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Register a new userJ/$psi$ and $psi(2S)$ measurement in p+p collisions at $sqrt{s} =$ 200 and 500 GeV with the STAR experiment
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Authors
Barbara Trzeciak
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In this paper, results on the J/psi cross section and polarization measured via the dielectron decay channel at mid-rapidity in p+p collisions at 200 and 500 GeV in the STAR experiment are discussed. Also, first measurements of the J/psi production as a function of the charged-particle multiplicity density and of psi(2S) to J/psi ratio at 500 GeV are reported.
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We report on new measurements of inclusive J/$psi$ polarization at mid-rapidity in p+p collisions at $sqrt{s}$ = 200 GeV by the STAR experiment at RHIC. The polarization parameters, $lambda_theta$, $lambda_phi$, and $lambda_{thetaphi}$, are measured as a function of transverse momentum ($p_T$) in both the Helicity and Collins-Soper (CS) reference frames within $p_T< 10$ GeV/$C$. Except for $lambda_theta$ in the CS frame at the highest measured $p_T$, all three polarization parameters are consistent with 0 in both reference frames without any strong $p_T$ dependence. Several model calculations are compared with data, and the one using the Color Glass Condensate effective field theory coupled with non-relativistic QCD gives the best overall description of the experimental results, even though other models cannot be ruled out due to experimental uncertainties.
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 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.
We present a measurement of inclusive $J/psi$ production at mid-rapidity ($|y|<1$) in $p+p$ collisions at a center-of-mass energy of $sqrt{s}$ = 200 GeV with the STAR experiment at the Relativistic Heavy Ion Collider (RHIC). The differential production cross section for $J/psi$ as a function of transverse momentum ($p_T$) for $0<p_T<14$ GeV/$c$ and the total cross section are reported and compared to calculations from the color evaporation model and the non-relativistic Quantum Chromodynamics model. The dependence of $J/psi$ relative yields in three $p_T$ intervals on charged-particle multiplicity at mid-rapidity is measured for the first time in $p+p$ collisions at $sqrt{s}$ = 200 GeV and compared with that measured at $sqrt{s}$ = 7 TeV, PYTHIA8 and EPOS3 Monte Carlo generators, and the Percolation model prediction.
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.
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