We present the measurement of the transverse single-spin asymmetry of weak boson production in transversely polarized proton-proton collisions at s radical =500GeV by the STAR experiment at RHIC. The ...measured observable is sensitive to the Sivers function, one of the transverse-momentum-dependent parton distribution functions, which is predicted to have the opposite sign in proton-proton collisions from that observed in deep inelastic lepton-proton scattering. These data provide the first experimental investigation of the nonuniversality of the Sivers function, fundamental to our understanding of QCD.
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 v1even, as well as an observed similarity between its excitation function and that for v3, could serve as constraints for initial-state models. The v1even 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.
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.
We present STAR measurements of strange hadron ( K S0, Λ , Λ ¯, Ξ -, Ξ ¯+, Ω -, Ω ¯+ , and Φ ) production at midrapidity ( |y|<0.5 ) in Au+Au collisions at sNN = 7.7–39 GeV from the Beam Energy Scan ...Program at the Relativistic Heavy Ion Collider (RHIC). Transverse-momentum spectra, averaged transverse mass, and the overall integrated yields of these strange hadrons are presented versus the centrality and collision energy. Antibaryon-to-baryon ratios ( Λ ¯/ Λ , Ξ ¯+/ Ξ -, Ω ¯+/ Ω - ) are presented as well and used to test a thermal statistical model and to extract the temperature normalized strangeness and baryon chemical potentials at hadronic freeze-out ( μB/Tch and μS/Tch ) in central collisions. Strange baryon-to-pion ratios are compared to various model predictions in central collisions for all energies. The nuclear modification factors ( RCP ) and antibaryon-to-meson ratios as a function of transverse momentum are presented for all collision energies. The K S0 RCP shows no suppression for pT up to 3.5 GeV/c at energies of 7.7 and 11.5 GeV. The Λ ¯/ K S0 ratio also shows baryon-to-meson enhancement at intermediate pT ( ≈2.5 GeV/c ) in central collisions at energies above 19.6 GeV. Lastly, both observations suggest that there is likely a change of the underlying strange quark dynamics at collision energies below 19.6 GeV.
We present three-particle mixed-harmonic correlations 〈cos(mϕa+nϕb−(m+n)ϕc)〉 for harmonics m,n=1−3 for charged particles in sNN=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 viscosity and longitudinal structure of the initial state at RHIC.
The experimental data on inclusive spectra of the π
+
mesons produced in
p
+
A
collisions at the incident proton momentum of 400 GeV/
c
obtained by G. Leksin group at FNAL are analyzed in the ...framework of
z
-scaling. Self-similarity of the hadron production in the low-
p
T
cumulative region is verified. Scaling function ψ(
z
) for the Li, Be, C, Al, Cu, Ta nuclei is constructed. It is expressed via the invariant cross section and average multiplicity density of charged particles. Results of the analysis of the low-
p
T
data are compared with the high-
p
T
data sets obtained by J. Cronin, R. Sulyaev and D. Jaffe groups. A microscopic scenario of
p
+
A
interactions in terms of momentum fractions
x
1
,
x
2
is discussed. Indication on self-similarity of the cumulative pion production in
p
+
A
collisions over a wide kinematical range has been found. Based on the universality of the shape of the scaling function the inclusive cross sections of the π
+
mesons produced in
p
+
A
collisions on the Li, Be, C, Al, Cu, Ta targets in deep-cumulative region (
x
2
≫ 1/
A
) are predicted.
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