We report on measurements of directed flow as a function of pseudorapidity in Au + Au collisions at energies of square root of SNN = 19.6, 62.4, 130 and 200 GeV as measured by the PHOBOS detector at ...the BNL Relativistic Heavy Ion Collider. These results are particularly valuable because of the extensive, continuous pseudorapidity coverage of the PHOBOS detector. There is no significant indication of structure near midrapidity and the data surprisingly exhibit extended longitudinal scaling similar to that seen for elliptic flow and charged particle pseudorapidity density.
We present the first measurements of the pseudorapidity distribution of primary charged particles in Cu+Cu collisions as a function of collision centrality and energy, sqrts_{NN}=22.4, 62.4, and 200 ...GeV, over a wide range of pseudorapidity, using the PHOBOS detector. A comparison of Cu+Cu and Au+Au results shows that the total number of produced charged particles and the rough shape (height and width) of the pseudorapidity distributions are determined by the number of nucleon participants. More detailed studies reveal that a more precise matching of the shape of the Cu+Cu and Au+Au pseudorapidity distributions over the full range of pseudorapidity occurs for the same N{part}/2A rather than the same N_{part}. In other words, it is the collision geometry rather than just the number of nucleon participants that drives the detailed shape of the pseudorapidity distribution and its centrality dependence at RHIC energies.
Spectator fragments resulting from relativistic heavy ion collisions, consisting of single protons and neutrons along with groups of stable nuclear fragments up to nitrogen (Z = 7), are measured in ...PHOBOS. These fragments are observed in Au+Au (root s(NN) = 19.6 GeV) and Cu+Cu (22.4 GeV) collisions at high pseudorapidity (eta). The dominant multiply-charged fragment is the tightly bound helium (alpha), with lithium, beryllium, and boron all clearly seen as a function of collision centrality and pseudorapidity. We observe that in Cu+Cu collisions, it becomes much more favorable for the alpha fragments to be released than lithium. The yields of fragments approximately scale with the number of spectator nucleons, independent of the colliding ion. The shapes of the pseudorapidity distributions of fragments indicate that the average deflection of the fragments away from the beam direction increases for more central collisions. A detailed comparison of the shapes for alpha and lithium fragments indicates that the centrality dependence of the deflections favors a scaling with the number of participants in the collision.
Strangeness measurements with the PHOBOS experiment Veres, Gábor I; Back, B B; Baker, M D ...
Journal of physics. G, Nuclear and particle physics,
12/2006, Letnik:
32, Številka:
12
Journal Article, Conference Proceeding
The PHOBOS apparatus includes a charged particle multiplicity detector covering almost all of 4
π in solid angle. The broad coverage in pseudorapidity,
η, which is unique at RHIC, combined with the ...ability to collect a large sample of events with minimal bias, makes possible a study of correlations and fluctuations over most of the pseudorapidity range, even at the highest beam energy. Long range correlations, short range correlations at large
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η
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, event-by-event fluctuations in the total number of charged particles, and event-by-event variation in the full shape of the pseudorapidity distribution can all be studied. Preliminary results for the first exploration of these capabilities of the PHOBOS detector, along with some average properties of the pseudorapidity distributions, are presented.
We present the first measurement of the pseudorapidity density of primary charged particles in Au+Au collisions at root squares(NN) = 200 GeV. For the 6% most central collisions, we obtain ...dN(ch)/d(eta)/(/eta/<1) = 650+/-35(syst). Compared to collisions at root squares(NN) = 130 GeV, the highest energy studied previously, an increase by a factor of 1.14+/-0.05 at 90% confidence level, is found. The energy dependence of the pseudorapidity density is discussed in comparison with data from proton-induced collisions and theoretical predictions.
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