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T. Mart

Publications and source records attributed to T. Mart.

At least 55 records · Page 3Linked to original sources
arXiv2008

Low-Density Instability of Multi-Component Matter with Trapped Neutrinos

The effect of neutrino trapping on the longitudinal dielectric function at low densities has been investigated by using different relativistic mean field models. Parameter sets G2 of Furnstahl-Serot-Tang and Z271 of Horowitz-Piekarewicz, along with the adjusted parameter sets of both models, have been used in this study. The role of the isovector adjustment and the effect of the Coulomb interaction have been also studied. The effect of the isovector adjustment is found to be more significant in the Horowitz-Piekarewicz model, not only in the neutrinoless matter, but also in the matter with neutrino trapping. Although almost independent to the variation of the leptonic fraction, the instability region of matter with neutrino trapping is found to be larger. The presence of more protons and electrons compared to the neutrinoless case is the reason behind this finding. For parameter sets with soft equation of states at low density, the appearance of a large and negative epsilon_L (q, q0 = 0) in some parts of the edge of the instability region in matter with neutrino trapping is understood as a consequence of the fact that the Coulomb interaction produced by electrons and protons interaction is larger than the repulsive isovector interaction created by the asymmetry between the proton and neutron numbers.

nucl-th↗
arXiv2008

Photo- and Electroproduction of the Hypertriton on 3He

Differential cross sections of the photo- and electroproduction of the hypertriton have been calculated by utilizing modern nuclear wave functions and the elementary operator of KAON-MAID. It is found that a proper treatment of Fermi motion is essential for the two processes. While the average momentum approximation can partly simulate the Fermi motion in the process, the ``frozen nucleon'' assumption yields very different results, especially at lower energies. The Coulomb effect induced by the interaction between the positively charged kaon and the hypertriton is found to be negligible. The influence of higher partial waves is also found to be relatively small, in contrast to the finding of the previous work. The off-shell assumption is found to be very sensitive in the case of electroproduction rather than in photoproduction. It is shown that the few available experimental data favor the assumption that the initial nucleon is off-shell and the final hyperon is on-shell. This seems to be reasonable, since the hyperon in the hypertriton is less bound than the nucleon in the initial 3He nucleus. The effect of the missing resonance D_{13}(1895) is more profound in the longitudinal cross sections. Excluding this resonance reduces the longitudinal cross sections by one order of magnitude, but does not change the effects of various off-shell assumptions on the cross sections.

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arXiv2008

Can we extract the pion electromagnetic form factor from a t-channel diagram only?

We show that we are able to extract the pion electromagnetic form factor by using the recent charged pion electroproduction data from JLab and a simple t-channel diagram. For this purpose we have performed the Q2-independent and dependent analyses. The result of the first analysis is in good agreement with those of previous works and fit the Maris and Tandy model as well as the monopole parameterization which describes a pion radius of 0.672 fm. The result of the second analysis corroborates the findings in the first analysis. Our findings therefore provide a direct proof that at the given kinematics the t-channel diagram really dominates the process. This could also set a new constraint to the phenomenological models that try to describe the process.

hep-ph↗
arXiv2008

Gerasimov-Drell-Hearn Sum Rule and the Discrepancy between the New CLAS and SAPHIR Data

Contribution of the K^+Λchannel to the Gerasimov-Drell-Hearn (GDH) sum rule has been calculated by using the models that fit the recent SAPHIR or CLAS differential cross section data. It is shown that the two data sets yield quite different contributions. Contribution of this channel to the forward spin polarizability of the proton has been also calculated. It is also shown that the inclusion of the recent CLAS C_x and C_z data in the fitting data base does not significantly change the result of the present calculation. Results of the fit, however, reveal the role of the S_{11}(1650), P_{11}(1710), P_{13}(1720), and P_{13}(1900) resonances for the description of the C_x and C_z data. A brief discussion on the importance of these resonances is given. Measurements of the polarized total cross section σ_{TT'} by the CLAS, LEPS, and MAMI collaborations are expected to verify this finding.

nucl-th↗
arXiv2007

Analysis of the consistency of kaon photoproduction data with Lambda in the final state

The recent CLAS 2005, SAPHIR 2003, LEPS, and the old, pre-1972, data on K^+ Lambda photoproduction are compared with theoretical calculations in the energy region of E_gamma^lab < 2.6 GeV in order to learn about their mutual consistency. The isobaric models Kaon-Maid and Saclay-Lyon, along with new fits to the CLAS data are utilized in this analysis. The SAPHIR 2003 data are shown to be coherently shifted down with respect to the CLAS, LEPS, and pre-1972 data, especially at forward kaon angles. The CLAS, LEPS, and pre-1972 data in the forward hemisphere can be described satisfactorily by using the isobaric model without hadronic form factors. The inclusion of the hadronic form factors yields a strong suppression of the cross sections at small kaon angles and c.m. energies larger than 1.9 GeV, which is not observed in the existing experimental data. We demonstrate that the discrepancy between the CLAS and SAPHIR data has a significant impact on the predicted values of the mass and width of the ``missing-resonance'' D_{13}(1895) in the Kaon-Maid model.

nucl-th↗
arXiv2007

Instabilities of relativistic mean field models and the role of nonlinear terms

The instability of nuclear matter due to particle-hole excitation modes has been studied in the frame-work of several relativistic mean field (RMF) models. It is found that both the longitudinal and the transversal modes depend sensitively on the parameter sets used. The important impact of the vector and vector-scalar nonlinear terms on the stability of both modes is demonstrated. Our finding corroborates the result of previous studies, namely that certain RMF models cannot be used in high density applications. However, we show that for certain parameter sets of RMF models this shortcoming can be alleviated by adding these nonlinear terms.

nucl-th↗
arXiv2007

From Pauli Principle to Hypernucleus, Neutron Star, and Econophysics

Proposed by Wolfgang Pauli more than 80 years ago, the exclusion principle has been proven to have a far-reaching consequence, from femtoscopic world to macroscopic, super-dense, and fully relativistic physics. Starting from this principle, we discuss two interesting research topics, which have currently drawn considerable attention in the nuclear- and astrophysics communities; the hypernuclear and neutron star physics. Special attention is given to the electromagnetic production of the hypertriton and the consequences of the neutrino electromagnetic properties in dense matter. We also touch on the new arena which could also be fascinating for physicists; the econophysics.

nucl-th↗
arXiv2007

Multipole approach for photo- and electroproduction of kaon

We have analyzed the experimental data on K+Lambda photoproduction by using a multipole approach. In this analysis we use the background amplitudes constructed from appropriate Feynman diagrams in a gauge-invariant and crossing-symmetric fashion. Results of our analysis reveal the problem of mutual consistency between the new SAPHIR and CLAS data. We found that the problem could lead to different conclusions on ``missing resonances''. We have also extended our analysis to the finite Q^2 region and compared the result with the corresponding electroproduction data.

nucl-th↗
arXiv2006

Kaon photoproduction in a multipole approach

The recently published experimental data on K+Lambda photoproduction by the SAPHIR, CLAS, and LEPS collaborations are analyzed by means of a multipole approach. For this purpose the background amplitudes are constructed from appropriate Feynman diagrams in a gauge-invariant and crossing-symmetric fashion. The results of our calculation emphasize the lack of mutual consistency between the SAPHIR and CLAS data previously found by several independent research groups, whereas the LEPS data are found to be more consistent with those of CLAS. The use of SAPHIR and CLAS data, individually or simultaneously, leads to quite different resonance parameters which, therefore, could lead to different conclusions on ``missing resonances''. Fitting to the SAPHIR and LEPS data simultaneously indicates that the S_{11}(1650), P_{13}(1720), D_{13}(1700), D_{13}(2080), F_{15}(1680), and F_{15}(2000) resonances are required, while fitting to the combination of CLAS and LEPS data leads alternatively to the P_{13}(1900), D_{13}(2080), D_{15}(1675), F_{15}(1680), and F_{17}(1990) resonances. Although yielding different results in most cases, both SAPHIR and CLAS data indicate that the second peak in the cross sections at W = 1900 MeV originates from the D_{13}(2080) resonance with a mass between 1911 - 1936 MeV. Furthermore, in contrast to the results of currently available models and the Table of Particle Properties, both data sets do not exhibit the need for a P_{11}(1710) resonance. The few data points available for target asymmetry can not be described by the models proposed in the present work.

nucl-th↗
arXiv2006

Low Densities Instability of Relativistic Mean Field Models

The effects of the symmetry energy softening of the relativistic mean field (RMF) models on the properties of matter with neutrino trapping are investigated. It is found that the effects are less significant than those in the case without neutrino trapping. The weak dependence of the equation of state on the symmetry energy is shown as the main reason of this finding. Using different RMF models the dynamical instabilities of uniform matters, with and without neutrino trapping, have been also studied. The interplay between the dominant contribution of the variation of matter composition and the role of effective masses of mesons and nucleons leads to higher critical densities for matter with neutrino trapping. Furthermore, the predicted critical density is insensitive to the number of trapped neutrinos as well as to the RMF model used in the investigation. It is also found that additional nonlinear terms in the Horowitz-Piekarewicz and Furnstahl-Serot-Tang models prevent another kind of instability, which occurs at relatively high densities. The reason is that the effective sigma meson mass in their models increases as a function of the matter density.

nucl-th↗
arXiv2006

Effects of the neutrino electromagnetic form factors on the neutrino and antineutrino mean free paths in dense matter

We have studied the effects of the nucleon weak magnetism and the neutrino electromagnetic properties on the neutrino and antineutrino mean free paths for all types of neutrinos. In the calculation, we consider matters with and without neutrino trapping as the target. We have found that the difference between the two mean free paths depends not only on the neutrino energy, but also on the matter density as well as matter constituents. Compared to the nucleon weak magnetism, the neutrino electromagnetic properties are found to have negligible effects on this difference.

nucl-th↗
arXiv2006

Neutron structure effects in the deuteron and one neutron halos

Although the neutron (n) does not carry a total electric charge, its charge and magnetization distributions represented in momentum space by the electromagnetic form factors, $F_1^{(n)} (q^2)$ and $F_2^{(n)} (q^2)$, lead to an electromagnetic potential of the neutron. Using this fact, we calculate the electromagnetic corrections to the binding energy, $B_d$, of the deuteron and a one neutron halo nucleus (11Be), by evaluating the neutron-proton and the neutron-charged core (10Be) potential, respectively. The correction to $B_d$ (~9 keV) is comparable to that arising due to the inclusion of the $Δ$-isobar component in the deuteron wave function. In the case of the more loosely bound halo nucleus, 11Be, the correction is close to about 2 keV.

nucl-th↗
arXiv2006

Differential cross section and photon beam asymmetry for the gamma n -> K+ Sigma- reaction at Egamma=1.5-2.4 GeV

Differential cross sections and photon beam asymmetries have been measured for the gamma n -> K+ Sigma- and gamma p -> K+ Sigma0 reactions separately using liquid deuterium and hydrogen targets with incident linearly polarized photon beams of Egamma=1.5-2.4 GeV at 0.6<cosTheta<1. The cross section ratio of sigma(K+Sigma-)/sigma(K+Sigma0), expected to be 2 on the basis of the isospin 1/2 exchange, is found to be close to 1. For the K+Sigma- reaction, large positive asymmetries are observed indicating the dominance of the K*-exchange. A large difference between the asymmetries for the K+Sigma- and K+Sigma0 reactions can not be explained by simple theoretical considerations.

hep-ex↗
arXiv2006

Polarization observables in exclusive kaon photoproduction on the deuteron

Single and double polarization observables for kaon photoproduction on the deuteron are studied theoretically with modern hyperon-nucleon forces. The kinematical region of the kaon scattered forward with large momentum is thoroughly investigated where either the quasifree scattering leading to the kaon and hyperon or the final-state interaction between hyperon and nucleon are expected. The quasifree scatterings show characteristic peaks in the inclusive cross sections. The final-state interaction effects are significant, especially around the Lambda-N and Sigma-N thresholds. The double polarization C_z is found to be sensitive to the final-state interaction effects. Precise data would help to clarify the property of the Lambda-N--Sigma-N interaction and also help to extract the information on the elementary amplitude from the quasifree scattering region.

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arXiv2006

K0 photoproduction on the deuteron and the extraction of the elementary amplitude

The photoproduction of K0 on the deuteron has been investigated with the inclusion of YN and KN final-state interaction (FSI), as well as the pion-mediated process gamma d --> pi NN --> KYN. The YN rescattering effects for the inclusive cross section are found to be large in the threshold regions. Polarization observables show sizable FSI effects at larger kaon and hyperon angles. It is shown that the extraction of the elementary gamma N --> KY amplitude is possible in the quasi-free scattering region where FSI effects are negligible. Furthermore, the cross sections in this region are large, indicating that measurements in this kinematical region are favored.

nucl-th↗
arXiv2006

High Impact but Less Popular

By using the SLAC-SPIRES database it is shown that, in spite of obtaining a high impact, Nature and Science are still less popular in the particle physics community.

physics.soc-ph↗
arXiv2006

Neutrino Electromagnetic Form Factors Effect on the Neutrino Cross Section in Dense Matter

The sensitivity of the differential cross section of the interaction between neutrino-electron with dense matter to the possibly nonzero neutrino electromagnetic properties has been investigated. Here, the relativistic mean field model inspired by effective field theory has been used to describe non strange dense matter, both with and without the neutrino trapping. We have found that the cross section becomes more sensitive to the constituent distribution of the matter, once electromagnetic properties of the neutrino are taken into account. The effects of electromagnetic properties of neutrino on the cross section become more significant for the neutrino magnetic moment mu_nu > 10^{-10} mu_B and for the neutrino charge radius R > 10^{-5} MeV^{-1}.

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