Ultraviolet energy dependence of particle production sources in relativistic heavy-ion collisions

The energy dependence of particle production sources in relativistic heavy-ion collisions is investigated from RHIC (Relativistic Heavy Ion Collider) to LHC (Large Hadron Collider) energies. Whereas charged-hadron production in the fragmentation sources follows a $ln(s_{NN}/s_0)$ law, particle production in the mid-rapidity gluon-gluon source exhibits a much stronger dependence $\propto {ln}^3(s_{NN}/s_0)$, and becomes dominant between RHIC and LHC energies. The production of particles with pseudorapidities beyond the beam rapidity is also discussed.

Figure 1

The RDM pseudorapidity distribution functions for charged hadrons in central AuAu (RHIC) and PbPb (LHC) collisions at c.m. energies of 19.6 GeV, 130 GeV, 200 GeV, 2.76 TeV, and 5.02 TeV shown here are optimized in ${\chi }^2$ fits with respect to the PHOBOS [1, 27] (bottom) and ALICE [28] (top) data, with parameters from [3]. The upper distribution function is an extrapolation to the LHC design energy of 5.52 TeV. At the lowest energy, only the fragmentation sources contribute (dash-dotted curves).

Figure 2

The RDM pseudorapidity distribution functions for charged hadrons in central 200 GeV AuAu (top frame) and 2.76 TeV PbPb collisions are adjusted through ${\chi }^2$ minimizations to the PHOBOS [1] (see also [6]) and ALICE [28] data; see [3]. The underlying particle production sources are shown: dash-dotted curves are the fragmentation sources, dashed curves the mid-rapidity gluon-gluon sources, and dotted curves the central sources without the effect of the Jacobian transformation from rapidity to pseudorapidity. The particle content in the gluon-gluon source rises strongly with increasing c.m. energy, and constitutes the largest source at LHC energies.

Figure 3

Number of produced charged hadrons as function of the c.m. energy $\sqrt{s_{NN}}$ from RDM fits of the available data for central heavy-ion collisions at 0.019, 0.062, 0.13, 0.2 TeV (RHIC, AuAu), 2.76 TeV (LHC, PbPb), plus extrapolation to 5.52 TeV. Circles are the total numbers, following a power law $\propto s_{NN}^{0.23}$. Triangles are particles from the fragmentation sources $\propto ln(s_{NN}/s_0)$. Squares are hadrons produced from the mid-rapidity source, with a dependence $\propto {ln}^3(s_{NN}/s_0).$ A power law $\propto s_{NN}^{0.44}$ [3] is also shown (short-dashed curve), but fails to fit the extrapolated 5.52 TeV yield. The gluon-gluon source (dashed) becomes the main source of particle production between RHIC and LHC energies.

Figure 4

The total charged-hadron production in central AuAu and PbPb collision in the energy region 19.6 GeV to 5.52 TeV follows a power law $N_{\mathrm{tot}}\propto {(s_{NN}/s_0)}^{0.23}$ (solid line), whereas the particle content in the fragmentation sources is $Nqg\propto ln(s_{NN}/s_0)$ (dash-dotted curve). The particle content in the mid-rapidity source obeys $N_{gg}\propto {ln}^3(s_{NN}/s_0)$ (dashed curve, not too far from a power law (short-dashed line) only in the intermediate energy range 0.1–2.76 TeV. The energy dependence of the mid-rapidity yield is shown as a dotted line, with PHOBOS data [1] at RHIC energies, and ALICE data [29] at 2.76 TeV.

Figure 5

Produced charged particles in central AuAu collisions at $\sqrt{s_{NN}}=130$ and 200 GeV (RHIC/PHOBOS data [1]), bottom, and in 2.76 TeV PbPb [28], top, in comparison with the RDM solutions. The values of the beam rapidities are indicated as arrows ($y_{\text{beam}}=4.932,5.362,7.987)$. The pseudorapidity yields extend beyond $y_{\text{beam}}$, which is particularly evident in case of the 130 GeV PHOBOS data.