# Hadron formation and resonance decays

Fluid to hadron conversion in heavy-ion models

Best fit hadron spectra comparison with ALICE data

How the colour-neutral particles are produced from the quark-gluon plasma, which is a deconfined state of matter with manifest QCD colour degrees of freedom, is a poorly understood fundamental physics problem. The current approach, called the Cooper-Frye procedure, converts the fluid fields like temperature and velocity directly to a distribution of hadron resonances gas. Remarkably, the measured particle yields are in very good agreement with thermal par- ticle production at chemical freeze-out temperature of $T_\text{chem} \approx 156\, \text{MeV}/k_B$ even for a weakly bounded hyper-nuclei.

Most of the produced hadron resonances are short lived and decay to more stable particles before detection. Therefore comparison to momentum resolved experimental data requires numerically costly calculations of resonance decays. We developed a novel way of directly calculating the observed particle spectra by pre-calculating the final spectra in the fluid rest-frame. Such fast and efficient technique allowed use to easily include the important effect of resonance decays in a routine experimental analysis procedure of blast-wave fit. In addition, we integrated the fast resonance calculation in a hydrodynamic heavy-ion model and performed a detailed analysis of identified particle spectra at LHC (see figure). We found that there are statistically significant deviations from experimental measured spectra in the low momentum pion spectra, which cannot be rectified even within the range of model parameters and even a larger set of primary resonances.

##### Aleksas Mazeliauskas
###### Theoretical Physicist

I am a theoretical physicist working on many-body phenomena emerging from fundamental interactions of elementary particles.