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Register a new userMeasurements of elliptic and triangular flow in high-multiplicity $^{3}$He$+$Au collisions at $sqrt{s_{_{NN}}}=200$ GeV
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We present the first measurement of elliptic ($v_2$) and triangular ($v_3$) flow in high-multiplicity $^{3}$He$+$Au collisions at $sqrt{s_{_{NN}}}=200$ GeV. Two-particle correlations, where the particles have a large separation in pseudorapidity, are compared in $^{3}$He$+$Au and in $p$$+$$p$ collisions and indicate that collective effects dominate the second and third Fourier components for the correlations observed in the $^{3}$He$+$Au system. The collective behavior is quantified in terms of elliptic $v_2$ and triangular $v_3$ anisotropy coefficients measured with respect to their corresponding event planes. The $v_2$ values are comparable to those previously measured in $d$$+$Au collisions at the same nucleon-nucleon center-of-mass energy. Comparison with various theoretical predictions are made, including to models where the hot spots created by the impact of the three $^{3}$He nucleons on the Au nucleus expand hydrodynamically to generate the triangular flow. The agreement of these models with data may indicate the formation of low-viscosity quark-gluon plasma even in these small collision systems.
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Measurements of anisotropic flow Fourier coefficients ($v_n$) for inclusive charged particles and identified hadrons $pi^{pm}$, $K^{pm}$, $p$, and $bar{p}$ produced at midrapidity in Cu+Au collisions at $sqrt{s_{_{NN}}}=200$ GeV are presented. The data were collected in 2012 by the PHENIX experiment at the Relativistic Heavy Ion Collider (RHIC). The particle azimuthal distributions with respect to different order symmetry planes $Psi_n$, for $n$~=~1, 2, and 3 are studied as a function of transverse momentum $p_T$ over a broad range of collisions centralities. Mass ordering, as expected from hydrodynamic flow, is observed for all three harmonics. The charged-particle results are compared to hydrodynamical and transport model calculations. We also compare these Cu$+$Au results with those in Cu$+$Cu and Au$+$Au collisions at the same $sqrt{s_{_{NN}}}$, and find that the $v_2$ and $v_3$, as a function of transverse momentum, follow a common scaling with $1/(varepsilon_n N_{rm part}^{1/3})$.
We present the $p_{T}$ spectra, elliptic flow ($v_2$) and coalescence parameters $B_{2}$ for $d$, $bar{d}$ ($1<p_{T}<4$ GeV/c) and $B_{3}$ for $^{3}He$, $bar{^{3}He}$ ($2<p_{T}<6$ GeV/c) produced at mid-rapidity in Au+Au col lisions at $sqrt{s_{_{NN}}} = 200$ GeV. The results are measured in the STAR experiment at RHIC. The spectra of the light nuclei show softer $p_T$ distributions than calculations from a blast-wave model in which the parameters were fixed from pion, kaon and proton $v_2$($p_T$) and $p_T$ distributions. The coalescence volume is found to track with pion HBT re sults for different collision geometries. The $v_2$ measurement for $d(overline{d})$ as a function of transverse momentum $p_T$ is found to follow an approximate atomic mass number ($A$) scaling while that of $^{3}He(bar{^{3}He}) $ deviates slightly from the scaling. A negative $v_{2}$ has been observed for $bar{d}$ at low $p_{T}$, consiste nt with large radial flow in Au+Au collisions.
We present measurements of the transverse-momentum dependence of elliptic flow $v_2$ for identified pions and (anti)protons at midrapidity ($|eta|<0.35$), in 0%--5% central $p$$+$Au and $^3$He$+$Au collisions at $sqrt{s_{_{NN}}}=200$ GeV. When taken together with previously published measurements in $d$$+$Au collisions at $sqrt{s_{_{NN}}}=200$ GeV, the results cover a broad range of small-collision-system multiplicities and intrinsic initial geometries. We observe a clear mass-dependent splitting of $v_2(p_{T})$ in $d$$+$Au and $^3$He$+$Au collisions, just as in large nucleus-nucleus ($A$$+$$A$) collisions, and a smaller splitting in $p$$+$Au collisions. Both hydrodynamic and transport model calculations successfully describe the data at low $p_T$ ($< 1.5$ GeV/$c$), but fail to describe various features at higher $p_T$. In all systems, the $v_2$ values follow an approximate quark-number scaling as a function of the hadron transverse kinetic energy per constituent quark($KE_T/n_q$), which was also seen previously in $A$$+$$A$ collisions.
We present measurements of elliptic and triangular azimuthal anisotropy of charged particles detected at forward rapidity $1<|eta|<3$ in Au$+$Au collisions at $sqrt{s_{_{NN}}}=200$ GeV, as a function of centrality. The multiparticle cumulant technique is used to obtain the elliptic flow coefficients $v_2{2}$, $v_2{4}$, $v_2{6}$, and $v_2{8}$, and triangular flow coefficients $v_3{2}$ and $v_3{4}$. Using the small-variance limit, we estimate the mean and variance of the event-by-event $v_2$ distribution from $v_2{2}$ and $v_2{4}$. In a complementary analysis, we also use a folding procedure to study the distributions of $v_2$ and $v_3$ directly, extracting both the mean and variance. Implications for initial geometrical fluctuations and their translation into the final state momentum distributions are discussed.
Asymmetric nuclear collisions of $p$$+$Al, $p$$+$Au, $d$$+$Au, and $^{3}$He$+$Au at $sqrt{s_{_{NN}}}=200$ GeV provide an excellent laboratory for understanding particle production, as well as exploring interactions among these particles after their initial creation in the collision. We present measurements of charged hadron production $dN_{rm ch}/deta$ in all such collision systems over a broad pseudorapidity range and as a function of collision multiplicity. A simple wounded quark model is remarkably successful at describing the full data set. We also measure the elliptic flow $v_{2}$ over a similarly broad pseudorapidity range. These measurements provide key constraints on models of particle emission and their translation into flow.
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