract) Alpha-induced reactions on 127I have been studied using the activation technique in order to provide cross section data for the modeling of the astrophysical gamma process. The relative intensity of the 536.1 keV gamma transition was measured precisely, its uncertainty was reduced from 13% to 4%. By measuring the yield of the characteristic X-rays, the cross sections of the 127I(alpha,gamma)131Cs reaction have been determined for the first time close to the astrophysically relevant energy region, at energies 9.50 < Ec.m. < 15.15$ MeV. The 127I(alpha,n)130C…
In a kinematically complete experiment at the Mainz microtron MAMI, pion angular distributions of the $^3$He(e,e'$π^+)^3$H reaction have been measured in the excitation region of the $Δ$ resonance to determine the longitudinal ($L$), transverse ($T$), and the $LT$ interference part of the differential cross section. The data are described only after introducing self-energy modifications of the pion and $Δ$-isobar propagators. Using Chiral Perturbation Theory (ChPT) to extrapolate the pion self energy as inferred from the measurement on the mass shell, we deduce a reduction of the $π^+$ mass of…
High-statistics differential cross sections for the reactions gamma p -> p eta and gamma p -> p eta-prime have been measured using the CLAS at Jefferson Lab for center-of-mass energies from near threshold up to 2.84 GeV. The eta-prime results are the most precise to date and provide the largest energy and angular coverage. The eta measurements extend the energy range of the world's large-angle results by approximately 300 MeV. These new data, in particular the eta-prime measurements, are likely to help constrain the analyses being performed to search for new baryon resonance states.
The 18F(p,a)15O reaction is recognized as one of the most important reaction for nova gamma-ray astronomy as it governs the early <= 511 keV emission. However, its rate remains largely uncertain at nova temperatures due to unknown low-energy resonance strengths. We report here on our last results concerning the study of the D(18F,pa)15N reaction, as well as on the determination of the 18F(p,a)15O reaction rate using the R-matrix theory. Remaining uncertainties are discussed.
We present a possibility of direct resonance production of pionic atoms (Coulomb bound states of a negative pion and a nucleus) with a rate of up to $\sim10^{10}$ per second using the gamma-ray beams from the Gamma Factory.
The remarkable observations in the pion induced and charge exchange reactions on a nucleus are the significant shift and broadening of the $Δ(1232)$-peak relative to free pion nucleon scattering. For the forward going massless leptons, the weak process $(ν_l,l)$ on a nucleon, according to Adler's partially conserved axial current theorem, is connected to the pion nucleon scattering. This mechanism is also applicable to the nucleus. Therefore, the modification of the $Δ$-peak in a nucleus can be seen in the $(ν_l,l)$ reaction since it is connected to the pion nucleus scattering. To investigate …
The paper discusses the features of the behavior of pion production cross section as a function of the atomic mass of the target nucleus for the reaction of fragmentation of the incident deuterons in the pions produced in the so-called "twice-cumulative" kinematic region. A distinctive feature of the twice-cumulative pions is that for their production the target nucleus must be heavier than hydrogen. The simulation results show that the dependence of the cross sections for pion production in the twice-cumulative region differs from the analogous dependence for the cumulative region. The paper …
The question whether there is a pion transparency in 500 MeV $C(π, π^{'})$ scatterings is studied using a semiclassical, hadronic transport model. The double differential cross sections of this reaction measured at LAMPF can be largely accounted for, if one uses energy-dependent, anisotropic angular distributions which are fitted to pion-nucleon scattering data for the decay of $Δ(1232)$ and $N^*(1440)$ resonances. The remaining discrepancy between the data and the calculation sets a limit on effects of more exotic processes.
We have applied the Giessen BUU (GiBUU) transport model to the description of the double charge exchange (DCX) reaction of pions with different nuclear targets at incident kinetic energies of 120-180 MeV . The DCX process is highly sensitive to details of the interactions of pions with the nuclear medium and, therefore, represents a major benchmark for any model of pion scattering off nuclei at low and intermediate energies. The impact of surface effects, such as the neutron skins of heavy nuclei, is investigated. The dependence of the total cross section on the nuclear mass number is also dis…
Photon-induced reactions during the astrophysical p- (or gamma-) process occur at typical temperatures of 1.8 < T9 < 3.3. Experimental data of (gamma,n), (gamma,p), or (gamma,alpha) reactions - if available in the relevant energy region - cannot be used directly to measure astrophysical (gamma,n), (gamma,p), or (gamma,alpha) reaction rates because of the thermal excitation of target nuclei at these high temperatures. Usually, statistical model calculations are used to predict photon-induced reaction rates. The relations between experimental reaction cross sections, theoretical predictions, and…
The $ρ^0-ω$ interference has been studied in the dilepton invariant mass distribution spectra in the photonuclear reaction, but that is not done for the gamma-nucleon reaction. Recent past, the $e^+e^-$ invariant mass distribution spectrum in the $γp$ reaction, i.e., $γp \to pe^+e^-$ reaction, was measured at Jefferson Laboratory to look for the $ρ^0 -ω$ interference in the multi-GeV region. To study the mechanism of this reaction, the differential cross section of the $e^+e^-$ invariant mass distribution is calculated in the quoted energy region. The reaction is assumed to proceed as $γp \to …
"Subthreshold pions" and so-called "hard photons" are two important channels for producing less than 1 GeV $γ$-rays and $e^\pm$ pairs from nuclear collisions with energy per nucleon below the $π$-meson production threshold. I use publicly available experimental data to parametrize these two channels' $γ$-ray and $e^\pm$ production cross sections and extend the pion contribution to these particles spectra at higher energies using their corresponding spectra from $pp$ interactions. These parametrizations are valid for collision energy $T_p\leq 100$ A GeV and agree reasonably well with the availa…
Pion Virtual Compton Scattering (VCS) via the reaction pi e --> pi e gamma was observed in the Fermilab E781 SELEX experiment. SELEX used a 600 GeV/c pi- beam incident on target atomic electrons, detecting the incident pi- and the final state pi-, electron and gamma. Theoretical predictions based on chiral perturbation theory are incorporated into a Monte Carlo simulation of the experiment and are compared to the data. The number of reconstructed events (9) and their distribution with respect to the kinematic variables (for the kinematic region studied) are in reasonable accord with the predic…
The $f_{1}(1420)$ productions via pion and kaon induced reactions on a proton target are investigated in an effective Lagrangian approach. Two treatments of the $t$-channel Born term, the Feynman model and the Regge model, are introduced to calculate the total and differential cross sections of the $π^{-}p\rightarrow f_{1}(1420)n$ and $K^{-}p\rightarrow f_{1}(1420)Λ$ reactions. The numerical results indicate that the experimental data of the total cross section of the $π^{-}p\rightarrow f_{1}(1420)n$ reaction can be reproduced in both the Feynman and the Regge models. Based on the parameters d…
We present an overview of our efforts to analyze pion-nucleon elastic scattering data, along with data from related photo- and electroproduction reactions, in order to study the baryon spectrum. We then focus on the Delta(1232) resonance. Fits to pion photo- and electroproduction data have been used to extract values for the R_EM = E2/M1 and R_SM = S2/M1 ratios as functions of Q^2. These results are compared to other recent determinations.
The nucleosynthesis of heavy neutron-deficient nuclei in a stellar photon bath at the temperatures relevant for the astrophysical gamma process was investigated. In order to derive (gamma,n) cross sections and reaction rates, the stellar photon bath was simulated by the superposition of several bremsstrahlung spectra with different endpoint energies. As a first test for this method, the (gamma,n) reaction rates of the platinum isotopes 190Pt, 192Pt, and 198Pt were derived. The results are compared to other experimental data and theoretical calculations.
We have investigated the 6Li(gamma, d) reaction theoretically for the formation of the eta'(958) mesic nucleus. We have reported the numerical results in this article.
Tetraneutron ($^4n$) has come back in the limelight, because of recent observation of a candidate resonant state at RIBF. We propose to investigate the pion double charge exchange (DCX) reaction, i.e. $^4\mathrm{He}(π^- , π^+)$, as an alternative way to populate tetraneutron. An intense $π^-$ beam with the kinetic energy of ~850 MeV, much higher than that in past experiments at LAMPF and TRIUMF, will open up a possibility to improve the experimental sensitivity of the formation cross section, which will be much smaller than hitherto known DCX cross sections such as $^9\mathrm{Be}(π^-, π^+)^9\m…
The 6.1, 6.9 and 7.1 MeV photon yields in the reaction with protons in the 1.32 to 1.42 MeV energy range were determined from the comparison between experimental and simulated spectrum. The gamma-ray spectra were measured with a HPGe detector which was 72.5 mm in diameter and 60.5 mm in length. The reaction kinematics and the detector response function were simulated by different programs using the Monte Carlo method. The relative photon yields were obtained from the least-squares fit of the experimental gamma-ray spectra to the convolution of the detector response function with the photon ene…
The value of the pion polarizability is predicted with high precision by Chiral Perturbation Theory. However, the existing experimental values are at tension with this prediction as well as among themselves. The COMPASS experiment at the CERN SPS accesses pion-photon reactions via the Primakoff effect, where high-energetic pions react with the quasi-real photon field surrounding the target nuclei. Flagship channel is the Primakoff reaction in which a single real photon is produced, giving access to pion Compton scattering. Using this process the pion polarizability is extracted from the measur…
We demonstrate that the Dubna-Mainz-Taipei (DMT) meson-exchange dynamical model, which starts from an effective chiral Lagrangian, for pion photoproduction provides an excellent and economic framework to describe both the pi^0 threshold production and the Delta deformation, two features dictated by chiral dynamics.
Based on a Relativistic Boltzmann-Uehling- Uhlenbeck transport model, proton and $^{3}$He induced reactions on $^{197}$Au target at beam energies of 2.8, 5, 10 and 16.587 GeV/nucleon are studied. It is found that compared with proton induced reactions, $^{3}$He induced reactions give larger cross sections of pion production, about 5 times those of the proton induced reactions. And more importantly, pion production from $^{3}$He induced reaction is more inclined to low-angle emission. Neutrino production via positively charged pion is also discussed accordingly.
A resonance model for two-pion production in the pion-nucleon reaction is developed that includes information obtained in the analysis of pion-nucleon scattering in a meson-exchange model. The baryonic resonances Delta(1232), N*(1440), N*(1520), N*(1535), and N*(1650) are included. The model reproduces the total cross sections up to kinetic energies of the incident pion of 350 MeV and obtains the shapes of the differential cross sections in reasonable agreement with the data.
We investigate decay and production of neutral pions in strong magnetic fields. In the presence of strong magnetic fields, transition between a neutral pion and a virtual photon becomes possible through the triangle diagram relevant for the chiral anomaly. We find that the decay mode of a neutral pion into two photons cannot persist in the dominant mode in strong magnetic fields, and that decay into a dilepton instead dominates over the other modes. We also investigate the effects of magnetic fields on prompt virtual photons created in ultrarelativistic heavy-ion collisions. There is no anisot…
The 14C(alpha,gamma) reaction rate at temperatures below 0.3 GK depends on the properties of two near threshold resonances in 18O, the 1- at 6.198 MeV and the 3- at 6.404 MeV. The alpha+14C Asymptotic Normalization Coefficients (ANCs) for these resonances were determined using the alpha-transfer reactions 14C(7Li,t) and 14C(6Li,d) at sub-Coulomb energies. The 14C(alpha,gamma) reaction rate at low temperatures has been evaluated. Implications of the new reaction rate on the evolution of accreting helium white dwarfs and on the nucleosynthesis of low mass stars during the asymptotic giant branch…
In standard potential-model descriptions of the Be7(p,gamma)B8 reaction the Be7+p spectroscopic factors S appear in the cross section. We argue that the microscopic substructure effects which are represented by S are short-ranged and cannot affect the asymptotic normalization of the wave function. We believe that the standard way of describing reactions in a potential model may be incorrect and the low-energy cross section should not depend on S in the case of external capture reactions, like Be7(p,gamma)B8
DWIA calculations of Lambda-hypernuclear production rates in stopped K- reactions on several p-shell targets used recently in experiments by the FINUDA Collaboration are reported. Chirally motivated K- + N -> pion + Lambda in-medium transition amplitudes are employed and the sensitivity of the calculated rates to the initial K- atomic wavefunctions and final pion distorted waves is studied. The calculated rates are compared with measured rates, wherever available, confirming earlier observations that (i) the calculated rates are generally lower than the measured rates, and (ii) the deeper the …
[Background] A quantitative understanding of neutrino interactions with nuclei is needed for precision era neutrino long baseline experiments (MINOS, NOvA, DUNE) which all use nuclear targets. Pion production is the dominant reaction channel at the energies of these experiments. [Purpose] Investigate the influence of nuclear effects on neutrino-induced pion production cross sections and compare predictions for pion-production with available data. [Method] The Giessen Boltzmann--Uehling--Uhlenbeck (GiBUU) model is used for the description of all incohrent channels in neutrino-nucleus reactions.…
We investigate the reaction $π^- p \to π^- J/ψp$ via the open-charm hadron rescattering diagrams. Due to the presence of the triangle singularity (TS) in the rescattering amplitudes, the TS peaks can simulate the pentaquark-like resonances arising in the $J/ψp$ invariant mass distributions, which may bring ambiguities on our understanding of the nature of the exotic states. Searching for the heavy pentaquark in different processes may help us to clarify the ambiguities, because of the highly process-dependent characteristic of the TS mechanism.
Nucleosynthesis processes involve reactions on several thousand nuclei, both close to and far off stability. The preparation of reaction rates to be used in astrophysical investigations requires experimental and theoretical input. In this context, two interesting aspects are discussed: (i) the relevant gamma transition energies in astrophysical capture reactions, and (ii) the newly discovered Coulomb suppression of the stellar enhancement factor. The latter makes a number of reactions with negative Q value more favorable for experimental investigation than their inverse reactions, contrary to …
The He3(He4,gamma)Be7 and H3(He4,gamma)Li7 reactions are studied in an extended two-cluster model which contains alpha+h/t and Li6+p/n clusterizations. We show that the inclusion of the Li6+p/n channels can significantly change the zero-energy reaction cross sections, S(0), and other properties of the Be7 and Li7 nuclei, like the quadrupole moments Q. However, the results agree with the known correlation trend between S(0) and Q. Moreover, we demonstrate that the value of the zero-energy derivatives of the astrophysical S-factors are more uncertain than currently believed.
We study the strangeness and charm productions induced by the pion beam, i.e. the $π^-$p $\rightarrow$ $K^{*0}Λ$ and $π^-$p $\rightarrow$ $D^{*-}Λ_c^+$ reactions, based on two different theoretical frameworks: an effective Lagrangian method and a Regge approach. In order to estimate the magnitude of the charm production relative to that of the strangeness production, we assume that the coupling constants for the charmed meson and baryon vertices are the same as those for the strangeness channel. We found that the total cross section for the charm production was about $10^3 - 10^6$ times smalle…
In this talk, we report the study of $π^- p \to K^{*0} Λ$ and $π^- p \to D^{*-} Λ_c^+$ reactions by using an effective Lagrangian method and a hybrid Regge model. The total and differential cross sections for the $K^{*0} Λ$ production are first calculated and then those for the $D^{*-} Λ_c^+$ one are estimated. The two models yield different results, each exhibiting specific features. Our prediction for the charm production provides valuable information about the upcoming J-PARC experiment.
Light, beyond-the-standard-model particles $X$ in the 1-100 MeV mass range can be produced in nuclear and hadronic reactions but would have to decay electromagnetically. We show that simple and well-understood low-energy hadronic processes can be used as a tool to study $X$ production and decay. In particular, the pion capture process $π^- p \to X n \to e^+ e^- n$ can be used in a new experimental setup to search for anomalies in the angular distribution of the electron-positron pair, which could signal the appearance of dark photons, axion-like particles and other exotic states. This process …
We investigate neutrino induced one pion production on nucleons. The elementary neutrino--nucleon cross section is calculated as the sum of the leading Delta pole diagram and several background diagrams obtained within the non-linear sigma model. This approach does not introduce any new adjustable parameters, which allows unambiguous predictions for the observables. Considering electroproduction experiments as benchmark, the model is shown to be applicable up to pion-nucleon invariant mass $W<1.4\GeV$ and provides a good accuracy. With respect to the total one pion cross section, the model pre…
We solve a radial Schrödinger equation for the case of a multichannel square well plus an exponential potential in one of the channels. The solution is obtained by summing exactly the infinite terms of the perturbative series for the evolution operator of the system. Analytical expressions for the scattering matrix and the scattering length are given, a Deser-like formula which connects approximate ground energies and scattering length is obtained for a particular case. Possible physical applications of these results are discussed briefly.
We estimate the valence quark contributions for the gamma* Y -> Lambda* (Y=Lambda, Sigma0) electromagnetic transition form factors. We focus particularly on the case Lambda*=Lambda(1670) as an analog reaction with gamma* N -> N(1535). The results are compared with those obtained from chiral unitary model, where the Lambda* resonance is dynamically generated and thus the electromagnetic structure comes directly from the meson cloud excitation of the baryon ground states. The form factors for the case Y=Sigma0 in particular, depend crucially on the two real phase (sign) combination, a phase betw…
