Multiplicity dependence of the freezeout parameters in high energy hadron-hadron collisions

Abstract

We examined the transverse momentum ($p_T$) spectra of various identified particles, encompassing both light-flavored and strange hadrons, across different multiplicity classes in proton-proton collisions (p-p) at a center-of-mass energy of $\sqrt{s}$ = 7 TeV. Utilizing the Tsallis and Hagedorn models, parameters relevant to the bulk properties of nuclear matter were extracted. Both models exhibit good agreement with experimental data. In our analyses, we observed a consistent decrease in the effective temperature (T) for the Tsallis model and the kinetic or thermal freeze-out temperature ($T_0$) for the Hagedorn model, as we transition from higher multiplicity (class-I) to lower multiplicity (class-X). This trend is attributed to the diminished energy transfer in higher multiplicity classes. Additionally, the transverse flow velocity ($\beta_T$) experiences a decline from class-I to class-X. The normalization constant which represents the multiplicity of produced particles is observed to decrease as we move towards higher multiplicity classes. While the effective and kinetic freeze-out temperatures, as well as the transverse flow velocity, show a mild dependency on multiplicity for lighter particles, this relationship becomes more pronounced for heavier particles. The multiplicity parameter for heavier particles is noted to be smaller in comparison to lighter particles, indicating a greater abundance of lighter hadrons compared to the heavier ones. Various particle species are observed to undergo decoupling from the fireball at distinct temperatures: lighter particles exhibit lower temperatures, while heavier ones show higher temperatures, thereby supporting the concept of multiple freeze-out scenarios. Moreover, we identified a positive correlation between the kinetic freeze-out temperature and transverse flow velocity, a scenario where particles experience stronger collective motion at higher freeze-out temperature. The reason for this positive correlation is that as the multiplicity increases, more energy is transferred into the system. This heightened energy causes greater excitation and pressure within the system, leading to a quick expansion. Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. Article funded by SCOAP3 and published under licence by Chinese Physical Society and the Institute of High Energy Physics of the Chinese Academy of Science and the Institute of Modern Physics of the Chinese Academy of Sciences and IOP Publishing Ltd