Abstract
In this letter we report the first multi-differential measurement of correlated pion-proton pairs from 2 billion Au+Au collisions at sNN=2.42 GeV collected with HADES. In this energy regime the population of Δ(1232) resonances plays an important role in the way energy is distributed between intrinsic excitation energy and kinetic energy of the hadrons in the fireball. The triple differential d3N/dMπ±pdpTdy distributions of correlated π±p pairs have been determined by subtracting the πp combinatorial background using an iterative method. The invariant-mass distributions in the Δ(1232) mass region show strong deviations from a Breit-Wigner function with vacuum width and mass. The yield of correlated pion-proton pairs exhibits a complex isospin, rapidity and transverse-momentum dependence. In the invariant mass range 1.1<Minv(GeV/c2)<1.4, the yield is found to be similar for π+p and π−p pairs, and to follow a power law 〈Apart〉α, where 〈Apart〉 is the mean number of participating nucleons. The exponent α depends strongly on the pair transverse momentum (pT) while its pT-integrated and charge-averaged value is α=1.5±0.08st±0.2sy.
Highlights
Understanding the structure and bulk properties of hot and dense QCD matter created in heavy-ion collisions is one of the most complex challenges in modern physics
We present the Minv − pair transverse momentum (pT)− rapidity ( y) distributions of correlated π−p and π+p pairs, in particular their pT-dependent line-shape parameters, multiplicity per event as a function of event centrality as well as inverse slope parameters as a function of rapidity
Efficiency and acceptance corrected mass distributions of correlated π±p pairs are shown in Fig. 2 for four centrality classes within the HADES rapidity coverage
Summary
Understanding the structure and bulk properties of hot and dense QCD matter created in heavy-ion collisions is one of the most complex challenges in modern physics. At high values of μB , reached in fixedtarged collisions at beam energies of few GeV per nucleon, excited baryons play an important role, so that the term resonance matter is sometimes used [13]. It was demonstrated that baryon resonances are key ingredients in modeling the medium modification of vector meson spectral functions [15,16,17] and the production of strange particles below their free nucleon-nucleon production threshold [18,19,20,21]. The role of baryon resonances in the production of dileptons and strange particles in heavy-ion collisions around 1A GeV has been addressed in recent works [22,23,24,25,26,27,28]. A direct reconstruction of short-lived (cτ ∼ 1 fm/c) baryon resonances has the potential to further constrain different model calculations
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
