119303742
Strange and non-strange sea quark–gluon effects in nucleons
Abstract Within a statistical approach, strange and non-strange quark–gluon Fock state contributions are analyzed for their low energy properties. A suitable wave function is written for a nucleon that consists of three valence quarks ( qqq ) and the sea ( g , q q ¯ ). Expansion of the nucleonic system in terms of Fock states that contain ( g , q q ¯ ) is assumed and the probabilities of all possible Fock states, that lead to such a wave-function containing strange and non-strange quark–gluon contents in the sea are determined. Various approximations are entertained to validate the authenticity of the model used. The statistically determined coefficients strongly favor a vector-dominated sea where the sea includes s s ¯ pairs. Additionally, the sea is constrained to have a limited number of components. The phenomenological implications that affect the low energy properties are discussed. The obtained results are compared to existing theoretical models and experimental data.
118632691
SOME ASPECTS OF LOW ENERGY PROPERTIES OF NUCLEONS
We conclude that nucleon is a many body complex system whose low-energy behaviour is determined mainly by strong interaction. Non-perturbative approach to QCD, such as QCD sum rule and the QCD based effective theory, and the models such as a statistical model, have a complementary role in exposing different aspects of nucleonic properties.
117767760
Charge symmetry breaking in pion-nucleon coupling constant : QCD sum rule approach
Using the vacuum-to-pion matrix element of the correlation function of the interpolating fields of the two nucleons, the isospin splitting in the diagonal pion-nucleon coupling constant has been studied in the framework of the conventional QCD sum rule. Some of the implications of this splitting has also been discussed.
118473195
Importance of sea contribution to nucleons
Abstract 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 10 ¯ and H 1 G 10 ¯ in three gluon states. Under the 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.
119998491
Isospin breaking in diagonal pion–nucleon coupling constant: QCD sum rule approach
Using the vacuum-to-pion matrix element of the correlation function of the interpolating fields of two nucleons, isospin splitting in the diagonal pion–nucleon coupling constant has been studied in the framework of the conventional QCD sum rule. The quark mass dependent terms, π0–η mixing and electromagnetic corrections to meson–quark vertices have been included as well. Some of the implications of the isospin splitting have also been discussed.
118257407
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 {\alpha} and {\beta}. 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..
54773207
Optimization of Nonlinear Wakefield Amplitude in Laser Plasma Interaction
Nonlinear, large amplitude, plasma waves are excited in the wake of an intense laser pulse propagating in a cold plasma, providing acceleration gradients ~ GeV/m. Linear analytic theory has shown that the wakefield amplitude is optimal for a certain ratio of the pulse length and plasma wavelength [1,2]. Here we present simulation studies to optimize the wake amplitude. The wake amplitude of a Gaussian pulse profile is maximized with respect to the laser pulse length. Using two dimensional simulations, it is seen that for a Gaussian pulse profile, the optimal pulse length derived from linear theory is also close to optimal (higher charge, smaller energy spread) for the generation of a quasi-monoenergetic electron beam in the bubble regime of laser plasma interaction. We also show, by varying the spot-size but keeping the intensity constant, that the magnitude of the trapped charge is a function primarily of the ratio P/Pc.
15233182
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 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.
145031396
SIMULATION OF ELECTRON ACCELERATION BY TWO LASER PULSES PROPAGATING IN A HOMOGENOUS PLASMA
We study electron acceleration by two laser pulses copropagating one behind the other in a homogeneous plasma. We show, using one-dimensional simulations, that the wake amplitude can be amplified or diminished depending on the time delay between the two lasers, in agreement with linear analytic theory [1]. We extend the study to the bubble regime using two-dimensional simulations. We find that the one-dimensional optimization holds in two dimensions also. Trapping and acceleration of quasi-monoenergetic electrons (up to around 300 MeV) is found in the bucket behind the second laser, even for low intensities, where there is no trapping with a single laser. Thus, this scheme could be very useful for achieving a desired accelerated energy with less intense lasers, or, equivalently, increasing the accelerated energy for a given laser intensity.