Z. G. Tan, 1, ∗ L. Y. Huang, 1 and C. B. Yang 2 $^{1}$Department of Electronics and Communication Engineering, Changsha University,Changsha, 410003,P.R.China $^{2}$Institute of Particle Physics, Hua-Zhong Normal University, Wuhan, 430079, China We treat the mass of a proton as the total static energy which can be separated into two parts that come from the contribution of quarks and gluons respectively. We adopt the essential of the bag model of hadron to discuss the structure of a proton and find that the calculated temperature, proton radius, the bag constant are compare well with QCD results if a proton is a thermal equilibrium system of quarks and gluons. PACS numbers: 12.39.Ba, 14.20.Dh Exploring proton structure [1–3] is still one of most important subjects for more profound enhancement of human knowledge on strong interactions. It is also very helpful for people to search for a new matter state–quark gluon plasma (QGP) which is the deconfined state of strongly interacting matter. Most theoretical investi- gations focus on Quantum Chromodynamics (QCD) [4]. However,there are a few phenomenological models about nucleon structure and interactions. The classical string model describes mesons as string segments executing lon- gitudinal expansion and contraction [5]. The bag model describes quarks being confined inside a hadron [6]. In high energy collisions, the string model represents the process of particle production in the fragmentation of a stretching string by creating pairs of quark and anti- quark. It worked well [7] for elementary collisions where strings can be formed among the few initial partons and break up to form the soft final state hadrons. However, in relativistic heavy ion collisions (RHIC), there are thou- sands initial partons. It is intractable to pair partons and have a string for each pair. Even if the strings are formed, they must be modified by the presence of many other color charges. The independent fragmentation ap- proach [7], though valid for high Q 2 partonic processes in the vacuum, cannot explain experimentally observed large p/π ratio in central Au + Au collisions at RHIC [8]. Another possible hadronization mechanism, the decon- fined quark (fled out from the bag) recombination model, has been able to reproduce spectra for almost all stable particles for different colliding systems. It provides a natural explanation for the baryon/meson ratio and the nuclear suppression factor observed at RHIC[9]. A natural mechanism for quark confinement is given by the bag model [6]. While the bag model has a few different versions, we shall in this paper keep the essen- tial characteristics of the phenomenology of quark con- finement. The gluons are mediate bosons which transfer where N$_{f}$ is the number of flavors and g$_{i}$ = N$_{c}$N$_{s}$ is the degeneracy number for a parton and equals to the product of quantum numbers of quark’s color and spin. f$_{i}$ is the distribution function which is of Fermi-Dirac for Let us first consider a thermally equilibrated quark- gluon plasma (QGP) system at first. When its temper- ature T and volume V are given, the total energy and particle number can be calculated: The organization of this paper is as follows. In Sec.II, we will discuss some features about a thermally equili- brated QGP system. Then in Sec.III, we get an estimate of the maximum kinetic energy of a confined quark in a spherical cavity of radius R . Combining the discussions in section II and III by assuming its origin from the con- tribution of gluons, the magnitude of the hadronic bag pressure is discussed in Sec.IV. The last section is for conclusions and discussions. the interactions between quarks . Their effect can be re- placed by the bag pressure which confines the quarks in a hadron. On the other hand, if all interactions among partons in the bag are neglected, we assume that the par- tons might be treated as a thermally equilibrated system with a given volume. Then properties of a hadron can be investigated and some characteristic parameters for the hadron can be obtained in the bag model. I. INTRODUCTION arXiv:1001.0891v3 [hep-ph] 9 Jan 2010 Some Characteristic Parameters of Proton from the Bag Model II. FREE EQUILIBRATED QGP E = N$_{f}$ ∑ i = − N$_{f}$ g$_{i}$ (2 π ¯ h ) 3 ∫ f$_{i}$ ( T ) p $^{0}$d Γ = N$_{f}$ ∑ i = − N$_{f}$ g$_{i}$V 2 π $^{2}$¯ h 3 ∫ f$_{i}$ ( T ) p $^{0}$| p | $^{2}$dp , (1) N = N$_{f}$ ∑ i = − N$_{f}$ g$_{i}$ (2 π ¯ h ) 3 ∫ f$_{i}$ ( T ) d Γ = N$_{f}$ ∑ i = − N$_{f}$ g$_{i}$V 2 π $^{2}$¯ h 3 ∫ f$_{i}$ ( T ) | p | $^{2}$dp , (2) ∗ tanzg@iopp.ccnu.edu.cn