QCD Collisional Energy Loss in an Increasingly Interacting Quark Gluon Plasma

The discovery of the jet quenching in central Au + Au collisions at the Relativistic Heavy-ion Collider (RHIC) at Brookhaven National Laboratory has provided clear evidence for the formation of strongly interacting dense matter. It has been predicted to occur due to the energy loss of high energy partons that propagate through the quark gluon plasma. In this paper we investigate the dependence of the parton energy loss due to elastic scatterings in a parton plasma on the value of the strong coupling and its running with the evolution of the system. We analyze different prescriptions for the QCD coupling and calculate the energy and length dependence of the fractional energy loss. Moreover, the partonic quenching factor for light and heavy quarks is estimated. We found that the predicted enhancement of the heavy to light hadrons ($D/\pi$) ratio is strongly dependent on the running of the QCD coupling constant.Comment: 16 pages, 8 figures. Version to be published in the International Journal of Modern Physics

Additional J/ΨJ/\Psi Suppression from High Density Effects

At high energies the saturation effects associated to the high parton density should modify the behavior of the observables in proton-nucleus and nucleus-nucleus scattering. In this paper we investigate the saturation effects in the nuclear $J/\Psi$ production and estimate the modifications in the energy dependence of the cross section as well as in the length of the nuclear medium. In particular, we calculate the ratio of $J/\Psi$ to Drell-Yan cross sections and show that it is strongly modified if the high density effects are included. Moreover, our results are compared with the data from the NA50 Collaboration and predictions for the RHIC and LHC kinematic regions are presented. We predict an additional $J/\Psi$ suppression associated to the high density effects.Comment: 13 pages, 5 figures, version to be published in Eur. Phys. J.

Efeito da interrupção da inundação da cultura do arroz na população do gorgulho-aquático e produção de grãos.

bitstream/item/31532/1/comunicado-230.pd

Elastic Energy Loss in an Expanding QGP

The discovery of the jet quenching in central Au + Au collisions at the Relativistic Heavy-ion Collider (RHIC) has provided clear evidence for the formation of strongly interacting dense matter. It has been predicted to occur due to the energy loss of high energy partons that propagate through the quark gluon plasma. Since the medium is not static and it cools while expands, the strong coupling is not fixed, running with the evolution of the system. In this work, we present an investigation of the dependence on the value of the strong coupling in the parton energy loss due to elastic scatterings in a parton plasma. We analyze different prescriptions for the QCD coupling and calculate the energy and length dependence of the fractional energy loss. Moreover, the quenching factor for light and heavy quarks is estimated. We found that the predicted enhancement of heavy to light hadrons (D/π) ratio is strongly dependent on the running of the QCD coupling constant. Keywords: Quark Gluon Plasma; Elastic energy loss; Running coupling constant In the last years, the understanding of the partonic energy loss has been extensively developed. It was provocated by the expectation of the Quark Gluon Plasma (QGP) formation in the early stages of the collision. The discovery of jet quenching in central Au+Au collisions at RHIC has provided evidences for the formation of this strongly interacting dense matter. Basically, high parton density produced in heavy ion collisions could induce a large amount of energy loss for hard partons produced in the initial stage of the collision during its propagation through the fireball, due to their interactions with the medium. The total energy loss of a particle in a medium can be decomposed into an elastic and a radiative contribution. At large energies one expects that radiative energy loss becomes much larger than the collisional one, as in the electromagnetic case. However, since at lower energies the elastic and radiative processes can contribute equally, for small values of the parton energy the collisional one can dominate. So, an open question is to quantify the contribution of each process in the RHIC kinematical region. Recent studies of elastic mechanism contributions to energy loss Besides, we have to consider that the medium properties and interactions change with time (For a discussion of the medium evolution see, e.g. Refs

D meson production in d+Au process using a perturbative approach

The D meson production at forward rapidities in d+Au processes is calculated using a pQCD based model, assuming that this treatment could be used as a baseline for distinct dynamical and medium effects. It is analysed how the nuclear effects in the nuclear partonic distributions may affect this process at RHIC and LHC energies. An enhancement in the moderate qT region for RHIC, due to anti-shadowing in the nuclear medium, is found. Our prediction for LHC suggests that shadowing will suppress the D meson spectra for qT < 14 GeV

Effect of Sciatic Nerve Transection on acetylcholinesterase activity in spinal cord and skeletal muscles of the bullfrog Lithobates catesbeianus

<div><p>Abstract Sciatic nerve transection (SNT), a model for studying neuropathic pain, mimics the clinical symptoms of “phantom limb”, a pain condition that arises in humans after amputation or transverse spinal lesions. In some vertebrate tissues, this condition decreases acetylcholinesterase (AChE) activity, the enzyme responsible for fast hydrolysis of released acetylcholine in cholinergic synapses. In spinal cord of frog Rana pipiens, this enzyme’s activity was not significantly changed in the first days following ventral root transection, another model for studying neuropathic pain. An answerable question is whether SNT decreases AChE activity in spinal cord of frog Lithobates catesbeianus, a species that has been used as a model for studying SNT-induced neuropathic pain. Since each animal model has been created with a specific methodology, and the findings tend to vary widely with slight changes in the method used to induce pain, our study assessed AChE activity 3 and 10 days after complete SNT in lumbosacral spinal cord of adult male bullfrog Lithobates catesbeianus. Because there are time scale differences of motor endplate maturation in rat skeletal muscles, our study also measured the AChE activity in bullfrog tibial posticus (a postural muscle) and gastrocnemius (a typical skeletal muscle that is frequently used to study the motor system) muscles. AChE activity did not show significant changes 3 and 10 days following SNT in spinal cord. Also, no significant change occurred in AChE activity in tibial posticus and gastrocnemius muscles at day 3. However, a significant decrease was found at day 10, with reductions of 18% and 20% in tibial posticus and gastrocnemius, respectively. At present we cannot explain this change in AChE activity. While temporally different, the direction of the change was similar to that described for rats. This similarity indicates that bullfrog is a valid model for investigating AChE activity following SNT.</p></div