No Arabic abstract
We present measurements of the differential cross sections of inclusive $J/psi$ meson production as a function of transverse momentum ($p_{T}^{J/psi}$) using the $mu^{+}mu^{-}$ and $e^{+}e^{-}$ decay channels in proton+proton collisions at center-of-mass energies of 510 and 500 GeV, respectively, recorded by the STAR detector at the Relativistic Heavy Ion Collider. The measurement from the $mu^{+}mu^{-}$ channel is for 0 $< p_{T}^{J/psi} <$ 9 GeV/$c$ and rapidity range $|y^{J/psi}| < $ 0.4, and that from the $e^{+}e^{-}$ channel is for 4 $< p_{T}^{J/psi} <$ 20 GeV/$c$ and $|y^{J/psi}| < $ 1.0. The $psi(2S)$ to $J/psi$ ratio is also measured for 4 $< p_{T}^{rm meson} <$ 12 GeV/$c$ through the $e^{+}e^{-}$ decay channel. Model calculations, which incorporate different approaches toward the $J/psi$ production mechanism, are compared with experimental results and show reasonable agreement within uncertainties.
We report measurements of the charge-separated $W^{+(-)} to e^{+(-)} + u_e(bar{ u}_e)$ and $Z/gamma^* to e^+e^-$ production cross sections at mid-rapidity in proton-proton collisions at $sqrt{s}$ = 500 GeV. These results are based on 13.2 pb$^{-1}$ of data recorded in 2009 by the STAR detector at RHIC. Production cross sections for W bosons that decay via the $e u$ channel were measured to be $sigma(pp to W^+ X) cdot BR(W^+ to e^+ u_e)$ = 117.3 pm 5.9(stat) pm 6.2(syst) pm 15.2(lumi) pb, and $sigma(pp to W^- X) cdot BR(W^- to e^- bar{ u}_e)$ = 43.3 pm 4.6(stat) pm 3.4(syst) pm 5.6(lumi) pb. For $Z/gamma^*$ production, $sigma(pp to Z/gamma^* X) cdot BR(Z/gamma^* to e^+ e^-)$ = 7.7 pm 2.1(stat) $^{+0.5}_{-0.9}$(syst) pm 1.0(lumi) pb for di-lepton invariant masses $m_{e^+e^-}$ between 70 and 110 GeV/$c^2$. First measurements of the W cross section ratio, $sigma(pp to W^+ X) / sigma(pp to W^- X)$, at $sqrt{s}$ = 500 GeV are also reported. Theoretical predictions, calculated using recent parton distribution functions, are found to agree with the measured cross sections.
The PHENIX experiment has measured the spin alignment for inclusive $J/psirightarrow e^{+}e^{-}$ decays in $p$+$p$ collisions at $sqrt{s}=510$ GeV at midrapidity. The angular distributions have been measured in three different polarization frames, and the three decay angular coefficients have been extracted in a full two-dimensional analysis. Previously, PHENIX saw large longitudinal net polarization at forward rapidity at the same collision energy. This analysis at midrapidity, complementary to the previous PHENIX results, sees no sizable polarization in the measured transverse momentum range of $0.0<p_T<10.0$ GeV/$c$. The results are consistent with a previous one-dimensional analysis at midrapidity at $sqrt{s}=200$ GeV. The transverse-momentum-dependent cross section for midrapidity $J/psi$ production has additionally been measured, and after comparison to world data we find a simple logarithmic dependence of the cross section on $sqrt{s}$.
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 $dsigma^{J/psi}_{pp}/dy (1.2<|y|<2.2, 0<p_T<10~mbox{GeV/$c$}) =$ 54.3 $pm$ 0.5 (stat) $pm$ 5.5 (syst) nb.
We report the first measurement of the fraction of $J/psi$ mesons coming from $B$-meson decay ($F_{B{rightarrow}J/psi}$) in $p$+$p$ collisions at $sqrt{s}=$ 510 GeV. The measurement is performed using the forward silicon vertex detector and central vertex detector at PHENIX, which provide precise tracking and distance-of-closest-approach determinations, enabling the statistical separation of $J/psi$ due to $B$-meson decays from prompt $J/psi$. The measured value of $F_{B{rightarrow}J/psi}$ is 8.1%$pm$2.3% (stat)$pm$1.9% (syst) for $J/psi$ with transverse momenta $0<p_T<5$ GeV/$c$ and rapidity $1.2<|y|<2.2$. The measured fraction $F_{B{rightarrow}J/psi}$ at PHENIX is compared to values measured by other experiments at higher center of mass energies and to fixed-order-next-to-leading-logarithm and color-evaporation-model predictions. The $bbar{b}$ cross section per unit rapidity ($dsigma/dy(pp{rightarrow}bbar{b})$) extracted from the obtained $F_{B{rightarrow}J/psi}$ and the PHENIX inclusive $J/psi$ cross section measured at 200 GeV scaled with color-evaporation-model calculations, at the mean $B$ hadron rapidity $y={pm}1.7$ in 510 GeV $p$$+$$p$ collisions, is $3.63^{+1.92}_{-1.70}mu$b, and it is consistent with the fixed-order-next-to-leading-logarithm calculations.
Transverse single spin asymmetry, $A_{N}$, of very forward $pi^{0}$ production from polarized $p + p$ collisions provides new information toward an understanding of its production mechanism. $A_{N}$ of forward $pi^{0}$ in the pseudorapidity region of $3 < eta < 4$ has been described by the partonic structure of the proton in the perturbative QCD framework. However, recent data indicates a potential contribution from not only partonic but also diffractive interactions. In order to provide a new insight on the origin of the $A_{N}$, we measured the very forward $pi^{0}$ production in the pseudorapidity region of $6 < eta$ from $sqrt{s}$ = 510 GeV polarized $p + p$ collisions at RHIC in 2017. We report our measurement of the very forward $pi^{0}$ over the transverse momentum range of $0 < p_{T} < 1$ GeV/$c$ and the preliminary result.