Experimental signatures of phase transition to quark matter in high-energy collisions of nuclei

Abstract

Colliding high-energy heavy nuclei is the only known way to experimentally study the phase transition from nucleonic to quark matter. Observations are, however, frustrated by the fact that secondary rr mesons are formed in the later stages of the interaction and are therefore insensitive to the early stages when quark matter is formed. We speculate on two types of experimental signatures of phase transition to quark matter. (i) The structure in the rapidity distribution of the secondaries from a near central collision of two heavy nuclei. We estimate that the reduction in shear viscosity between the colored quark-gluon plasma and the peripheral spectator part of each nucleus leads to an observable separation in rapidity of the secondaries from each component. (ii) Abundant production of prompt photons with n , / n ,~3 0 % for central collisions with about 50 GeV energy per nucleon.

Measurements of transverse energy distributions inAu+Aucollisions atsNN=200Adams1, Aggarwal2, Ahammed3 et al. 2004Phys. Rev. C

“…An excess photon yield may result from the formation of a long-lived deconfined phase, as suggested in Ref. [42]. The predictions from HIJING simulations are also presented.…”

“…The electromagnetic fraction of the transverse energy for the 5% most central events obtained in this work is ͗dE T em / d͘ / ͗dE T / d͘ = 0.35± 0.02, consistent with a final state dominated by mesons. Some models [42] expect that the formation of a long-lived deconfined phase in central events may increase the yield of direct photon production and, therefore, an increase in the electromagnetic fraction of the transverse energy. We, however, observe that the electromagnetic fraction of the transverse energy is constant, within errors, as a function of centrality.…”

Abnormal photonic energy ? a signal of Quark matter possibly seen in exotic cosmic ray events

“…On the other hand, one also expects a continuous increase of gamma production of non-pionic origin at progressively higher energies [28]. They are produced in collisions of quarks and gluons of high transverse momentum and from annihilation of q~-quarks in interacting hadrons and more so in a Quark-Gluon plasma [29]. It is interesting to note that the gamma to pion ratio, observed in p-p interactions, increases from about a few percent at ]/s'-~20GeV to about 25% at V~=63GeV and is expected to reach unity in the 100 to 1000 TeV energy range [28].…”

Observation of Direct Photons in Central158AGeVP208bAggarwal1, Agnihotri2, Ahammed3 et al. 2000Phys. Rev. Lett.1853970View full textAdd to dashboardCite

“…Following early estimates of photon emission rates [5][6][7][8], Kapusta et al [9] made detailed comparisons of the emissivity of the QGP and a hadron gas as two contrasting scenarios. It was demonstrated that the thermal emission rates of a hadron gas and a QGP were very similar and dependent essentially only on the temperature T .…”