The PHENIX experiment at the Relativistic Heavy Ion Collider has measured the differential cross section, mean transverse momentum, mean transverse momentum squared of inclusive $J/\psi$ and cross-section ratio of $\psi(2S)$ to $J/\psi$ at forward rapidity in \pp collisions at \sqrts = 510 GeV via the dimuon decay channel. Comparison is made to inclusive $J/\psi$ cross sections measured at \sqrts = 200 GeV and 2.76--13 TeV. The result is also compared to leading-order nonrelativistic QCD calculations coupled to a color-glass-condensate description of the low-$x$ gluons in the proton at low transverse momentum ($p_T$) and to next-to-leading order nonrelativistic QCD calculations for the rest of the $p_T$ range. These calculations overestimate the data at low $p_T$. While consistent with the data within uncertainties above $\approx3$ GeV/$c$, the calculations are systematically below the data. The total cross section times the branching ratio is BR $d\sigma^{J/\psi}_{pp}/dy (1.2<|y|<2.2, 0
The total cross section times the branching ratio.
The inclusive $J/\psi$ differential cross section as a function of $p_T$ at 1.2 < $|y|$ < 2.2 at 510 GeV.
The inclusive $J/\psi$ differential cross section integrated over 0 < $p_T$ < 10 GeV/$c$ as a function of rapidity at 510 GeV.
Charmonium is a valuable probe in heavy-ion collisions to study the properties of the quark gluon plasma, and is also an interesting probe in small collision systems to study cold nuclear matter effects, which are also present in large collision systems. With the recent observations of collective behavior of produced particles in small system collisions, measurements of the modification of charmonium in small systems have become increasingly relevant. We present the results of J/ψ measurements at forward and backward rapidity in various small collision systems, p+p, p+Al, p+Au and 3He+Au, at √sNN =200 GeV. The results are presented in the form of the observable RAB, the nuclear modification factor, a measure of the ratio of the J/ψ invariant yield compared to the scaled yield in p+p collisions. We examine the rapidity, transverse momentum, and collision centrality dependence of nuclear effects on J/ψ production with different projectile sizes p and 3He, and different target sizes Al and Au. The modification is found to be strongly dependent on the target size, but to be very similar for p+Au and 3He+Au. However, for 0%–20% central collisions at backward rapidity, the modification for 3He+Au is found to be smaller than that for p+Au, with a mean fit to the ratio of 0.89±0.03(stat)±0.08(syst), possibly indicating final state effects due to the larger projectile size.
J/psi invariant yields in p+p collisions as a function of pT at forward and backward rapidity. The statistical and systematic uncertainties vary point-to-point and are listed for each measured value. An additional global systematic uncertainty is provided in each column heading, which applies to all data points per column.
J/psi nuclear modification in p+Al, p+Au and 3He+Au collisions as a function of centrality and rapidity. The statistical and systematic uncertainties vary point-to-point and are listed for each measured value. An additional global systematic uncertainty is provided in each column heading, which applies to all data points per column.
J/psi nuclear modification in p+Al collisions as a function of centrality and rapidity. The statistical and systematic uncertainties vary point-to-point and are listed for each measured value. An additional global systematic uncertainty is provided in each column heading, which applies to all data points per column.
The PHENIX experiment has studied nuclear effects in $p$$+$Al and $p$$+$Au collisions at $\sqrt{s_{_{NN}}}=200$ GeV on charged hadron production at forward rapidity ($1.4<\eta<2.4$, $p$-going direction) and backward rapidity ($-2.2<\eta<-1.2$, $A$-going direction). Such effects are quantified by measuring nuclear modification factors as a function of transverse momentum and pseudorapidity in various collision multiplicity selections. In central $p$$+$Al and $p$$+$Au collisions, a suppression (enhancement) is observed at forward (backward) rapidity compared to the binary scaled yields in $p$+$p$ collisions. The magnitude of enhancement at backward rapidity is larger in $p$$+$Au collisions than in $p$$+$Al collisions, which have a smaller number of participating nucleons. However, the results at forward rapidity show a similar suppression within uncertainties. The results in the integrated centrality are compared with calculations using nuclear parton distribution functions, which show a reasonable agreement at the forward rapidity but fail to describe the backward rapidity enhancement.
RpA of charged hadrons as a function of pT at forward and backward rapidity in p+Al 0%-100% centrality.
RpA of charged hadrons as a function of pT at forward and backward rapidity in p+Au 0%-100% centrality.
RpA of charged hadrons as a function of eta at forward and backward rapidity in p+Al and p+Au 0%-100% centrality.
We report on the nuclear dependence of transverse single-spin asymmetries (TSSAs) in the production of positively-charged hadrons in polarized $p^{\uparrow}+p$, $p^{\uparrow}+$Al and $p^{\uparrow}+$Au collisions at $\sqrt{s_{_{NN}}}=200$ GeV. The measurements have been performed at forward rapidity ($1.4<\eta<2.4$) over the range of $1.8
$A_N$ as a function of $A^{1/3}$ for positively-charged hadrons at 1.4 < $\eta$ < 2.4, 0.1 < $x_F$ < 0.2, and 1.8 < $p_T$ < 7.0 GeV/$c$ in $p^{\uparrow}$+$p$, $p^{\uparrow}$+Al, and $p^{\uparrow}$+Au collisions.
$A_N$ as a function of $N^{Avg.}_{coll}$ for positively-charged hadrons at 1.4 < $\eta$ < 2.4, 0.1 < $x_F$ < 0.2, and 1.8 < $p_T$ < 7.0 GeV/$c$ in $p^{\uparrow}$+$p$, $p^{\uparrow}$+Al, and $p^{\uparrow}$+Au collisions.
The PHENIX collaboration has measured high-$p_T$ dihadron correlations in $p$$+$$p$, $p$$+$Al, and $p$$+$Au collisions at $\sqrt{s_{_{NN}}}=200$ GeV. The correlations arise from inter- and intra-jet correlations and thus have sensitivity to nonperturbative effects in both the initial and final states. The distributions of $p_{\rm out}$, the transverse momentum component of the associated hadron perpendicular to the trigger hadron, are sensitive to initial and final state transverse momenta. These distributions are measured multi-differentially as a function of $x_E$, the longitudinal momentum fraction of the associated hadron with respect to the trigger hadron. The near-side $p_{\rm out}$ widths, sensitive to fragmentation transverse momentum, show no significant broadening between $p$$+$Au, $p$$+$Al, and $p$$+$$p$. The away-side nonperturbative $p_{\rm out}$ widths are found to be broadened in $p$$+$Au when compared to $p$$+$$p$; however, there is no significant broadening in $p$$+$Al compared to $p$$+$$p$ collisions. The data also suggest that the away-side $p_{\rm out}$ broadening is a function of $N_{\rm coll}$, the number of binary nucleon-nucleon collisions, in the interaction. The potential implications of these results with regard to initial and final state transverse momentum broadening and energy loss of partons in a nucleus, among other nuclear effects, are discussed.
The Gaussian width differences between $p$+$A$ and $p$+$p$ are shown in two $x_E$ bins as a function of $N_{coll}$.
Asymmetric nuclear collisions of $p$$+$Al, $p$$+$Au, $d$$+$Au, and $^{3}$He$+$Au at $\sqrt{s_{_{NN}}}=200$ GeV provide an excellent laboratory for understanding particle production, as well as exploring interactions among these particles after their initial creation in the collision. We present measurements of charged hadron production $dN_{\rm ch}/d\eta$ in all such collision systems over a broad pseudorapidity range and as a function of collision multiplicity. A simple wounded quark model is remarkably successful at describing the full data set. We also measure the elliptic flow $v_{2}$ over a similarly broad pseudorapidity range. These measurements provide key constraints on models of particle emission and their translation into flow.
Charged hadron $dN_{ch}/d\eta$ as a function of pseudorapidity in high-multiplicity 0%-5% central $^3$He+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV.
Charged hadron $dN_{ch}/d\eta$ as a function of pseudorapidity in high-multiplicity 0%-5% central $d$+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV.
Charged hadron $dN_{ch}/d\eta$ as a function of pseudorapidity in high-multiplicity 0%-5% central $p$+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV.
The experimental study of the collisions of heavy nuclei at relativistic energies has established the properties of the quark-gluon plasma (QGP), a state of hot, dense nuclear matter in which quarks and gluons are not bound into hadrons. In this state, matter behaves as a nearly inviscid fluid that efficiently translates initial spatial anisotropies into correlated momentum anisotropies among the produced particles, producing a common velocity field pattern known as collective flow. In recent years, comparable momentum anisotropies have been measured in small-system proton-proton ($p$$+$$p$) and proton-nucleus ($p$$+$$A$) collisions, despite expectations that the volume and lifetime of the medium produced would be too small to form a QGP. Here, we report on the observation of elliptic and triangular flow patterns of charged particles produced in proton-gold ($p$$+$Au), deuteron-gold ($d$$+$Au), and helium-gold ($^3$He$+$Au) collisions at a nucleon-nucleon center-of-mass energy $\sqrt{s_{_{NN}}}$~=~200 GeV. The unique combination of three distinct initial geometries and two flow patterns provides unprecedented model discrimination. Hydrodynamical models, which include the formation of a short-lived QGP droplet, provide a simultaneous description of these measurements.
$v_2$for 0-5% central p+Au collisions
$v_2$for 0-5% central d+Au collisions
$v_2$for 0-5% central $^3$He+Au collisions
Recently, multiparticle-correlation measurements of relativistic $p/d/^3$He$+$Au, $p$$+$Pb, and even $p$$+$$p$ collisions have shown surprising collective signatures. Here we present beam-energy-scan measurements of 2-, 4-, and 6-particle angular correlations in $d$$+$Au collisions at $\sqrt{s_{_{NN}}}$=200, 62.4, 39, and 19.6 GeV. We also present measurements of 2- and 4-particle angular correlations in $p$$+$Au collisions at $\sqrt{s_{_{NN}}}$=200 GeV. We find the 4-particle cumulant to be real-valued for $d$$+$Au collisions at all four energies. We also find that the 4-particle cumulant in $p$$+$Au has the opposite sign as that in $d$$+$Au, indicating that the correlations are geometrical and therefore collective in origin. Further we find that the 6-particle cumulant agrees with the 4-particle cumulant in $d$$+$Au collisions at 200 GeV, which indicates that nonflow effects are subdominant and provides strong evidence of collectivity.
Components $\langle\langle$4$\rangle\rangle$ and 2$\langle\langle$2$\rangle\rangle^{2}$ and cumulant $c_2${4} = $\langle\langle$4$\rangle\rangle$ - 2$\langle\langle$2$\rangle\rangle^{2}$ as a function of $N^{FVTX}_{tracks}$. (a) and (b) show the components and cumulant, respectively, in $p$+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV. (c) and (d) show the components and cumulant, respectively, in $d$+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV. (b) and (d) also show the cumulant as measured in AMPT for $p$+Au and $d$+Au, respectively, indicated by the green line. The shaded green band indicates the statistical uncertainty on the AMPT values.
Components $\langle\langle$4$\rangle\rangle$ and 2$\langle\langle$2$\rangle\rangle^{2}$ and cumulant $c_2${4} = $\langle\langle$4$\rangle\rangle$ - 2$\langle\langle$2$\rangle\rangle^{2}$ as a function of $N^{FVTX}_{tracks}$. (a) and (b) show the components and cumulant, respectively, in $p$+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV. (c) and (d) show the components and cumulant, respectively, in $d$+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV. (b) and (d) also show the cumulant as measured in AMPT for $p$+Au and $d$+Au, respectively, indicated by the green line. The shaded green band indicates the statistical uncertainty on the AMPT values.
$v_2${2}, $v_2${2, |$\Delta\eta$| > 2}, and $v_2${4} as a function of $N^{FVTX}_{tracks}$ in $d$+Au collisions with $\sqrt{s_{NN}}$= (a) 200 GeV, (b) 62.4 GeV, (c) 39 GeV, and (d) 19.6 GeV; also shown in (a) is $v_2${6} for $\sqrt{s_{NN}}$= 200 GeV. The arrowheads on the statistical uncertainties indicate cases where the standard 1$\sigma$ uncertainty on the $c_2${4} crosses zero. For 19.6 GeV, the combined confidence interval for $v_2${4} to be real is 79%.
During 2015 the Relativistic Heavy Ion Collider (RHIC) provided collisions of transversely polarized protons with Au and Al nuclei for the first time, enabling the exploration of transverse-single-spin asymmetries with heavy nuclei. Large single-spin asymmetries in very forward neutron production have been previously observed in transversely polarized $p$$+$$p$ collisions at RHIC, and the existing theoretical framework that was successful in describing the single-spin asymmetry in $p$$+$$p$ collisions predicts only a moderate atomic-mass-number ($A$) dependence. In contrast, the asymmetries observed at RHIC in $p$$+$$A$ collisions showed a surprisingly strong $A$ dependence in inclusive forward neutron production. The observed asymmetry in $p$$+$Al collisions is much smaller, while the asymmetry in $p$$+$Au collisions is a factor of three larger in absolute value and of opposite sign. The interplay of different neutron production mechanisms is discussed as a possible explanation of the observed $A$ dependence.
Forward neutron $A_N$ in $p$+$A$ collisions for $A$ = 1 ($p$), 27 (Al), and 197 (Au), for ZDC inclusive, ZDC $\otimes$ BBC-tag, and ZDC $\otimes$ BBC-veto triggered samples. The 3% scale uncertainty is from the polarization normalization uncertaintiy.
The cross section and transverse single-spin asymmetries of $\mu^{-}$ and $\mu^{+}$ from open heavy-flavor decays in polarized $p$+$p$ collisions at $\sqrt{s}=200$ GeV were measured by the PHENIX experiment during 2012 at the Relativistic Heavy Ion Collider. Because heavy-flavor production is dominated by gluon-gluon interactions at $\sqrt{s}=200$ GeV, these measurements offer a unique opportunity to obtain information on the trigluon correlation functions. The measurements are performed at forward and backward rapidity ($1.4<|y|<2.0$) over the transverse momentum range of $1.25
$A_N$ of negatively-charged muons from open heavy-flavor decays as a function of $p_T$ in the backward ($x_F$ < 0) and forward ($x_F$ > 0) regions.
$A_N$ of positively-charged muons from open heavy-flavor decays as a function of $p_T$ in the backward ($x_F$ < 0) and forward ($x_F$ > 0) regions.
$A_N$ of negatively-charged and positively-charged muons from open heavy-flavor decays as a function of $x_F$, where $x_F$ > 0 is along the direction of the polarized proton.
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