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A. Upadhyay

Publications and source records attributed to A. Upadhyay.

30 records · Page 2Linked to original sources
arXiv2013

Strange and nonstrange sea quark-gluon effects in nucleons

Probabilities of various Fock states with strange and nonstrange quark-gluon sea contents are calculated to probe the hadronic structure. Particularly for nucleon, we find various contributions to the low energy properties from scalar, vector and tensor sea in addition to three valence quarks. We focus on the importance of individual sea contributions to the low energy parameters of nucleon by taking the strange and non strange quark-gluon content to the hadron sea. We confirm that the extended Fock space wavefunction is capable of explaining the experimental results where vector sea plays a crucial role in studying hadronic structure while scalar and tensor sea appears to be less dominating due to quark-spin flip process but cannot be neglected. Some of the properties like spin distribution and gA/gV ratio seem to be the most affected by the change in the statistically determined coefficients. Detailed analysis includes different approximations within the statistical approach to test the validity of the model chosen. Phenomenological implication of such sea affecting these properties is also discussed and the results are compared with the experiments.

hep-ph↗
arXiv2013

Sea Quark and Gluon contributions to Strange Baryons and their Properties

We treat the hadrons as an ensemble of quark-gluon Fock states where contributions from sea-quarks and gluons can be studied in detail for the properties of low lying baryons. Statistical model is applied to calculate individual probabilities from various scalar, vector and tensor sea components in flavor, spin and color subspaces for each quark-gluon Fock state. The mass of strange quark is imposed in terms of constraints to the availability of strange quarks in the sea and free energy of gluons in conformity with experimental indications. We calculate multiplicities for different sets of Fock states to compute the role of strange sea for cascade doublet Ξ+, and Ξ-.The low energy properties like magnetic moment, weak decay matrix elements and axial coupling constant ratios have been studied. The incorporation of strange quark gluon sea is discussed and they found to affect the results by almost 46% . The results provide deeper understanding for baryon structure thereby motivating experiments for further inspection, especially the spin distribution among the quarks and gluons.

hep-ph↗
arXiv2013

Detailed Balance and Spin Content of Λ using Statistical Model

In this study, we assume the hadrons as an ensemble of quark-gluon Fock states and apply statistical effects to explain the spin distribution of quarks for lambda hyperon. We extend the principle of detailed balance given by Zhang et al. [9] to calculate the probability of every Fock state in lambda. Using these probabilities, we have calculated quark distribution of spin, hyperon weak decay constant, SU(3) reduced matrix elements and their ratio and magnetic moment etc. using the statistical model proposed in ref.[17]. The extension of statistical model comes here with inclusion of more sub processes like etc. Finally the matching of our results with other models like chiral quark soliton model has also been analyzed.

hep-ph↗
arXiv2012

Importance of Sea Contribution to Nucleons

We studied the statistical model of nucleons consisting of sea having various quark-gluon Fock states in addition to valence quarks. Using statistical consideration and taking 86% of the total Fock states contributing to the low energy properties of nucleon, we aim to find the contributions to these properties coming from the scalar, vector and tensor sea. We checked its validity against the assumption where the contributions from scalar and tensor sea have been suppressed and justified to be unimportant. We took the approximation that sea is getting a zero contribution from H_0 G_\bar10 and H_1 G_\bar10 in three gluon states. Under above considerations, the calculated magnetic moment, spin distribution and weak decay coupling constant ratio for proton and neutron states have been tabulated. We hereby confirm that the suppression of the scalar and tensor sea leads to modification in the parameters of the nucleons showing deviation from the experimental data.

hep-ph↗
arXiv2012

Natural noise and external wake field seeding in a proton-driven plasma accelerator

We discuss the level of natural shot noise in a proton bunch-driven plasma accelerator. The required seeding for the plasma wake field must be larger than the cumulative shot noise. This is the necessary condition for the axial symmetry of the generated wake and the acceleration quality. We develop an analytical theory of the noise field and compare it with multi-dimensional simulations. It appears that the natural noise wake field generated in plasma by the available at CERN super-protons-synchrotron (SPS) bunches is very low, at the level of a few 10 kV/m. This fortunate fact eases the requirements on the seed. Our three dimensional simulations show that even a few tens MeV electron bunch precursor of a very moderate intensity is sufficient to seed the proton bunch self-modulation in plasma.

physics.plasm-ph↗
arXiv2011

Phenomenology of neutrino mixing in vacuum and matter

Neutrino oscillation is the new physics beyond standard model. In this paper we have revisited the issue of neutrino oscillation in simple and delicate manner. Starting from the fundamental quantum mechanical treatment for the neutrinos, we calculated the probabilities for the neutrino oscillating within three flavors. Normal and inverted hierarchy have been taken into account for the solar and atmospheric cases, in vacuum and matter. The probabilities have been plotted for all the cases and discussed.

hep-ph↗
arXiv2011

Heavy quark effective theory for charmed mesons

Within the framework of heavy quark effective theory and chiral perturbation theory, masses and splittings of heavy charm mesons are studied. A mass formula is used for comprehensive analysis of low lying charm meson states.The variation of mass splittings and spin splittings with respect to various symmetry conserving and symmetry breaking parameters have also been focussed.

hep-ph↗
arXiv2011

Scalar and Tensor Sea Contributions to Nucleons

Statistical approach for proton and neutron have been used to study the low energy properties of nucleons. Nucleons is assumed as a composite system of three quarks and "sea" where sea is assumed to be in S-wave consisting of quark-antiquark pairs (u]\bar{u},d\bar{d} only) and gluons. Here the contributions from scalar, vector and tensor sea is taken into consideration to find α and β. Distribution of spin among valence quarks and sea-quark for proton and neutron are denoted by I_1^pand I_1^n respectively. Statistical model predicted the values as 0.132 and -0.011 which is close to EMC experimental value 0.136 and -0.013 for I_1^p and I_1^n respectively. Although the statistical model predictions give close to EMC data for neutron spin distribution. The results have also been compared with the Simple quark model results that matches well with SU(6) model..

hep-ph↗
arXiv2011

Phase velocity and particle injection in a self-modulated proton-driven plasma wakefield accelerator

It is demonstrated that the performance of the self-modulated proton driver plasma wakefield accelerator (SM-PDPWA) is strongly affected by the reduced phase velocity of the plasma wave. Using analytical theory and particle-in-cell simulations, we show that the reduction is largest during the linear stage of self-modulation. As the instability nonlinearly saturates, the phase velocity approaches that of the driver. The deleterious effects of the wake's dynamics on the maximum energy gain of accelerated electrons can be avoided using side-injections of electrons, or by controlling the wake's phase velocity by smooth plasma density gradients.

physics.plasm-ph↗
arXiv2007

Puzzles of excited charm meson masses

We attempt a comprehensive analysis of the low lying charm meson states which present several puzzles, including the poor determination of masses of several non-strange excited mesons. We use the well-determined masses of the ground states and the strange first excited states to `predict' the mass of the non-strange first excited state in the framework of heavy hadron chiral perturbation theory, an approach that is complementary to the well-known analysis of Mehen and Springer. This approach points to values for the masses of these states that are smaller than the experimental determinations. We provide a critical assessment of these mass measurements and point out the need for new experimental information.

hep-ph↗
arXiv2005

The derivative of the topological susceptibility at zero momentum and an estimate of $η'$ mass in the chiral limit

The anomaly-anomaly correlator is studied using QCD sum rules. Using the matrix elements of anomaly between vacuum and pseudoscalars $π, eta$ and $η'$, the derivative of correlator $chi'(0)$ is evaluated and found to be $\approx 1.82 \times 10^{-3}$ GeV$^2$. Assuming that $χ'(0)$ has no significant dependence on quark masses, the mass of $η'$ in the chiral limit is found to be $\approx$723 MeV. The same calculation also yields for the singlet pseudoscalar decay constant in the chiral limit a value of $\approx 178$ MeV.

hep-ph↗