Abstract
Recent experimental results in proton-proton and in proton-nucleus collisions at Large Hadron Collider energies show a strong similarity to those observed in nucleus-nucleus collisions, where the formation of a quark-gluon plasma is expected. We discuss the comparison between small colliding systems and nucleus-nucleus collisions, for: a)~the strangeness suppression factor $\gamma_s$ and yields of multi-strange hadrons; b)~the average transverse momentum, $p_t$, with particular attention to the low $p_t$ region where soft, non-perturbative effects are important; c)~the elliptic flow scaled by the participant eccentricity. The universal behavior in hadronic and nuclear high energy collisions emerges for all these observables in terms of a specific dynamical variable which corresponds to the entropy density of initial system in the collision and which takes into account the transverse size of the initial configuration and its fluctuations.
Highlights
Recent experimental results in proton-proton and proton-nucleus collisions at the Large Hadron Collider (LHC) and Relativistic Heavy Ion Collider (RHIC) show a strong similarity to those observed in nucleus-nucleus (AA) collisions, where the formation of a quark-gluon plasma is expected
Recent experimental results in proton-proton and in proton-nucleus collisions at Large Hadron Collider energies show a strong similarity to those observed in nucleus-nucleus collisions, where the formation of a quark-gluon plasma is expected
The universal behavior in hadronic and nuclear high energy collisions emerges for all these observables in terms of a specific dynamical variable which corresponds to the entropy density of initial system in the collision and which takes into account the transverse size of the initial configuration and its fluctuations
Summary
Recent experimental results in proton-proton (pp) and proton-nucleus (pA) collisions at the Large Hadron Collider (LHC) and Relativistic Heavy Ion Collider (RHIC) show a strong similarity to those observed in nucleus-nucleus (AA) collisions, where the formation of a quark-gluon plasma is expected. [11,12] by considering a specific dynamical variable corresponding to the initial entropy density of the collisions, which takes into account the transverse size (and its fluctuations) of the initial configuration in high multiplicity events [13,14]. [17,18,19], where the scaling of pt as a function of the variable Ntrack/AT (Ntrack being the multiplicity and AT the transverse area of the initial system) was explored in the framework of color glass condensate (CGC), where the geometrical scaling of direct-photon production in hadron collisions at RHIC and LHC energies has been obtained in terms of the saturation scale, proportional to the transverse entropy density [20]. Density driven mechanism for the particle production across different colliding systems
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