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M. Sajjad Athar

Publications and source records attributed to M. Sajjad Athar.

At least 91 records · Page 5Linked to original sources

Nuclear medium effects in structure functions of nucleon at moderate $Q^2$

Recent experiments performed on inclusive electron scattering from nuclear targets have measured the nucleon electromagnetic structure functions $F_1(x,Q^2)$, $F_2(x,Q^2)$ and $F_L(x,Q^2)$ in $^{12}C$, $^{27}Al$, $^{56}Fe$ and $^{64}Cu$ nuclei. The measurements have been done in the energy region of $1 GeV^2 < W^2 < 4 GeV^2$ and $Q^2$ region of $0.5 GeV^2 < Q^2 < 4.5 GeV^2$. We have calculated nuclear medium effects in these structure functions arising due to the Fermi motion, binding energy, nucleon correlations, mesonic contributions from pion and rho mesons and shadowing effects. The calculations are performed in a local density approximation using relativistic nucleon spectral function which include nucleon correlations. The numerical results are compared with the recent experimental data from JLab and also with some earlier experiments.

nucl-th↗

Electron and Muon production cross sections in quasielastic $ν(\barν)$-Nucleus scattering for $E_ν< 1~GeV$

In this work, we have studied (anti)neutrino induced charged current quasielastic scattering from some nuclear targets in the energy region of $E_ν< 1~GeV$. Our aim is to confront electron and muon production cross sections relevant for $ν_μ\leftrightarrow ν_e$ or $\barν_μ\leftrightarrow \barν_e$ oscillation experiments. The effects due to lepton mass and its kinematic implications, radiative corrections, second class currents and uncertainties in the axial and pseudoscalar form factors are calculated for (anti)neutrino induced reaction cross sections on free nucleon as well as the nucleons bound in a nucleus where nuclear medium effects influence the cross section. For the nuclear medium effects we have taken some versions of Fermi gas model(FGM) available in literature. The results for (anti)neutrino-nucleus scattering cross section per interacting nucleons are compared with the corresponding results in free nucleon case.

nucl-th↗

Weak charged and neutral current induced one pion production off the nucleon

We present a study of neutrino/antineutrino induced charged and neutral current single pion production off the nucleon. For this, we have considered $P_{33}(1232)$ resonance, non-resonant background terms, other higher resonances like $P_{11}(1440)$, $S_{11}(1535)$, $D_{13}(1520)$, $S_{11}(1650)$ and $P_{13}(1720)$. For the non-resonant background terms a microscopic approach based on SU(2) non-linear sigma model has been used. The vector form factors for the resonances are obtained by using the relationship between the electromagnetic resonance form factors and helicity amplitudes provided by MAID. Axial coupling $C_5^{A}(0)$ in the case of $P_{33}(1232)$ resonance is obtained by fitting the ANL and BNL $ν$-deuteron reanalyzed scattering data. The results are presented with and without deuteron effect for the total scattering cross sections for all possible channels viz. $ν_l(\barν_l)~+~N\rightarrow l^-(l^+)~+~N^\prime~+~π^i$; $ν_l(\barν_l)~+~N\rightarrow ν_l(\barν_l)~+~N^\prime~+~π^i$, where $N, N^\prime=p,n$, $π^i=~π^\pm$ or $π^0$ and $l=e, μ$.

hep-ph↗

Atmospheric neutrino flux calculation using the NRLMSISE00 atmospheric model

In this paper, we extend the calculation of the atmospheric neutrino flux~\cite{hkkm2004,hkkms2006,hkkm2011} to the sites in polar and tropical regions. In our earliest full 3D-calculation~\cite{hkkm2004}, we used DPMJET-III~\cite{dpm} for the hadronic interaction model above 5~GeV, and NUCRIN~\cite{nucrin} below 5~GeV. We modified DPMJET-III as in Ref.~\cite{hkkms2006} to reproduce the experimental muon spectra better, mainly using the data observed by BESS group~\cite{BESSTeVpHemu}. In a recent work~\cite{hkkm2011}, we introduced JAM interaction model for the low energy hadronic interactions. JAM is a nuclear interaction model developed with PHITS (Particle and Heavy-Ion Transport code System)~\cite{phits}. In Ref.~\cite{hkkm2011}, we could reproduce the observed muon flux at the low energies at balloon altitude with DPMJET-III above 32 GeV and JAM below that better than the combination of DPMJET-III above 5~GeV and NUCRIN below that. Besides the interaction model, we have also improved the calculation scheme according to the increase of available computational power, such as the "virtual detector correction" introduced in Ref.~\cite{hkkms2006} and the optimization of it in Ref.~\cite{hkkm2011}. The statistics of the Monte Carlo simulation is also improved at every step of the work.

astro-ph.HE↗

Weak Production of Strange Particles and $η$ Mesons off the Nucleon

The strange particle production induced by (anti)neutrino off nucleon has been studied for $|ΔS|=0$ and $|ΔS|=1$ channels. The reactions those we have considered are for the production of single kaon/antikaon, eta and associated particle production processes. We have developed a microscopical model based on the SU(3) chiral Lagrangian. The basic parameters of the model are $f_π$, the pion decay constant, Cabibbo angle, the proton and neutron magnetic moments and the axial vector coupling constants for the baryons octet. For antikaon production we have also included $Σ^*$(1385) resonance and for eta production $S_{11}$(1535) and $S_{11}$(1650) resonances are included.

hep-ph↗

Weak Quasielastic Production of Hyperons and Threshold Production of Two Pions

We have studied quasielastic charged current hyperon production induced by $\barν_μ$ on free nucleon and the nucleons bound inside the nucleus and the results are presented for several nuclear targets like $^{40}Ar$, $^{56}Fe$ and $^{208}Pb$. The hyperon-nucleon transition form factors are determined from neutrino-nucleon scattering and semileptonic decays of neutron and hyperons using SU(3) symmetry. The nuclear medium effects(NME) due to Fermi motion and final state interaction(FSI) effect due to hyperon-nucleon scattering have been taken into account. Also we have studied two pion production at threshold induced by neutrinos off nucleon targets. The contribution of nucleon, pion, and contact terms are calculated using Lagrangian given by nonlinear $σ$ model. The contribution of the Roper resonance has also been taken into account. The numerical results for the cross sections are presented and compared with the experimental results from ANL and BNL.

hep-ph↗

Nuclear medium effects in Drell-Yan process

We study nuclear medium effects in Drell-Yan processes at small target x using quark parton distribution functions and nucleon structure functions for a bound nucleon calculated in a microscopic nuclear model which takes into account the effect of Fermi motion, nuclear binding and nucleon correlations through a relativistic spectral function. The contributions of $π$ and $ρ$ mesons, target mass corrections and nuclear shadowing are also included. The results are compared with the theoretical and experimental results. The model is able to successfully explain the low target x results of E772 and E866 Drell-Yan experiments and is applicable to the forthcoming experimental analysis of E906 Sea Quest experiment at Fermi Lab.

nucl-th↗

EM vs Weak Structure Functions in DIS processes

We obatin the ratio $F_i^A/F_i^{D}$(i=2,3, A=Be, C, Fe, Pb; D=Deuteron) in the case of weak and electromagnetic nuclear structure functions. For this, relativistic nuclear spectral function which incorporate the effects of Fermi motion, binding and nucleon correlations is used. We also consider the pion and rho meson cloud contributions and shadowing and antishadowing effects.

nucl-th↗

Nuclear Dependence in Weak Structure Functions and the Determination of Weak Mixing Angle

We have studied nuclear medium effects in the weak structure functions $F^A_2(x)$ and $F^A_3(x)$ and in the extraction of weak mixing angle using Paschos Wolfenstein(PW) relation. We have modified the PW relation for nonisoscalar nuclear target. We have incorporated the medium effects like Pauli blocking, Fermi motion, nuclear binding energy, nucleon correlations, pion $\&$ rho cloud contributions, and shadowing and antishadowing effects.

nucl-th↗

Weak Strangeness and Eta Production

We have studied strange particle production off nucleons through $ΔS =0 $ and $|ΔS| = 1$ channels, and specifically single kaon/antikaon, eta, associated particle production for neutrino/antineutrino induced processes as well as antineutrino induced single hyperon production processes. We have developed a microscopical model based on the SU(3) chiral Lagrangians. The basic parameters of the model are $f_π$, the pion decay constant, Cabibbo angle, the proton and neutron magnetic moments and the axial vector coupling constants for the baryons octet. For antikaon production we have also included $Σ^*(1385)$ resonance and for eta production $S_{11}(1535)$ and $S_{11}(1650)$ resonances are included.

hep-ph↗

${\barν}_l$ induced pion production from nuclei at $\sim$1 GeV

We have studied charged current $\barν_l$ induced one pion production from $^{12}$C and $^{16}$O nuclear targets at MiniBooNE and atmospheric antineutrino energies. The calculations have been done for the incoherent pion production process as well as for the pions coming from the hyperons in the quasielastic production of $Λ$ and $Σ$. The calculations are done in the local density approximation. For the inelastic processes the calculations have been done in the $Δ$ dominance model and we take into account the effect of Pauli blocking, Fermi motion of the nucleon and renormalization of $Δ$ properties in the nuclear medium. The effect of final state interaction(FSI) of pions is also taken into account. For the hyperon production, the nuclear medium effects due to Fermi motion and FSI effects due to hyperon-nucleon scattering have been taken into account. These results may be quite useful in the analysis of SciBooNE, MicroBooNE, MINER$ν$A, and ArgoNeuT experiments when the pion analysis is done by using antineutrino beams.

nucl-th↗

Weak production of strange particles off the nucleon

The strange particle production off the nucleon induced by neutrinos and antineutrinos is investigated at low and intermediate energies. We develop a microscopic model based on the SU(3) chiral Lagrangian. The studied mechanisms are the main source of single kaon production for (anti)neutrino energies up to 1.5 GeV. Using this model we have also studied the associated production of kaons and hyperons. The cross sections are large enough to be measured by experiments such as MINER$ν$A, T2K and NO$ν$A.

hep-ph↗

A-dependence of weak nuclear structure functions

Effect of nuclear medium on the weak structure functions $F_2^A(x,Q^2)$ and $F_3^A(x,Q^2)$ have been studied using charged current (anti)neutrino deep inelastic scattering on various nuclear targets. Relativistic nuclear spectral function which incorporate Fermi motion, binding and nucleon correlations are used for the calculations. We also consider the pion and rho meson cloud contributions calculated from a microscopic model for meson-nucleus self-energies. Using these structure functions, $F_i^A/F_i^{proton}$ and $F_i^A/F_i^{deuteron}$(i=2,3, A=$^{12}C$, $^{16}O$, $CH$ and $H_{2}O$) are obtained.

nucl-th↗

Determination of $sin^{2}θ_W$ using $ν(\barν)$-Nucleus scattering

We have studied nonisoscalarity and medium effects in the extraction of weak mixing angle using Paschos and Wolfenstein relation in the iron nucleus. Paschos and Wolfenstein(PW) relation is valid for an isoscalar target. We have modified the PW relation for nonisoscalar target as well as incorporated the medium effects like Pauli blocking, Fermi motion, nuclear binding energy and pion rho cloud contributions. In our calculations we have used the relativistic nuclear spectral function which includes nucleon correlations. Finally local density approximation is applied to translate the numerical results to the finite nuclei. We have studied the dependence of $sin^{2}θ_W$ on Bjorken variables $x$ and $y$, four momentum transfer square ($Q^2$), energy of the neutrino and antineutrino, and effect of excess neutrons over protons in the nuclear target.

nucl-th↗

Weak $η$ production off the nucleon

The weak $η$-meson production off the nucleon induced by (anti)neutrinos is studied at low and intermediate energies, the range of interest for several ongoing and future neutrino experiments. We consider Born diagrams and the excitation of $N^\ast (1535)S_{11}$ and $N^\ast(1650)S_{11}$ resonances. The vector part of the N-$S_{11}$ transition form factors has been obtained from the MAID helicity amplitudes while the poorly known axial part is constrained with the help of the partial conservation of the axial current (PCAC) and assuming the pion-pole dominance of the pseudoscalar form factor.

hep-ph↗

Effects of nuclear medium and nonisoscalarity in extracting $sin^2θ_W$ using Paschos-Wolfenstein relation

We study the nuclear medium effects and nonisoscalarity correction in the extraction of weak mixing angle sin$^2θ_W$ using Paschos-Wolfenstein (PW) relation. The calculations are performed for the iron nucleus. The results are discussed along with the experimental result inferred by NuTeV collaboration. The nuclear medium effects like Fermi motion, binding, shadowing and antishadowing corrections and pion and rho meson cloud contributions have been taken into account. Calculations have been performed in the local density approximation using a relativistic nuclear spectral function which includes nucleon correlations. These studies may be useful for the ongoing MINER$ν$A experiment as well as for the proposed NuSOnG experiment.

nucl-th↗

Charged lepton induced one kaon production off the nucleon

We study single kaon production off the nucleon induced by electrons (positrons) i.e. $e^-(e^+) + N \rightarrow ν_e (\bar ν_e) + \bar K (K) + N^\prime$ at low energies. The possibility of observing these processes with the high luminosity beams available at TJNAF and Mainz is discussed, taking into account that the strangeness conserving electromagnetic reactions have a higher energy threshold for $\bar K (K)$ production. The calculations are done using a microscopic model that starts from the SU(3) chiral Lagrangians, includes background terms and the resonant mechanisms associated to the lowest lying resonance $Σ^*(1385)$.

hep-ph↗

Atmospheric neutrino flux at INO, South Pole and Pyhäsalmi

We present the calculation of the atmospheric neutrino fluxes for the neutrino experiments proposed at INO, South Pole and Pyhäsalmi. Neutrino fluxes have been obtained using ATMNC, a simulation code for cosmic ray in the atmosphere. Even using the same primary flux model and the interaction model, the calculated atmospheric neutrino fluxes are different for the different sites due to the geomagnetic field. The prediction of these fluxes in the present paper would be quite useful in the experimental analysis.

hep-ph↗