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Register a new userRelativistic diffusion model and analysis of large transverse momentum distributions
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In order to describe large transverse momentum ($p_T$) distributions observed in high energy nucleus-nucleus collisions, a stochastic model in the three dimensional rapidity space is introduced. The fundamental solution of the radial symmetric diffusion equation is Gaussian-like in radial rapidity. We can also derive a $p_T$ or radial rapidity distribution function, where a distribution of emission center is taken into account. It is applied to the analysis of observed large $p_T$ distributions of charged particles. It is shown that our model approaches to a power function of $p_T$ in the high transverse momentum limit.
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Large transverse momentum distributions of identified particles observed at RHIC are analyzed by a relativistic stochastic model in the three dimensional (non-Euclidean) rapidity space. A distribution function obtained from the model is Gaussian-like in radial rapidity. It can well describe observed transverse momentum $p_T$ distributions. Estimation of radial flow is made from the analysis of $p_T$ distributions for $bar{p}$ in Au + Au Collisions. Temperatures are estimated from observed large $p_T$ distributions under the assumption that the distribution function approaches to the Maxwell-Boltzmann distribution in the lower momentum limit. Power-law behavior of large $p_T$ distribution is also derived from the model.
To describe large momentum distributions of charged particles observed at RHIC, a diffusion equation in the three dimensional hyperbolic space is introduced.
We investigate the predictive power of transverse-momentum-dependent (TMD) distributions as a function of the light-cone momentum fraction $x$ and the hard scale $Q$ defined by the process. We apply the saddle point approximation to the unpolarized quark and gluon transverse momentum distributions and evaluate the position of the saddle point as a function of the kinematics. We determine quantitatively that the predictive power for an unpolarized transverse momentum distribution is maximal in the large-$Q$ and small-$x$ region. For cross sections the predictive power of the TMD factorization formalism is generally enhanced by considering the convolution of two distributions, and we explicitly consider the case of $Z$ and $H^0$ boson production. In the kinematic regions where the predictive power is not maximal, the distributions are sensitive to the non-perturbative hadron structure. Thus, these regions are critical for investigating hadron tomography in a three-dimensional momentum space.
We investigate the relations between transverse momentum dependent parton distributions (TMDs) and generalized parton distributions (GPDs) in a light-front quark-diquark model motivated by soft wall AdS/QCD. Many relations are found to have similar structure in different models. It is found that a relation between the Sivers function and the GPD $E_q$ can be obtained in this model in terms of a lensing function. The quark orbital angular momentum is calculated and the results are compared with the results in other similar models. Implications of the results are discussed. Relations among different TMDs in the model are also presented.
Transverse momentum spectra of protons and anti-protons from RHIC ($sqrt{s}$ = 62 and 200 GeV) and LHC experiments ($sqrt{s}$= 0.9 and 7 TeV) have been considered. The data are fitted in the low $p_T$ region with the universal formula that includes the value of exponent slope as a main parameter. It is seen that the slope of low-$p_T$ distributions is changing with energy. This effect impacts on the energy dependence of average transverse momenta, which behaves approximately as $s^{0.06}$ that is similar to the previously observed behavior for $Lambda^0$-baryon spectra. In addition, the available data on $Lambda_c$ production from LHCb at $sqrt{s}= 7$ TeV were also studied. The estimated average $<p_T>$ is bigger than this value for protons proportionally to masses. The preliminary dependence of hadron average transverse momenta on their masses at LHC energy is presented.
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