C. Allgower

Multiplicity Distribution and Spectra of Negatively Charged Hadrons in Au+Au Collisions at

The minimum-bias multiplicity distribution and the transverse momentum and pseudorapidity distributions for central collisions have been measured for negative hadrons ( h(-)) in Au+Au interactions at square root of ([s(NN)]) = 130 GeV. The multiplicity density at midrapidity for the 5% most central interactions is dN(h(-))/d(eta)/(eta = 0) = 280+/-1(stat)+/-20(syst), an increase per participant of 38% relative to pp collisions at the same energy. The mean transverse momentum is 0.508+/-0.012 GeV/c and is larger than in central Pb+Pb collisions at lower energies. The scaling of the h(-) yield per participant is a strong function of p( perpendicular). The pseudorapidity distribution is almost constant within /eta/<1.

Measurement of the absolute n p scattering differential cross section at 194 MeV

We describe a double-scattering experiment with a novel tagged neutron beam to measure differential cross sections for np backscattering to better than +/-2% absolute precision. The measurement focuses on angles and energies where the cross section magnitude and angle dependence constrain the charged pion-nucleon coupling constant, but existing data show serious discrepancies among themselves and with energy-dependent partial-wave analyses. The present results are in good accord with the partial-wave analyses, but deviate systematically from other recent measurements.

Measurement of the absolute differential cross section for np elastic scattering at 194 MeV

A tagged medium-energy neutron beam was used in a precise measurement of the absolute differential cross section for np backscattering. The results resolve significant discrepancies within the np database concerning the angular dependence in this regime. The experiment has determined the absolute normalization with {+-}1.5% uncertainty, suitable to verify constraints of supposedly comparable precision that arise from the rest of the database in partial wave analyses. The analysis procedures, especially those associated with the evaluation of systematic errors in the experiment, are described in detail so that systematic uncertainties may be included in a reasonable way in subsequent partial wave analysis fits incorporating the present results.

Measurement of Inclusive Antiprotons from Au + Au Collisions at sqrt(sNN) = 130 GeV

We report the first measurement of inclusive antiproton production at midrapidity in Au + Au collisions at roots(NN) = 130 GeV by the STAR experiment at RHIC. The antiproton transverse mass distributions in the measured transverse momentum range of 0.25 ) < 0.95 GeV/c are found to fall less steeply for more central collisions. The extrapolated antiproton rapidity density is found to scale approximately with the negative hadron multiplicity density.

Identified particle elliptic flow in √sNN = 130 GeV

We report first results on elliptic flow of identified particles at mid-rapidity in Au+Au collisions at

Pion Interferometry of

\sqrt{s_{_{NN}}}=130

Observation of the charge symmetry breaking d + d → 4He + π0 reaction near threshold

GeV using the STAR TPC at RHIC. The elliptic flow as a function of transverse momentum and centrality differs significantly for particles of different masses. This dependence can be accounted for in hydrodynamic models, indicating that the system created shows a behavior consistent with collective hydrodynamical flow. The fit to the data with a simple model gives information on the temperature and flow velocities at freeze-out.

Determination of the quadratic slope parameter in eta -> 3 pi(0) decay

Two-pion correlation functions in Au+Au collisions at square root of [s(NN)] = 130 GeV have been measured by the STAR (solenoidal tracker at RHIC) detector. The source size extracted by fitting the correlations grows with event multiplicity and decreases with transverse momentum. Anomalously large sizes or emission durations, which have been suggested as signals of quark-gluon plasma formation and rehadronization, are not observed. The Hanbury Brown-Twiss parameters display a weak energy dependence over a broad range in square root of [s(NN)].