The coefficients that describe the anisotropy in the azimuthal distribution of particles are lower when the particles are recorded in a detector with finite granularity and measures only hits. This ...arises due to loss of information because of multiple hits in any channel. The magnitude of this loss of signal depends both on the occupancy and on the value of the coefficient. These correction factors are obtained for analysis methods differing in detail, and they are found to be different.
Dihadron angular correlations in d+Au collisions at sNN=200 GeV are reported as a function of the measured zero-degree calorimeter neutral energy and the forward charged hadron multiplicity in the ...Au-beam direction. A finite correlated yield is observed at large relative pseudorapidity (Δη) on the near side (i.e. relative azimuth Δϕ∼0). This correlated yield as a function of Δη appears to scale with the dominant, primarily jet-related, away-side (Δϕ∼π) yield. The Fourier coefficients of the Δϕ correlation, Vn=〈cosnΔϕ〉, have a strong Δη dependence. In addition, it is found that V1 is approximately inversely proportional to the mid-rapidity event multiplicity, while V2 is independent of it with similar magnitude in the forward (d-going) and backward (Au-going) directions.
A beam energy scan has been carried out at the Relativistic Heavy Ion Collider at Brookhaven National Laboratory to search for the onset of deconfinement and a possible critical point where the ...transition from a Quark Gluon Plasma to a hadronic phase changes from a rapid cross-over to a first order phase transition. Anisotropy in the azimuthal distribution of produced particles such as the second and third harmonics v2 and v3 are expected to be sensitive to the existence of a Quark Gluon Plasma phase and the Equation of State of the system. For this reason, they are of great experimental interests. In this Letter we report on calculations of v2 and v3 from the AMPT model in the Default (Def.) and String Melting (SM) mode to provide a reference for the energy dependence of v2 and v3 for sNN from 7.7 GeV to 2.76 TeV. We expect that in the case that collisions cease to produce QGP at lower colliding energies, data will deviate from the AMPT String Melting calculations and come in better agreement with the Default calculations.
The acceptance-corrected dielectron excess mass spectra, where the known hadronic sources have been subtracted from the inclusive dielectron mass spectra, are reported for the first time at ...mid-rapidity |yee|<1 in minimum-bias Au+Au collisions at sNN=19.6 and 200 GeV. The excess mass spectra are consistently described by a model calculation with a broadened ρ spectral function for Mee<1.1 GeV/c2. The integrated dielectron excess yield at sNN=19.6 GeV for 0.4<Mee<0.75 GeV/c2, normalized to the charged particle multiplicity at mid-rapidity, has a value similar to that in In+In collisions at sNN=17.3 GeV. For sNN=200 GeV, the normalized excess yield in central collisions is higher than that at sNN=17.3 GeV and increases from peripheral to central collisions. These measurements indicate that the lifetime of the hot, dense medium created in central Au+Au collisions at sNN=200 GeV is longer than those in peripheral collisions and at lower energies.
Dihadron correlations are analyzed in sNN=200 GeVd+Au collisions classified by forward charged particle multiplicity and zero-degree neutral energy in the Au-beam direction. It is found that the ...jetlike correlated yield increases with the event multiplicity. After taking into account this dependence, the non-jet contribution on the away side is minimal, leaving little room for a back-to-back ridge in these collisions.
A honeycomb detector consisting of a matrix of 96 closely packed hexagonal cells, each working as a proportional counter with a wire readout, was fabricated and tested at the CERN PS. The cell depth ...and the radial dimensions of the cell were small, in the range 5–
10
mm
. The appropriate cell design was arrived at using GARFIELD simulations. Two geometries are described illustrating the effect of field shaping. The charged particle detection efficiency and the preshower characteristics have been studied using pion and electron beams. Average charged particle detection efficiency was found to be 98%, which is almost uniform within the cell volume and also within the array. The preshower data show that the transverse size of the shower is in close agreement with the results of simulations for a range of energies and converter thicknesses.
Recent interest in fluctuations in the anisotropy coefficients enhances the need for an accurate determination of their values. It is argued, and shown using the help of simulated data, that the ...measured value of anisotropy coefficients obtained using certain commonly used methods to eliminate the contribution of non-flow correlations, may also be a manifestation of event by event fluctuations. In all cases, the deviation from the mean values of flow is decided by the magnitude of fluctuation.
Measurements of direct photon production in p+Pb and p+C collisions at $\sqrt{s_\mathrm{NN}} = 17.4\mathrm{GeV}$ are presented. Upper limits on the direct photon yield as a function of $p_\mathrm{T}$ ...are derived and compared to the results for Pb+Pb collisions at $\sqrt{s_\mathrm{NN}} = 17.3$ GeV. The production of the $\eta$ meson, which is an important input to the direct photon signal extraction, has been determined in the $\eta \rightarrow 2\gamma$ channel for p+C collisions at $\sqrt{s_\mathrm{NN}} = 17.4\mathrm{GeV}$.
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