Abstract
Inclusive pion production at high transverse momenta (pT≳2 GeV/c) in nucleus–nucleus (A+A) collisions at CERN-SPS (sNN≈20 GeV) is revisited and systematically compared to all existing proton–proton data in the same range of center-of-mass energies. The ratio of A+A to p + p pion cross-sections (nuclear modification factor) for central Pb + Pb, Pb + Au and S + Au reactions does not show a strong enhancement as a function of pT as previously found, but is consistent with scaling with the number of nucleon–nucleon (NN) collisions. Neutral pion yields per NN collision in head-on Pb + Pb reactions are suppressed, whereas peripheral yields are enhanced. These results together indicate that some amount of “jet quenching” may already be present in central heavy-ion reactions at sNN≈20 GeV.
Highlights
Lattice calculations of bulk Quantum Chromodynamics (QCD) in thermal equilibrium [1] predict the transition of hadronic matter to a deconfined and chirally symmetric system of quarks and gluons above energy densities of the order ǫcrit ≈ 0.7 ± 0.3 GeV/fm3
Several observations in central Pb+Pb collisions [3] are consistent with expected Quark-Gluon Plasma” (QGP) signals, e.g. the “anomalous” suppression of charmonium states due to Debye screening of the color potential in the plasma [4], other expected signatures such as “jet quenching” due to parton energy loss in the dense deconfined medium [6] seem to be significatively absent from the data
Using Blattnig’s parametrization [34] as proton-proton reference, and the corresponding mean number of collisions Ncoll for each centrality quoted in the original papers 4, we present in Fig. 4 the nuclear modification factors for high pT pion produced near midrapidity in the three A+A reactions studied at Super Proton Synchrotron (SPS) (Table 4) at comparable centrality bins
Summary
Lattice calculations of bulk Quantum Chromodynamics (QCD) in thermal equilibrium [1] predict the transition of hadronic matter to a deconfined and chirally symmetric system of quarks and gluons above energy densities of the order ǫcrit ≈ 0.7 ± 0.3 GeV/fm. Using Blattnig’s parametrization [34] as proton-proton reference, and the corresponding mean number of collisions Ncoll for each centrality quoted in the original papers 4 , we present in Fig. 4 the nuclear modification factors for high pT pion produced near midrapidity in the three A+A reactions studied at SPS (Table 4) at comparable centrality bins. RAA being unity up to pT ≈ 3.5 GeV/c, and the top 1% most central Pb+Pb reactions are found to be suppressed (RAA ≈ 0.6) in this pT range as already reported in the original work of the WA98 collaboration [7] These results clearly indicate, regardless of the p+p → π0+X reference used in the denominator of RAA, that hard hadron production in head-on Pb+Pb collisions at CERN-SPS is quenched by a factor of ∼2 compared to peripheral collisions
Sign-in/Register to view highlights & summary 
Published Version
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 callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
