Measurements of the midrapidity transverse energy distribution, $d\Et/d\eta$, are presented for $p$$+$$p$, $d$$+$Au, and Au$+$Au collisions at $\sqrt{s_{_{NN}}}=200$ GeV and additionally for Au$+$Au collisions at $\sqrt{s_{_{NN}}}=62.4$ and 130 GeV. The $d\Et/d\eta$ distributions are first compared with the number of nucleon participants $N_{\rm part}$, number of binary collisions $N_{\rm coll}$, and number of constituent-quark participants $N_{qp}$ calculated from a Glauber model based on the nuclear geometry. For Au$+$Au, $\mean{d\Et/d\eta}/N_{\rm part}$ increases with $N_{\rm part}$, while $\mean{d\Et/d\eta}/N_{qp}$ is approximately constant for all three energies. This indicates that the two component ansatz, $dE_{T}/d\eta \propto (1-x) N_{\rm part}/2 + x N_{\rm coll}$, which has been used to represent $E_T$ distributions, is simply a proxy for $N_{qp}$, and that the $N_{\rm coll}$ term does not represent a hard-scattering component in $E_T$ distributions. The $dE_{T}/d\eta$ distributions of Au$+$Au and $d$$+$Au are then calculated from the measured $p$$+$$p$ $E_T$ distribution using two models that both reproduce the Au$+$Au data. However, while the number-of-constituent-quark-participant model agrees well with the $d$$+$Au data, the additive-quark model does not.
Et EMC distributions for sqrt(sNN) = 62.4 GeV Au+Au collisions shown in 5% wide centrality bins.
Et EMC distributions for sqrt(sNN) = 62.4 GeV Au+Au collisions shown in 5% wide centrality bins.
Et EMC distributions for sqrt(sNN) = 62.4 GeV Au+Au collisions shown in 5% wide centrality bins.
Characteristics of the hadronic final state of diffractive deep inelastic scattering events, ep -> eXp, were studied in the kinematic range 4 < M_X < 35 GeV, 4 < Q^2 < 150 GeV^2, 70 < W < 250 GeV and 0.0003 < x_pom < 0.03 with the ZEUS detector at HERA using an integrated luminosity of 13.8 pb^{-1}. The events were tagged by identifying the diffractively scattered proton using the leading proton spectrometer. The properties of the hadronic final state, X, were studied in its center-of-mass frame using thrust, thrust angle, sphericity, energy flow, transverse energy flow and ``seagull'' distributions. As the invariant mass of the system increases, the final state becomes more collimated, more aligned and more asymmetric in the average transverse momentum with respect to the direction of the virtual photon. Comparisons of the properties of the hadronic final state with predictions from various Monte Carlo model generators suggest that the final state is dominated by qqg states at the parton level.
Thrust distribution for a DIS hadronic final state mass between 11 and 17.8GeV.
Thrust distribution for a DIS hadronic final state mass between 17.8 and 27.7 GeV.
Sphericity distribution for a DIS hadronic final state mass between 11 and 17.8 GeV.
Forum