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 $d\sigma^{J/\psi}_{pp}/dy (1.2<|y|<2.2, 0<p_T<10~\mbox{GeV/$c$}) =$ 54.3 $\pm$ 0.5 (stat) $\pm$ 5.5 (syst) nb.
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.
We report on a polarization measurement of inclusive $J/\psi$ mesons in the di-electron decay channel at mid-rapidity at 2 $<p_{T}<$ 6 GeV/$c$ in $p+p$ collisions at $\sqrt{s}$ = 200 GeV. Data were taken with the STAR detector at RHIC. The $J/\psi$ polarization measurement should help to distinguish between different models of the $J/\psi$ production mechanism since they predict different $p_{T}$ dependences of the $J/\psi$ polarization. In this analysis, $J/\psi$ polarization is studied in the helicity frame. The polarization parameter $\lambda_{\theta}$ measured at RHIC becomes smaller towards high $p_{T}$, indicating more longitudinal $J/\psi$ polarization as $p_{T}$ increases. The result is compared with predictions of presently available models.
Uncorrected cos$\theta$ distribution after the combinatorial background subtraction for $2 < p_{T}^{J/\psi} < 3$ GeV/c
Uncorrected cos$\theta$ distribution after the combinatorial background subtraction for $3 < p_{T}^{J/\psi} < 4$ GeV/c
Uncorrected cos$\theta$ distribution after the combinatorial background subtraction for $4 < p_{T}^{J/\psi} < 6$ GeV/c
The $\jpsi$ $\pt$ spectrum and nuclear modification factor ($\raa$) are reported for $\pt < 5 \ \gevc$ and $|y|<1$ from 0\% to 60\% central Au+Au and Cu+Cu collisions at $\snn = 200 \ \gev$ at STAR. A significant suppression of $\pt$-integrated $\jpsi$ production is observed in central Au+Au events. The Cu+Cu data are consistent with no suppression, although the precision is limited by the available statistics. $\raa$ in Au+Au collisions exhibits a strong suppression at low transverse momentum and gradually increases with $\pt$. The data are compared to high-$\pt$ STAR results and previously published BNL Relativistic Heavy Ion Collider results. Comparing with model calculations, it is found that the invariant yields at low $\pt$ are significantly above hydrodynamic flow predictions but are consistent with models that include color screening and regeneration.
The invariant yield versus transverse momentum for |y| < 1 in 0-20% centrality in Au+Au collisions (solid circles). The results are compared to high-$p_T$ (3 < $p_T$ < 10 GeV/c) results from STAR [9] (solid squares) and PHENIX data [8] (open squares).
The invariant yield versus transverse momentum for |y| < 1 in 20-40% centrality in Au+Au collisions (solid circles). The results are compared to high-$p_T$ (3 < $p_T$ < 10 GeV/c) results from STAR [9] (solid squares) and PHENIX data [8] (open squares).
The invariant yield versus transverse momentum for |y| < 1 in 40-60% centrality in Au+Au collisions (solid circles). The results are compared to high-$p_T$ (3 < $p_T$ < 10 GeV/c) results from STAR [9] (solid squares) and PHENIX data [8] (open squares).
Measurements of $\gamma p \rightarrow K^{+} \Lambda$ and $\gamma p \rightarrow K^{+} \Sigma^0$ cross-sections have been obtained with the photon tagging facility and the Crystal Ball calorimeter at MAMI-C. The measurement uses a novel $K^+$ meson identification technique in which the weak decay products are characterized using the energy and timing characteristics of the energy deposit in the calorimeter, a method that has the potential to be applied at many other facilities. The fine center-of-mass energy ($W$) resolution and statistical accuracy of the new data results in a significant impact on partial wave analyses aiming to better establish the excitation spectrum of the nucleon. The new analyses disfavor a strong role for quark-diquark dynamics in the nucleon.
Excitation function at cos(Theta_K+)cm = -0.8
Excitation function at cos(Theta_K+)cm = -0.7
Excitation function at cos(Theta_K+)cm = -0.6
We report the measurement of $K^{*0}$ meson at midrapidity ($|y|<$ 1.0) in Au+Au collisions at $\sqrt{s_{\rm NN}}$~=~7.7, 11.5, 14.5, 19.6, 27 and 39 GeV collected by the STAR experiment during the RHIC beam energy scan (BES) program. The transverse momentum spectra, yield, and average transverse momentum of $K^{*0}$ are presented as functions of collision centrality and beam energy. The $K^{*0}/K$ yield ratios are presented for different collision centrality intervals and beam energies. The $K^{*0}/K$ ratio in heavy-ion collisions are observed to be smaller than that in small system collisions (e+e and p+p). The $K^{*0}/K$ ratio follows a similar centrality dependence to that observed in previous RHIC and LHC measurements. The data favor the scenario of the dominance of hadronic re-scattering over regeneration for $K^{*0}$ production in the hadronic phase of the medium.
$p_{\mathrm T}$-differential yield of $\mathrm{K^{*0}} + \bar{\mathrm{K^{*0}}}$ in AuAu collisions at $\sqrt{s_{\mathrm{NN}}}~=~$7.7 GeV (Multiplicity class 0-20%).
$p_{\mathrm T}$-differential yield of $\mathrm{K^{*0}} + \bar{\mathrm{K^{*0}}}$ in AuAu collisions at $\sqrt{s_{\mathrm{NN}}}~=~$7.7 GeV (Multiplicity class 20-40%).
$p_{\mathrm T}$-differential yield of $\mathrm{K^{*0}} + \bar{\mathrm{K^{*0}}}$ in AuAu collisions at $\sqrt{s_{\mathrm{NN}}}~=~$7.7 GeV (Multiplicity class 40-60%).
The measurement of $K^{*}(892)^0$ resonance production via its $K^{+}\pi^{-}$ decay mode in inelastic p+p collisions at beam momentum 158 GeV/$c$ ($\sqrt{s_{NN}}=17.3$ GeV) is presented. The data were recorded by the NA61/SHINE hadron spectrometer at the CERN Super Proton Synchrotron. The $\textit{template}$ method was used to extract the $K^{*}(892)^0$ signal and double differential transverse momentum and rapidity spectra were obtained. The full phase-space mean multiplicity of $K^{*}(892)^0$ mesons was found to be $(78.44 \pm 0.38 \mathrm{(stat)} \pm 6.0 \mathrm{(sys)) \cdot 10^{-3}}$. The NA61/SHINE results are compared with the E$_{POS}$1.99 and Hadron Resonance Gas models as well as with world data from p+p and nucleus-nucleus collisions.
Numerical values of mass and width of $K^{∗}(892)^0$ mesons fitted in 0<y<0.5 and presented in Fig.8. The first uncertainty is statistical, while the second one is systematic.
Numerical values of double-differential yields $d^{2}n/dydp_{T}$ presented in Fig. 10, given in units of $10^{−3} (GeV/c)^{−1}$. The first uncertainty is statistical, while the second one is systematic
Numerical values of double-differential yields $d^{2}n/dydp_{T}$ presented in Fig. 10, given in units of $10^{−3} (GeV/c)^{−1}$. The first uncertainty is statistical, while the second one is systematic
The ATLAS Collaboration has measured the inclusive production of $Z$ bosons via their decays into electron and muon pairs in $p+$Pb collisions at $\sqrt{s_{NN}}=5.02$ TeV at the Large Hadron Collider. The measurements are made using data corresponding to integrated luminosities of 29.4 nb$^{-1}$ and 28.1 nb$^{-1}$ for $Z \rightarrow ee$ and $Z \rightarrow \mu\mu$, respectively. The results from the two channels are consistent and combined to obtain a cross section times the $Z \rightarrow \ell\ell$ branching ratio, integrated over the rapidity region $|y^{*}_{Z}|<3.5$, of 139.8 $\pm$ 4.8 (stat.) $\pm$ 6.2 (syst.) $\pm$ 3.8 (lumi.) nb. Differential cross sections are presented as functions of the $Z$ boson rapidity and transverse momentum, and compared with models based on parton distributions both with and without nuclear corrections. The centrality dependence of $Z$ boson production in $p+$Pb collisions is measured and analyzed within the framework of a standard Glauber model and the model's extension for fluctuations of the underlying nucleon-nucleon scattering cross section.
The centrality bias factors derived from data as explained in the text. Model calculations shown in the Figure are found in arXiv:1412.0976.
The differential $Z$ boson production cross section, $d\sigma/dy^\mathrm{*}_{Z}$, as a function of $Z$ boson rapidity in the center-of-mass frame $y^\mathrm{*}_{Z}$, for $Z\rightarrow ee$, $Z\rightarrow\mu\mu$, and their combination $Z\rightarrow\ell\ell$.
The differential cross section of $Z$ boson production multiplied by the Bjorken $x$ of the parton in the lead nucleus, $x_{Pb} d\sigma /dx_{Pb}$, as a function of $x_{Pb}$.
The PHENIX experiment has measured $\phi$ meson production in $d$$+$Au collisions at $\sqrt{s_{_{NN}}}=200$ GeV using the dimuon and dielectron decay channels. The $\phi$ meson is measured in the forward (backward) $d$-going (Au-going) direction, $1.2<y<2.2$ ($-2.2<y<-1.2$) in the transverse-momentum ($p_T$) range from 1--7 GeV/$c$, and at midrapidity $|y|<0.35$ in the $p_T$ range below 7 GeV/$c$. The $\phi$ meson invariant yields and nuclear-modification factors as a function of $p_T$, rapidity, and centrality are reported. An enhancement of $\phi$ meson production is observed in the Au-going direction, while suppression is seen in the $d$-going direction, and no modification is observed at midrapidity relative to the yield in $p$$+$$p$ collisions scaled by the number of binary collisions. Similar behavior was previously observed for inclusive charged hadrons and open heavy flavor indicating similar cold-nuclear-matter effects.
Invariant yields of $\phi$ meson production as a function of $p_T$ at different $d$+Au centrality classes. Type B represents uncertainties that are correlated from point to point.
Invariant yields of $\phi$ meson production as a function of $p_T$ at different $d$+Au centrality classes. Type B represents uncertainties that are correlated from point to point.
Invariant yields of $\phi$ meson production as a function of $p_T$ at different $d$+Au centrality classes. Type B represents uncertainties that are correlated from point to point.
The PHENIX experiment at the Relativistic Heavy Ion Collider (RHIC) has measured $\phi$ meson production and its nuclear modification in asymmetric Cu$+$Au heavy-ion collisions at $\sqrt{s_{NN}}=200$ GeV at both forward Cu-going direction ($1.2<y<2.2$) and backward Au-going direction ($-2.2<y<-1.2$), rapidities. The measurements are performed via the dimuon decay channel and reported as a function of the number of participating nucleons, rapidity, and transverse momentum. In the most central events, 0\%--20\% centrality, the $\phi$ meson yield integrated over $1<p_T<5$ GeV/$c$ prefers a smaller value, which means a larger nuclear modification, in the Cu-going direction compared to the Au-going direction. Additionally, the nuclear-modification factor in Cu$+$Au collisions averaged over all centrality is measured to be similar to the previous PHENIX result in $d$$+$Au collisions for these rapidities.
Invariant yield as a function of the number of participating nucleons for 1.2 < $|y|$ < 2.2 and 1 < $p_T$ < 5 GeV/$c$. Type A represents uncertainties that are uncorrelated from point to point, Type B represents uncertainties that are correlated from point to point, and Type C represents uncertainties in the overall normalization.
Invariant yield as a function of transverse momentum for 1.2 < $|y|$ < 2.2 and 0%–93% centrality. Type A represents uncertainties that are uncorrelated from point to point, Type B represents uncertainties that are correlated from point to point, and Type C represents uncertainties in the overall normalization.
Invariant yield as a function of rapidity for 1 < $p_T$ < 5 GeV/$c$ and 0%–93% centrality. Type A represents uncertainties that are uncorrelated from point to point, Type B represents uncertainties that are correlated from point to point, and Type C represents uncertainties in the overall normalization.
Vector mesons may be photoproduced in relativistic heavy-ion collisions when a virtual photon emitted by one nucleus scatters from the other nucleus, emerging as a vector meson. The STAR Collaboration has previously presented measurements of coherent $\rho^0$ photoproduction at center of mass energies of 130 GeV and 200 GeV in AuAu collisions. Here, we present a measurement of the cross section at 62.4 GeV; we find that the cross section for coherent $\rho^0$ photoproduction with nuclear breakup is $10.5\pm1.5\pm 1.6$ mb at 62.4 GeV. The cross-section ratio between 200 GeV and 62.4 GeV is $2.8\pm0.6$, less than is predicted by most theoretical models. It is, however, proportionally much larger than the previously observed $15\pm 55$% increase between 130 GeV and 200 GeV.
Acceptance corrected invariant mass distributions for the coherently produced $\rho^0$ candidates collected with trigger A (left) and B (right). The fit function (solid) encompasses the Breit-Wigner (dashed), the mass independent contribution from direct $\pi^+\pi^-$ production (dash-dotted), and the interference term (dotted). The hatched area is the contribution from the combinatorial background. The statistical errors are shown.
Acceptance corrected invariant mass distributions for the coherently produced $\rho^0$ candidates collected with trigger A (left) and B (right). The fit function (solid) encompasses the Breit-Wigner (dashed), the mass independent contribution from direct $\pi^+\pi^-$ production (dash-dotted), and the interference term (dotted). The hatched area is the contribution from the combinatorial background. The statistical errors are shown.
Transverse momentum distribution of the $\rho^0$ candidates (open distribution) overlaid by the combinatorial background estimated with like-sign pairs (not corrected to the acceptance and reconstruction efficiency) and scaled to match in the high transverse momentum region, $p_T$ ≥ 250 MeV/$c$ (hatched distribution). The plot is based on the dataset collected with trigger B.
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