We report a new measurement of
D
0
-meson production at mid-rapidity
(
|
y
|
<
1
)
in Au + Au collisions at
√
s
NN
=
200
GeV
utilizing the heavy flavor tracker, a high resolution silicon detector at ...the STAR experiment. Invariant yields of
D
0
mesons with transverse momentum
p
T
≲
9
GeV
/
c
are reported in various centrality bins (0–10%, 10–20%, 20–40%, 40–60%, and 60–80%). Blast-wave thermal models are used to fit the
D
0
-meson
p
T
spectra to study
D
0
hadron kinetic freeze-out properties. The average radial flow velocity extracted from the fit is considerably smaller than that of light hadrons
(
π
,
K
, and
p
)
, but comparable to that of hadrons containing multiple strange quarks
(
ϕ
,
Ξ
−
)
, indicating that
D
0
mesons kinetically decouple from the system earlier than light hadrons. The calculated
D
0
nuclear modification factors reaffirm that charm quarks suffer a large amount of energy loss in the medium, similar to those of light quarks for
p
T
>
4
GeV
/
c
in central 0–10% Au + Au collisions. At low
p
T
, the nuclear modification factors show a characteristic structure qualitatively consistent with the expectation from model predictions that charm quarks gain sizable collective motion during the medium evolution. The improved measurements are expected to offer new constraints to model calculations and help gain further insights into the hot and dense medium created in these collisions.
We present three-particle mixed-harmonic correlations 〈$ \cos (m\phi_a + n\phi_b - (m+n) \phi_c)$ 〉for harmonics $m,n=1-3$ for charged particles in $\sqrt{s_{NN}}=$200 GeV Au+Au collisions at RHIC. ...These measurements provide information on the three-dimensional structure of the initial collision zone and are important for constraining models of a subsequent low-viscosity quark-gluon plasma expansion phase. We investigate correlations between the first, second and third harmonics predicted as a consequence of fluctuations in the initial state. The dependence of the correlations on the pseudorapidity separation between particles show hints of a breaking of longitudinal invariance. We compare our results to a number of state-of-the art hydrodynamic calculations with different initial states and temperature dependent viscosities. These measurements provide important steps towards constraining the temperature dependent transport and the longitudinal structure of the initial state at RHIC.
We present a measurement of inclusive J/psi production at mid-rapidity (|y|<1) in p+p collisions at a center-of-mass energy of sqrt(s)=200 GeV with the STAR experiment at the Relativistic Heavy Ion ...Collider (RHIC). The differential production cross section for J/psi as a function of transverse momentum (pT) for 0<pT<14 GeV/c and the total cross section are reported and compared to calculations from the color evaporation model and the non-relativistic Quantum Chromodynamics model. The dependence of J/psi relative yields in three pT intervals on charged-particle multiplicity at mid-rapidity is measured for the first time in p+p collisions at sqrt(s)=200 GeV and compared with that measured at sqrt(s)=7 TeV, PYTHIA8 and EPOS3 Monte Carlo generators, and the Percolation model prediction.
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.
New measurements of directed flow for charged hadrons, characterized by the Fourier coefficient v1 , are presented for transverse momenta pT, and centrality intervals in Au+Au collisions recorded by ...the STAR experiment for the center-of-mass energy range √sNN = 7.7 – 200 GeV. The measurements underscore the importance of momentum conservation, and the characteristic dependencies on √sNN, centrality and pT are consistent with the expectations of geometric fluctuations generated in the initial stages of the collision, acting in concert with a hydrodynamic-like expansion. The centrality and pT dependencies of veven1, as well as an observed similarity between its excitation function and that for v3, could serve as constraints for initial-state models. Furthermore, the veven1 excitation function could also provide an important supplement to the flow measurements employed for precision extraction of the temperature dependence of the specific shear viscosity.
The transversity distribution, which describes transversely polarized quarks in transversely polarized nucleons, is a fundamental component of the spin structure of the nucleon, and is only loosely ...constrained by global fits to existing semi-inclusive deep inelastic scattering (SIDIS) data. In transversely polarized p" + p collisions it can be accessed using transverse polarization dependent fragmentation functions which give rise to azimuthal correlations between the polarization of the struck parton and the final state scalar mesons. This letter reports on spin dependent di-hadron correlations measured by the STAR experiment. The new dataset corresponds to 25 pb-1 integrated luminosity of p"+p collisions at p s = 500 GeV, an increase of more than a factor of ten compared to our previous measurement at p s = 200 GeV. Non-zero asymmetries sensitive to transversity are observed at a Q2 of several hundred GeV and are found to be consistent with the former measurement and a model calculation. We expect that these data will enable an extraction of transversity with comparable precision to current SIDIS datasets but at much higher momentum transfers where subleading effects are suppressed.
PDF
