It is expected that the magnetic fields in heavy ion collisions are very high. In this work, we investigate the effects of a strong magnetic field on particle ratios within a thermal model of particle production. We model matter as a free gas of baryons and mesons under the influence of an external magnetic field varying from zero to through an？？ fitting to some data sets of the STAR experiment. For this purpose, we use the Dirac, Rarita-Schwinger, Klein-Gordon, and Proca equations subject to magnetic fields in order to obtain the energy expressions and the degeneracy for spin 1/2, spin 3/2, spin 0, and spin 1 particles, respectively. Our results show that, if the magnetic field can be considered as slowly varying and leaves its signature on the particle yields, a field of the order of produces an improved fitting to the experimental data as compared to the calculations without magnetic field. 1. Introduction According to quantum chromodynamics, the quark-gluon plasma (QGP) phase refers to matter where quarks and gluons are believed to be deconfined and it probably takes place at temperatures of the order of 150 to 170？MeV. In large colliders around the world (RHIC/BNL, ALICE/CERN, GSI, etc.), physicists are trying to find a QGP signature looking at heavy ion collisions and, in the last years, it has become evident that a strong magnetic field dependence is present in all experimental processes. Moreover, it has also been shown that the QCD phase diagram is modified by the presence of a magnetic field. Its effects have been calculated both within relativistic models [1, 2] and lattice simulations [3]. Possible experiments towards the search for the QGP are Au-Au collisions at RHIC/BNL and Pb-Pb collisions at SPS/CERN. The hadron abundances and particle ratios are normally used in order to determine the temperature and baryonic chemical potential of the possibly present hadronic matter-QGP phase transition and this calculation is done through thermal equilibrium models [4, 5] Particle ratios are convenient quantities to be analysed because after the chemical freezeout they remain practically unaltered. In previous papers, a statistical model under chemical equilibration was used to calculate particle yields [4, 5] and in these works the densities of particles were obtained from free Fermi and Boson gas approximations. To achieve a better description of the data, an excluded volume term was assigned to all particles with the aim of mimicking the repulsive interactions between hadrons at small distances. Also, after thermal production, resonances and
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