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Nimai C. Mukhopadhyay

Publications and source records attributed to Nimai C. Mukhopadhyay.

At least 19 recordsLinked to original sources
arXiv1998

Weak Form Factors of the Nucleon

We limit ourselves basically to the SU(2) flavor sector of the CKM matrix, as probed in processes like nuclear $β$-decay, normal and radiative muon capture and neutrino reactions. Current interests in this primarily stem from our aspirations to interpret the weak form factors of the nucleon in the framework of QCD. Given a standard set of known form factors, we can look also in these processes for possible physics signals beyond the standard model.

nucl-th↗
arXiv1998

Problems with Extraction of the Nucleon to Delta(1232) Photonic Amplitudes

We investigate the model dependence and the importance of choice of database in extracting the {\it physical} nucleon-Delta(1232) electromagnetic transition amplitudes, of interest to QCD and baryon structure, from the pion photoproduction observables. The model dependence is found to be much smaller than the range of values obtained when different datasets are fitted. In addition, some inconsistencies in the current database are discovered, and their affect on the extracted transition amplitudes is discussed.

nucl-th↗
arXiv1998

Extraction of Electrostrong Parameters of $N^{*}(1520)$ from Eta Photoproduction

Recently obtained polarized target and photon asymmetry data in eta photoproduction are shown to be very powerful, in conjunction with the differential cross-section data, in yielding model-insensitive constraints on the electrostrong parameters for the excitation and decay of the $N^{*}(1520)$ resonance. The extracted ratio of its electromagnetic helicity amplitudes, $A_{3/2}/A_{1/2}$, provides a critical test for the QCD-inspired hadron models.

nucl-th↗
arXiv1998

Parity-Violating $Δ$(1232) Electroweak Production: Axial Structure and New Physics

We consider prospects for studying the parity-violating electroweak excitation of the $Δ(1232) $ resonance with polarized electron scattering (see nucl-th/9801025). We discuss the experimental feasibility and theoretical interpretability of such a measurement as well as the prospective implications for hadron structure theory. We also analyze the extent to which a PV $N\toΔ$ measurement could constrain various extensions of the Standard Model.

nucl-th↗
arXiv1998

Approach to Perturbative Results in the N-Delta Transition

We show that constraints from perturbative QCD calculations play a role in the nucleon to Delta(1232) electromagnetic transition even at moderate momentum transfer scales. The pQCD constraints, tied to real photoproduction data and unseparated resonance response functions, lead to explicit forms for the helicity amplitudes wherein the E2/M1 ratio remains small at moderately large momentum transfer.

hep-ph↗
arXiv1998

Inclusive Muon Capture in Light Nuclei

We study total muon capture rates in light nuclei, taking into account renormalizations of the nuclear vector and axial vector strengths. We estimate the influence in the results of uncertainties of the spin-isospin interaction parameter and nuclear densities. A few of these reactions are theoretical benchmarks for physics involving searches for neutrino oscillations. New experiments in muon capture in several targets are suggested, in the light of some discrepancies with theory, crudeness of some experimental results and relevance to neutrino physics.

nucl-th↗
arXiv1998

Inclusive Neutrino Scattering in C-12: Implications for nu_mu to nu_e Oscillations

We study inclusive nu_e and nu_mu cross sections in C-12 in a theory that takes into account significant nuclear renormalization of strengths. Our calculation is in excellent agreement with the measured inclusive muon capture rate and the flux-averaged nu_e cross section, but overestimates the flux-averaged nu_mu inclusive cross section. These reactions are of crucial relevance to the issue of possible nu_mu to nu_e oscillations.We also calculate the flux-averaged cross sections in C-13 and Al-27, which are found to be consistent with the available experimental result.

nucl-th↗
arXiv1998

Perturbative Duality in the Resonance Spin Structure Functions

We investigate the relations between the spin structure functions in the scaling and resonance regions. We examine the possible duality between the two, and draw inferences for the behavior of the asymmetry A_1 at large x. Finally, we point out the importance of additional polarized structure function data in the resonance region in terms of testing the hysteresis of perturbative physics.

hep-ph↗
arXiv1996

Theory of Eta Photo- and Electroproduction

We analyze the available data on eta photo- and electroproduction, around W~1535 MeV, in the framework of the effective Lagrangian approach, and extract, in a nearly model-independent fashion, the electrostrong amplitude for the gamma+N--> N*(1535)--> N+eta processes. Quark model approaches are shown to be quite inadequate to explain this property at all Q^2. In particular, at high Q^2, the extracted amplitude falls much slower than the predictions of the quark model, as a function of Q^2, a situation similar to the electroexcitation and decay of Delta(1232). A QCD explanation of these observations is urgently needed.

nucl-th↗
arXiv1996

A Precise Determination of the Pion-Nuclear Coupling Parameter from Weak Processes in ^3He

We utilize precise weak interaction experiments on atomic muon capture and beta decay in the A = 3 nuclei, and take into account the effects of nuclear "anomalous thresholds" to extract the pseudoscalar pi-^3He-^3H coupling parameter, G^{eff}(m_π^2) = 45.8+- 2.4. This is an order of magnitude improvement in precision over that from the use of pion-nuclear scattering data and dispersion relations.

nucl-th↗
arXiv1996

Model-Independent Extraction of the N*(1535) Electrostrong Form Factor from Eta Electroproduction

We analyze the existing data on electroproduction of eta mesons in the region of W~1.5GeV, and extract an electrostrong form factor for the N*(1535) electroexcitation and decay into the eta-N channel, which is found to be relatively insensitive to the uncertainties of the effective Lagrangian approach. this extracted quantity is of interest in the QCD description of relevant baryons.

nucl-th↗
arXiv1995

Photoproduction of Etas and N$^*$(1535) Electrostrong Properties

From the new Mainz data of eta photoproduction off protons\cite{ref1} and deuterons\cite{ref2}, we can extract, via the effective Lagrangian approach (ELA)\cite{ref3}, the electrostrong parameters $ξ_{p}$ and $ξ_{n}$ for the N$^*$(1535) excitation. These parameters are, in units of $10^{-4} MeV^{-1}$, $(2.20\pm 0.15)$ and $(-1.86\pm 0.20)$ respectively. They yield the ratio of the helicity amplitudes for the excitation of N$^*$(1535) by photons off neutrons and protons to be $A^{n}_{1/2}/A^{p}_{1/2}=-0.84\pm 0.15$, a quantity of fundamental importance in the baryon structure. Best estimates in the quark model are close to this ratio.

nucl-th↗
arXiv1995

Extraction of the Ratio of the N^*(1535) Electromagnetic Helicity Amplitudes from Eta Photoproduction off Neutrons and Protons

Using the recent precise measurements of eta photopro- duction in proton and deuteron targets, we extract the ratio of the helicity amplitudes A^n_1/2 / A^p_1/2, for the excitation of N^*(1535), in the effective Lagrangian approach, It is fairly model-independent, free from the final-state interaction effects, and negative as predicted by the quark models. We stress the importance of polarization observables in further elucidation of the N^*(1520) photoexcitation amplitudes.

hep-ph↗
arXiv1995

Photoproduction of the Etas near Threshold

We extract a parameter $ξ$, a characteristic product of the strong and electromagnetic amplitudes for the N^*(1535), to be (2.20+-0.15) in unit of 10^(-4)MeV^(-1) from the new data on photoproduction of etas off proton.

hep-ph↗