The STAR Time Projection Chamber (TPC) is used to record the collisions at the Relativistic Heavy Ion Collider. The TPC is the central element in a suite of detectors that surrounds the interaction ...vertex. The TPC provides complete coverage around the beam-line, and provides complete tracking for charged particles within ±1.8 units of pseudo-rapidity of the center-of-mass frame. Charged particles with momenta greater than
100
MeV/c
are recorded. Multiplicities in excess of 3000 tracks per event are routinely reconstructed in the software. The TPC measures
4
m
in diameter by
4.2
m
long, making it the largest TPC in the world.
We report the timing and spatial resolution from the Muon Telescope Detector (MTD) installed in the STAR experiment at RHIC. Cosmic ray muons traversing the STAR detector have an average transverse ...momentum of 6GeV/c. Due to their very small multiple scattering, these cosmic muons provide an ideal tool to calibrate the detectors and measure their timing and spatial resolution. The values obtained were ~100ps and ~1–2cm. These values are comparable to those obtained from cosmic-ray bench tests and test beams.
Global polarization of Λ hyperons has been measured to be of the order of a few tenths of a percent in Au+Au collisions at √SNN = 200 GeV, with no significant difference between Λ and Λ¯. These new ...results reveal the collision energy dependence of the global polarization together with the results previously observed √SNN = 7.7 – 62.4 GeV and indicate noticeable vorticity of the medium created in non-central heavy-ion collisions at the highest RHIC collision energy.
The Λ (Λ¯) hyperon polarization along the beam direction has been measured in Au+Au collisions at sNN=200 GeV, for the first time in heavy-ion collisions. The polarization dependence on the ...hyperons' emission angle relative to the elliptic flow plane exhibits a second harmonic sine modulation, indicating a quadrupole pattern of the vorticity component along the beam direction, expected due to elliptic flow. The polarization is found to increase in more peripheral collisions, and shows no strong transverse momentum (pT) dependence at pT greater than 1 GeV/c. The magnitude of the signal is about 5 times smaller than those predicted by hydrodynamic and multiphase transport models; the observed phase of the emission angle dependence is also opposite to these model predictions. In contrast, the kinematic vorticity calculations in the blast-wave model tuned to reproduce particle spectra, elliptic flow, and the azimuthal dependence of the Gaussian source radii measured with the Hanbury Brown–Twiss intensity interferometry technique reproduce well the modulation phase measured in the data and capture the centrality and transverse momentum dependence of the polarization signal.
Fluctuations of conserved quantities such as baryon number, charge, and strangeness are sensitive to the correlation length of the hot and dense matter created in relativistic heavy-ion collisions ...and can be used to search for the QCD critical point. We report the first measurements of the moments of net-kaon multiplicity distributions in Au+Au collisions at sNN=7.7, 11.5, 14.5, 19.6, 27, 39, 62.4, and 200 GeV. The collision centrality and energy dependence of the mean (M), variance (σ2), skewness (S), and kurtosis (κ) for net-kaon multiplicity distributions as well as the ratio σ2/M and the products Sσ and κσ2 are presented. Comparisons are made with Poisson and negative binomial baseline calculations as well as with UrQMD, a transport model (UrQMD) that does not include effects from the QCD critical point. Within current uncertainties, the net-kaon cumulant ratios appear to be monotonic as a function of collision energy.
We report the first measurement of rapidity-odd directed flow (v1) for D0 and D0¯ mesons at midrapidity (|y|<0.8) in Au+Au collisions at sNN=200 GeV using the STAR detector at the Relativistic Heavy ...Ion Collider. In 10–80% Au+Au collisions, the slope of the v1 rapidity dependence (dv1/dy), averaged over D0 and D0¯ mesons, is −0.080±0.017(stat)±0.016(syst) for transverse momentum pT above 1.5 GeV/c. The absolute value of D0 meson dv1/dy is about 25 times larger than that for charged kaons, with 3.4σ significance. These data give a unique insight into the initial tilt of the produced matter, and offer constraints on the geometric and transport parameters of the hot QCD medium created in relativistic heavy-ion collisions.
We report the first measurements of the moments--mean (M), variance (σ(2)), skewness (S), and kurtosis (κ)--of the net-charge multiplicity distributions at midrapidity in Au+Au collisions at seven ...energies, ranging from sqrtsNN=7.7 to 200 GeV, as a part of the Beam Energy Scan program at RHIC. The moments are related to the thermodynamic susceptibilities of net charge, and are sensitive to the location of the QCD critical point. We compare the products of the moments, σ(2)/M, Sσ, and κσ(2), with the expectations from Poisson and negative binomial distributions (NBDs). The Sσ values deviate from the Poisson baseline and are close to the NBD baseline, while the κσ(2) values tend to lie between the two. Within the present uncertainties, our data do not show nonmonotonic behavior as a function of collision energy. These measurements provide a valuable tool to extract the freeze-out parameters in heavy-ion collisions by comparing with theoretical models.
The forward time projection chamber in STAR Ackermann, K.H.; Bieser, F.; Brady, F.P. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
03/2003, Volume:
499, Issue:
2
Journal Article
Peer reviewed
Two cylindrical forward TPC detectors are described which were constructed to extend the phase space coverage of the STAR experiment to the region 2.5<|
η|<4.0. For optimal use of the available space ...and in order to cope with the high track density of central Au+Au collisions at RHIC, a novel design was developed using radial drift in a low diffusion gas. From prototype measurements a 2-track resolution of 1–
2
mm
is expected.
We report on the first measurement of the charmed baryon Λc± production at midrapidity (|y|<1) in Au+Au collisions at sNN=200 GeV collected by the STAR experiment at the Relativistic Heavy Ion ...Collider. The Λc/D0 denoting (Λc++Λc−)/(D0+D¯0) yield ratio is measured to be 1.08±0.16 (stat)±0.26 (sys) in the 0%–20% most central Au+Au collisions for the transverse momentum (pT) range 3<pT<6 GeV/c. This is significantly larger than the pythia model calculations for p+p collisions. The measured Λc/D0 ratio, as a function of pT and collision centrality, is comparable to the baryon-to-meson ratios for light and strange hadrons in Au+Au collisions. Model calculations including coalescence hadronization for charmed baryon and meson formation reproduce the features of our measured Λc/D0 ratio.
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